1999/2000 - finale navorsingsverslag : winetech · • wetenskaplike publikasie. • finale...
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1999/2000 - FINALE NAVORSINGSVERSLAG : WINETECH
VRUGSOORT: Druiwe PROJEKNOMMER: WW 03/07
ORGANISASIE: Nietvoorbij NAVORSER: W.J. Conradie
PROJEKTITEL: Ondersoek na grondkundige- en wingerdboukundige praktyke wat 'n optimale
stikstofinhoud in mos sal verseker.
DOELWITTE VAN PROJEK:
Die doel van hierdie projek is om grondkundige- en wingerdboukundige praktyke, wat 'n aanvaarbare
stikstofinhoud in mos sal verseker, te identifiseer. Toepassing van sodanige praktyke sal die
byvoeging van addisionele stikstof uitskakel terwyl wynkwaliteit ook verhoog behoort te word.
DOELWIT VIR HUIDIGE JAAR:
Die ondersoek word in twee Sauvignon blanc wingerde (Nietvoorbij en Boschendal) uitgevoer.
Doelwitte vir die huidige jaar:
1. Projek word met finale verslag en wetenskaplike publikasie afgesluit.
2. Resultate word aan bedryf bekend gestel.
BEVINDINGE TOT OP DATUM:
1. Resultate is in wetenskaplike publikasie saamgevat.
2. Lesing is by 1999 se SAWWV Kongres aangebied.
VOORDELE AAN BEDRYF:
Huidig word di-ammoniumfosfaat tot mos bygevoeg om probleme met slepende gisting te oorkom.
Hierdie praktyk lei egter tot verhoogde P-inhoude in wyne. Oorsese regulasies ten opsigte van die
toelaatbare P-inhoud van wyn (tans 300 mg.l1), gaan bes moontlik strenger gemaak word, wat kan
beteken dat 'n groot deel van Suid-Afrika se wynuitvoere (tans geraam op R700 miljoen/jaar)
geaffekteer sal word. Hierdie projek kan meehelp om sodanige probleem to oorkom.
AANBEVELINGS VIR VOLGENDE JAAR:
1. Wetenskaplike publikasie sal gedurende 2000/2001 verskyn.
2. Resultate moet op deurlopende basis aan bedryf bekend gestel word.Monique/Naverslg/Winetech.2000/WW0307uit
ARC • LNR
ARC-FRUIT, VINE AND WINE RESEARCH INSTITUTE
LNR-NAVORSINGSINSTITUUT VIR VRUGTE, WINGERD EN WYN
TNFRTJTTF.C
Private Bag / Privaatsak X5013, Stellenbosch 7599, South Africa / Suid- AfrikaTel: (021) 809 3100 • Fax (021) 809 3400 » (Int: +27 21)
E-mail: [email protected] • Web site: www.arc.agric.za
NIETVOORBIJ
Private Bag /Privaatsak X5026, Stellenbosch 7599, Souíh Africa /Suid- AfrikaTel: (021) 809 3100 . Fax (021) 809 3002 . (Int: +27 21)
E-mail: [email protected] • Web site: www.arc.agric.za
VERTROULIK
1999/2000 FINALE NAVORSINGSVERSLAG : WINETECH
PROJEKNOMMER WW 03/07
PROJEKTITEL Ondersoek na grondkundige- en wingerdboukundige praktyke wat 'n optimale
stikstofinhoud in mos sal verseker.
PROJEKLEIER W.J. Conradie
AANVANGSDATUM : 1994EINDDATUM : 2000
No section of this document may be reproduced, in any form, or otherwise, without written permission by theARC Infruitec-Nietvoorbij.
AN INSTITUTE OF THE AGRICULTURAL RESEARCH COUNCIL'N INSTITUUT VAN DIE LANDBO UNA VORSINGSRAAD
FINALE NAVORSINGSVERSLAG (1999/2000)
PROJEKNOMMER PROJEKLEIER MEDEWERKER(S)
WW 03/07 W.J. Conradie J.J. Hunter
N. Volschenk
P. Olivier
I. van Huyssteen
PROJEKTITEL
Ondersoek na grondkundige- en wingerdboukundige praktyke wat 'n optimale stikstofinhoud in mos
sal verseker.
ERKENING
Winetech vir gedeeltelike befondsing van hierdie navorsing. Distillers Korporasie vir FAN-bepalings.
Boschendal vir beskikbaarstelling van een van die proefpersele.
PROBLEEM AANGESPREEK/DOEL OF HIPOTESESTELLING
Die stikstofinhoud van Suid-Afrikaanse moste is oor die algemeen relatief laag, wat 'n negatiewe effek
op gistingstempo het. In die praktyk is dit dus dikwels nodig om stikstof tot die mos by te voeg, 'n
praktyk waarteen daar wêreldwyd toenemende weerstand is. Die doel van hierdie projek is om
grondkundige-en wingerdboukundige praktyke, wat 'n aanvaarbare stikstofinhoud in mos sal verseker,
te identifiseer. Toepassing van sodanige praktyke sal die byvoeging van addisionele stikstof uitskakel
terwyl wynkwaliteit ook verhoog behoort te word.
NAVORSINGSBEHOEFTE AANGESPREEK
Winetech Tegniese Komitee 1996 : Prioriteit A.
DOELWITTE VAN VERSLAGJAAR
• Handel aminosuurontledings af.
• Bepaal ressuiker en alkohole op eksperimentele wyne.
• Beoordeel eksperimentele wyne van 1998 en 1999.
• Stel resultate bekend in lesing by SAWWV kongres.
• Wetenskaplike publikasie.
• Finale verslag.
MATERIAAL EN METODES
Die veldwerk in Sauvignon blanc wingerde (Nietvoorbij en Boschendal) is in 1998/99 afgehandel.
Behandelings word in Tabel 1 aangetoon. Die mikpunt was om die effek van verskillende
stikstoftoedienings, in kombinasie met verskillende loofbestuurspraktyke, op die vry-amino-stikstof
(FAN) in mos te bepaal. Besproeiing is in meeste gevalle konstant gehou, maar die effek van
droëlandverbouing is ook in twee behandelings gekwantifiseer. Gedurende 1999/2000 is
aminosuurontledings afgehandel, terwyl eksperimentele wyne wat gedurende 1998 en 1999 berei is, in
Augustus beoordeel is.
RESULTATE EN BESPREKING
Die twee oorheersende aminosure (vir beide wingerde) was arginien en prolien, terwyl redelike
hoeveelhede alonien, aspartiensuur, glutamiensuur, glutamien en histidien ook gevind is (Tabelle 2 en
3). By Boschendal was ook heelwat asparagien teenwoordig. Hierdie profiel stem grootliks ooreen
met die wat reeds vir Bukettraube gevind is, behalwe dat die konsentrasies van aspartiensuur en
glutamiensuur in laasgenoemde geval relatief laag was. Dit was opvallend dat prolien by Boschendal
die laagste was vir die kontrole, wat daarop neerkom dat 'n groter fraksie van totale amino N by
bemeste behandelings in die vorm van prolien teenwoordig was. Aangesien prolien normaalweg nie
deur giste ge-assimileer kan word nie, dui hierdie resultaat daarop bemesting die verhouding tussen
assimileerbare en nie-assimileerbare N negatief beïnvloed het. Origens het min betekenisvolle
verskille vir individuele aminosure voorgekom en dit was moeilik om verskille wat wel voorgekom het,
sinvol te irtterpreteer. Verhoudings tussen individuele aminosure sou 'n effek op gistingstempo kon
hê. In die aanvanklike beplanning van hierdie projek nie nie voorsien om trosanalises ("cluster
analysis") op aminosuurprofiele uit te voer nie. Daar word in elk geval beplan om hierdie verwerkings
te laat doen. Enige sinvolle resultate sal tot die konsep-publikasie (aangeheg) toegevoeg word.
Wyne van die 1998 oesjaar is in 1999 (na 18 maande) vir 'n tweede keer geproe (Tabel 4A). By
Nietvoorbij het die kontrole se algehele kwaliteit iaer geneig, wat ooreenstem met die lae N-inhoud in
die mos (verslag vir 1997/98 verwys). Die rede vir die laer kwaliteit, was waarskynlik te min vars
vegatatiewe karakter (gras/soetrissie). Tydens veroudering verskuif die balans vanaf 'n vegetatiewe
na 'n vrugtige/tropiese karakter. Dit was opvallend dat vrugtige karakters hoër was by die kontrole
(No. 1), en by die behandeling wat slegs na-oes bemesting ontvang het (No. 2), in vergelyking met die
twee behandelings (No's 6 en 7) wat N-bemesting by vrugset sowel as deurslaan ontvang het.
Laasgenoemde twee behandelings het ook die vinnigste gegis (vorige verslag verwys), wat dui op 'n
betekenisvolle interaksie tussen stikstofbemesting, stikstof in mos en wyngehalte. Die paneel het
duidelik voorkeur gegee aan die aromaprofiel van No's 6 en 7, in vergelyking met die kontrole. Vir die
behandeling wat slegs teen vrugset bemes is (No. 9) is 'n hoër punt vir vegetatiewe karakter verkry as
vir die een (No. 8) wat slegs teen deurslaan bemes is. Daar is voorheen gevind dat bemesting op
Nietvoorbij nie te laat toegedien moet word nie, aangesien daar dan min effek op die stikstofinhoud
van mos verkry word. Dit lyk of die paneel, ten opsigte van algehele wynkwaliteit (8 vs. 9), effens
meer gehou het van die balans wat met bemesting teen vrugset verkry is. By Boschendal het die
kontrole, ten opsigte van algehele kwaliteit, minstens net so goed as bemeste behandelings gevaar.
Dit was ook opvallend dat behandelings wat teen vrugset sowel as deurslaan bemes is (No's 6 en 7)
nie besondere hoë punte vir vegetatiewe karakter gekry het nie. Die feit dat groeikrag gestimuleer is
het dus níe óf op stikstofinhoude van mos (vorige verslag verwys) óf op wynstyl gereflekteer nie. Dit
wil eerder voorkom of luuksueuse groei veroorsaak het dat minder aroma komponente na trosse
gevoer is.
Wyne vir 1998/99 (beoordeel na ses maande) het nie óf vir Nietvoorbij óf vir Boschendal (Tabel 4B) 'n
duidelike patroon gewys nie. Waardes wat vir ressuikers en alkohole verkry is (nie getoon), het
daarop gedui dat alle wyne droog gegis het. Vorige ondervinding het egter gewys Sauvignon blanc
wyne nog nie na ses maande stabiliteit bereik het nie. Daar word dus beplan om wyne weer in
Augustus 2000 te evalueer. Hierdie resultate sal ook in die konsep-publikasie bygewerk word.
Resultate wat in hierdie projek verkry is, is in 1999 by die SAWWV Kongres aangebied en in 2000 by
die OIV Kongres. Die konsep wetenskaplike publikasie waarna reeds verwys is, word by hierdie
verslag aangeheg. Hierdie publikasie moet nog deur Nietvoorbij se publikasiekomitee evalueer word,
maar sal voor einde 2000 aan Am. J. Enol. Vitic. vir publikasie voorgelê word. 'n Konsep populêre
publikasie, wat aan Wynboer voorgelê sal word, word ook aangeheg.
'n Samevatting van resultate wat oor die verloop van die projek ingesamel is, word kortliks hier onder
opgesom.
GEVOLGTREKKINGS EN AANBEVELINGS
1. Dit is duidelik dat daar nie 'n "standaard" stikstofbemestingsprogram, vir die verkryging van
optimale stikstofinhoude in mos, vir alle gronde gevolg kon word nie. Onder Wes-Kaapland se
klimaatsbestande voorsien gronde met hoë organiese materiaal tot en met vrugset meer as
voldoende N om in wingerd se behoeftes te voorsien. Vir gronde met lae organiese materiaal is
na-oes bemesting nie voldoende nie en is bemesting na bot aangewese. Bemesting moet
normaalweg nie voor einde September toegedien word nie, aangesien winterreën stikstof kan
uitloog voordat stokke dit kan benut.
2. By droëlandwingerde is grondwater normaalweg laag vanaf begin/middel Desember (ertjiekorrel
stadium) tot oestyd. Onder sulke toestande vind min mineralisasie van organiese materiaal
plaas, gevolglik verskil die N-leweringsvermoë van gronde met hoë en lae organiese materiaal
nie in hierdie periode meer so baie nie. In die geval van gronde met hoë organiese materiaal,
word anorganiese stikstof egter oorgedra uit die vorige groeistadium (bot tot vrugset), terwyl dit
nie vir gronde met lae organiese materiaal die geval is nie. Bemesting is dus aangewese. Selfs
waar aanvullende besproeiing toegepas word, is grondwater vir aansienlike periodes relatief
laag en vind min mineralisasie plaas. Die situasie sal egter heeltemaal anders wees vir
wingerde wat intensief besproei word. Onder sulke omstandighede droog die grond nooit
heeltemaal uit nie en vind mineralisasie van organiese materiaal geredelik plaas.
Stikstofbemesting, selfs op gronde met lae organiese materiaal, sal dus met veel meer
omsigtigheid toegedien moet word.
3. By droëlandwingerde is dit normaalweg nie die moeite werd om bemesting na vrugset toe te
dien nie, aangesien reënval te laag is om bemesting in te was. By wingerde wat aanvullend
besproei word, kan bemesting (waar benodig) egter óf met vrugset óf met deurslaan toegedien
word. Resultate het daarop gedui dat beter resultate met die toediening teen vrugset behaal
word. 'n Enkeltoediening teen vrugset behoort normaalweg voldoende te wees, maar dit kan in
sommige gevalle aangevul word met bemesting teen deurslaan. 'n Enkeltoediening teen
deurslaan is normaalweg nie effektief nie, waarskynlik omdat die tydsperk vanaf deurslaan tot
oes te kort is om 'n wesenlike verandering in die stikstofinhoude van mos teweeg te bring. Aan
die ander kant, waar stikstofbemesting nje benodig word nie sal bemesting teen vrugset groter
skade aanrig as dié teen deurslaan. In eersgenoemde geval word groei oormatig gestimuleer
wat veroorsaak dat die stikstofhuishouding en geurkomponente van trosse nadelig beïnvloed
word.
4. Waar gronde met 'n lae stikstofstatus nie voldoende bemes word nie, is die stikstofinhoud van
mos laag en gisting kan nadelig beïnvloed word. Dit lei by Sauvignon blanc tot wyne met 'n lae
vegetatiewe (gras/soetrissie) karakter, terwyl tropiese karakter (pynappel, spanspek, piesang,
koejawel) oorheersend is. Waar wingerde teen bot (droëland) of teen vrugset (aanvullend
besproei) bémes word, word stikstofinhoude in mos verhoog en toon wyne 'n goeie balans
tussen vegetatiewe en tropiese karakter. Dit moet egter beklemtoon word dat hierdie resultaat
slegs verkry word waar N-bemesting wel benodig word. Waar dit nie benodig word nie het N-
bemesting min/geen effek op die N-inhoud van mos en kan die geurstofbalans van wyne nadelig
beïnvloed word.
5. By wingerde wat oormatig groei kan optimale lowerbestuurspraktyke meehelp om die
stikstofinhoud van mos te verhoog, terwyl stikstofbemesting min/geen positiewe rol kan speel
nie. By wingerde wat minder geil groei het lowerbestuur uiteraand 'n veel kleiner effek.
6. Die organiese materiaalinhoud van grond kan as 'n breë riglyn dien by die daarstelling van
stikstofbemestingsriglyne (Tabel 5). Hierdie riglyne sal aangepas moet word aan die hand van
wingerd se groeikragtigheid, maar kan dien as breë vertrekpunt.
LYS VAN PUBLIKASIES
1. CONRADIE, W.J., 1998. The effect of nitrogen fertilization on the nitrogen content of must
(Afrikaans). Handbook for Short Course on "The role of nitrogen in wine making", 6th August
1998, Stellenbosch, 6pp.
2. CONRADIE, W.J., 2000. Effect of nitrogen fertilizer timing on yield, juice composition and wine
quality, for Sauvignon blanc on two different soils. Am. J. Enol. Vitic, to be submitted for
publication.
3. CONRADIE, W.J., 2000. Praktiese riglyne om die stikstofinhoud van mos te optimiseer.
Wynboer, moet voorgelê word vir publikasie.
Tabel 1. Behandelings wat vanaf 1995/96 in twee veldproewe op Nietvoorbij en Boschendal
toegepas word, om die effek daarvan op stikstofinhoud van mos te bepaal.
Behandeling
1
2
3
4
5
6
7
8
9
Besproei*
Ja
Ja
Ja
Nee
Nee
Ja
Ja
Ja
Ja
Lower-
bestuur
Slegs top
Normaal
Slegs top
Normaal
Slegs top.
Normaal
Slegs top
Normaal
Normaal
Stikstofbemesting (kg/ha)***
Na-oes
0
20
20
20
20
20
20
20
20
Bot
0
0
0
40
40
0
0
0
0
Vrugset
0
0
0
0
0
20
20
0
20
Deurslaan
0
0
0
0
0
20
20
20
0
Totaal
0
20
20
60
60
60
60
40
40
Waar besproeiing toegepas word, word wingerd met vrugset en met deurslaan besproei.
Waar aangedui as normal, word praktyke soos tans deur Nietvoorbij voorgeskryf, gevolg. Dit behels
insteek van lote, suier, top en uitbreek van blare. By die behandelings wat slegs getop word, word lote
ook ingesteek, maar origins word geen loofbestuurspraktyke toegepas nie.
Na-oes bemesting word as standard beskou en deurgaans toegepas, met uitsondering van no. 1
(kontrole).
Tabel 2. Aminosuurinhoud vir mos vanaf Nietvoorbij (1998/99).
Aminosuur (µmol N/L)
Alanien
Arginien
Asparagien
Aspartiensuur
Glisien
Glutamiensuur
Glutamien
Histidien
Isoleusien
Leusien
Lisien
Fenielalanien
Prolien
Serien
Treonien
Valien
Ander
Totale amino-N (mg/L)(4)
F A N (mg/L)(5)
Totale N (mg/L)
Behandeling
1(1)
421a2
1934ab
153a
271a
60a
172a
194a
308b
75a
77a
96a
55a
801 a
162a
162ab
170a
127a
374a
784a
435a
2
530a
2455b
86a
338ab
76ab
192a
266a
Oa
82a
94ab
114ab
68a
912a
169a
179ab
224a
Oa
413a
796a
437a
3
509a
2198ab
82a
241a
83ab
207a
253a
41 ab
75a
93ab
114ab
55a
920a
154a
165ab
163a
Oa
382a
950b
517abc
4
396a
1815ab
133a
315ab
90ab
153a
181a
83ab
79a
86ab
115ab
59a
1051a
144a
179ab
183a
58a
366a
964b
589c
5
363a
1622a
193a
212a
78ab
157a
158a
86ab
73a
73a
110ab
51a
1008a
136a
129a
161a
80a
335a
968b
537bc
6
561a
2442b
170a
233a
144b
202a
185a
221ab
80a
90ab
116b
64a
1151a
166a
195b
174a
78a
448a
994b
552bc
7
476a
2181ab
88a
211a
84ab
179a
249a
Oa
75a
89ab
113ab
58a
855a
135a
175ab
174a
Oa
367a
1010b
535bc
8
487a
1903ab
124a
212a
121ab
180a
226a
302ab
84a
92ab
113ab
63a
1021a
157a
176ab
201a
86a
397a
994b
493ab
9
542a
2470b
135a
473b
105ab
198a
225a
148ab
84a
104b
113ab
62a
1121a
177a
188b
221 a
54a
459a
1060b
592c
( ' Sien Tabel 1 vir volledige beskrywing van behandelings(3) Sisteïen, metionien, en tirosien.(5) Standaard (nat) metode
Syfers binne rye verskil nie betekenisvol, indien gevolg deur dieselfde letter (p < 0.05)(4) Bereken vanaf afsonderlike aminosuurinhoude
Tabel 3. Aminosuurinhoud vir mos vanaf Boschendal (1998/99).
Aminosuur (µmol N/L)
Alanien
Arginien
Asparagien
Aspartiensuur
Glutamiensuur
Glutamien
Histidien
Isoleusien
Leusien
Lisien
Fenielalanien
Prolien
Serien
Treonien
Valien
Ander(3)
Totale amino-N (mg/L)(4)
FAN (mg/L)(5)
Totale N (mg/L)
Behandeling
1(1)
563al(2)
1310a
180a
368bcd
193ab
229a
237a
63a
71a
72a
45ab
527a
177a
187a
108a
31a
309a
942a
481 a
2
595a
1570a
206ab
379bcd
212ab
269a
389a
67a
77a
107a
46ab
902abc
118a
143a
123a
16a
373a
908a
466a
3
646a
2232a
342abc
269a
180ab
281a
172a
69a
93a
112a
47ab
743abc
134a
157a
159a
Oa
398a
812a
476a
4
652a
1778a
384bc
339ab
178ab
254a
369a
57a
84a
74a
48ab
990bc
85a
145a
141a
68a
403a
850a
467a
5
874a
2493a
401 bc
431 cd
217ab
345a
380a
49a
76a
78a
39ab
1039bc
153a
163a
140a
33a
493a
978a
534a
6
677a
1902a
301abc
344abc
217ab
293a
350a
46a
77a
39a
29a
955abc
124a
158a
132a
29a
409a
936a
485a
7
884a
2447a
426c
455d
265b
383a
404a
47a
77a
75a
37ab
1178c '
161a
185a
141a
16a
513a
952a
515a
8
371a
989a
199ab
256a
138a
180a
233a
39a
64a
36a
29a
615ab
83a
96a
87a
14a
245a
896a
495a
9
559a
1324a
274abc
287a
159ab
266a
271 a
33a
66a
52a
44ab
728abc
97a
132a
113a
19a
319a
876a
467a
(1) Sien Tabel 1 vir volledige beskrywing van behandelings(3) Sisteïen, metionien, en tirosien.(5) Standaard (nat) metode
(2) Syfers binne rye verskil nie betekenisvol, indien gevolg deur dieselfde letter (p < 0.05)(4) Bereken vanaf afsonderlike aminosuurinhoude
Tabel 4A. Wynkwaliteit vir 1997/98 se wyne, soos beoordeel na 18 maande.
Behandeling (1)
1
2
3
4
5
6
7
8
9
Nietvoorbij
Algehelekwaliteit
(%)
49.6a(2)
54.7ab
51.7ab
55.5ab
52.5ab
51.8ab
51.6ab
52.0ab
57.7b
Varsvegetatief
(%)
25.9a
33.5abc
40.9c
36.0bc
32.9ab
35.0bc
39.5bc
33.5abc
39.6bc
Vrugtigheid(%)
43.5bc
44.7c
35.3ab
38.3abc
39.5abc
32.8a
30.4a
32.2a
38.7abc
Boschendal
Algehelekwaliteit
(%)
51.7a
47.0a
51.6a
53.9a
49.0a
51.2a
48.9a
50.0a
55.2a
Varsvegetatief
(%)
23.0ab
34.4bc
36.6c
40.2c
30.4abc
20.1a
29.0abc
22.6ab
36.2c
Vrugtigheid(%)
32.9ab
34.6ab
36.1ab
32.2a
30.1a
39.8ab
29.2a
46.9b
37.3ab
(1) Sien Tabel 1 vir beskrywing van behandelings.Syfers binne kolomme verskil nie betekenisvol, indien gevolg deur dieselfde letter (p <0.05)
Tabel 4B. Wynkwaliteit vir 1998/99 se wyne, soos beoordeel na 6 maande.
Behandeling (1)
1
2
3
4
5
6
7
8
9
Nietvoorbij
Algehelekwaliteit
(%)
48.0a(2)
58.1a
58.8a
52.8a
56.4a
56.1a
48.4a
56.5a
56.5a
Varsvegetatief
(%)
30.6a
40.4a
33.7a
30.2a
37.2a
31.8a
30.4a
37.6a
34.8a
Vrugtigheid(%)
38.6a
40.5a
46.9a
56.4a
46.9a
43.1a
47.1a
48.1a
37.3a
Boschendal
Algehelekwaliteit
(%)
35.4a
34.2a
46.9b
46.4b
34.8a
34.2a
40.6ab
46.5b
37.6ab
Varsvegetatief
(%)
20.0ab
34.3d
30.3cd
29.7cd
22.1abc
24.0abc
18.2a
32.6d
26.8bcd
Vrugtigheid(%)
38. Oa
34.8a
40.5a
46.2a
32.7a
34.2a
37.7a
43.8a
32.3a
(1)
(2)Sien Tabel 1 vir beskrywing van behandelings.Syfers binne kolomme verskil nie betekenisvol, indien gevolg deur dieselfde letter (p <0.05)
10
Tabe l 5. Bemestingsriglyne gebaseer op die organiese material in grond
Koolstof
> 0 . 9
0.6-0.9
0.3-0.6
<0.3
Stikstofbemesting (kg N/ha)
Na-oes
-
20
20
20
Bot
-
-
-
20
Vrugset
-
-
(20)(2)
20
Deurslaan
-
-
-
(20)(2)
(1) Normaalweg van toepassing vir gronde wat > 6% klei bevat. Vir sander ige gronde kan stikstof inmeer paaiemente verdeel word.
(2) W o r d s legs toegedien waar stokke se groeikragt igheid swakker as normaal/ ideaal is.
OPSOMMING VAN FINALE NAVORSEVGSVERSLAG (1999/2000)
PROJEKNOMMER PROJEKLEIER MEDEWERKERSWW 03/07 W.J. Conradie J.J. Hunter
N. VolschenkP. Olivier
I. van Huyssteen
PROJEKTITELOndersoek na grondkundige-en wingerdboukundige praktyke wat 'n optimale stikstofinhoud in mos salverseker.
Die ondersoek, uitgevoer oor drie seisoene (1996/97 tot 1998/99), was daarop gemik om 'n optimalestikstofinhoud in mos te verkry. Twee Sauvignon blanc wingerde, op twee verskillende gronde, isgebruik. Die eerste grond (A) het min organiese materiaal (0,50% C) bevat, in vergelyking met 'n relatiefhoë konsentrasie (1,14% C) by die tweede (B). Verskillende hoeveelhede stikstof (N) is op verskillendetye gedurende die seisoen (na-oes, bot, vrugset en deurslaan) toegedien. In kombinasie hiermee is dieeffek van 'n optimale lowerbestuurspraktyk (top, suier, insteek van lote, uitbreek van blare) ook vergelykmet 'n minimum praktyk (top, insteek van lote). Meeste van die behandelings is aanvullend besproei,maar 'n droëlandbehandeling is ook ingesluit, ten einde effek van grondwater op mineralisasie vanorganiese N vas te stel.
By A was 'n enkeltoediening van N (20 kg/ha) onvoldoende om vry-amino-stikstof (FAN) in mos totrealistiese vlakke te verhoog. Waar na-oes toediening gekombineer is met 'n enkeltoediening teen bot(20-40) of met gesplete toedienings van 20 kg/ha teen vrugset sowel as bot (20-20-20), is die FAN-inhoud van mos egter betekenisvol verhoog. 'n Toediening in die na-oes periode, gekombineer met 'nenkeltoediening teen vrugset (20-20), het ook FAN-vlakke verhoog , maar nie altyd soveel as 20-40 en20-20-20 nie. Op hierdie grond was 'n toediening in die na-oes periode, gekombineer met 'nenkeltoediening teen deurslaan, minder suksesvol om FAN-inhoud te verhoog. Oor die algemeen hetgistingstempo's ooreengestem met FAN inhoude. In die geval van 20-20-20 was tempo egter effenshoër as vir 20-40, waarskynlik as gevolg van verskillende aminosuurprofiele. Wyne vanaf persele wat ófgeen óf net na-oes bemesting ontvang het, het tydens veroudering 'n oorheersende vrugtige karakterontwikkel, terwyl vars vegetatiewe karakter (gras/soetrissie) verlaag is. Daar is oor die algemeenvoorkeur gegee aan wyne vanaf persele wat in die lente bemesting ontvang het, waarskynlik omdat daarna veroudering steeds 'n goeie balans tussen vegetatiewe en vrugtige karakters bestaan het.
In die geval van B, het N bemesting geen effek op die FAN-inhoud van mos gehad nie. Daar was ookgeen positiewe effek op wyngehalte waameembaar nie. Inteendeel, dit het voorgekom asof N-bemestingdie balans tussen vars vegetatiewe en vrugtige karakter in meeste gevalle negatief beïnvloed het. Ophierdie grond, waar geil groei voorgekom het, het optimale lowerbestuurspraktyke egter in meestegevalle 'n positiewe effek op die stikstofinhoud van mos en op wyngehalte gehad.
Onder droëlandtoestande was grondwater laag vanaf vrugset tot oestyd, wat mineralisasie van organieseN en opname van N beperk het. Waar voldoende stikstofbemesting vroeg in die seisoen toegedien was,was die N-inhoud van mos egter steeds aanvaarbaar, terwyl wyne ook goed gebalanseerd was.
Dië studie het getoon dat sinvolle N bemesting, by gronde met lae organiese materiaal, 'n positiewe effekop die FAN-inhoud van mos, gistingstempo en wyngehalte kan hê. Verskillende benaderings moet egteronder verskillende omstandighede gevolg word. Vir wingerde op gronde met hoë organiese materiaal,het N-bemesting min effek op die FAN-inhoud van mos, gistingstempo en wyngehalte. Onder sulkeomstandighede kan optimale lowerbestuurspraktyke 'n positiewe effek hê.
SUMMARY OF FINAL RESEARCH REPORT (1999/2000)
PROJECT NUMBER PROJECT LEADER CO-WORKERSWW 03/07 W.J. Conradie J.J. Hunter
N. VolschenkP. Olivier
I. van Huyssteen
PROJECT TITLEInvestigation of soil scientific and viticultural practices, which will ensure an optimal nitrogencontent in must.
The investigation, carried out over three seasons (1996/97 to 1998/99), was aimed at ensuring anoptimal nitrogen content in must. Two Sauvignon blanc vineyards, on two different soils, wereused. The first soil (A) contained little organic material (0,50% C), in comparison to a relativelyhigh concentration (1,14% C) for the second (B). Varying amounts of nitrogen (N) were appliedat different times during the season (post-harvest, budbreak, fruitset and véraison). Inconjunction with this, the effect of an optimal canopy management practice (top, suckering, shoot-positioning and removal of leaves) was also compared against a minimum practice (top, shoot-positioning). Most of the treatments received supplementary irrigation, but a dryland treatmentwas also included, in order to determine the effect of soil water on the mineralization of organic N.
In the case of A, a single application of N (20 kg/ha) during the post-harvest period failed toincrease the free amino nitrogen (FAN) in must to realistic levels. However, where post-harvestapplication of N (20 kg/ha) was combined with either a single application (40 kg/ha) at budbreak(20-40), or split applications (20 kg/ha) at fruitset as well as veraison (20-20-20), FAN levels inmust were increased significantly. A single application during the post-harvest period, incombination with a single application at fruit set (20-20), also íncreased FAN levels, albeit usuallynot as much as 20-40 and 20-20-20. On this soil a single application during the post-harvestperiod, in combination with a single application at veraison was less successful in increasing FANlevels. In general, fermentation rates correlated with FAN contents. However, the rate for 20-20-20 was slightly higher than that of 20-40, suggesting a different amino acid profile. Wines fromplots that were either unfertilized, or fertilized in the post-harvest period only, developed apredominant fruity character during maturation, while fresh vegetative character (grass/greenpepper) was reduced. In general, wines from plots that received fertilization during spring werepreferred, due to an acceptable balance between vegetative and fruity characters that still existedafter maturation.
In the case of B, nitrogen fertilization did not affect the FAN content of must. Furthermore, nopositive effect on wine quality could be detected. On the contrary, in most cases it appeared as ifN fertilization affected the balance between vegetative and fruity characters negatively. On thissoil, where vines were growing luxuriously, optimal canopy management practices generallyaffected the N content of must and wine quality positively.
Under dryland conditions soil water levels were low from fruitset to harvest, thus impedingmineralization of organic N and uptake of N. However, where N fertilization was sufficient durïngthe early season, the N content of must was acceptable, while wines were also well balanced.
The study showed that judicious N fertilization can have a beneficial effect on FAN content andfermentation rate, for vineyards on soils with low organic material. Different approaches have tofollowed for different situations. For vineyards on soil with high organic material, nitrogenfertilization has virtually no effect on the FAN content of must, fermentation rate and wine quality.Under such conditions optimal canopy management practices will have a positive effect.
Aanhangsel 1
1 CONCEPT ONLY23 Effect of Nitrogen Fertilizer Timing on Yield, Juice Composition and Wine Quality4 for Sauvignon blanc on two Different Soils.56 W. J. Conradie78 ARC-Fruit, Vine and Wine Research Institute, Nietvoorbij Centre for Vine and Wine,9 Private Bag X5026, Stellenbosch, 7599, Republic of South Africa.
1011 Acknowledgement: Partial funding by Winetech and technical assistance by staff of the12 Soil Science section at Nietvoorbij is gratefully acknowledged.131415 ABSTRACT16
17 The investigation, carried out over three seasons (1996/97 to 1998/99), was aimed at
18 ensuring an optimal nitrogen (N) content in must. Two Sauvignon blanc vineyards, on
19 two different soils, were used. The first soil (A) contained little organic material (0,50%
20 C), in comparison to a relatively high concentration (1,14% C) for the second (B).
21 Varying amounts of nitrogen (N) were applied at different times during the season (post-
22 harvest, budbreak, fruitset and véraison). In conjunction with this, the effect of an
23 optimal canopy management practice (top, suckering, shoot-positioning and removal of
24 leaves) was also compared against a minimum practice (top, shoot-positioning). Most of
25 the treatments received supplementary irrigation, but a dryland treatment was also
26 included, in order to determine the effect of soil water on the mineralization of organic N.
27
28 In the case of A, a single application of N (20 kg/ha) during the post-harvest period failed
29 to increase the free amino nitrogen (FAN) in must to realistic levels. However, where
30 post-harvest application of N (20 kg/ha) was combined with either a single application
31 (40 kg/ha) at budbreak (20-40), or split applications (20 kg/ha) at fruitset as well as
32 veraison (20-20-20), FAN levels in must were increased significantly. A single
33 application during the post-harvest period, in combination with a single application at
34 fruitset (20-20), also increased FAN levels, albeit usually not as much as 20-40 and 20-
35 20-20. On this soil a single application during the post-harvest period, in combination
36 with a single application at veraison was less successful in increasing FAN levels. In
37 general, fermentation rates correlated with FAN contents. However, the rate for 20-20-
38 20 was slightly higher than that of 20-40, suggesting a different amino acid profile.
39 Wines from plots that were either unfertilized, or fertilized in the post-harvest period only,
1 developed a predominant fruity character during maturation, while fresh vegetative
2 character (grass/green pepper) was reduced. In general, wines from plots that received
3 fertilization during spring were preferred, due to an acceptable balance between
4 vegetative and fruity characters that still existed after maturation. In the case of B,
5 nitrogen fertilization did not affect the FAN content of must. Furthermore, no positive
6 effect on wine quality could be detected. On the contrary, in most cases it appeared as if
7 N fertilization affected the balance between vegetative and fruity characters negatively.
8 On this soil, where vines were growing luxuriously, optimal canopy management
9 practices generally affected the N content of must and wine quality positively.
10
11 Under dryland conditions, soil water levels were low from fruitset to harvest, thus
12 impeding mineralization of organic N and uptake of N. However, where N fertilization
13 was sufficient during the early season, the N content of must was acceptable, while
14 wines were also well balanced.
15
16 The study showed that judicious N fertilization can have a beneficial effect on FAN
17 content and fermentation rate, for vineyards on soils with low organic material. Different
18 approaches have to followed for different situations. For vineyards on soil with high
19 organic material, nitrogen fertilization has virtually no effect on the FAN content of must,
20 fermentation rate and wine quality. Under such conditions optimal canopy management
21 practices will have a positive effect.
22
23 INTRODUCTION
24 The importance of nitrogen (N) for yeast growth and fermentation has been discussed in
25 recent publications (Henschke & Jiranek, 1993; Spayd etal., 1994; Jiranek, Langridge
26 & Henschke, 1995; Conradie, 2000b). Even though the exact amount of assimilable N
27 required for a satisfactory rate of fermentation may differ from situation to situation, a
28 concentration of 400 mg/L (Jiranek et al., 1995) is generally regarded as acceptable. At
29 lower concentrations (120 - 140 mg N/L) fermentation rate is unsatisfactory (Agenbach,
30 1977; Spayd, Nagel & Edwards, 1995), leading to the formation of undesirable
31 components, such as H2S (Vos & Gray, 1979). A low N content in must may also affect
32 wine aroma negatively (Bell, Ough & Kliewer, 1979; Ough& Lee, 1981; Rapp & Versini,
33 1991; Henschke & Jiranek, 1993; Conradie, 2000b). Cultivation practices should
34 therefore be aimed at optimizing the N content of must.
1
2 Recent studies showed that N fertilization can have a major effect on the nitrogenous
3 compounds in grapes (Dukes et a/., 1991; Spayd et. al., 1994; Treeby, Holzapfel &
4 Walker, 1995; Larchevêque et.al., 1998; Conradie, 2000b). However, because factors
5 like soil N status (Conradie, 1986; Spayd et al., 1994; Conradie, 2000b),
6 cultivar/rootstock (Treeby et al., 1995; Berger et a/., 1999), climate (Larchevêque et al.,
7 1998; Conradie, 2000b) and cultivation practices (Larchevêque et al., 1998; Conradie,
8 2000b) may override the effectiveness of N fertilizers, results have been conflicting.
9
10 In the coastal region of South Africa, grapevines are cultivated either under dryland
11 conditions or under supplementary irrigation. The latter usually entails two irrigations,
12 applied at fruitset and veraison, respectively. Rainfall during winter and spring is
13 normally sufficient to maintain soil water contents at field capacity up to the time of
14 bloom (Van Zyl & Weber, 1981). Under these conditions (moist soil, relatively high
15 temperatures), mineralization of soil organic matter (SOM) proceeds at a relatively fast
16 rate. Even on soil with low SOM (0,27% C), enough inorganic N can be supplied
17 (Conradie 2000a) to satisfy the demand of grapevines up to bloom (end of October).
18 From fruitset to harvest dry soil conditions, even where supplementary irrigations are
19 applied (Van Zyl & Weber, 1981; Conradie 2000a), impede the mineralization of SOM.
20 As grapevines require more N from bloom to veraison, in comparison to the period
21 preceding bloom (Conradie, 1980), it is essential to have sufficient, albeit not excessive,
22 amounts of N in the root zone during this stage. For irrigated vines, N fertilizers (where
23 necessary) can be applied with the irrigations at fruitset and veraison. Under dryland
24 conditions, however, the efficiency of such applications is questionable, due to low
25 rainfall during the summer months (November, December and January). The only viable
26 option under dryland conditions is to apply N fertilizers a few weeks after budbreak
27 (normally end of September). Usually rainfall during the last part of September and
28 October will be sufficient to wash N into the soil (Conradie, 2000a), while leaching of N
29 should not occur as readily as during the winter months (May to August). However, it
30 has been found that relatively large applications of N at budbreak can cause excessive
31 vegetative growth and dense canopies (Goldspink & Gordon, 1991; Conradie, 2000a),
32 which may lead to bunch rot and lower wine quality. Under such conditions optimal
33 canopy management practices can increase the N content of must.
34
1 The first objective of this study was to compare the effects of N application at budbreak
2 (dryland conditions) and applications at fruitset and veraison (supplementary irrigation),
3 on total N in must, on amino acid profiles and on wine quality. As a second objective the
4 effect of two different canopy management practices were also evaluated. All treatments
5 received post-harvest N applications as a standard practice. The study was carried out
6 on two soils, containing different amounts of SOM.
7
8 MATERIALS AND METHODS
9 Experimental vineyards:
10 The investigation was carried out in two commercial vineyards, both 12 years old, using
11 Vitis vinifera L. cv. Sauvignon blanc, grafted onto 99 Richter as test material. The first
12 vineyard (A) was situated ín the district of Stellenbosch and the second (B) in
13 Franschhoek. In the case of A, vines were trained onto a slanting trellis and for B onto a
14 lengthened Perold (Zeeman, 1981). Soils were classified as being of the Glencoe and
15 Glenrosa forms for A and B, respectively (Soil Classification Working Group, 1991).
16
17 Experimental layout and treatments:
18 For both vineyards the experimental layout comprised a randomized block design, with
19 nine treatments and five replicates. Two border rows and three border vines within the
20 row separated individual plots. Twelve experimental vines per plot were used. The nine
21 treatments (Table 1), commenced in August 1995 and were continued up to the end of
22 the 1998/99 season. The required amounts of N were applied by hand as límestone
23 ammonium nitrate (28% N). Both vineyards were irrigated by means of 50 L/hr micro
24 sprinklers, spaced 1.5 m apart.
25
26 Measurements:
27 Soils were sampled at the start of the investigation and analysed for: pH (1.0 M KCI), P
28 (Bray No. 2), K, Ca and Mg (extracted with 1.0 M ammonium acetate), organic C (The
29 Non-Affiliated Soil Analysis Work Committee, 1990) and total N by means of a Kjedahl
30 digestion (Bremner & Mulvaney, 1982). During the course of the investigation, soils
31 were sampled annually at budbreak, fruitset and veraison, while petioles were sampled
32 at full blootn. All samples were analyzed for NH4-N and NO3-N, by means of an
33 automated colorimetric method (The Non-Affiliated Soil Analysis Work Committee,
34 1990). Leaves (blades and petioles separately) were also sampled annually at fruitset.
1 A Leco Nitrogen Determinator was used to determine total N. Plant tissue levels of P, K,
2 Ca and Mg were determined following dry ashing in a microwave furnace and uptake
3 into acidified aqueous solution, using a Varian 200 inductively coupled plasma atomic
4 emission spectrometer. From December to March soil water contents were measured
5 every two weeks, using the neutron scattering technique, with one access tube per plot.
6 Leaf water potentials were measured at the same time, using the pressure chamber
7 technique of Scholander et al. (1965). Canopy densities were measured at veraison and
8 at harvest, using the point quadrant method (Smart et al., 1990). Shoot mass was
9 determined annually, at which point vines were spur pruned according to vigour.
10 Starting at veraison, berries were sampled at two-week intervals, up to harvest. Berry
11 size was determined, after which berries were crushed in a hydraulic press. Free run
12 juice, was analyzed for sugar content, pH, titrable acidity, total N, P, K, Ca and Mg as
13 already described (Conradie, 2000b). Free amino nitrogen (FAN) was determined with
14 an automated ninhydrin method (Lie, 1973). Results were expressed relative to
15 ammonium sulphate, thus not representing an exact value for amino N concentration.
16 During 1997/98 and 1998/99, individual amino acids were also determined on the juice
17 collected at harvest, using the HPLC method described by Spayd et al. (1994).
18
19 Grapes were harvested at optimum ripeness, as evaluated by vintners. At this stage the
20 sugar content was usually around 21,0°B. Experimental vines were made for three
21 years (1996/97 to 1998/99). After being crushed and de-stemmed, grapes undérwent a
22 skin contact period of 6 hours at 14°C. The rest of the winemaking procedures have
23 been described previously (Conradie, 2000b). During 1998/99, rate of fermentation was
24 determined through regular weighing of the 20 L stainless steel canisters in which juice
25 was fermenting. Wines were evaluated by an experienced panel on a nine-point score
26 card (Tromp & Conradie, 1979).
27
28 RESULTS AND DISCUSSION
29
30 Soil water status:
31 Seasonal fluctuation in soil water contents followed a similar pattern to that described in
32 detail by Van Zyl & Weber (1981), for soil with comparable texture. Basically, plant
33 available water in the topsoil (0-600 mm) was totally depleted before veraison in the
34 case of the dryland treatments (No's 4 and 5). For the irrigated treatments, soil water
1 was replenished to field capacity, in the 0-600 mm layer, at fruitset and at veraison. In
2 between these irrigations, however, plant available water in the topsoil was nearly
3 depleted, while it was totally depleted between the veraison irrigation and harvest. In
4 conjunction with this, leaf water potentials showed lower water stress for irrigated
5 treatments after the irrigation at fruitset, but values were comparable to that of dryland
6 treatments during the period immediately preceding the irrigation at veraison. Following
7 the irrigation at veraison, water stress was reduced, but after approximately three weeks
8 no differences could again be detected between irrigated and dryland treatments.
9 Values, measured between 12:00 and 14:00 were sometimes as low as - 1800 kPA. In
10 spite of this, visual signs of water stress were hardly encountered. This is in agreement
11 with the theory of Van Zyl & Weber (1981), i.e. that the deeper soil layers (> 600 mm)
12 can act as a large reservoir for water supplied by winter rainfall. During summer this
13 reservoir is emptied slowly by the upward movement of water into the root zone.
14
15 Chemical soil analyses:
16 The P-content of soil from vineyard A, averaged 19 mg/kg (Table 2) over the sampling
17 depth (0-600 mm), which should be adequate for this type of soil (Saayman, 1981). A
18 much higher P-content (average of 49 mg/kg over the sampling depth) was found for
19 vineyard B. Such high values may suppress the uptake of K (Conradie & Saayman,
20 1989a). Potassium content was around 60 mg/kg for both soils, thus being normal for
21 this type of soil in the Western Cape (Saayman, 1981). The C-content of soil from
22 vineyard A was appreciably lower than that of B, especially in the subsoil. The same
23 pattern applied for total N. The N supplying capacity of A should, therefore, be
24 appreciably lower than that of B. This could have a major effect on the annual
25 requirement for N fertilizers (Conradie, 2000a).
26
27 Application of N at budbreak was reflected by higher NO3-N in soil from Treatment 4
28 (Table 3). At this stage NO3-N in soil from control plots showed lower values for
29 vineyard A than for vineyard B, confirming a higher N-supplying capacity for soil from
30 vineyard B. At véraison, however, topsoil (0-150 mm) from control plots contained
31 comparable amounts of NO3-N for A and B, even though NO3-N in subsoil (150-300 mm
32 and 300-600 mm) still tended to be lower for A than for B. This pointed towards largely
33 different N-supplying capacities during the early part of the season, for soils containing
34 varying amounts of organic material, but relatively small differences during the latter part
1 of the season. This was probably due to relatively low soil water contents during the
2 latter parts of the growing season. Under such conditions mineralization of organic N
3 and uptake of inorganic N can be impeded (Haynes, 1986). Comparable results have
4 been obtained on a sandy soil with low organic material (Conradie, 2000b). It can be
5 expected that much higher NO3-N contents would have been found, especially in the
6 case of B, if the vineyards had been irrigated intensively. At veraison topsoil (0-150 mm)
7 reflected application of N at this stage (Treatments 6 and 8), for both A and B. Values
8 tended to be slightly lower where N was applied at budbreak (Treatment 4) or at fruitset
9 (Treatment 9). For both soils a much lower value, similar to that of the control, was
10 found for Treatment 2, which received post-harvest fertilization only. Higher values were
11 therefore the result of N fertilization during the growing season. Some of the N, which
12 was applied at budbreak under dryland conditions (Treatment 4), was obviously still
13 available at veraison. The same applied to N applied just before the irrigation at fruitset
14 (Treatment 9).
15
16 Leaf analysis:
17 When petioles were sampled (bloom) for NO3-N determination, the budbreak application
18 of N had already been made (Treatments 4 and 5). For vineyard A, these applications
19 were clearly reflected by the NO3-N values (Table 4). Higher NO3-N concentrations were
20 found for vineyard B, while the effect of budbreak applications of N could not be
21 detected. These results suggested a positive reaction to budbreak fertilization for the
22 soil with the lowest N-supplying capacity, while fertilization was probably not necessary
23 for the soil with the higher N supplying capacity. Results from the current trial confirmed
24 (Conradie, 2000b) that the NO3-N levels in petioles from grapevines under
25 supplementary irrigation tends to be low, in comparison to values of higher than 1000
26 mg/kg for vines under intensive irrigation (Conradie & Van Huyssteen, 1993). However,
27 in spite of the low values, a threshold value of 100 mg/kg for Sauvignon blanc under
28 supplementary irrigation is suggested (Table 4). None of the fertilization treatments
29 affected the total N content of petioles. In contract to NO3-N values, there was also no
30 differences between total N levels for vineyards A and B. This confirmed the greater
31 sensitivity of NO3-N in comparison to total N, for identifying differences in N nutritional
32 status (Kliewer, 1991; Conradie, 2000b).
33
34 Shoot mass and grape yield:
8
1 In spite of the larger trellising system at A, shoot masses were comparable for the two
2 vineyards (Table 5), indicating more vigorous growth in the case of B. This was also
3 illustrated by a higher crop load (yield/shoot mass) for vineyard A (average of 4.01), in
4 comparison to B (average of 2,62).
5
6 Nitrogen fertilization, regardless of timing, did not affect shoot mass of vineyard A. This
7 is in contrast to certain studies where N fertilization increased shoot mass significantly
8 (Conradie & Saayman, 1989a; Spayd et a/., 1983; Conradie, 2000a). However, in
9 other studies (Bravdo & Hepner, 1987; Wolf & Pool, 1988) N fertilization did not affect
10 pruning weight. This is in agreement with the theory that the N requirement of vines can
11 be satisfied by soil N and that vine N concentrations may increase (Table 4), without
12 shoot mass being affected (Wolf & Pool, 1988). In the case of vineyard B, higher shoot
13 masses were obtained for Treatments 1, 3 and 7. This was probably on account of
14 these treatments not being suckered at fruitset. As for vineyard A, nitrogen fertilization,
15 regardless of timing, did not affect shoot mass.
16
17 Even though nitrogen fertilization did not affect the yield of vineyard A significantly, the
18 control (Table 5) yielded 8,3% less than the fertilized treatments (average of 10,18
19 ton/ha). Under certain situations it may take several years of no N fertilizer before yield
20 will be reduced (Lóhnertz, 1991), while a rapid reaction may be found in other cases
21 (Spayd et al, 1993; Conradie 2000a). In the case of vineyard A, a significant response
22 to N fertilization may have been found if the trial had been continued for a longer time.
23 In contrast to vineyard A, the control had the highest yield for vineyard B. The significant
24 lower yield of Treatment 5 can, as in the case of shoot mass, be ascribed to canopy
25 management practices. For this vineyard, on soil with high organic material, a response
26 to N fertilization is unlikely, even over the long term.
27
28 Canopy management appeared to increase sugar concentration for vineyard A (2 vs 3, 4
29 vs 5, 6 vs 7). Apart from this, fertilization at veraison (Treatments 7 & 8) appeared to
30 reduce sugar concentration. Titrable acidity (TA) and pH were not affected significantly
31 for vineyard A. For vineyard B, highest sugar concentrations were found for some of the
32 treatments (1, 8 and 9) that received optimal canopy management practices. No clear
33 response to N fertilization could be detected, even though Treatment 7, split applications
34 of N at fruitset and veraison, together with minimum canopy management) had the
1 lowest sugar content. The highest TA and the lowest pH was also found for this
2 treatment.
3
4 Canopy density:
5 Evaluation, according to the method of Smart et al. (1990), indicated a much denser
6 canopy for vineyard B. Where minimal canopy management was done, leaf layer
7 number (LLN) amounted to 3,5 for vineyard A, in comparison to 4,8 for vineyard B. Less
8 than 10% of the bunches in vineyard B was exposed, against approximately 20% for
9 vineyard A. Optimal canopy management practices did not affect LLN too much for
10 vineyard A, but in the case of vineyard B it was reduced to 3,4, while bunch exposure
11 was increased to 30%, for both vineyards.
12
13 Juice analysis:
14 Total N (TN) in juice from vineyard A (Table 6) was lowest for the control and for the
15 treatment where post-harvest fertilization was combined with optimal canopy
16 management (Treatment 2). Where post-harvest fertilization was combined with
17 minimum canopy management, TN tended to be higher. This result was unexpected, as
18 canopy management did not seem to affect TN for the other treatments (4 vs 5; 6 vs 7).
19 No significant differences in TN occurred between treatments fertilized during spring (4-
20 9). However, application during the post-harvest period, in combination with an
21 application at veraison (Treatment 8), resulted in slightly lower TN. This may have been
22 on account of the period from veraison to harvest being too short to affect any major
23 increase in TN, or on account of the lower sugar content (Table 5). The fact that a single
24 post-harvest application of N was relatively ineffective in increasing TN, is in contract to
25 results obtained for Bukettraube and Heroldrebe on Ramsey (Conradie, 2000b), but is in
26 agreement with results obtained for Sauvignon blanc on Schwarzmann rootstock
27 (Goldspink & Gordon, 1991). It has been suggested that different responses can be
28 expected for different scion/rootstock combinations (Treeby et al., 1995; Berger et al.,
29 1999). Vine vigour, being largely affected by scion/rootstock combinations, as well as
30 soil-N content, cultural practices and climatic factors, can override the effectiveness of N
31 fertilizer in increasing TN of juice (Conradie 2000b). The post-harvest application (20 g
32 N/ha), may also have been too small. Where positive responses to single post-harvest
33 applications of N were found, application rates were usually around 50 kg N/ha (Peacock
34 et al., 1991; Christensen et al., 1994; Conradie, 2000b). In general, TN for vineyard A
10
1 did not correlate with NO3-N in petioles (Table 4). This is in agreement with results
2 obtained for Chardonnay (Treeby et a/., 1998). However, on soils with low organic
3 material (not exceeding 0,3% C), where significant yield responses to N fertilization were
4 found (Spayd et a/., 1995; Conradie, 2000b), a relationship between TN and NO3-N in
5 petioles did exist. For vineyard A, FAN correlated with TN and differences for FAN
6 appeared to be slightly more pronounced than found for TN. For vineyard B, neither TN
7 nor FAN was affected significantly by N fertilization. However, in the case of FAN it
8 appeared as if optimal canopy management practices caused a slight, albeit
9 insignificant, increase (2 vs 3; 4 vs 5; 6 vs 7). In general, TN and FAN values for
10 vineyard B tended to be low, in comparison to their counterparts for vineyard A. This
11 implied that excessive vigour may be detrimental to the formation of nitrogeneous
12 substances in juice.
13 The most abundant amino acids (for vineyard A) were arginine and proline, followed by
14 alanine, aspartic acid, glutamic acid, glutamine and histidine (Table 7). In general, this is
15 in agreement with profiles identified by others (Henschke & Jiranek, 1993; Larchêveque
16 et al., 1998, Hernandez-Orte et al., 1999). In a South African study (Conradie, 2000b)
17 with Bukettraube, relatively low concentrations of aspartic acid and glutamic acid were
18 found, probably because concentrations of individual amino acids may vary from season
19 to season (Larchevêque et al., 1999). In contrast to TN and FAN, N fertilization did not
20 affect total amino N (sum of individual amino acids) significantly. For the control, 86% of
21 the total N in juice appeared to be present as amino acids, in contrast to only 62% where
22 N was applied as a síngle increment at budbreak (Treatments 4 and 5). Little is known
23 about the factors affecting the distribution between assimilable N (mainly amino acids)
24 and non-assimilable N (mainly peptides and proteins). As for Bukettraube and
25 Heroldrebe (Conradie, 2000b), fertilization at budbreak increased NO3-N in petioles
26 (Table 4), but not necessarily the concentration of assimilable N.
27
28 No clear tendencies for either amino acid profiles or total amino N could be detected for
29 vineyard B (not shown). In general, distribution of amino acids was comparable to that
30 of vineyard A.
31
32 Fermentation rate:
33 Fermentation rates showed appreciable differences for vineyard A. For greater clarity
34 results for only six treatments are presented in Figure 1. Juice from the control
11
1 fermented slowest, followed by the treatments that received post-harvest fertilization only
2 (No's 2 and 3). Fermentation was not yet completed after 11,63 days. In contrast,
3 where N was applied at fruitset as well as veraison (No's 6 and 7), fermentation was
4 completed after 8,02 days. An intermediate fermentation rate was found where N was
5 applied at budbreak (No. 5). Treatments not shown in Figure 1 (No's 4, 8 and 9) also
6 fermented at intermediate rates. In general, fermentation rate correlated with FAN
7 content (Table 6). Fermentation rate for vineyard B (not shown) was not affected by N
8 fertilization and fermentation was completed after approximately 10 days.
9
10 Wine quality:
11 Organoleptic evaluation of experimental wines tended to be more consistent after 18
12 months, in comparison to evaluation after 6 months. As an example, results for wines
13 from 1997/98, evaluated after 18 months, are shown in Table 8A. For vineyard A,
14 overall quality was lowest for the control and highest where post-harvest fertilization was
15 combined with a single application at fruitset (Treatment 9). During maturation
16 vegetative character was reduced, while a fruity characters developed. In the case of
17 the control, the imbalance between vegetative/fruity character, resulted in this wine being
18 slightly inferior to the others. Overall wine quality did not differ for vineyard B. In this
19 case some of the treatments that received N fertilizer at fruitset and/or at veraison (No's
20 6, 7 and 8) scored relatively low for vegetative character. Even though vegetative
21 growth was stimulated through N fertilization at fruitset or veraison, the concentration of
22 aromatic components was apparently not increased. Due to the competition between
23 vegetative and reproductive growth (Conradie, 1991), N fertilization may even reduce the
24 concentration of aromatic components. No significant difference occurred for 1998/99
25 wines from vineyard A, when evaluated after six months. (Table 8B). For vineyard B,
26 fertilization during the post-harvest period (No. 3), at budbreak (No. 4) or at veraison
27 (No. 8), increased wine quality. The reason for this was unclear. As in the case of
28 1997/98 wines (Table 8A), the treatments that received N fertílization at fruitset (No's 6,
29 7 and 9) again received a relatively low score for vegetative character. The 1998/99
30 wines still have to be evaluated after 18 months.
31
12
1 LITERATURE CITED
2
3 AGENBACH, W.A., 1977. A study of must nitrogen content in relation to incomplete
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33 CONRADIE, W.J., 1991. Translocation and storage of nitrogen by grapevines as affected by time
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13
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12
13 CONRADIE, W.J. & SAAYMAN, D., 1989(b). Effects of long-term nitrogen, phosphorus and
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15 Am. J. Enol. Vitic. 40, 91-98.
16
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20
21 DUKES, B., GOLDSPINK, B., ELLIOTT, J. & FRAYNE, R., 1991. Time of nitrogen fertilization
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25
26 GOLDSPINK, B. & GORDON, C, 1991. Response of Vitis vinifera cv. Sauvignon blanc
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30
31 HAYNES, R.J., 1986. Mineral nitrogen in the plant-soil system. Academic Press Inc, Orlando,
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33
34 HENSCHKE, P.A. & JIRANEK, V., 1993. Yeasts-metabolism of nitrogen compounds. In: G.H.
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36 Chur, Switzerland, pp. 77-164.
37
14
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4
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8
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12
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17
18 LIE, S., 1973. The EBC-ninhydrin method for determination of free alpha amino nitrogen. J. Inst.
19 Brew. 79, 37-41.
20
21 LÓHNERTZ, 0., 1991. Soil nitrogen and the uptake of nitrogen in grapevines. In : J.M. RANTZ
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24
25 OUGH, C.S. & LEE, T.H., 1981. Effect of vineyard nitrogen fertilization level on the formation of
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27
28 PEACOCK, W.L., CHRISTENSEN, L.P. & HIRSCHFELT, D., 1991. Influence of timing of
29 nitrogen fertilizer application on grapevines in the San Joaquin Valley. Am. J. Enol.
30 Vitic. 42, 322-326.
31
32 RAPP, A. & VERSINI, G., 1991. Influence of nitrogen compounds in grapes on aroma
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35
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15
1
2 SCHOLANDER, P.F., HAMMEL, H.T., BRADSTREET, E.D. & HEMMINGSEN, E.A., 1965. Sap
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4
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8
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11
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16
17 SPAYD, S.E., WAMPLE, R.L, STEVENS, R.G., EVANS, R.G. & KAWAKAMI, A.K., 1993.
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21
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25
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28
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32
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36
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4
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7
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11
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13 of grape must. Am. J. Enol. Vitic. 30, 187-197.
14
15 WOLF, T.K. & POOL, R.M., 1988. Effects of rootstock and nitrogen fertilization on the growth
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17
18 ZEEMAN, A.S., 1981. Oplei. In: J. Burger & J. Deist (eds), Wingerdbou in Suid-Afrika.
19 Nietvoorbij, Stellenbosch, South Africa, pp. 185-201.
17
Table 1: Treatments applied in two Sauvignon bianc vineyards from 1995/96 to 1998/99.
Treatment
1(C)
2 (PH + CM)
3(PH)
4 (BB + CM)
5(BB)
6(F + V + CM)
7(F + V)
8 (V + CM)
9 (F + CM)
lrrigated(1)
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Canopy
Management(2)
Normal
Optimal
Normal
Optimal
Normal
Optimal
Normal
Optimal
Optimal
Nitrogen Applied (kg N/ha/yr)(3)
Post-harvest
0
20
20
20
20
20
20
20
20
Bud-break
0
0
0
40
40
0
0
0
0
Fruitset
0
0
0
0
0
20
20
0
20
Veraison
0
0
0
0
0
20
20
20
0
Total
0
20
20
60
60
60
60
40
40
(1) Where applicable, vines were irrigated at fruitset and at veraison.(2) Where indicated as "normal", vines were topped and shoots were positioned. No further canopy management was
done. Where indicated as "optimal", additional canopy management practices.entailing suckering at budbreak and
removal of one third of the leaves on the basal part of shoots, were applied(3) Fertilizer applied as limestone ammonium nitrate (28% N)
18
Table 2: Chemical analysis of soils, planted to Sauvignon blanc, at the start of the investigation (average for
all treatments, as measured in 1995).
Vineyard
A
Sampling
Depth (mm)
0-15
15-30
30-60
PH
5.93
5.59
5.23
P (mg/kg)
33.3
12.6
11.4
K (mg/kg)
80
65
69
Ca
(cmol/kg)
3.12
1.88
1.55
Mg
(cmol/kg)
0.67
0.47
0.43
C (%)
0.89
0.39
0.35
N (%)
0.035
0.033
0.031
B
0-15
15-30
30-60
6.08
5.86
5.76
71.7
42:2
33.3
64
46
43
4.97
3.91
3.30
0.81
0.59
0.61
1.31
1.16
1.04
0.081
0.060
0.056
19
Table 3 Nitrate content of soils, planted to Sauvignon blanc, as measured at budbreak and veraison
in 1997/98 (mg N/kg)
Vineyard
A
Treatment(1)
1(C)
2 (PH+CM)
4 (BB+CM)
6 (F+V+CM)
8 (V+CM)
9 (F+CM)
Budbreak
0-150 mm
3.6 a(2)
5.5 ab
10.6 a
4.1 a
3.4 a
4.3 a
150-300
mm
1.8a
1.9a
3.2 a
1.9 a
1.5 a
3.7 a
300-600
mm
1.2 a
1.4 a
2.0 a
1.3 a
1.0a
1.3a
Veraison
0-150
mm
4.1 a
3.3 a
7.0 a
13.8 b
9.0 ab
4.8 a
150-300
mm
3.2 a
2.5 a
2.9 a
2.7 a
5.2 a
3.2 a
300-600
mm
2.0 a
2.2 a
3.0 a
2.9 a
3.6 a
2.8 a
B
KC)
2 (PH+CM)
4 (BB+CM)
6 (F+V+CM)
8 (V+CM)
9 (F+CM)
9.3 a
10.7 a
43.8 c
11.1 a
8.4 b
8.9 b
5.4 a
3.3 a
6.2 c
2.7 a
3.4 a
2.9 a
4.7 a
1.8a
9.0 a
2.3 a
2.8 a
2.1 a
3.4 a
4.3 ab
9.7 ab
18.9 c
11.8 b
7.1 ab
4.6 a
3.2 a
5.5 a
5.6 a
8.6 a
4.3 a
4.5 a
3.4 a
5.6 a
8.9 a
8.6 a
4.3 a
(1) See Table 1 for full details of treatments.
Values within columns followed by the same letter do not differ significantly (p < 0.05).
20
Table 4: Petiole analysis for two Sauvignon blanc vineyards, planted on different
soils (mean values for 1996/97 - 1998/99).
Treatment('1)
1(C)
2 (PH + CM)
3(PH)
4 (BB + CM)
5(BB)
6(F + V + CM)
7(F + V)
8 (V + CM)
9 (F + CM)
Vineyard A
NO3-N
(mg/kg)
66a(2)
74a
87a
124ab
163b
89a
94a
88a
98a
Total N (%)
0.58a
0.62a
0.59a
0.65a
0.66a
0.64a
0.66a
0.68a
0.69a
Vineyard B
NO3-N
(mg/kg)
222a
190a
187a
149a
155a
167a
185a
151a
152a
Total N (%)
0.61a
0.59a
0.59a
0.59a
0.58a
0.62a
0.61a
0.62a
0.60a
(1) See Table 1 for full details of treatments.
(2) Value within columns followed by the same letters do not differ significantly (p<0.05).
21
Table 5. Shoot mass, yield and grape analysis for two Sauvignon blanc vineyards, planted on two different
soils (mean values for 1996/97 to 1998/99).
Treatment(1)
1 (C)2 (PH+CM)
3(PH)
4 (BB+CM)
5(BB)
6 (F+V+CM)
7(F+V)
8 (V+CM)
9 (F+CM)
Vineyard A
Shoot
mass
(ton/ha)
2.62 a
2.25 a
2.60 a
2.32 a
2.65 a
2.64 a
2.50 a
2.59 a
2.47 a
Yield
(ton/ha)
9.33 a
9.75 a
10.51 a
9.53 a
10.09 a
10.40 a
10.51 a
10.98 a
9.73 a
Sugar
(°B)
20.89 ab
20.87 ab
21.13a
20.79 ab
20.75 ab
20.76 ab
20.49 b
20.36 b
20.81 ab
TTA(2)
(g/L)
9.42 a
9.13 a
9.23 a
8.97 a
9.39 a
9.31 a
9.74 a
9.63 a
9.49 a
PH
3.05 a
3.01 a
3.05 a
3.05 a
3.04 a
3.03 a
3.02 a
3.00 a
3.02 a
Vineyard B
Shoot
mass
(ton/ha)
2.91 a
2.44 ab
2.89 a
2.34 b
2.56 ab
2.48 ab
2.95 a
2.61 ab
2.53 ab
Yield
(ton/ha)
7.82 a
6.98 ab
7.61 ab
5.90 b
7.20 ab
5.99 ab
7.18 ab
5.99 ab
7.46 ab
Sugar
(°B)
20.76 ab
20.49 a
20.67 ab
21.44 b
20.97 ab
20.78 ab
20.41 a
21.16 ab
21.19 ab
TTA(2)
(g/L)
9.95 a
9.55 ab
9.83 ab
9.04 b
9.92 a
9.33 ab
10.39 a
9.41 ab
9.18 ab
PH
3.04 a
3.01 ab
3.03 ab
3.02 ab
3.00 b
3.02 ab
3.00 b
3.01 ab
3.01 ab
(1) See Table 1 for full details of treatments.
(2) TTA = Total titratable acidity.
22
Table 6. Juice analysis for two Sauvignon blanc vineyards, planted on different soils (mean values for 1996/97 to 1998/99)
Treatment(1)
1(C)
2 (PH+CM)
3(PH)
4 (BB+CM)
5(BB)
6 (F+V+CM)
7(F+V)
8 (V+CM)
9 (F+CM)
Total
408a
401a
474ab
528b
520b
511b
540b
465ab
513b
Vineyard
N (mg/L)
A
FAN (mg/L)(2)
705a
730a
854b
964bcd
973cd
984cd
1034d
911bc
946bcd
Total
434a
391a
420a
440a
431a
434a
438a
439a
442a
Vineyard
N (mg/L)
B
FAN(mg/L)(2)
770a
772a
701a
857a
836a
858a
813a
811a
831a
<1) See Table 1 for full details of treatments.
FAN = free amino nitrogen, determined with a wet chemical method. Not absolute values. Refer to section on Materials and Methods.
Table 7. Amino acids in juice from vineyard A (1998/99).23
Amino acid (µmol N/L)
Alanine
Arginine
Asparagine
Aspartic acid
Glycine
Glutamic acid
Glutamine
Histidine
Isoleucine
Leucine
Lycine
Phenylalanine
Proline
Serine
Threonine
Valine
Other(2)
Total amino-N (mg/L)(3)
FAN (mg/L)(4)
Total N (mg/L)
Treatment
421 a
1934ab
153a
271a
60a
172a
194a
308b
75a
77a
96a
55a
801 a
162a
162ab
170a
127a
374a
784a
435a
2
530a
2455b
86a
338ab
76ab
192a
266a
Oa
82a
94ab
114ab
68a
912a
169a
179ab
224a
Oa
413a
796a
437a
3
509a
2198ab
82a
241 a
83ab
207a
253a
41ab
75a
93ab
114ab
55a
920a
154a
165ab
163a
Oa
382a
950b
517abc
4
396a
1815ab
133a
315ab
90ab
153a
181a
83ab
79a
86ab
115ab
59a
1051a
144a
179ab
183a
58a
366a
964b
589c
5
363a
1622a
193a
212a
78ab
157a
158a
86ab
73a
73a
110ab
51a
1008a
136a
129a
161a
80a
335a
968b
537bc
6
561a
2442b
170a
233a
144b
202a
185a
221ab
80a
90ab
116b
64a
1151a
166a
195b
174a
78a
448a
994b
552bc
7
476a
2181ab
88a
211a
84ab
179a
249a
Oa
75a
89ab
113ab
58a
855a
135a
175ab
174a
0a
367a
1010b
535bc
8
487a
1903ab
124a
212a
121ab
180a
226a
302ab
84a
92ab
113ab
63a
1021a
157a
176ab
201a
86a
397a
994b
493ab
9
542a
2470b
135a
473b
105ab
198a
225a
148ab
84a
104b
113ab
62a
1121a
177a
188b
221a
54a
459a
1060b
592c
(1) See Table 1 for description of treatments(3) Calculated from individual amino acid contents
(2) Cysteine, methionine, and tyrosine(4) Standard (wet chemical) method
24
Table 8. Wine quality for two Sauvignon blanc vineyards, planted on different soils.
A: Quality of 1997/98 wines, evaluated after 18 months.
Treatment(1)
1
2
3
4
5
6
7
8
9
Overall winequality
(%)
49.6a
54.7ab
51.7ab
55.5ab
52.5ab
51.8ab
51.6ab
52.0ab
57.7b
Vineyard A
Vegetativecharacter
(%)
25.9a
33.5abc
40.9c
36.0bc
32.9ab
35.0bc
39.5bc
33.5abc
39.6bc
Fruitycharacter
(%)
43.5bc
44.7c
35.3ab
38.3abc
39.5abc
32.8a
30.4a
32.2a
38.7abc
Vineyard B
Overall winequality
(%)
51.7a
47.0a
51.6a
53.9a
49.0a
51.2a
48.9a
50.0a
55.2a
Vegetatívecharacter
(%)
23.0ab
34.4bc
36.6c
40.2c
30.4abc
20.1a
29.0abc
22.6ab
36.2c
Fruitycharacter
(%)
32.9ab
34.6ab
36.1ab
32.2a
30.1a
39.8ab
29.2a
46.9b
37.3ab
(1) See Table 1 for description of treatments.
B: Quality of 1997/98 wines, evaluated after 6 months.
Treatment (1 )
1
2
3
4
5
6
7
8
9
Vineyard A
Overall winequality
(%)
48.0a
58.1a
58.8a
52.8a
56.4a
56.1a
48.4a
56.5a
56.5a
Vegetativecharacter
(%)
30.6a
40.4a
33.7a
30.2a
37.2a
31.8a
30.4a
37.6a
34.8a
Fruitycharacter
(%)
38.6a
40.5a
46.9a
56.4a
46.9a
43.1a
47.1a
48.1a
37.3a
Vineyard B
Overall winequality
(%)
35.4a
34.2a
46.9b
46.4b
34.8a
34.2a
40.6ab
46.5b
37.6ab
Vegetativecharacter
(%)
20.0ab
34.3d
30.3cd
29.7cd
22.1abc
24.0abc
18.2a
32.6d
26.8bcd
Fruitycharacter
(%)
38.0a
34.8a
40.5a
46.2a
32.7a
34.2a
37.7a
43.8a
32.3a
(1) See Table 1 for description of treatments.
Aanhangsel 2
KONSEP ALLEENLIK
Praktiese riglyne om die stikstofinhoud van mos te optimiseer.
W.J. Conradie
LNR Navorsingsinstituut vir Vrugte, Wingerd en Wyn. Nietvoorbij Sentrum vir Wingerd en Wyn,
Privaatsak X5026, 7599 Stellenbosch.
'n Ondersoek, wat daarop gemik was om 'n optimale stikstofinhoud in mos te verseker, is oor drie
seisoene (1996/97 tot 1998/99) uitgevoer. Twee Sauvignon blanc wingerde, op twee verskillende
gronde, is gebruik. Die eerste grond het min organiese materiaal (0,50% C) bevat, in vergelyking
met 'n relatief hoë konsentrasie (1,14% C) by die tweede. Verskillende hoeveelhede stikstof (N)
is op verskillende tye gedurende die seisoen (na-oes, bot, vrugset en deurslaan) toegedien. In
kombinasie hiermee is die effek van 'n optimale lowerbestuurspraktyk (top, suier, insteek van
lote, uitbreek van blare) ook vergelyk met 'n minimum praktyk (top, insteek van lote). Meeste van
die behandelings is aanvullend besproei, maar 'n droëlandbehandeling is ook ingesluit, ten einde
effek van grondwater op mineralisasie van organiese N vas te stel. Resultate wat oor verloop
van die ondersoek ingesamel is, kan as volg opgesom word:
1. Dit is duidelik dat daar nie 'n "standaard" stikstofbemestingsprogram, vir die verkryging van
optimale stikstofinhoude in mos, vir alle gronde gevolg kon word nie. Onder Wes-Kaapland
se klimaatsbestande voorsien gronde met hoë organiese materiaal tot en met vrugset meer
as voldoende N om in wingerd se behoeftes te voorsien. Vir gronde met lae organiese
materiaal is na-oes bemesting nie voldoende nie en is bemesting na bot aangewese.
Bemesting moet normaalweg nie voor einde September toegedien word nie, aangesien
winterreën stikstof kan uitloog voordat stokke dit kan benut.
2. By droëlandwingerde is grondwater normaalweg laag vanaf begin/middel Desember
(ertjiekorrel stadium) tot oestyd. Onder sulke toestande vind min mineralisasie van
organiese materiaal plaas, gevolglik verskil die N-leweringsvermoë van gronde met hoë en
lae organiese materíaal nie in hierdie periode meer so baie nie. In die geval van gronde
met hoë organiese materiaal, word anorganiese stikstof egter oorgedra uit die vorige
groeistadium (bot tot vrugset), terwyl dit nie vir gronde met lae organiese materiaal die
geval is nie. Bemesting is dus aangewese. Selfs waar aanvullende besproeiing toegepas
word, is grondwater vir aansienlike periodes relatief laag en vind min mineralísasie plaas.
Die situasie sal egter heeltemaal anders wees vir wingerde wat intensíef besproei word.
Onder sulke omstandighede droog die grond nooít heeltemaal uit nie en vind mineralisasie
van organiese materiaal geredelik plaas Stikstofbemesting, selfs op gronde met lae
organiese materiaal, sal dus met veel meer omsigtigheid toegedien moet word.
3. By droëlandwingerde is dit normaalweg nie die moeite werd om bemesting na vrugset toe
te dien nie, aangesien reënval te laag is om bemesting in te was. By wingerde wat
aanvullend besproei word, kan bemesting (waar benodig) egter óf met vrugset óf met
deurslaan toegedien word. Resultate het daarop gedui dat beter resultate met die
toediening teen vrugset behaal word. 'n Enkeltoediening teen vrugset behoort normaalweg
voldoende te wees, maar dit kan in sommige gevalle aangevul word met bemesting teen
deurslaan. 'n Enkeltoediening teen deurslaan is normaalweg nie effektief nie, waarskynlik
omdat die tydsperk vanaf deurslaan tot oes te kort is om 'n wesenlíke verandering in die
stikstofinhoude van mos teweeg te bring. Aan die ander kant, waar stikstofbemesting nje
benodig word nie sal bemesting teen vrugset groter skade aanrig as dië teen deurslaan. In
eersgenoemde geval word groei oormatig gestimuleer wat veroorsaak dat die
stikstofhuishouding en geurkomponente van trosse nadelig beïnvloed word.
4. Waar gronde met 'n lae stikstofstatus nie voldoende bemes word nie, is die stikstofinhoud
van mos laag en gisting kan nadelig beïnvloed word. Dit lei by Sauvignon blanc tot wyne
met 'n lae vegetatiewe (gras/soetrissie) karakter, terwyl tropiese karakter (pynappel,
spanspek, piesang, koejawel) oorheersend is. Waar wingerde teen bot (droëland) of teen
vrugset (aanvullend besproei) bemes word, word stikstofinhoude in mos verhoog en toon
wyne 'n goeie balans tussen vegetatiewe en tropiese karakter. Dit moet egter beklemtoon
word dat hierdie resultaat slegs verkry word waar N-bemesting weí benodig word. Waar dit
nie benodig word nie het N-bemesting min/geen effek op die N-inhoud van mos en kan die
geurstofbalans van wyne nadelig beïnvloed word.
5. By wingerde wat oormatig groei kan optimale lowerbestuurspraktyke meehelp om die
stikstofinhoud van mos te verhoog, terwyl stikstofbemesting min/geen positiewe rol kan
speel nie. By wingerde wat minder geil groei het lowerbestuur uiteraand 'n veel kleiner
effek.
6. Die organiese materiaalinhoud van grond kan as 'n breë riglyn dien by die daarstelling van
stikstofbemestingsriglyne (Tabel 1). Hierdie riglyne sal aangepas moet word aan die hand
van wingerd se groeikragtigheid, maar kan dien as breë vertrekpunt.
Tabel 1. Bemestingsriglyne gebaseer op die organiese material in grond (1).
Koolstof
>0.9
0.6-0.9
0.3-0.6
<0.3
Stikstofbemesting (kg N/ha)
Na-oes
-
20
20
20
Bot
-
-
-
20
Vrugset
-
-
(20) (2)
20
Deurslaan
-
-
-
(20) (2)
(1) Normaalweg van toepassing vir gronde wat > 6% klei bevat. Vir sanderige gronde kanstikstof in meer paaiemente verdeel word.
(2) Word slegs toegedien waar stokke se groeikragtigheid swakker as nomnaal/ideaal is.