Thesis (MScAgric)--University of Stellenbosch, 2001.ENGLISH ABSTRACT: Yield and fruit quality of Citrus species relative to foliar sprays of macronutrients
Marginal fruit colour and poor internal quality have been primary problems in the production of
early-maturing mandarins in the Western Cape region (34 Os t 9°E). This leads to a reduction in the
percentage of exportable fruit, a delay in the picking and consequent reduction in internal quality
due to over-maturity. Therefore, a well-developed rind colour and internal quality of citrus are
quality parameters of major importance in the fruit market.
The effect of soil-applied limestone ammonium nitrate (LAN) and foliar low-biuret on fruit colour,
yield and internal fruit quality of 'Mihowase' Satsuma on 'Troyer' citrange rootstock were
evaluated. A significant reduction in leaf N levels was recorded where soil N has been reduced
from 168 kg N/ha per annum to 126 kg Nlha per annum. Nitrogen applications influenced internal
quality, although differences between treatments were too small to be of commercial importance.
Despite tree appearance being more yellow in some years where N was predominantly applied as
foliar spray, no consistent reduction in fruit size or yield was found. There were no clear significant
differences in fruit colour, probably due to the fact that leaf N-Ievels were still within or below the
norms suggested for Satsuma.
The effect of Seniphosf , a mineral mixture of 31Og/L P20S, 56g/L CaO and 30g/L total N, and
mono-potassium phosphate (MKP) [52% P20Sand 34% K20] on fruit colour, yield and internal fruit
quality of mandarins, viz., 'Mihowase' Satsuma and 'Nules' Clementine on 'Troyer' citrange
rootstock were evaluated. Seniphos'" and MKP applied during autumn colour break also did not
influence fruit colour, yield and internal fruit quality, viz., juice content (%), total soluble solids
(TSS), titratable acid (TA) and TSS:TA ratio of 'Nules' Clementine and 'Mihowase' Satsuma. In the Citrusdal region of South Africa (Western Cape Province), rind roughness is a general
problem which often limits the percentage of exportable fruits. The effect of foliar mono-potassium
phosphate (MKP) applied at 3% or 5% and urea ammonium phosphate (UAP) at 2% at 4 or 6
weeks, respectively, after full bloom (AFB) on yield, internal and external fruit quality (rind
texture) of Citrus spp on rough lemon rootstock were evaluated. MKP and UAP had no consistent
effect on yield, juice content (%), TSS, TA and TSS:TA ratio of 'Nouvelle' tangor, 'Valencia'
orange, 'Shamouti' midseason and 'Oroval' Clementine. MKP and UAP sprays significantly, but
inconsistently improved rind texture of 'Nouvelle' tangor, 'Shamouti' midseason and 'Valencia'
orange. However, no positive effect was found on rind texture of 'Oroval' Clementine and
'Eureka' lemon. Inconsistent effects ofMKP and UAP sprays were also found on % leafN, P and
K.AFRIKAANSE OPSOMMING: Opbrengs en vrugkwaliteit van sitrus spesies relatief tat blaar toedienings van makroelemente
Marginale vrugkleur en swak interne kwaliteit is die prim ere produksieprobleme in vroee seisoen
mandaryne in die Wes-Kaap (34 Os 19°E). Die gevolg is 'n lae persentasie uitvoerbare vrugte
omdat die oesdatum uitgestel word wat 'n afname in interne kwaliteit veroorsaak weens oorrypheid.
Goed ontwikkelde skilkleur en interne kwaliteit is dus van groot belang vir bemarking van die
vrugte.
Grond-toegediende kalksteen-ammonium-nitraat (KAN) en lae biuret ureum se effek op vrugkleur,
oesgrootte en interne vrugkwaliteit van 'Mihowase' Satsuma op 'Troyer citrange' onderstamme is
ge-evalueer. 'n Betekenisvolle afname van die N viakke in die blare is gevind nadat grondtoediening
van N vanaf 168 kg N/ha/jaar na 126 kg N/ha/jaar venninder is. N toedienings het
interne kwaliteit beinvloed, maar die verskille tussen die behandelings was nie van kornmersiele
waarde nie. Al was die boomvoorkoms geler in sommige jare waarin N hoofsaaklik as
blaarvoedings toegedien is, was daar nie konstante afnames in vrug-of oesgrootte nie. Daar was
geen betekenisvolle verskille in vrugkieur nie, waarskynlik omdat die blaarvlakke van N steeds
binne die nonne daarvoor in Satsumas was.
Die effek van Seniphos ('n minerale mengsel van 310g/L P20S, 56g/L CaO en 30g/L totaal N en
monokaliumfosfaat (MKP) [52% P20S en 34% K20] op vrugkleur, oesgrootte en interne
vrugkwaliteit van 'Mihowase' Satsumas en 'Nules' Clementine op Troyer citrange onderstarnme is
geevalueer. Seniphos en MKP, toegedien tydens kleurbreek in die herfs, het ook nie skilkleur of
interne vrugkwaliteit (sappersentasie, totale oplosbare vaste stowwe (TOV), suurheid (TS) en
TOV:TS) betekenisvol bemvloed nie. In die Citrusdal-omgewing in die Wes-Kaap Provinsie (Suid-Afrika) is skilgrofheid 'n algemene
probleem wat die hoeveelheid uitvoerbare vrugte beperk. Die effek van blaartoegediende MKP teen
3 en 5% en ureum-amrnoniurn-fosfaat (UAP) teen 2%, op onderskeidelik 4 of 6 weke na volblom, is
geevalueer ten opsigte van oesgrootte, interne en ekstenne (skil grofheid) vrug kwaliteit in Citrus
spp op growweskilsuurlemoen onderstam. Nie MKP of UAP het konsekwente verskille getoon
t.o.v. oesgrootte, sappersentasie, TOV, TS, of TOV:TS in 'Nouvelle' tangor, 'Valencia' orange,
'Shamouti' midseison of 'Oroval' Clementine nie. Skiltekstuur is egter betekenisvol, hoewel
inkonsekwent, verbeter in laasgenoemde drie. Skiltekstuur van 'Oroval' Clementine en 'Eureka'
suurlemoen is nie bemvloed nie. Blaarpersentasies van N, P en K is ook inkonsekwent deur MKP
en UAP beinvloed
