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Quantifying root growth dynamics and nutrient uptake in apple trees

Van Zyl, Frederik Jacobus (2016-03)

Thesis (MScAgric)--Stellenbosch University, 2016.

Thesis

ENGLISH SUMMARY: The dynamics of white roots were quantified using minirhizotrons (MR) over two consecutive seasons in four apple orchards in the Elgin-Vyeboom region of the Western Cape, South Africa. The cultivars monitored in this study were as follows: young, non-bearing ‘Corder Gala’/M7; young, bearing ‘Fuji’/M793; mature, bearing ‘Golden Delicious’/M793 and ‘Cripps Pink’/M793. Root growth patterns were related to soil water and temperature dynamics to determine the influence of the soil environment on white root dynamics. Changes in photosynthesis for the non-bearing ‘Corder Gala’ and bearing ‘Golden Delicious’ orchards were also quantified in order to determine possible correlation between white root activity and tree physiology. Nutrient uptake and distribution in relation to white root dynamics and established uptake periods were also investigated for one-year-old potted ‘Golden Delicious’/M7 trees (glasshouse) and for mature bearing ‘Golden delicious’/M793 (field). In the potted trial, the effect of timing and application rate of soil applied Ca(NO3)2 was evaluated with reference to Ca concentration and distribution amongst the roots, trunk and new growth. In the field trial, the effect on fruit tree performance was evaluated following the soil application of Ca(NO3)2 during white root flushes (determined by MR images) compared to recommended phenological based timmings (90 % petal drop and post-harvest). A bimodal white root growth pattern was confirmed for the bearing orchards with the first root flush in summer and a second, often longer flush, in winter. The winter root flush during tree dormancy is unique compared to existing literature on apple root growth dynamics and is attributed to the warmer winter climate of our region. For the non-bearing orchard, no defined white root growth pattern was observed. It appears that white root production occurs throughout the growing season in varying quantities from spring until autumn. White root growth dynamics in this study was not determined by the seasonal variation in soil temperature, although soil environmental conditions did play a role. The consistent white root growth flush for bearing orchards during winter indicate suitable environmental soil conditions for root growth - which is in contrast to climatic regions where winter temperatures result in cold (<5C) soils supressing root growth. Similarly, soil water fluctuation did not appear to influence the timing of the flushes, especially for the bearing ‘Golden Delicious’ orchard. Soil water and temperature in this study was therefore condusive to root growth throughout the year. This suggests that other factors e.g. endogenous tree physiological factors probably control the temporal pattern of white root production in these orchards. Changes in white root numbers and photosynthesis from spring to autumn indicated a possible relationship in the non-bearing orchard, but was not evident in the mature bearing orchard. In the potted trial, both the timing and concentration of soil applied Ca(NO3)2 affected Ca distribution in roots and new growth. The effect of application time significantly influenced the Ca concentration of both the roots and new growth and confirmed previous findings, whereas the effect of application rate only influenced the Ca concentration of the new aerial growth. Higher rates of Ca(NO3)2 in summer was neccesary to significantly increase the Ca concentration of new arial growth, whereas the standard rate was suffice in autumn for significant increases in the root system. In the field trial however, no significant affect of additional Ca(NO3)2 for the applied rates was observed as quantified by leaf and fruit mineral analysis or fruit yield and quality.

AFRIKAANSE OPSOMMING: Wit wortel dinamika is gemonitor in vier appelboorde en gekwantifiseer met behulp van minirhizotrons (MR) oor twee seisoene in die Elgin-Vyeboom streek van die Wes-Kaap, Suid- Afrika. Die kultivars in die studie was soos volg: jong nie-draende ‘Corder Gala’/M7; jong, draende ‘Fuji’/M7; volwasse, draende ‘Golden Delicious’/M793 en ‘Cripps Pink’/M793. Wortel groeipatrone is vergelyk met grondwater en -temperatuur dinamika om die invloed van die grondomgewing op wit wortel dinamika te bepaal. Verandering in fotosintese vir die jong nie-draende ‘Corder Gala’/M7 en die volwasse, draende ‘Golden Delicious’/M793 boorde is ook gekwantifiseer om ‘n moontlike verwantskap te ondersoek tussen witwortel aktiwiteit en boom fisiologie. Ca opname en weefsel verspreiding ten opsigte van witwortel dinamika en bepaalde tydperke van Ca opname is ook bepaal vir een-jaar-oue ‘Golden Delicious’/M7 bome in potte onder glashuis toestande en vir volwasse, draende ‘Golden Delicious’/M793 onder veldtoestande. In die potproef is die effek van tydsberekening (somer, herfs sowel as somer en herfs) en toedieningsdosis (1X of 3X) van Ca(NO3)2 grondtoedienings ge-evalueer ten opsigte van Ca-konsentrasie en -weefselverspreiding tussen die wortels, stam en nuwe groei (lote en blare). In die veldproef, is die effek van additionale Ca(NO3)2 grondtoedienings tydens die aktiewe witwortel groei periodes (bepaal deur MR data) teenoor die aanbevele fenologies gebasseerde toedienings tye (90 % blomblaarval en na-oes), sowel as n kontrole (geen additionele Ca(NO3)2), vergelyk ten opsigte van boom prestasie. ‘n Bi-modale wortel groeipatroon is bevestig vir die draende boorde, met die eerste witwortel groei fase in somer en die tweede, dikwels groter groei fase, in die winter. Die winter wortel groeifase gedurende dormansie is egter uniek. Vir die nie-draende boord is geen duidelike patroon opgemerk nie. Dit het egter voorgekom asof witwortel produksie regdeur die seisoen vanaf lente tot herfs plaasvind, alhoewel dit in wisselende hoeveelhede gedurende hierdie tydperk voorkom. Witwortel groei tendense het dus verskil tussen draende en nie-draende bome. Witwortel dinamika in hierdie studie was nie gekorreleer aan die seisoenale verandering in grondtemperatuur nie, alhoewel grondtemperatuur wel ‘n rol speel. Die konstante witwortel groeifase gedurende die winter in die draende boorde in hierdie studie, dui op geskikte omgewingstoestande vir wortelgroei gedurende die winter wat in kontras is met ander klimaatstreke waar koue (<5C) grondtemperature wortelgroei in die winter onderdruk. Soortgelyk blyk dit dat grondwater ook nie die aanvang en duur van ‘n wortel groeifase beheer nie, veral nie vir die draende ‘Golden Delicious’ boord nie. Grondwater en -temperatuur in hierdie studie was dus gunstig vir wortelgroei regdeur die jaar. Dit is dus moontlik dat ander faktore bv. interne boom fisiologiese faktore die tydsberekening van die wortel groeifases in hierdie boorde bepaal in die Elgin-Vyeboom area. Veranderinge in witwortel getalle en fotosintese gedurende die lente tot herfs is ‘n aanduiding van ‘n moontlike verwantskap in die nie-draende boord, maar dit is nie waargeneem in die draende boord nie. In die pot proef het beide die tydsberekening sowel as die konsentrasie van Ca(NO3)2 toediening ‘n betekenisvolle effek op die verspreiding van Ca in die wortels en nuwe groei gehad. Die effek van tyd van toediening het die Ca konsentrasie van die wortels en nuwe groei noemenswaardig beïnvloed in ooreenstemming met bestaande literatuur, terwyl die effek van toedieningsdosis net die Ca konsentrasie van die nuwe groei betekenisvol beïnvloed het. ‘n Hoër Ca(NO3)2 dosis in die somer was nodig om die Ca konsentrasie van die nuwe groei noemenswaardig te laat toeneem, terwyl die standard dosis in die herfs voldoende was om die Ca konsentrasie van die wortels te verhoog. Daarinteen is geen noemenswaardige invloed opgemerk met betrekking tot die effek van Ca(NO3)2 in reaksie op die aanbevole dosis op die Ca-konsentrasie van blare en vrugte, sowel as opbrengs en vrugkwaliteit in die veldproef nie.

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