Verwantskap tussen anorganiese grondstikstof en mielie-opbrengs met beheerde verkeer

Abstract

English: Nitrogen fertilizer recommendations for maize production in South Africa are based on yield to be achieved. Inorganic soil nitrogen is seldom used. This approach causes difficulties in the meaningful seasonal adoption in application rates to be made due to variance in inorganic soil nitrogen due to climatic variations such as too much rain or drought. Therefore the relationship between inorganic soil nitrogen and inorganic soil nitrogen with maize yield under controlled traffic practices was carried out. Data of fertilizer trials at Viljoenskroon on a Clovelly soil (1993/94 to 1997/98) and at Heidelberg on a Avalon soil (1991/92 to 1997/98) were used to determine the relationship between applied nitrogen and maize yield, applied nitrogen and inorganic soil nitrogen as well as inorganic soil nitrogen and maize yield. At both localities the nitrogen rates were factorially combined with phosphor rates and replicated three times in a "roosterontwerp". The grain yield was determined annually at both localities. Soil samples were annually taken from two weeks after nitrogen side dressing in a 300 mm band over the maize row (intra row samples) and before plant in a 1200 mm band between the maize rows (inter row samples) on each plot at both localities. These samples were analysed to determine the amount of inorganic nitrogen in the row as well as total soil volumes. The relationship between applied nitrogen and grain yield was parabolic, between applied nitrogen and inorganic soil nitrogen quadratic and between inorganic soil nitrogen and grain yield parabolic. These relationships had explained more variance at Viljoenskroon than at Heidelberg throughout the study. According to the variance, the relationship of soil reaction on nitrogen application predicted by both localities over years was reliable. Plant reaction was predicted at by both localities over years by the relationship between soil nitrogen in the intra row maize rows and relative yield. According to this nitrogen application recommendations can be made for the optimum amount of soil nitrogen in the intra row for a certain relative maize yield. The amount of nitrogen required to raise inorganic nitrogen content of intra row soil to the desirable level was obtained by the use of the regression equation. The general practice for maize production in South Africa is that a third of the nitrogen is band placed at planting and the remainder applied four to six weeks after planting as top dressing. The abovementioned information could help the farmer to calculate the amount of nitrogen that should be applied to adjust inorganic soil nitrogen levels before and/or during a specified season. This approach has the advantage that where the maize yield varies according to inconsistent rainfall nitrogen applications may be adjusted. It must be accentuated that this approach puts greater demands to farmers, soil annalistic laboratories and fertilizer providers. Over- and under fertilization should considerable decreased due to this approach. More research is however needed for exploitation in other ecotypes.Afrikaans: In Suid-Afrika word stikstofbemestingsaanbevelings vir mielies hoofsaaklik op 'n opbrengsmikpunt gebaseer en anorganiese grondstikstof word selde in berekening gebring. Die benadering bring mee dat daar moeilik sinvolle seisoenale aanpassings aan toedieningshoeveelhede gemaak kan word vir variërende anorganiese grondstikstof wat deur wisselende klimaatsomstandighede soos oormaat reën of droogte te weeg gebring word. Daarom is hierdie ondersoek na die verwantskap tussen anorganiese grondstikstof en mielie-opbrengs met beheerde spoorverkeer gedoen. Data van bemestingsproewe by Viljoenskroon op 'n Clovellygrond (1993/94 tot 1997/98) en by Heidelberg op 'n Avalongrond (1991/92 tot 1997/98) is gebruik om die verwantskappe tussen stikstoftoediening en mielie-opbrengs, stikstoftoediening en anorganiese grondstikstof asook anorganiese grondstikstof en mielie-opbrengs te bepaal. By beide lokaliteite is stikstofpeile faktoriaal gekombineer met fosforpeile en drie keer in 'n roosterontwerp herhaal. Die graanopbrengs is jaarliks by beide lokaliteite op elke perseel gemeet. Daar is ook jaarliks grondmonsters twee weke na kantbemesting van stikstof in 'n 300 mm strook oor die mieliery (baanmonsters) en voor planttyd in 'n 1200 mm strook tussen die mielierye (tussenbaanmonsters) op elke perseel by beide lokaliteite geneem. Hierdie monsters is ontleed sodat die hoeveelheid anorganiese stikstof in die baan en totale grondvolumes bereken kon word. Die verwantskap tussen stikstoftoediening en graanopbrengs was parabolies, die tussen stikstoftoediening en anorganiese grondstikstof kwadraties en die tussen anorganiese grondstikstof en graanopbrengs parabolies van aard. Hierdie verwantskappe het deurgaans meer variasie by Viljoenskroon as by Heidelberg verklaar. Volgens die verklaring van variasie was die verwantskappe wat grondreaksies op stikstoftoedienings voorspel by beide lokaliteite oor jare betroubaar. Plantreaksies is oor jare by beide lokaliteite slegs deur die verwantskap tussen grondstikstof in bane oor die mielierye en relatiewe opbrengs betroubaar voorspel. Hiervolgens kan aanbevelings vir stikstoftoedienings op die optimum hoeveelheid grondstikstof in bane oor mielierye vir 'n bepaalde relatiewe opbrengs gebaseer word. Die hoeveelheid stikstof wat toegedien moet word om die anorganiese stikstofinhoud van die bane oor mielierye tot die verlangde vlak te verhoog kan met regressievergelykings bereken word. In Suid-Afrika is die algemene praktyk dat ongeveer 'n derde van die stikstofmet die aanplanting van mielies gebandplaas word en die res so vier tot ses weke na opkoms as kantbemesting toegedien word. Bogemelde inligting wat bereken kan word stel die boer in staat om die hoeveelheid stikstof wat toegedien moet word aan te pas na aanleiding van die anorganiese grondstikstof voor en/of tydens 'n bepaalde seisoen. So 'n benadering het voordele waar die opbrengs van mielies jaarliks baie varieer weens wisselvallige reënval soos ook in hierdie ondersoek ondervind is. Dit moet beklemtoon word dat so 'n benadering groter else aan boere, grondontledingslaboratoriums en kunsmisverskaffers sal stel. Oor- of onderbemesting behoort volgens die benadering aansienlik teenoor die bestaande benadering verminder te word. Meer navorsing is egter noodsaaklik vir ekstrapolasie na ander ekotope.