Developing nitrogen fertiliser management strategies for wheat (Triticum aestivum) under conservation agriculture practices within the Western Cape

Neethling, Paul Johannes (2018-03)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Nitrogen (N) is one of the most limiting plant nutrients. Supplying enough N to growing crops is one of the most critical factors influencing wheat production. There has been a strong drive towards conservation agriculture in South Africa, especially within the Western Cape Province. Conservation agriculture brings forth changes in soil physical, chemical and biological properties that influence the plant-available soil mineral N content, specifically an increased potentially mineralisable N content. The aim of this study was to do a complete analysis of the effect that different preceding crops, N rates, forms of N, and timing of N application would have on the yield, yield components and protein content of wheat, whilst monitoring the effect of different N rates on the soil mineral N concentration throughout the growing season. The first objective of the study was to determine the effect of different fertiliser rates on the grain yield, selected yield components, quality parameters and N use efficiency. The second objective was to determine the effect of a late-season foliar N application on the yield and grain protein content of the wheat crop. The third objective was to test the effect of different N sources on crop growth, yield and quality of wheat. This study was conducted during 2016 and 2017 on nine sites within the dryland grain producing areas of the Western Cape. The trial was subdivided into two separate studies: i) topdressed N rates with or without foliar applications of N and ii) N sources at topdress. Increasing topdress N rates had a less profound effect on crop yields than expected, where most of the sites in both years showed no increase (P > 0.05) in yield with increasing topdress N rate. Five of the research sites in Year 1 and all the research sites in Year 2 showed no response (P > 0.05) in the number of ear-bearing tillers, as influenced by increasing topdress N rates. An increase (P < 0.05) in grain protein content with the increasing topdress N rates was recorded at all the research sites in Year 1. The N use efficiency of wheat decreased (P < 0.05) with increasing topdress N rates in both years. Foliar N application at post-anthesis had limited success in increasing yield and grain protein content of wheat. No profound effect of fertiliser N source on the yield, yield components or quality of wheat was recorded. After doing a complete analysis of the N requirement of wheat produced under conservation agriculture practices and dryland conditions in the Western Cape Province, it was apparent that fertiliser N recommendations will possibly have to be adjusted. The N guidelines to produce wheat lead to over-fertilisation in some areas, which may, in turn, lead to environmental pollution and economic losses. Determining the optimal N source might entail choosing the most cost-effective and accessible source.

AFRIKAANSE OPSOMMING: Stikstof (N) is een van die mees beperkende plant voedingstowwe. Die voorsiening van genoeg N aan groeiende gewasse is een van die mees kritiese faktore wat koringproduksie beïnvloed. Daar is ‘n sterk drywing na bewaringslandbou in Suid-Afrika, veral in die Wes-Kaap. Bewaringslandbou lei tot veranderinge in die fisiese-, chemise- en biologiese eienskappe van die grond wat die plant-beskikbare grond N beïnvloed, veral ‘n verhoging in potensieël mineraliseerbare N. Die mikpunt van hierdie studie was om ‘n volledige analise te doen oor die effek wat verskillende rotasiestelsels, N peile, N bronne en tydsberekening van N toediening sal hê op die opbrengs, opbrengskomponente en proteininhoud van koring, terwyl die effek van verskillende N peile op grond minerale N-inhoud regdeur die groeiseisoen gemonitor was. Die eerste doelwit van die studie was om die effek van verskillende kunsmis peile op die graanopbrengs, geselekteerde opbrengskomponente, gehalteparameters en N-verbruiksdoeltreffendheid te bepaal. Die tweede doelwit was om die effek van 'n laatseisoen blaar N toediening op die opbrengs en graan proteïen inhoud van die koring gewas te bepaal. Die derde doelwit was om die effek van verskillende N bronne op die groei-, opbrengs- en kwaliteit van koring te bepaal. Hierdie studie is gedurende 2016 en 2017 op nege lokaliteite in die droëland graanproduserende gebiede van die Wes-Kaap uitgevoer. Die proef is onderverdeel in twee afsonderlike studies: i) topbemestings N peile met of sonder blaaraanvullings van N en ii) verskillende N bronne as topbemesting. Die verhoging van topbemestingspeile het 'n kleiner uitwerking op gewasopbrengste gehad as wat verwag is, waar die meeste van die lokaliteite in beide jare geen toename (P > 0,05) in opbrengs, met toenemende topbemestingspeile getoon het nie. Vyf van die lokaliteite in jaar 1 en al die lokaliteite in jaar 2 het geen reaksie (P > 0.05) in die aantal aardraende halms, soos beïnvloed deur vehogende N topbemestingspeile, getoon nie. 'n Toename (P < 0,05) in graan proteïeninhoud met toenemende N topbemestingspeile is by al die lokaliteite in jaar 1 aangeteken. Die N-verbruiksdoeltreffendheid van die koring het afgeneem (P < 0.05) met toenemende N topbemestingspeile in albei jare. Die toediening van laat-seisoen vloeibare N het beperkte sukses gehad om die opbrengs en graan proteïeninhoud van koring te verhoog. Geen diepgaande effek van kunsmis N-bron op die opbrengs, opbrengskomponente of koringkwaliteit is aangeteken nie. Nadat 'n volledige analise van die N-vereiste van koring wat onder bewaringslandboupraktyke en droëlandtoestande in die Wes-Kaap geproduseer word gedoen is, was dit duidelik dat die aanbevelings van kunsmis N moontlik aangepas moet word. Die N-riglyne vir koringproduksie kan lei tot moontlike oorbemesting in sommige gebiede, wat op sy beurt kan lei tot omgewingsbesoedeling en ekonomiese verliese. Om die optimale N-bron te bepaal kan neerkom op die kies van die mees koste-effektiewe en toeganklike bron.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103727
This item appears in the following collections: