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

[摘要] 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.

[发布机构] Stellenbosch University