The effect of nitrogen fertiliser sources on wheat (Triticum aestivum L.) yield parameters and partial profit under Conservation Agriculture

Abstract

In the Mediterranean climate of the Western Cape, wheat (Triticum aestivum) is the main rainfed grain crop, rotated with pastures, canola (Brassica napus) and barley (Hordeum vulgare). Nitrogen (N) fertiliser is a major input cost, and its selection is critical due to the varying prices and efficiencies. A field trial (2016–2020) evaluated the effects of different top-dressed N sources—ammonium sulphate (AMS), limestone ammonium nitrate (LAN), LAN + sulphur (S), urea, and urea + urease inhibitor—on biomass, grain yield and quality in a Conservation Agriculture system. In South Africa, wheat grain is graded based on protein content, influencing the market price. The biomass, harvest index, grain yield, hectoliter mass and protein content varied significantly by year, but not by N source. Partial profit differences among N sources were not significant in 2017 and 2020. However, in 2016, LAN + S yielded lower profits than urea + inhibitor, while in 2018, both LAN + S and urea + inhibitor outperformed LAN. In 2019, AMS had higher profits than urea + inhibitor. Overall, crop rotation had a greater influence on yield and quality than the choice of N fertiliser.