The effect of nitrogen and sulphur on the grain yield and quality of canola (Brassica napus L.) grown in the Western Cape, South Africa

Abstract

On average low grain yields of less than 1.5 t ha⁻¹ are obtained with canola in the Western Cape province of South Africa. Injudicious use of fertiliser has been suggested as a major cause, hence the study was done to determine the effect of soil and climatic conditions, as experienced at different localities, on grain yield and quality response of canola to nitrogen (N) and sulphur (S) applications in a three-year study. Treatments consisted of five N (0, 30, 60, 90 and 120 kg N ha⁻¹) and three S (0, 15 and 30 kg S ha⁻¹) rates laid out in a randomised complete block design with a factorial split-plot arrangement. The study showed that the effect of N supply increased with S supply and was greater in high rainfall areas and seasons than in drier conditions. Low rainfall during flowering and podding may limit yield responses to N applications, with applications of 120 kg N ha⁻¹ and 15–30 kg S ha⁻¹ needed in high rainfall areas to obtain yields of more than 2.0 t ha⁻¹. Application of S also improves the oil content of canola though this compromises protein content.

Keywords: canola yields, nitrogen, oil and protein content, sulphur

South African Journal of Plant and Soil 2014, 31(2): 69–75