Deficit irrigation of rapeseed for water-saving: Effects on biomass accumulation, light interception and radiation use efficiency under different N rates

Rapeseed is one of the most important oilseed crops worldwide and there is a high potential for expansion of its cultivation, particularly in arid and semi-arid regions. Management practice effects on radiation use efficiency (RUE) have not been well documented for rapeseed. It is thought that reduction of aboveground dry matter (ADM) in crops after decreased RUE occurs due to shortage of nitrogen and irrigation. To test this hypothesis, we applied deficit watering techniques to rapeseed with contrasting nitrogen supply. Treatments included three levels of nitrogen supply, namely low level (LN, 8 g N m−2), normal level (NN, 12 g N m−2) and high level of nitrogen (HN, 16 g N m−2), in combination with three levels of irrigation (IR1, 7500; IR2, 4500; and IR3, 3000 m3 water ha−1). Then, traits of ADM, grain yield (GY), leaf area index (LAI), nitrogen nutrition index (NNI), leaf chlorophyll (SPADi), capture ratio (CR), penetration ratio (PR), reflection ratio (RR), accumulated PAR (∑iPAR) and RUE were measured. The ANOVA revealed that the N and irrigation treatments exerted significant effects on all traits. RUE in IR1 and IR2 treatments was comparable to, or higher than, that in IR3 (0.756 and 0.745 vs. 0.477 g μmol−1). However, the interaction of irrigation levels × N rates affected only ADM, GY, ∑iPAR and RUE. Maximum values of these traits remained unchanged at IR1 × NN, IR1 × HN, IR2 × NN and IR2 × HN combined treatments. In conclusion, the IR2 × NN treatment can be recommended for rapeseed under field conditions in order to maximize the yield.

► Rapeseed yield was statistically different between irrigation and nitrogen regimes.
► Effect of consumption of 4500/7500 m3 water ha−1 and 12/16 g N m−2 was similar.
► Higher PAR, RUE, and dry matter were recorded by normal deficit irrigation (4500 m3) and 12 g N applying.
► Application of 4500 m3 water ha−1 with 12 g N m−2, can save greater amounts of the irrigation water and N fertilizer up to 40 and 25%, respectively.