Dual-purpose winter wheat: interactions between crop management, availability of nitrogen and weather conditions

Dual-purpose wheat has been adopted in many farming systems, but interactions between management, supply of resources, and seasonal conditions are still not dearly elucidated. Two experiments were established in the Loess Plateau of China to measure yield and its components, evapotranspiration, water-use efficiency (yield per unit evapotranspiration), accumulation and apparent remobilisation of stem water soluble carbohydrates (WSC), and economic benefit of dual-purpose winter wheat. Experiment 1 combined factorially three defoliation treatments, i.e. winter defoliation (DC23), spring defoliation (DC29) and untreated control, two seeding rates (currently recommended, and 125% recommended), and over four seasons. Experiment 2 combined factorially two defoliation treatments (spring defoliation and control), two nitrogen rates (low: 120-150 kg N ha(-1), high: 180-200 kg N ha(-1)), three levels of soil water at sowing (low: rainfed; medium: rain + 67 mm; high: rain +133 mm), and over three seasons. Defoliation was largely neutral for grain yield and water-use efficiency, and improved translocation of WSC to grain by 8%, harvest index by 7% and net income by 15% across conditions. Grain yield was unaffected by the interaction between defoliation and seeding rate, but significantly impacted by interactions of defoliation x initial soil water level and defoliation x nitrogen rate. Defoliated wheat yield was greater at high than at medium and low initial soil water content, and at low than at high nitrogen rate. Spring defoliation produced similar yield as winter defoliation but the former increased forage income. Increasing seeding rate or nitrogen rate increased forage income but reduced net income due to lower grain income and higher cost. Thus, dualpurpose winter wheat was more profitable (i) when defoliated in spring, (ii) at the lower seeding density, (iii) under the lower nitrogen rate, and (iv) with higher soil water content at sowing. Apparent translocation of stem WSC partially mediated the effect of defoliation on grain yield. It is concluded that dual-purpose winter wheat is feasible under straw mulching in semiarid environment.