Effects of soil water content and foliar fertilization with nitrogen and phosphorus in late season on the yield and composition of wheat

Wheat was grown in reconstructed profiles of a sandy red-brown earth in pots 120 cm deep. Ammonium sulfate (90 mg nitrogen per pot) and/or monocalcium phosphate (75 mg phosphorus per pot) were added to the topsoil. In one experiment, water treatments were introduced when the wheat reached ear emergence to provide (a) dry topsoil and water shortage; (b) dry topsoil but ample water supply in the subsoil; or (c) ample water supply, with both topsoil and subsoil wet. Additional nitrogen (82–164 mg per pot as urea) and/or phosphorus (9–18 mg per pot as phosphoric acid) were added to the plants in foliar sprays after ear emergence. In a second experiment in which water treatment (b) was applied, the dry surface soil was wetted at different stages of plant growth, viz. ear emergence, anthesis or the dough stage. In both experiments the yield and concentration of nitrogen and phosphorus in the wheat were measured at maturity. Total dry matter production was little affected by the water content of the soil after ear emergence, but grain yield was increased relative to that of straw where the topsoil was wet at the dough stage. Application of nitrogen at the time of sowing generally increased the yield of grain and straw, but phosphorus had little effect on yield. Additional foliar application of nitrogen after ear emergence increased grain yield where water stress was low: foliar application of phosphorus increased grain yield only when applied with nitrogen. Nitrogen concentration in the grain was little affected by adding nitrogen to the soil but was increased by late foliar application of nitrogen. Phosphorus concentrations were increased by phosphorus and decreased by nitrogen applications.