Straw mulch, irrigation water and fertiliser N management effects on yield, water use and N use efficiency of wheat sown after rice

摘要

Two replicated field experiments were conducted during 2005-06 to investigate options for optimising irrigation and N management for wheat mulched with rice straw. The first experiment investigated the interactions between irrigation scheduling and mulching. There were two mulching treatments (±mulch) and four irrigation schedules based on recommended practice, the ratio of irrigation water to cumulative pan evaporation minus rainfall, and soil matric potential (SMP). Wheat grain yield was not significantly affected by mulching or irrigation scheduling treatment. The total amount of irrigation water was not influenced by mulching within any irrigation scheduling treatment. However, using SMP-based scheduling, irrigations of the mulched treatment were always delayed, by up to 24 days compared with the non-mulched treatment. The second experiment investigated N management (method and time of application, using the recommended rate of 120 kg N/ha) for wheat mulched with rice straw. There were eight N management treatments for the wheat mulched with rice straw, including the recommended practice (half broadcast before sowing, half broadcast before the first irrigation after sowing). There was also an unmulched control treatment with N applied using recommended practice. Fertiliser application with three split doses (50% drilled at sowing + 25% broadcast before the each of the first and second irrigations) resulted in significantly higher grain yield, agronomic efficiency and N recovery efficiency than all other treatments. In the presence of mulch, drilling the urea at sowing gave higher yields and efficiency than broadcasting. The effect of irrigation scheduling on crop performance, irrigation amount and water productivity will vary depending on the incidence and amount of rain, and requires further investigation in field and modelling studies for wheat mulched with rice straw. Likewise, development of guidelines for optimum N management for wheat mulched with rice straw will depend on seasonal conditions and requires further investigation with field and modelling studies.