Finding the fertilization optimization to balance grain yield and soil greenhouse gas emissions under water-saving irrigation

Abstract

Efficient nitrogen fertilizer management is critical for increasing winter wheat production and ensuring the long-term protection of the agricultural environment. Determining the features of soil greenhouse gas (GHG) emissions and the driving factors of split nitrogen fertilization is important for optimizing cropland nitrogen management. To date, few studies have comprehensively evaluated the trade-offs between reducing greenhouse gas intensity and improving grain yield in winter wheat cropping systems using split nitrogen applications under water-saving irrigation conditions. Here, a two year field trial using split nitrogen fertilization under water-saving irrigation was done to determine the impacts of split nitrogen fertilizer on soil greenhouse gas intensity and wheat yield. The soil GHG fluxes, inorganic nitrogen, water moisture, and grain yield were measured for five nitrogen treatments. The nitrogen application rate was 240 kg ha−1, and five fertilizer ratios of base to topdressing of N1 (100 % basal and 0% dressing fertilizer), N2 (70 % basal and 30 % dressing fertilizer), N3 (50 % basal and 50 % dressing fertilizer), N4 (30 % basal and 70 % dressing fertilizer), and N5 (0% basal and 100 % dressing fertilizer) were applied. Our results showed that the split nitrogen fertilization strategy had a significant influence on the GHG emissions. And our findings suggested that soil inorganic nitrogen and water moisture was the key variable affecting the soil GHG emissions in the winter wheat cropping system. Compared with the other treatments, the N3 treatment changed the soil inorganic nitrogen and water moisture more effectively with regards to decreased the soil N2O, CH4 and CO2 cumulative emissions, as well as decreased global warming potential and greenhouse gas intensity. The 15N tracer experiments showed that N3 significantly increased the absorption and utilization rate of nitrogen fertilizer and soil nitrogen by winter wheat. The average grain yield and nitrogen use efficiency with the N3 treatment increased by 5.29∼15.34 % and 5.25∼13.14 %, compared with other treatments, respectively. If the basal/topdressing fertilization rate is 50 %:50 %, the split nitrogen fertilizer can maintain a higher grain yield and reduce GHG emissions.