Effects of water and nutrient management and biochar application on crop yield, phosphorus use efficiency, and phosphorus leaching

Excessive water and chemical fertilizer application is often reported in North China winter wheat-summer maize rotation systems, resulting in economic losses and environmental issues. Therefore, optimizing water and nutrients (e.g., P) for crop yield is important. A 3-year field lysimeter experiment was performed on Lou soil (loess-derived and developed on natural cinnamon soil) in Yangling, Shaanxi Province, Northwest China, to investigate P use efficiency and P leaching of winter wheat-summer maize rotation systems in cinnamon soil. Seven treatments were used to investigate crop yield, P partial productivity (PFP_P), and P leaching: conventional practices (CP1, lysimeter depth = 120–150 cm; CP2, lysimeter depth = 100 cm), CP1 plus reduced water supply (CP1-W), CP1 plus reduced nutrient supply (CP1-F), CP1 plus reduced water and nutrient supplies (OPT), CP2 plus biochar application (CP2+B), and OPT plus biochar application (OPT+B). The results showed that the mean wheat, maize, and total wheat + maize yields were similar among CP1, CP1-W, CP1-F, and OPT. Compared with CP1, CP1-F and OPT significantly increased PFP_P by an average of 69.3% and 56.4%, respectively. CP1-W and CP1-F did not affect P leaching, but annual particulate phosphorus leaching decreased significantly under OPT treatment (by 58.4%). Biochar use did not affect the mean annual crop yield, but CP2+B significantly increased PFP_P (by 43.6%) compared with CP2. OPT-B did not affect PFP_P compared with OPT. Each year, all forms of leached P were similar between CP2 and CP2+B. In the first treatment year, OPT+B significantly decreased (compared with OPT) the dissolved organic phosphorus, particulate phosphorus, and total phosphorus (TP) leaching losses by 60.0%, 57.1%, and 62.4%, respectively, but TP leaching increased significantly in the following 2 years. The 3-year average showed that biochar application did not affect P loss. Therefore, only reducing water and fertilizer applications to cinnamon soil may improve P use efficiency and reduce P leaching while maintaining crop yield. Applying wheat straw biochar did not affect crop yield or P leaching, and the effect on PFP_P was inconsistent. Further studies are needed to clarify the effectiveness of biochar application.