Effects of field management practices on nitrogen and phosphate leaching in the cinnamon soil area of China

Excessive application of nitrogen (N) and phosphate (P) fertilizers have increasingly caused agricultural nonpoint source pollution and groundwater contamination in China since the 1990s. Understanding N and P leaching is critical for reducing groundwater contamination. Field survey data, long-term experimental data, and recent experimental results were used to investigate N and P leaching from arable cinnamon soil across northern China. The results suggested that wheat and corn yield decreased with increasing N or P fertilization in a wheat-corn rotation system. Large amounts of nitrate accumulated in the soil across the region, and the accumulation amount and its downward movement was a potential risk to groundwater. The Olsen-P surplus (>20 mg·kg^-1) accounted for 80% of the arable soils in the region. There were strong relationships between NP fertilization rates, crop yield, and residual NP amounts and were into three phases: efficient NP-environmentally friendly phase, low NP efficiency-environmentally low risk phase, and inefficient NP-environmentally harmful phase. Optimized water and fertilizer use ensured crop yield, improved nitrogen use efficiency, and reduced nitrogen leaching losses, but the effects of biochar application and straw incorporation were inconsistent. The nitrate leaching-preventing effects of crop straw incorporation was resulted from soil microbial biomass increase, nitrification potential decreased or denitrification potential increase. Other issues also require investigation, such as tracing regional sources of underground water nitrate pollution, the effects of legacy NP accumulation from excess river anthropogenic inputs, and the environmental consequences of legacy NP accumulation in crop-fruit ecological agriculture.