Effects of rainfall on nitrogen and phosphorus leaching in rainfed spring maize black soil farmland in Jilin Province, China

The black soil area of Jilin Province is important for maize production in China, where agricultural development and nonpoint source pollution risks are intensifying. Understanding the effects of nitrogen and phosphorus leaching from rainfed spring maize farmland is important for the sustainable development of the region. This study investigated rainfall and leaching amounts, nitrogen and phosphorus leachate concentrations, and leaching intensity from 2016 to 2019 at four nonpoint source pollution monitoring stations in Jilin Province, China, and analyzed the relationship between rainfall and farmland nitrogen and phosphorus leaching. The results showed that the inter-annual and inter-regional rainfall differences were large, ranging from 424 to 554 mm. The average rainfall during spring maize growth season was 475 mm. Tonghua monitoring station had the most rain (593–785 mm), followed by Gongzhuling station (512–699 mm) and Lishu station (305–434 mm); Nong'an station had the least rain (197–342 mm). Tonghua and Nong'an growth seasons had primarily light and moderate rain, and Gongzhuling and Lishu had moderate and heavy rain and thunderstorms. There was a significant positive correlation between the leaching amount and rain intensity (P < 0.01). For every 10 mm·(24h)^-1 increase in rain intensity, the leaching amount increased by 1.81 mm. Rainfall during the spring maize growth season (April to October) was also significantly correlated with the leaching amount (P < 0.05). For every 100 mm rain increase, the leached sample number and the leaching probability increased (3 times and 6%, respectively). When the growing season rainfall exceeded 74 mm, the leaching probability increased, and when it exceeded 217 mm, leaching could occur. Leaching occurred when rain levels were 10.0–24.9 mm (moderate rain) and 25.0–49.9 mm (heavy rain). There was a significant positive correlation between leaching amount and total nitrogen concentration, but no correlation with total phosphorus concentration. The total nitrogen leaching intensity had a strong positive correlation (P < 0.01) with rain intensity; for every 10 mm·(24h)^-1 increase in rain intensity, the total nitrogen leaching intensity increased by 0.73 kg·hm^-2. The total phosphorus leaching intensity did not correlate with rain intensity. Nitrogen primarily leached from black soil area farmland in Jilin Province during the rainfed spring maize growth season and was correlated with rainfall. Agronomic measures should be adopted to prevent agricultural nonpoint source pollution at the source.