The effect of reduced irrigation and chemical fertilizers on phosphorus accumulation and leaching in Mollisol vegetable fields

Excessive fertilization and irrigation have led to phosphorus leaching in Mollisol vegetable fields, and optimization of these practices is critical for reducing phosphorus pollution. A leaching monitoring experiment was performed in a Mollisol eggplant field using the following three treatments: standard irrigation and chemical fertilizer amounts (WF), standard irrigation + 80% chemical fertilizer (W80%F), and 80% irrigation + standard chemical fertilizer (80%WF). The soil phosphorus storage, available phosphorus dynamics, and phosphorus leaching amounts were analyzed to determine the effects of irrigation and fertilization treatments on phosphorus leaching. After one growing season, phosphorus storage in the 0–100 cm soil layers were 9.69 t·hm^-2 (WF), 9.36 t·hm^-2 (W80%F), and 8.84 t·hm^-2 (80%WF), which were 26.5%, 27.5%, and 7.1% higher than before planting, respectively. These results showed that phosphorous accumulation occurred, which increased the leaching risk. During the extended eggplant growing period, the available phosphorus in the 0–20 cm soil layer increased and then decreased, and was highest in the 80%WF treatment, ranging between 145.17–224.55 mg·kg^-1. The available phosphorus in the 20–40 cm soil layer did not change under WF treatment and increased under 80%WF treatment. The available phosphorus fluctuated with W80%F but was significantly higher than that in the other treatments, except during the full fruit period. The phosphorus leaching amounts were 17.84 kg·hm^-2 (WF), 17.47 kg·hm^-2 (W80%F), and 9.02 kg·hm^-2 (80%WF). Organic phosphorus leaching was more than 90% of the total phosphorus leaching, differing from other soil types. There were significant positive correlations between phosphorus leaching and increased phosphorus storage, available phosphorus in the 0–40 cm layer at the full fruit stage and in the 0–20 cm layer at the withering stage (P < 0.05). This indicates that changes in phosphorus storage and the available phosphorus content may help predict phosphorus leaching in Mollisols. After one growing season, phosphorus storage in the 0–100 cm layer increased in all treatments; the smallest increase was in the W80%F treatment, indicating that reduced irrigation lowers the phosphorous leaching risk. Reducing chemical fertilizers did not affect phosphorus leaching or the leaching risk. These results provide information for preventing phosphorus leaching, which may be used to develop new techniques for Mollisol vegetable fields.