Maize Yield and Nutrient Losses as Affected by Different Fertilizer Rates

This project continued to evaluate the effects of different application rates of N, P and K fertilizers on maize yield and nutrient losses from Sichuan's sloping farmlands during the summer rainy season. The fertilizer application rates were the same as in 2012, i.e., five rates of N (0, 225, 300, 375, and 450 kg N/ha), three rates of P (0, 150 and 300 kg P₂O₅/ha) and three rates of K (0, 75 and 150 kg K₂O/ha). Nitrogen was applied as urea (N 46%), P as MAP (N 11% and P₂O₅ 44%), and K as KCl (K₂O 60%). Nitrogen was split applied four times (basal application at seeding, topdressing at seedling, elongation and tasseling stages in 10:20:20:50 ratio). The P and K fertilizers were applied once at seeding.

Results showed that the optimal fertilizer rates in 2013 were 225-150-75 kg N-P₂O₅-K₂O/ha, which produced maximum maize grain yields of 6.9 t/ha along with the highest N use efficiency (NUE) of 47%. The NUE decreased at N rates above 225 kg/ha. All the NPK treatments significantly reduced soil erosion and water losses compared to the treatments omitting either N, P or K. Nutrient losses from the soil were affected by N application rates, described as a quadratic relationship. Minimal nutrient losses from the soil due to N fertilization were observed when 225 kg N/ha, 300 kg P₂O₅/ha and 375 kg K₂O/ha were applied. The optimal K rate helped reduce losses of N by 55%, P by 23% and K by 24% compared to the K omission plot. Nutrient losses in runoff increased again as K rates surpassed the optimal level. Except for the P omission treatment that significantly increased N loss, different P application rates did not significantly affect losses of soil, water and P and K. The results further confirmed that good nutrient management will not only increase maize yields, but can also decrease soil erosion and nutrient losses from the soil and protect the environment.