Effect of slow-release compound fertilizer on nitrogen nutrient in soil and ryegrass

Soil incubation and pot-experiment methods were used to study the effects of uncoated slow-release compound fertilizer (SRCF) on forms of soil nitrogen (NH₄⁺-N, NO₃^－-N, alkali-hydrolysis N, microbial nitrogen and fixed-ammonium) and nitrogen content of ryegrass. The results indicate that the trend of soil NH₄⁺-N in CCF (common compound fertilizer) and SRCF treatments has uni-modal curve. Soil NH₄⁺-N in SRCF is higher than that in CCF treatment in the middle and final incubation period. However, soil NO₃^－-N in SRCF1 is lower than that in CCF1 treatment. Also soil NO₃^－-N in SRCF2 is higher in the early incubation period and lower in the latter period than that in CCF1 treatment. The trend of alkali-hydrolysis N and soil microbial nitrogen (SMBN) in SRCF treatments exhibits a di-modal curve, with peaks respectively appearing on the 21st and 105th day of incubation. Variations in soil fixed-ammonium are consistent and minimal. Soil ammonium fixation in SRCF is higher than that in CCF treatment. The height, biomass, dry-weight and nitrogen content of ryegrass in SRCF1-3 treatment are higher than those in CCF1 treatment. In comparison with CCF, SRCF treatment is more suitable in terms of ryegrass nitrogen uptake and yield under the same nutrient conditions. Ryegrass nitrogen uptake is negatively correlated with soil NH₄⁺-N and SMBN. It is, however, positively correlated with NO₃^－-N and fixed-ammonium.