Ammonia volatilization in winter wheat/summer maize rotation system of purple soil in hilly area of Central Sichuan Basin Characteristics of soil ammonia volatilization and the absorption and utilization of nitrogen, phosphorus and potassium of pepper under slow-release fertilizer application Effects of NBPT urease inhibitor on ammonia volatilization in paddy fields with wheat straw application Nitrogen use efficiency in stereoscopic planting rice field in North China Characteristics of ammonia volatilization and nitrous oxide emission of different fermentation beds in pig pens