Applying Different Organic Amendments Optimizes Soil Nitrogen Management and Increases Greenhouse Tomato Yield

When used as organic amendment, both livestock manure and crop residue can improve soil fertility. However, application of livestock manure alone may cause excessive accumulation of nitrate, and application of crop residue alone may lead to available N deficiency. Therefore, chicken manure was combined applied with rice husk to balance N supply and demand in this study. Greenhouse tomato was grown for three consecutive seasons. Chicken manure and rice husk were applied alone or together at 1:4 or 1:2 mass ratio. The contents of NO3–N and NH4+-N in the topsoil and their distribution in the subsoil were investigated, soil physical properties were analyzed, and tomato yield was recorded. The organic amendments were also incubated in the field to investigate their N release characteristics. Application of chicken manure alone resulted in high soil available N supply, higher tomato yield, and high NO3–N accumulation in the subsoil, whereas application of rice husk alone led to low soil available N supply, low yield, and low NO3–N accumulation in the subsoil. The combined application of chicken manure and rice husk at 1:2 ratios achieved the highest tomato yield with low subsoil NO3–N accumulation. Soil physical properties, such as water retention, were better in the rice husk-added treatments than in the treatment applied only with chicken manure. Combined application of chicken manure and rice husk optimized soil available N management and created a better soil physical environment, thus increasing tomato yield and reducing NO3–N leaching risk as well.