Crop Yield and Soil Responses to Long-Term Fertilization on a Red Soil in Southern China*1

A 15-year fertilization experiment with different applications of inorganic N, P and K fertilizers and farmyard manure (M) was conducted to study the yield and soil responses to long-term fertilization at Qiyang, Hunan Province, China. Average grain yields of wheat and corn (1 672 and 5 111 kg ha−1, respectively) for the treatment NPKM were significantly higher than those (405 and 310 kg ha−1) of the unfertilized control and single inorganic fertilizer treatments. Compared with the corresponding initial values of the experiment, all treatments showed a yield decline of 9 to 111 kg ha−1 year−1 in wheat and 35 to 260 kg ha−1 year−1 in corn, respectively, and a significant pH decline of 0.07 to 0.12 pH year−1, except for the treatments PK and NPKM. After long-term fertilization, the soil organic C, soil available P, exchangeable Ca2+ and Mg2+ and available Cu2+ and Zn2+ contents were higher in the treatment NPKM than in the treatments applied with inorganic fertilizer only. Compared to the treatment NPK, the treatment NPKM, where manure partially replaced inorganic N, had a positive impact on arresting the decline of soil pH. This improved grain yields of wheat and corn, suggesting that application of NPK fertilizer in combination with farmyard manure is important to maintain soil fertility and buffering capacity in red soil.