Soil fertility evolution and its effects on maize production in a long-term experiment on red soil

Based on the characteristics of red soil in the Yungui Plateau, a 30 year field experiment was carried in the Qujing of Yunnan province to study soil fertility evolution and its effects on maize production by applying N, NP, NM, NPM and NPK fertilizers. The result show that maize grain yields of the N treatment are not harvested after the 8 year N fertilization, the yields of the NP treatment are larger than those of the N treatment at the early years, are not stable for the long term application and are not harvested after the 23 year NP fertilization. The yield of the NPM treatment is 6875 kg/ha in the last 10 years which is about 4628 kg/ha higher than the yield of the first 10 years. The NPK treatment is the application of 112.5 K2O kg/ha on the basis of the NP treatment. The yield of the NPK treatment is about 2264 kg/ha higher than that of the NP treatment, and indicates that there is a great increase. Soil organic matter content is not decreased in the non-organic fertilization for 28 years, while, it is significantly increased by applying organic manure and NP fertilizers. Potassium is balanced when the organic manure application amount is 30 t/ha (without chemical potassium application). However, the depletion of potassium occurs when there is no chemical potassium or organic manure applications. Soil available phosphorus is significantly increased when there is P fertilization. The natural P supply capacity of the red soil is extremely low with 3.6%–15.7%. The soil P supply capacity is 3.6%–15.7% without P fertilization or organic manure application, and is increased with P fertilization or organic manure application. The P supply capacity is decreased from 35%–68% to 11.09%–23.2% for the 11year NP application.