Effects of long-term different fertilization on nitrogen recovery efficiency of maize in red soil

The effects of an 18year different fertilization on nitrogen recovery efficiency(NRE)of maize, yield, N accumulation and NRE were studied in upland red soil. There were four treatments: unfertilized control(CK), inorganic fertilization(NPK), combined inorganic with manure fertilization(NPKM)and manure(M). Soil pH and its relationship with NRE were also studied. The results indicate that compared with the NPK application, the grain yield and N accumulation in plants of maize are increased by 61.5% and 63.1% under the NPKM fertilization, respectively. The yield and NRE of maize show a constant trend in the M fertilization, which are higher than those of the CK, and lower than those in NPKM. The nitrogen recovery efficiency keeps constant in the beginning of 8 years after the NPK is applied, while it significantly decreased with a rate of 3.34% per year at 8-18 years, and its NRE is 247% on average of the 18 years. The NRE in the NPKM is increased with a rate of 1.24% per year, and its NRE reaches to 42.6% on average of the 18 years. There is positive linear relationship between NRE and soil pH(r = 0542)in the NPK and NPKM, which suggests that every decrease of 1 pH would result in the decrease of 10.9% NRE when soil pH is in the range of 4.5-6.3. Soil pH shows a decrease trend in the NPK, and keeps constant in the CK, NPKM and M, which indicates that the inorganic fertilization would reduce soil pH and leads to a low NRE, while manure application could remit the acidification, further improve the NRE and grain production. Chemical fertilizer in combination with manure is a more effective fertilization to improve grain yield and maintain soil fertility, and it is strongly recommended for sustainable agriculture.