Effects of long-term fertilization on pH of red soil, crop yields and uptakes of nitrogen, phosphorous and potassium

The effects of long-term (18 years) fertilization on pH of red soil, crop yields and uptakes of nitrogen, phosphorus and potassium were investigated in a wheat-maize experiment located in Qiyang, Hunan province. The results indicate that pH values of the red soil are significantly decreased under the applications of chemical nitrogen fertilizers, single application of chemical nitrogen fertilizer, mixed-application of chemical nitrogen and phosphorus fertilizers and mixed-application of chemical nitrogen, phosphorus and potassium fertilizers. The greatest decrease of 1.5 units of soil pH under the single chemical nitrogen fertilizer treatment is observed after 18 years fertilization compared with its initial pH value. The soil pH values under the chemical nitrogen fertilizer treatments are decreased significantly and then become stable after 8-10 years when soil pH4.5, while the application of manure or manure combined with chemical fertilizers could maintain or increase soil pH compared with their initial pH values of the experiment, in which the highest increase value of 1.0 unit is found in the manure treatment. Compared with the corresponding initial yields of the experiment, the yields for the no fertilizer and chemical nitrogen fertilizer treatments show decline trends of 11 to 104 kg/(haa) for wheat and 24 to 210 kg/(haa) for maize, respectively. However, in the manure combined with chemical fertilizers treatment, the yield of wheat has no remarkable change, and the yield of maize is increased 101 kg/(haa). The yields and uptakes of nitrogen, phosphorus and potassium for wheat and maize have significant positive correlations with soil pH under the chemical nitrogen fertilizer treatments (except yield and uptake in the treatment of mixed-application of nitrogen, phosphorus and potassium fertilizers). Soil acidification is one of the main factors limiting nutrient uptakes and crop yields. Application of manure could increase soil pH value, decrease soil acidity. Addition of manure combined with chemical fertilizers could maintain high yields of wheat and maize in the long run and is the best fertilization mode.