Influence of different fertilization modes on soil fertility and crop yield in Dongting Lake upland areas

An experiment was conducted under cotton-rapeseed crop rotation system in upland areas of Dongting Lake to determine the effect of different fertilization modes on soil fertility and crop yield. The treatments in the experiment included none fertilization (control), conventional fertilization (TF), formula fertilization (NPK) and different combinations of chemical and organic fertilizers (10%OM, 30%OM and 50%OM, in which 10%, 30% and 50% of total N was from organic fertilizer). The results indicated that combined inorganic and organic fertilizer application greatly improved yields of cotton and rapeseed, with the highest yield under 50%OM treatment. The order of yields from high to low was: 50%OM, 30%OM, 10%OM, NPK, TP and CK. The yields of cotton and rapeseed under 50%OM were respectively 24.52% and 29.57% higher than those under TP and also 46.03% and 49.07% higher than those under NPK. The inter-annual variation in crop yields under organic fertilizer treatments was less than 20%, which was obviously lower than those under TP, NPK and control. Organic fertilizer application not only improved crop yield, but also supported stable production. 50%OM treatment increased soil organic matter, total N, alkali-hydrolyzable N and quick-acting K respectively by 57.5%, 38.2%, 65.1% and 48.1% over those before the experiment. Soil available P increased with increasing application of P fertilizer. However, soil organic matter and nutrient content decreased in control treatment. The linear equation (y=ax+b) well fitted the changes in soil organic matter and nutrient (y) with time (x). Reasonable application of organic plus inorganic fertilizers had significant potential to improve crop yield and soil fertility in upland soils in Dongting Lake area. The 50%OM treatment showed the best effects under the experimental conditions.