Yield, phosphorus use efficiency and balance response to substituting long-term chemical fertilizer use with organic manure in a wheat-maize system

The over-application of mineral phosphorus (P) fertilizer has become common in the North China Plain, meanwhile, most of organic manure cannot be recycled into the soil. To make full use of organic manure and decrease the applied rate of mineral P fertilizer, a 20-year fertilization experiment in a continuous wheat-maize rotation was carried out to assess the long-term effects of substituting mineral fertilizer with organic manure on the yield, P use efficiency, and P balance. Treatments included organic compost (OM), half compost in combination with half mineral fertilizer NPK (1/2 OM), mineral fertilizer NPK (NPK), mineral fertilizer NK (NK), and an unfertilized control (CK). The results showed that the grain yield in the NK plots was less than 1.0 t ha-1 for both wheat and maize. The highest grain yield was obtained for the NPK treatment, which was slightly higher than the yields of the 1/2 OM treatment over all the years. The effects of the compost application were greater on the maize yield than on the wheat yield. Compost addition can significantly increase the P content and P uptake. The mean P fertilization use efficiencies were 53.7, 59.9 and 61.7% in the NPK, 1/2 OM and OM treatments for the wheat-maize system, respectively. In considering the P from the fertilizer, seed and irrigation as inputs and P uptake from crops and P storage in the 0-20 cm soil layer as outputs, no significant P loss was observed in all the treatments. The results indicated that an application of mineral fertilizer alone at a reasonable level could result in a high crop yield and a relatively high P use efficiency. Considering the improvements in the P use efficiency and the benefits of soil fertility, replacing less than half the chemical fertilizer with organic fertilizer might be a promising alternative in the North China Plain.