Yield, nitrogen use efficiency and balance response to thirty-five years of fertilization in paddy rice-upland wheat cropping system

Optimal soil nitrogen management is vital to crop production and environment protection. Little knowledge is available on crop yield, nitrogen uptake, use efficiency and balance in paddy rice-upland wheat cropping system of China. A thirty-five-year long-term field experiment was designed with nine treatments, including an unfertilized treatment (control), nitrogen (N), phosphorus (P), potassium (K) fertilizer, manure (M), and manure combined with mineral fertilizer treatments. Crop yield, N uptake, use efficiency, and N surplus or deficit amount were determined. The results indicated that rice, wheat yield and N uptake amount in the manure combined with mineral fertilizer treatments were higher than that in the manure alone or mineral fertilizer alone treatments. N use efficiency was the highest in the treatment with manure alone. Soil N input indicated a surplus in the mineral fertilizer in combination with manure treatment, but soil N input indicated a deficit in the control, NPK and M treatments. Considering crop yields, N use efficiency and N balance, recommended N application amount is almost 220 kg N/ha/year in the paddy rice-upland wheat cropping system. Taking into account labour and fertilizer sources, half mineral N and half organic N applications were recommended.