Effects of different organic resources application combined with chemical fertilizer on yield and nitrogen use efficiency of main grain crops in China

Objectives The remarkable growth in agricultural production in China largely relies on the heavy input of chemical fertilizers, which causes ecosystem safety and sustainable concerns. We summarized the field experiment data published across China over the past decades, trying to find out the potential of organic source replacement in total nitrogen fertilizer input in the main grain crop production of China, and to provide a base for the fertilizer reducing project of the country.

Methods The data of crop yield and nitrogen application rate were only collected in the experiments of ≤ 5 years, and the considered treatments included no fertilizer control (CK), chemical nitrogen (F), organic resources (ORs), organic resources plus chemical nitrogen (F+ORs). The crop yield increment, N use efficiencies were compared between the chemical fertilizer treatments and chemical plus organic resources ones.

Results Pairwise comparison showed that, compared to the CK, F, ORs and F+ORs significantly increased crop yield by 58.7%, 32.1% and 61.8%, respectively. Compared to F, the crop yields were not significantly changed in ORs treatments, but those of F+ORs were significantly increased (7.4%). According to the results of experiments containing all the four treatments, the average crop yields in CK, F, ORs and F+ORs were 4778, 7000, 6009 and 7422 kg/hm², respectively. The yields in the fertilization treatments were significantly higher than those of CK, but not significant between F+ORs and F, and those in both F+ORs and F were significantly higher than those in ORs. Yield improving effect depended on crop types and organic resources. In addition, the chemical N input in F+ORs treatments was generally not decreased, while the nitrogen partial factor productivity (PFP_N) was improved significantly (32.5%). The PFP_N in wheat, maize and rice were increased from 35.0, 45.2, 42.8 kg/kg in the F treatments to 45.2, 60.6, 56.4 kg/kg in F+ORs, respectively. The replacing potential of chemical N were different among the organic resources. The chemical N application rate in treatments of F+ORs containing farm manure and straws were similar to those in F, while the PFP_N were significantly increased by 9.4% and 71.7%, respectively. In F+ORs using biogas-residue, the chemical N proportion was often reduced, and the PFP_N was thus significantly increased by 90.3%.

Conclusions Through large number of field experiment results of longer or shorter periods in China, we conclude that proper rate of chemical nitrogen fertilizer application is necessary for maintaining the high and stable yields of wheat, maize and rice in China. Under the current soil fertility levels, combining application of chemical fertilizer and organic resources could further increase the yields and fertility of farmlands, in case of not reducing the chemical N input; otherwise would not decrease the yield but increase the PFP_N when there is no extra N input from the organic resources. Among the organic resources, manure and biogas-residue are available to replace a certain proportion of chemical N, while straw returning is not suggested.