Apparent nitrogen balance in different crop rotation systems when substituting mineral fertilizers with manure in the North China Plain

We aimed to the explore the apparent N balance in different forage and crop rotation systems when substituting mineral fertilizer with solid and liquid manure in the North China Plain. To achieve this, we measured the aboveground biomass and N uptake, residual amounts of inorganic N in the 0~200 cm soil profile, and apparent N loss in the soil(0~100 cm)-crop system. Several forage crop rotation systems[grain maize-wheat (T1), silage corn/cowpea intercropping-catch ryegrass(T2), sweet sorghum-ryegrass (T3), silage corn-ryegrass (T4), sorghum hybrid sudangrass-ryegrass(T5)] were studied, substituting 50% of the chemical fertilizer-N(C) with solid manure(S) or liquid manure(L) in the North China Plain. The increases in aboveground biomass and N uptake in the summer-autumn(Sum-Aut) periods were larger under T5, followed by T3, than under T1; however, the highest yields of aboveground biomasses were under T1 in the winter-spring(Win-Spr) periods. Compared with the application of mineral fertilizer NPK(C), the S and L applications significantly reduced the aboveground biomass and N uptake to less than 15% in the Sum-Aut periods but had no significant effects in the Win-Spr periods. Compared with the T1, the T3 and T5 significantly increased crop N harvest and, thus, reduced the residual amounts of inorganic N in the 0~200 cm soil profile and apparent N loss in the soil(0~100 cm)-crop system. Substitution of S and L significantly reduced crop N harvest and residual amounts of inorganic N in the 0~200 cm soil profile, thus, significantly increasing the apparent N loss in the crop-soil system. Therefore, the substitution of 50% of the mineral-N with solid or liquid manure in the agriculture of sweet sorghum-ryegrass and sorghum hybrid sudangrass-ryegrass is conducive to sustainable agriculture and animal husbandry in the North China Plain.