5. Conclusions
In this paper, we studied the compound effects of soil C: N: P ratio and enzyme stoichiometry under different land use patterns in the YRD, and better revealed the biochemical cycle and microbial nutrient limitation of YRD. The results showed that: (1) AG and WM could promote the formation of soil macro-aggregates (> 0.25mm). AG was beneficial to promote the mineralization of C, N, and P, but its effect on the sequestration of TC and TP was not as good as WM. (2) According to the soil C: N: P ratios, the levels of soil C and N in the YRD were low, and AG could alleviate the limitation of aboveground vegetation growth by N. (3) According to the enzyme stoichiometric, soil microorganisms were generally limited by P in the YRD, while PC could reduce the C limitation of soil microorganisms due to less soil disturbance. Accordingly, we suggest that human disturbance, such as mowing and soil disturbance, should be minimized in the agricultural production of YRD, to alleviate C restriction. Reasonable planting of alfalfa can alleviate N limitation. Meanwhile, we should increase the input of soil P and carry out reasonable N management to deal with the possible N limitation. In general, ecological stoichiometry provided a theoretical basis for the rational land use in the YRD.