Soil carbon and nitrogen and soil enzyme activities of different forage planting models on the Loess Plateau

A long-term field experiment comparing the effects of different alfalfa-crop rotations on soil carbon and nitrogen forms and related enzyme activities was conducted at Dingxi, western Loess Plateau. Six rotation patternsalfalfa-alfalfa, alfalfa-fallow, alfalfa-wheat(Triticum aestivum), alfalfa-corn(Zeamays), alfalfa-potato(Solanum tuberosum) and alfalfa-millet(Setaria italica)were compared. The results showed that the alfalfa crop rotation is not conducive to accumulation of soil total organic carbon and total nitrogen, and alfalfa ploughing maintains higher soil organic carbon levels. Compared to alfalfa-alfalfa, soil organic carbon and total nitrogen of alfalfa crop rotation system were decreased by 1.60%~23.11% and 3.81%~21.83%.Owing to differences insoil nutrient uptake among crops, soil enzyme content will be changed. Compared with continuous alfalfa cropping, soil catalase and protease activity of alfalfa crop rotation were reduced, and the soil nitrate reductase activity was increased; the soil catalase activity and the protease activity decreased by 5.20%~12.30% and 15.03%~43.43%, and the nitrate reductase activity increased by 1.26%~28.79%. There was no significant difference between continuous alfalfa cropping and alfalfa crop rotation on soil urease activity (P>0.05), but it was higher than that in the alfalfa fallow treatment. Moreover, correlation analysis showed thatsoil urease activity and soil organic carbon and total nitrogen content were significantly positively correlated. These can be used as indices of soil fertility.