[Effects of grass cover combined with different fertilization regimes on soil nutrients and enzyme activities in apple orchard in Weibei dryland, China.]

The split-plot design was adopted in this experiment, with main treatments of grass cover and control and sub-treatments included four fertilization regimes: no fertilization, CK; manure, M; N,P and K fertilizer, NPK; and NPK fertilizer combined with manure, MNPK. Microplate fluorimetry was used to study the effects of grass cover combined with different fertilization regimes on the enzyme activities in apple orchard. The results showed that after mowing the grass (the residues were left on the soil surface as mulch), the soil water content, available P, nitrite nitrogen and the activities of βX, NAG, βG, CBH were increased compared to the control, with no significant differences for total nitrogen, soil organic carbon, and AKP activity. For grass cover treatment, the total nitrogen, soil organic carbon, and the activities of βX, NAG, βG, CBH, AKP were both improved before and after mowing the grass. However, the soil water content, available phosphorus, and nitrate nitrogen of grass cover treatment were lower than that of the control before mowing the grass. Under grass cover condition, the total nitrogen, available P, and soil organic carbon of M and MNPK were higher than that of CK and NPK in both before and after mowing the grass periods, with the activities of βX, NAG, βG, CBH, AKP of MNPK higher than that of NPK. Under the control condition, the available P, soil organic carbon (SOC), nitrite nitrogen, total nitrogen and the activities of βG, CBH, AKP of MNPK higher than that of CK and NPK before and after mowing the grass. Redundancy analysis showed that the activities of soil enzymes were significantly correlated with the soil nutrients, and could reflect the soil fertility. Thus, grass cover combined with MNPK significantly increased the soil nutrient contents and soil enzyme activities, and was an important practice to prevent the decrease of soil fertility and benefit the sustainability of local apple industry.