Abstract:
Background In order to explore the improvement effect of slope microtopographic modification soil and water conservation measure-contour reverse-slope terrace (CRT) on soil fertility and its ecological restoration function in sloping farmland, it is necessary to pay attention to the effect of CRT on soil nutrients and enzyme activities related to nutrient conversion, as well as its contribution and mechanism to crop yield.
Methods Soil nutrients (TN, TP, NH4+-N, NO3--N and AP) and soil urease (S-UE), soil β-1, 4-N-acetylglucosidase (S-NAG), soil leucine aminopeptidase (S-LAP) and acid phosphatase (S-ACP) were analyzed in the sloping farmland 0-5 cm soil of two terrace positions (aboveandbelow the terrace) under CRT treatments, and the corresponding position of the unaltered sloping farmland (CK) was taken as the control. The effects and mechanism of soil nutrient conversion related enzymes on yield and 1 000-grain weight (TGW) of kidney bean (Phaseolus vulgaris) under CRT were investigated.
Results 1) Compared to CK, the contents of soil TN, NO3--N, TP and AP in CRT increased by 21.2%, 86.2%, 14.1% and 28.4% in the slope above the terrace, but 7.3%, 77.4%, 21.8% and 30.1% in the slope below the terrace. The NH4+-N increased by 2.8% in the slope above the terrace and decreased by 22.5% below the terrace in CRT. The enhancement effect on NO3--N was higher than that on TN and NH4+-N, and the enhancement effect on AP was better than that on TP. 2) Compared to CK, the S-UE, S-NAG, S-LAP and S-ACP activities increased by 13.4%, 55.9%, 56.8% and 44.6% in above the terrace of CRT, and 48.3%, 72.3%, 70.9% and 34.6% in below the terrace of CRT. Moreover, the increase rate of below the terrace was greater than that of above the terrace. 3) The per hectare yield of kidney bean were 20.0 and 23.2 kg/hm2, and TGW were 448 and 376 g in CK sloping farmland (above and below the terrace), while yield increased by 66.7% and 289% (above and below the terrace), TGW increased by 8.6% and 26.6% (above and below the terrace) under CRT treatment. And the increase rate of below the terrace was greater than that of above the terrace. 4) Compared with CK, CRT changed kidney bean yield and S-UE from non-correlation to significant positive correlation (P < 0.05), the correlation coefficient (R) increased from 0.12 to 0.91, and the TGW of kidney beans in slopingfarmland land changed from negative correlation (P < 0.05) to correlation with nitrogen, phosphorus nutrients and enzymes (S-NAG, S-LAP and S-ACP). S-LAP, S-NAG and NH4+-N had significant effects on yield and TGW of kidney bean (P < 0.01), explains rate were 48.4%, 29.2% and 18.0%, respectively.
Conclusions CRT accelerates the conversion of organic nutrient to inorganic nutrient, promotes the growth and development of kidney bean, and increases the yield and TGW by improving the spatial distribution of soil nutrients, which increases the activities of related enzymes in sloping farmland.