Recovery Role in Soil Structural, Carbon and Nitrogen Properties of the Conversion of Vegetable Land to Alfalfa Land in Northwest China

Abstract

Soil structural, carbon (C), and nitrogen (N) properties could be influenced by land-use change. The objective of this study was to investigate the effects of the conversion from vegetable (Brassica pekinensis) planting for 7 years (2007–2014) to alfalfa (Medicago sativa L.) planting with 5 nitrogen levels (N0~N4) for 3 years (2015–2017) on soil structural, C, and N properties. After vegetable cultivation, soil structural, C, and N properties declined significantly. However, after alfalfa planting, especially in 2017, the lowest values of bulk density (N1 = 1.32 g m−3, N2 = 1.33 g m−3) and the highest values of macroaggregate proportion (N1 = 78.17%, N2 = 77.33%) were obtained. The highest values of SOC (N1 = 11.11 g kg−1, N2 = 11.08 g kg−1), SMBC (N1 = 390.97 mg kg−1), and sucrase (N1 = 17.47 mg g−1 d−1) were appeared. The maximum values of available nitrogen (N1 = 57.83 mg kg−1, N2 = 59.82 mg kg−1), SMBN (N1 = 56.01 mg kg−1, N2 = 58.14 mg kg−1), and urease (N2 = 2.71 mg g−1 d−1) were obtained. Taken together, our findings suggest that the conversion of vegetable land to alfalfa land with low N level could significantly improve soil structural, C, and N properties.