Soil and Microbial Biomass Response to Land-Use Changes in the Loess Plateau

Vegetation restoration is a critical strategy for addressing ecosystem degradation globally. However, understanding the specific impacts of land-use changes, particularly the conversion of farmland to forestland and grassland, on soil nutrients and microbial biomass in the Loess Plateau remains limited and requires further evaluation. Therefore, this study was conducted to explore how these conversions affect soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and microbial biomass components under various land-use patterns. We studied the SOC, TN, TP, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) content and their ratios under six land-use patterns (Farmland (FL), Abandoned cropland (ACL), Natural grassland (NG), Alfalfa grassland (Medicago sativa L. (MS)), Spruce forestland (Picea asperata Mast. (PA)) and Cypress forestland (Platycladus orientalis (L.) Franco (PO))). The conversion of FL to grassland and forestland significantly increased C:N and C:P by 9.82~64.12%, 10.57~126.05%, and 51.44~113.40%, 22.10~116.09%, respectively. The conversion of FL to ACL reduced the C:N and C:P by 5.34~13.57% and 1.51~7.55%, respectively. The conversion of FL to NG can increase soil N:P. The conversion of FL to grassland and forestland increased soil MBC, MBN, and MBP by −31.54~84.48%, −48.39~1533.93%, −46.55~173.85%, and −34.96~17.13%, 68.72~432.14%, −38.39~318.46%, respectively. However, the MBC, MBN, and MBP contents in the soil converted from FL to ACL varied from −28.21~11.95%, 11.17~531.25%, and −82.64~70.77%, respectively. Soil SOC, TN, TP, available potassium (AK), pH, and soil bulk density (BD) are the main factors causing microbial biomass differences. These results indicate that converting farmland into forestland and grassland can improve soil nutrient structure and increase soil microbial biomass and carbon accumulation. The results of this study provide theoretical support for the scientific management of regional land.