Changes in soil organic carbon fractions and enzyme activities in response to tillage practices in the Loess Plateau of China

The responses of soil labile organic carbon fractions and enzyme activities to tillage practices are important to address the issues of agricultural sustainability. However, how these critical soil characteristics change throughout the various growth stages of winter wheat under different tillage practices are less clearly understood. A long-term field experiment (11 years) of six tillage practices (no tillage, NT; subsoiling tillage, ST; plow tillage, PT; NT with ST rotation, NT/ST; ST with PT rotation, ST/PT; and PT with NT rotation, PT/NT) was started in the Loess Plateau in 2007, and the changes in soil labile organic carbon fractions and enzyme activities were measured at the sowing, jointing, filling, and harvest stages in 2018. This experiment led to several conclusions: (1) NT/ST, NT, ST, ST/PT, and PT/NT treatments significantly increased soil organic carbon (SOC) by 2.05%-43.93%, microbial biomass carbon (MBC) by 9.13%-84.61%, permanganate oxidizable organic carbon (POXC) by 3.64%-89.62%, and particulate organic carbon (POC) by 6.41%-77.59% throughout all stages of growth when compared with PT; (2) The activities of cellobiohydrolase (CBH), beta-glucosidase (BG), beta-xylosidase (BXYL), beta-N-acetylglucosamines (NAG) and alkaline phosphatase (AP) were 17.15%-169.16%, 2.85%-65.72%, 6.69%-96.99%, 22.76%-136.65% and 0.12%-29.11% higher after the NT/ST, NT, ST, ST/PT, and PT/NT treatments, respectively, than after PT throughout all the stages of growth; (3) These conservation tillage practices improved the soil ecoenzymatic stoichiometry by increasing the ratios of Ln(CBH + BG + BXYL): Ln (AP) and Ln(NAG):Ln(AP) and by reducing the ratio of Ln(CBH + BG + BXYL): Ln(NAG) compared with PT; (4) Soil enzyme activities were positively associated with the SOC fractions. Redundancy analyses (RDA) found that the key factors driving the changes in soil enzyme activities were POXC and SOC at the sowing stage, SOC and MBC at the jointing and harvest stages, and SOC and POC at the filling stage; (5) the NT/ST treatment was associated with the highest SOC fractions, soil enzyme activities and yield, and thus was a sustainable, efficient method to improve soil quality and crop yield in the Loess Plateau.

Automated summary

Long-term tillage practices significantly impact the soil labile organic carbon fractions and enzyme activities during the growth stages of winter wheat. Conservation tillage practices can increase soil organic carbon, microbial biomass carbon, enzyme activities, and improve soil ecoenzymatic stoichiometry, positively associated with soil organic carbon fractions.