Long-term conservation tillage improves surface soil carbon and nitrogen content and rhizosphere soil enzyme activities

Objectives Long-term tillage affects the C and N contents and enzyme activities in rhizosphere and non-rhizosphere soils of crops, and then affects the correlation between soil C and N contents and the activities of enzymes associated with C and N transformation. The paper compared the effect of different tillage measures to provide reference for selecting rational and effective tillage technology in the tested area.

Methods The long-term tillage experiment, began in 1999, was conducted in Mengjin County, Henan Province, which is located at the east edge of Loss Plateau, the soil was loam Loessal and 50−100 m in depth. The tillage treatments included: weed field (GL), conventional tillage (CT), no-tillage and mulch (NT) and sub-soiling and mulch tillage (SM). Samples of 0−20 cm and 20−40 cm deep in non-rhizosphere and rhizosphere soil were collected in 2016. The contents of total C, organic C and total N, and the activities of β-glucosidase (BG), β-D-cellobioside (CBH), β-xylosidase (BXYL), β-N-acetylglucosaminidase (NAG) and leucineaminopeptidase (LAP) were analyzed. The correlation between soil C and N content and enzyme activity was analyzed.

Results 1) Compared with the CT, the total C, organic C and total N contents in the 0−20 cm non-rhizosphere and rhizosphere soils were significantly increased by NT and SM, but those in the 20−40 cm non-rhizosphere soil were significantly decreased. The contents of total C, organic C and total N in rhizosphere soil, organic C content in 0−20 cm non-rhizosphere soil were significantly increased in GL, but the total C content in non-rhizosphere soil and organic C content in 20−40 cm layer of non-rhizosphere were significantly reduced. SM significantly decreased the C/N in rhizosphere and non-rhizosphere soil. NT and GL significantly decreased C/N in 20−40 cm layer non-rhizosphere, but GL significantly increased C/N in 0−20 cm non-rhizosphere. 2) Compared with CT, the activities of BG, CBH, BXYL and NAG in rhizosphere soil were significantly increased by NT and SM. The LAP activity in rhizosphere soil was significantly increased in GL, but significantly decreased by NT and SM. 3) There was a positive correlation between carbon conversion enzymes and nitrogen conversion enzymes (except CBH with LAP). The activities of C and N transformation enzymes were significantly and positively correlated with the soil total C, total N and organic C (except LAP with TC) and negatively correlated with C/N.

Conclusions Soil enzymes associated with carbon and nitrogen transformation have mutually reinforcing relationship and participate in the transformation of soil carbon and nitrogen. Long-term conservation tillage (No tillage and mulching, Sub-soiling and mulching) can effectively increase the total carbon, organic carbon and total nitrogen contents in surface soil, increase the enzyme activities in the rhizosphere soil, facilitate the circulation and transformation of carbon and nitrogen, as well as the absorption and utilization of crops. Long-term conservation tillage is a reasonable and effective tillage method.