No abstract

Straw retention is an effective method to conserve soil water content and improve soil carbon stocks. However, how soil carbon dynamics respond to different straw retention practices remains unclear. In this study, we investigated soil respiration and soil carbon sequestration at depths of 0–100 cm. We conducted a two-year field experiment with three crop rotation treatments and three straw retention treatments in northwest China. The straw retention treatments included no straw retention (NS), retention of half the straw (HS), and retention of the total amount of straw (TS). The crop rotations treatments included winter wheat plus summer soybean (WS), winter wheat plus summer maize (WM), and winter wheat plus summer fallow (WF). Mean soil respiration rates under WS, WM, and WF treatments were 5.14, 6.53, and 5.49 μmol·m-2·s-1; and 5.67, 5.47, and 6.03 μmol·m-2·s-1 under TS, HS, and NS treatments. The mean soil water content were 15.50%, 15.57%, and 15.74% under WS, WM, and WF rotations, and 15.81%, 15.41%, and 15.50% under TS, HS, and NS treatments. The soil organic carbon (SOC) concentration was higher with increased straw retention, and lower at deeper soil depths. Mean SOC concentrations under different rotations and straw treatments of TS, HS, and NS, respectively were as follows: WS: 6.91, 6.63, 6.39 g/kg; WM: 6.90, 6.72, 6.57 g/kg; and WF: 6.49, 6.52, 6.37 g/kg. Soil temperature was the main determinant of soil respiration rates. We conclude that WS rotation resulted in lower soil respiration, WM rotation resulted in a higher soil carbon sequestration potential, and WF rotation resulted in higher soil water content. However, continued, long-term monitoring is needed to confirm the effect of rotations and straw retention on soil respiration and carbon sequestration in dryland cropping systems in northern China.

Developing environmentally friendly and sustainable nitrogen (N) fertilizer management strategies is crucial in mitigating carbon dioxide (CO2) emission from soil. How N fertilizer management practices influence soil CO2 emission rates under different crop rotations remains unclear. The aim of this study was to assess the impact on soil CO2 emission and soil physicochemical properties of three N fertilizer treatments including traditional rate (TF), optimized rate (0.8TF), and no fertilizer (NF) under three different crop rotation treatments: wheat-fallow (WF), wheat-soybean (WS), and wheat-maize (WM) over two years in a field experiment in northwest China. The rates were 5.51, 5.60, and 5.97 μmol·m−2·s−1 of mean soil CO2 emission under the TF, 0.8TF, and NF treatments, respectively. Mean soil CO2 emission rates were 21.33 and 26.99% higher under the WM rotation compared with the WF and WS rotations, respectively. The WS rotation showed higher soil nutrient content and lower soil CO2 emissions, and reduced fertilizer application. Importantly, soil organic carbon (SOC) concentration in the topsoil can be maximized by including either a summer legume or a summer maize crop in winter wheat rotations, and by applying N fertilizer at the optimal rate. This may be particularly beneficial in the dryland cropping systems of northern China.

Straw retention and wheat-soybean rotation play critical role in maintaining soil quality. However, the correlation between bacterial diversity and community structure, and soil nutrients is unknown, and a systematic understanding of their responses to straw retention is lacking. In the field experiment, the straw retention treatments included no straw (NS), half straw (HS), and total straw (TS) retention during long-term wheat-soybean rotation. The mean contents of soil total nitrogen (TN), nitrate-N (NO3−-N), and microbial biomass nitrogen (MBN) increased by 15.06%, 21.10%, and 38.23%, respectively, with straw retention relative to NS, while that of ammonium-N (NH4+-N) reduced by 3.68%. The concentration of carbon components increased as straw retention increased. The levels of soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), and soil organic carbon (SOC) increased by 4.34%, 7.63%, and 9.34%, respectively, with straw retention relative to NS. Soil bacterial alpha diversity was reduced with straw retention. Soil pH and nutrient content were identified as the main factors affecting the soil microbial diversity and structure at the phylum level. Accordingly, straw retention and soybean-wheat rotation enable sustainable agriculture in the dryland of northern China.