Dynamics in soil organic carbon of wheat-maize dominant cropping system in the North China Plain under tillage and residue management.

A site experiment was conducted to assess temporal dynamics of soil organic carbon (SOC) and the drivers under no-tillage (NT) and residue retention (RR) in the North China Plain (NCP). The results indicated that NT and RR can significantly increase SOC up to a depth of 30 cm. On average, NT increased SOC by 8.1-34.5% compared with PT, and RR increased SOC by 3.5-14.4% compared with R0 at 0-10 cm. Increases in SOC under NT or RR could be increased by 4-10 percentage points through the significantly positive interactions of NT and RR. Among the sources of SOC variations, tillage-induced variations accounted for 74.4 and 44.3% of the total variations in SOC at 0-5 cm for wheat and maize season, respectively. Experimental duration was also a significant source of variation. Stepwise regression indicated dynamics in SOC at 0-5 cm mainly due to the positive effects of precipitation, the negative effects of soil bulk density for the wheat season, the negative effects of radiation for the maize season, and antagonistic effects of temperature between wheat and maize season. Generally, positive effects of NT and RR on SOC were both confirmed, but fluctuations and variations induced by interactions of practices and seasonal climatic conditions were also significant in the NCP.

Management-induced greenhouse gases emission mitigation in global rice production.

Mitigating greenhouse gases (GHGs) emissions from rice paddy (Oryza sativa L.) and balancing the trade-offs between reducing emission and sustaining food security have raised global concerns. A global meta-analysis of rice experimental data was conducted to assess changes in emissions of GHGs (CH4 and N2O) and global warming potential (GWP) in response to improvements through 12 field management practices. The results indicated that changes in GWP were mainly attributed to CH4 emission even though N2O emission was significantly affected by conversion of field management practices. Specifically, GWP per unit rice plant area (area-scaled) was significantly increased by 20.1%, 66.2%, and 84.5% with nitrogen (N) fertilizer input, manuring, and residue retention (P < 0.05), along with significant increments in area-scaled CH4 emission under the above management practices by 8.9%, 60.4%, and 91.8%, respectively (P < 0.05). Due to the significant increase in rice yield, a decreasing trend for GWP per unit rice yield (yield-scaled) was observed with N fertilizer input. In addition, CH4 and GWP decreased significantly at both area- and yield-scale under non-flooding irrigation but with a reduction in rice yield by 3.3% (P < 0.05). Improvement in rice variety significantly enhanced crop yield by 15.3% while reducing area-scaled GWP by 27.7% (P < 0.05). Furthermore, other management practices, such as application of herbicides, biochar, and amendments (non-fertilizer materials) reduced yield-scaled GWP while increasing rice yield. Thus, changes in field management practices have the potential to balance the trade-offs between high yield and low emission of GHGs. However, in-depth studies are needed to determine the interactions between field management practices and site-specific soil/climate conditions.

Effects of mine wastewater irrigation on activities of soil enzymes and physiological properties, heavy metal uptake and grain yield in winter wheat.

In China, coal-mining industries are mainly located in the water shortage areas including arid or semiarid areas. Mine wastewater is used for irrigation of agricultural land in these areas. However, few studies have been conducted to address ecological and food safety risks caused by mine wastewater irrigation. In this research, a pot experiment was performed to examine the effects of mine wastewater irrigation on soil enzymes, physiological properties of wheat and potential risks of heavy metal contamination to wheat crop. Plants were subjected to three mine wastewater irrigation treatments: leacheate of coal gangue (T1), coal-washing wastewater (T2) and precipitated coal-washing wastewater (T3). Plants irrigated with well water were taken as the control (CK). The results showed that mine wastewater irrigation caused adverse effects on soil enzymes, physiological properties and grain yield of winter wheat. At anthesis, T1, T2 and T3 treatments significantly reduced the activities of soil enzymes (urease, sucrase and catalase), root activity and net photosynthetic rate of wheat compared to CK. At maturity, grain yield was decreased by 17.8%, 15.4% and 9.8% by T1, T2 and T3, respectively, as compared to that of CK. Importantly, mine wastewater irrigation resulted in accumulation of heavy metals (Cr, Pb, Cu and Zn) in wheat grain. Contents of these heavy metals in grains of winter wheat subjected to mine wastewater irrigation were significantly higher than those in CK. The comprehensive contamination indexes of wheat grain in T1, T2 and T3 all reached high pollution level. Our results showed that mine wastewater irrigation significantly increased the pollution risk of heavy metals, thus unsuitable for crop irrigation.

[Effects of irrigation with mine wastewater on physiological characters and heavy metals accumulation of winter wheat].

A pot experiment was conducted to study the effects of irrigation with mine wastewater on the physiological characters and heavy metals accumulation of winter wheat. Three treatments were installed, i. e., irrigation with coal-washing wastewater (T1), irrigation with coal-washing wastewater after its precipitation (T2), and irrigation with coal gangue leacheate (T3), taking the well water irrigation as the control (CK). The plants were irrigated with mine wastewater after the turning green stage. Irrigation with mine wastewater had negative effects on the winter wheat growth and grain yield. At anthesis stage, the leaf area, dry mass per stem, root activity, and net photosynthetic rate of winter wheat in treatments T1, T2, and T3 were significantly lower than those in CK (P < 0.05), the plant height and leaf chlorophyll content in T3 decreased significantly (P < 0.05), and the grain yield in T1, T2 and T3 was decreased by 15.4%, 9.8%, and 17.8%, respectively. In addition, the heavy metals (Cr, Pb, Cu and Zn) contents in the grain of winter wheat under mine wastewater irrigation were significantly higher than those in CK, suggesting that the irrigation with mine wastewater could result in the heavy metals accumulation in wheat grain.