Agricultural management strategies for balancing yield increase, carbon sequestration, and emission reduction after straw return for three major grain crops in China: A meta-analysis.

Straw return can improve crop yield as well as soil organic carbon (SOC) but may raise the possibility of N2O and CH4 emissions. However, few studies have compared the effects of straw return on the yield, SOC, and N2O emissions of various crops. Which management strategies are the best for balancing yield, SOC, and emission reduction for various crops needs to be clarified. A meta-analysis containing 2269 datasets collected from 369 studies was conducted to investigate the influence of agricultural management strategies on yield increase, soil carbon sequestration, and emission reduction in various crops after the straw return. Analytical results indicated that, on average, straw return increased the yield of rice, wheat, and maize by 5.04%, 8.09%, and 8.71%, respectively. Straw return increased maize N2O emissions by 14.69% but did not significantly affect wheat N2O emissions. Interestingly, straw return reduced the rice N2O emissions by 11.43% but increased the CH4 emissions by 72.01%. The recommended nitrogen application amounts for balancing yield, SOC, and emission reduction varied among the three crops, while the recommended straw return amounts were more than 9000 kg/ha. The optimal tillage and straw return strategies for rice, wheat, and maize were plow tillage combined with incorporation, rotary tillage combined with incorporation, and no-tillage combined with mulching, respectively. A straw return duration of 5-10 years for rice and maize and ≤5 years for wheat was recommended. These findings provide optimal agricultural management strategies after straw return to balance the crop yield, SOC, and emission reduction for China's three major grain crops.

Spatial patterns and driving factor analysis of recommended nitrogen application rate for the trade-off between economy and environment for maize in China.

Appropriate nitrogen (N) application increases crop yield, while its unreasonable application results in environmental problem. Determining the appropriate N application rate is the key to sustainable development. Here, the denitrification-decomposition (DNDC) model was used to analyze the effects of N fertilizer on maize yields, economic benefits, nitrate leaching, and nitrous oxide emissions in China. The N application rate for the trade-off between economy and environment at the county scale was further determined. The geodetector model was used to identify the main driving factors and their interactions of the recommended N rate in each agricultural zone. The results showed that the recommended N rate was generally high in the northwest but low in the south, consistent with the spatial patterns of yield potential. However, clay soils with clay ratios greater than 34% in southern China and sandy soils with bulk densities greater than 1.5 g cm-3 on the Huanghuaihai Plain experienced high N levels and low yields, and thus soils need to be improved. Potential grain yield was the main driving factor in most zones, yet its effects gradually weakened from north to south. The influence of soil characteristics increased from north to south. It was found that the current average N application rate of farmers in China was 249 kg N/ha, and 86.55% of counties had excessive N applications. Compared to the regional optimal N rate at a regional scale, a differentiated N application strategy at the county scale determined in this study increased maize yield and economic benefit by 10.51% and 10.85%, respectively, and reduced N2O emissions and NO3- leaching by 28.72% and 33.60%, respectively. The current research provides a scientific basis for China to formulate a win-win N management strategy for economy and environment and provides a method reference for other countries.

A recommended nitrogen application strategy for high crop yield and low environmental pollution at a basin scale.

Mitigating environmental pollution and sustaining grain production have been foundational issues in sustainable development, however, ascertaining the optimal balance remains poorly investigated. This study used the Soil and Water Assessment Tool (SWAT) model to simulate crop growth and nitrogen loss, established the mapping relationship between nitrogen input to yield and water quality, and proposed a general method to determine a nitrogen application strategy for high yield and low pollution at a basin scale. Lake Xiaoxingkai basin, which is the primary maize producing area in China as well as an internationally important wetland distribution area, was used as a case study. First, we designed application scenarios for 10 base fertilizers (B1-B10) and 10 topdressing fertilizers (T1-T10) and evaluated their combined effects of maize growth to identify the critical nitrogen fertilizer rates determined under fixed and dynamic base/topdressing ratios. Then, the critical base and topdressing fertilizer rates were determined. Based on the mapping relationship between nitrogen fertilizer rate and nitrogen loss, we then revealed water quality at the basin outlet under the critical base and topdressing fertilizer rates. Finally, we proposed alternative nitrogen application strategies for high yield and low pollution while considering the different preferences of decision-makers for the economy, agriculture, and environment. We found that adjusting the ratio of base to topdressing fertilizer may create a win-win situation for agriculture and the environment, which will provide a scientific basis for sustainable development.

Comparing the Impacts of Sediment-Spiked Cadmium on Chironomidae Larvae in Laboratory Bioassays and Field Microcosms and the Implications for Field Validation of Site-Specific Threshold Concentrations.

Information on the effects of pollutants in sediments at an ecosystem level to validate current and proposed risk-assessment procedures is scarce. The most frequent criticism of these procedures is that responses of surrogate species in the laboratory are not representative of responses of natural populations. A tiered approach using both laboratory and microcosm exposures (96-h and 21-d laboratory bioassays and a 3-mo field microcosm) was conducted to compare the impacts of sediment-spiked cadmium on the mortality, development, and abundance of Chironomidae larvae. The 96-h and 21-d lethal concentrations of sediment-spiked Cd to 50% of the species Chironomus riparius were estimated to be 201.07 and 172.66 mg/kg, respectively. In the 21-d laboratory bioassay, the endpoints, including the development rate and emergence ratio, were compared, and the lowest-observed-effect concentration (LOEC) values were 325.8 and 10.7 mg/kg, respectively. The abundance, richness, and biomass of field-collected larvae were compared among the different treatments in the field microcosm, and it was found that the order of sensitivities using different endpoints was biomass (2.6/5.2 mg/kg of no-observed-effect concentration/LOEC) > diversity (10.7/21.2 mg/kg) > abundance (41.2/82.7 mg/kg). The toxicity values based on lethal/sublethal changes in the laboratory bioassays might not fully protect field organisms against damage from chemicals, such as Cd, unless an assessment factor of 5 is used. These findings highlight the need to conduct field validation of criteria/guidelines before they are introduced to protect organisms/ecosystems in the field and provide a preliminary template for future field validation of criteria elsewhere. Environ Toxicol Chem 2021;40:2450-2462. © 2021 SETAC.

Source contribution analysis of nutrient pollution in a P-rich watershed: Implications for integrated water quality management.

It is still a great challenge to address nutrient pollution issues caused by various point sources and non-point sources on the watershed scale. Source contribution analysis based on watershed modeling can help watershed managers identify major pollution sources, propose effective management plans and make smart decisions. This study demonstrated a technical procedure for addressing watershed-scale water pollution problems in an agriculture-dominated watershed, using the Dengsha River Watershed (DRW) in Dalian, China as an example. The SWAT model was improved by considering the constraints of soil nutrient concentration, i.e., nitrogen (N) and phosphorus (P), when modeling the nutrient uptake by a typical crop, corn. Then the modified SWAT model was used to quantify the contributions of all known pollution sources to the N and P pollution in the DRW. The results showed that crop production and trans-administrative wastewater discharge were the two dominant sources of nutrient pollution. This study further examined the responses of nutrient loss and crop yield to different fertilizer application schemes. The results showed that N fertilizer was the limiting factor for crop yield and that excessive levels of P were stored in the agricultural soils of the DRW. An N fertilizer application rate of approximately 40% of the current rate was suggested to balance water quality and environmental protection with crop production. The long-term impact of legacy P was investigated with a 100-year future simulation that showed the crop growth could maintain for 12 years even after P fertilization ceased. Our study highlights the need to consider source attribution, fertilizer application and legacy P impacts in agriculture-dominated watersheds. The analysis framework used in this study can provide a scientifically sound procedure for formulating adaptive and sustainable nutrient management strategies in other study areas.