Abstract
Sustainable agricultural management implies optimization of resources for crop production while minimizing adverse impacts on the environment. This requires a better understanding of the synergies and trade-offs of agronomic management while accounting for the controlling effects of site-specific factors (covariates). We systematically evaluated 113 meta-analytical studies assessing impacts of crop management measures (rotation, cover cropping, residue retention), soil and water measures (irrigation, tillage), soil amendments (enhanced efficiency, biochar), fertilizer use (organic, mineral, combined organic-mineral) and “4R'” fertilizer strategies (right source, rate, timing, placement) on sustainability indicators. These indicators include crop yield, crop N and P (content, uptake, and use efficiency), soil quality indicators (soil organic C, N and P contents, compaction), soil emissions of ammonia (NH3) and greenhouse gases (CO2, N2O), and nutrient losses to water (N and P surplus or leaching). Nutrient management, including 4R practices as well as enhanced efficiency amendments, had the largest impact, increasing crop yields and N uptake while reducing N2O and NH3 emissions as well as N surplus, whereas effects on CO2 emissions were variable. Although all measures positively impacted soil C, the largest effect was due to biochar, followed by organic fertilizer input. Biochar positively impacted crop yield, diminished N2O and NH3 emissions as well as N surplus, and increased CO2 emissions. Within crop management, only cover cropping had a significant positive effect on crop yield, while both cover crops and rotation slightly enhanced N uptake and the sequestration of C and N in soil, thus reducing N2O emissions and N surplus. Minimal tillage practices generally increased SOC, while results for crop yield, N surplus and N2O emissions were variable. Site-specific factors had substantial impacts on the evaluated impacts of measures, most importantly climate, crop type, soil texture, soil pH, soil organic C, N dose, and experimental duration. Considering the variation among meta-analytical protocols followed, we recommend that field studies and meta-analytical work adhere to harmonized guidelines with respect to the reporting of site-level data, experimental design, and the statistical procedures used. This will ensure data comparability between studies, improve the quality of meta-analysis results, and give better insights into currently uncertain or unknown impacts of agronomic measures.
Highlights
Agricultural activities during the last half century have undoubtedly led to societal tradeoffs, most notable being the large increase in food production in comparison to the various negative effects of intensifica tion (Pretty, 2008)
We quantify impacts for the following indicators: crop yield, crop N uptake, crop P uptake, soil quality, greenhouse gas emissions (CO2, N2O) and nutrient losses to air (NH3) and water. The effect of both site properties and experimental factors on the impacts of the various measures is investigated but limited to crop yield, soil organic carbon (SOC), N surplus and N2O, in response to the main types of measures grouped by cropping diversity, tillage and organic fertilization, which we found to be the most important combinations of measures and impacts
The dynamic behavior of inorganic N in soil limits their use for environmental impact assessments (Cardoso et al, 2013) and we focus on total organic N only (Fig. 6)
Summary
Agricultural activities during the last half century have undoubtedly led to societal tradeoffs, most notable being the large increase in food production in comparison to the various negative effects of intensifica tion (Pretty, 2008). We quantify impacts for the following indicators: crop yield, crop N uptake (estimated via crop N content, N uptake or N use efficiency), crop P uptake (estimated via crop P content, P uptake, or P use efficiency), soil quality (estimated via SOC, N and P contents as well as compaction), greenhouse gas emissions (CO2, N2O) and nutrient losses to air (NH3) and water (via N and P surplus or leaching) The effect of both site properties and experimental factors (the sum of both being defined as site-specific factors) on the impacts of the various measures is investigated but limited to crop yield, SOC, N surplus and N2O, in response to the main types of measures grouped by cropping diversity, tillage and organic fertilization, which we found to be the most important combinations of measures and impacts. We pro vide a comprehensive overview of meta-studies covering multiple ag roecological zones, management options, and indicators for the sustainability of agriculture, and evaluate the strengths and weaknesses of the meta-analytical approaches in order to guide further research
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