One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts, all under more variable and extreme climate conditions in the future. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia. However, conservation agriculture is highly debated, with respect to both its effects on crop yields and its applicability in different farming contexts. Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till, the original and central concept of conservation agriculture, with conventional tillage practices across 48 crops and 63 countries. Overall, our results show that no-till reduces yields, yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage. Importantly, when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation, its negative impacts are minimized. Moreover, no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates, suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world. However, any expansion of conservation agriculture should be done with caution in these areas, as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems, thereby increasing the likelihood of yield losses rather than gains. Although farming systems are multifunctional, and environmental and socio-economic factors need to be considered, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed.

a b s t r a c tNo-till agriculture represents a relatively widely adopted management system that aims to reduce soil erosion, decrease input costs, and sustain long-term crop productivity. However, its impacts on crop yields are variable, and an improved understanding of the factors limiting productivity is needed to support evidence-based management decisions. We conducted a global meta-analysis to evaluate the influence of various crop and environmental variables on no-till relative to conventional tillage yields using data obtained from peer-reviewed publications (678 studies with 6005 paired observations, representing 50 crops and 63 countries). Side-by-side yield comparisons were restricted to studies comparing conventional tillage to no-till practices in the absence of other cropping system modifications. Crop category was the most important factor influencing the overall yield response to no-till followed by aridity index, residue management, no-till duration, and N rate. No-till yields matched conventional tillage yields for oilseed, cotton, and legume crop categories. Among cereals, the negative impacts of no-till were smallest for wheat (−2.6%) and largest for rice (−7.5%) and maize (−7.6%). No-till performed best under rainfed conditions in dry climates, with yields often being equal to or higher than conventional tillage practices. Yields in the first 1-2 years following no-till implementation declined for all crops except oilseeds and cotton, but matched conventional tillage yields after 3-10 years except for maize and wheat in humid climates. Overall, no-till yields were reduced by 12% without N fertilizer addition and 4% with inorganic N addition. Our study highlights factors contributing to and/or decreasing no-till yield gaps and suggests that improved targeting and adaptation, possibly including additional system modifications, are necessary to optimize no-till performance and contribute to food production goals. In addition, our results provide a basis for conducting trade-off analyses to support the development of no-till crop management and international development strategies based on available scientific evidence.

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Manually delaying pollination in maize restricted kernel growth and induced abortion by suppressing cell wall invertase activity and repartitioning assimilates.

Ultisols in China need phosphorus (P) fertilization to sustain crop production but are prone to P loss in runoff. Balancing P inputs and loss requires detailed information about soil P forms because P speciation influences P cycling. Analytical methods vary in the information they provide on P speciation; thus, we used sequential fractionation (SF), solution P nuclear magnetic resonance (P-NMR), and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to investigate organic P (P) and inorganic P (P) species in Chinese Ultisols managed for different crops and with different fertilizer inputs in the first study to combine these techniques to characterize soil P. Sequential fractionation showed that moderately labile NaOH-P was the largest P pool in these soils, P varied from 20 to 47%, and residual P ranged from 9 to 31%. Deoxyribonucleic acid (1-5%) and -inositol hexakisphosphate (-IHP, 4-10%) were the major P forms from P-NMR. Orthophosphate diesters determined by NMR were significantly correlated with labile NaHCO-P in SF ( > 0.981; < 0.001). Soil P was shown to be predominantly associated with iron and soluble calcium (Ca) by XANES. Furthermore, XANES identified hydroxyapatite in the soil receiving the highest rates of Ca-phosphate fertilizer, which had the highest HCl-P pool by SF, and also identified IHP (7%) in the soil with the highest proportion of -IHP from P-NMR. These results strongly suggest that a combined use of SF, solution P-NMR, and P K-edge XANES spectroscopy will provide the comprehensive information about soil P species needed for effective soil P management.

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