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A global meta-analysis of conservation agriculture principles indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed. Does conservation agriculture work? Advocates of conservation agriculture, which integrates ecological management (namely zero tillage, permanent soil cover and crop rotation) with modern agricultural production techniques, see it as a means of sustainably increasing global food supply. So far it has proved difficult to establish conclusively whether crop yields are maintained by conservation agriculture and whether it can be applied effectively in widely differing farming contexts. In this meta-analysis of more than 5,000 observations from 610 studies, Cameron Pittelkow and colleagues show that farming using a combination of conservation agriculture techniques can yield as much or more than conventional farming under certain conditions. The use of 'no-till' alone, the central concept of conservation agriculture, negatively impacts yields. But used with the other two conservation agriculture techniques of residue retention and crop rotation, no-till can increase rainfed crop productivity in dry climates, suggesting it may become an important climate-change adaptation strategy. 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.sup.1,2,3,4. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge.sup.5,6, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia.sup.7. However, conservation agriculture is highly debated, with respect to both its effects on crop yields.sup.8,9,10 and its applicability in different farming contexts.sup.7,11,12,13. 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.sup.14,15,16, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed., Author(s): Cameron M. Pittelkow [sup.1] [sup.8] , Xinqiang Liang [sup.2] , Bruce A. Linquist [sup.1] , Kees Jan van Groenigen [sup.3] , Juhwan Lee [sup.4] , Mark E. Lundy [sup.1] [...]

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 [...]

Effective nutrient management to reduce high N losses and to improve N use effciency has been an important focus of agricultural and environmental science research. Understanding the influence of duckweed (Lemma minor L.), a common floating macrophyte in flooded rice (Oryza, sativa L.) fields, on N[H.sub.3] volatilization and grain yield is required for better management of applied N fertilizer. We conducted an on-farm experiment with three levels of urea (0, 90, 180 kg urea N [ha.sup.-l]) applied alone or in combination with duckweed. Our results indicate that total ammoniacal-N concentration, pH, and temperature of the floodwater were significantly lower in the plots with a duckweed cover. As a consequence, N[H.sub.3] volatilization rates were reduced by duckweed from 20.0 to 53.7% and from 19.0 to 33.2% in plots supplied with 90 and 180 kg utca-N [ha.sup.-1] respectively. Duckweed increased rice grain yields by apptoximately 0.7 and 07 Mg [ha.sup.-1] (9.8 and 9.4%) in plots supplied with 90 and 180 kg urea N [ha.sup.-1], respectively. Ammonia losses from urea-N applications can be reduced and N use efficiencies can be improved by' the presence of duckweed in flooded rice fields. Abbreviations: DW, duckweed; TAN, total ammoniacal nitrogen. doi: 10.2136/sssaj2008.0230