Rice–wheat generated the maximum economic return with CA, which was 29.0% higher than with the conventional practice . Increase in economic return was similar among the maize–wheat, rice–maize and other systems. Crop-based analyses showed higher yields for wheat and maize than for rice under CA practices . Crops in the ‘others’ category exhibited a 3.8% increase in yield. The trend was similar in on-station and on-farm data for maize and wheat crops . However, yield in rice was higher in on-farm studies, but there was no change in on-station studies. Wheat and maize had much higher water use efficiency compared with rice . Other crop systems had 12.7% higher water use efficiency. CA-based practices increased the economic return for all crops, with the highest in wheat and lowest in rice .Meta-analyses of key parameters of on-station and on-farm studies, including all crops and systems in response to the sub-levels of CA , are shown in Table 2. The beneficial effects tend to increase from CA1 to CA2, while the differences between CA2 and CA3 are negligible. Compared with conventional practice, grain yield increased 3.0% in CA1, 5.8% in CA2 and 5.5% in CA3. The increase in PEY followed a similar trend. Likewise,macetas de plástico water use efficiency increased 8.3% in CA1, 12.6% in CA2 and 11.6% in CA3.
The increase in net economic return was, however, the largest in CA3 compared with conventional practices. The increase in net return was higher in CA2 compared with CA1 . In on-station studies, grain yield increase was similar in CA2 and CA3 with no change in CA1; in on-farm studies, all the CA sub-levels had similar yield gains . The PEY showed a similar response as in grain yield . Cropping-system analyses showed the highest yield increase in the maize–wheat system, ranging from 13.7% to 24.2%, which did not differ among three sub-levels of CA. The rice–wheat system had the highest increases in grain yield in CA2 , which was similar to CA3 but higher than CA1 . The rice– maize system, for which data of only CA1 and CA2 were available, showed similar increases of 2.2% in CA1 and 4.5% in CA2.In the rice–wheat and rice–maize systems, the water use efficiencies were similar among CA1, CA2 and CA3. In the maize– wheat system, CA2 and CA3 had comparable increases in water use efficiency of 25.1% and 26.0% . CA3 had the highest increase in economic return in rice–wheat, but in the maize–wheat system, all three CA practices brought similar economic return. In the rice–maize system, greater increase in economic return was achieved in CA2 compared with CA1 . Crop-based analyses showed higher wheat and maize yields in all the CA sub-levels, and water use efficiencies were significantly higher in all three CA sub-levels .As a function of soil texture, yield responses were nominal on sandy soil with increasing responses for fine clayey , medium loamy and moderately coarse loamy soils . The PEY had a trend similar to grain yield.
The moderately fine loam had the highest increase in grain yield and water use efficiency . In maize–wheat, the highest yield gain was obtained from medium loamy soils , which is comparable to the yield increase in moderately fine loamy soils, but moderately fine loamy soils resulted in the highest increase in water use efficiency . In rice–wheat, moderately fine loamy soils contributed to the highest yield gain, but increases in water use efficiency were similar for all the textures. In the rice–maize system, both moderately fine and medium loamy soils showed the largest gains in yield and water use efficiency. Moderately coarse loamy soil appears to be better suited for the ‘others’ category, improving both the yield and water use efficiency compared with conventional practice. The net return was higher in all soil textures except the coarse sandy soils and closely followed the trend in yield gains. Crop-based analysis showed the most significant performance gains in the loamy soils for all the crops while the sandy soils had the poorest response, with marginally positive to negative effect . Clay also did not seem to be favourable under CA. Among the sub-classes of loam, fine loam was the most favourable for all three cereals, with the maximum yield advantage of 16.0% in wheat. Maize performed similarly in all three sub-classes of loam, with grain yield increases ranging from 6.1% to 8.9%. Rice had the maximum yield advantage of 3.6% in fine loam and relatively poor or no responses in other soil texture classes. Increase in water use efficiency in wheat was similar in all textures, except in coarse sandy soil, which was significantly lower.
Maize had comparable increases in water use efficiency in moderately fine and moderately coarse loamy textured soils. In rice, water use efficiency was higher only in medium loamy soils, with no change in other soil texture classes.Our meta-analysis of 1,353 field studies with major cereal-based cropping systems conducted on research stations and farmers’ fields closes a data gap for South Asia that has limited the regional inferences that can be drawn from earlier meta-analyses. Our analysis reveals the positive average effects of full and partially implemented CA on crop yield , water use efficiency and economic return in the cereal-based cropping systems of South Asia. Although all three combinations of CA sub-levels had significant positive effects, the impacts tended to be more positive when both the cereals had ZT with residues retained in one or both the crops across the cropping system. However, the net economic return was 40.5% higher in CA3 compared with around 20% in CA1 and 26% in CA2, suggesting that a full or close to full extent of CA would maximize the economic benefits, which is an important consideration in the farmers’ decision making. Superiority of CA2 and CA3 over CA1 may also indicate cumulative effects of ZT and residue retention resulting from a carryover effect in a system. However, since there were only a limited number of published studies examining long-term effects of CA in South Asia, it was not possible to evaluate the carryover effects in multiple years in the present study. The ZT with surface residue retention has been reported to produce higher crop yield than without residue. In a global meta-analysis, average yield loss of 9.9% was documented with ZT, a decline that was reduced to 5.2% when residue was retained. By contrast, our results show more positive effects on crop yield and other parameters. This could be because South Asia was not well represented in earlier meta-analyses published in 2015. The literature search in the present study revealed 48 new studies after the meta-analysis published in 2015. In addition, our study included data from 1,197 on-farm trials. Earlier meta-analyses had no on-farm data. Our results demonstrate that CA benefits vary among crops, cropping systems and soil textures. The CA practices tend to perform best for upland crops and non-rice cropping systems,cultivo del frambueso a result consistent with earlier findings in South Asia. Higher yield gains with CA in maize–wheat than in the rice-based system provide ample opportunity for much-needed diversification. Diversification is a key to address not only the issues of a faster-declining water table but also the perceived challenges of food and nutrition security. While all the studies included in the meta-analysis had grain yield data, most did not have all the performance parameters, namely, grain and PEYs, water use efficiency and net economic return; hence, analyses may not have captured the relative performance of CA. Research on CA in South Asia is largely focused on rice-based and maize-based systems, resulting in fewer studies in other cropping systems.
Nevertheless, it is notable that rice-based and maize-based are the most dominant cropping systems in South Asia. Published data on GHG emissions under CA were limited, and only emissions from on-station studies in the rice–wheat system were available. Most studies also lacked soil information . Another notable limitation was that there were not many long-term studies to assess the residual effects of CA on succeeding crops. All the crops, including rice, had higher average yields in loam than in clay or sand. These results may explain the variable performance of CA reported by those that did not consider soil texture as a factor. These findings highlight the need for a better environmental characterization for targeting CA by appropriately defining recommendation domains. Greater benefits in the field studies carried out by the researchers compared with those implemented by farmers are probably attributable to knowledge gaps that influence appropriate implementation of CA practices. The use of CA not only provides significant private benefits but can contribute to several ecosystem services. In our data, GWP was reduced by 12.4% in CA1 and 33.5% in CA2 in rice–wheat systems, values that are consistent with others. Moreover, public benefits are not limited to GHG emissions. Residue burning is a serious public health threat in South Asia, and approximately 23 million tons of rice residues are burned every year in Northwest India. The CA-based practices provide an economically feasible alternative to burning, which has been made possible with the development of ‘next generation’ seeders that permit ZT into heavy residues. Beyond the potential benefits that our study directly assessed, CA is largely mechanized and hence provides opportunity for timeliness of operations, reducing risks, increasing use efficiency of fertilizers through precise placement and reducing drudgery and hence attracting youth and women to remain engaged in agriculture. Our extensive literature examination of published studies on CA and a large number of on-farm trials revealed the need for a pragmatic approach to scaling CA practices. Few farmers in South Asia are able to adopt all three elements of CA at once, but benefits of partial adoption are clear. Some of the impediments to full adoption include the conflicting edaphic requirements of crops in a system; for example, rice grown in a rainy or wet season gets flooded before planting, which makes residue retention difficult. However, our analysis suggests that the classical definition of CA should not limit the smallholder farmers from adopting CA elements as their application separately or in tandem has potential benefits. Most farmers in South Asia follow ZT in only one crop, and few farmers retain complete residue cover at the soil surface throughout the annual cropping cycle. This situation has been observed and discussed by others but has not been resolved in terms of characterizing CA. According to our findings, if 50% of the area under the dominant cereal-based cropping systems of South Asia is brought under CA by 2030, there will be additional outputs of 3.6 million metric tons of grain and 0.5 million metric tons of grain protein on an annual basis . In addition, water used for irrigation will be reduced by 14,100 millionm3 , GWP will be reduced by 2.9 million tons and farmer income will increase by US$1,771 million. A concerted effort involving public and private stakeholders supported by an effective enabling environment for technology scaling is required. A renewed eco-regional initiative like the Rice–Wheat Consortium for the Indo-Gangetic Plains is perhaps part of the answer, with the provision that market-led approaches must be at the centre of the approach16. It is noteworthy that the Rice–Wheat Consortium pioneered and led much of the strategic and adaptive research on CA in South Asia, resulting in an accumulation of knowledge, which largely made this meta-analysis possible. Our results clearly show that while adoption of full CA is often superior on the basis of multi-criteria assessment, it is not always necessary to achieve meaningful benefits in the South Asian context. Since the benefits of partial adoption of CA practices are consistently observed in the cereal-based cropping systems in South Asia, rigid adherence to an ‘all or nothing’ approach to scaling CA does not seem warranted. More fundamentally, our results suggest that conclusions regarding the potential of CA derived from global meta-analyses or those reported from Africa do not hold true for the cereal-based cropping systems of South Asia. It is important to note that agriculture in South Asia is different from that in the rest of the world. The cropping system in South Asia is predominantly under irrigated management and is very intensive, with two or more crops in a year.