Olaf Erenstein

Crop residue mulching in tropical and semi-tropical countries: An evaluation of residue availability and other technological implications

Abstract Crop residue mulching (CRM) can be defined as a technology whereby at the time of crop emergence at least 30% of the soil surface is covered by organic residue of the previous crop. The present study proposes CRM as the most adequate term for the technology in view of the substantial controversy and confusion surrounding existing terms, particularly conservation tillage. CRM is a dual-purpose technology that combines conservation and productivity effects. Its conservation potential hinges on the presence of the crop residues as mulch. This mulch provides a protective layer to the soil surface that is extremely effective in halting soil erosion and also amends the soil ecology. Its productivity potential is twofold. First, the mulch tends to stabilise, and occasionally even enhance, crop yield. Second, it implies factor substitution and input use efficiency alterations. The paper presents the residue balance as an analytical tool to assess the current availability of residues—both in terms of current residue production and current residue destinations. Residue destinations typically include extraction, burning in situ, incorporation, weathering and retention as mulch. CRM has profound implications for crop management. First, CRM implies a set of necessary practices so as to ensure the retention of sufficient residues as mulch. Second, CRM may imply complementary adaptations in order to be able to grow a crop and/or maintain productivity levels. Therefore, CRM is not a simple add-on technology, but instead a complete package of cultural practices. The actual potential of the CRM technology depends on a comprehensive assessment of the socio-economic implications of the implied changes. This potential is site-specific and will diverge between the private and social viewpoint. CRM therefore is a promising dual-purpose technology—but no panacea for soil conservation in (semi-)tropical countries.

Smallholder conservation farming in the tropics and sub-tropics: a guide to the development and dissemination of mulching with crop residues and cover crops

Abstract Mulching offers great agro-ecological potential: it typically conserves the soil, improves the soil ecology, stabilizes and enhances crop yield and provides various environmental services. However, mulching is not a simple single component technology that can be easily transferred. It is a complex basket of interrelated practices—including (i) necessary practices so as to ensure the production and retention of sufficient mulch and (ii) complementary practices in order to be able to grow a crop and/or maintain yield levels. This typically implies several adaptations to the entire farm production system. Whether mulching actually is a viable component for smallholder conservation farming in developing countries depends on a number of factors, including bio-physical, technological, farm level and institutional factors. The combination of these factors determine the feasibility of and the economic returns to mulching practices—and thereby farmer acceptance. The development and dissemination of mulching for smallholders in (sub)tropical developing countries highlights a number of promising experiences—particularly in (sub)humid areas. Crop residue mulching can offer significant savings implied by reduced tillage and the potential to alleviate binding constraints for crop growth and/or farm productivity (e.g. water conservation; timeliness of land preparation and crop establishment). Its economic potential to a large extent depends on the opportunity costs of retaining the mulch and the opportunity cost of complementary changes (e.g. need for mulch adapted seeding equipment; alternative weed, pest and disease management practices). Cover crop mulching offers opportunities for smallholders by addressing soil fertility and weed management constraints. However, the potential of cover crop mulching seems to be restrained to the (sub)humid zones and instances where the opportunity cost of using land to grow cover crops is limited. Significant opportunities exist in agricultural systems with limited external input use and/or periodic fallowing. The pure investment nature of cover crop mulching remains problematic. Mulching only tends to be viable when property rights over residual crop biomass are observed and tenure is secure. It typically implies a transition phase before becoming fully socio-economically viable—in terms of farmer learning, investments, local adaptation and fine-tuning and institutional change. Further success in the development and dissemination of mulching for smallholders requires targeting areas with specific economic opportunities for mulching and an integrated approach with a practical orientation, farmer participation, community involvement, flexibility and a long-term perspective.

Conservation Agriculture in Maize- and Wheat- Based Systems in the (Sub)tropics: Lessons from Adaptation Initiatives in South Asia, Mexico, and Southern Africa

Conservation agricultures underlying principles—minimal soil disturbance, soil cover and crop rotation—are increasingly recognized as essential for sustainable agriculture. This article summarizes three contrasting cases of adapting conservation agriculture (CA) to smallholder conditions in the (sub)tropics: a) irrigated rice-wheat systems in South Asia; b) rainfed maize/wheat and irrigated wheat systems in Mexico; and c) rainfed maize in Southern Africa. In the South Asia case, farm surveys show rapid and widespread adoption of zero tillage wheat—primarily due to a substantial cost saving (15–16%). In the other cases, uptake so far has been limited—although long-term trials show continuously higher and more stable yields both for maize and wheat. Under marginal conditions CA can generate substantial yield increases—averaging some 50% over conventional smallholder maize yields of 1 ton per ha over 6 years in on-farm trails in Southern Africa. The diverse experiences attest to the wide adaptability of CA systems, which can generate clear economic and potentially enormous environmental benefits. The case studies and wider literature however also reiterate the substantial challenges in terms of targeting, adapting and adopting CA—particularly for smallholders in the (sub)tropics. CA systems are best developed in situ through a multi-stakeholder adaptive learning process to create viable CA-based options that are technically sound, economically attractive, and socially acceptable.

Beyond conservation agriculture

Global support for Conservation Agriculture (CA) as a pathway to Sustainable Intensification is strong. CA revolves around three principles: no-till (or minimal soil disturbance), soil cover, and crop rotation. The benefits arising from the ease of crop management, energy/cost/time savings, and soil and water conservation led to widespread adoption of CA, particularly on large farms in the Americas and Australia, where farmers harness the tools of modern science: highly-sophisticated machines, potent agrochemicals, and biotechnology. Over the past 10 years CA has been promoted among smallholder farmers in the (sub-) tropics, often with disappointing results. Growing evidence challenges the claims that CA increases crop yields and builds-up soil carbon although increased stability of crop yields in dry climates is evident. Our analyses suggest pragmatic adoption on larger mechanized farms, and limited uptake of CA by smallholder farmers in developing countries. We propose a rigorous, context-sensitive approach based on Systems Agronomy to analyze and explore sustainable intensification options, including the potential of CA. There is an urgent need to move beyond dogma and prescriptive approaches to provide soil and crop management options for farmers to enable the Sustainable Intensification of agriculture.

Drivers of household food availability in sub-Saharan Africa based on big data from small farms

Significance We collated a unique dataset covering land use and production data of more than 13,000 smallholder farm households in 93 sites in 17 countries across sub-Saharan Africa. The study quantifies the importance of off-farm income and market conditions across sites differing strongly in agroecology and derives generally applicable threshold values that determine whether farm households have enough food available to feed their families. These results show there is a strong need for multisectoral policy harmonization and incentives and improved interconnectedness of people to urban centers and diversification of employment sources, rather than a singular focus on agricultural development of smallholder farmers in sub-Saharan Africa. We calculated a simple indicator of food availability using data from 93 sites in 17 countries across contrasted agroecologies in sub-Saharan Africa (>13,000 farm households) and analyzed the drivers of variations in food availability. Crop production was the major source of energy, contributing 60% of food availability. The off-farm income contribution to food availability ranged from 12% for households without enough food available (18% of the total sample) to 27% for the 58% of households with sufficient food available. Using only three explanatory variables (household size, number of livestock, and land area), we were able to predict correctly the agricultural determined status of food availability for 72% of the households, but the relationships were strongly influenced by the degree of market access. Our analyses suggest that targeting poverty through improving market access and off-farm opportunities is a better strategy to increase food security than focusing on agricultural production and closing yield gaps. This calls for multisectoral policy harmonization, incentives, and diversification of employment sources rather than a singular focus on agricultural development. Recognizing and understanding diversity among smallholder farm households in sub-Saharan Africa is key for the design of policies that aim to improve food security.

A survey of factors associated with the adoption of zero tillage wheat in the irrigated plains of South Asia

SUMMARY There is a quest for resource-conserving technologies that can save water, reduce production costs and improve production to address the slow down in productivity growth in the Indo-Gangetic Plains, the cereal bowl of South Asia. Findings from farm surveys are used to evaluate the farm household factors that affect the adoption of zero tillage (ZT) wheat in the rice-wheat systems of India’s Haryana State and Pakistan’s Punjab province. Three adoption classes are distinguished in each site: ZT adopters, dis-adopters and non-adopters. Bivariate analysis shows that adopters typically have the most favourable values for most of the indicators compiled and the non-adopters the least favourable, with dis-adopters often taking an intermediate position. The study highlights that ZT adoption in the initial diffusion stage is strongly linked to the wealth of the farm household. This indicates the need for closer consideration of equity implications in future research and development. The structural differences between adoption categories also easily confound the assessment of ZT impact.

THE PARADOX OF LIMITED MAIZE STOVER USE IN INDIA'S SMALLHOLDER CROP-LIVESTOCK SYSTEMS

SUMMARY Cereal residues are an important feed source for ruminants in smallholder crop-livestock systems in the (sub)tropics. In many areas of India maize is a relatively new cash crop where farmers and development agents alike generally perceive maize stover to have limited utility, in contrast with the intensive feeding of other cereal residues in India and the intensive use of maize stover in sub-Saharan Africa and Latin America. A comparative assessment of maize stover quality (based on a brief review and a feeding trial) indeed confirms its potential as a ruminant feed according to its relative nutritive value. The paper then explores the apparent paradox through a scoping study of maize stover use (based on village surveys) in three contrasting maize-growing districts in India – including both traditional and non-traditional maize producers. The limited maize stover use appears to alleviate seasonal shortages, with tradition and technology helping explain the preferential use of other cereal residues. The paper thereby provides further impetus to India’s apparent food-feed paradigm – whereby farmers’ staple food preferences coincide with crop residue feed preferences. The paper argues the case for investing in maize stover R&D in India and thus reigniting earlier feed research in general. Indeed, maize stover use is a relatively neglected area by India’s agricultural R&D and merits more attention so as to exploit its potential contribution and alleviate eventual tradeoffs.

U-impact pathway for diagnosis and impact assessment of crop improvement

SUMMARY Agricultural research has contributed enormously to poverty reduction and increased food security worldwide. Wheat crop improvement is a good example of this contribution. Public investments in wheat research from the Green Revolution onwards led to significant productivity increases : following the widespread adoption of semi-dwarf varieties, annual yield growth rates peaked at 2 . 75 % p.a. in the 1980s. Since then, public and private investments in crop (including wheat) research have been modest despite the potential of such research to contribute substantially to the first Millennium Development Goal (MDG) of halving hunger and poverty by 2015. Drawing on a wide spectrum of recent literature, the present paper broadens the usual frame of reference for diagnosing the adoption of improved technology and measuring impact. The adoption of improved varieties and management practices is influenced on the supply side by the nature and performance of the input delivery pathway from research to the farm (input value chains), and on the demand side by the characteristics of the farm household system and the marketing or value-adding chains from the farm to the consumer (output value chains). These three elements (input value chains, farm household system characteristics, and output value chains) can be viewed as a U-impact pathway. This pathway determines the rate and extent of adoption of improved varieties and practices, the magnitude of direct and indirect impacts, and the potential for feedback loops leading to improved functioning of the input and output value chains. The U-impact pathway provides a framework to identify an expanded set of beneficiaries from crop improvement which extend beyond the common focus on producers and final consumers ; conventional surplus analysis can then be used to estimate the wider benefits to crop improvement. Additional metrics may be needed to estimate impact related to non-economic benefits, such as poverty, health and social capital. The implication of this fuller accounting of impacts is that the benefits accruing to agricultural research may be greater, and more widely distributed across the economy, than previously recognized by research managers and policy-makers. This strengthens the case for maintained or increased public and private sector investment in crop improvement.

Factors associated with small-scale agricultural machinery adoption in Bangladesh: Census findings

There is strong advocacy for agricultural machinery appropriate for smallholder farmers in South Asia. Such ‘scale-appropriate’ machinery can increase returns to land and labour, although the still substantial capital investment required can preclude smallholder ownership. Increasing machinery demand has resulted in relatively well-developed markets for rental services for tillage, irrigation, and post-harvest operations. Many smallholders thereby access agricultural machinery that may have otherwise been cost prohibitive to purchase through fee-for-service arrangements, though opportunity for expansion remains. To more effectively facilitate the development and investment in scale-appropriate machinery, there is a need to better understand the factors associated with agricultural machinery purchases and service provision. This paper first reviews Bangladesh’s historical policy environment that facilitated the development of agricultural machinery markets. It then uses recent Bangladesh census data from 814,058 farm households to identify variables associated with the adoption of the most common smallholder agricultural machinery – irrigation pumps, threshers, and power tillers (mainly driven by two-wheel tractors). Multinomial probit model results indicate that machinery ownership is positively associated with household assets, credit availability, electrification, and road density. These findings suggest that donors and policy makers should focus not only on short-term projects to boost machinery adoption. Rather, sustained emphasis on improving physical and civil infrastructure and services, as well as assuring credit availability, is also necessary to create an enabling environment in which the adoption of scale-appropriate farm machinery is most likely.

VILLAGE SURVEYS FOR TECHNOLOGY UPTAKE MONITORING: CASE OF TILLAGE DYNAMICS IN THE TRANS-GANGETIC PLAINS

SUMMARY Agricultural research and development (R&D) would benefit from reliable yet cheap technology uptake indicators to guide decision making. The paper explores the use of village surveys to monitor technology use and illustrates this through two empirical case studies into tillage dynamics in the Trans-Gangetic Plains in northwest India. The first case study is a revisit of 50 communities surveyed earlier in Haryana State. The second case study is a new and wider representative sample of 120 villages across Haryana and Punjab States. The case studies illustrate that after an initial rapid spread of tractor-drawn zero tillage drills for wheat seeding in these intensive systems, the zero + reduced tillage area seems to have stabilized there at between a fifth and a quarter of the wheat area. Conventional tillage for wheat continues to decline, with an increased use of rotavators making up the difference – but its intensive shallow tillage goes against the conservation agriculture tenets. The paper illustrates the potential of village surveys to provide timely and cost-effective feedback to agricultural R&D.