Elsevier

Field Crops Research

Volume 132, 14 June 2012, Pages 18-32
Field Crops Research

Conservation agriculture for small holder rainfed farming: Opportunities and constraints of new mechanized seeding systems

https://doi.org/10.1016/j.fcr.2011.11.026Get rights and content

Abstract

Small holder farmers in rainfed agriculture believe that soil tillage is needed to maximize crop yields. However, as cropping intensity, and hence tillage intensity, increases there may be a decline in particular physical, chemical and biological properties of the soil which limit crop yield. This is primarily caused by declining soil organic matter, its oxidation being accelerated by tillage, particularly in warmer climates, and exacerbated by the limited return of above-ground biomass to the soil due to its competing use for other purposes. In large-scale commercial agriculture declining soil quality has been effectively addressed by conservation agriculture—cropping systems based on minimum tillage, crop residue retention and appropriate crop rotations and associations, preferably including legumes. This has required development of minimum tillage planting equipment along with herbicide technology to achieve weed control that is traditionally achieved through tillage. However, a shortage of mechanized options suitable for small holder farmers is creating an impediment to the adoption of conservation agriculture practices that would arrest the decline in soil quality in their fields. In South Asia, two-wheel tractors are replacing animal-drawn ploughing in small holder plots. This speeds the tillage operation and hence the turnaround time between crops, which may increase opportunities for crop intensification, but the problems associated with full tillage remain. Over the previous decade planter attachments to two-wheel tractors have been developed which permit seed and fertilizer placement with minimum to zero tillage in a single-pass. Recent tests have demonstrated that use of these implements can produce crop yields equal to or better than conventional tillage involving hand broadcasting of seed and fertilizer. Further, fuel and labour costs, seed and fertilizer inputs and turnaround time between crops can be reduced. In Africa, the introduction of animal-drawn rippers and direct seeders, originally developed for small-scale farmers in Brazil, is considered as a major breakthrough to small-scale farmer mechanization. It significantly reduces labour required for planting and benefits may be even greater if herbicides can be effectively used for weed control. Nevertheless, movement towards minimum tillage with two-wheel tractor mounted planters and animal-drawn direct seeding equipment is constrained by weed management issues. There are problems of availability and of safe and effective use of herbicides by resource-poor farmers and there is a need to develop more integrated weed management strategies that can be combined with small-scale planters. There is also a need to optimize the performance of small-scale planters to suit farmers’ needs in different agro-ecological environments. Tools and concepts are now available to implement conservation agriculture for small holders and thereby increase profitability of their cropping practices and at the same time improve soil quality and sustainability of their livelihoods. However, much more adaptive research and on-farm evaluation is needed across a diverse range of soils, cropping systems and agro-ecological regions to bring conservation agriculture to more small holders.

Highlights

Minimum tillage implements suitable for use by small holder farmers are reviewed. ► These can provide a basis for conservation agriculture for small holders. ► Substantial changes in agronomic practices from traditional ones are needed. ► In particular, integrated weed management systems need to be developed. ► Participatory approaches are essential to advance conservation agriculture.

Introduction

Most crop production in Asia, Africa and Latin America is based on subsistence agriculture implemented by resource-poor small holder farmers. This form of agriculture is characterized by limited application of inputs, distorted markets, deteriorating soil conditions, and now increasingly uncertain weather patterns (Christensen et al., 2007). The factors leading to soil degradation over time include limited organic matter returns to the soils, minimal and unbalanced fertilizer addition, limited options for crop rotation and the perceived need for regular tillage. Small holder farmers generally try to maximize tillage, within their constraints of time, labour and available implements, primarily for the purpose of weed management and to create a seed bed with a fine soil tilth suitable for germination and seedling establishment. Additional reasons for small holder farmers to practice conventional tillage, by manual, animal powered or mechanized means, include mineralization of nutrients, incorporation of fertilizers, crop residues and soil amendments, temporary alleviation of compaction, and management of some soil-borne diseases and insects (Hobbs et al., 2008, Kassam et al., 2009). However, regular tillage breaks down soil organic matter through mineralization, more so in warmer climates (Kirschbaum, 1995), thus contributing to deteriorating soil physical, chemical and biological properties (Wall, 2007). The physical effects of tillage also adversely affect soil structure, with consequences for water infiltration and soil erosion through runoff, and create hardpans below the plough layer (Thierfelder and Wall, 2009). These adverse effects of tillage have been addressed over recent decades by the development of conservation agriculture (CA) (Garcia-Torres et al., 2003). CA is defined as cropping systems based on minimal soil disturbance, permanent surface cover through crop residue retention and diverse crop rotations and associations (Hobbs et al., 2008, Kassam et al., 2009). Most progress in CA has been made in large-scale commercial agriculture where powerful tractors are available to pull minimum tillage seeding equipment and herbicides are routinely used for weed control. Derpsch et al. (2010) estimated that 111 million ha would be cropped using the principles of CA but that this was mainly under commercial farming systems in the Americas and Australia. CA has received increasing attention by the commercial farming sector as it drastically reduces fuel costs, reduces the drudgery and labour requirement of multiple tillage operations, and minimizes machinery wear and tear (Raper et al., 1994, Thomas et al., 2007).

Small holder farmers primarily reliant on rainfall rather than irrigated systems have generally not adopted CA practices yet, for various reasons—lack of knowledge about CA and how it could potentially improve their own agriculture, the perceived complexity of this new cropping system, unavailability of appropriate minimum tillage implements, limited access to herbicides, and the change of mind set required to shift from the habits of multiple tillage to minimum tillage (Wall, 2007). However, opportunities are opening up to make it easier for small holder farmers to change from excessive tillage to various forms of minimum tillage. There are options using hand or animal-drawn implements (Thierfelder and Wall, 2010) and increasingly for planters mounted on two-wheel tractors. In the last two decades numbers of two-wheel tractors (Haque et al., 2004) and shallow-tillage single-pass planters have rapidly expanded in Asia (Miah Monayem et al., 2010). These were primarily designed for rotary tillage, which can even exacerbate the problems of soil tillage. Over the recent decade, however, there have been innovations made to both two-wheel tractor as well as animal-drawn direct seeding implements that do permit adequate seeding into minimally disturbed soil. This provides a window of opportunity to introduce CA among small holder farmers, not only in terms of reduced soil disturbance but also with respect to biomass cover and crop rotation. Effective CA practices for small holders would also enable them to capture the economic benefits already enjoyed by the large-scale users of CA, reduced fuel and labour costs and improved timeliness of operations.

However, there are many biophysical and socio-economic constraints to small holder farmers in adopting CA (Giller et al., 2009) and it will be necessary to develop effective strategies to transfer the emerging technologies to them. It is noted that CA in many areas evolved through innovation networks linking farmers, extension personnel, researchers, engineers/mechanics, input suppliers, and credit providers (Ekboir, 2002, Pieri et al., 2002, Thomas et al., 2007, Hobbs et al., 2008). Such a collaborative approach would also seem necessary in bringing CA to small holder farmers, but with modifications tailored to the limited resources available to them. This review examines recent innovations in minimum tillage implements suitable and adaptable for small holder agriculture. It also discusses how these could catalyze widespread adoption of CA practices in resource-poor environments, and suggests possible pathways to adoption.

Section snippets

Characteristics of small holder agriculture in Asia and Africa

This review focusses on small holder agriculture in South and South-East Asia, China and southern Africa drawing from the authors’ particular experience in these regions. It is recognized that many innovations in CA, in both commercialized and small holder farming, have occurred in South America, but we only draw on that information as it relates to our focus area. We define small holder agriculture as that conducted by farmers using predominantly family labour and for whom the farm provides

Large-scale commercial farming

Although the universally accepted practice of tillage was queried in the 1940s (Faulkner, 1943), the practical application of minimum tillage on a large scale did not occur until two decades later. This was prompted by increasing concerns of soil erosion exacerbated by traditional practices of regular and thorough tillage (Thomas et al., 2007). It became feasible by the development of low-cost herbicides such as Roundup® containing the active ingredient glyphosate (N-(phosphono-methyl) glycine)

A new agronomy

As has happened in large-scale commercial agriculture, a change to CA in small holder farms requires substantial adjustment of traditional agronomic practice (Baker and Saxton, 2007a), starting with fundamental changes in the ways in which farmers perceive the crop production process. This process is just beginning for small holder farmers reliant on hand, animal-drawn or two-wheel tractor mounted minimum tillage implements. Thus we can suggest some of the areas where major changes in agronomy

Quantification of effects of CA on crops and soils

The effects of CA on crops and soils evolve over time. There are short term effects on nutrient availability that require alterations in fertilizer recommendations for the transitional phase. There are longer term changes in mineralization of organic matter, the spectrum of weeds, and prevalent diseases and insects. Hence there is a strong case for long term trials strategically placed in regions that are implementing CA. It is preferable that they be placed on-farm, despite the lesser control

Conclusion

The key to furthering CA among small holders is development and deployment of affordable and effective minimum tillage implements. In Sub-Saharan Africa several manual CA seeding systems such as dibble sticks, planting basins and jab-planters are promoted along with mechanized animal traction systems such as different types of tine rippers and direct planters. Minimum tillage implements compatible with two-wheel tractors are now reaching early stages of adoption, mainly in South Asia. These

Acknowledgements

Studies reported here relating to development of seeding devices for two-wheel tractors since 2006 have been supported by the Australian Centre for International Agricultural Research (ACIAR) projects LWR/2005/001 and CIM/2007/027 and by CIMMYT.

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