Small holder farmers in rain fed 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.

The article concludes that 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 developments provide an opening for the other two main pillars of CA—more ground cover and more diverse crop rotations. Where two-wheel tractors have become ubiquitous, there has been a consequent decline in draft animals thereby rendering more crop residue available for ground cover. However, for small holder, resource-constrained farmers various bottlenecks to adoption of CA remain, as elaborated by Giller et al. (2009, 2011), despite the recent emergence of suitable minimum tillage implements. A particular challenge is development of integrated weed management strategies that will at least compensate the weed control afforded by conventional tillage. Although herbicide chemicals exist for most weed situations, access of small holders to them and the knowledge required for their effective and safe use is limited. Priority is thus required in establishing integrated weed management strategies for particular cropping situations, drawing upon the entire toolkit of options available—herbicides, mechanical, rotations, weed seed bank management, etc. Introduction of minimum tillage also demands radical changes to other aspects of conventional agronomy, such as planting pattern, fertilizer use and pest and disease management.

There is obviously a need for re-writing of the research originally targeted at conventional agriculture (e.g. full tillage and broadcast systems), but it is urged that in this case the research be done in full participatory mode with farmers on their fields. Indeed, introduction of CA in the Americas, Australia and the IGP of India has pioneered methods of participatory on-farm research, development and extension, and this mode needs to be further pursued for CA for small holders. A major compulsion for this is that, although the principles of CA have wide applicability across many agro-ecological and physiographical environments, they need to be adjusted to a farmer’s particular conditions to make them valid and applicable.

This is an extract from a journal article by C. Johansen, M.E. Haque, R.W. Bell, C. Thierfelder , R.J. Esdaile published in Field Crops Research 132 (2012) 18–32