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.