Tillage is the agricultural preparation of the soil by mechanical, draught-animal or human-powered agitation, such as ploughing, digging, overturning, shovelling, hoeing and raking. Small-scale farming tends to use smaller-scale methods using hand-tools and in some cases draught animals, whereas medium to large-scale farming tends to use the larger-scale methods such as tractors. The overall goal of tillage is to increase crop production while conserving resources (soil and water) and protecting the environment (IBSRAM, 1990).
Conservation tillage refers to a number of strategies and techniques for establishing crops in a previous crop’s residues, which are purposely left on the soil surface (see Figure 1 and Figure 2). Conservation tillage practices typically leave about one-third of crop residue on the soil surface (see Figure 3). This slows water movement, which reduces the amount of soil erosion. Conservation tillage is suitable for a range of crops including grains, vegetables, root crops, sugar cane, cassava, fruit and vines.
Conservation tillage is a popular technology in the Americas, with approximately 44 per cent practised in Latin America. Studies suggest there is great potential to bring this technology to Africa, Asia and Eastern Europe, although limiting factors have to be taken into account (see Barriers below) (Derpsch, 2001; GTZ, 1998).
The most common conservation tillage practices are no-till, ridge-till and mulch-till.
No-till is a way of growing crops without disturbing the soil. This practice involves leaving the residue from last year's crop undisturbed and planting directly into the residue on the seedbed. No-till requires specialised seeding equipment designed to plant seeds into undisturbed crop residues and soil. No-till farming changes weed composition drastically. Faster growing weeds may no longer be a problem in the face of increased competition, but shrubs and trees may begin to grow eventually. Cover crops – ‘green manure’ – can be used in a no-till system to help control weeds. Cover crops are usually leguminous which are typically high in nitrogen can often increase soil fertility.
In ridge-till practices, the soil is left undisturbed from harvest to planting and crops are planted on raised ridges (Figure 4). Planting usually involves the removal of the top of the ridge. Planting is completed with sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between ridges. Weed control is accomplished with cover crops, herbicides and/or cultivation. Ridges are rebuilt during row cultivation.
Mulch-till techniques involve disturbing the soil between harvesting one crop and planting the next but leaving around a third of the soil covered with residues after seeding. Implements used for mulch-till techniques include chisels, sweeps, and field cultivators.
Unpredictability of rainfall and an increase in the mean temperature may affect soil moisture levels leading to damages to and failures in crop yields. Conservation tillage practices reduce risk from drought by reducing soil erosion, enhancing moisture retention and minimising soil impaction. In combination, these factors improve resilience to climatic effects of drought and floods (Smith, 2009). Improved soil nutrient recycling may also help combat crop pests and diseases (Holland, 2003).
Conservation tillage benefits farming by minimising erosion, increasing soil fertility and improving yield. Ploughing loosens and aerates the soil which can facilitate some deeper penetration of roots. Tillage is believed to help in the growth of microorganisms present in the soil and helps in the mix the residue from the harvest, organic matter and nutrients evenly in the soil. Conservation tillage systems also benefit farmers by reducing fuel consumption and soil compaction. By reducing the number of times the farmer travels over the field, farmers make significant savings in fuel and labour. Labour inputs for land preparation and weeding are also reduced once the system becomes established. In turn, this can increase time available for additional farm work or off-farm activities for livelihood diversification. Also once the system is established, requirement for herbicides and fertilisers can be reduced. According to Sorrenson et al (1998), total economic benefits arising from adoption of the no-tillage technique in small farms of generally less than 20ha in Paraguay have reached around $941 million.
Conservation tillage may require the application of herbicides in the case of heavy weed infestation, particularly in the transition phase, until the new balance of weed populations is established (FAO, no date). The practice of conservation may also lead to soil compaction over time; however this can be prevented with chisel ploughs or subsoilers. Initial investment of time and money along with purchases of equipment and herbicides will be necessary for establishing the system. Higher levels of surface residue may result in higher plant disease and pest infestations, if not managed properly. There is a strong relationship between this technology and appropriate soil characteristics. This is detrimental in high clay content and compact soils.
The cost of equipment for conservation will depend on whether the land is tilled with motorised traction, animal-draught or manpower. The most important cost for larger producers will be machinery and fuel. However, higher herbicide applications could offset these savings, especially in the initial adoption stages. On smaller-sized farms, savings in labour costs could be substantial. A study in Nigeria has shown conservation tillage practices to reduce labour inputs by around 50 per cent compared to traditional systems (Ehui et al, 1990). Financial incentives and subsidies may be required to assist farmers to adopt this practice. In Brazil, monetary incentives were found to be highly successful in motivating group formation among farmers, leading to an increase in cooperation and technology uptake (World Bank, 2000).
Farmers can be supported by national, regional and local farmer’s organisations to equipment. In Zambia, the Africare Smallholder Agricultural Mechanisation Promotions (SAMeP) programme has assisted small-scale farmers to access technologies for conservation tillage through working with rural entrepreneurs to broaden the equipment supply base and provide spare parts (Sakala, 1999). This style of programme could be broadened to improve access to other inputs such as cover crop seeds, herbicides and fertilisers. Private and public sector equipment suppliers also have a role in responding to demands from different types of farmers for adapted tools and equipment.
Farmers need extensive training to implement conservation tillage.This includes knowledge of crop rotation; analysing soil conditions; monitoring soil temperature and moisture; adjusting nutrient and weed management approaches; and selecting appropriate equipment. Studies in Latin America have shown that the main limitation to the spread of no-tillage technology has been a lack of specific site knowledge about weed control. Information on common weeds, herbicide products (including details of chemical and toxicological characteristics) and application technologies are therefore a key knowledge requirement for application of no-tillage technologies (Derpsch, 2001).
A lack of locally-appropriate knowledge and/or poor research and development for conservation tillage technology presents one of the main barriers to uptake (Derpsch, 2001). Likewise, where there is no local production or availability of equipment and other inputs, such as herbicides, then costs will rise significantly and may present a barrier to implementation. Ecological barriers to no-tillage production systems include low precipitation with low biomass production, short growing seasons and soils at risk of water logging. Socio-economic constraining factors include: strong demand for crop residues as forage for livestock, uncertain land use rights, poorly developed infrastructure (market, credit, extension service) (GTZ, 1998).
In Latin America, the uptake of this technology was greatly facilitated by exchange of information through farmers associations (World Bank, 2000), provision of publications with adequate, practical information on technology implementation and studies showing positive economic returns (Derpsch, 2001).
Derpsch, R. (2001) Keynote: Frontiers in conservation tillage and advances in conservation practice, in Stott D. E., Mo htar, R. H., and Steinhart G. C (Eds.) Sustaining the global farm. Selected papers from the 10th International Soil Conservation Organisation Meeting held May 24-29, 1999 at Purdue University and the USSA-ARS National Soil Erosion Research Laboratory.
Ehui, S. K., B. T. Kang, and D. S. C. Spencer (1990) Economic analysis of soil erosion effects in alley cropping, no-till and bush fallow systems in south western Nigeria. Agricultural Systems, 34, 349-368.
FAO (Food and Agriculture Organisation) (no date) Conservation Agriculture: Matching production with sustainability, FAO
GTZ (1998) Conserving natural resources and enhancing food security by adopting no-tillage. An assessment for the potential for soil-conserving production systems in various agro-ecological zones of Africa, GTZ Eschborn, Tropical Ecology Support Programme, TÖB Publication.
Holland, J. M. (2004) The environmental consequences of adopting conservation tillage in Europe: reviewing the evidence, Agriculture, Ecosystems and Environment 103, 1-25
IBSRAM (International Board for Soil Research and Management) (1990) Organic-matter management and tillage in humid and sub-humid Africa. IBSRAM Proceedings No. 10. Bangkok: IBSRAM.
Sakala, I. (1999) Efforts and initiatives for supply of conservation tillage equipment in Zambia in Kaumbutho P G and Simalenga T E (eds), 1999. Conservation tillage with animal traction. A resource book of the Animal Traction Network for Eastern and Southern Africa (ATNESA). Harare. Zimbabwe. 173p.
Smith, P. (2005) Agriculture and Climate Change: An agenda for negotiation in Copenhagen, IFPRI Focus 16.
Sorrenson, W. J., C. Duarte, and J. López-Portillo, (1998) Economics of non-till compared to conventional cultivation Systems on small farms in Paraguay, policy and investment implications, Report Soil Conservation Project MAG-GTZ, August 1998
World Bank (2000) Implementation completion report Brazil: Land management II - Santa Catarina project: implementation completion report (Loan 3160-BR). Report #20482, Washington, DC, World Bank.