Soil management in Conservation Agriculture

Each context brings different problems regarding the implementation of Conservation Agriculture, and many technologies can be adapted, including traditional ones. Technical solutions should be found through close partnerships between farmers, private sector industries, extension services and researchers. This approach has already permitted to develop and adapt Conservation Agriculture for small and big farms, manual, animal traction and mechanized agriculture, in various agro-ecological zones and socio-economic contexts, and for many farming systems

The physical and chemical structure, and biological activity of soil, including the spatial arrangement of soil components, are fundamental to sustaining agricultural productivity and determine in their complexity the soil health and fertility. Soil management should maintain and improve soil fertility by minimizing losses of soil, nutrients, and agrochemicals from erosion, runoff, and leaching into surface- or ground water, and surrounding natural vegetation and wildlife in absolute terms as well as in relative terms below the self recovery of the respective ecosystems. Good agricultural practice should:

• Establish a detailed knowledge of the nature, properties, distribution, and potential uses of soils of the farm.
• Avoid mechanical soil disturbance to the extent possible.
• Avoid soil compaction beyond the elasticity of the soil.
• Maintain or improve soil organic matter during rotations until reaching an equilibrium level.
• Maintain organic cover through crop residues and cover crops to minimize erosion loss by wind and/or water.
• Maintain balanced nutrient levels in soils.
• Avoid contamination with agrochemicals, organic and inorganic fertilizers and other contaminants by adapting quantities, application methods and timing to the agronomic and environmental requirements.
• Maintain a record of the annual use and inputs and outputs of each individual land-management unit.

Maintaining and managing a permanent soil cover

Farm planning and crop rotations design

The planning of farm activities in Conservation Agriculture systems requires skills, knowledge and moreover, practice. It has to take in account crop rotations (2-3 year planning), soil cover management, other farm activities such as livestock, marketing or food processing as well as other factors (climate, labour availability, etc.). The design of crop rotations and the choice and management of cover crops must ensure that the biomass production is sufficient to satisfy all the needs (permanent soil cover, human and livestock feeding, fibres, etc.), that soil water and nutrient resources are adequate for the crop and that the use of agrochemical inputs such as desiccants and herbicides can be minimised.

Choice of cover crops

Cover crops must be multi-purpose crops and must be carefully managed through appropriate technologies. For example Crotalaria juncea L. is a good source of fibre, very effective for nematode control as well as soil properties and fertility improvement (N fixation, high level of Organic matter, etc.). This cover crop is used in orchards or in rotation with many crops. This choice of cover crops must also include socio-economic criteria such as access to appropriate seeds and possible seed production by the farmer.

Management of crop residues and cover crops

After harvest, crop residues are left in the field, usually without chopping them. Cover crops may be managed by using desiccants or by mechanical means such as knife rollers – recommended for small farmers. Mechanical tools have been developed by manufacturers, but many of them can be adapted by farmers themselves. However, they must be adapted to the cover crop (appropriate weight) and must not harm the soil.

Minimum soil disturbance – zero tillage and direct planting

Planting crops through the soil cover can be done by direct seeding, direct planting or broadcasting into the soil cover, depending on the specific conditions (soil, climate, seeds and cover properties). Most important before introducing zero tillage is to correct soil limitations such as hard pan, levelling, surface crusting or compaction, and eventually to address chemical limitations by incorporating lime, organic matter or other amendments. However, the introduction of appropriate crops in the rotation – selected for the properties of their roots, for example use of radish for decompaction – must ensure this role from the first year of introduction

Most machinery already exists for manual, animal-drawn or mechanised agriculture. However, if it is not locally available or accessible through import, it is an option for example, farmers, researchers and local blacksmith (or other professionals) to develop the appropriate tools. In this task, they may be supported by experts or companies from other countries or regions in order to benefit from existing experiences.

Pest, weed and fertility management

Pest, weed and fertility management are critical issues in any farming system. Before implementing Conservation Agriculture, any limitation related to pest, weed and soil fertility must be assessed and addressed. This may imply chemical and labour inputs at the beginning which might partly exceed conventional levels. To the extent that a new balance between the organisms and the farm ecosystems – pests and beneficial organisms, crops and weeds – becomes established and the farmer learns to manage the cropping systems, the use of synthetic pesticides, herbicides and mineral fertilizer tends to decline to a level below the original “conventional” farming.

In case of a lack of resources or access to chemical inputs, some solutions have been found by farmers: weed control with mechanical tools and through crop rotations; use of manure, Biological nitrogen fixation (BNF) and other crops for soil fertility; home-made “soups” for disease control, etc. Combining Conservation Agriculture with Organic Agriculture is also an option which has been adopted by mostly small scale farmers.

Pest management

New, or in their appearance so far unknown pests, might occur in the beginning, which may involve inputs of chemicals. However, crop rotations and appropriate use of cover crops should also help in this task, since the beginning, by interrupting the infection chain between subsequent crops. In Conservation Agriculture systems, pest and disease control are based on Integrated Pest Management (IPM) technologies. Again, information, knowledge and training are very important in IPM, and Farmer Field Schools (FFS) one possible approach to enhance farmer’s understanding of biological processes and their capabilities to respond to new problems

Weed management

Synthetic chemical herbicides may be necessary in the first years, but have to be used with very much care to reduce the negative impact on soil life. Mulch cover and cover crops, crop rotations, desiccants and herbicides are the technologies to control weeds. Mechanical weed control through rolling, cutting or breaking can also be applied. For exceptional cases mechanical weeders exist for animal traction and tractors which can work through a mulch cover. With time, the amount of herbicides needed decreases because the farmer becomes more experiences in managing the system and the weed population decreases. Biological weed control may be very effective through appropriate choice of cover crops. In southern Brazil, for example, Black Oat is integrated in the rotations to suppress weeds. It can also be used as fodder and its straw is quite persistent, which is an advantage in areas where crop residues tend to mineralise too quickly to ensure surface cover.

Fertility management

Any soil limitations, such as acidity, salinity or toxicity problems must be addressed before and during the implementation of Conservation Agriculture. Soil Organic Matter (SOM) and judicious choice of crops and cover crops play a key role in soil fertility management, and especially SOM provided by root decomposition. The integration of livestock in the system can also be a solution, especially for the farmers with poor resources or access to mineral fertilisers. The use of organic and mineral fertilisers may be necessary. Appropriate application can be done with combined tools for direct seeding-fertilisation.