Good Agricultural Practices
The basic resource for agricultural production is the soil on which crops and feed for livestock are grown. The quality and condition of the soil is the main determining factor for successful crop or livestock production. This section on “Land Management” therefore looks at the interaction between agricultural practices and soil, as well as related land and water management practices and techniques. The heading “Good Agricultural Practices” is plural, indicating that different good practices can be employed. For this discussion, as well as for the recommended practices listed in the table below, the following three approaches to farming are considered:
- Conventional farming. This refers to commonly used agricultural practices. At present these are characterized by high levels of expensive, external, industrial produced inputs such as machinery, fuel, synthetic fertilizers, and agro-chemicals. It can be argued that this type of agriculture is based on the seasonal agriculture of the temperate climates and was introduced during the colonial era. Some of the common features of conventional agriculture are; repeated soil disturbance by ploughing or by hand-hoeing, and mono-cropping of annual crops.
- Conservation agriculture (CA). As the name indicates, these agricultural practices are aimed at conserving soil nutrients and moisture for plant growth. This is achieved by improving and maintaining optimal soil conditions. The three main principles of CA are; minimum soil disturbance (no ploughing), permanent vegetative soil cover, and crop diversification (rotation). The objective of these principles is to achieve optimal crop growing conditions through increased soil biological activity (soil life) and soil organic matter content, which will contribute to improved soil structure, water holding capacity, and soil fertility. CA requires less external inputs than conventional agriculture.
There are several other farming approaches that use principles similar to CA, and that strive towards more natural and sustainable forms of crop and livestock production, such as; restoration agriculture, regenerative agriculture, holistic grazing, and permaculture. (One of the principles of permaculture is: “Work with nature, not against it”)
Organic farming. The main characteristic of this farming approach is that it uses inputs from natural, organic sources (eg. organic fertilizers, compost, bio-pesticides). Organic farming is gaining increased interest from consumers who are concerned about the nutritional quality and safety of food items.
Observation and critical reflection on the selected site should be the starting point for agricultural practices.
Observe the physical land shape and how that may affect agricultural practices. Look for signs of soil erosion or water logging. This will indicate the need for soil conservation or earth works. The gradient and direction of slopes will influence land preparation and planting patterns and may influence crop choice.
It is important to know the past land use of the site under consideration. Has the land been under mono-cropping with a heavy feeder crop and the use of synthetic fertilizers, or has it been under crop rotation, including the use of compost.
It is equally important to know what the past land preparation methods have been. Repeated ploughing may have resulted in a plough pan.
In case the land has not been utilized for some time, the natural vegetation may be an indication of prevailing soil conditions. Weeds are often useful indicator plants.
A healthy soil is the foundation for successful agricultural practices.
Conventionally soils are looked at from physical (texture, water holding capacity) or chemical (pH, soil nutrient analysis) considerations. This results in physical and chemical oriented recommendations for land and crop management.
However, the factor that has the most profound influence on crop growth, soil biology, has until recently hardly been considered. Soil biology looks at the often very complex interactions between the many life forms (bacteria, fungi, arthropods, nematodes, etc.) in the soil and their role in the provision of nutrients for plants. This complex network is referred to as the Soil Food Web.
Different types of bacteria absorb nutrients from soil particles and make them available to plants in exchange for sugars that the plant exudates through its hair roots.
Fungi play a similar role as their extensive rhizome (?) network can source nutrients far away from the plan roots. Fungi are sometimes called the internet of the soil.
Without soil life, plants will only absorb water-soluble nutrients. Land management practices should aim at improving soil biology. This in turn will improve soil structure and soil fertility.
The type and nature of conservation works is largely determined by the slope of the land and the soil condition. Soils with little organic matter content have less cohesion and are more susceptible to erosion.
Land slopes are generally expressed in percentage. This is calculated as vertical rise, times 100, divided by the horizontal distance.
Simple tools for determining land slope are line level or water hose level. These same tools, or a simple A-frame, can also be used to set out contour lines.
In flat to very gently sloping land (0 – 2 %) it will be sufficient to cultivate along, or in the general direction of the contour. Continuous vegetative soil cover (as in CA) will provide sufficient erosion protection.
On gentle to moderately sloping land (2 – 10 %) it is recommended to plant vegetative barriers (Cross-slope Vegetative Barrier) on contour. Depending on the rainfall pattern of the area, Vetiver grass (drought tolerant), or other deep rooting grasses or legumes (Napier, Brachiaria) are planted in single or double lines. These barriers will slow down rainwater run-off and trap soil particles and promote water infiltration. It is important that the barriers are planted exactly on contour to avoid concentration of run-off in low spots, with the risk of erosion. Crop cultivation will be done parallel to the planted barriers.
Land with steeper slopes (10 – 20 %) will require extensive earthworks to reduce soil erosion and promote rainwater infiltration. Such earthworks may range from infiltration ditches (Fanya Juu / Fanya Chini) to swales, to terracing. These earthworks are generally constructed on contour, or with a small slope for controlled drainage. The effectiveness of these soil and water conservation structures can be enhanced by planting fruit or other trees, grasses, or fodder crops on them.
This is linked to the three basic agricultural practices as described in the Overview above.
Conventional farming is characterised by ploughing followed by harrowing. Main arguments for ploughing are; loosening and aeration of the soil, and burying vegetation (weeds, grasses, stover) from previous cultivation. However, this process of inverting the soil will negatively affect soil biology and soil structure. The bare soil resulting from ploughing will be exposed to the intense sunlight of the tropics, leading to loss of soil moisture, organic matter (carbon) and nitrogen from the soil through oxidation. Conventional agriculture is a major contributor to the release of carbon dioxide into the atmosphere.
Furthermore, the bare and disturbed soil is susceptible to erosion and crusting (sealing) due to rainfall. Ploughing will bring buried seeds from previous seasons to the surface where they can germinate. The growth of broad-leaved plants (weeds) and grasses are nature’s response to damaged and exposed soil.
Conservation agriculture (CA) advocates no-till or minimum tillage practices. Such practices include planting and harvesting of cover crops and direct seeding of the main crop. This can be done mechanically or by hand with minimal disturbance of the soil. Aeration of the soil or improvement of water infiltration can be achieved by sub-soiling (ripping). The main objective of CA is to improve soil biology and soil structure, including increased soil organic matter content. In addition, other benefits include reduced soil erosion, soil moisture conservation, improved crop yields and reduced production costs.
Organic agriculture generally uses the same land preparation practices as under Conservation Agriculture.
Crop rotation / soil cover
The practice of continuous crop cover will improve soil conditions.
The practice of crop rotation and cover cropping will:
- Increase soil organic matter
- Increase soil fertility/nutrients
- Reduce soil erosion
- Reduce soil compaction
- Conserve soil moisture
- Control weeds
- Improve soil structure
- Increase crop yields and
- Reduce pollution through reduced need for fertilizer and pesticide application.
Crop rotation will further break disease cycles and limit insect and other pest infestations.
A challenge with cover crops is the limited availability of seeds, and the perceived low (market) value. However, cover crops can be grown for seed production, and reduce the need for synthetic fertilizers.
The repeated growing of the same (mono) crop in the same location increases the risk of pests and diseases. This makes the use of agro-chemicals necessary, which in turn negatively affects the soil biology, and with that the availability of nutrients for the crop. Growing annual crops as mono crops, according to the rain seasons, further leaves the soil bare and exposed for the time periods in between. This exposure often leads to a gradual loss of nutrients and organic matter, which leads to deterioration of soil biology and structure, and eventually contributes to declining soil fertility.
Overall farm management should aim at a seasonal rotation between heavy feeding crops (maize, cotton, tobacco) with legume and/or cover crops to restore soil fertility. It should further be considered to include perennial legumes (eg. pigeon pea, Leucaena, Moringa, etc.) in the overall cropping pattern.
The growing of a variety of crops in rotation or as intercropping will not only improve the soil condition, but also reduce production cost and spread the production risk of the overall farm enterprise.
Conventional farming generally promotes use of synthetic fertilizers. These are produced through industrial processes that require large amounts of raw materials and energy. In addition, the movement of raw materials and the distribution of the final products to the rural areas involves significant transport costs (including environmental cost).
Compound fertilizers are the most commonly used synthetic fertilizers. They are produced in various combinations (percentages) of nitrogen (N), phosphorus (P), and potassium (K), and commonly referred to as NPK fertilizer. They are generally added during planting as they stimulate plant and root development.
Recently, fertilizer producers have started to add other elements (eg. calcium, magnesium, manganese, boron, sulphur, etc.) to these compounds to produce balanced fertilizers for specific crop requirements.
Other widely used synthetic fertilizers are the ammonium-based ones such as DAP and Urea. They contain high levels of nitrogen and are used as top-dressing to boost vegetative growth. A side-effect of these ammonium-based fertilizers is that they release H+ ions in the soil moisture causing a gradual increase in soil acidity (lower pH) over time. High soil acidity will cause nutrients to become unavailable to plants (phosphorus fixation) or cause toxicity (aluminium). It will also negatively affect soil microbial life.
Synthetic fertilizers are produced as water-soluble salts, which are taken up by the plants through their taproots, bypassing the nutrient supply by bacteria and fungi. The increase in salt concentration causes the plant to absorb more water than necessary, making them attractive to pests. Other disadvantages of synthetic fertilizers are that they can cause plant damage to leaves and roots; enhance weed growth; pollute the environment and their application does not improve soil structure. However, despite these disadvantages, synthetic fertilizers are easy to apply, reliable, give faster/immediate crop response to application and lead to tremendous yield increases.
Organic farming and conservation agriculture promote the addition of organic materials to the soil. Such materials include compost, manure, crop residues, bone meal, fish meal, wood ash, waste material from crop processing, and others. These organic materials are gradually decomposed to plant-available nutrients by the various microbial lifeforms in the soil. This decomposition process can be sped up through controlled composting. In this process it is important to have a correct nitrogen (N) to carbon (C) ratio. Recommended C:N ratios are 10:1 to 20:1. High levels of nitrogen from manure will also lead to acidification of the soil. Compost should be worked into the soil (eg. at planting) or covered with mulch to avoid nutrient loss.
As opposed to synthetic fertilizers, organic fertilizers are sustainable and environmentally friendly. Their use reduces the need for pesticides; They increase species diversity; They improve the soil structure, allowing it to hold water longer, and increase the bacterial and fungal activity in the soil.
However, their main disadvantages are:
- Nutrient levels are low and they exhibit slow release of nutrients; hence crops take longer to give observable response.
- Many don’t contain significant quantities of primary nutrients (NPK)
Integrated Soil Fertility Management (ISFM) aims at managing soil by combining different methods of soil fertility amendment together with soil and water conservation. It takes into account all farm resources and is based on 3 principles:
- maximising the use of organic sources of fertilizer;
- minimising the loss of nutrients;
- judiciously using inorganic fertilizer according to needs and economic availability.
Agroforestry represents a land use management system in which woody perennials (trees or shrubs) are grown around or among agricultural crops or pastureland. It combines crops, livestock and forestry technologies to create a more diverse, productive, profitable, healthy, and sustainable land use.
There are three main classifications of agroforestry systems, namely, agro-silviculture (crops and trees), silvo-pastoralism (pasture/animals and trees), and agro-silvo-pastoralism (crops, pasture/animals and trees).
Successful agroforestry practices offers the following benefits:
- Consistent restoration of the fertility status of the soil through the recycled litter deposition and nitrogen fixing mechanism of trees.
- A variety of products, firewood, poles, woodcraft, fodder, medicinal herbs and food for livestock and man respectively.
- Prevention of wind and water erosion by trees acting as wind break and intercepting the raindrop impact on the soil respectively.
- Improving the micro-climate effect of the immediate and adjourning environment.
- Restoration of water table to an absorbable level for crops use.
- Increased income opportunities.
- Increased economic stability.
- Increased ability to manage for sustained yield.
However, the system has some disadvantages which include:
- Labour intensive system
- It takes a long time (many years) to reap the products
- Limited market opportunities
- Competition for resources: Crops have to compete with trees for light, nutrients and water.
IPM is the most preferred approach to crop protection and acts as a pillar of both sustainable crop production and pesticide risk reduction.
IPM aims at reducing pest populations to avoid damage levels that cause yield losses.
Climate change, soil degradation and indiscriminate use of pesticides and fertilizers put sustainable food and agricultural systems at risk. In particular, the overuse of pesticides is known to eliminate important ecosystem services resulting into secondary pest outbreaks which could potentially jeopardize food security. Intensive overuse of extremely and highly hazardous chemicals by small-holder farmers threaten farm activities, public health, nutrition and the overall future of agriculture. IPM is promoted as an ecological approach to managing pests and combines various strategies (biological, cultural, physical, chemical, regular field monitoring, etc.) that focuses on reduction of pesticide use to sustainably manage dangerous pests.
The use of IPM technologies offers the following benefits;
- Promotes healthy growth of crops with minimal usage of pesticides.
- Reduces environmental risk associated with pest management.
- Reduces potential for problems of pest resistance or resurgence.
- Maintains a balanced ecosystem. Use of pesticides can result in species/biodiversity loss due to destruction of non-target organisms. IPM targets specific species, thus preventing loss of other species.
- Increases consumer confidence in the safety and quality of food products.
- Cost effective in the long term due to reduced expenses on pesticides.
Challenges that exist with the use of IPM include:
- More involvement in the technicalities of the method: IPM has many variables that require farmer education to learn and adopt.
- Time and energy consuming: IPM application takes time and energy and has to be closely monitored for effectiveness.
More resources needed in the short term as compared to the pesticides because IPM has various techniques and methods to be applied.