Forms of farm diversification

Crop diversification involves the introduction or adoption of new plant species or crop varieties as well as production technologies that can stabilise or increase yields; improve drought, pests, and diseases resistance; or help capture new market opportunities. For example, crop rotations can break insect and disease cycles, reduce weeds, curb erosion, supplement soil nutrients, improve soil structure and conserve soil moisture. While intercropping with specific companion crop or plant species can reduce pest attacks – and thus reduce economic risk associated with pest damage in any one crop.

However, there is need to identify crops and varieties that develop well in the target environment and suit the farmer preferences. Either way, these new crops and/or varieties should fit well into the existing cultivation system and general farm management to limit additional major changes. In addition, diversifying from routine cultivation of traditional staples can also have important nutritional benefits for smallholder farming families. The introduced crops, like vegetables which require less land, can support the farmer to be more self-reliant in terms of food production. Crop diversification can enable farmers gain access to national and international markets with new products, food, and medicinal plants.

Different crops can be introduced and arranged in such a manner to take advantage of their complementary characteristics. However, the introduced crops should be arranged in such a way that they complement rather than compete with each other.

• Rotating or mixing of crops based on nutrient needs. The crops can be grouped based on their nitrogen (or nutrient) demand, distinguishing heavy feeders, moderate feeders, light feeders and fertility builders. Heavy feeders include crops such as maize, cabbage or leek. These crops depend on high amounts of nitrogen to produce good yields. Moderate feeders include root and tuber crops, and fruit as well as leafy vegetables. Fertility builders include legume crops such as beans, peas, and (leguminous) green manures that are mainly cultivated for soil fertility improvement. The nitrogen that is provided by fertility builders is best exploited, if a legume crop is followed by a heavy feeder. Heavy feeders should then be followed by a moderate feeder. After heavy feeders such as corn or cabbages, only few nutrients remain in the soil. Growing two heavy feeders after each other requires a high nutrient supply with fertilisers.
• Rotating or mixing of crops based on their susceptibility to diseases and pests. Crop diversification not only plays a key role for soil fertility management, but it is also important for soil-borne pests and diseases such as nema­todes or fungi. For this reason, crops of different botanical plant families can be rotated, intercropped or alley cropped (i.e. cultivation of food, forage or specialty crops between rows of trees). To prevent build-up of soil-borne pests and diseases, most crops should not be grown on the same field more than every third or fourth season.

Agroforestry is where trees and shrubs are grown in the fields with crops, on the edges of crop fields, on fallow plots or pastureland. It includes interactions bet­ween trees and other components of the farm within fields (tree-crop production for both annual and perennial crops) and within the farm, where trees may provide fodder for livestock, fuel, food, shelter, or income from products including timber. Agroforestry therefore involves a wide range of trees that are protected, regenerated, planted, or managed in farms as they interact with annual crops, livestock, wildlife, and humans.

Agroforestry systems show a higher and better stabilised self-regulation to prevent epidemics of pests and diseases, as biodiversity is higher than in monocultures. The combination with trees allows a better use also of the third dimension of the productive area. Thus, with a smart combination of complementary crops and an appropriate, careful management, these systems can secure yield, be profitable and highly sustainable.

There are three basic types of agroforestry systems:

• Agrosilviculture – a combination of crops and trees, such as alley cropping.
• Silvopastoral system – a combination of forestry and grazing of domesticated animals on pastures, rangelands, or on-farm.
• Agrosilvopastoral system – a combination of the three elements (trees, animals and crops) for example where a home garden involves livestock as well as scattered trees on croplands used for grazing after harvests.

Other forms of agroforestry can be defined as e.g. apiculture (bees with trees), aquaculture (fish farming with trees and shrubs) and multipurpose tree lots.

Beekeeping is:

• Very compatible with tree crops like fruit trees
• Improves pollination of crops on the farm
• Low cost of establishment and management

For more information on organic beekeeping see the module 10-1 of the African Organic Agriculture Training Manual at www.organic-africa.net.

Fish farming is:

• Suitable for smallholder farmers who have access to good quality water
• Complementary to other farm enterprises
• Modest in terms of labour requirement

For more information on aquaculture, see the module 9-10 of the African Organic Agriculture Training Manual at www.organic-africa.net.

The major consideration when selecting agroforestry trees is competition with other components in the same area, which should be as little as possible. Smallholders have limited land holdings, so very competitive trees (e.g. Eucalyptus spp., Acacia mearnsii) may not be considered by the farmers even if they are fast growing and have varied uses. Eucalyptus has roots distributed both near the soil surface and deeper down in the soil profile.

Trees with a deep root system (e.g. Acacia spp., Albizia spp. or Grevillea) are usually less competitive with crops than those with many shallow roots. However, when the main goal is to stabilise the soil, then shallow root systems may be desirable. Examples of trees with shallow roots are Casuarina spp., Leucaena leucocephala, Cupressus lusitanica, and Sesbania sesban, although the latter does not compete with crops since its overall root system is small and this species fixes its own nitrogen.

Trees with dense shade compete with light-demanding crops such as cereals. Shading can be reduced through tree canopy management. Other trees naturally have a light shade, e.g. Acacia spp., Sesbania sesban, Casuarina spp. and Entada abyssinica. Such trees may either have small leaves, or vertically oriented leaves or be bare or partly bare during the crop-growing season. Some trees have rather dense shade but that can be easily managed to reduce the shade, for example, Grevillea robusta, Markhamia lutea, Cordia abyssinica, Croton spp., Leucaena leucocephala and Calliandra calothyrsus.

The introduction of trees may present certain risks related either to failures of one component, e.g. the trees do not perform well, or they negatively affect other components through a chemical process called allelopathy, emitting too much shade or introduction of pests or diseases. Other risks may be that trees turn out to be weeds requiring more labour, or that they prove to be a nuisance, e.g., they are poisonous or easily break and destroy or damage other components. The risks are usually fewer with indigenous, well-known species than with exotic or introduced species.

Green manuring means growing plants with the primary purpose of incorporating their biomass into the soil to supply “organic food” and thus improve the soil nutrient content and fertility. Cover crops and green manures are near synonyms - while the main purpose of growing cover crops is to cover the soil with a low vegetation cover to protect it from sun and rain as well as to suppress weeds, for example in perennial crops, green manures are grown with the main purpose to build maximum biomass. Mostly, leguminous plants are used for green manuring, as they can collect considerable amounts of nitrogen from the air and fix it in their roots in addition to providing food for soil organisms. While grain legumes are grown for harvesting the grains, green manures are ideally harvested when they are still green and have produced maximum biomass.

Green manures are a farm-grown fertiliser and are, therefore, a cheap alternative to purchased fertilisers. They complement animal manures well and are of high value on farms where animal manure is scarce. Green manures can provide an incentive to abandon harmful traditional practices, such as burning crop residues.

One reason, why farmers do not grow green manures is that they do not know which species to plant and how to integrate them into their cropping system. It is important to know where, when and how to plant which species to obtain satisfying results. Other bottlenecks relate to ready availability of seed for the green manure crops, labour intensiveness, and unreliable performance of the green manures.

Before large scale planting, it is advisable that farmers try out, on smaller pieces of land, the different types of green manure plants and observe, how they grow in the local conditions, and that they practice on managing them. The selection of appropriate green manures is essential to maximise their potential and minimise possible inconveniences. Green manures must suit the local climate, soil, and pest and disease situation, and fit into the cropping system. Annual green manures must be fast growing, have vigorous growth and be non-woody. They should grow well in the poorest soils and not need any fertiliser, nor irrigation, nor pesticide, and they should not be closely related to the incoming crop to avoid promotion of pests and diseases that may affect the following crop.

The most obvious use of green manures in the common cropping systems is through an improved fallow. The higher fertilisation value of leguminous green manures may allow shortening the fallow period, as soil fertility restoration is speeded up. Alternatively, green manures can be sown among traditional row crops or relay intercropped towards the harvesting time of the main crop. Competition to food crops is reduced, as green manures primarily grow during the dry season. Alternatively, green manures such as jack bean or velvet bean can be grown in alleys. Evaluation of traditional cropping systems in Africa showed that rotation of legumes with other crops is more productive than intercropping.

Legumes do not significantly contribute to higher soil nitrogen contents when their grains and residues are removed for human and/or animal nutrition. If the legume biomass or residue is burnt or fully removed from the fields, negative nutrient balances arise. It is therefore important to ensure that all or at least part of the legume residues is retained in the field, if soil organic matter content is to be maintained.

If green manures are left as mulch on the soil surface, they effectively contribute to erosion and weed control and retain moisture in the soil. However, nutrients from mulches are released only slowly. If green manures are incorporated into the soil, a relevant share of the nutrients are mineralised in one season. Thus, the fertilising effect on the subsequent crop is greater after incorporation. At the end, the total amount of nutrients that is made available to plants is about the same whether green manure residues are left as mulch or incorporated.

The dense plant covers of green manures not only protect the soil from erosion by wind and water, but also prevent propagation of weeds saving time for weed control. If green manures leave a thick dry mulch cover, they can provide favourable conditions for planting of the following crop without any need for weeding or soil preparation.

Some green manure species provide generous amounts of high protein fodder for livestock. This could be a good justification for a crop-livestock diversification. Despite all the benefits, green manures may, as a sole soil fertility management measure, may not be sufficient to maintain or even improve soil fertility.

Domestic animals play many important roles on a farm. They provide various products depending on the species, including dairy products, eggs, fibre and leather, draft power and transport, and manure to fertilise crops and for fuel. They also play cultural roles in many societies, in addition to being used as capital and for social security.

The main challenge for livestock keepers is how to increase production to meet the increasing demand for livestock products, without necessarily increasing the sizes of herds amidst the decreasing land sizes. Some farmers have resorted to improved exotic breeds with varying levels of success. These improved breeds have higher requirements in terms of feed, labour, infrastructure, and veterinary management which most smallholders, especially in rural areas, cannot afford. Other farmers are focusing on crossbreeding as a way of improving production of their local breeds. Irrespective of whether the farm has pure improved, cross, or local breeds, diversification of livestock species on the farm is helpful in terms of reducing risk in case of a disease outbreak that affects a particular species.

A farmer who has been growing crops only or keeping livestock only can also diversify by introducing one or more crops and livestock on the farm respectively. Crop-livestock diversification implies that farmers produce crops and rear livestock simultaneously. This helps to optimally utilise farm resources, for example labour, management, and land. In addition, outputs from crop production, like crop residues or prunings from boundary or intercrops, serving as fodder for the livestock, while manure from livestock production improving soil fertility for crop production.

This form of diversification is also a means to minimise risks and insurance against failures in either crop or livestock enterprises, as they res­pond differently to uncertain conditions. Crop production is heavily dependent on climate variables, seeds, water, soil nutrients and biodiversity as compared to livestock production. Evidence shows that smallholder farmers who practice both crop and livestock production have higher and more stable farm incomes as compared to smallholders that only raise crops or keep animals.

On the other side, there is also a potential competition for space and resour­ces between crops and livestock which needs to be considered.

Farmers can also employ existing farm inputs and resources (capital, labour, and land) to other activities on top of producing agricultural goods, with the aim to sell them in the market and increase their income. Similar to crop and livestock diversification, non-agricultural diversification spreads the risks by creating income streams which are additional to income from agriculture. Commonly, farmers focused on the on-farm processing of primary goods as well as non-agricultural services, such as on-farm tourism, renewable energy production or rendering contract labour services outside the farm. However, nowadays farmer services have expanded into many recreational, educational, and social services (e. g. care or social farming). In the beginning, returns from non-agricultural diversification may represent a small but important share of the total farm income, but tends to increase as well as the job opportunities it offers to the family members of the farmer and non-agricultural workers leading to better societal outcomes.