Adaptation of crop management practices

Crop management practices affect soil health, soil structure, soil nutrient content and soil climate, and can serve as an adaptation strategy to climate change.

Crop rotations (temporal diversity) and mixed cropping (within field di-versity) are widespread throughout SSA. Well managed and synchronised crop rotations (for example, growing green manure legumes as fallow crops) help revitalise the soil and reduce the persistence and spread of crop pests and diseases (Borron 2006). Plants with a deep root system serve well for drought resistance and carbon sequestration (e. g. perennial crops and trees) while those with shallow roots (mainly annual crops) serve well for quick establishment of plants. As these different plants explore differ-ent and complemdiffer-entary regions of the soil profile they increase the water use efficiency and nutrient cycling (FAO 2005c; Thorup-Kristensen 2006).

Switching to other/high value crops is one form of adapting to climate change provided the crop is tolerant to heat or to dry conditions (which most high-yielding varieties are not). Pasternak et al. (2005) report that increasing the proportion of or switching to high value crops like Roselle (Hibiscus sabdariffa) – an annual herbaceous plant widely grown in the Sahel, can improve farmer incomes. The authors report that in the Sahel, farmers normally plant Roselle in small plots in the periphery of their millet fields. The dried succulent calices of this plant are used to produce a drink called Bissap or Zobbo herbal teas (in Sahel or in Nigeria), and are used as a natural food colorant. Roselle also has potentials as an income

earner in the export market. Since cash crops generate higher income, increasing the proportion cultivated can increase smallholder income, provided that the storage and marketing aspects are well managed.

To adapt to a reduction in the length of the rainy season, maize, millet or guinea corn varieties as well as local groundnut varieties that have a long growing period, are substituted by other types that mature faster. Interest-ingly, Laube, Awo and Schraven (2008) report that production of ground-nuts has increased in northern Ghana as farmers find that groundground-nuts do well in less fertile soils.

Fallowing entails non-cultivation of arable lands for a certain period with the aim to restore soil fertility. This can be in terms of bush fallows or improved fallows. Although fallowing is no longer as widespread as it once was in Africa due to pressure on land, certain fast growing local shrubs could be grown between seasons or on degraded lands. Since the soil surface is covered by the crops, soil loss is reduced and soil structure improved. Improved fallowing can be in form of green manure, that is, plants grown for the purpose of reinvigorating the soil, either to use them as manure or for mulching. Biologically fixed nitrogen from legumes (green manure) can be used to adapt to climate change. By growing nitro-gen fixing crops, soil fertility can be increased without causing emissions as is the case when using inorganic fertilizers. In arid and semi-arid tropi-cal regions, where water is limited between periods of crop production, drought-resistant green manures can be used to fix nitrogen. Through biological nitrogen fixation, grain legumes like groundnut (Arachis hypo-gea), velvet beans (Mucuna pruriens), soybeans (Glycine max.) and pigeon pea (Cajanas cajan) contribute to soil fertility, thereby lowering the costs of soil fertility management (Tchale / Wobst 2005; IFOAM 2006). Alter-natively, intercropping and alley cropping with leguminous trees can also increase biologically fixed nitrogen.

Alley cropping increases nutrient cycling through increased total biomass production with or without fertilizer. Alley cropping can improve nutrient cycling whereby nitrogen-fixing trees are planted in parallel rows to crops.

Through alley cropping, biomass production can also be increased. Food crops are then planted in between the rows in the "alley" while the trees protect the soil from erosion and fix nitrogen in the soil. Products from the tree like wood, fruits, livestock fodder can enhance farmers’ incomes.

able products is reduced through competition and removing the already limited biomass for construction or as carry away fodder for livestock reduces the effectiveness of alley cropping for nutrient cycling. For cases where the soil nutrient status is low, alley cropping with nitrogen-fixing species requires many years to replenish the soil with Nitrogen (Leihner 2000). For such cases a mix of various soil replenishment methods is needed.

With climate change some areas will become drier than before. Such areas could adopt the crops which are currently being grown in current dry areas (e. g. Mali). Areas where maize is currently being grown may in future be more suitable for sorghum and millet. However, those areas that are al-ready dry, like the arid areas and which may become drier as a result of climate change will have fewer options than to shift completely from agri-culture to other sectors. This will also depend on whether climate change is gradual or abrupt (in decades). With gradual change people and ecosys-tems may have enough time to adopt in contrast to abruptly changed con-ditions. Adapting to such changed conditions requires that social and eco-logical systems have buffer capacities in terms of diversification and flexi-bility to migrate (also plants and animals) and to take up other livelihoods.

Contributions to resilience to climate change:

Contributions to ecological resilience

– Through crop rotation and mixed cropping, crop management practices reduce the susceptibility of the farm to crop pests and diseases since a diversified range of crops is grown. This agro-biodiversity also stabilises farm production as climate risks do not affect all crops to the same degree. For example, mixing drought tolerant crops with non-drought tolerant crops ensures some harvests under non-drought conditions.

Similarly, the nitrogen fixing plants contribute to soil fertility and by mixing both annual and perennial crops, efficient use is made of nutrients in different soil profiles.

Contributions to economic resilience

– Crop diversification ensures that income can be derived from produce as different crops have different market values. Using nitrogen-fixing plants reduces the amount of money needed to purchase inorganic fertiliser, thereby reducing the cash expenditure of smallholder farms.

Contributions to social resilience

– Like for soil management practices, adapting crop management to climate change also holds some potential for greater social resilience by building social capital – crop rotation and mixed cropping are good farm management practices that ensure that the farm does not become a source of risk for surrounding farms through the concentration of crop pest and disease as would happen without crop rotation or mixed cropping.