Characterisation of farming systems in southern Rwanda

PART II. OVERVIEW OF MAJOR FARMING SYSTEMS IN SUB-SAHARIAN AFRICA (SSA)

II.1. Definition

Farming system is a unique and reasonably stable arrangement of farming enterprises that the household manages according to well-defined practices in response to the physical, biological, and socioeconomic environments and in accordance with the household's goals, preferences, and resources (Shaner et al., 1981). It is also defined as a complex inter-related matrix of soils, plants, animals, implements, labor and capital, inter-dependent farming enterprises (Dixon et al., 2001). Clearly, farming system is a simple combination of all production activities on a farm, the number and types of activities may be diversified. The type of farming systems can vary from a simple system where only one or two activities are run to the more complex systems where several enterprises are undertaken together on the farm.

II.2. Types of farming systems found in Rwanda

Farming system is broadly divided into three subsystems: Cropping systems, livestock systems and mixed systems referring to the interaction between crops and livestock (Shaner et al., 1981).

II.2.1. cropping systems

Cropping systems simply means a combination of crops in the time and space. Appropriate cropping systems that will improve plant nutrition, increased water and nutrient use efficiency, and build-up of soil organic matter form the bedrock of sustainable agriculture (Antoni, 2000).

II.2.1.1. Intercropping

Intercropping is the growing of two or more crops on the same piece of land within the same years. Various forms of intercropping have been a central feature of many tropical agricultural systems for countries. Beets (1982) has proposed that intercropping can be divided into three general categories: full relay and sequential intercropping depending on the extent of physical association between the crops. Full intercropping involves complete association between crops planted at the same time, while relay cropping involves only partial association, in which a second crop is planted into an already standing crop before harvested. Sequential intercropping where there is no physical association is the extreme case where two crops are grown on the same land in the same year but not at the same time. The main advantages of intercropping reside in reduction of the risk of total crop failure and product diversification. Food crops are often mixed with cash crop ensuring both subsistence and income for farmers. Intercropping is most likely to be practiced on small farms, in area where land is scarce, forcing the simultaneous production of different crops on the same area of land. Relatively better-off farmer with large farms are less reliant on intercropping, being able to fallow and/or control production with other inputs such as water and inorganic fertilizers (Graves et al., 2004)

II.2.1.2. Rotation

Crop rotation is the practice of growing a series of dissimilar types of crops in the same space in sequential seasons to avoid the buildup of pathogens and pests that often occurs when one species is continuously cropped. Crop rotation also seeks to balance the fertility demands of various crops to avoid excessive depletion of soil nutrients. A traditional crop rotation system is the cropping system involving cereals rotating with legume crops such as bean ( www.wikipedia.org/wiki (April, 2007)).

According to Rayar (2000), the advantages of crop rotation are manifested in the Addition of organic matter through incorporation of crop residues and nitrogen through the inclusion of legume in the rotation but this helps also in effective control of insects and diseases while breaking their reproductive cycle. Rotation can also allow a better exploitation of moisture and nutrients at different soil depth by differences in the rooting pattern of crop, resulting in greater potential for obtaining nutrients. This system is also an important tool in weed and soil erosion control.

In subsistence farming, it also makes sense to grow beans and grains at the same time in different fields. In Rwanda, the commonly used rotation is: tubers-legume-cereal, illustrating how Rwandan people know the importance of legume in crop rotation. For example: Bean comes after sorghum or vice versa. Through symbiotic N fixation, beans grow well on soils weakened by sorghum export. Beans benefit of the N from mineralization of the stable humus formed out of the incorporation of sorghum residues (Hitimana, 1989).