Factors Influencing Shift from Pastoralism to Irrigated Agriculture and its Impact on Soil Quality in Kajiado
Crop cultivation in the arid and semiarid ecosystems is mainly constrained by inadequate and unreliable rainfall. Smallholder irrigation in such areas is therefore necessary to supplement l rainfall to meet crop water requirements. As cultivated agriculture encroaches into marginal ecosystems that are fragile and delicate, there is need to understand the drivers of the transition from pastoral to irrigated agriculture and the effects of irrigation on soil quality for better management of the smallholder irrigation systems towards increased and sustainable crop production. A study was therefore carried out to investigate the factors influencing the transition to irrigation farming and the effects of the transition on soil quality and subsequently the soil conservation management practices adopted under the new farming regime. The study objectives were to: (1) Investigate the social-economic factors that influence transition from pastoral grazing to irrigated smallholder crop production. (2) Assess existing soil management practices and the socioeconomic factors that influence the farmers' decision on whether to or not to conserve soil. (3) Assess the quality of irrigation water at different times/seasons in the year. (4) Asses the effect of smallholder irrigated crop production on sele cted soil ph ysical and chemical properties along the Olkeriae River basin. Primary data on socioeconomics was collected through personal interviews using a semi-structured questionnaire. Pro bit regression was used to analyse the factors driving the transition to irrigated-crop farming and factors determining soil management practices. Water samples were collected from the shallow wells used for irrigation and analysed. To examine the effect of change in land use on the soil quality, surface soil (0-10cm) was sampled from randomly selected fields under irrigation and under natural vegetation along the river. Both chemical and physical properties of the soils were analysed. The socio-economic factors th~t influenced the shift to irrigation included education and age of the household head, household size, distance to the agricultural agent, access to information, distance to market and access to hired labour. The factors that influenced the use of soil management practices included age and education of household head, household size, access to information, access to hired labour, irrigation experience and involvement of the farmer in promotion of soil conservation activities. Irrigation water had medium salinity with a mean electrical conductivity of 0.94 dSm-1 during the dry season and 0.85 dSm-1 during wet season. The sodium level was high and ranged between 4.50 me/l to 2.48 me/I for dry and wet season, respectively. The water was found to be of marginal quality for irrigation and therefore there is a likelihood of the soils becoming saline over time. Bulk density, available water capacity and saturated hydraulic conductivity were higher in the grazed sites compared to the cultivated sites, while total porosity was lower. Soil texture was silty clay loam for all sites. The soils were nonsaline and non-sodic with very low organic matter in the cultivated areas and high electrical conductivity in the grazing sites. There is therefore need for adoption of appropriate soil management practices such as application of organic fertilizers, adequate water application and deep tillage to prevent build-up of salts in the cultivated areas.