The impact of irrigated agriculture in dry lands on the natural environment: a case study of chala ward in taita taveta county, Kenya

Abstract

This research project investigated the impact of irrigation on the environment. The research examined farming practices that could affect the environment, impact of irrigation on soil and water as well as examining the state of the environment in rivers whose water has been diverted for irrigation. Interviews, through the use of questionnaires, were held with 25 from each irrigation scheme: Chala Tuhire, Kithito, Njukini and the management of Ziwani Estate Gicheha Farms. The respondents were selected using a systematic random sampling method. Five composite soil samples, each composed of five core samples, were also collected from each irrigation scheme using the systematic random sampling method by taking a zigzag route across the irrigation fields. Soil properties from the irrigation fields were then compared with soils from the surrounding non-irrigated areas to find out the significant difference using the Mann-Whitney U-test. Two water samples from each irrigation schemes were also picked and taken for analysis to establish whether the diversion of water into irrigation farms affects its quality. Soil and water analysis were done at the University of Nairobi‟s Land Resource Management and Agricultural Technology (LARMAT) laboratories at Kabete. The results showed that there was a significant difference (p≤ 0.05) in soil pH levels between the non-irrigated areas and Chala Tuhire, Kithito and Njukini irrigation schemes. Water pH and calcium levels within the irrigation schemes were higher than at the diversion points. The results also showed that 100% (all) the farmers were using chemical fertilizers and pesticides/fungicides. The common fertilizers were DAP, CAN, NPK and granular urea. Pyrethroid insecticides, by the trade names of Polytrine, Tata Alpha and Karate Zeon were the most common ones, while the fungicides; Thiovit Jet, Bayleton and Tornado usually contain remarkable levels of sulfur. The study also showed that respondents relied on information on the choice and usage of insecticides from sources such as agro-chemical sellers, fellow farmers, extension officers and personal discretion. An assessment of the riparian ecosystems of the rivers diverted for irrigation showed that River Lumi had dried up completely and the aquatic vegetation; rushes and sedges, had completely disappeared. Prosopis juliflora, an exotic, invasive, dry land species was colonizing some dry sections of River Lumi. Irrigation therefore has negative impact on the environment. There is need therefore for local authorities and regulatory bodies such as National Environmental Management Authority (NEMA) and Water Recourse Management Authority (WARMA) to intervene by putting in place relevant mitigation and adaptation measures.