Evaluation of the suitability of soils for irrigation in lower Kuja, Nyatike District, Kenya
Soils are important components of the environment and their understanding is essential in planning and management for environmental conservation and sustainable use of natural resources. However, reliable soils information is scarce, not detailed enough and also not site specific. A semi detailed soil survey study was conducted of about 7,000 ha of Lower Kuja Irrigation Development Project area in Nyatike District, Migori county. The sudy aimed at evaluating and classifying the soils for irrigation suitability. The study involved quantitative investigations of soil properties, inventory of land use systems and an assessment of the ecological potential and constraints as determined from a balance sheet anaysis of resources and landuse requirements as related to irrigation. Six soil mapping units found in four physiographic units, were identified and their distribution and extent are shown in the annexed soils suitability map, at scale 1:50, 000 Soils of Footridges (slopes 6 – 10%) soil mapping unit RBp, are excessively drained, very shallow, very stony and very rocky; considered Unsuitable for irrigated agriculture. While soils of the Sedimentary Plains (slopes 0 – 3%) soil mapping unit PSB, are well drained, shallow to moderately deep, clay loam to clay, in most places over murrum. Considered Marginally suitable for general irrigation but can be upgraded to Moderately suitable if the area is considered for growing shallow rooted crops under suitable irrigation methods. Soils found in the Lacustrine Sedimentary Plains, soil mapping unit PLB1 are Imperfectly drained deep to very deep, (Eutric Vertisols, Sodic phase). These soils cover a large portion of blocks 1;2;3;4/1;4/2 and 4/3. Though considered Marginally suitable for general irrigated agriculture; it can be upgraded to Highly suitable if paddy rice were to be the main crop. Rice can do well with ESP’s of up 20 and the range in this unit is 2.3 to 18.0 and the EC is very low; 0.3 to 0.4ds/M. Workability which puts the unit to marginally suitable would be an advantage to paddy rice and with proper drainage and good water quality the excess salts can be leached. Soil mapping Unit PLB2 soils are poorly drained to imperfectly drained, moderately deep to deep, sandy clay loam to clay, strongly saline to very strong sodic (sodic solonchaks). These soils cover small portion of blocks 1 and 4/3 and the main area is in block 5/1. The soils are very strongly alkaline pH-H20>9; extremely sodic ESP%>35; very high exchangeable Sodium 18.0 to 46.0 Cmol/kg. Because of these attributes, the soils are rated unsuitable for irrigated agriculture. xvi Soils found in the Alluvial Plains soil mapping unit AA1 are moderately well drained to well drained, very deep, loam to clay loam, (Eutric Cambisols, Sodic phase). These soils occupy the greater part of blocks 8,7,6 and 5/2 and are rated Moderately suitable for general irrigated agriculture but can be upgraded to Highly suitable if proper crops are selected since the main problem is the ESP which is slightly sodic to non-sodic. Some suggested crops are paddy rice for the moderately well drained area and horticultural crops like tomatoes; spinach; pepper and kales among others. Soils of the maping unit AA2 are excessively drained, very deep, loamy sand to sand (Haplic Arenosols). The soils occupy small portions in blocks 4/3 and 8. They are rated Unsuitable for irrigated agriculture because of their texture which is very high in the sand fractions 75 to 89% Soil organic carbon was positively correlated with the infiltration rate at (P≤ 0.01) significant levels.