Soil hydraulic properties of a Nitisol in Kabete, Kenya

Water relations are among the most important physical phenomena that affect the use of soils for agricultural, ecological, environmental, and engineering purposes. To formulate soil-water relationships, soil hydraulic properties are required as essential inputs. The most important hydraulic properties are the soil-water retention curve and the hydraulic conductivity. The objective of this study was to determine the soil hydraulic properties of a Nitisol, at Kabete Campus Field Station. Use of an internal drainage procedure to characterize the hydraulic properties and soil and water retention curves allowed for the establishment of the moisture and matric potential at field capacity and permanent wilting point. The Bt2 (84 -115) and Bt3 (115 - 143 cm) had the highest clay contents of 619 compared to Ap, AB and Bt1 horizons. The PWP was attained at soil moisture contents of 0.223, 0.284, 0277, 0.307 and 0.314 m3m-3 in the Ap, AB, Bt1, Bt2, and Bt3 horizons, respectively. Horizontal saturated hydraulic conductivity (Ksat) was high at 6.0 cm hr-1 in Ap horizon and decreased to 0.4 cm hr-1 in the subsurface horizon (Bt3). Ksat in the vertical direction was higher than horizontal and ranged from 8.3 cm hr-1 in surface layer to 0.6 cm hr-1 in Bt3 horizon, with exception of Bt1 and Bt2 where horizontal Ksat was greater than vertical. The Ap horizon also had the highest crop extractable water. Though the AB and Bt1 had the same water content at low matric suction, the variation was very wide as the SWRC approached saturation point. Bt1 and Bt2 also had similar water contents at suction range of – 7kPa after which Bt1, tended towards Bt3. Bt3 had the narrowest range of crop extractable water and thus was attributed to texture. The Bt3 retained the most amount of water at 0.314 m3m-3concluding that θPWP increased with depth. The total available water capacity between FC and PWP in the profile was 79.2 mm m-1. The study observed that the field capacity, crop available water contents and hydraulic conductivities were influenced positively by soil organic matter. The Van Genuchten parameters of air entry value (α) and pore size distribution (n) indicated that pore size distribution was not even in the AP and AB horizons. The field capacity was attained at higher matric potential at -5kPa for Bt1 while Bt2 and AP, AB, Bt2 and Bt3 was at -10kPa.The functional relationship, K(θ) = aθb that deals with water redistribution as a result of soil hydraulic properties and evaporative demand of the atmosphere was highly correlated to soil moisture content and texture with R2 values > 0.85

Predicted land use and land cover outlook for semi-arid Lokere and Lokok catchments in Karamoja region, Uganda

The semi-arid Lokere and Lokok catchments in northeastern Uganda are experiencing land use and land cover (LULC) change driven by policies and actions aimed at pastoralist sedentarisation. While these efforts present a trajectory of a landscape dominated by farming, livestock herding or grazing persists. The objective of this study was to project medium, and long-term LULC for Lokere and Lokok catchments in Karamoja, Uganda. We applied automatic multi-perceptron neural network, built on Markov chain modeling method, along with multi-criteria evaluation strategies; all embedded in the IDRISI Land Change Modeler (LCM) to project the catchments\u2019 LULC to the year 2030 and 2050. The model was trained using 1994 and 2003 LULC, and validated with 2013 LULC. Results of three modelled policy scenarios; business as usual (BAU), pro-livestock and pro-farming; to the years 2030 and 2050 showed that small scale farming (SSF) would increase in all scenarios, even if policy shifts to promote livestock rearing. Pro-farming policies would, in both 2030 and 2050, result in reduction of grassland as SSF increases; doubling the 2003 land area by 2050. The results of this study facilitate assessment of potential impacts of the future LULC and policy evaluation in the catchments.Les bassins versants semi-arides de Lokere et de Lokok dans le nord-est de l\u2019Ouganda connaissent un changement d\u2019utilisation des terres et de couverture terrestre (UTCT) motiv\ue9 par des politiques et des actions visant la s\ue9dentarisation des pasteurs. Si ces efforts pr\ue9sentent une trajectoire d\u2019un paysage domin\ue9 par l\u2019agriculture, l\u2019\ue9levage ou le p\ue2turage persiste. L\u2019objectif de cette \ue9tude \ue9tait de projeter une UTCT \ue0 moyen et long terme pour les bassins versants de Lokere et Lokok \ue0 Karamoja, en Ouganda. Nous avons appliqu\ue9 un r\ue9seau neuronal multi-perception automatique, construit sur la m\ue9thode de mod\ue9lisation de cha\ueene de Markov, ainsi que des strat\ue9gies d\u2019\ue9valuation multicrit\ue8res; tous int\ue9gr\ue9s dans le mod\ue8le IDRISI Land Change Modeler (LCM) pour projeter le UTCT des bassins versants jusqu\u2019en 2030 et 2050. Le mod\ue8le a \ue9t\ue9 form\ue9 \ue0 l\u2019aide de 1994 et 2003 UTCT, et valid\ue9 avec UTCT de 2013. R\ue9sultats de trois sc\ue9narios de politique mod\ue9lis\ue9s; business as usual (BAU), pro-b\ue9tail et pro-agriculture; a montr\ue9 que l\u2019agriculture \ue0 petite \ue9chelle (SSF) augmenterait dans tous les sc\ue9narios, m\ueame si les politiques changeaient pour promouvoir l\u2019\ue9levage pour les ann\ue9es 2030 et 2050. Des politiques favorables \ue0 l\u2019agriculture entra\ueeneraient, en 2030 et 2050, une r\ue9duction des prairies \ue0 mesure que les champs de culture augmentent; doubler sa superficie de 2003 d\u2019ici 2050. Les r\ue9sultats de cette \ue9tude facilitent l\u2019\ue9valuation des impacts potentiels de UTCT future et l\u2019\ue9valuation des politiques dans les bassins versants

Environmental Influence on Water characteristics of Soils in Two Semi-Arid Catchments in Laikipia, Kenya

Influence of soil type and landuse on soil water retention and availability in the semi-arid Sirima and Mukogodo catchments in Laikipia District, were investigated. Representative soils, six in Sirima and four in Mukogodo, surveyed at a detailed level, were assessed using samples taken from 0-10, 20-30 and 40-50 cm depths of bush, greass, bare ground and cultivated sites. Sirima soils retained more water than Mukogodo soils due to differences in clay type and textural composition. All Sirima layers were clay while Mukogodo topsoils were sandy loan and subsurface layers sandy clay loam. Mukogodo soils were more compact and had significantly lower carbon content than Sirima soils at all depths. For each area, only the surface layer had significant difference (P<0.05) in water retention among landuses, with bare ground retaining the most especially at higher pressures. However, no distinction could be made between soil types in each area based on plant water availability. Unlike the increase in clay content with depth, bulk density and carbon content were not significant in influencing plant water availability

Characteristics of Soil Crusts and their Influence on Some Soil Properties in Mukogodo Catchment, Kenya

Physical and chemical properties of soil surface crusts formed on overgrazed bare ground, in Mukogodo catchment in Kenya were investigated. These were compared with those of underlying soils and of adjacent grass and bush covered topsoils. Crusting effects on infiltration, hydraulic conductivity and water content were also investigated. The crusts were moderately strong to strong with a thickness of 1-5 mm. Crusts had higher amounts of sand, silt and clay than the underlying layer, while their total N was lower and organic C content higher than the underlying layer. On average, the contents of Ca, Mg and Na were higher in the crusts than in the underlying layers. Similarly, soil pH, EC and ESP were higher in the crusts than in the underlying layer. Cation exchange capacity and K were slightly higher in the underlying layer than in the crusts. Infiltration rate, hydraulic conductivity and soil water content in both the rainy and dry seasons in bare ground were significantly lower than those of the bush and grass covered topsoils. Bare ground surface soil bulk density was higher compared to vegetated topsoils and subsurface layers

Environmental Influence on Water characteristics of Soils in Two Semi-Arid Catchments in Laikipia, Kenya

Influence of soil type and landuse on soil water retention and availability in the semi-arid Sirima and Mukogodo catchments in Laikipia District, were investigated. Representative soils, six in Sirima and four in Mukogodo, surveyed at a detailed level, were assessed using samples taken from 0-10, 20-30 and 40-50 cm depths of bush, greass, bare ground and cultivated sites. Sirima soils retained more water than Mukogodo soils due to differences in clay type and textural composition. All Sirima layers were clay while Mukogodo topsoils were sandy loan and subsurface layers sandy clay loam. Mukogodo soils were more compact and had significantly lower carbon content than Sirima soils at all depths. For each area, only the surface layer had significant difference (P<0.05) in water retention among landuses, with bare ground retaining the most especially at higher pressures. However, no distinction could be made between soil types in each area based on plant water availability. Unlike the increase in clay content with depth, bulk density and carbon content were not significant in influencing plant water availability

Environment influence on water characteristics of soils in two semi-arid catchments in Laikipia, Kenya

No Abstract

Characteristics of Soil Crusts and their Influence on Some Soil Properties in Mukogodo Catchment, Kenya

Physical and chemical properties of soil surface crusts formed on overgrazed bare ground, in Mukogodo catchment in Kenya were investigated. These were compared with those of underlying soils and of adjacent grass and bush covered topsoils. Crusting effects on infiltration, hydraulic conductivity and water content were also investigated. The crusts were moderately strong to strong with a thickness of 1-5 mm. Crusts had higher amounts of sand, silt and clay than the underlying layer, while their total N was lower and organic C content higher than the underlying layer. On average, the contents of Ca, Mg and Na were higher in the crusts than in the underlying layers. Similarly, soil pH, EC and ESP were higher in the crusts than in the underlying layer. Cation exchange capacity and K were slightly higher in the underlying layer than in the crusts. Infiltration rate, hydraulic conductivity and soil water content in both the rainy and dry seasons in bare ground were significantly lower than those of the bush and grass covered topsoils. Bare ground surface soil bulk density was higher compared to vegetated topsoils and subsurface layers