Browsing by Author "Senzanje, Aidan"

Now showing 1 - 8 of 8
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    Publication
    Coupling hydrological and crop models for improved agricultural water management
    (Bulgarian Journal of agricultural science, 2018-06-01) Kanda, Edwin; Mabhaudhi, T.; Senzanje, Aidan
    Understanding the relationships among plant, soil, and water is important in agricultural water management practices. Simulation of the soil water balance is central to improving crop water productivity. Individual crop or hydrological models have shortcomings due to the simplification of the surface or subsurface processes. Coupling of crop and hydrological models helps in understanding the complex processes involved in crop production. This review highlights the application of coupled crop and hydrological models in simulation of crop response to water availability. The hydrological models considered are CHAIN-2D, HYDRUS-1D, HYDRUS 2D/3D, and MODFLOW. The crop growth models considered are the water-driven model (AquaCrop), solar-radiation driven model (EPIC), and the carbon-driven models (WOFOST and DSSAT). HYDRUS-2D is the successor to CHAIN-2D. MODFLOW is a popular model especially in simulating groundwater flow while HYDRUS is satisfactory in the simulation of water dynamics in the vadose zone. From the review, it can be deduced that HYDRUS-1D has been coupled with all the crop models considered except DSSAT. EPIC – CHAIN-2D and MODFLOW-DSSAT were the other applications. Further research needs to consider linking 2D soil water models with any of the crop growth models for a better representation of the soil water dynamics and therefore accurate simulation of the soil water balance.
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    Publication
    Coupling hydrological and crop models for improved agricultural water management a review
    (Bulgarian Journal of Agricultural Science, 2019-04-09) Kanda, Edwin K.; Mabhaudh, Tafadzwanashe; Senzanje, Aidan
    Understanding the relationships among plant, soil, and water is important in agricultural water management practices. Simulation of the soil water balance is central to improving crop water productivity. Individual crop or hydrological models have shortcomings due to the simplifi cation of the surface or subsurface processes. Coupling of crop and hydrological models helps in understanding the complex processes involved in crop production. This review highlights the application of coupled crop and hydrological models in simulation of crop response to water availability. The hydrological models considered are CHAIN-2D, HYDRUS-1D, HYDRUS 2D/3D, and MODFLOW. The crop growth models considered are the water-driven model (AquaCrop), solar-radiation driven model (EPIC), and the carbon-driven models (WOFOST and DSSAT). HYDRUS-2D is the successor to CHAIN-2D. MODFLOW is a popular model especially in simulating groundwater fl ow while HYDRUS is satisfactory in the simulation of water dynamics in the vadose zone. From the review, it can be deduced that HYDRUS-1D has been coupled with all the crop models considered except DSSAT. EPIC – CHAIN-2D and MODFLOW-DSSAT were the other applications. Further research needs to consider linking 2D soil water models with any of the crop growth models for a better representation of the soil water dynamics and therefore accurate simulation of the soil water balance.
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    Publication
    Coupling Hydrus 2D/3D and AquaCrop Models for Simulation of Water Use in Cowpea (Vigna Unguiculata (L.) Walp)
    (Springer Link, 2021-01-01) Kanda, Edwin; Senzanje, Aidan; Mabhaudhi, T.
    Simulation of the soil water balance requires reliable representation of the main hydrological processes such as infiltration, drainage, evapotranspiration and run off. In a cropping system, the determination of the soil water balance is necessary to facilitate decisions regarding water management practices such as irrigation scheduling. This may require the coupling of hydrological and crop models. This study sought to determine the water use of cowpea under irrigated conditions in different environments of South Africa. The study considered two irrigation types, subsurface drip irrigation (SDI) and Moistube irrigation (MTI) and two environments characterized by clay and sandy soils. The study was accomplished using a hydrological model (HYDRUS 2D/3D) and AquaCrop (crop model). The crop characteristics were obtained using AquaCrop while HYDRUS 2D/3D was used to generate optimum irrigation schedules and the soil water balance. Thereafter, the water use and yield of cowpea was determined. The average grain yield and biomass was 2600 kg ha−1 and 10,000 kg ha−1, respectively, with the difference between the two sites being less than 5% under both SDI and MTI. The water use and water use efficiency (WUE) varied from 315 to 360 mm and 0.67 to 1.02 kg m−3, respectively, under the two irrigation types in the two sites considered. The WUE was higher under SDI than MTI, but the differences were less than 10%. This showed that response of cowpea under MTI was not different from SDI.
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    Publication
    Hydraulic and clogging characteristics of Moistube irrigation as influenced by water quality
    (IWA, 2018-06-12) Kanda, Edwin Kimutai; Mabhaudhi, Tafadzwanashe; Senzanje, Aidan
    Irrigation consumes approximately 70% of total freshwater use worldwide. This necessitates the use of efficient irrigation methods such as micro-irrigation. Moistube irrigation (MI) is a new subsurface irrigation technology where the water emits from a semi-permeable membrane of the Moistube at a slow rate depending on the applied pressure and soil water potential. There is currently limited information on the performance of Moistube tapes with respect to discharge as a function of pressure or water quality. The aim of this study was to determine the flow characteristics of Moistube tapes as a function of pressure and the effect of suspended and dissolved solids on the emission characteristics. The pressure–discharge relationship was determined within a range of 20 kPa and 100 kPa. The clogging of the Moistube was determined using water containing low, moderate and high concentrations of suspended and dissolved solids at 20 kPa and 30 kPa. The results indicated that the Moistube discharge follows a power function with the applied pressure. The discharge decreased linearly over time because of clogging. Suspended solids had a more severe clogging effect on Moistube than dissolved solids. The results of this study should help in the design, operation and maintenance of MI systems.
  • Publication
    Publication
    Modelling soil water distribution under Moistube irrigation for cowpea (VIGNA unguiculata (L.) Walp.) crop*
    (Wiley, 2020-12-01) Kanda, Edwin Kimutai; Senzanje, Aidan; Mabhaudhi, Tafadzwanashe
    Moistube irrigation (MTI) is a type of technology which uses a semipermeable membrane to emit water continuously in response to soil water potential and applied pressure. Soil water dynamics under MTI incorporating plant water uptake have not been studied. Therefore, this study aimed at determining the soil water distribution under MTI, using cowpea as a reference crop. The effect of Moistube placement depth on the soil water dynamics under MTI was also determined. The experiment was carried out in tunnels with MTI and subsurface drip irrigation (SDI) as a control. The HYDRUS 2D/3D model was calibrated and thereafter used to simulate soil water dynamics for different placement depths. The soil water content above the Moistube/drip lateral was higher under SDI than MTI, while the lateral movement of water was similar for both irrigation types. The simulated soil water contents closely matched (coefficient of determination [R2] ≥ 0.57, root mean square error [RMSE] ≤ 0.029 cm3 cm−3, normalized root mean square error [NRMSE] ≤ 14.7% and efficiency [EF] ≥ 0.20) the observed values for both MTI and SDI. This showed that HYDRUS 2D/3D could be used to simulate water dynamics of irrigated cowpea. There was no significant difference (p > .05) between the root water uptake (RWU) in SDI and MTI. The Moistube placement depth did not significantly affect (p > .05) the RWU in loam soil but increased with increased placement depth in clay soil. The optimum placement depth of Moistube laterals for cowpea was 15 cm in loam and 20 cm in clay. This study forms the basis for design of MTI in terms of optimum placement depths for cowpea grown in loam and clay soils.RėsumėL'irrigation par tuyau poreux (MTI) est un type de technologie qui utilise une membrane semi‑perméable pour émettre de l'eau en continu en réponse au potentiel hydrique du sol et à la pression appliquée. La dynamique de l'eau dans le sol sous MTI intégrant l'absorption d'eau des plantes n'a pas été étudiée. Par conséquent, cette étude visait à déterminer la distribution de l'eau dans le sol sous irrigation par tuyau poreux, en utilisant le niébé comme culture de référence. L'effet de la profondeur de positionnement des tubes poreux sur la dynamique de l'eau dans le sol sous MTI a également été déterminé. L'expérience a été réalisée dans des tunnels avec MTI et de l'irrigation goutte à goutte souterraine (SDI) comme contrôle. Le modèle HYDRUS 2D/3D a été calibré puis utilisé pour simuler la dynamique de l'eau dans le sol pour différentes profondeurs de positionnement. La teneur en eau dans le sol au‑dessus du tube poreux/latéral en goutte à goutte était plus élevée sous SDI que MTI, tandis que le mouvement latéral de l'eau était similaire pour les deux types d'irrigation. Les teneurs en eau simulées dans le sol correspondaient étroitement (R2 ≥ 0,57, RMSE ≤ 0,029 cm3 cm−3, NRMSE ≤ 14,7% et EF ≥ 0,20) aux valeurs observées pour le MTI et le SDI. Cela a montré que HYDRUS 2D/3D pouvait être utilisé pour simuler la dynamique de l'eau du niébé irrigué. Il n'y avait pas de différence significative (p > ,05) entre l'absorption d'eau des racines (RWU) dans SDI et MTI. La profondeur de positionnement du tube poreaux n'a pas affecté de manière significative (p > ,05) la RWU dans le sol limoneux mais a augmenté avec l'augmentation de la profondeur de positionnement dans le sol argileux. La profondeur de positionnement optimale des latéraux de tube poreux pour le niébé était de 15 cm dans le limon et de 20 cm dans l'argile. Cette étude constitue la base de la conception du MTI en termes de profondeurs de positionnement optimales pour le niébé cultivé dans des sols de limon et d'argile.
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    Nutritional yield and nutritional water productivity of cowpea (Vigna unguiculata L. Walp) under varying irrigation water regimes
    (Water Sa, 2020-08-12) Kanda, Edwin Kimutai; Senzanje, Aidan; Mabhaudhi, Tafadzwanashe; Mubanga, Shadrack Chisenga
    There is a need to mainstream traditional crops in sub-Saharan Africa, in order to tackle food and nutritional insecurity through incorporating  nutritional quality into crop water productivity, in the wider context of the water–food–nutrition–health nexus. The objective of the study was to determine the effect of irrigation water regimes on the nutritional yield (NY) and nutritional water productivity (NWP) of cowpea under Moistube irrigation (MTI) and subsurface drip irrigation (SDI). We hypothesized that NY and NWP of cowpea were not different under MTI and SDI and that deficit irrigation improved NWP. The experiment was laid as a split-plot design arranged in randomized complete blocks, replicated 3 times, with 3 irrigation water regimes: 100% of crop evapotranspiration (ETc), 70% of ETc, and 40% of ETc. Irrigation type and water regime did not significantly (p > 0.05) affect the nutritional quality of cowpea. Similarly, NWP of crude fat (28.20–39.20 g∙m-3), ash (47.20–50.70 g∙m-3) and crude fibre (30.70–48.10 g∙m-3) did not vary significantly. However, protein and carbohydrate NWP showed significant (p < 0.05) differences across irrigation water regimes and irrigation type. The highest protein NWP (276.20 g∙m-3) was attained under MTI at 100% ETc, which was significantly (p < 0.05) higher than SDI (237.1 g∙m-3) and MTI (189.8 g∙m-3) at 40% ETc. Cowpea is suited for production in water-scarce environments; however, there are trade-offs with carbohydrate NWP. This should not be of concern as often diets are already energy-dense but lacking in other micronutrients. Keywords: deficit irrigation nutritional quality proximate composition subsurface irrigation traditional legume
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    Publication
    Soil water dynamics under Moistube irrigation
    (Elsevier, 2020) Kanda, Edwin Kimutai; Senzanje, Aidan; Mabhaudhi, Tafadzwanashe
    The design and management of irrigation systems require knowledge of soil water movement. There are few studies on soil water dynamics of Moistube irrigation (MTI) since it is a relatively new type of subsurface irrigation technology. It was hypothesised that soil texture influences soil water distribution under MTI. We determined soil water distribution, experimentally and numerically, using HYDRUS 2D/3D model for two soil textures (loamy sand and sandy clay loam). The experiment consisted of a soil box filled with soil and Moistube, supplied with water under a constant pressure head of 60 kPa, placed at 20 cm below the soil surface. Soil water content (SWC) was measured using Decagon MPS-2 sensors installed at depths of 5 cm, 10 cm, 15 cm, 20 cm, 30 cm, 40 cm and 50 cm and laterally at 10 cm, 20 cm and 30 cm over a period of 72 h. Results showed that simulated SWC closely matched (R2 ≥ 0.70 and RMSE ≤ 0.045 cm3 cm−3) observed values for all depths considered for the two soil textures. The model slightly under- or over-estimated SWC (<15.6%). There was no significant difference (p > 0.05) between the soil water distribution in lateral and downward direction for both sandy clay loam soil and loamy sand. However, the SWC upward of the Moistube placement depth was significantly (p < 0.05) lower than both lateral and downward. SWC in loamy sand at 10 cm upward, downward and lateral after 24 h were 0.08 cm3 cm−3, 0.23 cm3 cm−3 and 0.20 cm3 cm−3, respectively. The corresponding values for sandy clay loam were 0.28 cm3 cm−3, 0.32 cm3 cm−3 and 0.31 cm3 cm−3 at 10 cm upward, downward and lateral, respectively. The simulations for wetted distance in both soil textures were also close to the observed values (R2 ≥ 0.97, RMSE ≤ 3.99 cm). Soil texture had a significant (p < 0.05) effect on soil water movement with upward movement faster in sandy clay loam than in loamy sand. The lateral and downward distances were 23 cm and 24.6 cm, respectively, for loamy sand after 24 h. Similarly, for sandy clay loam, the lateral and downward distance was 19 cm. These wetting distances should be considered in the design of MTI in terms of depth of placement and lateral spacing. The results of this study demonstrated the usefulness of HYDRUS-2D/3D model in the prediction of soil water movement for optimum design of MTI.
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    Water resource management: IWRM strategies for improved water management. A systematic review of case studies of East, West and Southern Africa
    (PLoS One, 2021-05-25) Dirwai, Tinashe Lindel; Kanda, Edwin Kimutai; Senzanje, Aidan; Busari, Toyin Isiaka
    Objective The analytical study systematically reviewed the evidence about the IWRM strategy model. The study analysed the IWRM strategy, policy advances and practical implications it had, since inception on effective water management in East, West and Southern Africa. Methods The study adopted the Preferred Reporting Items for Systematic Review and Meta-analysis Protocols (PRISMA-P) and the scoping literature review approach. The study searched selected databases for peer-reviewed articles, books, and grey literature. DistillerSR software was used for article screening. A constructionist thematic analysis was employed to extract recurring themes amongst the regions. Results The systematic literature review detailed the adoption, policy revisions and emerging policy trends and issues (or considerations) on IWRM in East, West and Southern Africa. Thematic analysis derived four cross-cutting themes that contributed to IWRM strategy implementation and adoption. The identified four themes were donor effect, water scarcity, transboundary water resources, and policy approach. The output further posited questions on the prospects, including whether IWRM has been a success or failure within the African water resource management fraternity.