The effect of soil texture on MTI soil water dynamics was also determined. Soil water dynamics under MTI while incorporating root water uptake indicated that there was no significant difference between root water uptake in SDI and MTI (p > . 0.05).
INTRODUCTION
- Improving Water Productivity Using Efficient Irrigation Methods
- Cowpea: An Under-utilized Indigenous Legume
- Modelling as a Tool for Improving Agricultural Water Management
- Research Objectives
- Thesis Outline
- References
A similar study by Lyu et al. 2016) found that MTI achieved 38% water savings than drip irrigation. It was used to assess the response of different crops to water (Vanuytrecht et al., 2014).
MOISTUBE IRRIGATION TECHNOLOGY
Introduction
A recent review by Lamm et al. 2012) highlighted the general applicability of FDI in the United States of America. To eliminate some of the above problems, a relatively new technology (wet irrigation) was developed in China using nanotechnology (Yang et al., 2008; Yang, 2016).
Description of Moistube Irrigation
The third generation (which is the current product illustrated in Figure 2.2) involved improving the anti-clogging performance of the second generation. The semi-permeable membrane pipes have a nominal diameter of 16 mm and thickness of about 1 mm (Yu et al., 2017).
Design and Operation
- Operation requirements
- Water flow mechanism
- Spacing and depth of Moistube laterals
Thus, the pressure-discharge relationship in buried point emitters is given by equation 2.2 (Shani et al., 1996); In another study, Guo et al. 2017) proved that a planting depth of 3.5 cm for onions gave higher yields than at 7 cm.
Soil Water Dynamics
- Field and laboratory experiments
- Simulation of soil water distribution under Moistube irrigation
- Spatial and temporal irrigation uniformity
The study found that the shape of groundwater distribution in MTI and SDI was symmetrical in the initial phase of irrigation. Another study by Yu et al. 2017) found that the uniformity of groundwater distribution depended on soil texture.
Increasing Water Use Efficiency and Crop Yield Under Moistube Irrigation
CU values also increased with increasing pressure head with a greater effect on sand than on fertile silt and sandy loam.
Clogging Characteristics in Moistube Irrigation
For example, Lili et al. 2015) found a discharge reduction of up to 85% after 35 days of drip irrigation with hard water (water hardness = 500 mg l-1) and the main component responsible for the blockage was calcium carbonate. Blockage of droplet emitters due to biological agents such as bacterial film in recycled wastewater (Li et al., 2009; Yan et al., 2010).
Conclusions and Recommendations
In these studies, clogging occurs due to the growth of bacterial slime along the flow path of the emitter. This can be determined using suitable crop models such as AquaCrop or by integrating crop models and hydrological models.
An experimental study on the dynamic growth of onion with Moistube irrigation technology in greenhouse. Effects of Tomato Growth and Water Use Efficiency in Sunlight Greenhouse by Moisttube Irrigation.
HYDRAULIC AND CLOGGING CHARACTERISTICS OF MOISTUBE
- Introduction
- Methodology
- Pressure – discharge relationship
- Emission characteristics due to clogging
- Statistical analysis
- Results and Discussion
- Pressure – discharge relationship
- Emission uniformity along the lateral
- Clogging effect on emission characteristics
- Conclusions and Recommendations
- References
The study also included determining the effect of suspended solids and dissolved solids on the clogging properties of Moistube. The effect of suspended and dissolved solids was determined by examining the relative discharge over the duration of the experiment.
SOIL WATER DYNAMICS UNDER MOISTUBE IRRIGATION
Introduction
The movement and distribution of water in the soil is necessary for the planning and management of irrigation systems. Design and management aspects such as wetland volume, emitter spacing, irrigation schedules, etc. depend on soil water distribution (Lubana and Narda, 2001). It was based on the hypothesis that soil texture affects soil water distribution below the MTI.
Materials and Methods
- Laboratory experiment
- Numerical modelling
- Scenarios
From the studies above, it is clear that HYDRUS 2D/3D is suitable for the simulation of groundwater distribution under irrigation systems. The findings of this study will help in understanding the groundwater distribution under MTI which will be useful in its design and management. The initial soil hydraulic properties in Table 4.2 were adjusted until the model simulations closely matched the observed soil water content.
Results and Discussion
- Soil water distribution
- Wetting pattern dimensions
- Effect of discharge on the wetting dimensions
The uphill distance reached the soil surface in sandy loam and thus, the wet distance from the top is not shown. On average, the drop distance was 26% farther in the loamy sand than in the sandy clay. For a given discharge, the size of the wetted volume was smaller in the sandy clay. loam than in molten sand.
Conclusion
The results of this study indicated that groundwater distribution in MTI depends on soil texture and runoff. Further research on heavy-textured soils would help fully understand groundwater dynamics under MTI. Soil water dynamics in subsurface irrigation are influenced by crop characteristics in addition to soil texture and system parameters.
68. RSME ≤ 3.99 cm and PBIAS ≤ 19.3%) indicating the suitability of the model in determining soil water distribution under MTI. Therefore, further studies are required to determine the soil water dynamics of wet irrigation considering root water uptake and under actual field conditions. Modeling soil water and salinity dynamics under pulsed and continuous surface drip irrigation of almond and system design implications.
SOIL WATER DISTRIBUTION UNDER MOISTUBE IRRIGATED COWPEA
Introduction
HYDRUS 2D/3D is widely used in the simulation of soil water distribution in irrigated or rainfed agricultural systems. This therefore means that in order to better represent the distribution of water in the soil, it is necessary to take into account the uptake of water from the roots during irrigation. This study therefore had two objectives; a) to determine the soil water dynamics at the Moistuba irrigated slope and b) to determine the effect.
Materials and Methods
- Tunnel experiments
- Numerical modelling
- Effect of Moistube placement depth and soil texture on soil water dynamics
This was based on the hypothesis that root water uptake is affected by the Moistube placement depth. The potential root water uptake corresponds to the potential evapotranspiration and is therefore influenced by climatic parameters (Šimůnek and Hopmans, 2009). The HYDRUS 2D/3D water survey and root parameters used in the study are indicated in Table 5.3.
Data Analysis and Model Evaluation
This was obtained by simulating soil water dynamics under four moisture establishment depths of 10 cm, 15 cm, 20 cm and 30 cm and two soil types viz.
Results and Discussion
- Soil water content
- Soil water distribution
- Root water uptake and drainage fluxes
- Effect of Moistube placement depth and soil texture on soil water dynamics
The distribution of soil water between MTI and SDI in fertile soil (CEF experiment) is illustrated in Figure 5.7. Soil water content above the moisture/drip lateral was higher under SDI than MTI. The soil water content was within the FC within the 10 cm radius below the moisture establishment depth of 10 cm and 15 cm.
Conclusion
Further studies should be conducted to determine the compensated dynamics of root water uptake under water stress conditions. The finding in this study, showing that root water uptake was not significantly different under MTI and SDI, was further explored in Chapter 6 where the response of pea under the two types of irrigation was determined.
Effects of Moistube depth and distance on groundwater and salt transport of tomato in solar greenhouse. Coupling DSSAT and HYDRUS-1D for simulations of groundwater dynamics in the soil-plant-atmosphere system. Root development of transplanted cotton and simulation of groundwater movement under different irrigation methods.
RESPONSE OF COWPEA (Vigna unguiculata (L.) Walp) TO VARYING WATER
Introduction
Biyyoota Awurooppaa naannoo Meditiraaniyaanii jiran kan akka Turkii keessattis ni biqila (Peksen, 2007; Basaran et al., 2011). Akkasumas bulchiinsa KwaZulu-Natal, Mpumalanga fi Limpopo keessatti bosona keessatti argamu (Van Rensburg et al., 2007). Dameen jallisii Afrikaa Kibbaa itti fayyadama bishaanii waliigalaa keessaa tilmaamaan %60 gumaacha (Reinders et al., 2010).
Materials and Methods
- Study area and experimental design
- Determination of crop water requirements
- Data collection and analysis
The water regimes implemented included full irrigation to meet crop water requirements (100% ETc) and DI 70% ETc and 40% ETc. Crop water requirements (ETc) for each crop growth stage were determined using potential evapotranspiration and crop coefficients as described in Equation 5.4 (Chapter 5). b) The net irrigation demand (Inet) was equal to ETc because there was zero rainfall c) The volume of irrigation water was calculated using equation 6.1. Where dgross = gross depth of irrigation (mm) and Ea = field application efficiency taken as 90% for MTI and SDI. f) Irrigation interval (T), calculated by equation 6.4.
Results and Discussion
- Time to flowering
- Leaf area index
- Yield and yield components
- Water use efficiency
Similarly, Abayomi and Abidoye (2009) found reduced pod weight and number of seeds per plant due to water deficit. In another study, Hamidou et al. 2007) reported an average reduction of 60% in the number of pods per plant due to water deficit. A decrease in HI in cowpea due to water deficit was also reported by Hamidou et al.
Conclusion
The cowpea variety (mixed brown) used in this study promotes vegetative growth and therefore produces more biomass than grain yield (Ilunga, 2014). Grain WUE was improved by water shortage under SDI, but only by 70% ETc under MTI. The mixed brown variety of cowpea used in this study is highly vegetative and thus suitable for biomass production rather than grain yield.
Effect of water stress on yield of cowpea (Vigna unguiculata L. Walp.) genotypes in the Delmarva region of the United States. Growth and yield of cowpea (Vigna unguiculata L.) cultivars under water deficit at different growth stages. Effect of water deficit at different developmental stages on the yield components of cowpea (Vigna unguiculata L. Walp) genotype.
PARAMETERISATION AND TESTING OF AQUACROP MODEL FOR FULL
Introduction
Deficit irrigation helps improve water productivity by ensuring that all water is in the root zone for crop use (Fereres and Soriano, 2007) and by allowing the crop to withdraw more water from soil reservoirs (Hsiao et al. , 2007). ) through compensatory mechanisms for root water uptake. Crop models can be used in assessing the response of crops to varying environmental and management conditions. Using this criterion, crop models can be water-driven, carbon-driven, and radiation-driven, as described by Todorovic et al.
Methodology
- Model description
- Experimental design
- Data collection
- Parameterisation of AquaCrop model
- Model evaluation
The model was parameterized using MTI data that was different from the SDI data used for testing. The statistics used to evaluate model performance were the coefficient of determination (R2) and root mean square error (RMSE), as described in Chapter 4. The other statistical techniques used to evaluate model performance were normalized RMSE ( NRMSE), Index of Agreement (d), and model efficiency (EF) calculated using equations 7.7 to 7.9 (Yang et al., 2014).
Results and Discussion
- Parameterisation
- Model testing
The model underestimated and overestimated the yield in optimal and deficit water conditions, respectively. In this study, the model simulated a slower rate of canopy expansion in the initial stages than the observed values. The performance of the model in simulating soil water content in this study was consistent with that reported by other researchers.
Conclusion
The results obtained in this study show that AquaCrop can be used with reasonable accuracy, considering few data requirements and model simplicity, in the simulation of cowpea responses to varying water regimes. Crop models such as AquaCrop may have some limitations in simulating groundwater dynamics because they adopt the tipping bucket approach in simulating groundwater flow in the vadose zone. These crop models simulate soil water dynamics in a one-dimensional manner, while water flow from irrigation is a multi-dimensional problem.
Evaluation of AquaCrop model for predicting wheat yield and water productivity under irrigated saline regimes. Parameterization and evaluation of the FAO-AquaCrop model for a South African taro (Colocasia esculenta L. Schott) landrace. Evaluation of the AquaCrop model for simulating yield response of winter wheat to water on the southern loess plateau of China.
COUPLING HYDRUS 2D/3D AND AQUACROP MODELS FOR SIMULATION
- Introduction
- Methodology
- Experimental sites
- Modelling
- Development of optimum irrigation schedules
- Assumptions
- Results and Discussion
- Irrigation thresholds and scheduling
- Soil water balance
- Grain yield and biomass
- Water productivity
- Conclusion
- References
2018) combined DSSAT and HYDRUS 1D in soil water balance simulation for peanut and soybean under rainfed systems. The simulated scenarios for the two locations were based on the following assumptions: a) Planting date was in October as recommended by the Department of Agriculture (DAFF, 2014). HYDRUS 2D/3D, being suitable for simulating soil water dynamics, was used to generate optimized irrigation schedules and simulate actual evaporation.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
Therefore, the hypothesis that the response of cowpea to water availability under MTI was similar to that of SDI was partially true. This showed that the AquaCrop model can be used satisfactorily in evaluating the response of cowpea to different water regimes. The simulation of cowpea yield response to optimal water conditions at MTI was simulated using a symbiotic combination of HYDRUS 2D/3D and AquaCrop models.
Recommendations
It was determined that MTI can best be designed as intermittent irrigation, where water is supplied every 2 days instead of the conventional one, where water is supplied continuously. This indicates that AquaCrop and HYDRUS 2D/3D could be used together for optimal water management. The yield and biomass for the two locations were similar, indicating that irrigation can be used to stabilize production in agriculture.
HYDRUS-2D simulation of soil moisture model with horizontal wet irrigation and analysis of its influencing factors Transactions of the Chinese Society of Agricultural Engineering. Numerical simulations of water movement in a subsurface drip irrigation system under field and laboratory conditions using HYDRUS-2D. Effects of buried depth and pressure head on wetland water movement during wet irrigation.
APPENDICES
Appendix A: Calibration of Sensors
Appendix B: Soil Water Retention Characteristics
