Performance of physically based models in designing rain water harvesting crop systems
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Date
1996
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Publisher
Sokoine University of Agriculture
Abstract
Three physically based models were used to simulate the effects of rain water harvesting on Sorghum yield in semi-arid Hombolo, Dodoma, Tanzania over three seasons. The models are Runoff estimation Model (THIRST) Crop Growth Model (PARCH) Soil water availability Model Different components of the. models relevant to rain water harvesting were combined to form a complete model to estimate runoff, soil moisture content and crop yield. Rain water harvesting with storage was simulated by supplying runoff collected and stored in reservoirs as supplementary irrigation water for days when soil moisture content was below the allowable value. The performance of the models was tested by comparison between estimated and measured values using regression analysis. There is a fairly good agreement between observed and simulated runoff for a 10 x 20 m catchment with r: = 0.804. .2 For a 10 x 40 m catchment the correlation between measured and estimated runoff is relatively low with r2 = 0.712.3 The simulated moisture trend is the same when compared to the measured soil moisture with correlation coefficient r2 = 0.607, however the model tends to overpredict the soil moisture content. The trend of simulated sorghum yields direct show relationship of increase in yield due to increase in water quantity and distribution with a correlation coefficient 0.622. r2 the model show. inadequacy in predicting the upper limit of water input and hence the effects of water logging on crop yield. From the study it is recommended that: the runoff sub-model. Should incorporate a subroutine for simulating surface depression storage resulting from the changing surface micro relief. rain intensity files should be provided where possible for more reliable results, and further work should be done on the simplified rainfall disaggregate to develop more reliable results. validation of Raws and Brakensiek (1989) pedo transfer functions for soils of semi-arid areas is required. The soil water balance sub-model of modified to PARCH should be simulate the lateral soil water flows, infiltration and drainage with greater perfection. the PARCH model should develop the ability to simulate the effects of anaerobic in the root zone with greater perfection by either reducing establishment during early growth, or by reducing root uptake of water during later growth stages.
Description
Dissertation
Keywords
Physically based models, Designing rain water harvesting, Harvesting water, Crop systems, Harvesting, Harvesting crop systems