Simulation of soil moisture profiles in a post-rainy season sorghum crop | |
| Author | Lakshminarayanan, R. |
| Call Number | AIT Thesis no.AE-91-59 |
| Subject(s) | Sorghum Soil moisture--Mathematical models |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | The purpose of the study is to simulate soil moisture profiles in a post - rainy season sorghum crop on a vertisol using water balance model, to validate the model and assess the need for supplemental irrigation in case of water stress in the crop. Crop and soil parameters required for the study were extracted from a Water Interaction with Nitrogen Experiment in which crop water uptake was parametrised in 6 levels of nitrogen and two water regimes (Rainfed and Irrigated). The water balance model chosen for the study is a combination of a crop growth model, SORGF (ARKIN 1978), evapotranspiration model (RITCHIE 1972) and a water balance model suggested by STINSON (1979). From the initial experimental runs of the model using daily weather and fie l d data, it was found that simulated results could be improved if the crop growth aspects of the model were modified. Revisions to the model were made by making observed leaf area as model input instead of using values simulated by the model. Simulated output for the rainfed treatments showed good agreement with observed value in water use of layers 30 to 150 cm. It showed excessive water use in the top 5 to 30 cm layer. In the deep layers of 150 to 180 cm there was at least 20 mm of available water even at late growth stages 3 and 4 of the crop when the roots had fully developed and reached these layers. In the stage-wise analysis of crop water use, it was found that in growth stage 2, there was an underestimation of water use. In the irrigated treatments the trend of water use in the crop stages and from the soil profile was similar to that of the rainfed treatments. However, an underestimation of total water use was seen in all irrigated treatments. Simulated results were better in the 0, 30, 60 N than higher N levels in the two water regimes. The crop showed no moisture stress in the rainfed treatments evident from high values of water stress coefficient (WATSCO) ranging around 0.98 at 67 DAE and 0.6 at 97 DAE. The crop consumed around 180 mm of water in the rainfed treatments and 340 mm in the irrigated treatment giving a grain yield of 2.8 and 3.6 T/ha respectively. Based on the evaluation of the model it was concluded that the revised model was reliable and its application in the rainfed treatment yielded better results than in the irrigated treatment. Underestimation of water use was related to the underprediction of evapotranspiration by the model which needs further validation. The overuse of water was attributed to the root growth model which increased root activity in the top 5 to 30 cm layer. As the crops showed no water stress even at final stages of crop growth it could be suggested that supplemental irrigation was not necessary to achieve a normal grain yield under the the post-rainy condition. |
| Year | 1991 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Murty, V.V.N.; |
| Examination Committee(s) | Koga, Kiyoshi;Nielsen, J.M.; |
| Scholarship Donor(s) | Canadian International Development Agency (CIDA); |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1991 |