DYNAMIC MODELING OF DAILY WATER USE BY SUMMER PEARL MILLET ' (Pennisetum americanum L.)
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Date
1995
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AAU, Anand
Abstract
Crop water use is a complex function of the climatic conditions, stage of the crop development and the soil water content. Models have been developed earlier using various approaches and levels of details to improve the prediction of evapotranspiration. Functional models with some empiricism can be used for routine applications than the mechanistic models. Transpiration from the pearl millet was found to be strongly influenced by leaf area than by stomatal conductance. Field experiments during the summer season of the years 1994 and 1995 were conducted with pearl millet cv. GHB-30. The experiments were laid out in split-plot design, with three dates of sowing as the main plot and four irrigation levels as the sub-plot treatments which were replicated four times. The results obtained in this investigation revealed that, air temperature had a profound influence on the growth and development of summer pearl millet. The optimum date of sowing was found to be February 15th , which would provide optimum environmental conditions for the growth and development of the crop. Different dates of sowing did not show any significant effect on the grain yield. Irrigating the crop at 25% depletion of available soil moisture gave the highest grain and biomass yields but its WUE was lower than that for the other irrigation levels. Pearl millet required about 310 GDD in summer season to build considerable GLAI and about 800 GDD to attain the maximum GLAI. A second-order polynomial was developed for estimating GLAI using the accumulated GDD. The FAO Kc, values had over-estimated ET rates and a second-order polynomial was developed to estimate daily Kc values from the accumulated GDD for non-stressed pearl millet. The rate of ET in pearl millet was found to decrease with an increase in soil moisture deficit and approached zero at a soil moisture depletion of 65% of the available soil moisture. PLANTGRO and MCD models when evaluated against the field data collected through this experiment, predicted ET reasonably better for nonstressed treatments than for stressed treatments. Of the two models, the MCD model predicted better for stressed condition than the PLANTGRO model. The functional relations for the PET estimation and root water uptake in the MCD model needed substantial modification. The separation of the PET in the PLANTGRO model did not suit the summer pearl millet. A one-day time step model BAJRAWAT had been developed in the 'C' language during the course of the present study, and was made User-friendly. Irrigation amount and the PET being its main driving forces, the partitioning of PET into soil evaporation and transpiration had been accomplished in BAJRAWAT by GLAI. The actual evaporation and transpiration depended on the availability of water in the surface soil and in the root zone and also on the depth of root penetration. The evaporation was assumed to take place from the surface soil only and the soil was further divided into four layers, from which water was assumed to have been removed by transpiration and drainage. Infiltration was assumed to have been taking place depending on the amount and the location of water already in the soil layers. The transpiration was computed as a function of GLAI and the available moisture in the root zone. The development of GLAI was considered to be controlled by thermal time and a moisture stress factor. The BAJRAWAT model when validated along with PLANTGRO and MCD models predicted ET better than the latter two models. The relative transpiration of summer pearl millet was found to be more closely associated with relative dry matter yield than with the relative grain yield
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AGRICULTURAL METEOROLOGY, A STUDY