S T U D Y O F E V A P O T R A N S P I R A T I ON O F W H E A T C R O P IN V A R Y I NG S O I L M O I S T U R E C O N D I T I O NS
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Date
1991-06-28
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MAHATMA PHULE AGRICULTURAL UNIVERSITY Rahuri-413 722 (Maharashtra)
Abstract
The present investigation to study the evapotranspiration, water use efficiency, and crop coefficient of wheat crop in varying soil moisture conditions was conducted by laying out a field experiment on the Agronomy Farm at College of Agriculture, Pune-5 during the post-rainy season of 1989-90. The objectives of the investigation were to study the evapotranspiration, water use efficiency at different soil moisture depletion levels, to work out the crop coefficient at different growth stages and to schedule the irrigation of wheat crop for optimum yield. The experiment has seven treatments and was replicated two times. The irrigation was given to each treatment as per IW/CPE ratio. The soil moisture was taken just before irrigation with the help of neutron probe. The evapotranspiration (ET) was calculated by using soil moisture depletion method. The various biological observations like leaf number, plant height, total dry matter and its components, leaf area and leaf area index were recorded at various physiological growth stages. The potential evapotranspiration (PET) was calculated by using modified Penman method. The vapour pressure deficit (VPD) was calculated by using psychrometric chart. The data required for calculations of PET and VPD like maximum and minimum temperature, bright sunshine hours, open pan evaporation, vapour pressure etc. was collected from the Central Agricultural-Meteorological observatory located on the farm of the College of Agriculture, Pune-5. The experimental field was 400 meter away from the observatory. The water use efficiency was calculated by taking the ratio of total dry matter produce to consumptive use. The crop coefficient was calculated at different physiological growth stages by taking the ratio of AET to PET. Evapotranspiration increased with the increase in number of irrigations as per IW/CPE ratio. Treatment with IW/CPE of 1.0 which was given five irrigations showed the highest evapotranspiration while the treatment with IW/CPE of 0.4 which was given two irrigations showed the lowest evapotranspiration. The other treatments were in between the above two treatments. Growth characters such as plant height, number of tillers, number of functional leaves, leaf area and dry matter were observed to be by and large proportionate with increase in irrigation number. Yield contributing character such as length of earhead, number of spikelets, number of grains, grain weight per earhead and thousand grain weight also increased as the number of irrigations increased. Treatment with IW/CPE of 0.7 which was given three irrigations, shows the highest water use efficiency. Crop coefficient values are useful in scheduling irrigation to wheat at various growth stages. Increase in evapotranspiration gives more dry matter production and thus yield. In this experiment IW/CPE of 1.0 gave highest potential yield. But the increase in number of irrigations beyond certain limit may not be profitable when the cost of irrigation is taken in to account. In the present study treatment with IW/CPE of 0.7 was found to be the best in respect of water use efficiency.
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