Determination of evapotranspiration and crop ...

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Rice crop (variety Jaya) was transplanted in both lysimeters at row spacing of 20 and. 15 cm between plants on 4 July in 1994 and 30 days old seedlings were ...
Agricultural Water Management 45 (2000) 41±54

Determination of evapotranspiration and crop coef®cients of rice and sun¯ower with lysimeter N.K. Tyagi (Director), D.K. Sharma (Senior Scientist)*, S.K. Luthra (Senior Scientist) Central Soil Salinity Research Institute, Karnal-132001, India Accepted 9 August 1999

Abstract Lysimeter experiments were conducted on rice during rainy season (July±October) and sun¯ower during summer seasons (March±June) in a set of two electronic weighing type lysimeters of 2 m  2 m  2 m size to measure the hourly evapotranspiration of these crops from 1994 to 1995 at Karnal, India. The average weekly ET of rice varied from 6.6 mm per day at milking stage. The peak ETc was 6.61 mm per day and it occurred 11 weeks after transplanting at reproductive stage when LAI was 3.4. In case of sun¯ower, ETc was 3). During the reproductive phase starting from 9 to 14th week after transplanting, Kc of rice slightly decreased from 1.26 to 1.01 and 1.17 to 1.1 with Penman±Monteith and FAO± Blaney and Criddle methods, respectively because the LAI reduced to less than 1.3 during this stage. Crop coefficient declined rapidly to 0.85 and 0.88 by respective methods during last stage covering the period from 15 to 17 WAT. The computed Kc values by Penman±Monteith method during initial, crop development, reproductive and last stages were 1.15, 1.23, 1.14 and 1.02, respectively and these values estimated by and FAO±Blaney and Criddle and FAO±radiation methods were 1.11, 1.19, 1.09 and 0.97 and 1.1, 1.29, 1.11 and 0.92 in respective stages (Table 5). The estimated Kc values calculated by Penman±Monteith and FAO±Blaney and Criddle during all the stages are closer to the values reported by FAO. 3.3.2. Sun¯ower In the initial stage covering the period from sowing to end of the 3rd week after sowing (WAS), crop coefficients increased from 0.36 to 0.96, 0.30 to 0.88 and 0.42 to 0.99 by Penman±Monteith, FAO-ID-24 corrected Penman and PanE methods, respectively (Fig. 4). The Kc values during this stage increased very slowly because LAI was less Table 5 Values of crop coef®cient derived from different methods for rice (1994) and sun¯ower (average values of 1994 and 1995) Methods

Rice Penman±Monteith FAO-corrected Penman Kimberly Penman FAO±Blaney and Criddle FAO±radiation FAO Sun¯ower Penman±Monteith FAO-corrected Penman FAO±Radiation PanE FAO

Crop stages I

II

III

IV

Average

1.15 1.05 1.18 1.11 1.10 1.1±1.15

1.23 0.88 1.12 1.19 1.29 1.1±1.5

1.14 0.87 1.13 1.09 1.11 1.1±1.3

1.02 0.82 0.99 0.97 0.92 0.95±1.05

1.14 0.90 1.10 1.09 1.11 1.05±1.2

0.63 0.54

1.09 1.11

1.29 1.14

0.40 0.37

0.85 0.79

0.52 0.75 0.3±0.4

1.10 1.15 0.7±0.8

1.32 1.25 1.05±1.2

0.41 0.39 0.55±0.85

0.83 0.88 0.6±0.8

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Fig. 4. Crop coef®cients (Kc) of sun¯ower.

than 0.5 during this period. Crop coefficient increased rapidly from 1.06 to 1.39, 1.05 to 1.28 and 1.1 to 1.38 by respective methods in crop development stage starting from fourth to ninth week after sowing (Fig. 4). The maximum values of crop coefficients were also estimated during the ninth week after sowing mainly because of the LAI was more than 4.0 during this week. Sin (1989) reported that Kc values was curvilinearly related to the LAI. The reproductive phase starting from the 10 to 13th weeks after sowing, crop coefficient decreased slowly upto 0.62, 0.53, and 0.56 by Penman±Monteith, FAO-

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corrected Penman and PanE methods, respectively, could be due to LAI during this week decreased to 2.16. Table 5 summarizes the growth stages wise computed Kc values for sunflower. The estimated Kc values by Penman±Monteith method in the first, second and third stages were 80.0%, 45.3% and 15.1%, respectively, higher than the FAO Kc values. The estimated Kc value was lower than the FAO Kc value by 42.8% in the last stage. On the other hand, observed seasonal Kc value was slightly higher than the FAO Kc value.

4. Conclusions The estimated Kc values for this region during the first, second, third and fourth growth stages for rice are 1.15, 1.23, 1.14 and 1.02, respectively, and the corresponding values for sunflower are 0.63, 1.09, 1.29, and 0.40. The estimated values of crop coefficients for sunflower differ considerably at all the stages from those suggested by FAO, but in case of rice calculated values are very close to the values given by FAO. Local calibration of crop coefficients is therefore an essential.

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