Determination of Actual Evapotranspiration and Crop Coefficients of Tropical Indian Lowland Rice (Oryza sativa) Using Eddy Covariance Approach

Accurate estimation of evapotranspiration of rapeseed is essentially required for irrigation scheduling and water management. The present study was undertaken during 2015-16 and 2017-18 in ICR Farm, Assam Agricultural University, Jorhat to determine the crop coefficients (Kc) and estimate evapotranspiration of rapeseed using lysimeter and eight reference evapotranspiration models viz. Penman-Monteith, Advection-Aridity (Bruitsaert-Strickler), Granger-Gray, Makkink, Blaney-Criddle, Turc (1961), Hargreaves-Somani and Priestly-Tailor models. During 2015-16, the crop coefficients were developed by these models. Actual evapotranspiration was determined by three weighing type lysimeters. During 2017-18, evapotranspiration was estimated by multiplying reference evapotranspiration with Kc derived by different models and compared with actual evapotranspiration estimated by lysimeter during similar growing periods. All the models except Turc (1961) showed less than 10% deviation between actual and estimated ET. The estimated evapotranspiration using Penman-Monteith and Priestly-Tailor reference evapotranspiration recorded the lowest MAE and RMSE. The study revealed that estimated evapotranspiration using Penman-Monteith reference evapotranspiration gave the best estimate of evapotranspiration of rapeseed followed by Priestly-Tailor. The crop coefficients for initial, mid and end stages were 0.83, 1.20 and 0.65, respectively for Penman-Monteith and 0.70, 1.05 and 0.55, respectively for Priestly-Tailor.These results can be used for efficient management of irrigation water for rapeseed.

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Annual Evapotranspiration and Crop Coefficients of Ligustrum japonica Growing in Three Container Sizes

HortScience ◽

10.21273/hortsci.33.3.512c ◽

1998 ◽

Vol 33 (3) ◽

pp. 512c-512

Author(s):

R.C. Beeson

Keyword(s):

Reference Evapotranspiration ◽

Actual Evapotranspiration ◽

Rooted Cuttings ◽

Supplemental Irrigation ◽

Mean Size ◽

Crop Coefficients ◽

Marketable Size

The objective of this study was to determine crop coefficients (KC) for Ligustrum japonica growing in three container sizes using the Penman equation to calculate reference evapotranspiration (ETR). Rooted cuttings were transplanted into 3-liter containers and upcanned as needed into 10- and 23-L containers. Production was scheduled such that a series of plants in each container size were about 2 months from commercial marketable size every 4 months. Beginning 1 Jan. 1995 until 31 Dec. 1996, three uniform plants of each size were suspended in weighing lysimeters and surrounded by similar size plants filling an area 3.7 by 4.9 m. Plants within each area were overhead irrigated at 2000 h as needed, based on a 30% moisture allowed deficit. Plants were exchanged every 4 months such that the annual mean size was that of a marketable plant. Actual evapotranspiration (ETA) was calculated from half-hour measurements of each plant's weight and adjusted for rainfall. From these and daily calculated ETR, KC were determined for each size of container. KCs ranged from 1.06 to 1.50 when ETA was converted to mm/day based on allocated bed space. Comparisons of volumes of supplemental irrigation to ETA and effects of assumptions required in converting ETA to mm/day will be discussed.

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