2.3. Estimation of crop water requirement
Reference crop evapotranspiration (ETo) was calculated on a daily basis using Penman–Monteith's semi-empirical formula (Allen et al., 1998). The actual evapotranspiration was estimated by multiplying reference evapotranspiration with crop coefficient values (ETc = ETo × Kc) for different months based on crop growth stages. Potato is about 130 days duration crop and it may divide into four stages, namely initial, 25 days; developmental, 30 days; middle, 45 days; and tuber maturity, 30 days. The crop coefficient during the crop season was 0.50, 0.65, 1.15 and 0.75 at initial, developmental, middle and tuber maturity stages, respectively (Allen et al., 1998). The ETo value during the irrigation differential period was 479 mm and ETc was 362 at the full irrigation supply. The total actual amount of irrigation water applied, taking initial watering into account, ranged from 328 mm in W1.0 to 131 in W0.4, respectively. During the initial stage of growth, when tuber formation had not yet started, potato plants up to developmental stage were irrigated daily to encourage establishment, but thereafter irrigation frequency was running every 2 days. The irrigation treatments started at 14 DAP and ended at 120 DAP, respectively (15 days before maturity and harvest to prevent secondary growth).
2.3. Estimation of crop water requirement
Reference crop evapotranspiration (ETo) was calculated on a daily basis using Penman–Monteith's semi-empirical formula (Allen et al., 1998). The actual evapotranspiration was estimated by multiplying reference evapotranspiration with crop coefficient values (ETc = ETo × Kc) for different months based on crop growth stages. Potato is about 130 days duration crop and it may divide into four stages, namely initial, 25 days; developmental, 30 days; middle, 45 days; and tuber maturity, 30 days. The crop coefficient during the crop season was 0.50, 0.65, 1.15 and 0.75 at initial, developmental, middle and tuber maturity stages, respectively (Allen et al., 1998). The ETo value during the irrigation differential period was 479 mm and ETc was 362 at the full irrigation supply. The total actual amount of irrigation water applied, taking initial watering into account, ranged from 328 mm in W1.0 to 131 in W0.4, respectively. During the initial stage of growth, when tuber formation had not yet started, potato plants up to developmental stage were irrigated daily to encourage establishment, but thereafter irrigation frequency was running every 2 days. The irrigation treatments started at 14 DAP and ended at 120 DAP, respectively (15 days before maturity and harvest to prevent secondary growth).
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