Parametrizing Simple Model between Yield and Evapotranspiration for Amaranthus cruentus under Drip and Sprinkler Irrigations

Amaranthus cruentus, an annual vegetable crop, is known to be highly productive under rain-fed conditions and during the dry season when supplied with water. However, for good water management, there is need to accurately quantify the water consumed by the crop. This paper investigates the water use and biomass yield of differentially irrigated Amaranthus cruentus at different developmental stages: emergence/vegetative, fruiting and maturity. Field experiments were conducted between January and March of 2005 and 2006. The experiment was a 2×3×3 combination of two irrigation methods (drip and sprinkler systems) three crop phenological stages (Emergence/vegetative, fruiting and maturity), and three water stress levels. A randomized complete block design (RCBD) was adopted. Soil moisture storages within the root zone depth (10-30 cm) of Amaranthus were highest (13.86 and 13.23 cm) on drip plots at the 71 day of year (DOY) during the 2005 and 2006 experiment respectively. This has direct influence on the evapotranspiration of the crop. The highest evapotranspiration were 12.87 and 9.96 mm day-1 during 2005 and 2006 respectively on plots irrigated under drip system. The highest and the lowest crop yield were 13.94 and 4.2 tonha-1, respectively in plots irrigated under drip irrigation system, and 11.16 and 3.39 tonha-1, respectively in plots irrigated under sprinkler system. The non-linear model used for yield prediction showed good agreement with the field data with r2 = 0.94 and 0.74 for A. cruentus grown under drip and sprinkler irrigation systems, respectively. The correlation coefficient (r) between relative yield and relative evapotranspiration were 0.78 and 0.74 for crop under drip and sprinkler irrigation systems, respectively.