Abstract
The study was conducted at the University of Zambia, Research Field Station, Lusaka, Zambia to evaluate the root zone soil water balance under full, and deficit irrigated sunflower. The specific objectives were: 1) to assess the sunflower growth and yield under varying irrigation water regimes; 2) to evaluate the root-zone water balance; and 3) to evaluate the water use efficiency of sunflower. Sunflower (Helianthus annuus, var Milika) was planted in a Randomized Complete Block Design (RCBD) with four irrigated water regimes in four replications. The treatments comprised: treatment (T1) = 30% ETc; treatment (T2) = 54% ETc; treatment (T3) = 65% ETc; and treatment (T4) = 100% ETc. The sunflower crop was irrigated on a weekly irrigation schedule using sprinklers. The measured parameters included: weather data, soil moisture profiles, growth stages (emergence, flowering, maturity), above-ground biomass, and grain yield. The results of the study showed that growth parameter (biomass and seed yield) decreased with a decrease in applied irrigation water. The sunflower seed yield varied from 0.22 to 1.40-ton·ha-1 with an average yield of 0.81-ton·ha-1. The highest grain yield was obtained under treatment (T4), and the least grain in yield harvest was at treatment (T1). The statistical analysis showed significant differences in seed yield among the treatments. The treatments (T1 and T2) were not significantly different (p > 0.05). These results showed that when water deficit was set at 65% and 100% ETc and uniformly distributed throughout the sunflower growth, there were no significant differences in biomass, stover and seed yield. In literature, the allowable soil moisture depletion factor for irrigation scheduling of sunflower is set at 45%. The yield components decreased as irrigation levels decreased for each irrigation interval. The 65% ETc treatment could be recommended for sunflower irrigated in semi-arid regions and be used as a good basis for improved irrigation strategy development under water stressed environment.
Highlights
Irrigated agriculture uses about 72% of available fresh water resources [1]
The results for the components of the root-zone soil moisture indicated that crop water use, drainage below the root-zone and change in soil moisture storage increased with increased irrigation water application The results significantly demonstrated the effects of the amount of the irrigation water as a major factor for obtaining higher yields of sunflower production under Zambian conditions
The maximum average yield was obtained from T4 (100% ETc) treatment as averaging 1.40-ton∙ha−1 which was not significantly different from T3 (65% ETc) treatment indicating definite crop water requirements for sunflower growth
Summary
Irrigated agriculture uses about 72% of available fresh water resources [1]. The world population and its corresponding demand for extra water force the agricultural sector to use irrigated water more efficiently for food production. Defining optimum strategies for sustainable management of available fresh water resources is becoming a priority for the agricultural sector [2]. Promising irrigation strategies in agriculture water management have been observed under deficit irrigation [1] [3]-[10]. The physical model of water flux in the Soil-Plant-Atmosphere Continuum (SPAC) is primarily controlled by the hydraulic resistances in the root, stem, leaf, stomata and cuticular is the basis of our understanding of plant water relations. The SPAC is the pathway for water moving from soil through plants to the atmosphere. The continuous nature of water connection through the pathway is a result of the low water potential of the atmosphere, and relatively higher water potential inside leaves leads to a diffusion gradient across the stoma
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