Evaluation of water use efficiency in upland Rice (Oryza sativa L) Under deficit irrigation)

Abstract

In the light of increasing pressure on limited fresh water resources, the growing world population and increasing greenhouse gas emission, maximizing crop water use becomes an important topic. Considerable research is being done on deficit irrigation. However, there is limited published work elaborating the water use efficiency of upland rice grown under deficit irrigation in Sub-Saharan Africa (SSA). In this study, the growth of upland rice (Oryza sativa L.) was evaluated under deficit irrigation in the greenhouse at the University of Zambia. The aim of the study was to evaluate the effect of deficit irrigation on the growth and water use of upland rice. The study was arranged as a Randomized Complete Block Design (RCBD) with four levels of irrigation water regimes in four replications. NERICA 4 rice, a recommended upland variety grown in Zambia, was used in this study. The irrigation water regimes based on irrigation intervals were: one day (I1), two days (I2), three days (I3), and four days (I4). The irrigation treatments were exerted at the start of the reproductive stage till harvest. Observations made on growth parameters were namely: tiller number, plant height, the number of panicles, aboveground biomass, 1000 grain weight, grain yield, and harvest index (HI). Other parameters included crop consumptive water use (ETc), crop coefficient (Kc), crop response factor (Ky) and water use efficiency (WUE). Irrigation interval significantly affected (p<0.001) plant height, panicle length, aboveground biomass, grain yield, 1000 grain weight and harvest index (HI). These parameters increased with increased frequency of water application. I4 had the lowest actual seasonal consumptive water use (ETa) of 750.1 mm while I1 and I2 were not significantly different with 967.3 mm and 997.1 mm, respectively. The potential maximum yield (Ym) was estimated as the sum of the average and the standard deviation of grain yield in the control (I1) treatment. Yield reduction from Ym ranged from 7.1% for I1 to 81.7% for I4 while evapotranspiration deficit ranged from 3.66% for I2 to 28.68% for I4. Treatment I2 had a smaller relative ET reduction (3.66%) than I1 (10.14%) but bigger relative yield reduction (41.0% and 7.1%, respectively), even though their seasonal ET were not significantly different (P>0.05). At reproductive stage, the average ETc value for I1 was significantly (P<0.001) higher than the one for I2 by 51.8 mm. This lower consumptive water use accounted for the higher yield reduction under treatment I2 as rice is highly sensitive vi to moisture stress at reproductive stage. Irrigation intervals also had highly significant (P<0.001) effect on ETc and Kc at both reproductive and maturity stages. Both ETc and Kc reduced with an increase in the irrigation interval from 341.8mm to 170.8mm and from 2.63 to 1.32, respectively, during the reproductive stage. The average ETc values at maturity stage were 316.4 mm, 374.1 mm, 320.3 mm and 268.0 mm while Kc values were 1.94, 2.30, 1.97 and 1.64 in order of widening irrigation interval. In conclusion, under the conditions of this study, both biomass and grain WUE will increase with increase in irrigation interval and depth of water applied. The results of this study did not show an optimum WUE. Key words: NERICA, Evapotranspiration, Water balance, Yield reduction, Evapotranspiration deficit, Water stress.