WATER USE EFFICIENCY AND YIELD-DEPENDENCES FOR CANOLA (Brassica napus, L.) UNDER IRRIGATION

Abstract

WATER USE EFFICIENCY AND YIELD-DEPENDENCES FOR CANOLA (Brassica napus, L.) UNDER IRRIGATION SUMMARY Worsened water availability conditions caused by the recent processes of climate warming evoke the attention of the scientists to the efficiency of the water use by crops. A useful tool for successful yield and water management is the yield-water relationship. The goal of the paper is to study the interrelations between water, water use efficiency and yield of canola and to calibrate some yield-water dependencies which can be recommended for prediction of the irrigation water amounts and the yield. A moderately early canola hybrid (Brassica napus, L.) was studied for its sensitivity and response to water. A field experiment in Sofia region, Bulgaria, was conducted. Three levels of soil moisture conditions in a chromic luvisols were tested: rain-fed; deficit moisture, managed by 50% deficit irrigation; and normal moisture conditions, managed by full irrigation at a refill point 80% of field capacity. The data from the experiment was processed by analysis of variance and regression analysis. The results show that soil moisture level has statistically significant impact on the yield accumulation. It contributed to increasing the seed yield from a minimum 1.319 Mg/ha at ET=189.0 mm under rain-fed conditions to a maximum of 4.889 Mg/ha at ET=310.0 mm under normal moisture conditions. The maximum irrigation water use efficiency in the experiment was 1.78 kg/m 3 at an irrigation depth of 94 mm, ET=268.5 mm and seed yield-4.189 Mg/ha. The maximum water use efficiency occurs earlier than the maximum yield. By managing 12% less (than needed) seasonal evapotranspiration, the yield losses were only 6%. Elasticity (sensitivity of the crop to water) can be used as an indicator for the critical range of the seasonal evapotranspiration, in which the water use efficiency and the yield are maximal (0≤EWP≤1). The yield response factor K y of FAO linear function was established as 1.52. The parameters of the local Davidov equations were calibrated as a=3.53 and k=1.58 for the single-power equation and q=2.39 and r=13.63 for the two-power equation. Davidov equations Moteva et al 404 are recommended with priority for forecasting of canola yields on the base of the seasonal crop evapotranspiration. INTRODUCTION Worsened water availability conditions caused by the recent processes of climate warming evoke the attention of the scientists to the efficiency of the water use by crops. In the countries, where the water resources are insufficient and unevenly distributed over the territory, yield is predicted by means of models that guarantee high water use efficiency, for the purpose of obtaining economically acceptable production results. A useful tool for successful yield and water management in these models is the yield-water relationship, written down in different analytical forms with calibrated coefficients for particular crops and environments. The yield-water dependences describe the impact of water on the yield accumulation at different water supply levels. Some authors have the opinion that when crop suffers of an evenly distributed throughout the growing season water deficit, the yield is a linear function of the evapotranspiration (Jensen, 1968; Stewart et al., 1973; Doorenbos, Kassam, 1979; Tzakiris, 1981; Varlev, Popova., 1999, Varlev, 2004). Dоwney, 1972 notices that the plants grown in an open field are not exposed to constant water deficit because the evapotranspiration after rain or an irrigation application is the maximum. The water stress starts when the soil starts to dry. The dynamics of the soil water regime is a good reason to think that the yield losses are not a simple function of the evapotranspiration. The results from testing the impact of a proviso regular throughout the growing season water deficit have revealed so far that the yield losses are dependent on the weather conditions. There are many authors who think that the yield-water dependence is a power function, which can be represented by a series of two-incurvation curves with an inflection point. These authors are convinced that except the meteorological peculiarities of the individual years, the yield-water dependence reflects the biological characteristics of the crops (Pare, Olivier, 1969; Davidov, 1982, 2004; Mate, 2001; Zhukov, Davidov, 2003). Stewart et al. (1973) have established that the reduction of the yield is not proportionate to the reduction of the water given by irrigation. Consistent with that, Zhivkov, (1994, 1995) has obtained 4-10%; 9-15%, 14-25 and 51% reduction of corn yield by 20, 40, 60, and 75% reduction of the irrigation depth. By applying 50% irrigation water deficit the yield reduction of corn on haplic chernozems is around 5-6% (Rafailov et al., 1998). The goal of the paper is to study the interrelations between water, water use efficiency and yield of canola and to calibrate some yield-water dependencies which can be recommended for prediction of the irrigation water amounts and the yield in the temperate continental climate conditions of Bulgaria.