Component production of castor bean crop irrigated by different soil water tensions

• Castor bean crop in the autumn–winter, showed the greatest gains in all components.
• Castor bean production decreased linearly with increasing restriction of soil water.
• Water consumption by castor bean throughout the cycle was 486 mm.
• Maximum fruit masses by irrigated castor bean, yielding a total crop of 1994 kg ha−1.

With the growing global energy demand, greater attention has been focused on the production of oilseeds as alternative energy sources, which will necessitate increased production and, correspondingly, increased irrigation. The aim of this work was to study the effect of different soil water tensions on drip-irrigated castor beans (cv Al Guarany 2002). The experiment was conducted in Lavras, Minas Gerais State, Brazil (21°14′ S, 45°00′ W, altitude, 918.8 m) during the period from 1/24/2008 to 8/30/2008. The experiment used a randomized block design with four replications and five treatments, exposing the crop to soil water tensions of 15, 30, 45, 60 and 75 kPa beyond the tension found with no irrigation (Ni), at a depth of 0.20 m. The variables analyzed were as follows: fruit mass of the primary (MPR), secondary (MSR) and tertiary (MTR) racemes; their grain yields (YPR, YSR and YTR, respectively); the total yield (YTC); the 100-seed weight (W100S); and the fruit seed conversion factor (FSF). It was observed that fruit mass and grain yield (MPR, MSR, and MTR and YPR, YSR, YTR, and YTC) decreased linearly with increasing water restriction for all racemes, with soil moisture near field capacity showing the highest values (185, 122, and 39 g raceme−1 and 678, 891, 425, and 1994 kg ha−1, respectively). In the control treatment (Ni), MPR (86 g raceme−1) was similar to MPR at 60 and 75 kPa, and YPR (316 kg ha−1) corresponded to 80% of YTC. In soil water tensions up to 45 kPa, MPR was the most sensitive to water deficit, followed by MSR and MTR, although this pattern inverted at higher tensions.