Seed yield and yield components of castor influenced by irrigation

Abstract

An understanding of yield components is critical to the successful development of castor cultivars (Ricinus communis L.) adapted for different cropping systems (such as mechanical harvest) and growing regions. A detailed study was made on the changes occurring in the castor oil yield components in response to irrigation. The experiments were conducted in Lubbock, TX in 2009 and 2010. Six castor cultivars highly divergent in seed weight, plant height, and number of racemes were cultivated on a subsurface irrigation system with total water (including precipitation) varying from 188 to 897mm. Seeds were harvested, counted, and weighed from individual racemes. Irrigation increased seed yield in all the cultivars. The largest increase in seed yield was observed in the cv. BRS Nordestina which was raised from 232kgha−1 under 188mm (rainfed) to 2758kgha−1 under 897mm of precipitation+irrigation. There were large differences in the magnitude of yield components among cultivars; however, in all cultivars most of the variation in the oil yield was explained by the number of racemes, followed by the number of seeds per raceme, and then by the seed weight. The changes in seed oil content had negligible importance for the determination of the oil yield. For example, comparing plants of the cv. BRS Energia under rainfed and maximum irrigation, the number of racemes increased by 151% (from 7.5 to 18.8 raceme plant−1), the number of seeds decreased 17% (from 72 to 60 seed raceme−1), the seed weight increased 23% (from 235 to 289mg), but the seed oil content increased only 7% (from 462 to 493gkg−1). Three quarters of the seeds matured in 42 days prior to 130 days after planting, while only 8% matured in the following 45 days. A discussion was made on the trade-offs between yield components and the ability of castor plants to adapt to the environment, and how this information can be used to improve the crop management and breeding of this oilseed crop.