Growth, yield, and fatty acids as affected by water-deficit and foliar application of nitrogen, phosphorus, and sulfur in castor bean

Castor bean (Ricinus communis L.) has not been well studied despite its use in medicine. The objective of this investigation was to determine the effect of foliar application of nitrogen (N), sulfur (S), and phosphorus (P) on growth, yield, and fatty acid composition of oil in castor bean grown under normal and water-deficit conditions. All the studied traits were significantly affected by water-deficit stress, except stearic acid. Water stress decreased plant height, seed number per plant and 1000-seed weight as well as seed yield, oil percentage, and oil yield. Oil content was the only trait that was affected by foliar application of nutrients; and the maximum (41.33%) and minimum (37.33%) values were obtained for P and N application, respectively. All fatty acids, except linolenic acid, were significantly affected by foliar application of nutrients. All fatty acids showed a significant irrigation by nutrient interaction. This interaction was also significant for sub-branch numbers and inflorescence growth rate. The highest sub-branch number (1.87 per plant) and inflorescence growth rate (6.01 g/day) were achieved under full irrigation and foliar application of N. The highest ricinoleic acid (87.35%) and oleic acid (5.54%) concentrations were obtained under full irrigation and foliar application of N and S. Water-deficit stress increased linoleic and palmitic acid content, which are important determinants of crop quality. In general, water availability, especially at seed-filling stage and foliar application of P and S played a key role in increasing seed and oil yields as well as in improving oil quality.