The effect of bio-fertilizers and a super-absorbent on the quantitative and qualitative characteristics of castor bean (Ricinus communis L.) under water-deficit conditions

The effect of bio-fertilizers and super-absorbents on the modification of water-deficit stress was studied in castor. A field experiment was conducted with a split-plot design based on a completely randomized block design with three replications. The first factor included four levels (70, 100, 130, and 160 mm of evaporation pan A Class) in the main plot; the sub-factor was the application of four bio-fertilizer treatments (Azospirillum, Citrobacter, Azospirillum + Citrobacter, and control); and the superabsorbent at two levels (superabsorbent consumption and control) as a factorial was placed in the sub-plots. With the intensification of the water-deficit stress from 70 to 160 mm of evaporation, the number of seeds per plant, the 1,000-kernel weight, and the oil percentage significantly dropped. All three bio-fertilizer treatments significantly increased the number of grains, 1,000 kernel weight, and oil percentage compared to the control. Citrobacter in all four irrigation levels significantly increased the content of photosynthetic pigments, grin yield, oil yield and proline content and decreased the catalase activity and malondialdehyde content. The application of the super-absorbent under the stress condition of 160 mm significantly raised the content of chlorophyll b, soluble sugar, grain yield, oil yield, and proline compared to the control treatment. Among the combinations of bio-fertilizer and super-absorbent treatments, the highest photosynthetic pigments’ content, grain yield, and oil yield and the lowest catalase enzyme activity belonged to Azospirillum + superabsorbent consumption. However, the maximum soluble sugars and the minimum malondialdehyde content belonged to Citrobacter + superabsorbent.