Blends of castor meal and castor husks for optimized use as organic fertilizer

Abstract Production of oil from castor ( Ricinus communis ) generates two main by-products: husks and meal. For each ton of castor oil, 1.31 ton of husks and 1.13 ton of meal are produced. Castor meal is the most important by-product due to its high nitrogen content, and presently it is predominantly used as an organic fertilizer. This greenhouse study aimed to find optimized blends of castor husks and meal as organic fertilizer for growth of castor plants. The by-products were mixed to sandy soil in the doses (v:v) of 0 + 10%, 2.5 + 7.5%, 5.0 + 5.0%, 7.5 + 2.5% and 10.0 + 0% of castor meal and castor husks, respectively. At 50 days after sowing, data was taken on plant growth and shoot nutrients content. Blends of castor meal and castor husks used as fertilizer promoted substantial plant growth up to the dose of 4.5% (in volume) of meal. Doses higher than 4.5% caused reduction in plant growth and even plant death. It seems that rapidly mineralizing nitrogen from the castor meal is the reason for both the intensive plant growth in low doses, and the reduction of plant growth in high doses due to excessive mineral N. Increments in castor meal dose resulted in increased N and Ca shoot contents. Other macronutrients were not influenced. Castor meal is a good organic fertilizer, due to its high N and P contents, but blending with castor husks is not necessary.