Standardization of critical boron level in soil and leaves of coconut palms grown in a tropical Entisol

Abstract

An experiment was conducted to standardize the critical boron level in soil and leaf samples of coconut palms grown in a typical Entisol of the Onattukara region of Kerala, India. Graded levels of boron as borax were applied at 0, 6, 12, 18 and 24 g per palm per year in four split doses. The critical boron level in soil and leaves was standardized using the following methods: the Cate and Nelson graphical (CN) method, the Mistcherlich equation (ME), and the quadratic plateau response (QP) method. In the CN method, the critical level of boron in soil and leaves was 0.48 mg kg-1 and 11.5 mg kg-1, respectively. In the ME model, the critical boron level in soil and leaves was 0.46 mg kg-1 and 7.55 mg kg-1, respectively. In the QP response curve, the critical level of boron in soil was estimated to be 0.87 mg kg-1, and in the leaf, the critical level was found to be 13.27 mg kg-1. Because the level estimated via the graphical method and by the Mistcherlich equation is similar with regard to the soil boron, 0.48 mg kg-1 can be considered as the critical boron level in soil. Regarding the critical boron level in the leaf, values estimated via the CN method and the QP response curve are in proximity, and, hence, the critical boron level in leaf is 13.27 mg kg-1. These results suggest the application of 160 g of borax in four split doses when the levels of boron in soil and leaves fall below the estimated critical values for better use efficiency.