Assessment of critical limit of boron for cowpea in piedmont soils of Arunachal Pradesh

A study was conducted with 24 piedmont soils of Arunachal Pradesh (India) to estimate the critical limit of available boron (B) in soil and cowpea plant for predicting the response of cowpea (Vigna unguiculata L. Walp.) to B application. The critical concentration of available B in these soils was established by graphical procedure at 0.48 mg kg^?1 for soil and at 24.5 mg kg^?1 in the plant tissues. Soil containing available B below the critical limit responded appreciably to B fertilization. A negative response to B application was also observed in soils at higher level of available B. The average dry matter yield increased with the increasing level of B application up to 1.5 mg kg^?1. The yield response to B application in cowpea on B deficient soils was 34.5%. Based on the critical value of 0.48 mg kg^?1, 10 soils were rated to be adequate and 20.0% soils belonging to this category responding to B application, whereas 85.7% soils below the critical value showed a positive response to B application. The hot water soluble B was significantly and positively correlated with organic carbon, cation exchange capacity and clay contents and negatively correlated with pH, silt and sand contents of soils.