Boron deficiency is expected to occur on Cotton plants (Gossypium hirsutum L.) grown on clay soil received high rate of P fertilizer and amended with crop residues (CR). This work aims to explore the response of cotton plants grown on such soil to B side- dressing. Two rates of B (0 and 2 kg B fed-1 as boric acid), four rates of P fertilizer (0, 100, 300 and 500 kg superphosphate fed-1) and two levels of CR were tested in an experiment carried out at the Experimental Farm of Assiut University, Assiut, Egypt.
Heavy application of superphosphate (500 kg SP fed-1) resulted in increasing hot water extractable B from 1.88 to 2.05 and from 2.68 to 3.01 ppm in soil samples collected at peak bloom of two growth seasons. Incorporation of CR into the soil significantly increased hot water extractable B to as high as 32.4, 26.3 and 43.6% more than the untreated soil samples while it significantly decreased B content in cotton leaves by 17.1, 20.9 and 12.2% in samples collected at peak bloom of the 1st season, peak bloom and 50% open boll of the 2nd season, respectively. With the application of 2 kg B fed-1, there were 38.1 and 57.7% increases in B contents of leaves sampled at peak bloom and 50% open boll growth
stages, respectively, over control.