Cotton (Gossypium hirsutum L.) grown in clay soil received high rate of P fertilizer and amended with crop residues (CR) is expected to suffer from B deficiency. The aim of this work is to explore the response of cotton plants grown in such soil to foliar application of B. Three rates of B foliar application (0, 0.12 and 0.24 kg B fed-1 as boric acid), four rates of P fertilizer (0, 100, 300 and 500 kg superphosphate (SP) fed-1, and two levels of crop residues (CR) were tested in an experiment carried out at the Experimental Farm of Assiut University, Assiut, Egypt, during two successive growth seasons of 2004 and 2005.
Incorporation of CR in soil enhanced the effect of P fertilization on increasing Olsen’ P in all P treatments. Phosphorus increased the B availability in soil. In contrary with the low rate of P fertilization (100 kg SP fed-1) the higher rate of SP (500 kg SP fed-1) significantly increases the amounts of extractable B in soil. The application of CR changed the effect of P application on available B to be significantly synergistic in all samples and with all P fertilization rates. Releasing B into soil during the decomposition of CR could be a good explanation for these results. The analyses of cotton leaves shows that application of P fertilizers alone or combined with CR resulted in decreasing B content significantly in cotton leaves. The results indicated that in spite of the effect of CR on increasing B availability in soil, CR either alone or combined with P fertilization decreased B content in cotton leaves.
Foliar application of B at rate of 0.12 kg Bfed-1 overcome the adverse effects of P fertilization and resulted in increasing the number of opened bolls and the boll weights, and thus increased the seed cotton yield 12.2% over control. Spraying of B at rate of 0.12 kg B fed-1 increases the seed cotton yield 14.2 and 10.4% over control without or with CR incorporation, respectively.