RELATIONSHIP OF SOIL EXTRACTABLE AND FERTILIZER BORON TO SOME SOIL PROPERTIES, CROP YIELDS, AND TOTAL BORON IN COTTON AND WHEAT PLANTS ON SELECTED SOILS OF PUNJAB, PAKISTAN

Boron (B) is an essential microelement, which is necessary for reproductive organs including pollen tube formation in wheat (Triticum aestivum L.), and flowering and boll formation in cotton (Gossypium hirsutum L.) The study was associated with wheat-cotton rotation in 80 farm fields, belonging to different soil series, in four districts of cotton belt of Punjab, Pakistan to assess concentrations of extractable B in soils [0.05 M hydrochloric acid (HCl) extractable B], and added fertilizer B and their relationship to some soil physico-chemical properties [pH, organic matter (OM), calcium carbonate (CaCO3) and clay content], yields and total B concentrations in wheat and cotton plants. All soils had alkaline pH (7.45 to 8.55), high CaCO3 content (2.14 to 8.65%), less than 1.0% OM (0.33 to 0.99%), low plant available-P (Olsen P less than 8 mg kg-1 soil) and medium ammonium acetate extractable potassium (K) (< 200 mg K kg-1 soil). Of the 80 soil samples, 65 samples (81%) were low in available B (<0.45 mg B kg-1, ranging from 0.11 to 0.43 mg B kg-1) Of the corresponding 80 plant samples, leaves B concentrations were below critical levels (<10 mg B kg-1 for wheat; <30 mg B kg-1 for cotton) for all the tested samples for wheat and cotton. The regression analysis between plant total B concentrations and soil extractable B concentrations showed strong linear positive relationships for both wheat (R2 = 0.509***, significant at P <0.001) and cotton (R2 = 0.525***, significant at P <0.001). Further regression analysis between extractable soil B and wheat grain yield as well as between wheat leaves total B and wheat grain yield also depicted strong linear relationships (R2 = 0.76 and 0.42, respectively). Boron fertilizer demonstration plots laid out at farmers fields low in extractable B, in each district not only enhanced grain yields of wheat crop but also contributed a significant increase towards seed cotton yield of succeeding cotton crop through residual B effect. In conclusion, the findings suggest that many soils in the cotton belt of Punjab may be low in extractable B for wheat and cotton, especially when these crops are grown on low OM soils with high CaCO3 content.