Wednesday, November 7, 2007
296-12
Boron Toxicity in Irrigated Cotton.
J. N. Ahmed1, M. Abid1, and Khandakar Islam2. (1) Bahauddin Zakaria University, New Multan, Multan, Pakistan, (2) Ohio State University - OARDC, OSU South Centers, 1864 Shyville Rd, Piketon, OH 45661-9749
Boron (B) toxicity, a nutritional disorder, is increasingly recognized in irrigated cotton plants under arid and semi arid climates. This is probably caused by high B fertilization, irrigation water containing B or natural B contents in soil. The response of cotton (CIM-473) to variable rates of B fertilization was investigated under sand and agricultural soil culture conditions. In sand culture, 15 treatments (control, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 40, 50 mg B kg-1 using boric acid) were imposed on cotton 30 days after sowing (DAS). However, in soil culture, only 10 treatments (control, 5, 10, 15, 20, 25, 30, 35, 40, 50 mg B kg-1) were applied on cotton 30 DAS. Total number of leaves, number of nodes, plant height, and leaf chlorophyll content of cotton plants were recorded 60 DAS. Results showed that there was a linear reduction in growth parameters of cotton with increasing B concentration in the media. There was a significant difference in B content among lower, middle and upper leaves with lowest B concentration in upper leaves compared to lower and middle leaves, respectively. On average, shoots contain more B than roots but lower than leaves. Leaf chlorophyll concentration decreased with increasing B levels in the media. Toxicity symptoms of B appeared first on older leaves of cotton and successive leaves became affected in sequence. Boron applied ³ 5 mg kg-1 showed toxicity symptoms on cotton leaves. Other plant growth parameters such as plant height, root length, and dry matter yield decreased significantly with increasing B levels.