Effects of NaCl and Manganese in Irrigation Water on Cotton Growth and Nutrient-Element Contents.

Brackish water is widely distributed in many arid and semi-arid regions of the world, and the NaCl and trace element contents in brackish water are higher than that in fresh water. Cotton (Gossypium hirsutum L.) is likely affected by simultaneous NaCl and Mn toxicity stress when irrigated with brackish water. Although NaCl and Mn stress and their independent effects on plant growth and yields have been extensively investigated, the combined effect of NaCl and Mn on nutrient element contents and cotton growth is unclear. Sand culture pot experiments were conducted, with 30 orthogonal tests containing six NaCl and five Mn concentration levels in a greenhouse. Cotton growth parameters such as height, root dry weight, stem dry weight, single boll dry weight, lint percentage, and element contents were measured and analyzed. The results showed that NaCl promoted the vegetative growth of cotton when the electrical conductivity (EC) of irrigation water was in the range of 2.90 to 6.11 dS m^-1, but inhibited vegetative growth when the EC further increased from 6.11 to 7.17 dS m^-1. Reproductive growth generally increased with the increase of EC in the irrigation water from 2.36 to 7.17 dS m^-1. A Mn concentration in irrigation water of less than 18 µmol L^-1 and higher than 36 µmol L^-1 inhibited cotton growth and yields. Applying the Abbott method for the pot experiments on cotton generally indicated an antagonistic relationship for the combined effect of NaCl and Mn. Cotton growth and yields were directly affected by the element contents observed in cotton plants. NaCl showed different effects on the absorption of nutrient elements in cotton. The nutrient element effect on cotton growth varied when the NaCl contents in the IW differed.