Effects of pH, P, and irrigation frequency on the yields and mineral composition of sugar cane grown under saline conditions

Segovia Rojas, Antonio Jose
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In a field experiment the effects of irrigation frequency, S application (pH) and P fertilization on the yields and mineral composition of sugarcane grown under saline conditions were investigated. Sugarcane variety H50-7209 was grown for 11 months in a saline field of Pioneer Mill Co. in Lahaina, Maui, and irrigated with saline water (6 mmhos/cm). Dry weight yields were significantly increased by daily irrigation, P fertilization and S application. Sulfur application reduced the concentration of K and Mg and increased the concentration of Mn in the leaf sheaths. Phosphorus application reduced sheath-Cl concentration, but had no effect on P concentration in the sheaths or 5th internode. Sulfur application also lowered soil pH and reduced exchangeable Mg and K levels, but did not affect exchangeable Na percentage (ESP) or soil electric conductivity (ECe) during the experiment. Heavy rainfall increased soil pH, but reduced ESP and ECe down to the 45 cm depth. Exchangeable Na percentage was more drastically reduced by rainfall when S was applied than when S was not. A greenhouse experiment was conducted with the same sugarcane variety, which was grown in a mixture of equal parts of perlite and vermiculite for 3.5 months. The treatments which were imposed for 2 months, consisted of factorial combinations of three osmotic potentials (OP), 0.05 (control) -2.0 and -4.0 bars established with 2 salts, NaCl and Na2S04; 3 concentrations of P in solution 1.7, 2.5 and 3.3 ppm, and also 2 pH levels, 5.0 and 7.0. Decreasing OP resulted in a significant reduction in dry weight, fresh weight, spindle growth, leaf osmotic potential (leaf ψs) and relative turgidity (RT), but a significant increase in stomatal diffusive resistance (Rs). The effects of OP on these plant parameters were greater with Na2SO4 than with NaCl. Leaf ψs decreased in proportion to OP for both salts indicating complete osmotic adjustment. Evidence of specific ion effects of 804 and/or Na was provided by the greater reduction in growth with Na2SO4 than with isosmotic concentrations of NaCl. Decreasing OP reduced Ca and Mg concentrations in the leaf sheath to deficiency levels. This reduction was greater with Na2SO4 than with NaCl, probably due to reduced uptake of Ca and Mg, as a result of the higher Na concentration in Na2SO4 than NaCl or to lower Ca and Mg activities in the 804 than CI salts.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1979.
Bibliography: leaves 145-157.
xii, 157 leaves ill. 29 cm
Soils, Salts in -- Hawaii -- Lahaina, Saline irrigation, Sugarcane -- Fertilizers -- Hawaii -- Lahaina, Sugarcane -- Irrigation -- Hawaii -- Lahaina
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Agronomy and Soil Science; no. 1320
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