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Influence of Salinity and N-P Fertility Levels on Mineral Content and Growth of Sorghum in Sand Culture¹

Plant growth is characteristically depressed at certain levels of salt concentrations yet it sometimes responds to fertilizers even though growth depression can be expected to reduce nutrient requirements and even though fertilizer application increases salinity to some degree. This study was designed to examine tension zones involving interactions between nutrient supply (N and P) and salt concentrations.

Grain sorghum (Sorghum bicolor (L.) Moench) chosen for this study because it is commonly grown in regions of irrigated agriculture where soil salinity is often a problem. Plants were grown to maturity in automatically operated sand culture equipment at two levels each of N and P, each subjected to added Ca-Na chloride salinity levels of zero, medium (EC = 10 mmho/cm) and high (EC = 20 mmho/cm).

Vegetative growth was depressed to about 50% of control at both medium and high salinity, while grain production was depressed to about 35% at medium salinity and to almost none at high salinity. Chemical composition of leaves, in addition to familiar dilution effects and ion competition, revealed increased accumulation of Ca, Na, and CI related to high level of P supply, at high salinity only. When sorghum was grown at salinity levels that permitted reasonable grain production, maintenance of optimum soil fertility was important. However, the required level of nutrient supply was lower in saline than in nonsaline soils because of reduced growth. A critical balance between optimum nutrition and increased salinity from applied fertilizers was also involved.

Key Words: Mixed Ca-Na chloride salinity • Dilution effect • Ion competition

² Formerly graduate student, now postdoctoral fellow, and professors of soil science and plant nutrition, respectively, Univ. of California, Riverside, CA 92502.

Received for publication July 11, 1974.