Halevy, J., Department of Soil Chemistry and Plant Nutrition, ARO, Research Scientist, The Volcani Center, Bet Dagan, Israel
Kramer, O., Senior Extension Officer, Extension Service, Afula District, Israel

A field experiment was carried out for two years on a grumusol (Typic chromoxerert) soil at Merhavya, Israel, to study the influence of different concentrations of N in soil solution on the growth and yield of drip-irrigated cotton (Gossypium hirsutum L.) var. 'Acala SJ-2'. The N-concentrations in the soil solution used were: 0, 12.5, 25, 50, 75 and 100 ppm N. The soil was analyzed for moisture and NO3-N every two weeks and the concentration of NO3-N in the soil solution was calculated. When the NO3-N concentration was less than the above-mentioned levels, N-fertilizer was added in the irrigation water to match these concentrations. If the tested soils showed higher concentrations, no N fertilizer was applied. The maximum yields of seed cotton obtained were 6.3 ton h-1 in the first year, and 5.7 ton ha-1 in the second year. Concentrations below 25 ppm N in the soil solution reduced the cotton seed and lint yields, but concentrations of 50 ppm N and above did not increase the yields and sometimes even decreased them. Application of more nitrogen caused excessive vegetative growth and less seed-cotton and lint. The results show that soil nitrate analysis during the cotton season can be used to monitor the N supplied by drip irrigation. © 1986 Springer-Verlag.