Effect of salt index, analysis, rate, and placement of fertilizer on cotton

The effects of salt index, analysis, rate of application, and placement of fertilizer on soluble salts in the soil of the root zone and in the plant, on plant emergence, and on final yields were determined in a series of field tests. High salt index fertilizers regardless of analysis gave a higher amount of soluble salts in the root zone soil than did the low salt index fertilizers. Placement, however, was the most important factor influencing the soluble salt content of the root zone soil. Side band placement, as compared with under seed placement, markedly decreased the soluble salts in the root zone. A high rate of fertilizer application increased the soluble salts to some extent. The effect on the soluble salts in the plant was not as marked although the high salt index fertilizers, the low analysis fertilizers, the 700-pound rate, and the under seed placement did all tend to increase the soluble salt content. There was only a fair correlation between the soluble salts in the plant and the soluble salt in the root zone soil. Plant emergence was retarded and imperfect stands resulted from the use of fertilizers with a high salt index. Fertilizers of the same salt index, whether of low analysis as the 6-8-4 and 6-8-8 fertilizers, or of high analysis as the 9-12-6 or 9-12-12 fertilizers, all had approximately the same effect on emergence and stand when used to supply equal amounts of nitrogen, phosphoric acid, and potash. The relative importance of side-band placement and salt index in influencing plant emergence was demonstrated. While the use of low salt index fertilizers as compared with high salt index fertilizers increased cotton stands, side-band placement increased the stands to a greater degree. The high salt index fertilizer reduced the yield of cotton only one year, in 1941. High analysis fertilizers increased the yield this same year. Side-band placement of the fertilizer as compared to under seed placement markedly increased yields. The 700-pound rate of fertilizer had a tendency to reduce yields when the fertilizer was placed under the seed. In 1944, under favorable environmental conditions, however, with side-band placement the 700-pound rate gave a highly significant increase in yield over the 400-pound rate. No increase in yield from the additional fertilizer was obtained with under seed placement. The potential injurious effect of a given amount of a fertilizer on cotton stands and on injury to surviving seedlings is influenced by the salt index and by placement; as the fertilizer rate is increased the potential injurious effect is increased. The direct injurious effects of fertilizers on cotton are due to the high amounts of soluble salts affecting germinations, rate of emergence, plant survival, and rapidity of growth. The extent of the injury is influenced by the moisture conditions prevailing during the emergence and seedling stages. Conditions favoring the movement of fertilizer salts from the fertilizer band to the root zone increase the injury. If the fertilizer injury is sufficiently severe to result in retarded plant development and in imperfect stands after the cotton is chopped, the yields are affected. Under a given set of environmental conditions the yield is the integrated product of the fertilizer effects. Potential fertilizer salt injury to cotton may be avoided by using high analysis fertilizers with a low salt index and by placing the fertilizer in side bands with a combination fertilizer distributor and planter. This practice will not only reduce the cost per unit of plant nutrients, but will make for a greater efficiency from each unit applied.