Effect of Applications of Sodium on the Composition and Yield of Cotton at Different Levels of Potash Fertilization

AT DIFFERENT LEVELS OF POTASH FERTILIZATION H. P. COOPER AND W. H. GARMAN TN 1881, Atterburg (2), using quartz sand and ••• nutrient solutions, showed sodium to be more effective than calcium in increasing yields of oats, especially when the level of potassium was low. Since that time there has been a vast amount of investigational work carried out in foreign countries, as well as in this country, with reference to the role of sodium in plant nutrition. As pointed out by Harmer and Benne (4), there is a copious literature on the subject which has been reviewed by Miller (7) and Willis (10). Since, in certain respects, sodium is closely related to potassium, much of this work has included the study of potassium as well as sodium. Many of these studies have resulted in the advancement of numerous practical and theoretical considerations in the field of mineral nutrition of plants, including selective absorption, ion antagonism, toxicity, substitution of one element for another, and soil studies of the effects of added sodium on the release of potassium. The extensive series of experiments at Rhode Island covering a period of 24 years, as summarized by Hartwell and Damon (5), showed quite conclusively that sodium was beneficial, especially when the supply of potassium was insufficient. In the soil experiments some of the benefits from sodium in increasing small grain yields were likely due to the action of sodium in replacing potassium, but in the solution experiments this could not have been the case. They concluded, therefore, that in the soil experiments at least a portion of the response obtained when sodium was added must have been due to the direct action of the sodium. The early work of Atterburg (2) called attention to the fact that the sodium in the Stassfurt potash salts should not be considered as useless material, but as possessing certain values for the nutrition of plants. Within recent years potash salts have been highly refined, thus very largely eliminating the sodium. Also, few complete fertilizers today carry any appreciable amount of their nitrogen as sodium nitrate. The result is that the complete fertilizer in common use today, in the absence of side-dressing, adds very little sodium to our soils. The present studies were initiated in 1931 to investigate the role of sodium in preventing apparent potash deficiency in the cotton plant. The senior author observed that potash deficiency symptoms were very common on the average farm, whereas this was not the case on the fields and experimental plots of the Experiment' Station and Substations. Even when farmers used 24 to 30 pounds of potash per acre in their cotton fertilizer, the same as used in numerous trials by the Experiment Station, they were often confronted with potash deficiency while the Station was not. Investigation revealed that cotton not receiving a side-dressing of nitrate of soda was frequently troubled with potash deficiency. It was believed, therefore, that this difference was due to the added sodium. This belief was further .substantiated by the fact that the Coastal Plain soils and the long-time cultivated and highly eroded Piedmont soils contain small amounts of available potassium. If sodium can in any way substitute for or supplement potassium in plant nutrition, it would be logical to expect that these phenomena would be most likely to occur on soils low in available potassium. It was on such soils that the nitrate of soda side-dressing largely prevented apparent potash deficiency. Therefore, it was thought desirable to conduct plot experiments to determine if the added sodium was responsible for these results, and if so, the extent to which sodium might be substituted for potassium in the fertilization of the cotton plant.