Influence of Factorially Combined Levels of Cations and Nitrate Ions Adsorbed on Ion-Exchange Resins on the Nutrient Absorption by Plants

The interaction of different levels of cations and nitrate nitrogen adsorbed on synthetic exchange resins upon nutrient absorption by plants was studied in a pot experiment. A factorial design of three levels of cations and three of N was used. Ca, Mg, and K were supplied at the same ratio at all three levels and P and S were unvaried. Three successive plantings were made. These were lemon cuttings, oats, and oats and radishes together. These two species were seeded together because their roots have different cation-exchange capacities. The adsorbed ions proved to be an excellent source of nutrients for the plants. A balance sheet was prepared for all nutrients removed by the crops. Yields were limited in the second and third crops by both N and cation levels. K proved to be the limiting cation. Ca and Mg absorption was depressed as the cation level increased because of increased K uptake. The m.e. of cations per 100 grams dry plant weight increased with increasing cation levels for two oat crops, but was more constant for a lemon and a radish crop. Increasing N levels resulted in increased N and in an increased total anion uptake, but resulted in depressed P and S uptake. The level of adsorbed N did not appear to influence the total cation content in lemon and radish, but there was a slight effect on oats, particularly in the first crop. The level of cations did not appear to influence the N or the m.e. sum of anions in the plants beyond the differences caused by yield variations. The cation-anion ratios in the plants were much narrower than those in the nutrient medium. Increases in N tended to result in increased K and Mg contents in the lemon cuttings and in oats when the supply of cations was high. When the cation level was low for oats, and at all levels for radishes, increases in N tended to result in decreased K. The latter effect was partly related to K depletion at the low cation levels combined with yield increases due to N.