THE RELATION BETWEEN THE CHEMICAL NATURE OF THE SUBSTRATE AND THE DEGREE OF CHLOROSIS IN CORN

Abstract

Five series of corn plants-grown in sand culture supplied with culture solns. by the continuous flow method are descr. When nitrate constituted the sole source of N there was a continual increase in severity of chlorosis of the plants with each increase in the pH value of the substrate from pH 3 to 7; at pH 8 the plants were free from chlorosis. When both nitrate and ammonium constituted the sources of N, there was much less chlorosis of the plants than when nitrate alone constituted the source of N. Plants grown in this series with culture soln. of pH values 5, 6, and 7 were free from chlorosis; those grown with solution of pH 3 and 8 were moderately chlorotic. When the proportion of anions and the pH value of the culture soln. were kept approx. constant, plants grown in the high K cultures were slightly chlorotie, those grown in the high Ca and high Mg cui-tures moderately chlorotic. Where the proportions of cations in the culture solns. were held approx. constant, plants grown in solns. high in phosphate and high in nitrate were severely chlorotie; plants grown with solns. high in sulfate were free from chlorosis. In general, high titrable acidity corresponded with high phosphate content of expressed juices. An interrelationship between pH value and P content of the expressed sap is suggested in explanation of iron precipitation and the degree of chlorosis in the plants. A close direct correlation was shown between nitrate N content of the plants and chlorotie intensity. It is suggested that iron precipitation and the presence of chlorosis are induced in high N plants by the higher proportions of metabolically active; tissue with relatively high pH as compared with the proportion found in low N plants. The presence of ammonium N in the culture medium was associated with a relatively higher P content and a lower pH value of the expressed sap than was the presence of nitrate N. Plants grown with culture solns. containing ammonia were relatively free from chlorosis as compared with plants grown with solns. containing nitrate as the sole source of N.