THE EFFECT OF SOIL MOISTURE ON THE AVAILABILITY OF NITRATE, PHOSPHATE, AND POTASSIUM TO THE TOMATO PLANT

Abstract

Brown to black clay loam soils were adjusted to 10, 20 and 40% moisture and tomatoes grown in them. The moisture was maintained and distributed through the soil by special apparatus and methods which utilized sand layers between layers of soil. Glass tubes carried water into the sand layers where it spread out and caused a uniform wetting of the soil. Determinations of nitrate, phosphate and K in the large lower mature petioles of the plant were made by methods previously described. The results and conclusions are as follows: Green color, nitrate in the soil and plant, and K in the plant increased with decreases in soil moisture, while succulence, green weight, phosphate, and moisture in the plant were decreased, the latter decrease being relatively small. It seems that the major effects of low soil moisture are: (a) lessened nitrification in the soil but not lessened ability to absorb nitrate by the plant; (b) lessened ability of the plant to absorb phosphate and consequent nitrate accumulation in the tissue because of retarded tissue formation; and (c) a decreased water content in the plant which probably limits both photosynthesis and general metabolic processes in the plant.