Significance of moisture translocation from soil zones of low moisture tension to zones of high moisture tension by plant roots
1947
Volk, G.M.
The investigations were made with plants having root systems divided between soil under high moisture tension and soil or sand adequately supplied with moisture. The critical soil moisture (that at equilibrium with the roots of a turgid plant) was 1.11 times the wilting point for Clyde silt loam and 1.12 times the wilting point for Plainfield sand. Corn grew roots into air-dry Plainfield sand and increased the moisture content to 2.3 the initial level. Corn also grew roots into Clyde silt loam at 0.7 and 0.9 of the wilting point, and showed a net translocation of moisture into the dry soil. Root growth into air-dry Plainfield sand to which a heavy application of fertilizer had been made, resulted in reduced plant growth and a higher percentage of potassium and nitrogen, but no change in phosphorus in the plant, as compared to a no-fertilizer treatment. There was an increase in both percentage and total potassium and nitrogen in plants which grew roots into dry Clyde silt loam of high fertility at below the wilting point, as compared to Plainfield sand of low fertility. There was very little, if any, increase in intake of phosphorus. Total nitrogen assimilated by millet transplanted with one-half of its root system in a high-nitrogen soil at the wilting point was 55% of that assimilated from the same soil at optimum moisture, and over six times that present in the check growing only in nitrogen-free sand nutrient solution culture. The dry weight yield of corn receiving phosphorus and potassium and part of its nitrogen from soil at slightly below the wilting point in a sealed container was 33% higher than for corn receiving these elements from the same soil in a container open to permit air-drying to take place. Potassium and phosphorus uptake were 50% and 70% higher, respectively, in the plant with part of its roots in a sealed container.
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