PHYSIOLOGICAL ASPECTS OF THE EFFECT OF CONTINUOUS SOIL AERATION ON PLANT GROWTH

Abstract

As compared with control plants grown in soil without aeration, sunflower and soy bean plants grown in aerated soil (sand and loam) are taller and heavier as a result of early rapid growth; have a larger, more fibrous, and more highly branched root system; their root cells are heavier walled and higher in reserve carbohydrates; they absorb nutrients more rapidly as shown by higher content of ash, Ca, K and P per plant (in terms of absolute weight of entire plants) ; contain more crude fiber, starch, total sugars, and N per plant; the expressed sap of tops and roots is more alkaline; tops have a higher buffer capacity, roots a lower buffer capacity, against alkali and acid; and have smaller top-root ratios in terms of fresh weight. The difference between sand and loam cultures is expressed by a tendency of % composition of certain components to run higher in controls, even though absolute amts. of such constituents are consistently higher in aerated plants. Sap hydrion values were generally higher in plants grown on sand. Moderate rates of continuous soil aeration with moist air increased size and growth rate of plants; very rapid aeration had the opposite effect. Species differed in their tolerance of soil aeration. The threshold of injury by rapid aeration is higher for soybeans than for sunflowers, especially when dry air is used.