A split‐root technique was devised in which the top portion of the roots of corn plants developed in sand culture while the remaining portion of the root system developed in soil adjusted to seven known moisture contents in the range of wilting point to field capacity. With this system, plants were grown from seed for a 25‐day period without addition of water to the soil and with only a small loss of the original soil water content. Plants were grown at two levels of atmospheric humidity at each level of soil moisture.
Dry weight of plant tops and roots developed in the soil increased linearly with increasing soil moisture. Both percent and total P, K, and Mg in the plants increased with increasing level of soil moisture. Level of humidity appears to interact with the effect of soil moisture on ion absorption.
Periodic field observations of the development of manganese deficiency symptoms in soybeans indicate that soil temperature and soil moisture may influence manganese absorption by soybean plants. These observations were explored in detail in a greenhouse study.
Glazed pots were filled with a manganese deficient clay soil, placed in constant temperature water baths and planted to soybeans. One bath was maintained at 15° C., a second at 27° C., while the third was maintained at 15° C. for the first 7 weeks of plant growth and increased to 27° C. for the remaining 5 weeks of growth. Two soil moisture levels were provided at each soil temperature.
A low soil temperature combined with high soil moisture was conductive to the development of severe foliar sympoms of manganese deficiency. High soil temperature combined with low soil moisture produced plants which exhibited only a slight manganese chlorosis. The total manganese per plant and the manganese concentration within the plant were significantly greater at the high than low soil temperature. In a solution culture study, increasing the temperature of the solution increased the manganese concentration in the soybean leaves indicating a physiological response of the plant to a change in root temperature.
Most Ohio soils release K (from a nonexchangeable form to exchangeable) upon air drying from the field-moist state. The amount released varies from 25 to 100 pounds per acre depending upon soil type. The effect of this release upon the interpretation of soil test recommendations was found to be not significant. Correlations between soil test level and corn yield response to K fertilization were the same or better using air-dried samples as compared with the field-moist samples. Further drying at 110°C. for 24 hours slightly increased or decreased the amount of exchangeable K depending upon the soil type. These values were, in some instances, poorly related to the yield response. Of the three procedures, air drying at room temperature prior to extraction gave the best estimate of the available K level.
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