Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Plant, Soil and Environmental Sciences

Major Professor

Donald D. Howard

Committee Members

Jeffrey D. Wolt, Charles R. Graves


Overwintering soil temperature may influence crop response to phosphorus (P) and indices of P availability in the humid temperate transitional climate of Tennessee. The effects of P fertilization and soil incubation temperature upon sorghum-sudangrass (Sorghum bicolor x S. sudanese) grown on a Typic Hapludalf was investigated in two greenhouse experiments at Knoxville, Tennessee. Soils were incubated for 9 months at a constant temperature of 6°C or a diurnal fluctuation of 24 and 36°C. Reagent grade Ca(H2PO4)2*H2O was used as the fertilizer source and applied at rates of: 0, 10, 20, and 30 mg P kg-1 for the first test and 0, 20, 40, 60, and 80 mg P kg-1 for the second test. Critical P concentration in the shoots for optimum yield was 1.25 μg g-1, corresponding to soil solution and labile P concentrations of 2.4 μmol L-1 and 90 μg L-1, respectively. Optimum yield occurred for applications of >40 mg P kg-1 and was unaffected by soil incubation temperature. Phosphorus fertilization rates affected the amounts of P extracted by five chemical extractants (Bray I, Bray II, Mehlich I, Mehlich III, and Mississippi), but soil incubation temperature had no affect. These extractants however, were poorly correlated to plant P uptake and no one extractant was superior to the others as an indicator of P availability. Indices of P availability to plants in general were not affected by soil incubation temperature.

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