| Abstract: | The effect of planting date and thermal energy intensity (TEI) on the rate of phosphorus (P) and potassium (K) accumulation by maize from a Hamerly clay loam soil (Aerie Calciaquoll) was examined with and without supplemental irrigation. Soil- and air-TEI expressed as growing degree days per day (GDD d?1) were determined from hourly temperature measurements taken within each plot. Net K accumulation occurred during the vegetative growth stage, reached maximal rates of about 62.2 to 91.4 mg plant?1 day?1, and attained maximal accumulations ranging from about 1.15 to 2.3 g plant?1. Accumulation of P occurred during vegetative and reproductive growth stages, reached maximal rates of about 4.6 to 10.3 mg and 6.5 to 12.1 mg plant?1 day?1, respectively and maximal accumulations of 0.175 to 0.27 g and 0.11 to 0.26 g plant?1, respectively. During vegetative growth, K and nitrogen (N) accumulation characteristics were closely correlated with about 2 moles of N accumulated per mole of K. Maximal accumulation of K (and N) consistently preceded that of P by about 5.2 to 8.3 days and that of the plant dry weight by about 15.9 to 20.5 days during the vegetative growth stage. Time required to reach maximal accumulation during the reproductive growth stage, tr followed the order N < P < dry weight for early plantings and followed the order N < P < dry weight for delayed plantings. Time coefficients for K and P accumulation were correlated closely with soil-TEI, but models of each coefficient relied on unique combinations of TEI. Time coefficients for dry matter accumulation were apparently unrelated to soil- or air-TEI. |
