Effect of Thermal Energy Intensity on Time and Rate of Nitrogen Accumulation by Maize (Zea mays L.)1

The effect of thermal energy intensity (TEI) on the rate of nitrogen (N) accumulation by maize from a Hamerly clay loam soil (Aerie Calciaquoll) was examined with and without supplemental irrigation. Soil- and air-TEI expressed as cumulative growing degree days (GDD) was determined from hourly temperature measurements taken within each plot at soil depths of 0.05-, 0.15-, and 0.3-m and at a height of 1.2-m above ground surface. A daily mean TEI (GDD per day) was calculated for each growth period. Estimates of time coefficient(s), k, in uni- and diphasic tanh[k(time)] functions, plotted against mean TEI for the periods; 1) planting to emergence, 2) emergence to eighth leaf, 3) eighth leaf to time(s) of maximum N accumulation rate, (t₀), 4) planting to t₀, 5) emergence to t₀, 6) first diphasic maximum accumulation rate (t₀₁) to 50 % silking, and 7) silking to second diphasic maximum accumulation rate t₀₂ showed several linear relationships. Uniphasic time coefficients were modelled as functions of air-TEI. The first diphasic time coefficient, k₁ was modelled as a function of pre- and post-emergent soil-TEI. Attempts to model k₂, the second time coefficient of the diphasic model were unsuccessful; however, this time coefficient was linearly related to TEI for the growth period ‘t₀₁, to 50 % silking’ and curvilinearly related to k₁.