The estimates are for only central Iowa, not for each county, so it overestimates for the north, underestimates for the south. A later version may move the soil temperature curve to better reflect each of the 99 counties. The computer program calculates the expected disposition of the applied nitrogen for the first day of the months of May, June, and July. No computations are done beyond the first of July because crop uptake of both nitrogen and water become significant and computations are not as crucial beyond this time. Chart shows average, normal range and observed extremes.
Temperatures are for central Iowa at a depth of four inches, under bare soil.
Soil temperature distribution according to week of the year for central Iowa. The use of a substance that limits the population or the activity of soil micro-organisms can influence the rate of nitrification. As with most biological processes, it is difficult to precisely describe the degradation of the inhibiting materials, the re-establishment of organisms, and the effects of temperature, moisture, pH, etc. on the process. This program computes the rate of nitrification with and without N-Serve using the gdd formulas derived for the field plot experiment, and it assumes that the relationship is generally correct for soils that are suitable for corn production. In most years the majority of nitrogen losses occur before corn becomes a major user of nitrogen.