We calculate growing degree units and and cumulative precipation to understand how these factors influence cover crop growth. This information is gathered from the Applied Climate Information System (ACIS).

Precipitation is calculated as the sum of all the measured precipitation that has fallen from when the cover crop was planted to when the biomass was sampled. The precipitation data is collected from the ACIS weather station nearest to participating field.

Growing degree units (GDU) are a measure of how much heat has accumulated over a season. This can indicate how favorable were conditions for plants. This is calculated as the sum of daily warming units over time window of when the cover crop was planted to when the biomass sample was collected. For our growing degree unit calculation we use the Baskerville-Emin method, this method does a better job of assessing heat units during cool periods, such as early in the spring. Michigan State University has a nice discussion of how this method is different from the averaging method. As with our precipation calculation, the minimum and maximum daily temperature data is collected from the ACIS weather station nearest the farm for which GDU is being caluclated. If the weather station has more than 10% of missing values for window period, then the next nearest weather station is used.