Uptake Calculator Notes
This spreadsheet incorporates a model that allows you to calculate the amount of nitrogen used by the crop between each irrigation period, or whatever other interval you specify. Remember that this is only the above-ground portion of the crop, early in the season you may wish to increase these values if you have reason to believe that the nitrogen that came from decomposing previous crop roots and incorporated residue may not be enough to supply the nitrogen needed for root growth of the current crop.
This version uses an equation for corn that was derived from midwest data. Over the past few years we have been collecting nitrogen uptake data for corn in Stanislaus County, and when that data has been analyzed and developed into a better equation, an updated version of this calculator will be posted.
Use this model at your own risk! Biological systems are far too complex for any model to be 100% accurate; never rely solely on a model when making management decisions. Please share your observations of how well this model seems to be predicting - or not predicting - your crop progress. We are relying on your real-life feedback to continually refine and adjust this tool.
Remember that many other factors besides temperature will affect the growth of crops. Disease, weeds, waterlogging, moisture stress and insect pests are some of these. This model assumes that the crop has all the nitrogen and other crop nutrients that is needs. If it doesn't, the growth will not match these predictions.
The model cannot be expected to accurately predict crop uptake for planting and harvest dates that are outside of the normal window for these events, are in climates other than the San Joaquin Valley, or are unusual varieties or species.
The daily temperatures that affect the crop can be very different than long term averages. This version of the spreadsheet is pre-loaded with long term average minimum and maximum temperatures for several locations in the San Joaquin Valley, in addition to a few years of recent data for Denair. Try selecting different years using the "Weather Data" toolbox button one the "Daily Uptake" tab and see how much it affects the predicted crop uptake.
Choose a data year for dates in the fall, and the next year for dates in the spring and summer. Choose a backup year for dates with data missing or that have not yet occurred. Cumulative corn growing degree units are calculated from the planting date specified for corn.
The temperature data is stored on the "MinMax" tab. You can put your own minimum and maximum temperature data into this tab and then select it to use in the model. Be sure to select an appropriate source of data for dates that haven't occurred yet.
IMPORTANT: if you are entering downloaded blocks of min max temperature data into the minmax data page, there is a row for February 29. If your data isn't from a leap year, you will need to either insert a blank row at Feb 29 into the downloaded data or cut and past the data in two blocks: from Jan 1 to Feb 28, and from Mar 1 to Dec 31. Otherwise, all the values after Feb 28 will be 1 day off and Dec 31 will be empty.
Soil temperature and precipitation are not used by the nitrogen uptake model but will be needed by the organic nitrogen mineralization and application planning models that we are currently developing.