The purpose of providing a previous crop is to provide the model with information about remaining crop residues and their influence on N availability (immobilization in high carbon residue, or additional N in legume residue). If the crop planted in the previous year is not listed as an option under Previous Crop, a crop with a similar growth pattern (planting density, crop residue) should be selected. Please contact email@example.com if you have any questions. Here are a few suggestions about how to generate the most accurate results:
- Small grains, straw harvested: Substitute silage corn for small grains. The reason for this is that, like silage, small grains after straw harvest leave a minimal amount of surface residue, so that little immobilization of nitrogen occurs. The amount of root residue left by densely planted grains is likely similar to more broadly spaced, but larger, corn root residue.
- Small grains, straw left on surface: When following small grains where straw was not harvested (if residue is still fairly thick by corn planting time) use “grain corn” as the previous crop, so that some immobilization of N in residue will be accounted for, although imperfectly.
- Vegetable crops/potatoes: Substitute soybean for vegetable crops/potatoes, but be sure to add the soybean N credit listed on your results page to your Adapt-N recommendation (15 lbs or 25 lbs, depending on location and soil type) for non-legume vegetable crops. Like soybeans, most vegetable crops leave minimal residue, but most do not fix nitrogen.
For Alfalfa, Grass Hay, Mixed Legume Hay, and Sod - a termination date, Legume Percentage, and Termination Method are also required for input. For any other prior crop, it should also be specified whether a forage-sod was planted in the last three years by clicking the checkbox below the dropdown. This will allow the model to account for N dynamics associated with that forage-sod.