What to the P-balance numbers on the Balance Sheet report mean?
Problem Description:After years of working with the same old Job Sheet report in both NutMan 1 and NutMan 2, the report's name changed to "Balance Sheet" and new information was added to support phosphorus based planning.
Answer: The new information on the report is highlighted in Figure 1 below. There are three new pieces of information on the Balance Sheet (a.k.a. the Job Sheet) related to phosphorus based planning:
Cumulative P2O5 removal column: This is a new column just to the right of the "Net Needs". It shows the cumulative P2O5 removal credit for each field's rotation. The number in each crop's row is not the removal credit for that crop alone. It is the cumulative total credit in lbs/acre through that point in the rotation. So, for each field, the number in the P2O5 removal column on the row of the last crop in the field's rotation is the field's total removal credit.
Field level P2O5 removal option: This is a code in parentheses appearing after each field name in the left-most column. The codes are defined just above each table. (N) means the field is nitrogen based. This means only the nitrogen balance is being managed for this field. So the P2O5 removal is not considered important to its nutrient balance. This was always the case before P2O5 removal accounting was added to NutMan. (1P) means the field is phosphorus based. The "1" indicates a field multiplier of 1 is applied to the P2O5 removal credit for crops in this field when determining phosphorus application limits. (1.5P) similarly indicates a phosphorus based field, but the removal credit will be scaled up by 50% when setting application limits for this field. (0P) also indicates a phosphorus based field. But here the field multiplier is zero, so effectively no P2O5 removal credit is considered when setting application limits. Currently, these options are set by the user in the Field Features tab of the Farm Edit Screen. We plan to change this to make it depend on the soil test information for each field.
Red P2O5 over-application warnings: If calculations indicate phosphorus is over-applied in a field, the excess amount will appear in red on the balance sheet in either the Net Needs, or P-Removal columns. Figure 2 below illustrates the logic NutMan uses to determine if there is an over-application. And if so, where the excess balance should appear. The idea is to compare the P2O5 applied to a field to either the total P2O5 nutrient needs or the total P2O5 removal credits of all the crops in the field. Whichever is greater. If the applied phosphorus exceeds the limit based on nutrient needs, the negative balance appears in the Net Needs column. If the phosphorus exceeds the limit based on removal, it appears in the P-Removal column.
