NutMan FAQ: Manure Input/Output Table on Cover Sheet
Why does the cover sheet show that manure production doesn't balance?
Problem Description: The table on the cover sheet report showing annual manure production and application rates indicates more manure is produced than is used. But the planner is certain that's not the case.
Answer: There are a couple of tricky situations that can confuse matters with the manure balance table on the cover sheet. To understand them, you have to understand how NutMan generates the numbers in that table. The annual production values are straightforward and should match the production amounts shown on the manure edit screens. But the annual application rates are more complicated because there's no requirement that a plan call for the same amount of manure application every year. So to come up with an annual application rate, NutMan calculates an average by dividing the total amount applied in the plan by the number of years the plan covers. The plan's length, in years, is calculated as the number of seasons divided by four.
Figure 1 below illustrates how it's supposed to work. In this super-simple example, 4 tons of manure are produced each year (one ton per season). And all of the manure is applied in the spring of each year. The arrows representing manure production at the bottom of the picture are balanced by the arrows representing manure application at the top.
Figure 1
One way this can get messed up is if the user has "extra" seasons at the end of the plan. For example, if the crop rotation in the plan only extends over two years, the planner might assume that's the end of the plan. And for most purposes, that's fine. Only two years will show on the balance sheet for example. But to the program, the length of the plan is determined by the start and end dates entered on the Farm Edit screen. So if the user enters a length of three years, but only enters two years worth of crops, there will be four unused seasons at the end of the plan. Figure 2 below illustrates this case. NutMan uses the plan start and end dates to calculate the number of years the plan covers. So it calculates a smaller average annual application rate than the planner was expecting. The work-around is to eliminate the extra seasons at the end of the plan by adjusting the plan end date.
Figure 2
The other way this calculation can go wrong is even more tricky. In some cases, the average annual application rate calculation can show an apparent unbalance when the plan covers a fractional number of years. Figure 3 below illustrates one way this can happen. It's the same example as before where 4 tons are applied every spring. But here the planner starts the plan in the fall. So only the second half of the first year is covered by this 2 and 1/2 year plan. Since the plan is longer than two years, but only sees two spring applications, NutMan calculates an average annual application rate that looks too low to balance the production. But the planner knows there's not really a problem. The annual application rate is actually 4 tons per year because the client applies manure every spring. But that knowlege depends on information about what happens outside the dates for which the plan is defined. So NutMan doesn't calculate it that way. This is a much tougher problem. If this happens to you and you really need to have the plan cover a fractional number of years, you may have no choice but to modify the cover sheet report in a word processor and make a note in your plan that you did so and why.
