Corn silage tons per acre: connect field yield with stored feed

20 as-fed tons per acre at 35% dry matter contain 7 dry matter tons per acre. At 30% dry matter, the same wet tonnage contains 6 dry matter tons. That one-ton difference comes from moisture, not acreage. These are labeled arithmetic examples, not a regional yield forecast or results from a named farm.

Use corn silage tons per acre to connect a field plan with a feed plan, but keep the basis attached to every number. The silage capacity calculator works in the other direction: dimensions and density estimate the tons in storage. Comparing the two can reveal a mismatch worth investigating. It cannot establish field yield without reliable harvested weights and harvested acres.

Define which yield you mean

Harvested as-fed yield is the net weight of the crop divided by the acres actually harvested for silage. Dry matter yield multiplies that wet yield by the dry matter fraction. Stored inventory is a different quantity measured after placement in a bunker, pile or bag. Feed available for a ration is different again if some material will be discarded or lost before feeding.

Write the basis in the column heading: as-fed US short tons per harvested acre, or dry matter US short tons per harvested acre. A US short ton is 2,000 pounds. Do not silently substitute metric tonnes in a record labeled tons. If a supplier works in another unit system, agree the conversion before comparing the quoted crop with your inventory estimate.

A worksheet should also say whether yield was calculated from scale records, a calibrated yield monitor or a preharvest estimate. Those methods answer the same broad question with different evidence. Keep the original source attached to the number. Replacing a measured yield with a convenient planning average makes it hard to explain a shortage later.

Work through the moisture conversion

For an arithmetic example, suppose net harvested weight is 800 as-fed tons from 40 harvested acres. Divide 800 by 40 to get 20 as-fed tons per acre. If a representative sample is 35% dry matter, multiply 800 by 0.35 for 280 dry matter tons across the field. Divide by 40 for 7 dry matter tons per acre.

If those same 800 wet tons were 30% dry matter, the field total would be 240 dry matter tons, or 6 per acre. More water raises wet weight without adding dry matter. Compare crops on a common moisture basis before comparing their yields. A higher as-fed yield alone does not establish that more nutrients were harvested.

Minnesota Extension’s Harvesting drought-stressed corn for silage emphasizes testing moisture rather than relying on a drought-stressed plant’s appearance (Stahl and colleagues, reviewed 2025). For inventory accounting, that means keeping sample dates and the crop represented by each sample. A value from one field may not describe a later harvest from another field.

Use harvested acres and net crop weights

Start from the area actually chopped, not the total acreage of a field that also produced grain or contained unharvested corners. Use the same area basis across the season. If acreage changes after the original crop plan, update the denominator before reporting tons per acre. An incorrect acreage figure can create an apparent yield change even when the scale total is right.

For loads, subtract the empty vehicle weight from the loaded weight. Keep tare records tied to the vehicle and the day rather than copying an old value without checking. Group the net crop weights by field, harvest date and destination storage when the records allow it. A total for the whole season is useful, but a total tied to a particular storage is easier to reconcile.

When combining loads with different dry matter percentages, calculate dry matter for each represented group and sum those dry matter weights. Do not take an unweighted average of percentages from a very small load and a very large one. Divide total dry matter weight by total wet weight if you need a combined dry matter fraction for the group.

Check whether the storage can hold the plan

The calculator’s 3-wall bunk example uses 40 feet of width, 200 feet of length and 12 feet of height, with the front end open at a 3:1 slope. That geometric solid contains 85,818 cubic feet. At 15 lb DM/ft³ it represents 643.635 dry matter tons. At a planning yield of 7 dry matter tons per acre, dividing 643.635 by 7 gives about 91.95 acres before any separate loss or reserve allowance.

This does not mean a real bunker will take exactly 92 acres. The result depends on the filled dimensions, shape and density matching the assumptions. End ramps and unused headspace can reduce filled volume. Different density changes how much dry matter fits in the same space. Read the bunker calculation example before applying wall dimensions to stored crop.

University of Wisconsin engineer Brian Holmes connects volume and stored density in Making a Feed Inventory (Holmes, 2012). Use the field total and the storage estimate as two separately documented checks. If they disagree, examine the dates and assumptions before deciding that the difference represents a loss.

Keep losses outside the yield conversion

Multiplying wet tons by dry matter percentage removes water from the accounting basis. It does not deduct fermentation, spoilage or feedout losses. Likewise, a geometric capacity calculation does not establish the usable feed remaining at the mixer. Make any loss allowance a separate, labeled line in your own planning sheet.

For illustration only, applying a hypothetical 10% loss allowance to 280 dry matter tons leaves 252 tons. That is a scenario, not a forecast of what your farm will lose. If the feed target were 280 usable dry matter tons under that same assumed allowance, you would need 280 ÷ 0.90 = about 311.11 harvested dry matter tons. Adding 10% to 280 would give a different and insufficient starting quantity.

Cornell PRO-DAIRY identifies storage capacity, quantity estimates, forage quality and spoilage as connected planning concerns in Strategies to ensure quality forage for the entire dairy herd (Hicks and Lawrence, 2020). A field-yield figure should therefore travel with its storage and feeding assumptions. It should not be presented as a guarantee of future ration supply.

Translate a feed target into acres

Consider a hypothetical 500-cow herd allocated 20 lb of corn silage dry matter per cow daily for 100 days. That requires 1,000,000 lb, or 500 dry matter tons, before losses or reserves. At the example yield of 7 dry matter tons per acre, the basic target is about 71.43 acres. Neither the allocation nor the yield is a recommendation for a particular herd.

Now change the yield assumption to 6 dry matter tons per acre while keeping the feed target fixed. The requirement becomes about 83.33 acres. The difference is almost 12 acres, which explains why moisture and yield assumptions deserve a line of their own in the plan. A sensitivity calculation can expose that difference before harvest decisions become difficult to change.

Keep the financial calculation separate too. If an illustrative dry matter ton were valued at $200, the example herd’s 5-ton daily allocation would cost $1,000, or $2/cow/day. This is one feed component, not a full ration budget or a current price quote. Reporting the assumption in $/cow/day lets the manager replace it with an actual farm figure. At a hypothetical 400 cwt shipped daily, it would equal $2.50/cwt.

Reconcile the records after harvest

Keep a dated opening inventory before new crop arrives, net incoming crop weights, any transfers and the feed removed during filling. Then compare the documented stock balance with a storage estimate made on a stated date. If feeding has already started, that removal belongs in the comparison. Different dates can explain a discrepancy that would otherwise look like missing feed.

For a drive-over storage, use the pile geometry guide to document shoulders and end ramps. Save the chosen density basis and dry matter sample with each estimate. When the result changes, you can identify whether the reason was new dimensions, a better density value, a changed moisture basis or recorded crop movement.

Run your filled storage dimensions in the silage capacity calculator, email the PDF, and compare its dry matter tons with your harvested acres and net crop records.