From the yield check to the manure rate
Nutrient planning · yield component method to spreader setting
Walking the corn in early October: the thousandth-acre counts average 7.5 ears per square metre, a representative ear carries about 520 kernels, and this hybrid runs near 90,000 kernels to the bushel at a 25.4 kg test weight. Grain corn removes about 12.5 kg of nitrogen per tonne harvested. The dairy's solid manure tests 5.5 kg N per tonne, of which about half is available in the first season. Estimate the yield, the nitrogen a matching crop removes, and the manure rate that would replace it.
Every number in this problem is editable — change any value below and the whole chain recalculates.
- E = 7.5 ears/m² — Ear count
- k = 520 kernels — Kernels per ear
- K = 90,000 kernels/bu — Kernels per bushel, hybrid
- w_b = 25.4 kg — Test weight per bushel
- k_N = 12.5 kg/t — Nitrogen removal per tonne of grain
- c = 5.5 kg/t — Manure nitrogen content
- a = 50 % — First-season availability
- (a)the estimated yield
- (b)the nitrogen the crop removes at that yield
- (c)the manure rate that replaces it
The yield component method is just multiplication with field-sized error bars: ears times kernels is kernels per square metre, and the hybrid's kernels-per-bushel turns count into mass. The counts here say 11.0 t/ha — carry it as an estimate wearing ±10 %, because the kernel count is a guess about grain fill that October hasn't finished making.
Carried onward at full precision, not this rounded figure.
Open the Corn Yield Estimate (Yield Component Method) solver →
Removal is what leaves on the truck, not what the crop touched: 11.0 t/ha at 12.5 kg N per tonne is 137.6 kg/ha of nitrogen gone with the grain. Stover returned to the field is why this figure is smaller than uptake — and why baling the stalks changes the arithmetic.
Carried onward at full precision, not this rounded figure.
Manure nitrogen is discounted twice — once for what the load contains, once for what this season can actually use. At 5.5 kg/t and 50 % availability, replacing 137.6 kg/ha takes just over 50 t/ha of manure: a heavy but real spreader setting, and the moment to ask whether phosphorus is about to be over-applied.
Carried onward at full precision, not this rounded figure.
Therefore the counts estimate 11.0 t/ha, a crop like it removes about 137.6 kg/ha of nitrogen, and replacing that with 5.5 kg/t manure at half availability takes 50.0 t/ha — at which point the limiting number is usually no longer nitrogen but the phosphorus riding along with it.
Why this order
The chain runs the direction nutrient planning actually runs: yield first, because every removal table is written per tonne of harvest; removal second, because that — not uptake — is what has left the field for good; the spreader setting last, because manure is a fertiliser whose analysis you inherit rather than choose. The two discounts in step (c) are the part worth internalising. The content c is a lab number that varies load to load; the availability a is an agronomic judgement — roughly half of solid manure's nitrogen is organic and mineralises over years, not months. Skip the availability discount and the rate looks halved and the crop runs yellow by July.
The trap at the end is the one the final statement names: manure carries its nutrients in fixed proportion, and a rate set to satisfy nitrogen usually over-supplies phosphorus two- to three-fold. Nitrogen decides the rate; phosphorus decides how many years in a row you may use it.
Carried values move at full precision, not the rounded figure shown — chaining rounded numbers compounds error.