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How Do I Work Out What Seed, Fertiliser and Sprays Actually Cost on Each Field?

Farm input invoices go into the accounts with no link to fields. We link seed, fertiliser and chemical invoices to field records to show costs per field.

Updated 3 min readBy SpiderHunts Technologies

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Quick answer — TL;DR

Seed, fertiliser and crop protection invoices are posted to broad accounts headings, while what actually went on each field is in the crop records, and the two never meet. We price each field's applications from the invoices that bought them, so you can see input costs per field and per crop, with the source of every figure.

A big inputs bill and no idea which fields ran it up

The accounts show what the farm spent on seed, fertiliser and sprays this year. The crop records, in notebooks, spreadsheets or crop recording software, show what went on each field. Nobody has ever joined the two, so when you ask what the second wheat on the heavy land cost to grow compared with the first wheat by the road, the answer is an estimate at best.

The agronomist's recommendations had prices on them, once. Then products were substituted, deliveries were split, a rebate arrived at the end of the season, and some seed was farm-saved. The real cost per field is in there somewhere, spread across dozens of invoices and hundreds of application records.

Why costs and fields do not meet

The reason is that invoices and field records describe the same thing in different units and at different times.

Invoice saysField record saysThe gap
Product, pack size, number of packs, priceProduct, rate per hectare, areaUnits differ, packs versus litres or kilos per hectare
Delivery dateApplication dateStock carried from one season to the next
One delivery for the whole farmMany fieldsNothing says which pack went where
Rebates and credit notes laterNothingThe true price changes after the fact
Farm-saved seed, no invoiceSeed rate and areaNo cost at all unless you add one

Accounts software is built to record what you spent and who you owe, and it does that well. It is not built to price a field. Crop recording software may hold costs if someone types them in, but in practice nobody types them in.

What you lose without field costs

Choices about rotations, rented land, marginal fields and scheme options all depend partly on what a field costs to crop. Those choices are yours, with your accountant and agronomist, but without field costs they are made on averages.

It also makes it hard to see where money goes within a year. When fertiliser prices move sharply, or a disease year means extra fungicide passes, you want to see which fields took the extra cost. Rented land is a particular case: whether a block is worth keeping at the next rent review is a much better conversation with field figures than without them.

How we price each field from the invoices

What we build is a costing layer that sits between your invoices and your field records.

  1. Input invoices are read as they arrive, by email or photo, or taken from your accounts software. Each line becomes a stock purchase: product, quantity in real units (litres, kilos, tonnes, seed units) and price.
  2. Credit notes and rebates are matched back to the purchases they relate to, so the price reflects what you actually paid.
  3. Application records, from your crop recording software, spreadsheets or our own capture screens, give product, rate and area for each field.
  4. Each application is priced from stock using a rule you choose, such as average cost of what is in store, and taken off stock. Farm-saved seed is costed at a value you set.
  5. Each field shows its inputs this season: seed, fertiliser, crop protection, each line priced, with the invoice behind it one click away. Totals per hectare and per crop follow.
  6. Stock left in store at year end is valued from the same records, which is useful for the accountant.

Where your crop software already holds costs, we check whether feeding it prices from invoices is simpler than building anything separate.

The awkward cases are handled openly rather than smoothed over. A delivery that covers two seasons is split by what was actually applied in each. A product substituted in the field at a different price is costed at what went on, not what was recommended. And anything that cannot be priced, such as an application with no matching purchase, shows as a gap to fix rather than a guessed figure.

Planning next season with real field costs

At harvest review, you sit down with the field costs. The first wheat and second wheat blocks sit side by side, input by input. One rented block had an extra fungicide and more nitrogen than the rest. The agronomist brings their view, the accountant brings yield and price, and you have the costs that were missing before.

During the season, when a new fertiliser invoice comes in, the price flows through to the fields as they are spread, and nobody types it twice.

Is this where your input costs stop?

  • Input invoices are posted to broad accounts headings only.
  • Nobody can say what inputs cost on a particular field.
  • Rebates and credit notes are never linked to what they relate to.
  • Chemical and fertiliser stock at year end is estimated.
  • Field decisions are made on farm averages rather than field figures.

FAQ

Frequently asked questions

The questions readers ask us after this guide.

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Do we have to change how we post invoices to the accounts?

No. Invoices still go to Xero, QuickBooks or Sage as now. The costing layer reads them alongside.

Does this need our crop records to be complete?

Field costs are only as good as the application records. If those are patchy, we usually fix the capture of records first.

How is farm-saved seed costed?

At a value you or your accountant choose. We make it visible so nobody mistakes it for a bought price.

Is this the same as gross margins?

It is the input costs part. Adding yields and sales gives margins per field if you want them, and we can build that too.

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