Know the true crop costs

The impact of inflation on the cost of various crops will be key to decisions farmers make on which fodder crops to grow, Kerry Dwyer writes.

Planning for next winter’s crops is on the agenda in the next months, with decisions to be made about what to grow and what processes to use in the growing. Budgeting for the coming year is more difficult than previous years because of inflated costs, which have not stopped rising yet.

Looking at the coming season, growing costs for two winter feed crops, fodder beet and kale, will be something like Table 1. This should be read with inflation in mind; and that these are not what you might be facing given the variation in different sources of inputs. Also, everyone has different methods and processes for growing crops which can give a wide range of costs, and results. The figures are indicative only.

Looking at the components of growing costs: seed bed preparation and sowing costs are generally higher with beet than kale, because a finer seed bed is aimed for and precision sowing is typically used. Some farmers like to stir the soil well and others less, I once saw a paddock cultivated 14 times before sowing a swede crop. Direct drilling may lower machinery cost but increase chemical cost.

Fodder beet is sown at about 100,000seeds/ha, while kale seed is calibrated as kg/ha. The beet seed is more expensive, but there is a range of cost for both crops depending on variety and source.

Fertiliser inputs for either crop should be related to the expected yield.

The beet might grow twice the crop of kale, so should have additional nutrient input to allow for that. Farmers often allow for some capital fertiliser application as part of the crop growing process. Note that fertiliser prices have risen considerably in the past 12 months, especially nitrogen-based products. Maybe this trend has eased?

Weed and pest control costs tend to be specific to farm, region and conditions. For example, kale in Canterbury last summer received large doses of everything in wet conditions while Southland crops were far less demanding in drier conditions.

A key point to consider is that it is difficult to get the best yield with the least inputs. And higher yield is lesser cost per unit than a low yield, at the same growing cost. It is common to see fodder beet ranging 9-16c/kg drymatter (DM) and kale 10-16c/kg DM grown.

Fertiliser value in crops

The dramatic lift in fertiliser prices over the past year should be taken into account when planning your fodder crops and supplements. First let’s look at what fertiliser nutrient value is carried in straw and silage. Some rough mathematics puts the current value of fertiliser nutrients at:

• Nitrogen $3/kg

• Phosphate $4.20/kg

•  otash $2.50/kg

• Sulphur $1.10/kg

Multiplying these up there is about $8 worth of fertiliser nutrient in a 200kg DM bale of straw (going through old files I found it was $2.25 in 1996); and about $15 worth of fertiliser nutrient in a 200kg DM bale of balage. That does not take into account any cartage and spreading cost of the fertiliser, which is an additional 15-25% cost in 2022. Allowing for that means at least $20 worth of fertility in 200kg DM balage.

A 15tonne DM/ha crop of kale has about $1400 worth of fertiliser nutrient in it while a 25t DM/ha fodder beet crop contains more than $2600 worth of fertiliser.

Much of that nutrient is absorbed from the soil nutrient bank without additional fertiliser application being required. But note the value if you are carting the crop off the paddock. In summary, consider what your crops cost to grow last year and factor some inflation on that. What yield did you get in relation to that cost? And consider the nutrient cost involved.

• Kerry Dwyer is a North Otago farm consultant and farmer.