What is your cost of Harvest Weed Seed Control?

Take home messages

• There is no single answer as to which HWSC tool is best. It depends!
• The Estimated Cost of HWSC model aims to give you the most accurate estimate of cost of HWSC based on what we know now.
• The total cost per hectare can be relatively small when all things are considered.
• Give the model (What’s the cost of harvest weed seed control for YOU?) a run with your numbers and see what you find.

Introduction

How much does it cost to run a car? It depends. Some cars are expensive to buy but have low maintenance and fuel costs, whereas others are cheaper to buy but guzzle the fuel and need a lot of work to keep them on the road. Harvest weed seed control (HWSC) is just the same. We need to look a bit deeper than the up-front capital cost to get the full story.

The do it yourself narrow windrow burning chute seems cheap at the time, but what is the true cost of this type of HWSC? The answer is, it depends on several factors!

The short answer:
HWSC costs $7 to $19 per hectare and there are only minor differences in the cost between the various tools.

The slightly longer answer:
For a large farm with lower yielding crops the cost is $7-$10/ha. For a small farm with higher yielding crops the cost is $18-$20/ha.

The whole story:
The cost of HWSC depends on a whole range of factors that differs from farm to farm. AHRI have developed an interactive model that enables you to input your details and obtain the best cost estimate for different HWSC methods. The model can be downloaded from the September 2019 AHRI insight

Table 1 demonstrates an example output from the model along with some details explaining all of the assumptions used in the model.

Table 1. Cost ($/ha) of various harvest weed seed control (HWSC) tools. Data from the Estimated Cost of HWSC model. This data represents farms of different sizes and crop yields, all harvested with one harvester.

n.b. crop area is 50% cereal, 25% legume and 25% canola.

Table 2. Assumptions used in the model to generate the results presented in Table 1.

Table 1 shows that the lowest cost of HWSC is achieved by larger farms with generally lower yields. This is because the capital cost of HWSC is spread out over a larger area, the nutrient removal costs are lower due to the lower yields, and harvest is not slowed by the mills due to the lower yields. In contrast, the highest cost of HWSC is associated with smaller farms with higher yields. In general, there’s only a relatively small difference in cost between all of the HWSC tools except for narrow windrow burning, which is always the most expensive due to the highest nutrient cost. The ‘bale direct’ tool was not included in this comparison, but in general it is a very high cost and can be profitable if a large market for straw bales exists close to the farm.

Capital cost

The capital cost of HWSC tools are always quickly quoted, but it’s important to remember that this is only part of the picture. Table 3 gives an estimate of the capital cost of the various tools but as the laws of competition come into play, these values will most likely change.

Table 3. Approximate capital costs of various harvest weed seed control (HWSC) tools.

If capital cost is only part of the picture, what is the rest of the story? To follow are some notes that describe the key assumptions that are used for the model.

Nutrients

One of the most important, and sometimes overlooked costs of HWSC is the value of the nutrients contained within the crop residue that is removed in the process.

In 2011, the amount of nutrients found in a range of chaff cart dumps and narrow windrows was measured (Table 4). Nutrient analysis was conducted by CSBP, Western Australian fertiliser distributor.

Table 4. Average nutrient content in chaff from chaff cart dumps in 2011 in Western Australia

n.b. Legume = lupin

Research by Dr. Michael Walsh has shown that chaff yield averages about 33% of grain yield. In other words, if you are harvesting a 1t/ha wheat crop, approximately 333kg of chaff will be diverted into the chaff cart or chaff line or seed impact mill. This assumption was used to calculate the value of nutrients per tonne of grain harvested (Table 5).

Table 5. The value of the nutrients contained in harvest residue per tonne of grain harvested based on 2019 fertiliser prices

Nutrient spread

For chaff lining and chaff decks, the residue is not removed from the paddock but is placed in narrow zones that are not available to the whole crop, so it is assumed that the nutrients are lost. The nutrient cost of seed impact mills is assumed to be zero as the pulverised crop residue is returned to the field. However, if the mill cannot evenly redistribute these nutrients, perhaps this cost needs to be included. When observing the mill, it’s important to consider if it’s achieving an even spread.

Cost of ownership

To calculate the cost of purchasing a HWSC tool, depreciation and interest rate are added together and multiplied by the capital cost. This value is then divided by the hectares harvested by each harvester to give a $/ha cost. Consultants generally use a figure of 10% depreciation per annum for agricultural machinery (some machinery depreciates faster and some slower). At this point in time there is no measure of how fast weed impact mills depreciate, and therefore, the average of 10% is used. Interest rate is included in the cost of purchasing as there is an opportunity cost for the money used to purchase the tool.

Harvest cost

The cost of harvest is important because if the HWSC tool slows the time taken to harvest the crop, there is an increase in the cost of harvest per hectare.

Growers should estimate their own harvest cost and it should include depreciation, fuel, labour, repairs and maintenance, interest, etc. Also don’t forget to include the cost of running the chaser bin as part of the harvest cost.

Reduction in harvest capacity

Some of the HWSC tools can slow harvest, although a wide range of stories have been reported from farmers. Most farmers with chaff carts comment that they do not slow harvest at all, whereas some farmers say they slow harvest a little bit by perhaps 5%. The seed impact mills can slow harvest if the harvester is limited by its horsepower. Some farmers chip the engine to boost horsepower and report no reduction in harvest capacity. In general, in lower yielding crops where horsepower is not limiting there is no reduction in harvest capacity with the use of HWSC tools. In higher yielding crops, 5 to 10% reduction in capacity is common, with some growers reporting as much as a 25% reduction.

Fuel

There are a range of extra fuel costs quoted for seed impact mills and chaff carts. The figure of 0.5L/ tonne of grain harvested of extra fuel for the mills is assumed in the model. Growers interviewed for this study, quoted anywhere from 0.3L/t grain to 1.5L/ tonne of grain.

Wearing parts of impact mills

Assuming the cost of wearing parts in impact mills is a moving target, now, due to the emphasis the manufacturers of the mills are placing on product development to reduce wear rates. A pair of mills costs in the order of $9000 to $11,000 to replace. Mill life can be anywhere from 150 to 700 hours with 400 hours being the current average. At 400-hour mill life and $9500 for a new set of mills, this works out to be roughly $3/ha.

Repairs and maintenance (R&M)

To estimate this cost, it is best to check with the seller of the machine. Values used in the model are an educated guess for all of the HWSC tools.

Other benefits of residue retention

There are benefits to the soil biology and moisture from retaining crop residue, however an accurate figure to use was not found.

Grazing chaff cart dumps, chaff lines and chaff deck with sheep

Grazing chaff can be both beneficial to the sheep and is likely to redistribute some of the nutrients back over the paddock. These benefits may negate some of the cost of these tools and in some cases may result in the HWSC tool being free; particularly in cases where grazing chaff dumps or lines reduces the cost of supplementary feeding of sheep.

Conclusion

There is no single answer as to which HWSC tool is best. It depends! The Estimated Cost of HWSC model aims to give you the most accurate estimate of cost of HWSC based on what we know now. Even though there can be a big difference in capital cost between the HWSC tools, the total cost per hectare can be relatively small when all things are considered. Give the model a run with your numbers and see what you find. The model can be downloaded here.

Acknowledgements

The research undertaken in this project was made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support.

Contact details

Peter Newman
petern@planfarm.com.au