Study shows benefit in moving harvest windrows

Burning windrow in a large field.

Weeds researcher Peter Newman is encouraging growers with autosteer on their headers who burn harvest windrows for weed seed control to move their windrows by one metre each year to minimise the amount of nutrients lost from windrowed stubble.

Mr Newman, from the Department of Agriculture and Food, Western Australia (DAFWA), estimates the value of potassium and nitrogen burnt in wheat windrows, if an autosteer harvester follows the same path each year, to be $42.75 per hectare. This drops to a loss of $13.15/ha if the harvester shifts across by one metre. 

Mr Newman says the reason for the change in cost is that when narrow windrows are burnt the nitrogen “goes up in smoke” and the potassium stays behind.

“If a header follows the same path each year all the potassium is placed in the same place, leaving a potassium-rich strip, while most of the paddock is depleted of potassium,” he says.

“In this situation potassium is assumed to be lost from the system because the whole paddock must be fertilised to overcome the deficiency.”

However, if the header follows a different path each year, the potassium is eventually redistributed across the paddock and only nitrogen is lost, Mr Newman says.

He says this is not as important for heavy soils high in potassium. But high-yielding, sandy soils are at great risk of nutrient depletion if narrow windrow burning continues and the header follows the same autosteer path annually.

Measurements by the DAFWA researcher show that a chaff cart removes 11 to 37 per cent of residue from the paddock, depending on crop type and chaff cart set up. “This is much lower than narrow windrow burning at 50 per cent,” he says.

When Mr Newman started researching narrow windrow burning in 2001, headers did not have autosteer and potash was cheaper than it is today. Now, with higher fertiliser prices and most headers fitted with autosteer, he says “the game has changed and we need to react accordingly”.

Mr Newman’s study showed chaff carts remove nutrients worth about $11/ha, while the Harrington Seed Destructor (HSD), by comparison, retains all residue and nutrients, spreading them more evenly across the paddock.

“The estimated total cost of a chaff cart when harvesting wheat in 2011 was $16.15/ha,” he says. “This compares with $12.20/ha for the HSD.” 

Mr Newman says the HSD is cost-effective, especially across larger areas of high-yielding crop where its higher purchase price can be recovered more quickly.

He encourages growers to consider the true cost of all systems when deciding which harvest weed seed management tool to adopt (Table 1).

“Harvest weed seed management tools are essential for growers who like to maintain a high percentage of crop,” he says. “They come at a similar cost in this comparison, apart from windrows placed in the same strip each year, which is roughly triple the cost of other systems.”

 TABLE 1 Estimated total cost of various harvest weed seed management systems.* 
 System  Running cost ($/ha)  Labour cost for burning ($/ha)  Cost of nutrients
removed (potassium
and nitrogen only) ($/ha)
 Total cost ($/ha)
 Harrington Seed Destructor  12.20  0  0  12.20
 Chaff carts  3.10  2  11.05  16.15
 Windrow burning1  0  2  13.15  15.15
 Windrow burning2  0  2  42.75 44.75
 * Running costs includes depreciation, interest and fuel. Based on 2011 trials in WA’s northern agricultural region. The costs were estimated by discussing average running costs with growers using these systems. The cost will vary significantly between growers. Above-average grain yields were experienced in WA in 2011, which elevated the nutrient removal cost.
1 Assuming the header moves across by one metre each year.
2 Assuming the header follows the same path each year.     Source: Peter Newman, DAFWA.

More information:

Peter Newman,
08 9956 8563,
peter.newman@agric.wa.gov.au

GRDC Project Code DAW00196

Region National, North, South, West