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What nutrients are lost when making hay from failed crops?

Cutting for hay is an option to get some economic value from a failed crop. Growers with an eye to the long term productivity of their paddocks weigh the value of the hay against the value of leaving the crop material in the paddock. Nutrients that would otherwise be recycled in the soil are lost when crop material is removed from the paddock.

One-off hay cutting of a crop that has failed due to drought can prompt some changes in your crop nutrition program and paddock management into the next season.

How much material is removed?Hay

  • Typical yields of stressed cereal or canola crops would yield 1.0 to 3.0 t/ha of hay.
  • A rule of thumb for unstressed cereal hay is that with a good plant density (~200 plants/m2), each 30 cm of growth above the cutting height will yield 2.5 t/ha of hay.

Nutrients removed with hay

Cutting hay will remove 2 to 3 times more nitrogen, and up to 10 times more potassium than if the crop was left for grain, and maybe 5 times more sulfur in both canola and cereals. This is talking in ballpark figures; nitrogen is always quite variable, as are phosphorous, sulfur and potassium, as all depend on soil nutrient status. Here are indicative values from a number of sources, including Rob Norton’s experiments in the Wimmera and Mallee during the period 1990 to 2003 with wheat and canola.
yield table

Crop nutrition issues in the following season:

Potassium deficiency in soils with low K reserves

If concerned, apply a test strip of muriate of potash (MOP) pre-sowing and monitor. Used at sowing, MOP can cause salt damage to the seed, so separate seed and fertilizer. Low soil K levels are a greater risk in sands or light textured soils, acid soils, high rainfall zones, and in paddocks with history of hay cutting. Wheat critical levels for Colwell K are 40 mg/kg on Tenosols and Chromosols, 50 mg/kg on Kandosols, and about 65 mg/kg on Brown Ferrosols (Brennan and Bell 2013).

Sulfur deficiency following canola hay cutting

Consider sulfur supplementation of the following crop, such as using S fortified fertilizers or gypsum applications.

Acidification and lime requirements

Hay cutting is considered the most acidifying of agricultural practises, and on acid soils can make the issue worse. The removal of cereal or canola hay requires 25 kg/ha of lime for each tonne of biomass removed, or 45 kg/ha for each tonne of annual legume hay removed, to neutralise the resulting acidity.

Soil carbon

Cutting hay reduces inputs of organic matter into the soil for that season. The size of the effect when the hay is cut from a failed crop might be roughly similar to organic matter lost from burning stubble residues from a good crop, compared to retaining the stubble. The importance depends on the soil carbon status of the paddock and the goals of the grower.

Erosion can lead to more nutrients lost

Following hay cutting as there is little residue cover (maybe 0.4 t/ha of residue after hay cutting versus 2.0 t/ha after harvest). Reduce grazing and traffic across these paddocks to reduce the hazard of wind and water erosion. Nutrients are lost with eroded soil.

More information

IPNI: Nutrients removed in hay crops

GRDC: Canola hay and silage fact sheet

VIC DEDJTR: Soil acidity (see table 4 for replacement liming rates for product removal)

Crop & Pasture Science: Soil potassium—crop response calibration relationships and criteria for field crops grown in Australia, Ross Brennan and Michael Bell, 2013.

 

Acknowledgements

Rob Norton, IPNI, Roger Armstrong, VIC DEDJTR.

Photos provided by the GRDC.

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