Investment drivers

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Investment in the management of non-wetting soils is best done at the farm scale, within the farm business investment capacity and over a realistic time frame.

The most effective and profitable long-term solutions to non-wetting are the amelioration methods of claying, spading and inversion ploughing. But, at a cost of $100 to $900 per hectare, few farm businesses can afford to apply these to the whole farm in a single year (Table 1).

Mitigation of non-wetting through modified seeding methods (adding wings to points or boots, sowing close to the previous row with or without banded wetter) does not provide as large a yield benefit as amelioration, but the methods are easier and cheaper to apply across an entire cropping area in one season, adding to whole farm profit (Table 1).

When calculated at a whole-farm scale for a typical Western Australian farm, increases in farm profit from seeder modifications have been estimated at 20 per cent if the cropped area is large and mainly non-wetting and dry sown. This amounts to about $40 to $115/ha at a cost of less than $10/ha (with a wheat price of $280/t). The analysis estimated the best use of an annual $20,000 investment between mitigation or amelioration strategies against non-wetting soil over a 10-year period.

The modelled farm was 5000ha with 75 per cent cropped and an annual wheat yield of two tonnes/ha and a wheat price of $280/t. A reliable yield increase of 600 kilograms/ha was assumed from amelioration costing $150/ha and a 10 per cent yield benefit from mitigation by smarter furrow sowing at $5/ha (including any costs of steering systems, points, boots, or banding kit or wetter). The amelioration benefit was assumed to last 10 years and mitigation one year.

 

Strategy  Management option  Typical cost ($/ha)  Longevity of benefits (years)
Table 1 Cost and effectiveness of management methods for non-wetting soils.
Mitigation Improved seeding systems (for example, on-row and winged points/boots)  < 5  1
Banded wetting agents  8–15/year  1
Blanket wetting agents  20–50/year  1–2
Amelioration One-way disc ploughing  40–60  3–5
Rotary spending  120–150  3+
Soil inversion (mouldboard plough or square plough)  100–150 5+
Clay spreading  450–900  >10
Clay delving  200–400  >10

Investment mix

Graph showing effect of non-wetting area and crop proportion sown dry versus mitigation methods to overcome water repellency

Figure 1 Effect of non-wetting area and proportion of crop sown dry on the most profitable allocation of a $20,000 investment in amelioration versus mitigation methods to overcome water repellency.

Analysis by the Department of Agriculture and Food, WA (DAFWA), suggests when 80 per cent of the farm is affected by water repellence, and 80 per cent is dry sown, the best distribution of a $20,000 per year non-wetting soils investment is about 40 per cent to amelioration and 60 per cent to mitigation (Figure 1). However, if 20 per cent or less of the farm is repellent all investment should generally be in amelioration.

The analysis used average yield responses for both amelioration (600kg/ha) and mitigation (10 per cent) based on trials over several years across the WA wheatbelt. However, yield responses to amelioration ranged from –0.3 to +2t/ha with many results between 200 and 700kg/ha. Yield response to mitigation methods also varied but to a lesser degree than amelioration.

The optimal mix between amelioration and mitigation options will therefore differ between farms, depending on the severity and size of the water-repellent area and the cost and expected yield benefit of different treatments. The analysis was very sensitive to the proportion of area that was repellent and the proportion dry sown:

  • as a general rule the more hectares that are repellent the more money that should be assigned to mitigation, as mitigation options have a largely fixed cost (such as different points on the seeding bar) – the more hectares this cost is spread over, the more attractive the investment;
  • large cropping programs reliant on dry sowing need relatively more investment in mitigation; and
  • relatively wet growing regions with relatively small areas of repellence require more investment in amelioration.

Other production constraints also skewed the non-wetting investment ratio. For example, the presence of herbicide-resistant weeds made amelioration with inversion ploughing a more valuable investment than mitigation. Similarly, a requirement for early crop establishment during warm conditions made dry furrow sowing (with winged points/boots), banded wetters and sowing near the previous row a better investment.

More information:

James Hagan, economist, DAFWA,
08 9956 8520,
james.hagan@agric.wa.gov.au

Combatting non-wetting soils

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Long-term non-wetting remedies

GRDC Project Code DAW00204

Region West