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How to prioritise soil constraint amelioration

Tillage ameliorations such as deep ripping can require considerable capital investment.
Photo: Evan Collis

Deciding where to start soil amelioration can be enough of an issue to stall the process.

This article briefly describes six ways to approach soil amelioration. No one strategy is better than another. The choice depends on your budget, equipment and experience with soil amelioration.

What all approaches have in common is that they start by looking at soil constraints across the whole farm. You cannot know which constraints cover the largest areas if you do not know where they are.

Part 1 of Tackling amelioration on variable soil types outlines how to assess soil constraints across the farm.

The best return on investment

This strategy targets ameliorations that will make the most money. The best way to assess profitability is to calculate costs and potential revenue for your situation. In its simplest form, this means estimating revenue (yield) uplift from amelioration and subtracting calculated costs.

Yield uplift will be specific to your soil type, farm and amelioration capability. Existing guidelines and research summaries, such as Table 7 in the GRDC publication “Ten years of managing water repellent soils research in Western Australia – a review of current progress and future opportunities” are a good starting point if you are gauging these numbers for the first time. Local experience or experience on your farm is far more valuable.

Costs should include equipment, replacement parts, repairs, ameliorants, labour and pre and post-amelioration work such as rolling. One way to gauge the maximum cost is to use a contractor’s rate. To run a profitable business, contractors will include all the costs you should, plus their margin. However, there may be additional costs to you for work the contractor does not do, such as rock picking or crushing.

The Ranking Options for Soil Amelioration (ROSA) tool is another good way to help work out likely returns.

Paddocks with a better return on investment (ROI) are typically those with inherently better soil types but where current productivity is limited by fixable soil constraints. Paddocks with other non-fixable issues, such as frost or waterlogging, are riskier propositions from an ROI perspective.

The returns need to be weighed up against absolute costs (capital and variable) of the ameliorations and their riskiness.

Some ameliorations are largely variable costs (wetters, moisture retainers) but others, especially tillage ameliorations such as deep ripping and soil mixing, can require considerable capital investment.

Largest area first

This approach starts by tackling constraints limiting yield on the largest areas of the farm. Prioritising amelioration this way is especially important if contemplating machinery purchases.

Simple-fix ameliorations

Easy options tend to be those that use existing machinery and avoid unfamiliar machinery and multiple or complex operations. On deep, lighter soils the starting point is typically deep ripping to smash a compaction throttle, ideally where there are no acidity problems. On non-wetting gravels it is typically using wetters/moisture retainers or mixing, or experimenting with equipment such as cultivator bars fitted with wide sweeps.

Simple-fix options are usually also low-risk options.

Low risk

A low-risk approach starts with ameliorations with limited scope for financial or operational mistakes; for example, ameliorations that do not leave the soil surface vulnerable to wind erosion or likely to lift poor-quality clay to the surface.

Starting with low-risk ameliorations is a good strategy if you are new to soil amelioration and/or concerned about how variability within paddocks will affect the overall amelioration result. Low-risk activities are:

  • cheaper to implement – for example, addressing non-wetting surface soil with wetters or cross-row sowing, as opposed to soil mixing; and
  • more likely to work, so there is less risk of wasted dollars.

Proof of concept

Some growers want proof in the paddock before deciding what to tackle or whether to buy machinery. It is a cheap way to build confidence before investing in machinery.

A proof of concept often means borrowing a machine or using a contractor to ameliorate the one paddock considered most likely to respond. It can also involve using a machine that you know is suboptimal (for example, a plough, cultivator or chisel plough) to see if it makes any difference. If it does, it builds confidence that investing in better machinery will deliver better results.

Existing machinery

One starting point is to check which of your amelioration options you have appropriate machinery for. This can rule some paddocks out of amelioration and prioritise paddocks that you have the gear and skills to do.

Read the guide to tackling soil amelioration on variable soil types for more advice on understanding and prioritising soil constraints amelioration across the farm.

This article was produced as part of the GRDC ‘Maintain the longevity of soils constraints investments and increase grower adoption through extension – western region’ investment (PLT1909-001SAX). This project is extending practical findings to grain growers from the five-year Soil Constraints – West suite of projects, conducted by the Department of Primary Industries and Regional Development, with GRDC investment.

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