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Cultivation/Tillage for Broadacre Cropping

Crusting | Waterlogging | Trafficability | Compaction | Cultivation/Tillage for Broadacre Cropping

The Cultivation Dilemma
Annual croppers have traditionally used cultivation for:

  • seedbed preparation;
  • weed control; and
  • moisture conservation (via mechanical fallowing).
Cultivation physically disrupts the soil, exposing the soil surface to erosive forces, and facilitating the oxidation of organic materials. Cultivation can include reduced infiltration, erosion, crusting, and reduced plant growth.

There is an imperative to minimise tillage. The development and use of herbicides has increased the options for minimising tillage. Strategic use of herbicides can replace the use of cultivation for both weed control and moisture conservation.

If cultivation/tillage is to be used the best time is when the soil is slightly moist (not wet) and the preferred strategy is one that controls weeds, maintains soil structure, will not cause erosion, controls root disease, allows early sowing, establishes good plant density with early vigorous growth, gives the greatest yield and is cost effective

Adjacent paddocks in the Mallee region during a wind storm - minimal tillage paddock on the left and cultivated paddock on the right

One of the challenges in discussing tillage is to have clear definitions. Minimum tillage methods worldwide have been described by different names such as no-till, zero-till, minimum-till, incomplete-tillage, reduced-tillage or direct-drill. The systems differ mainly in the degree to which the soil is disturbed prior to sowing. The term conservation tillage is often used to describe all systems which aim to reduce the impact of conventional cultivation. The no-till and zero-till systems generally have the least amount of soil disturbance and greatest soil cover remaining from previous crop residues.

We are standardising on six commonly used terms for Victoria:
  • Conventional cultivation
    Describes the common practice involving primary and secondary tillage operations which generally results in <30 % crop residue on the surface. It involves more than three (including seeding) tillage passes.
  • Minimum tillage
    All conservation broad acre cropping practices are aiming to minimise damage to soil structure, avoid the loss of soil, and reduce the evapo-transpiration of soil water. Conservation tillage leaves 30 % or more of the soil surface covered with crop residue. Minimum tillage simply describes the aim of conservation tillage. It involves three or less tillage passes (including seeding).

The following four practices can also be included as minimum tillage.
  • Reduced tillage
    Involves one or two cultivations before seeding and can still contribute significant damage compared to direct-drill, no-till and zero-till, it is convenient to call this reduced tillage to separate it from the fully minimized forms of tillage.
  • Direct-drill.
    Crop or pasture is sown directly into an untilled soil. The level of disturbance is variable.
  • No-till
    Crop is sown into an untilled soil but using narrow or knife points to minimise disturbance (<30%) to soil
  • Zero-till
    Crop is sown with one pass with a disc seeder

What are the benefits of minimum till systems?
Stubble retained as ground cover steadily adds to the reservoir of
soil organic matter. This in-turn will lead to improved soil structure and increased aggregate stability. Ground cover also decreases erosion with less exposure of the soil to erosive forces. Another significant benefit to minimum tillage systems are the savings on machinery hours and fuel. The economic benefit of minimum tillage will vary from farm to farm but savings on inputs are in the order of 15 % to 30 % Yields will not alter much for the first few years but histories show gradual yield increase from the fourth or fifth year and continuing up to 30 % (Tullberg et al. 2003). If combined with controlled traffic farming this can further increase input savings and yields. Various experiments across Australia are showing the potential for yield increase with the intelligent use of minimum tillage.

As an example of how soil type affects the management of soil, red loamy soils, unlike sandy soils, do not respond to cultivation. Even a zero-disturbance triple disc drill produced yields equal or better than cultivation, especially when adequate nitrogen was applied. With no benefit evident from cultivation of these soils, the system of lowest cost and superior erosion prevention is the best option (Anderson 2000).

Are there any limitations to minimum tillage systems?
Limitations of a minimum tillage system are weed management, herbicide resistance, machinery suitability, and occasional outbreaks of pests.

The pioneers and other long-term practitioners of minimum tillage cropping (particularly no-till systems) have developed strategic and effective herbicide management and application. This includes timely control of any summer weeds and a grass control product in a mix with a knockdown product in front of the seeder, then early application of any in-crop weed control if required.

Dry cultivation/tillage induced damage in the Mallee 2008.

Are there any areas of Victoria where these practices are common?
Controlled traffic farming (CTF) and no-till cropping in particular are being adopted throughout Victoria (Tullberg et al. 2007). Southern Farming Systems (SFS) were early adopters of CTF through their raised bed cropping to manage waterlogging in the higher rainfall zone. Since 1997, with dryer environmental conditions, the main farming system in SFS has leant towards CTF because of the soil health benefits learnt from the raised beds. These benefits are less compaction in the subsoil and better root and plant growth because of improved soil moisture conditions.

This lesson had already been learnt in the Wimmera and NE Victoria and parts of the Mallee where a number of farmers have been no-till cropping since the early to mid nineties with an increasing adoption since 2002. Some of the early adopters of no-till are embracing CTF to further improve their soil health through the benefits they have seen from minimising compaction from wheeled traffic.

The latest technology in tractors, air-seeders and guidance systems along with row spacings has created many opportunities for all farmers to improve their farming systems and production as well the environment and their quality of life.
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