What is no-till?

No-till is sowing a crop without prior cultivation and with very little soil disturbance at seeding. There are several terms that have evolved in WA agriculture. The main tillage terms from most to least cultivation are:

• multiple tillage (previously known as conventional tillage);
• reduced tillage which is one pass prior to seeding with a full cut-out;
• direct drilling which is one pass seeding with a full-cut;
• no-till which is narrow/knife point seeding with less than full cut-out;
• zero-till which is disc seeding. 

The term minimum tillage is confusing as it can mean all of these things except multiple tillage and therefore it should be dropped. Conservation tillage such as no-till and zero-till are promoted by WANTFA as these seeding systems have the least amount of soil disturbance and the greatest soil cover remaining from previous crop residues. 

Why no-till?

No-till with retained stubble has the potential to improve soil properties and increase sustainability. It can do this by lifting and modifying soil biological activity that gives excellent improvements in all aspects of soil fertility, being physical, chemical and biological. These improvements lead to better farm management as well as improved sustainability.  

The main benefits of no-till, with appropriate agronomic management, include:

• Reduced susceptibility to land degradation through stubble retention and proper grazing management (especially in sandy soils).
• Greater flexibility and timeliness of farm operations through less time used at seeding and other operations.
• More manageable soils and improved soil structure, especially in control traffic situations due to less trafficability.
• Higher levels of organic matter and biological activity.
• More precise seed placement with more even crop emergence, if seeded at correct moisture content.
• Greater amounts of water harvested to grow the crop in dry areas.
• Often less in-crop weed emergence and safer use of pre-emergent herbicide for weed control.
• Less labour, fuel and machinery costs per hectare. Better whole farm profitability and sustainability. 

Additional benefits in a zero-till farming system, include:

• Increased sowing speed and reduced horsepower requirements.
• Better stubble handling capabilities at higher stubble loads, if managed correctly.
• Reduced weed seed bank stimulation within the inter row at seeding.
• Less exposure of moist soil layers through soil throw at seeding. 

The key components of no-till and zero-till

• Permanent soil cover through stubble retention and cover crops

This is crucial to the success of a no-till and zero-till farming system as plant residues reduce evaporative water losses, increase water infiltration, reduce the risk of erosion and encourage biological cycling of nutrients. Discs can handle greater amounts of stubble than tynes, although for both seeding systems stubble handling at harvest is important for ease of sowing.

• Minimal soil disturbance at seeding and during other operations/practices

Reducing soil throw at seeding helps to reduce moisture loss, maintain soil structure and reduce stimulation of weed seeds. By limiting cultivated ground to a narrow seeding row only, this gives the crop enhanced seedling vigour over competitive weeds. Reduced soil throw, especially with tyne machines can also diminish crop damage caused by pre-emergent herbicides.

• Reduced compaction of soil by limiting mechanical traffic and livestock trampling

Before adopting no-till practices a deep cultivation may be required to amend compaction layers for certain soil types. Thereafter, to reduce the need for further cultivation and to allow crop roots to biologically aerate the soil, farm practices such as control traffic farming, constructing laneways and monitoring of stocking pressure are recommended. 

• High levels of system diversity, including but not limited to crop rotation and chemical rotation

Profitable no-till cropping requires excellent crop agronomy. Tillage has been used for thousands of years to kill pests, particularly weeds, reduce diseases and soften the soil for fast root growth and nutrient release. When adopting less tillage we need to manage these factors by other means. Rotation of crops is the principal tool that must be used for effective no-tilling. 

Taking a long term approach

Derpsch and Sá, both scientists specialising in conservation tillage promote a long term approach to no-till in order to reap the full benefits of the farming system. Below is a diagram showing the four phases involved in no-till adoption. 

Figure 1. Progression of the no-tillage system over time (derived from Sá, 2004)

Some of the benefits of no-till, like improved water harvesting, are seen immediately while others are only realised in the long term.

In the initial phase (0 to 5 years) the rebuilding of soil aggregates begins and measurable changes in the organic carbon content of the soil are not expected.  There are low crop residues and nitrogen needs to be added to the system. 

The next 5 years (5 to 10 years) are the transition phase where there is an increase in soil density, soil carbon, phosphorus and the amount of crop residues on the soil surface. 

In the consolidation phase (10 to 20 years) greater amounts of crop residue and soil carbon are achieved.  The soil water holding capacity and cation exchange capacity are increased and greater nutrient cycling is observed. 

It is only in the maintenance phase (>20 years) that the ideal situation with the maximum benefits for the soil is achieved and less fertiliser is required (Derpsch, 2005).

References:

• Derpsch, R.W. (2005). Situational Analysis of No-Tillage Systems in WA and Recommendations for the Way Forward.  A Report on a Consultancy to WANTFA, GRDC and DAFF.
  
• Sá, J.C. M., 2004: Adubação Fosfatada no Sistema de Plantio Direto. In: Sympósio sobre Fósforo na Agricultura Brasileira, Anais (ed.) T. Yamada, Silvia, R. S. Abdalla, p.201-222, Piracicaba, SP, POTAFÓS, 2004, 726p. 

Herbicides usage

One of the main challenges to no-till cropping is the increased use of herbicides for weed control, because cultivation is rarely used. Continued use of a narrow range of herbicides can result in the selection of weeds that are resistant to the specific chemicals.  It is important to consider an integrated approach to weed management and one of the key priorities is to diversify the rotations so that different chemicals, times of sowing and crop competitiveness can be utilised. 

Suitability of soils to no-till

All soils can be no-tilled, however, some compactable sandy soils (eg. Wongan Hills loamy sands) may require occasional deep ripping, even in a no-till system. In sandy soils, no-till with stubble retention minimises wind erosion and where it leaves furrows, makes water harvesting easier in water repellent soils.In clayey and loam soils, no-till minimises run-off and erosion by water and improves soil structure. In dispersive loamy or clayey soils, no-till with stubble retention reduces splash erosion as rain drop impact is minimised. No-till is excellent for soils that slake and/or disperse and form surface seals or crusts or set hard on drying, as well as for cracking clay soils. These 'Sunday soils' have a narrow-moisture-cultivation range and no-till allows early sowing and better trafficability when soil moisture is optimal. Some soils with clay contents greater than a loamy sand are prone to slaking and/or dispersion. Ideally, heavy soils should be no-tilled and grazing should be eliminated when the soil is wet. Biological soil improvements are still not well understood, yet their impact is often obvious after three or more years.