Conservation Tillage

Conservation Tillage (CT) is defined as “any form of tillage that minimises the number of tillage passes, where soil aggregate disruption is reduced, a minimum of 30% of the soil surface covered with residues, with the aim to reduce soil erosion” (CTIC) 2004. In one sense CT can be used as an umbrella term to describe crop establishment systems which aim to conserve soil and water relative to conventional tillage practices (i.e. ploughing).

A number of these establishment systems, such as Minimum Tillage, Strip Tillage and No-till/Direct Drilling may fall under the CT umbrella where the minimum requirement of 30% of the soil surface is covered by residues. Some would argue that 30% soil cover alone is not sufficient, and that a reduction in fuel usage by 50% or more compared to a conventional system is needed in order for cultivations to be considered conservation.

Internationally there are many, many definitions for the different establishments systems being employed by farmers across the globe. Non-inversion tillage, chisel ploughing, reduced tillage, minimum tillage, mulch tillage, conservation tillage, direct drilling, direct seeding, strip tillage, zero tillage and No tillage to name just a few. Some of these are distinct well-defined systems, whereas others are more regional descriptions of systems which have been modified to suit the local climate, soil type, cropping patterns and or farming system.

The four crop establishment systems used in Ireland are:

Conventional Plough base System
Minimum tillage
Strip-till
Direct drilling (no-till, zero-till)

Two noteworthy points should be considered. Firstly, the less intensive soil cultivation methods, namely minimum-till and direct drilling, were initially developed in drier and warmer climates with soils that may significantly differ from those in Ireland. Consequently, the delivery of these ecosystem services could be compromised due to our wetter autumn and spring periods and fewer moisture deficit periods.

Secondly, there exists considerable variation in tillage intensity (i.e., the extent of soil inversion) and depth within both plough-based and minimum-till systems. In some instances, the minimum-till system may operate at the same soil depth and intensity as a plough-based system.

Plough

Ploughing is Irish farmers' most common establishment system. It works to a depth of 17.5-27.5 cm (7-10 inches). The plough inverts the soil, buries crop residues, and cultivates. Adopting combined cultivation and sowing units (one-pass) in the 1980s facilitated winter crop establishment in spells of broken weather. In addition, it reduced traffic and wheeling damage and avoided excess moisture loss.

Figure 1. Ploughing: Inversion to 17.5 - 27.5cm deep, followed by secondary cultivation before sowing.

In spring, the plough and one-pass system allowed the often drier inverted soil to form the seedbed. Also, the loosened soil usually dries and warms quicker than less disturbed soil.

The need for secondary cultivation following ploughing on lighter textured soils was further reduced following the introduction of cultivator drills.

Benefits and Constraints of Plough-based Tillage Systems

Benefits	Constraints
A well-established system with known practices and techniques. Effective in controlling certain weeds and pests, as ploughing buries crop residues and other organic matter, which can harbour pests and diseases. Improves soil aeration and water infiltration by loosening compacted soil and increasing pore space, which can lead to better, near-surface drainage and reduced risk of waterlogging in winter and faster establishment in spring. Adaptable to various soil types and conditions and within-field variations, including headland compaction.	It can lead to soil structure damage and reduced water-holding capacity in the long term if poorly managed under wet conditions. Continuous mechanical restructuring of soil reduces the chances of developing vertical porosity in non-loosened soils. Soils loosened to depth are more prone to compaction It may: Increase soil erosion and runoff due to the significant soil disturbance and removal of surface cover, primarily when used in late autumn. Have reduced beneficial species such as earthworms compared to Non-inversion tillage systems Accelerate soil carbon loss. Restrict establishment and early growth in spring due to dried-out seedbeds.

Benefits

Constraints

A well-established system with known practices and techniques.
Effective in controlling certain weeds and pests, as ploughing buries crop residues and other organic matter, which can harbour pests and diseases.
Improves soil aeration and water infiltration by loosening compacted soil and increasing pore space, which can lead to better, near-surface drainage and reduced risk of waterlogging in winter and faster establishment in spring.
Adaptable to various soil types and conditions and within-field variations, including headland compaction.

It can lead to soil structure damage and reduced water-holding capacity in the long term if poorly managed under wet conditions.
Continuous mechanical restructuring of soil reduces the chances of developing vertical porosity in non-loosened soils.
Soils loosened to depth are more prone to compaction
It may:
- Increase soil erosion and runoff due to the significant soil disturbance and removal of surface cover, primarily when used in late autumn.

Have reduced beneficial species such as earthworms compared to Non-inversion tillage systems

Accelerate soil carbon loss.
Restrict establishment and early growth in spring due to dried-out seedbeds.

Below is ECT focus farmer Gavin Curran explains the plough based system.

Non-Inversion Tillage Systems

Non-inversion tillage encompasses all systems that refrain from soil inversion, comprising minimum-till (reduced tillage), strip-till, direct-drill (no-till, zero-till), and other methods besides ploughing. However, there is substantial variation within this category regarding the depth and intensity of cultivation. These factors dictate the degree of disturbance and the distribution of crop residue in the topsoil profile. Consequently, when describing each system, it is crucial to include information about the depth and cultivation intensity, reflecting the extent of soil mixing during cultivation.

Minimum Tillage

Minimum tillage describes shallow (50 to 100 mm) soil cultivation with the lowest cultivation necessary and retaining 30% of the previous crop residues on the soil surface. It is a reduced cultivation level (depth and intensity) compared to ploughing. A tine or disc cultivator completes the cultivation and is designed to cope with different surface residue levels.

Figure 2: Min-Till Drilling: Stubble cultivation to 5-20cm deep, to produce a stale seedbed, followed by herbicide application and seeding by a cultivator drill. It may be operated with a shallow initial cultivation post-harvest followed by deeper pre-drilling cultivation.

Initially, only one cultivation between crop harvest and sowing was practised. However, over time in Ireland, the depth and intensity generally increased with two frequently used cultivation runs up to 150 mm deep, but occasionally more, resulting in a similar level of soil disturbance as ploughing.

The type of cultivation equipment used and the depth and number of cultivations will depend on soil stone content, user preference, soil type, previous cropping, the crop to be sown, and the time of year.

Below, ECT focus farmer Simon Neville explains the min-till cultivation system.

Strip-Till

Strip-till limits cultivation to strips in a one-machine pass. For cereals, a lead tine working at 100 to 200 mm depth cultivates strips of soil at a row spacing of 300 to 330 mm in advance of a sowing coulter. Strip tillage typically cultivates about 33% of the field area, and seeds are sown in these strips of disturbed soil while the space between the sown strips is left untouched.

Figure 3. Cultivation in strips centred at approximately 30cm followed by a sowing coulter leaving about 40-60% of the soil undisturbed.

For weed and volunteer plant control, some farmers complete light surface cultivations followed by herbicide application to create a stale seedbed. Claydon and Mzuri are examples of strip-till drills used in Ireland.

Below, Michael Grace, ECT focus farmer, outlines the strip-till system.

No-Till (Direct Drill, Zero Till)

Direct drilling is a crop establishment method where crops are planted without disturbing the soil beyond that necessary to place the seed at the required depth. There are two machine types.

A disc drill, which makes a narrow slit in the soil, then puts the seed in the slit before covering it with soil.
A tine coulter machine opens a narrow band just deep enough to place the seed and then covers it with soil.

Figure 4. Direct Drill (no-till, zero-till): Direct placement of the seed with minimum soil disturbance.

No-till systems allow a more resilient soil structure, which may help to reduce carbon loss and increase biological activity.

Examples of direct drills used in Ireland include Weaving, John Deere, Cross Slot and Duncan machines.

Below ECT focus farmer Eoin Lyons explains the No-Till system.

Benefits and Constraints of Non-Inversion Tillage Systems

Benefits	Constraints
Reduced fuel, machinery and labour costs due to the tillage depth and intensity reduction. Reduced soil erosion due to minimal soil disturbance which preserves the soil structure and reduces runoff. Can produce yields equal to or greater than plough-based systems in most years. It can retain more organic matter near the soil surface, increasing water-holding capacity, soil stability, and friability. Potentially improved soil health and biodiversity due to reduced soil disturbance and improved soil organic matter status. Versatile drill suitable for deep sowing if required (beans) (Strip till) Soil bearing strength for machinery is high as it is undisturbed (Strip till/No- till).	It does not alleviate deeper (25 cm) soil compaction that may occur in wet seasons. There is an increased risk of poorer crop establishment in wet autumns, often forcing earlier sowing with consequences for more difficult disease and weed control. Where shallow cultivation is used before spring sowing, heavier textured soil may be slower to dry, resulting in later sowing. With heavier soils, nitrous oxide emissions may be increased due to greater water retention, resulting in more denitrification and increasing GHG emissions. If used in wetter conditions risk of smearing and compaction. Increased potential for problematic weed growth, as strip tillage disturbs only a portion of the soil, leaving other areas for weed growth. Grass weeds can increase in autumn as the wide rows provide more light, encouraging grass weed emergence and establishment (Strip Till). Initial investment costs for specialised equipment and technology can be high, particularly for small or medium-sized farmers. More likely to practice early planting to take advantage of drier soils, which may promote the growth and spread of weeds.

Benefits

Constraints

Reduced fuel, machinery and labour costs due to the tillage depth and intensity reduction.
Reduced soil erosion due to minimal soil disturbance which preserves the soil structure and reduces runoff.
Can produce yields equal to or greater than plough-based systems in most years.
It can retain more organic matter near the soil surface, increasing water-holding capacity, soil stability, and friability.
Potentially improved soil health and biodiversity due to reduced soil disturbance and improved soil organic matter status.
Versatile drill suitable for deep sowing if required (beans) (Strip till)
Soil bearing strength for machinery is high as it is undisturbed (Strip till/No- till).

It does not alleviate deeper (25 cm) soil compaction that may occur in wet seasons.
There is an increased risk of poorer crop establishment in wet autumns, often forcing earlier sowing with consequences for more difficult disease and weed control.
Where shallow cultivation is used before spring sowing, heavier textured soil may be slower to dry, resulting in later sowing.
With heavier soils, nitrous oxide emissions may be increased due to greater water retention, resulting in more denitrification and increasing GHG emissions.
If used in wetter conditions risk of smearing and compaction.
Increased potential for problematic weed growth, as strip tillage disturbs only a portion of the soil, leaving other areas for weed growth.
Grass weeds can increase in autumn as the wide rows provide more light, encouraging grass weed emergence and establishment (Strip Till).
Initial investment costs for specialised equipment and technology can be high, particularly for small or medium-sized farmers.
More likely to practice early planting to take advantage of drier soils, which may promote the growth and spread of weeds.