Cultivation methods have changed over time, partly driven by the necessity to reduce the cost per acre of crop production, and also to be more effective with the time and resources available. Here we review the different tillage methods available to the modern farmer from the origins of cultivation in the plough, to direct drilling and zero tillage.
Ploughing is a well-used, tried and tested tillage method that works well in most conditions and provides a number advantages that no other tillage method has. In one pass, the plough produces a trash-free surface and well loosened soil which can be turned into a seedbed and a new crop established. Ploughing is also extremely effective as a weed control method and is often used in a rotation to control the weed burden without excessive use of chemicals.
The plough is one of the earliest farming implements but this does not mean that it has stopped developing. The modern plough is easier to set up and adjust, and some of the more recent models have advanced technology and ISOBUS controls that improve efficiency.
Disadvantages of ploughing
A common problem in ploughing is the creation of a plough pan (a compacted layer just below ploughing depth). Ploughing depth should be varied year to year or a subsoiler should be used to break this up.
Ploughing is less suitable in dry conditions, since the soil loses relatively large amounts of moisture during ploughing, which can result in poor crop results if there are dry conditions after planting. Conversely too much rainfall after ploughing can also create issues, as the trash-free surface can form a crust on certain types of soil. In addition, heavy rainfall and wind can bring soil erosion in some soil types.
The main reason behind reduced use of ploughing is economic. While the plough itself is not a very expensive piece of equipment, low capacity means costs per acre are fairly high. In addition, time requirement per acre is high this create a problem on farms where available time is limited, particularly in a busy time of year such as autumn.
Creating a seedbed and drilling after ploughing
On light soils the plough leaves a surface that only requires some leveling and reconsolidation to produce a good seedbed. However on heavy soils, ploughing leaves a surface that requires more work before drilling. Traditionally several passes were required with cultivators, rollers and presses until a seedbed was created. Today cultivators such as a Vaderstad Carrier and similar are used in combination with other cultivators in order to reduce the number of passes. Cultivating seed drills such as the Vaderstad Rapid and Horsch Pronto can mean the seedbed requires less preparation than conventional seed drills.
In more recent years there has been an increase in ploughless tillage systems, this is often called reduced tillage and while this is not always correct, some deep tillage works the ground almost as much as ploughing; it does describe the goal of the system which is to reduce the amount of tillage required.
Deep tillage with a cultivator is often used:
- On light soils that require loosening
- When large amounts of trash need to be mixed into the soil
- Before compaction-sensitive crops such as oilseed rape
- When tramlines and compaction needs to be lifted
A cultivator such as a Vaderstad Topdown or Simba SL can be used for one or two passes or alternatively a tined cultivator can be used in combination with a disc cultivator.
When deep cultivation is carried out within the same depth range as ploughing the costs per acre are approaching those of ploughed systems. The most important factor in favour of deep reduced tillage, compared to ploughing, is the increased capacity per hour, machines of up to 8M are available saving considerable time.
For shallow reduced tillage, disc cultivators such as Vaderstad Carrier or Simba X-Press are most commonly used today. Some tined cultivators are also used, especially when the working depth exceeds 6-8cm. When large amounts of trash have been left on the field and have to be mixed into a limited amount of soil, it is important to pre-treat the harvest residues. Shallow reduced tillage gives savings in terms of both costs and time in lower horsepower and fuel requirements and an increase in working speed.
In recent years, the need for a more shallow cultivation option has increased for several reasons:
- Increased problems of herbicide resistant weeds
- Increased problems of oilseed rape volunteers.
- Increased usage of cover crops
Ultra-shallow tillage is a tillage practise that works the ground at only 2-3cm depth. A tool working that shallow needs a high capacity and speed coupled with a good ability to cope with trash.
Ultra-shallow tillage should be carried out immediately after harvest to help “chitting” (germination of weeds), seeds are triggered by light, meaning that most crops generally germinate at shallow depth. Burying seeds too deep often results in seed dormancy. This can last for years. Oilseed rape for example can germinate after 20 years of being buried. Many weeds, i.e. herbicide resistant blackgrass, also causes problems if left in dormancy, reducing yields for years to come.
Ultra-shallow tillage is faster and more cost effective than other tillage systems, requiring less horsepower and fuel.
Effects of reduced tillage
Using a shallow tillage system continuously can cause a dense layer in the soil that is similar, but at a shallower depth, to a plough pan. It is therefore important to alternate between shallow and deep cultivation. Soil types can also mean different methods are necessary, light soils often have a weaker structure than clay soils and require deeper cultivation to maintain crop yields.
Straw-borne diseases are a factor to consider in reduced tillage due to the crop residue not being buried and a good crop rotation is essential for success.
Volunteer weeds are another major problem in reduced tillage. In good conditions they can be eliminated with cultivation, but in wet conditions they are difficult to control without the use of chemicals. Another problem with reduced tillage is slug control, slug traps and pellets could be needed especially in sensitive crops such as oilseed rape.
During direct drilling, the seed is placed without any prior soil cultivation in the stubble of the previous crop. Avoiding cultivation naturally reduces the time requirement and costs per acre. The decreased time requirement is an important consideration on large farms and also in areas where the period between harvest and planting is very limited.
Leaving the majority of the soil surface undisturbed under a straw cover provides good protection against water and wind erosion. Losses of soil and plant nutrients via erosion have negative economic and environmental effects.
Omitting soil cultivation in a cropping system gives rise to certain problems:
- The spread of straw-borne diseases via crop residues on the soil surface
- Uneven distribution of trash cannot be corrected
- Pests such as slugs and weeds have to be controlled with chemicals
- Wheel tracks and soil compaction cannot be lifted with cultivation
The most important consideration when dealing with the above problems that occur with direct drilling is good crop rotation. However for some problems such as slugs and weeds, chemical control is necessary.
Controlled Traffic is becoming increasingly common in direct drilling systems, this mean that tramlines and compaction damage can be controlled and kept in particular areas.