Headlands are often considered problematic in crop production systems. They are generally associated with damaged soil structure and poor crop performance.

Headlands are typically cultivated, sown, sprayed and harvested in a pattern that differs to the main part of the field. They are the field areas where the majority of machinery turns occur and typically extend into the field, the width of the sprayer boom.

Turning headlands represent a significant percentage of field areas, and therefore they require careful management for best results. Headlands are considered to be lower-yielding and they are often subject to soil structural issues when worked in unsuitable soil moisture conditions.

Mark's work involved intensive field sampling.

The research, supervised by Dermot Forristal (Teagasc) and Prof Kevin McDonnell (UCD), was part of my PhD that aimed to quantify the impact of headlands on soil structure and crop performance in Irish tillage fields.

Zone approach

Forty commercial spring barley, winter barley and winter wheat crops were surveyed over three growing seasons. Only plough-based tillage fields that were cropped in cereals for at least three years prior to the study were selected.

An initial assessment of the machine-turning techniques used by each grower led us to develop a novel zone approach which was used for all measurements.

Zone dimensions were determined by machine operating widths, turning patterns and the overall headland turning widths chosen by operators. Four areas (three headland zones and one in-field area) were identified based on traffic intensities and replicated four times per site:

  • Field edge: the area next to the field boundary that is subject to moderate axle loads.
  • Turning: the area subject to the highest axle loads and where most turning occurs.
  • Transition: the area where overlapped machine operations occur as the headland merges with the in-field area.
  • In-field: main field area where no machinery turns take place.

    • Soil structural assessments

    At each site, mini-pits were excavated at all zones to reveal soil layers for evaluation. Visual soil structure quality scores were assigned according to detailed scorecards.

    Within the plough layer (0cm to 25cm soil depth), we conducted a VESS evaluation – a visual method developed by SRUC – while below plough depth (25cm to 40cm), we used the Double Spade method, a system recently developed by Teagasc and UCD. A range of quantitative soil structural measurements, including cone penetrometer and bulk density, were also taken at both depths.

    The soil measurements generally followed the pattern of increasing traffic, as indicated by the traffic zone.

    The in-field zone where no machinery turns occur had the best overall structural quality. The turning zone where the majority of machinery manoeuvres take place – with the greatest traffic intensity and highest axle loads – had the poorest soil structure.

    In-field visual scores were at least 15% better than the turning area at both soil depths. This same trend was documented for cone penetrometer readings and soil bulk densities. The transition zone, where headland and in-field cultivations meet, was only subject to minimal structural damage, whereas significantly greater damage occurred at the field edge zone.

    Crop performance study

    Crops were monitored for the entire growing season and indicators of crop performance, such as establishment plant density, tiller counts and canopy biomass measurements, were determined for all zones. Final yields were determined using an intensive sampling regime.

    Crop performance was affected by headlands and the zone in which it was grown. Although performance varied between crops and sites, the overall trend was for the in-field area to produce the best yields. The greatest yield reductions were between the in-field area and the field edge zones for all crop types.

    There was a general trend for yields to decrease moving from the in-field area to the field edge, with the most notable yield reductions noted for spring barley (24%) and winter wheat (30%).

    The field edge: lowest yields

    The higher levels of machinery traffic that occur in the turning and transition zones typically resulted in poorer soil structure and yield compared with the in-field area.

    While the transition zone often had higher establishment due to consolidation, greater levels of cultivation and overlapped seeding, they were lower-yielding due to an inability to maximise on ear and grain numbers as a result of adverse soil conditions.

    Crop performance disimproved on the field headlands and followed a similar pattern to the soil scores, but not exactly. While the field edge zone had greater levels of machinery traffic than the in-field area, which contributed to a reduction in yield, it had less traffic than the turning zone, but still had poorer yields.

    Mark had to assess the headland soil structure in the fields sampled.

    While the factors contributing to yield loss on headlands differs between zones, this finding indicates the impact of other potential edge effects that contribute to reduced crop performance at the field edge zone. This is supported by fewer ears/m2 and lower yields compared with the in-field area, despite the field edge zone having similar establishment and plant densities.

    This research suggests that there are many causes of headland yield variability. The impact of other edge effects, such as the evenness of fertiliser applications on headlands, also needs to be considered.

    Reducing the impact of traffic

    Growers need to consider other strategies to help protect their soils on headlands. Careful selection of machine size, whether mounted or trailed, and appropriate tyre selection and tyre pressure adjustment, can all lessen the pressure on soils. Avoiding working when the soil is wet is extremely important. Headland management strategies, such as cultivating the headland last after sowing the in-field area, or moving the turning areas to different headlands, also have a role to play.

    In short

  • We wish to acknowledge all the tillage farmers who participated in this study and who facilitated the trials on their headlands. Your help was greatly appreciated.
  • Soils on headland are frequently damaged by machinery traffic.
  • Crop performance on headlands was poorer than the in-field area and this was partially associated with soil structure damage.
  • Crop performance at the field edge is also affected by other factors and uneven fertiliser and lime spreading may be contributing to this.
  • Soil management approaches, such as reducing ground pressure and delaying headland cultivations until completion of in-field crop establishment activities, have a role to play.