Are your soils ready

Published 16 January 15

Are your soils ready?

As we start to look towards the 2015 grass season, now is a prime time to start considering whether your soils are fit for purpose.

Each year a typical dairy farm can harvest in excess of 1.2 million mega joules of energy from its grassland. However, poor soil conditions will hinder this severely, reducing sward productivity and increasing feed costs. Alongside the regular soil fertility sampling, February is also a good month for assessing soil structure for compaction.

Recent work from the DairyCo Soils, Forage and Grass Research Partnership suggests soil compaction can result in yield losses of up to 25%. Soil compaction, by reducing air spaces between soil particles, also reduces uptake of N and P, hinders water movement through the soil and impacts on grass growth. As a result, it is estimated to cost dairy farms up to £250/ha/year in both reduced sward productivity and lost working days.

February is a good time to assess soil structure in fields and DairyCo and EBLEX, in partnership with SRUC and ADAS, has developed Healthy Grassland Soils, a simple scoring system for assessing the level of compaction in soil. The four-step process helps assign a score to your soil from 1 = Friable (good structure) to 5 = Very compact. 

 

Soil assessment sheet 1Soil assessment sheet 2

The Healthy Grassland Soils assessment sheet can be downloaded from the DairyCo website.

 

Using aeration equipment

For soils that score 4 or 5, it may be an option to use spike aerators to remove compaction at 0-10cm depth or sward lifters to remove compaction at 10-35cm. Latest DairyCo research undertaken at SRUC and Harper Adams University (HAU) has shown that this equipment can have positive effects on soil structure and aid water movement through the soil. However, if the soil showed no signs of compaction there was limited effect on soil structure. In addition, if you’re loosening soil in the middle of the growing season or in very wet or dry soil conditions, grass yield can be significantly reduced so selecting the correct time and working conditions is key. See below top tips on using soil loosening equipment and assessing soil working conditions.

Soil working conditions

Using slit aerators in very wet conditions can result in surface damage and smearing of soil, whereas in very dry conditions the equipment will fail to penetrate sufficiently. Likewise, with sward lifters, very wet conditions can increase the risk of soil damage via smearing and wheel slip. Very dry conditions, in contrast, are likely to lead to the formation of large clods, sward tearing and excessive surface heave giving an uneven surface finish.

To assess whether soil is suitable for loosening, roll a handful into a tube and if it gives a moist smooth surface then it is too wet to work. However, if the soil starts to crack then it is suitable for slitting or sward lifting (see the image below). This works best for medium to heavy soils.

Soil assessment

Image 1: Soil which is too wet (left) and suitable (right) for soil loosening

Top tips for using slit aerators

  • Use wide working widths to treat a larger area relative to the tractor wheels
  • Travel slowly (1-2kph) to ensure adequate penetration
  • Adjust the depth of penetration, if the aerator tears or lifts the soil surface, by adding or removing weights
  • Use long, sharp and narrow blades to give greatest penetration and volume of the slot
  • Significant sward damage can result if the rotors are set at an 80 degree angle to the direction of travel, which can be sufficient to act as partial cultivation in an overseeding operation.

 

Top tips for using sward lifters

  • Tines need to be working around 5cm (2 inches) below the base of the compacted layer
  • Work above the ‘critical working depth’ of the implement used – around 6 times the tine width
  • Dig holes prior to use to the expected depth to check moisture content and friability
  • Preferably, sward lifting should be carried out in the autumn when grass growth is declining
  • Leading discs should be aligned with tine legs to avoid excessive sward tear
  • Tine wings should have a low rake angle to minimise surface damage
  • The ideal forward speed depends on soil moisture but should be sufficient to cause lift over the advancing tine without causing turf to ‘flip’ over the packer roller
  • Do not use on sward heights over 6cm to reduce the risk of sward damage
  • It is not recommended in poorly drained soils with no drainage system present.

Remember, when using any soil loosening equipment, it is important to dig a hole after a pass to check it is having the desired effect and not causing damage.