Costs of poor soil structure

Yield losses can occur as result of impacts in part of the growing/grazing season and/or as a result of on-going yield reduction which is detected in annual productivity.  Frequently poor soil structure will lead to a 10-20% reduction in grass growth; equating to around 1-2t DM/ha.

Consider linking soil sampling for nutrients with structural assessment

Poor soil structure can reduces yield by:

  • Restricting rooting
  • Reducing response to nitrogen and other fertilisers
  • Increasing drought stress
  • Increasing the duration of colder/wetter soils
  • Reducing rates of soil nutrient cycling
  • Reducing biological activity and earthworm numbers and slowing down the breakdown of dung and dead plant material

 

In addition poor structure can lead to:

  • A reduced quality forage may lead to reduced ryegrass and clover content and more weeds. A sward with 70% ryegrass will average over 11.5ME; over 1MJ higher than a sward dominated by weed grasses, this reduction in quality is equivalent to a loss of 2000l of milk per ha per year.
  • Fewer grazing and trafficking days caused by wetter soils can lead to a reduction in grass utilisation by 10% due to increased rejection can mean the loss of another 1tDM/ha. Extra days that cows are housed incurs additional labour, bedding, and slurry storage/ disposal costs.
  • Increased risks of cross compliance failures means poor soil structure may leads to greater risks of run-off, soil erosion and nutrient losses.

Soil structural limitations may be one reason why poor yields or forage quality declines even where pH and nutrient availability is apparently optimum; if roots can't get to the nutrients the grass can't use them.

Routine sampling of soil for pH and other soil fertility indicators can easily be linked into a farm programme which also assesses soil structure.

  • Note the locations of the sampling points you use in the "W" when collecting sample of soil across the field for analysis - these can be linked to soil structure
  • Assess a few of the sampling points for soil structure at the same time
  • Note any observations of soil biology together with the records of soil structure and fertility.

Optimising soil organic matter will help promote both soil structure and soil biology.