Early Season Nutrient Use

Published 8 February 12

 

Early season nutrient use

Make sure there are sufficient nutrients in your soil to drive early growth, says DairyCo extension officer Chris Duller.

"If soil temperatures rise above 5oC then ryegrass will grow - both in terms of developing leaf material and roots. To take maximum advantage of early season growing conditions it is vital that there are sufficient nutrients in the soil to drive this growth," says Chris.

"In early spring the levels of nitrates present in soil tend to be very low. As nitrates are soluble they tend to be leached away over winter and very little is being released from soil organic material because bacterial activity is slow at low temperatures.

"Grass growth response to nitrogen applications will not be massive in early season due to short day length and low temperatures but a response of 10kgDM for every kgN applied and daily growth rates of 10-15kgDM/ha is certainly possible through February.

"The key issue with early reason applications is minimising losses; if the nitrates aren't taken up quickly by the grass plant then they are likely to be leached way. Small applications of around 25kgN/ha (20units/acre) are the best approach to minimise the risks of leaching. If soils become waterlogged at any point after application there is also a great risk of losing nitrogen as nitrous oxide," Chris says.

"Urea does offer a certain amount of protection from leaching and is an attractive buy (around 70p/kgN as opposed to around 90p for ammonium nitrate) however, as all of its nitrogen is present in the form of ammonium it is vulnerable to loss as ammonia.

"Research conducted at IGER North Wyke showed very large losses using urea fertiliser as opposed to ammonium nitrate, particularly at high rates. However, at low application rates, and with applications made in damp conditions, urea can be a very cost effective fertiliser.

"Soil phosphates are essential for early season root growth and as they are relatively insoluble they are available to the growing plant - but if indexes are below 2 then the grass plant will struggle to access enough to produce new roots. Response to nitrogen will be far less if phosphate indexes are low."

Check list for early season nutrient applications

  • Buy a soil thermometer and check soil temperatures before applying nitrogen.
  • Small applications reduce the risks of losses
  • Urea can be a cost effective way to apply early season N - if used in the right conditions
  • Make sure P levels are satisfactory
  • Target your most productive fields for early nutrient application; south facing, lighter soils, young leys.