Grassland notes February 2009

Fertiliser prices reached an all time high last year with indications of continued high prices into the spring, despite declining oil prices.  With higher prices, you need to focus more on the nutritive value of slurry/manure and maximise grass production from this to reduce your fertiliser bill.  To do this efficiently you should consider:

Since soil nutrient levels and pH change slowly, soils under permanent grassland only need to be sampled every five to six years.  Soil samples are best taken during the winter, ideally in January or February when there are no grass growth requirements and before any slurry or fertiliser is applied.  Soil analysis has both economic and environmental benefits since it can help target slurry/manure to fields that need it from a P and K point of view, thereby making more efficient use of fertiliser.  

One sample should cover an area of around four hectares (10 acres).  Where fields are smaller, samples can be pooled where fields are of similar soil type and management, that is, grazed or cut for silage.  The ideal soil pH for grassland is 6.0 to 6.5.  Acidic soils restrict grass growth and fertiliser uptake, especially nitrogen and phosphorous, meaning less efficient use of fertiliser. Soil analysis should indicate how much lime is required to bring the soil pH up to the desired level.

Soil analysis gives an index for both phosphate and potash with the target index for each being 2.  At this level there is no requirement for phosphate or potash on grazing ground.  At phosphate index 1, production is reduced under intensive grazing or silage systems, but is adequate in extensive grazing systems, common on many beef and sheep farms. At phosphate index 3 or more there is a risk of phosphate leaching so the application of non-P fertiliser is recommended.

Potash levels can be low in many fields, particularly where two cuts of silage are taken.  This causes a decrease in productive grasses and ultimately reduces yields, especially in dry years.  Reserves of potash should therefore be maintained through either slurry or K fertiliser application.

Alternative slurry application methods such as trailing shoe or shallow injection increase the utilisation of slurry nitrogen.  If ground is too wet in February, this equipment will allow slurry spreading closer to cutting, even on good ground covers.  When using a contractor the potential saving in fertiliser generally more than covers the extra cost of trailing shoe operations.

Soil sampling can be used to reduce fertiliser costs