The lime, silage and slurry quandary
Untrafficable ground conditions hindered lime applications on many farms up until now. For some, it will be the first time lime will be applied in the summer months. With this comes questions on lime’s interactions with silage, slurry and even grazed grass.
Lime is the forgotten fertiliser on Irish farms. It plays a central role in correcting soil pH – the first step often required in soil fertility improvements, which lead to more efficient nitrogen (N) fertiliser usage at farm level.
Traditionally, the back end of the year was the main period for applying lime. Waiting until the late season to apply lime will generally result in poorer and less trafficable soil conditions and the opportunity to apply lime could be missed. Instead, aim to apply lime earlier in the year when soil and weather condition are move favourable.
To alter the timing of lime applications though, there are a number of important factors to keep in mind. These include paddock availability, lime residue on grass and the interactions between lime, slurry and grass pre-harvesting for silage.
Paddock availability
Once fields have been grazed off and grass covers are low, it is an ideal time to apply lime. Identify blocks of land that require lime; for example, this could require ordering a load of lime (20t) after each grazing rotation to correct soil pH (covers approximately 10ac at 2t/ac lime application rate). Aim to avoid high grass covers >800kg DM/ha.
Lime residue on grass
Ideally apply lime to low grass covers to reduce the risk of lime residues remaining. Rainfall will typically wash most of the lime from the grass down to the soil. A small amount of lime remaining on the leaf will not affect grazing animals.
Softening of the ground/sod
Soil types where a relatively thick (5-10cm) organic layer has formed above the topsoil may be more prone to poaching during wetter periods of the year. This organic layer holds a large store of acidity. Liming these soils to neutralise acidity and raise pH will create favourable conditions for biological activity (e.g., grass roots, earth worms) and the release of the nutrients stored in the organic matter.
As nutrients are released from organic matter, the resistance of the top few centimetres of soil to heavy trafficking may be temporarily reduced. To minimise these effects, apply lime on a little and often basis, and improve soil pH in stages over time. Don’t exceed 5t/ha in a single application or apply split applications (2.5t/ha) over a number of years.
Silage fields
Leave sufficient time (up to three months in dry weather) between applying lime and closing for grass silage for the lime to be fully washed into the soil. If lime is transported to the silage clamp or picked up in the baled silage, it may affect good preservation conditions for the silage (acidic conditions).
Lime and slurry
Spreading cattle slurry on fields that have received lime recently, where the lime has not had sufficient time or rainfall to be washed into the soil, can result in a loss of up to 50% of the available slurry N. To minimise these N losses from slurry, apply cattle slurry first and then apply the lime seven to 10 days later.
Lime and urea
For urea, there is a similar situation to cattle slurry where increased N loss (ammonia-N volatilisation) may occur where straight urea fertiliser is applied on recently limed land. Therefore, apply urea first and apply the lime seven to 10 days later to reduce the risk of N losses. However, where protected urea is being applied, early trial work indicates that it is safe to apply protected urea to fields that have been limed recently.
This article was adapted from Signpost Programme Factsheet on Lime. Access the full publication here, where the environmental and economic benefits of lime applications, along with other tip, are further outlined.