Apply lime after grass silage harvest

With first cut grass silage now complete on many farms, Mark Plunkett, Signpost Programme Training & Development Specialist, writes the time is right to apply lime and help unlock valuable soil nutrients such as nitrogen (N) and phosphorus (P) and increase the productivity of our soils.

Fertiliser prices have rose dramatically over the last number of months for many reasons and all indications are that price will remain high in the years ahead.

Lime is the soil ingredient to help reduce our dependence on expensive chemical fertilisers and improve the efficiency of both soil and applied nutrients.

Soil test results show that there is a large lime requirement nationally on mineral grassland soils and maintaining a soil pH 6.3 to 6.5 will deliver the following benefits:

1. Increase soil N supply by up to 70 kg N/ha/yr (56 units/ac/yr)
2. Increase grass production by up to 2.5t DM/ha (5 bales of grass silage per acre)
3. Increase the availability of soil P and efficiency of applied fertilisers
4. Improve animal health and performance
5. Opportunity to tailor N rates and reduce costs

Soil N Supply

Liming acid mineral soils to the optimum pH 6.3 to 6.5 will result in the soil N supply increasing by up to 70kgN/ha/year. This will replace expensive N fertilisers and support grass growth from soil N sources, while controlling fertiliser N costs by up to €140/ha (€57/ac) per year, delivering a return on lime investment in year of application.

Nitrogen Use Efficiency (NUE)

Maintaining optimum soil fertility increases the efficiency of applied N from 35% on low fertility fields to 63% on fields with optimum pH, P and K (see figure 1). Correcting soil pH alone results in an improvement in N efficiency from 35 to 53%. Spending money on lime to correct soil pH will ensure a better return from each kilo of N applied.  For example, for every 100 kg N/ha applied, the utilisable N increases from 35 to 53kgN/ha from correcting soil pH alone.

Figure 1: Percentage NUE and grass growth response to N fertiliser across grassland fields according to the status of soil pH, phosphorus (P) and potassium (K) fertility.

Soil P availability

Correcting the soil pH increases the availability of soil P and the utilisation of P as either cattle slurry or chemical P fertiliser by the growing crop. A study completed at Johnstown Castle demonstrates how critical lime application can be for increasing soil P availability (see figure 2 below).  For example, liming an acidic soil (pH<5.5) alone increased the soil P by ~6mg/l (2 Soil P Indexes).  On many, farms this would remove the cost (€375/ha) of building soil P levels and increases the grass productivity (+ 1 tonne dry matter/ha) at least cost.  Phosphorus is the most expensive nutrient and, in a more regulated environment, maintaining optimum soil pH pays many dividends for farm productivity and profitability.

Figure 2: Average change in soil test P (Morgan’s P test) across 16 mineral soils treated with P (100 kg/ha of P), Lime (5 t/ha of lime), and P + Lime and re-tested after 12 months (Sheils, T., et al, 2013).

Take every opportunity to apply lime

Now is the time to check soil test results and calculate farm lime requirements. Put plans in place to organise lime delivery and apply lime over the coming days/weeks after silage has been cut. Lime can be spread any day of the year provided soil and weather conditions are suitable. Lime is a major technology to improve the productivity of our soils, health of livestock while increasing farm sustainability and profitability for a small investment.

Lime and cattle slurry

Ideally apply cattle slurry first and apply lime 7 days later to maximise the utilisation of the N supplied by cattle slurry to the grass.

Lime in Action – Johnstown Castle Open Day 10^th June

Come and see a large display at the Farming for a Better Future Open Day at Johnstown Castle which will show the beneficial role that lime plays in the sustainability and productivity of Irish farming.

For further insights on the Farming for a Better Future Open Day, visit here.