Getting the soil and grass right as part of autumn farm management

By Colm Kelly, Climate Advisor, Teagasc

In this article I will discuss the benefits of Lime and Potassium application to correct deficiencies and some important dates ahead.

If lime is needed the current ground conditions and low grass covers are an opportunity to get ground limestone applied. At 2t/ac a load will cover 10 acres. Target is pH 6.3-6.5 for ryegrass and pH 6.5-6.8 for clover. Peat soils pH 5.8 as there is more organic matter in these soils. The importance of correcting low pH will be in optimising growth potential particularly this autumn and next spring.

A study has found that Nitrogen Use Efficiency (NUE) averaged at 35% on low pH soils. So, for every 100kg of Nitrogen applied 35kgs has actually been put to use. Correcting pH raised this to figure to 53%, and correcting Phosphorus and Potassium raised NUE to 63%. A tonne of lime would be expected to give 0.3 of a pH lift on a loam soil or 0.2 on a clay soil. Correcting pH would also increase Phosphorus availability in the soil.

There are some important dates ahead which I will discuss, which are correct as of 25/08/2026.

September 14th as the last day for chemical fertiliser applications with the 15th being the start date of the fertiliser closed period. This covers Nitrogen and Phosphorus fertilisers.

Straight Potassium fertiliser such as Muriate of Potash (MOP50) can still be applied. Fields that may benefit from Potassium application are silage fields that have had their last cut for the year or where soil tests show low index.

Typically, silage has a high offtake of K (10units/bale estimated) so paddocks or silage fields could be in deficit for the year particularly if slurry hasn’t been applied. Be mindful of grass tetany risk if grazing fields that have just received high K applications. Do not spread chemical fertiliser on land within 3 metres of any surface waters and be mindful of runoff potential with heavy showers or features with a higher buffer requirement.

There is predicted to be soil mineralisation of Nitrogen after the dry spell and for that reason it is recommended to allow 7-10 days after rain before application of chemical N (mindful also of closing date). As water gets into the soil the microbiological activity increases releasing Nitrogen which will be available to the plant.

The Teagasc Grass 10 programme advises fertilising to meet the growth potential at this time of year (20 units/acre), being mindful that declining daylight hours will be lowering growth rate potential. ‘Grass grows grass’ is important for the month of September. A significant amount of yield comes from the later stages of growth when plants have developed to the third leaf stage. Covers that are grazed light reduce the overall farm yield potential so supplementary feed may still have an important part to play even after rain (recommended 30-day rotation). An exception would be where grass has gone to stem and dried out due to conditions which will need grazing to encourage new growth.

The slurry closed period start date is listed as the 1st of October.

The buffer zones for the spreading of organic fertiliser increases from 5 metres to 10 metres for the two weeks before and after the prohibited spreading period.

Ensuring tanks are empty before the closed period is important to ensure maximum capacity is available for the winter months. In some cases, if animals were buffer fed indoors due to lower grass availability there may be more slurry in tanks than would be normally the case this time of year. In Galway & Clare 18 weeks storage is required for cattle manure.

The farmyard manure application closed period starts on November 1st. Increasing soil organic matter levels can improve the resilience of soils more prone to drought. Farmyard manure cannot be stored in the field between November 1st and January 15th in Galway and Clare (Zone B).

Where silage is being stored or moved farm to farm it is worth noting the following passage taken directly from the ‘Explanatory Handbook on Conditionality Requirements 2023-2027 Version 23-03’: “Silage bales cannot be stacked more than 2 bales high or stored within 20m of a surface water or water abstraction point unless there are storage facilities in place to collect any potential effluent. Supplementary feeding points cannot be placed within 20m of a watercourse or on bare rock. Sacrifice paddocks or designated areas of the farm where livestock are kept to ‘save the rest of the land’, particularly during the winter months, are not allowed.”