The closed period for the application of chemical Nitrogen (N) and Phosphorus (P) began on September 15th and will continue until January 12th for Zone A, which includes counties in the south and east of the country.
There are no restrictions on Potassium (K) application or timings during the closed period. The last day for the application of organic fertiliser (other than Farm Yard Manure) is October 14th. Farm Yard Manure (FYM) can be spread in all zones up until and including the 31st of October. Farmers should reference their soil samples and apply remaining slurry and FYM on fields that are low in K or on silage fields. Priority should also be given to fields with lower organic matter and Cation Exchange Capacity (CEC) values.
Cation Exchange Capacity value
CEC is a measure of soil reactivity, which indicates how well the soil can bind and retain nutrients applied through chemical and organic fertilisers. Cations are positively charged soil nutrients; for example, some basic cations are K, Mg, Ca and Sodium (Na). These cations are constantly moving from the soil particles to the soil solution where they are ingested by the plant.
Soils that have a low CEC value hold very little nutrients, but this can increase depending on the amount of organic matter present. Therefore, it is important to know the CEC value as it will provide you with more information on where best to spread your slurry and FYM to increase these levels. Sandy soils have a lower CEC value as they contain less clay particles and are more prone to leaching. This means they cannot retain the same level of nutrients in comparison with soils containing higher organic matter. CEC is measured in milliequivalents (meq) per 100g of sampled soil. Ideally, the CEC value should be between 20 – 30meq per 100g of soil.
It is also advisable to complete an analysis for micronutrients to identify any underlying issues in low yielding fields.
Additionally, you can request an analysis completed on organic matter percentage and CEC value, both of which are important soil characteristics.
Best practice for soil sampling
The closed period is an ideal opportunity to analyse overall farm fertility, identify fields that have underperformed during the growing season, and apply a soil sampling plan. It is recommended to soil test your fields every 3 – 5 years unless you are applying for Nitrates Derogation, which will result in mandatory soil sampling every 4 years.
According to the Fertiliser Association of Ireland, for accurate soil analysis, it is recommended to wait at least 3 months after the last P and K application and a minimum of 2 years after the most recent lime application.
It is not recommended to soil sample waterlogged or saturated soils. Soil sampling should be carried out by a farm advisor, farm owner or person who is trained and competent in correct sampling procedures. It is also important to use the correct sampling tool to obtain accurate cores.
Sample depth will depend on farm type; tillage or grass, and which cultivation technique is being used; minimum tillage (min till) or ploughing. Grassland and min till samples should be taken at a depth of 10cm or 4 inches consistently across the field and, where ploughing is taking place, ensure to obtain a sample from the ploughed layer.
When sampling, walk in a “W” pattern through the field, avoiding areas such as tramlines, feeder areas, wet spots, gateways, and waterways or buffer zones. Areas with large slopes or continuous bad slopes should sampled separately. There are no specific number of cores recommended to take however, it is advised to take at least 20 cores from fields less than 15 acres. When complete, place the cores in a bucket and mix to get a homogenous sample of a particular field, using it as one reference sample.
If a farmer is in derogation, an average of one sample is required for a maximum of every 5ha across the total farm area.
Soil sampling laboratories analyse the sample for P, K and lime status but you should also test for Calcium (Ca) and Magnesium (Mg) to determine whether to spread Calcium lime or Dolomitic (Mg) lime. Calcium lime is primarily made up of Ca carbonate, whereas Dolomitic lime is typically comprised of 50% Ca Carbonate and 40% Mg Carbonate. Dolomitic lime is generally chosen for soils with low levels of Mg, which are more prone to grass tetany.
It is recommended to target a soil pH of 6.3 for grassland and 6.5 for tillage fields. In peaty soils, target a soil pH of 5.5 – 5.8.
When ordering lime, request the type best suited to your soil type. Companies supplying lime are required to state their product particle size and lime score or Total Neutralising Value (TNV). This is a quality index system used to express the effectiveness of the material to reduce or neutralise soil acidity. It is also related to particle size and percentage Dry Matter (DM).
Lime standards as per the Department of Agriculture, Food and the Marine (DAFM) specifications (SI 248) state that products:
• Must have a TNV no lower than 90% and moisture content less than 3%.
• Must pass through a 3.35 mm sieve. 35% of the product must pass through a 0.15mm sieve.
Analysis and corrective action
Base saturation is another soil property calculated from CEC. This will allow your advisor to determine the correct type and amount of soil amendments to use for corrective purposes e.g. lime or gypsum.
Farmers should also test their winter forage through a herbage leaf analysis, which can then be compared with their soil analysis. Following this, you should speak with your advisor regarding correct sampling procedures and results analysis.
You should discuss your soil test results with your advisor or agronomist to ensure the best corrective action is taken.