We have now entered the prohibited period for application of chemical Nitrogen (N) and Phosphorus (P) since September 15th until January 12th for Zone A. Remember there are no restrictions on Potassium (K) application or timings over the closed period. Farmers have until October 14th to spread organic fertilisers and up until November 14th to spread farmyard manure, in all zones, prior to the closed period. Soil temperatures across the country are decreasing and grass growth rates are variable between 50 – 60 kg DM/Ha.
Autumn Grazing Management
The grazing season for next year starts this autumn and correct management decisions made now will pay off next spring. Farmers should graze paddocks with high covers now to ensure they are not caught with deteriorating soil conditions. It is advisable to close poorer paddocks first within the autumn rotation, leaving grass covers of around 500 – 600 Kg DM/Ha. This will allow for earlier and faster recovery in the spring. The target is to have 60% – 65% of the farm closed by the first week of November.
Time to Lime
It is important when ordering lime from your supplier to request lime that best suits your soil type. Therefore, when obtaining your soil sample ensure to test for Calcium and Magnesium to determine whether to spread calcium lime or dolomitic (Magnesium) lime. Calcium lime is primarily made up of calcium carbonate. Magnesium lime is typically comprised of 50% calcium carbonate and 40% magnesium carbonate. Dolomitic lime is generally chosen for soils with low levels of magnesium which are more prone to grass tetany.
Companies supplying lime are required to state the product particle size and the products lime score or TNV value (Total Neutralising Value). This is a quality index system used to express the effectiveness of the material to reduce or neutralise soil acidity and is related to particle size and percentage Dry Matter (DM).
Lime Standards as per the Department of Agriculture, Food and the Marine (DAFM) specification (SI 248) states that products:
- Must have a TNV of no less than 90% and moisture content less than 3%.
- Must pass through a 3.35mm sieve and 35% of the product must pass through 0.15mm sieve.
The primary purpose of lime application is to correct soil acidity levels. The optimum soil pH for grassland is 6.3 and 6.5 for tillage. In peaty soils, the optimum pH is between 5.5 – 5.8.
Time should be set aside to apply remaining slurry and farmyard manure (FYM) on silage fields and paddocks that are low in K. Priority then should be given to fields with lower organic matter and Cation Exchange Capacity (CEC) value. During the closed period is an ideal opportunity to study overall farm fertility and identify fields that have not performed during the growing season and put a soil sampling plan in place. It is recommended to soil test your fields every 3 – 5 years unless you are applying for Nitrates Derogation, which will result in mandatory sampling every 4 years.
Take similar management decisions in tillage situations and address soil compaction issues by sub soiling where conditions are favourable. Conduct soil tests and do a general farm analysis across the farm, taking a particular focus on fields with lower yields and address pH and K deficiencies.
For accurate soil analysis, it is recommended to wait at least 3 months after last chemical or organic P and K application and a minimum of 2 years after the last lime application.
It is not advised to soil sample waterlogged or saturated soils. A soil analysis is only as good as the sample that is taken on the day. Soil sampling should be carried out by a farm advisor/consultant, a farm owner or a person who is trained and competent in the correct sampling procedures. It is important to use the correct sampling tool to obtain more accurate cores. Sample depth will depend on farm type; tillage or grass and what cultivation technique is being used, minimum tillage (min till) or ploughing.
For grassland and min till, retrieve sample to a depth of 10 cm or 4 inches consistently across the field and where ploughing is taking place, ensure to obtain a sample from the plough layer. When sampling walk in a “W” pattern through the field, avoiding tramlines, feeder areas or near gates, wet spots, old drains, gateways, near waterways or buffer zones, under trees and headlands.
Generally, it is best to take a sample every 2 to 4 Ha. However, if a farmer is in derogation, an average of one sample is required every 5 Ha, across the total farm area. It is important to be sure of the uniformity of the site being sampled. Sample areas with large slopes or areas with continuous bad slopes separately. There is no specific number of cores you are recommended to take. However, with a soil sampler, it is advised to take 20 cores from fields less than 15 acres. Once finished, place the cores in a bucket and mix them to get a homogenous sample of a particular field, using this as one reference sample.
Soil Analysis and Corrective Action
For an additional cost when doing soil analysis, it is advisable to request organic matter percentage and a (CEC) Cation exchange capacity value. These are both important soil characteristics. CEC is a measure of soil reactivity, or to put simply it indicates how well a soil can bind and hold on to anything applied to it, chemical or organic fertilisers. Cations are positively charged soil nutrients. Cations include Potassium (K), Magnesium (Mg), Calcium (Ca) and Sodium (Na). These cations are consistently moving from the soil particles to the soil solution, where they are taken up by the plant. Soils that have a low CEC hold little nutrients and this value increases depending on the amount of organic matter present. Therefore, it is important to know this value as it will give you a better idea where to spread your slurry and FYM to build up these values.
Sandy soils have a lower CEC value as these soils contain less clay particles and are more prone to leaching. This means they have less retention to hold nutrients compared to soils with higher organic matter. CEC is measures in milliequivalents per 100 g of soil sample. The higher this value the better the retention capacity, ideally this figure should be between 20 – 30 meq per 100 grams of soil. It is also advised to do a few samples for micronutrients every year to see if there are any underlying issues, in particular low yielding fields.
Base saturation is another soil property that can be calculated from CEC. This will allow your advisor to determine the correct type and amount of soil amendments to use for corrective purpose e.g. lime or gypsum. Additionally, farmers should test their winter forage by doing herbage leaf analysis and cross referencing this with their soil analysis.
Always, use an accredited laboratory to acquire soil analysis and discuss the results with your advisor or agronomist for best corrective decision making. It is important to retain all results on file for ease of access and to build up a library of information on your soil samples, which will assist in long term decision making.
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