The Importance Of Soil Sampling
Author: Philip Kennedy
With the increased cost of chemical fertilisers, coupled with increased spreading restrictions into 2023, now is a perfect time to get organised and take up-to-date soil samples.
- All arable land sown from January 1, 2023, must have an up-to-date soil sample available (within 3 years). The soil sample results combined with previous yield records will allow the farmer or advisor to tailor a fertiliser plan for the crop
- From January 2022 all livestock farmers over 170kg N/ha must take soil samples and from January 2023 all livestock farmers over 130kg N/ha must take soil samples. In the absence of soil samples an index 4 value for phosphorus will be assumed and therefore applications of Phosphorus will be for the most part not permitted.
- Nitrate derogation farmers already have the above rules to adhere to.
- Nutrient management plans are becoming a necessity for most commercial farms.
- Chemical fertilisers are expensive, so it is more important than ever before to use the correct rate of the appropriate product at the optimum time and spread evenly in the right place.
Soil Sampling Procedure
- Leave at least 3 months between chemical fertiliser and slurry applications before taking a sample.
- Sample the field in a W pattern while avoiding gaps, old field boundaries, dung and urine patches or muddy areas. Soils are best sampled when they are not in a saturated state to give a more accurate pH reading.
- Samples from a 2 to 4 ha range are advised with similar soil types and rotations being taken together in smaller paddocks or fields.
- Ideally, sample to a depth of 10 cm with a mix of around 20 cores per sample mixed.
- Separate soil samples should be taken from areas that are of different soil types, previous cropping history, drainage, or persistent poor yields. The amount of soil required will depend on how detailed an analysis you are getting. For a full trace element analysis, more soil will be required.
When growing any crop, it is critical to ensure that the soil pH is at the correct level. The optimum soil pH is 6.3 for grassland and 6.5 for tillage crops, preferably with 60-70% calcium and 10-20% magnesium.
Lime is often a forgotten fertiliser that can impact soil fertility. There is no one size that fits all, therefore we must choose the correct lime to suit our soil type.
In general, calcium lime is the only type required in Wexford due to the elevated levels of magnesium in soils. Remember; Index 4 is as far as the scale goes for magnesium. You could be index 6 or 8 if the scale were to continue, therefore do not use dolomitic lime.
Having the correct type of lime and pH for your soil will make your Phosphorus (P) and Potassium (K) fertiliser work far more efficiently and can release up to 80 kg/ha of organic Nitrogen (N).
Know Your Offtakes
Spring barley for an 8 tonne per ha crop (3.2t/ac) will require 30 kg/ha of P (24 units/ac) and 90 kg of K per ha (73 units/ac). For P Index 2, add 10 kg (8 units), while P Index 1 will require 20 kg per ha (16 units/ac). For K Index 2, add 15 kg per ha (12 units/ac) and for K Index 1, add 30 kg per ha (24 units/ac).
When cutting grass silage, we must remember that each tonne of grass DM per ha will remove 4 kg/ha of P (3.2 units/ac) and 25 kg/ha of K (20 units/ac). Within a grazing situation, these nutrients are recycled and replaced from the animals through animal manure.
Sulphur (S) requirements will depend on your soil type. Light soils will leach S out more than heavy soils. As a rule of thumb, match your P requirements to your S requirements. Do not spread copious quantities of S during the breeding season to prevent selenium and iodine from locking up. Smaller quantities can be spread, however if you need ASN (16N 14S), Kieserite (15Mg 20S) or Calcium Sulphate (33 CA 22S), it is recommended to wait until after the breeding season as these products contain elevated levels of sulphur.
Contact Our Team Today
The Cooney Furlong Grain Company offer full detailed soil samples and most importantly, analysis and advice for the coming season. Samples can include calcium and magnesium totals as well as a full breakdown of S, CEC and trace elements.
Contact your local branch or area manager to organise what you need.
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