Farm Ireland
Independent.ie

Saturday 24 June 2017

Soil sampling can help to cut total fertiliser spend

Mark Plunkett

Now is the ideal time to identify parts of your farm that require up-to-date soil analysis and plan to have soil samples taken over the coming months. This is vital information to ensure that crop nutrient requirements are satisfied and will help avoid either under- or over-fertilising of crops for next year. Fertilisers now form a significant proportion of production costs and will have a large influence on farm productivity and profitability.

A well-taken soil sample will provide good soil test results. It is essential that soils are sampled correctly and taken with a suitable soil corer to the correct sampling depth of 10cm. This is important as soil results taken today will be the basis to nutrient applications for the next 3-5 years on your farm. Soil phosphorus (P) tends to accumulate in the top few centimetres of soil in grassland.

Therefore, incorrect sampling depths will result in inaccurate soil P readings, especially when samples are too shallow.

For soil test results to be comparable over time they must be sampled to the correct depth on each sampling occasion. The general recommendation is to sample once every 3-5 years. Therefore, you'll need a good soil corer and suitable soil conditions that allow you to get down deep enough. Guidelines for taking a soil sample:

•Soil sampling areas should be 2-4ha in size.

•Avoid tramlines or any unusual spots such as old field boundaries.

•Sample the top 10cm of soil with a suitable soil core.

•Leave three to six months between sampling and P and K applications.

•Take representative soil samples (Follow a 'W' soil sampling pattern).

•Take around 20 cores to make up the soil sample.

Fertiliser efficiency will be reduced where the soil pH is low. To maximise both production and economic response from applied N, P and K fertilisers, it is essential to lime soils to increase soil pH to target levels (see the table, below). Aim to apply lime once every five years and maintain mineral soils between pH 6.3-7.0 and peaty soils pH 5.2-5.5. Where more than 7.5t/ha of lime is recommended, apply no more than 7.5t/ha (3t/ac) now and the remainder in two years' time. For reseeding pastures, best results are achieved by spreading lime at the time of reseeding, when the lime can be tilled into the soil. Lime should be applied two years in advance of lime-demanding crops such as beet, peas and beans, and also for wheat and barley.

Soil sampling is a component of current nutrient legislation in that a soil sample is required for every 8ha and is valid for six years. Where soil samples are not available, one can assume a soil has a P index of 3. Where soils are fertilised upon this basis, it presents a number of risks. Firstly, insufficient P and K application may occur if the soil has low soil fertility levels equivalent to index 1 or 2. Secondly, very fertile soils closer to an index 4 will go unidentified and potential fertiliser financial savings will not be exploited.

Thirdly, where insufficient fertiliser P is applied in relation to production demands, soil fertility will decline over time and will be more costly to rebuild in future years.

Soil samples on derogations farms must be taken at least every four years. Therefore, fields that were soil sampled in October 2007 will now have to be re-sampled this October for derogation planning next year. The area per sample must be less than 5ha on average on farms applying for a derogation.

A five-year nutrient management plan was a requirement within the REPS scheme. This plan also satisfied requirements under cross-compliance and fertiliser planning. Most REPS 3 participants will finish their REPS plan over the next few months. All REPS 3 farmers must be compliant with the nitrates directive fertiliser limits after their REPS participation has expired. These farms should now be re-tested to check soil fertility levels. Assume soil index 3 and plan fertiliser requirements for the next five years. A fertiliser plan should be prepared and reviewed annually.

Applicants this year will require soil samples before March 31. For this year's soil organic matter, testing must be completed for continuous tillage soils. Continuous tillage equates to land that has been more than six years in tillage. Last year, 50pc of testing was completed and the remaining 50pc must be tested by December 31. Take one sample for every 4ha. Where the soil type and cropping history are similar, the sampling area can be increased to 8ha (link sampling areas to LPIS numbers). Soil sampling for organic matter is required only once every 10 years as soil organic matter levels change very slowly over time.

Where soil organic matter levels are above 3.4pc (2pc soil organic carbon), there are no remedial actions required. Where soil organic matter levels are below 3.4pc, the grower must seek advice from a farm adviser who specialises in cross- compliance and will determine what, if any, remedial action is required.

Indo Farming