It pays to know what’s in the soil

It’s pretty obvious that if you want to apply fertiliser, you need to know what your plants need, and what nutri­ents are avail­able in the soil. Unfor­tu­nately, soil testing is still not common prac­tice on most farms.

Soil analysis in Poland is carried out by the District Chem­ical and Agri­cul­tural Stations – a state insti­tu­tions estab­lished to under­take compre­hen­sive research for the farming sector. The National Chem­ical and Agri­cul­tural Station in Warsaw is the parent unit for 17 District Stations covering the whole of Poland.

Tasks include analysing soils, plants, agri­cul­tural and forestry crops, fertilisers, and horti­cul­tural substrates, as well as offering crop nutri­tion advice, fertiliser plans, expert reports and opin­ions on soil fertility.

When to perform the tests?

The station based in Poznańis is one of the largest in the country. “In 2023 it tested many samples in the essen­tial range, namely for macronu­tri­ents (phos­pho­rous, potas­sium and magne­sium (P, K and Mg)) and pH,” says Krzysztof Graf, head of the Agro­chem­ical Agri­cul­ture Service Depart­ment. “In the first three quar­ters of the year we analysed about 50,000 samples. The test is a tech­nical tool in the station’s port­folio, while the station’s main purpose is to provide advice. Farmers who receive the test results should obtain support so that they know how to use the results on their farms.”

Since the soil analyzes can take several weeks, sampling should begin well in advance before fertil­i­sa­tion starts.

In recent years, only about 10% of farms in the Greater Poland Voivode­ship have conducted soil testing, and about 8% of agri­cul­tural land has been tested. According to Krzysztof, similar figures can be assumed for the whole country.

In 2023, however, there were signif­i­cant changes due to eligi­bility condi­tions for addi­tional payments under the envi­ron­mental schemes. These require farmers to draw up and follow a fertiliser plan, based on oblig­a­tory soil testing. It is expected that more samples will be taken in the coming years as the programme will run until 2027.

The soil tests are valid for four years and only the basic tests (P, K, Mg and pH) are required. The levels of these macronu­tri­ents in the soil are quite stable (only potas­sium is prone to leaching). Nitrogen is a different case, the levels can vary greatly, even within a month, due to atmos­pheric factors and crop growth.

A nitrogen test should be carried out at least once a year, prefer­ably before vigorous crop growth. Its main purpose is to check the first dose of nitrogen to get plants off to a good start. This test can also be carried out in the autumn, and assump­tions can be used to calcu­late the nitrogen content expected in the spring.

The station also tests the level of micronu­tri­ents which are impor­tant to certain plant species, as well as sulphur, carbon, and humus in the soil. The two latter tests are becoming increas­ingly common due to the agri-envi­ron­ment scheme require­ments. In general, humus levels should not be allowed to decline – the scheme, among other things, aims to prevent a decline in soil organic matter, which is strategic in terms of yield and proper fertiliser manage­ment.

About 50% of soils in Poland need liming, a basic measure which is unfor­tu­nately often forgotten. For most crops, the optimum pH is between 5.5 and 6.5. If the pH is lower, plants will not fully utilise the fertiliser, despite being given the required dose. Fertiliser losses can then be as high as 50%. So, deter­mining the pH and the amount of lime required should be a priority task.

Once received, the samples go to the ware­house, where they are dried at room temper­a­ture for up to several weeks.
Dried soil samples from the ware­house go to the mill, where they are ground and sent for analysis.

Prin­ci­ples of sampling

To obtain a reli­able result it is impor­tant to take a sample that is repre­sen­ta­tive of the field. The total sample should be taken from a maximum area of 4ha but should consist of approx­i­mately 16-20 primary samples taken from evenly spaced points. The primary samples should be mixed, and about 0.5kg of mate­rial forming the total sample should be taken. In most cases, the farmer collects the samples, as the Poznań station has only 12 field workers.

In the case of diverse crops, frag­mented field struc­tures or uneven terrain, it is advis­able to sample a smaller area, even 0.5ha, so that precise fertiliser plans can be drawn up.

Increas­ingly, soil samples are taken in the field using specialised equip­ment mounted on an ATV.

The device for taking soil samples is attached to a pickup truck.

Off-road vehicle for taking soil samples

The station still uses a manual tech­nique with an Egner’s stick (soil probe), but it is increas­ingly common to find compa­nies using all-terrain vehi­cles equipped with drill rigs for this purpose, which take samples from GPS-defined points.

If a farm has a vari­able rate sprayer or fertiliser spreader, test results can be converted into preci­sion appli­ca­tion maps. Once the map is loaded it ensures the quan­tity of fertiliser applied is based on the fertility of the sample taken at the site.

Macronu­trient and nitrogen analysis

Map of Paweł Snuszka’s farm fields from the eAgronom appli­ca­tion

Macronu­trient samples are taken from a 0-20cm depth whereas nitrogen is sampled at 0-30cm and 0-60cm depth.

It is impor­tant to specify which sample comes from which depth because nitrogen is an unstable element – for example, it may not appear in the first layer but does in the second. This would mean that it may not be avail­able to plants in the early stages of devel­op­ment, but they can access it in later stages. Samples for nitrogen analysis can also be taken at a depth of 90cm.

Waiting for results can take up to several weeks, so it is better not to delay testing so that they can act in good time with the appro­priate fertiliser dose. Soil test results should be ready before the appli­ca­tion of compound fertilisers, ie, in the spring, and in autumn for winter crops. A similar range of tests can be carried out on grass­land, and the sampler should try to include as few plant parts as possible in the samples.

How does it work on-farm?

Paweł Snuszka, who runs a 118ha farm in Brod­nica (Greater Poland Voivode­ship, Śrem Poviat), regu­larly has his soil tested. Crop produc­tion is based on cereals: Wheat, trit­i­cale, barley, oilseed rape and maize (4ha for cattle). The farmer also grows sugar beet (20-25ha), while his second activity is live­stock produc­tion: Beef cattle (50 head) and pigs (1,500 porkers).

The farm has soils of classes IIIa to VI, with the predom­i­nance of class IVa and b – light soils for cultivation, with a 30-40cm layer of clay at a depth of about 1m, which retains water. Paweł has been no-till farming for almost 20 years and has been using strip-till tech­nology for all his crops for 11 years. “Soil testing every three to four years has always been the norm on our farm. We regu­larly took samples to the station. To put some­thing in the ground, you need to know what is already there,” he says. Currently, every field on his farm is tested every four years, and the sugar beet field every year for the last four years.

Farm in Brod­nica, Polen

is area of Paweł Snuszka’s farm

of wheat, trit­i­cale, barley, rape­seed and maize

50 bovine
and 1,500 pigs

20-25 ha
sugar beet

In March 2023, soil analysis was carried out for the first time by the Terra Nostra Foun­da­tion using the Mehlich 3 method. The Foun­da­tion is dedi­cated to helping farmers convert from conven­tional to regen­er­a­tive agri­cul­ture. Because Pawel uses large amounts of slurry, the soil was found to be defi­cient in calcium cations. To increase the plant avail­ability of this macronu­trient, it was neces­sary to apply chalk. Other than that, the test did not reveal any signif­i­cant defi­cien­cies in other nutri­ents.

The use of slurry alone has saved a lot of mineral fertiliser, but the knowl­edge gained from the tests is neces­sary to achieve this. The cost of the tests was 80 PLN/ha (£16/ha) in previous years and 300 PLN/ha (£60/ha) in 2023. However, this more expen­sive option provides detailed knowl­edge of what the plant needs, and whether there is a deficit or excess of a partic­ular nutrient. In the case of sugar beet, for example, it was found that there was too much potas­sium and phos­phorus.

Atomic absorp­tion spec­trom­eter for macro and micronu­trient analysis
Flow analyser for nitrogen deter­mi­na­tion

Currently, the cost of testing the entire area of Paweł’s farm is about 5,000-6,000 PLN (£995-£1,194), but this amount is only spent every four years. For orga­ni­za­tional and compar­a­tive purposes, Pawel has been conducting tests at the same time each year for many years, usually in February or March. Typi­cally, he needs to schedule a sampling appoint­ment one to two weeks in advance.

In the past, Pawel used to collect the samples himself by venturing out into the field with a stick, a phys­i­cally demanding task. However, the sampling process is now carried out by an ATV driver following a GPS-guided route, allowing for comple­tion within a single day. Subse­quently, a nutrient content map is gener­ated for each field. Pawel’s upcoming invest­ment will involve acquiring a GPS enabled fertiliser spreader to fully leverage the test results presented in this manner.

The money spent on testing can pay off in the first year through fertiliser savings.

Paweł Snuszka

Soil testing is worth it

One of the most common reasons given by farmers who do not test their soil is the cost of tests. In fact, the cost of testing a single sample in the basic range (pH, P, K, Mg) at the station is only 13.12 PLN (£2.63). This price can be applied to a total sample taken from a 4ha area, and if further divided by 1ha, and taking into account the fact that the test is carried out once every four years, the resulting amount is less than 1 PLN (20p). And the savings that can be achieved through this can be signif­i­cant. For example, saving 20-30kg/ha of compound fertiliser per year equates to savings of up to 200 PLN (£39.80).

Another advan­tage of using the right amount of fertiliser is its effect on yield. Soil testing is crucial for high yields and prof­itable produc­tion. The results can be used to apply the optimum dose of fertiliser, giving plants the nutri­ents they need to produce the most effec­tive yield in a given loca­tion. This avoids the need to apply exces­sive amounts of fertiliser which the crop does not use, which can lead to unnec­es­sary cost increases. Unused fertilisers also contribute to water pollu­tion.