Taking samples for plant nutrition

concentration of nutrients in the root environment. A reliable sample is the starting point for a reliable analysis result. Therefore the sample has to be taken properly, both when you take samples for plant nutrition test or for plant disease test. We take our samples according to a certain sampling procedure. When you take your samples yourself it is important that you do it the same way, to be able to compare test results. Therefore we explain in this email news letter how we work while taking samples for plant nutrition tests

Sampling procedure substrate (rock wool)
Take minimal 40 subsamples per ha or per greenhouse. The walking direction is as follows; do not sample the first and last gutter along the greenhouse front. Take half of the samples at the sunny side and half of the samples at the shade side, divided in 4 to 6 pathways (depending on the number of valves and the size of the valve sections). Always sample at the same spots per company.

Working method
The 40 subsamples (all the same size) have to be collected in a sample bottle. Divide the section into 4 or 6 blocks, depending on size and location of the path. Check if there are marking points, like valves, heater or block numbers. Check regularly if the amount of water corresponds with the section that has to be sampled. Also check the greenhouse roof so that you sample the same water quantity from both the sunny side and the shadow side in the greenhouse.
Take samples at the start of the cultivation, always under the rock wool block or plugs. Move to the middle later on, between the blocks or plugs. In that way you take samples as close to the active roots as possible. “Dead ends” – so-called spots where the one slab holds course against the other slab, or spots where the plastic is pulled up in the slab – should not be sampled. For a correct pH test you should take both a feed/drip sample under the dripper and in between two drippers.

Sampling frequency and analyses
Cut flowers have to be sampled once every 3 weeks, vegetables once every 2 weeks. Have the sample be tested for macro- and micronutrients, test code VW.

Sampling procedure substrate (perlite, pumice, hydroponics)
Follow the same working method as described for rock wool. Preferably take a drain water sample, when you want to sample in a just planted crop and you do not have a small water film under the substrate yet. It is not possible to get enough water out
of the substrate itself in that situation.

Sampling procedure substrate well water
Take care that you take a homogeneous sample. For pH and total iron test you must use two different sample bottles. In one of them the sample has to be acidified so that we are able to test for total iron concentration.

Sampling procedure greenhouse soil
Requirements
Sampling stick 30 cm, “thumb” and sample bag.
Starting point
Follow the sampling procedure substrate.
Working method
Take 40 subsamples with sampling stick and “thumb”. Eventually put minimal 300 gram soil in a sample bag. Sampling depth is 5-25 cm.
Soil sampling for pre-plant fertilizer application
Samples are taken before planting. Collect all soil in the sampling stick. The reason for this is that the topsoil layer is worked through the underlying soil layer. Based on the soil test results we recommend to rinse the soil with clean water to decrease any high salt concentration. Soil sampling for fertilizer application after planting The upper 5 cm from the soil is not sampled. The reason for this is that salt accumulates in the top soil layer.
Working method
Sample at both sides of the overhead irrigation system. Take the samples in the row, between the plants. In case of drip irrigation system, sample in the soil under the drip irrigation, close to the dripper. The reason for this is that we want to avoid that you sample soil too far away from the drippers, causing any wrong interpretation of the nutritional status of the soil. Use the lowest 2/3 part of the sampling stick.
Sampling frequency and analyses
A sample after planting is taken once every 4-6 weeks, depending on growth development. Send samples for macro- and micronutrients. Have the sample be tested for macro- and micronutrients, test code VG.

Sampling procedure peat substrate (pot plants)
Take subsamples from the whole section. Take always subsamples from the lowest 1/3 part from the container, near the active roots. Peat substrate in small container size is sampled by hand. Take the plant out of the container carefully with three fingers and take out a little substrate. Peat substrate in large container size is sampled with sampling stick. Take care that only the lowest 1/3 part of the subsample is put in the sample bag. In case of drip irrigation samples have to be taken in the substrate close to the dripper, not too far from the dripper.

Sampling procedure coco peat substrate
Take 40 subsamples potting soil per sample. One subsample is approximately 1 spoonful. For container size larger than 21 cm 25-30 subsamples are sufficient. Use the same walking direction as described by peat substrate.

Sampling procedure sport field and green
Minimal 40 subsamples per field. Sampling depth is 5-10 cm or 5-15 cm, depending on rooting depth. Walking direction is according to so-called sand glass line.