Save on fertilizer with nitrogen analysis

10 December 2021

Nitrogen fertilizer is becoming increasingly expensive. It is therefore sensible to take nitrogen in the soil and in animal manure into account. For winter crops, an Nmin analysis via Soil Check provides insight into the current situation. If you start calculating, it may turn out that you can easily recoup the cost of a sampling by saving on fertilizer.

Nitrogen fertilizer has risen dramatically in price in one year. In December 2020, 100 kg of lime ammonium nitrate still cost €20.10 while in September 2021 it was €29.45. This represents a price increase of almost 50%. Therefore, being economical with nitrogen fertilizer is the big challenge in the coming months. This challenge will probably only increase in the future.

Saving on nitrogen fertilizer can be done in two ways. By taking into account the nitrogen present in the soil and by applying more animal manure. In both cases, research provides insight into the amount of nitrogen that can be made available to the crop.

For the cultivation of winter cereals, it is now important to understand the directly absorbable supply of nitrogen in the soil.

Nitrogen in the soil

Nitrogen is fixed in the soil mainly in organic matter. The total amount of nitrogen (N total) in a soil ranges from about 2,000 to 10,000 kg of nitrogen per hectare. Nitrogen is food for soil life. Part of the nitrogen is consumed by soil life itself; the other part is released as available nitrogen. The amount of N total in the soil is mainly a result of the (fertilization) history and of the stability and quantity of soil organic matter.

During mineralization by soil life, nitrogen becomes available as ammonium (NH4+). This is then converted by soil life into nitrate (NO3- ). Nitrate is the nitrogen form that crops prefer to absorb. The sum of NO3- and NH4+ is the so-called Nmin. The amount of Nmin in the soil depends on weather conditions. When there is a lot of rain, Nmin washes out easily. While at higher soil temperatures, soil life becomes active and more nitrogen is released. 

A high nitrogen content in organic matter (a low C/N ratio) makes it easier for soil life to break it down. The N content of organic matter varies greatly by soil type. For example, dune soils often have relatively high levels of nitrogen in their organic matter because they have often had a lot of farmyard manure applied to them in the past. In contrast, in valley soils there is little nitrogen in the organic matter.

Insight in available nitrogen

Soil testing provides information on nitrogen in the soil. The complete soil test Fertilizer Manager gives insight in N-total and in the N-delivering capacity of the soil. These two key figures provide insight into the soil supply of nitrogen and the ability of the soil to supply nitrogen to the crop. In addition, there is the directly absorbable nitrogen (Nmin) determined with the Soil Check.

Examining available nutrients in the soil can be compared to looking at how much food you have left in the house in the basement, the kitchen, on the table and on your plate. If you approach nutrients in the soil in this way, Fertilization Guide is a basement and the kitchen determination and the Soil Check is a table and plate determination. More on the basement-kitchen-table-board approach.

During the cultivation of winter cereals, it is important to ensure that the crop has sufficient directly absorbable nitrogen. In other words, how much nitrogen is on the plate and table for the crop? A Soil Check gives an insight into the amount of nitrogen directly available.

Save on fertilizer

If it appears that the available nitrogen in the soil is high, it may be possible to save on KAS. Use a current result of Fertilizer Manager. The investment in sampling and analysis amounts to less than 10 euros per ha (assuming a period of use of 4 years and 5 ha per sample). The savings on nitrogen fertilizer will quickly run to a few tens per hectare per year.  

For the total fertilization plan it is also useful to take into account the nitrogen in animal manure. Manure research provides insight into the levels of nitrogen (and other nutrients) that are applied.