Case study: How automation makes better use of nitrogen balance data

Nitrogen is vital for plant growth but fertiliser is expensive and over application has detrimental environmental effects. In order to avoid unnecessary costs and pollution, the nitrogen balance of agricultural land must be calculated.

Nitrogen balance

The nitrogen balance is simply the difference between nitrogen inputs and outputs from an agricultural system.

Nitrogen is made available for crop growth through the application of inorganic fertiliser, manure and organic fertiliser, biological nitrogen fixation, atmospheric deposition, seeds and planting materials. These are the inputs.

The nitrogen-containing compounds in the harvested crops (including grass and fodder) are the outputs

The surplus (or deficit) nitrogen is released to the air, soil and water. This is the nitrogen balance for agricultural land which can be calculated for each individual field [1].

However, a more practical analysis – the farm-gate balance – can be calculated from the amount of nitrogen imported into the farm in fertilisers and exported from the farm in crops (excluding any fodder crops and grass which are consumed on the farm).

The output (yield) is measured at harvest, when both the total amount harvested and, potentially, the protein content of the grain can be measured and recorded [2,3]. Vegetation indices, explored in a previous step, can also be used to calculate crop biomass, a measure of output for some crops [4].

Calculating the input involves measuring the amount of nitrogen added in both inorganic and organic fertilisers. The nitrogen content of inorganic fertilisers should be supplied by the manufacturer, which, combined with the rate of application and the total area you are applying it to would give the total nitrogen applied.

For organic fertilisers the nitrogen content of the manure can be analysed by sampling or reference to averages for various manure types.

For more detail, you’ll find links to guides to sampling, calculating application rates, and a comprehensive guide to calculating the balance in the ‘See Also’ section at the end of the Step.

This type of balance is often used at individual farm level and does not consider inputs from atmospheric deposition or fixed in the soil through biological processes.

Why is it important?

Surplus nitrogen can cause environmental problems, polluting water and leading to the production of greenhouse gasses such as nitrous oxide [5]. Over application is also a financial waste [6]. On the other hand, if nitrogen levels or inputs are too low then productivity can be limited resulting in lower yields. There may also be regulatory measures covering the amount of nitrogen that can be applied to land. (Links to EU and UK Government guidance on using fertilisers in nitrate vulnerable zones are in the See Also section below).

The value of precision farming

Modern sensors attached to sprayers or applicators can now measure N input ‘on the go’ and adjust the application according to prescription maps [2], measuring and recording nitrogen input from both organic and inorganic fertilisers.

Precision manure application. © John Deere

Sensors using near-infrared spectroscopy (NIR) can determine the nutrient content of pig and cattle liquid manure, biogas digestate, fresh harvested crops or silage. It’s then possible to apply nutrients such as nitrogen (N), phosphate (P2O5) and potash (K2O) very precisely and specifically using specified target values in real time through automatic adjustments to the ground speed and/or flow rate.

Field analyser Beta calculating and adjusting manure application rates ‘on the go’ for variable rate application based on the nitrogen content of the manure. © John Deere

This video shows John Deere and Vogelsang technologies enabling high precision manure application.

By evaluating the application data against yield data, farmers can make fact-based decisions about the planting plans for specific fields, as well as specific plans for crop nutrition. For example, area-specific mineral and liquid manure fertilisation plans can be drawn up.