Use waste streams as fertilisers

“You don’t need to buy a broadcast spreader ever again. That equipment has had its day.” Herre Bartlema has a breezy way of expressing himself. But the underlying message is serious: in his view, the conventional centrifugal spreader for granular fertilisers can be easily replaced with a contemporary, sustainable method.

Use minerals from residual waste streams

From Bartlema’s viewpoint, the way to improve sustainability and precision fertilisation is to use minerals from residual waste streams originating in the agricultural sector and in the industry. “From a technological and logistical perspective, there are no insurmountable problems. It benefits the soil, the environment, and the overall yield.”

Educated at Wageningen University, Bartlema has spent a hardworking life being responsible for research into fertilisers at DSM (now OCI Nitrogen), making him an expert in the field. Over the past few years, he has been promoting the use of residual waste streams through the Netherlands’ Centre for Development of Band Application, which he set up, and through events such as the annual ‘Precision Fertilisation Day’.

‘Messing about’ with broadcast spreaders

Bartlema compares precision fertilisation using band application to picking low hanging fruit. “It’s efficient, with positive results for the crop and for the grower’s wallet. But look at what I regard as messing about with large-scale broadcasting spreaders. What haven’t they invented for even grain distribution? Fertiliser spreaders have become expensive and complicated. And yet corners of plots are still under-fertilised, and it’s still not possible to finish off your headlands neatly and to avoid creating ruts.”

“Band application of liquid fertilisers is possible during planting or while working the soil. Without the carry-on you get with grains that behave unpredictably. What you do have is certainty of even dosing, even in the side rows, and certainty that the minerals will be delivered directly to the roots.”

4 truths of skilled fertilisation

Bartlema substantiates his claim with the vision of Meststoffen Netherlands, the association of producers and distributors of mineral fertilisers, with regard to sustainable fertilisation. It includes what he calls the 4 truths of skilled fertilisation in the 21^st century. ‘Fertilisers need to be applied in the right place’, is the first truth.

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With band application, you can almost always reduce the amounts compared with broadcast fertilising

The other 3 concern the time of dosing, the choice of fertiliser, and attuning dosing to the needs of the crop and soil supply. As far as the right dosing is concerned: “With band application, you can almost always reduce the amounts compared with broadcast fertilising.”

For beans, potatoes, sugar beet, and onions, he suggests reducing phosphate by up to 50% and nitrogen by up to 15% compared with recommendations from soil sample analyses.

Residual waste streams

The key to closing the loop is replacing fertilisers with minerals from residual waste streams (or renewable sources). “The production and application of nitrogen in the form of fertiliser generates 8 kilos of CO₂ emissions per kilo of N. Fertilising potatoes with 200 kilos of N per hectare accounts for almost half of the total carbon footprint for that crop. We can reduce that.”

There is no shortage of residual waste streams. The agricultural sector itself provides, among other things, ammonium sulphate derived from scrubbers on pig- or poultry farms.

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Herre Bartlema: “The production and application of nitrogen in the form of fertiliser generates 8 kilos of CO2 emissions per kilo of N. Fertilising potatoes with 200 kilos of N per hectare accounts for almost half of the total carbon footprint for that crop. We can reduce that.” – Foto: Peter Roek

“This generates 40,000t of nitrogen per year, equal to the nitrogen content in 150,000 tonnes of calcium ammonium nitrate (CAN). Compost producers also generate 20,000t of nitrogen per year, while 50,000t comes from the production of caprolactam, a product used in plastics. Agricultural nitrogen consumption amounts to 200,000t every year. Over half of that can be met by these residual waste streams. The remaining nitrogen demand can be met through nitrogen fixation by clovers and by using the thin fraction of slurry.”

Quality does not have to be a problem either, as the nitrogen is present in these residual waste streams as ammonium, making it “ideal for spring application, while being insusceptible to run-off.”

‘Reducing nitrogen dosing’

Ammonium sulphate is available in 1000-litre vessels, with 4%, 5% or 6% nitrogen. In order to overcome any logistical difficulties, it is possible, for example, to add urea (46% N in granular form), thereby increasing the N-content to 15%. “Then you have a hybrid circular fertiliser. Urea is mass-produced as CAN, but requires far less energy and emits hardly any greenhouse gases. What’s more, urea can be manufactured using solar power.”

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Compared with broadcasting, the dose in band application can often be 15 to 20% lower

With 60 kg of nitrogen per cubic metre of ammonium sulphate waste, dosing need not be a problem. “Compared with broadcasting, the dose in band application can often be 15 to 20% lower. And that’s before we consider autonomous, driverless fertiliser spreaders. Not a reality yet, but not too long ago the use of liquid fertilisers wasn’t either.”

The benefits

The question is what financial and other benefits result from band application of residual waste streams. Bartlema produces a calculation for potatoes grown with band application of ammonium sulphate + urea. Taking account of a 3% increase in yield due to higher use of nitrogen, 2% additional production due to the full utilisation of the plot from one edge to the other, and a 15% saving in nitrogen due to precision fertilisation, he arrives at a cost saving of € 140 per hectare.

“It’s not much, but the real saving is made in the additional application capacity for organic fertiliser as a result of the mineral savings. The use of minerals from residual waste requires thinking outside the box and takes some getting used to, but it is easily achievable. We have sufficient residual waste sources, and we have the application technologies available.”