Profile
Herre Bartlema studied at Wageningen University in the Netherlands. He had a life spanning carreer with DSM (now OCI Nitrogen) as a fertiliser researcher. He was at the forefront with practical improvements like a fertiliser spreader calibration service. In recent years he is promo- ting the use of waste products as (partial) replacement for fertilisers.
Residual waste streams The key to closing the loop is replacing fertilisers with minerals from residual waste streams (or renewable sources). “The produc- tion 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. “This generates 40,000t of nitrogen per year, equal to the nitrogen content in 150,000 tonnes of calcium ammonium nitrate (CAN). Compost pro- ducers also generate 20,000t of nitrogen per year, while 50,000t comes from the production of caprolactam, a product used in plas- tics. 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.” With 60 kg of nitrogen per cubic metre of ammonium sulphate waste, dosing need not be a problem. “Compared with broadcast- ing, 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 calcu- lation 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% sav- ing 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 appli- cation capacity for organic fertiliser as a result of the mineral sav- ings. 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.”
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