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Efficiently Treated Sewage Sludge Supplemented with Nitrogen and Potassium Is a Good Fertilizer for Cereals

Tontti, Tiina, Poutiainen, Hannu, Heinonen‐Tanski, Helvi
Land degradation & development 2017 v.28 no.2 pp. 742-751
NPK fertilizers, barley, climate, heavy metals, hygiene, microorganisms, nitrates, nitrogen, nitrogen content, nutrients, organic matter, phosphorus, potassium, risk, sewage sludge, sewage treatment, soil, wheat
Sewage sludge contains phosphorus (P), nitrogen (N), potassium (K) and organic matter in both soluble and particulate forms. However, agricultural use of sludge is limited because of possible problems due to hygiene, heavy metals, inner quality variation and non‐balanced ratios of nutrients. We tested sustainable fertilization of cereals with (i) urea‐spiked granulated sludge, (ii) composted anaerobic sludge digestate, (iii) dried (dewatered), anaerobic thermophilic digestate sludge mixture and (iv) dried (dewatered) sludge. The sludge products were applied to barley and wheat with variable combinations of N and K supplements in Nordic climate. Sludge products supplemented with N and K and mineral NPK fertilizers containing soluble 70 kgN ha⁻¹ achieved barley dry yields above 3500 kg ha⁻¹. The grain N content was 22·3 g kg⁻¹ in barley fertilized with granulated sludge fortified with NK (soluble N 83 kg ha⁻¹), while grain N content was 20 g kg⁻¹ when fertilized with 90 kgN ha⁻¹ NPK. The wheat dry yields were 2890 and 2850 kg ha⁻¹ fertilized with granulated sludge fortified with NK when soluble N was 49 kg ha⁻¹ and NPK with 110 kgN ha⁻¹ of these grains containing N 29·2 and 29·0 g kg⁻¹. The results mean that correctly treated and formulated sludge products can be used. The risks caused by enteric microorganisms or heavy metals could be managed. The residual nitrate concentrations in soil were low. Sludge products could be developed by optimizing nutrient ratios and their structure. Sludge producers should provide farmers with detailed physicochemical data about each sludge portion. Copyright © 2016 John Wiley & Sons, Ltd.