Johannes Görl,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
Effect of co-composted biochar on nitrogen availability to spinach (2022) 31. International Horticultural Congress (IHC2022); International symposium on plant nutrition, fertilization, soil management .
Co-composted biochar is suspected to be an effective sorbent for nitrate and thus might reduce nitrate leaching from agricultural soils. However, the underlying mechanism is unknown now and the effect on nitrogen availability is under discussion. In the current study, a pot trial with spinach was conducted to evaluate the influence of two co-composted biochars on nitrogen availability. Two wood-based biochars were co-composted with grass clippings and woody scrap material from landscaping activities. Additionally, a compost without biochar was prepared. Composts were mixed to an arable soil at rates of 30, 60 and 120 t ha-1 and nitrate was applied on basis of 100 kg N per hectare. Afterwards, mixtures were filled in balcony boxes, moisturized and placed in a greenhouse for 40 days. As control the soil without compost was treated in the same way. Furthermore, additional treatments without and with the highest application rate, but without nitrogen fertilization, were prepared. After the 40 days these balcony boxes were also fertilized with 100 kg ha-1 of nitrogen and spinach – pre-cultivated in press pots – was planted in all balcony boxes. Irrespectively of application rates and – in case of the highest application rate – of date of nitrogen fertilization, no negative effect of co-composted biochar on N uptake was observed. In addition, the nitrogen balance for treatments with co-composted biochar was not significantly different from the control. However, for treatments with compost without biochar an increasing balance shortfall with increasing amounts of compost was observed. This might due to a nitrogen immobilization of woody residues. In view of the fact, that N uptake by plants was comparable and significant amounts of easily extractable nitrate were found in the soil at the end of the experiment, we assume that the co-composted biochars used in this experiment had no adsorption capacity for nitrate.
Dr. Dieter Lohr,
Johannes Görl,
Prof. Dr. Elke Meinken
Nitrogen dynamics of chopped hop bines - Effect of leaf to stem ratio (2021) 4th International Symposium on Horticulture in Europe, 09.-11.03.2021, virtual .
Beiträge zu wissenschaftlicher Konferenz/Tagung
Johannes Görl,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
Traditionally in Germany, chopped hop bines are returned to hop gardens after the harvest season in late autumn. However, due to more stringent legal regulations addressing the application of manure, this common practice is banned. Furthermore, the return of hop residues bears phytopathological risks, such as the spreading of Verticillium spores. Aerobic composting of hop bines might solve both problems. Nitrogen is conserved over winter, and pathogens are killed due to high temperatures during composting. However, nitrogen release from mature composts is relatively poor. Thus, in a pot trial, the nitrogen fertilizing effect of aerobically composted hop bines was compared to that of fresh hop bines (air-dried directly after harvest), aged hop bines (stored on a heap for four weeks according to common practice) as well as mature green waste compost and green manure (Phacelia). Lamb's lettuce was cultivated in balcony boxes filled with topsoil used for arable crops. The plant density was 116 plants m-2, and nitrogen was applied on a basis of 130 kg ha‑1. Nitrogen from hop bines, green waste compost, and green manure was estimated to become plant available at rates of 100, 75, 50, and 25%, respectively. The control was fertilized with ammonium nitrate. With the exceptions of composted hop bines and green manure, plant growth in organic fertilized treatments was significantly less compared to the control, even if only 25% of the nitrogen was estimated to become plant available. The fertilizing effect of composted hop bines was comparable to that of fresh hop bines and higher than aged ones. However, nitrogen release of all kinds of hop bines was significantly less compared to Phacelia. The results indicate that nitrogen in hop bines can be conserved over winter by aerobic composting, but due to remarkable gaseous N losses during the composting process, the overall efficiency is relatively poor.
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Dr. Dieter Lohr,
Johannes Görl,
Prof. Dr. Elke Meinken
Due to high nitrate loads in ground water, the German government tightened up legal regulations addressing the application of green manure crops during the last years. Among others, the current practice of putting back chopped hop bines to hop gardens after harvest was banned. However, there is a lack of knowledge about the nitrogen dynamics of chopped hop bines and their contribution to nitrate leaching. Indeed, pot trials revealed a fertilization effect of chopped hop bines, but in incubation experiments, no increase of mineral nitrogen was found. This might be due to the heterogeneity of hop bines, which consist of N rich, “green” parts (leaves, small branches) as well as the “woody” main stem. To test this hypothesis a pot trial with Italian ryegrass and an incubation experiment were conducted using “green” and “woody” hop material at various ratios. Therefore, entire hop bines were cut off and after removal of the cones divided into leaves, petioles, residues of cones and small side shoots (“green”) as well as into the lignified parts of the stem (“woody”). The two fractions were applied to an arable soil with ratios of 100:0, 70:30, 50:50, 30:70, 10:90 and 0:100 on a mass base, respectively. N uptake of ryegrass as well as net mineralization in unplanted Mitscherlich vessels were measured. Results confirmed the hypothesis: N uptake by plants was significantly higher than net mineralization in unplanted pots. For the woody material a nitrogen immobilization potential of about 4 to 5 g kg‑1 dry matter was found, whereas for green material a mineral fertilizer equivalent of 18% was calculated. Overall, the results indicate that application of chopped hop bines is not part of the nitrate problem but might be - in combination with catch crops - a good strategy to preserve the bounded nitrogen available for the next growing season.
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Johannes Görl,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
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