Die chronologische Liste zeigt aktuelle Veröffentlichungen aus dem Forschungsbetrieb der Hochschule Weihenstephan-Triesdorf. Zuständig ist das Zentrum für Forschung und Wissenstransfer (ZFW).
Due to depletion of global phosphorus resources, there is an increasing interest in phosphorus recycling products as fertilizer for growing media. However, in contrast to currently used fertilizers, which are almost completely based on calcium phosphates, at least in sewage-sludge based recycling products a remarkably amounts of phosphorus can be bound to iron or aluminum. In previous studies, the CaCl2/DTPA (CAT) and CAL method partly underestimated plant availability of such sewage-sludge based recycling products, which might be due to a low solubility of iron- and aluminium-bound phosphorus in these two extractants. Thus, a pot trial with marigold was done: plants were fertilized with mono-calcium phosphate (MCaP), di-calcium phosphate (DCaP), tri-calcium phosphate (TCaP), aluminium phosphate (AlP) or iron phosphate (FeP) at growing media pH of 5.5 and 6.5, respectively. No effect on plant growth was observed for the three calcium phosphates irrespectively of pH. However, plant fresh weight was reduced if P was applied as FeP and AlP, whereby no effect of pH was found for AlP but for FeP. Against expectations, plant availability was poorer at the higher pH. In contrary to fresh weight, P uptake of plants decreases from mono- to tri-calcium phosphate and with increasing pH. For aluminium and iron phosphates results for P uptake was comparable to those reported for fresh weight. Whereas plant availability of the three calcium phosphates was well reflected by CAT and overestimated by CAL, P uptake from iron phosphate was strongly underestimated by CAT but matches CAL soluble P. Availability of aluminum phosphate was strongly underestimated by both extractants as well as by the combination of CAT and CAL soluble phosphorus. This supports previous findings for various sewage-sludge based products and raises the question of the need of other extractants.
Mehr
Heinz-Josef Schmitz,
Ivonne Jüttner,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
Extensive green roofs are a key component of urban water management in the future. On the one hand, they should mitigate urban heat islands, for which evapotranspiration has to be maximized, and on the other hand, they are supposed to reduce the risk of urban floods after heavy precipitation events. To achieve these goals, an exact measurement of the water supply status is necessary. In arable soils as well as in organic growing media, dielectric sensors are widely common. However, there is only little knowledge about the suitability of this kind of sensors for mineral and coarse-textured substrates used for extensive green roofs. In the current research four dielectric sensors (EC-5, 10 HS, SMT 100 and Aquaflex TR) were tested using five different green roof substrates. The five substrates were filled in plastic boxes of 80 x 60 cm. Substrate height was 15 cm and the four sensors were placed at half height. Afterwards, white lupine was sown and cultivated up to a height of about 30 cm. For testing the sensors, the substrates were saturated with water and then they have been left to dry out until plants show severe signs of wilt. During dry out, the sensor signals as well as the weight of the boxes were recorded automatically every five minutes. For each substrate six consecutive drying cycles were done. With exception of the Aquaflex TR, for all sensors output signals were closely linear correlated to the weight loss and signal ranges were comparable for the six drying cycles. However, significant differences in output signals of the sensors between the five tested substrates were observed. This indicates a need for substrate specific calibrations. The relation between the output signal of the Aquaflex TR and the weight loss was not linear, but also reproducible and suitable to assess water supply status of plants.
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.
Mehr
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.
Mehr
Dr. Annette Bucher,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
Due to coarse textured, fast-draining growing media with poor buffer capacity, nitrogen leaching after heavy rainfall is a major concern in container nurseries. The amendment of growing media with Chabazite – a natural zeolite with high ammonium (NH4+) exchange capacity – in combination with NH4+ fertilization might reduce nitrogen losses significantly. This was tested in a pot trial with Photinia fraseri. Growing media amended with Chabazite were compared with a pumice containing growing medium as control. Chabazite was used on the one hand untreated and on the other hand it was charged with ammonium sulfate ((NH4)2SO4) with loads of 1 and 5 g ammonium nitrogen (NH4-N) pot‑1. During the first part of the trial, pots with untreated Chabazite were repeatedly fertilized with NH4+ and leached after each fertilizer application. Pots with charged Chabazite were also leached on the same dates. In the second part, pots with untreated Chabazite received an excessive NH4+ supply and were leached several times afterwards. In both parts of the trial, NH4+ was adsorbed by Chabazite after fertilization. Higher amounts of NH4+ were leached from growing media with pumice than from those with untreated Chabazite. In leachates from growing media with NH4+-charged Chabazite, higher amounts of nitrate (NO3-) were only found in the case of charging with 5 g N pot‑1. Whereas after excessive NH4+ fertilization leaching of NH4+ remained low in presence of Chabazite, summing up to 5% of the applied N, in the control leached NH4+ was 28% of fertilized NH4+. Thus, it can be concluded that fertilized NH4+ was adsorbed to Chabazite and thus protected from direct leaching as well as from nitrification and subsequent leaching as NO3-. This protection decreased with increasing NH4+ charging of Chabazite. Hence, the combination of Chabazite with repeated NH4+ fertilization is a promising approach to reduce nitrogen leaching from container nurseries.
Mehr
Dr. Annette Bucher,
Dr. Dieter Lohr,
Prof. Dr. Elke Meinken
Amendment of growing media with Chabazite, a natural zeolite with a high ammonium sorption capacity, in combination with ammonium fertilization might be a promising approach to reduce nitrogen leaching in container nurseries. However, it is unclear if ammonium, which is adsorbed to Chabazite is still plant-available. Thus, a pot trial with Photinia fraseri was conducted with growing media containing 25 vol % of either pumice or Chabazite. Chabazite firstly was used as received and secondly was charged with two levels of ammonium resulting in nitrogen loads of 1 and 5 g N pot‑1, respectively. The untreated Chabazite was fertilized with 1 g N pot‑1 as ammonium sulfate divided in repeated applications in accordance with the control (pumice). In these two treatments plant growth and nitrogen uptake was more or less the same. Plants in the growing media with NH4-charged Chabazite receiving also 1 g N pot‑1 produced a significantly lower fresh mass compared to the untreated Chabazite and pumice and suffered from slight nitrogen deficiency. If 5 g N pot‑1 were applied with charged Chabazite, plants grew better and took up more nitrogen. The results indicate that Chabazite did not influence negatively plant availability of fertilized ammonium. However, ammonium from charged Chabazite is only partly plant-available. With increasing NH4 charging of Chabazite, ammonium and nitrate accumulated in the growing media.
Mehr
Dr. Dieter Lohr,
Heinz-Josef Schmitz,
Ralf Walker,
Prof. Dr. Elke Meinken
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