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Next to nitrogen, phosphorus (P) is the most limiting nutrient for plant production worldwide. To secure food production, new nutrient management strategies using alternative P sources instead of mined P fertilizers need to be implemented. Struvite (MgNH4PO4 · 6 H2O) is a promising example of a recycled mineral P fertilizer. Besides positive agronomic results regarding crop yields, further investigations are required to improve the use efficiency of the product and thereby increase its value. Using an automated plant phenotyping platform, we investigated the dynamic response to struvite by two plant species (lupine and maize) with diverse P acquisition strategies in an acidic sandy substrate. Although at three weeks after germination both maize and lupine had reduced leaf area in the struvite treatments compared to the commercial triple superphosphate (TSP), from week four onwards struvite plants grew larger than the TSP‐treated plants, indicating a slow release fertilizing effect. Greater P uptake efficiency (g / root length), but reduced root length were observed in the combined treatment of struvite and ammonium, in comparison to struvite and nitrate. We propose that rhizosphere acidification in response to ammonium uptake may enhance P recovery from struvite. A possible additional acidification effect by lupine root exudation might explain the higher P uptake efficiency in this species compared to maize. We conclude that struvite combined with ammonium can be used as a sustainable slow‐release P fertilizer on acidic sandy soils. [ABSTRACT FROM AUTHOR]

The cultivation of perennial biomass plants on marginal soils can serve as a sustainable alternative to conventional biomass production via annual cultures on fertile soils. Sida hermaphrodita is a promising species to be cultivated in an extensive cropping system on marginal soils in combination with organic fertilization using biogas digestates. In order to enrich this cropping system with nitrogen (N) and to increase overall soil fertility of the production system, we tested the potential of intercropping with leguminous species. In a 3-year outdoor mesocosm study, we intercropped established S. hermaphrodita plants with the perennial legume species Trifolium pratense, T. repens, Melilotus albus, and Medicago sativa individually to study their effects on plant biomass yields, soil N, and above ground biomass N. As a control for intercropping, we used a commercial grass mixture without N2-fixing species as well as a no-intercropping treatment. Results indicate that intercropping in all intercropping treatments increased the total biomass yield, however, grass species competed with S. hermaphrodita for N more strongly than legumes. Legumes enriched the cropping system with fixed atmospheric nitrogen (N2) and legume facilitation effects varied between the legume species. T. pratense increased the biomass yield of S. hermaphrodita and increased the total biomass yield per mesocosm by 300%. Further, the total above ground biomass of S. hermaphrodita and T. pratense contained seven times more N compared to the mono-cropped S. hermaphrodita. T. repens also contributed highly to N facilitation. We conclude that intercropping of legumes, especially T. pratense and T. repens can stimulate the yield of S. hermaphrodita on marginal soils for sustainable plant biomass production. [ABSTRACT FROM AUTHOR]

The global demand for energy security and the mitigation of climate change are the main drivers pushing the production of crops for energy purposes (energy crops). However, the cultivation of these plants can cause land use conflicts since agricultural soil is mostly used for food crop production. A sustainable alternative to the conventional cultivation of food-based energy-crops is the cultivation of non-food energy crops on marginal lands. To further increase the sustainability of energy crop cultivation systems the dependency on synthetic fertilizers needs to be reduced via closed nutrient loops in the production chain for bioenergy. In the present study Sida hermaphrodita was used to evaluate its potential as an energy crop to be grown on a marginal sandy soil in combination with a fertilization using digestate from biogas production. With this dose-response experiment we identified an optimum digestate dose of 40t ha -1 corresponding to the highest biomass production, which was compared to an equivalent dose of mineral NPK-fertilizer. Further, 240t ha -1 had lethal effects on Sida hermaphrodita . A digestate dose of 5t ha -1 showed no fertilization effect. Digestate fertilization built up a pool of soil organic matter (SOM). The slow release of nitrogen from this organic pool could serve as long term fertilization and help to limit the high risk of leaching on marginal soils. Accordingly we see a potential of biogas digestate as a sustainable alternative to mineral fertilizers for the cultivation of the energy crop Sida hermaphrodita on marginal soils. [ABSTRACT FROM AUTHOR]