Bioavailability of recycled phosphates from all sources
We are able to provide now an assessment method which is highly repeatable. The method is based on a substrate which can be standardized and offered in identical qualities over many years (in contrast to soil-based experiments), but it shows basically all chemical and physical properties of an arable soil. The difference is that nutrient contents can be adjusted accordingly. We have tested the substrate over many experiments and it has proven to be virtually free of available phosphate. Using ryegrass and alfalfa (and alternatively: red clover upon demand) we can follow the long-term availability of the respective fertilizer sources, be it organic or inorganic fertilizers and raw materials.
The advantage of using two different species with contrasting rhizosphere reactions (acidifying vs. non-acidifying) provides additional information about species-specific access to sparingly soluble fertilizers, where ryegrass can be taken as representative for Poales (like our cereals). Repeated harvesting and nutrient analysis of the biomass allows us to excellently assess the long-term phosphorous availability as well. It has to be born in mind that this approach will deliver information about the maximum available phosphate. Modifications of the experimental approach can be used for the assessment of further nutrient availabilities after soil or foliar application.