The chemical processes of two Swiss soil tests for phosphorus availability were examined to allow a comparison: Extraction in the ratio of 1 g of soil to 2.5 ml of CO2-saturated water (CO2-P) and in the ratio 1:10 with pure water (H2O10-P), both followed by colorimetric P determination. Apart from orthophosphate up to 80 % of the result are due to other P species. Significant amounts of extracted organic P are not detected by this method. The extracts are saturated with respect to P: Using less soil with a constant volume of extractant, the P concentrations in the extract remain similar and may even increase. Likewise, only a small fraction of P added to the soil prior to the extraction are recovered in the extract. CO2-saturated water extracts between half and the fivefold of P compared with pure water. Calcium plays an important role: The addition of 1 % lime or Ca2+ to lime-free soils reduces the extracted P significantly. For lime-free samples CO2-P can be estimated from H2O10-P if H2O10-Ca is included in the calculation. With lime containing soils there are no useful correlations between CO2-P and H2O10-P.These «weak» extraction methods measure the «intensity», i.e. the P concentration in mg/L, and not soil P contents in mg/kg or kg/ha and can therefore not be used for an estimation of P fluxes or P balances.
Symbiotic nitrogen fixation by bacteria in the soil coexisting with legumes leads to reduced fertiliser requirement. It is not easy to measure this variable on farms, however. Now researchers from Agroscope have developed a method for estimating nitrogen input via symbiotic fixation at farm level.
With increasing global and regional temperatures, even in Switzerland the growing season has lengthened considerably. Using data from the Federal Office of Meteorology and Climatology, Agroscope has traced the development of the growing season since the start of the previous century.
The phosphate mineral reserves required for fertiliser production could be exhausted on a global scale in just a few decades. This study presents a method for recycling a Swiss industrial by-product into a phosphate fertiliser.