Op proefveld Mest Als Kans worden 12 organische mestsoorten en composten vergeleken met kunstmest. Na vijf jaar ontstaat er een constant beeld in opbrengstverschillen tussen kunstmest (laag), gemiddeld overige meststoffen en Postalmest compost (hoog). Het Pw-getal is in alle behandelingen gedaald waarbij Potstalmest er positief uitspringt (relatief geringe daling) en VAM compost negatief (relatief sterke daling). Bij veel behandelingen daalt het bodem organische stof gehalte. Positieve uitzonderingen zijn Rundvee dunne mest en Potstalmestcompost met relatief grote stijging ten opzichte van aangevoerde organisceh stof. VAM compost geeft de sterkste stijging maar kent ook de grootste aanvoer.
At the 'Manure as Opportunity' experimental field site, 12 organic manure and compost types were compared with artificial fertilizer during a 13-year field study. After five years, a pattern emerged of yield differences between artificial fertilizer (lowest yields), deep litter manure (highest yields) and other manures and composts (average yields). This pattern was maintained in later years. In all treatments, water extractable P (Pw) decreased over the years; this decrease was lowest in the deep litter manure treatment, and highest in the VAM compost treatment. Furthermore, soil organic matter content decreased in many treatments. Positive exceptions are the cattle slurry and composted deep litter manure treatments, where a relatively high soil organic matter increase was observed relative to the amount of organic matter added by the treatment. VAM compost resulted in the strongest increase, but in this treatment organic matter input was also highest.