Behaviour of hoof and horn during the storage of peat-based and peat/pumice-based growing media

Hoof and horn is one of the most widely used organic fertilizers by the Italian substrate manufacturers and it is frequently used for substrates devoted to organic production. Together with chemical fertilizers, it is used for long lasting conventional production. A recent national law (Leg. Decree n.75, 2010) set up a series of rules in substrate production and set tolerance degrees for pH and EC. At present there is little information regarding the influence of organic fertilizers on pH and electrical conductivity (EC) during the storage of growing media. An experiment has been carried out in order to investigate the behaviour of hoof and horn added to two growing media (a peat based media and a mixture of peat 80% and pumice 20% v/v). These media were stored for 12 months at a constant temperature of 21°C or kept at 40°C for 15 days and then at 21°C until the end of the trials. In all treatments pH decreased exceeding dramatically the degree of tolerance. The more aerated substrate promoted the fastest and widest pH reduction. The heat treatment reduced the acidification of media maintaining the final pH slightly higher than in samples non heated. The substrate containing pumice induced an early increase in EC values while both the heated media showed the highest differences between initials and final values. In both growing media EC values exceeded the admitted tolerance. Results showed a dramatic effect of temperature treatment and marked differences between the studied growing media.