Suitability of moist olive pomace as soil amendment

A laboratory experiment was performed to evaluate the suitability of moist olive pomace (MOP) as soil amendment. Moist olive pomace was obtained from a new olive-oil industrial process called the 'two-phases method'. Soil samples were mixed with MOP to approximate a field application of 40 t ha(-1) and incubated under aerobic conditions at 20 degreesC and 60% of soil water holding capacity. To estimate the effect of different loading rates and N supply on mineralization, 40, 80, 120 and 160 t ha(-1) of MOP and 200 ppm of N as (NH4)(2)SO4 were used. Cumulative CO2-C evolution, total microbial activity and biomass-C were monitored during a 60-day period. Results indicate that the CO2-C evolution from MOP depends on soil type and is temporarily inhibited in acidic soils. Evolution of CO2-C increases with incremental addition of MOP, but the percentages of the added C that were mineralized decreased with increasing application rates. Mineral N supplements result in more efficiency of the mineralization process. Among the kinetic models tested to describe the mineralization dynamics, a first-order exponential model including a constant term provides the best fit to the experimental data. Both amount and activity of soil microbial biomass are enhanced by MOP added at the 40 t ha(-1) rate, at least in the first period of incubation. At higher rates of MOP addition, a constant increase of biomass C during incubation is observed, while the biological activity decreases at the end of incubation. Following application of mineral N, both amount and activity of microbial biomass is enhanced