One controlled, randomized, replicated trial in Italy found that applying a high rate of compost increased soil organic matter levels, microbial biomass and fruit yield.
SOIL TYPES COVERED: Silty-clay.
Soil microbial biomass is the amount of tiny living organisms within a given area or amount of soil.
A controlled, randomized, replicated experiment in 2001-2009 on silty-clay soil in Italy (Baldi et al. 2010) found 169% more soil organic matter in soil receiving 10 t/ha/year of compost compared to an unfertilized control, after 8 years. Soil receiving 5 t/ha/year of compost applied had 75% more organic matter compared to the control. Mineral fertilizers had no effect on organic matter levels. Soils receiving compost at 10 t/ha/year had higher microbial biomass (12 mg/g soil) and fruit yield (51 kg/tree) compared to the control (6.6 mg/g soil and 43 kg/tree, respectively). Six treatments replicated four times were applied to nectarine Prunus persica trees: (1) unfertilized control, (2) mineral fertilizer including phosphorus (100 kg/ha), potassium (200 kg/ha) and nitrogen (70 kg/ha), (3) cow manure (10 decreasing to 5 t/ha), (4) compost at planting then 5 t/ha/year, (5) compost at 5 t/ha/year, (6) compost at 10 t/ha/year. Soil samples were collected annually in September to 40 cm depth. Nectarine trees were spaced at 5 m between rows and 3.8 m between trees. Compost and manure were measured in tonnes of dry weight.