Green compost influences yield and quality of carrots (Daucus carota L.) by enhancing root rot suppression to Sclerotinia sclerotiorum (Lib. De Bary)

The aim of this research, carried out in Bari and Policoro (Southern Italy) from March to June 2018, was to evaluate the effects of two different green composts on yield, quality, and root rot suppression of carrot (Daucus carota L.) cv. Rubrovitamin when compared to a mineral fertilizer and a plant growing media of peat-pumice. Green composts obtained from the municipal solid waste (Biovegetal) and olive pomace by olive mill were used in outdoor crop as fertilizer to enhance root yield and quality and in glasshouse to evaluate root rot suppression against Sclerotinia sclerotiorum. A randomized complete block design with six replicates was used. A total of eight treatments was compared in outdoor (mineral fertilization, three levels of each compost and unfertilized control). A total of five treatments was used in glasshouse: carrot was cropped in a growing media made of peat and pumice and fertilized with the two composts at two different levels, compared to an un-sterile potting mix of 60% peat with 40% pumice used as control. In the carrot grown outdoors the different composts did not influence either the length of the phenological phases or the entire crop cycle, but the highest dose of olive pomace (30 Mg ha-1) favored the greatest root production with an increase of 19.9% if compared to the mineral fertilizer. Biovegetal at the highest dose (30 Mg ha-1) provided non-statistically differences in root production from that obtained with the mineral fertilization, as well as the lowest rate (15 Mg ha-1) of composted olive pomace supplemented with 50 kg N ha-1. The highest carotenoids content, total soluble solids and specific weight were recorded by the amendment with the highest composted olive pomace rate. Concerning the root rot suppression effect, Biovegetal showed to be more effective than composted olive pomace. Thus, the use of green compost could represent a useful alternative to mineral fertilization and soil-borne disease control by synthetic fungicides through an adding-value due to by-products reusing and waste recycling.