**5.1. Results on olive orchards**

In some experimental trials, the assessment of the composting process in natural conditions was studied on two different typology of matrices, respectively composed by olive mill wastes and other crop by-products as structural biomass: i) wet pomace by two phases mill with olive leaves and cereals straw; ii) pomace and waste water by three phases mill with carved pruning residuals. All materials were placed on a beaten-soil platform, and remixed to homogenize the matrices. The evolution of bioxidation was monitored controlling the temperature and humidity of matrices, and assuring oxygenation and thermal drain by weekly blending with mechanical shovel on tractor front loader. At the end of the fermentation period, both biomass microbial pools and chemical parameters were analyzed to evaluate the characteristics of obtained composts. Results of composting parameters trend and microbiological analysis, indicate a correct way of aerobic process; and the compost analyses confirmed that a "mixed composted amendments" was obtained (Law 748/1984).

To evaluate amendment and nutritional efficiency, the composts were spread at doses of approx. 150 kg tree-1 (60 tons ha-1) on 6 x 4 scaled olive orchard, and buried with a light disk arrow tillage. At the following year's harvesting time, was compared the differences between treated and untreated soil characteristics, and yield responses of 15 treated vs. 15 untreated olive trees of a 15 years old "Nocellara messinese" cultivar for OP2 compost, and 20 years old "Leccino" cultivar for OP3 compost.

The amendment and nutritional efficiency of these kinds of composts was confirmed both by soil organic matter increment (+ 38.6%; + 40.6% for two phase and three phase compost, respectively), and trees productive responses at the following year harvesting time (+ 10.5% and + 15.1% oil yield increase on respective treated trees).

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growth and soil characteristics. The results of this research indicated that the untreated and treated WW application increased growth parameters, indicating the possible use of WW as an amendment to rye-grass. A significant increase of total, extracted and humified organic carbon in soil, and humification parameters (degree and not humified organic carbon) were found, whereas no accumulations of heavy metals in the soil were measured at the end of the experiment. Furthermore, N content in WW was used by rye-grass for plant growth that increases N uptake and consequently the dry matter accumulation (Montemurro et al.,

As already mentioned, the composting of olive pomaces could be recycled for agricultural purposes. In addition, a specific test could be performed to assess the phytotoxicity for both the raw pomace and the stabilized composts. The phytotoxicity is one of the most important criteria for evaluating the agronomical potential of organic materials as olive pomace, and can be measured by specific test. A method can be used to assess phytotoxicity of this residues, by combining the measurements of seeds germination and roots elongation of cress (*Lepidium sativum* L.). Different experiments indicate that the olive pomace composts were not phytotoxic. According to other researches, it can be suggested that repeated compost application might preserve the soil organic carbon content and supply macronutrients to crop. Finally, among different solutions, the addition to olive pomace of manure, as a nitrogen source, and pruning wastes, as bulking-agent, may generate organic amendments suitable for the organic cultivation management of some herbaceous crops.

Several experiments on herbaceous crops indicate that the use of organic pomace fertilizer, as a partial substitution of mineral fertilizers, reached the same yield of the highest mineral fertilizer treatment, ensured also an increase of soil total organic carbon and other soil properties. Furthermore, the application of these organic composted wastes also induce a lower nitrogen mineral soil level at the end of the experimental trials, indicating the possibility to reduce pollution risks. These findings were found in maize and barley in a

On the market are available different organic (peats, manures, urban wastes, barks, sawdusts) and inorganic (sand, pumice, clay, perlite, vermiculite) materials, usable in the preparation of olive nursery substrates. All these materials have some advantages, i.e. sterilization process not necessary, and commercial fertilizers can be added. Even though the peat is the more used organic material in the preparation of the substrates, other different material have been tested

In some experimental trials has been valued the compatibility and efficiency of composts, obtained from different olive mill wastes, in the composition of growth substrates for olive nursery, with the aim of mostly valorizing these biomasses as partial or total substitution of

**5.3. Results of pomace application on herbaceous crops** 

same experimental research (Montemurro et al., 2006).

with the aim to replace it, include the olive industry byproducts.

**5.4. Results on greenhouse olive nursery** 

2007).

Even if the condition of fermentative process (open air, natural conditions) was not optimal, the obtained compost demonstrate that the aerobic fermentation of olive mill residuals can run in a correct way also in natural conditions, producing an hygienized and partially stabilized organic amendment, that can be better spread out at the optimal time, and without the negative effects related to the raw olive mill wastes supply. At the used doses, both composts increased soil fertility, improved water retention and the availability of nutrients in amended soils, and improved plant productivity. The showed nutritional effect of these composts would allow a reduction in the use of chemical fertilizers, in agreement with the energetic and economic sustainability principles in the use of renewable resources. In common situations where industrial installations are unfeasible, the natural composting process of olive mill wastes can therefore be a interesting alternative to the raw pomace and waste-water spreading on soils; and could represent a solution of sustainable disposal problem, allowing to increase soil organic matter contents and to reduce the desertification processes (Casacchia et al., 2012; Toscano et al., 2009*b*).
