**5.2. Results of olive mill waste water application on herbaceous crops**

As mentioned before, the national law (Law 574/1996) allows the olive mill waste water (WW) spreading on soils with appropriate characteristics for agronomical use with the maximum amount of 80 m3 ha-1 yr-1 for the centrifuge system and of 50 m3 ha-1 yr-1 for the pressure method.

In a research carried out in the semi-arid environment of Southern Italy, the application of two WW rates without preliminary treatments was studied. To reach this objective, the effects on cereal and leguminous crops yield, quality, N uptake and on soil characteristics were recorded.

The results obtained indicate that the WW treatments (both doses) positively affected the yield of ryegrass, while a significant yield increase was found at the highest level of WW in proteic pea. The clover crop showed a species-specific sensitiveness, but the WW applications increased the protein content compared to the untreated plots. The WW rates also increased total organic content in the soil, in respect to the unfertilized control. At the end of this three-year experiment the values of soil total extracted carbon and humified organic carbon were higher compared to the initial ones. The values of soil available P and K of the control treatment found at the end of experiment were almost the same than those recorded at the beginning of the research confirming that the increases found in WW plots were due to the WW applications.

A two-year experiment was also carried out in controlled environment (lysimeters) to study the effects of applying untreated and treated WW as soil amendments on both rye-grass 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., 2007).
