**2.2. Organic Matter and nitrogen ratio**

40 Olive Germplasm – The Olive Cultivation, Table Olive and Olive Oil Industry in Italy

goal that guides management decisions.

properties (Kabata-Pendias & Mukherjee, 2007).

main chemical and physical soil properties.

**2.1. Soil texture, porosity and density** 

respective particle diameter size.

**2. Soil** 

greater vegetative and reproductive plant balance, and cost containment should be the main

Soil is defined as the top layer of the earth's crust. It is formed by mineral particles, organic matter, water, air and living organisms. It is in fact an extremely complex, variable and living medium, and represents a non-renewable resource which performs many vital functions: food and other biomass production, storage, filtration and transformation of many substances including water, carbon, nitrogen. As long as 100 years ago, Wollny (1898) described the positive effect of soil structure on root growth, water availability, gas transport in soils as well as the positive effects of soil structure on soil strength. He mentioned that the mechanisms involved in the interaction between soil structure and plant growth and yield needed to be investigated. Since then, the positive effects of a favorable soil structure and the negative effects of, for example, soil compaction on crop growth and/or yield have been repeatedly described (e.g. Blank, 1932-1939; Dexter, 1988; Hakansson et al., 1988; Kay, 1990). The anthropogenic activities such as tillage, mineral fertilization, waste disposal and industrial pollution, affect both chemical and physical natural soil

Recent improvements and new methods in analytical chemistry and increasing areas of environmental investigation have substantially added to our knowledge of agricultural soil science. For example, the soil characteristics of an olive plantation are especially important in terms of vulnerability to erosion and, to a lesser extent, to leaching of potentially contaminating elements contained in fertilisers and pesticides. The root system of the olive is concentrated in the top 50-70 cm of soil although it may send out roots to a depth of more than one meter to satisfy its water needs. Therefore, the soil must have an optimal texture, structure and composition to a depth of at least one meter. The management of a cropping system requires periodic evaluation that includes systematic testing, with the aim of determining the nutritional status of soils in order to assess the existence of any nutritional deficiency, excess or imbalance and form a basis for planning the nutrient supply as well as other practices (tillage, amendment, correction). The following is a brief description of the

The textural class is the first parameter that defines soil properties, and is determined by the relative percentage of the three major soil compounds: sand, silt and clay, defined by the

Clayey grounds are characterized by particles of a diameter of less than 0.002 mm, constituted by flinty minerals with different capacities to inflate in the presence of water and to contract in dry conditions, forming cracks which are typical of vertisols. Clayey soils show a low water permeability and high plasticity, which can induce stagnation phenomena and root asphyxia

in wet conditions; while in the dry state it has notable tenacity and cohesion.

The Organic Matter (OM) is a complex mixture of organic compounds deriving from metabolic wastes and decaying residuals of plants, animals and microorganisms, at different stages of decomposition. The OM percentage directly influences the structure and chemicalphysic properties of soil in terms of water infiltration and retention, element absorption, particle aggregations, Cation Exchange Capacity (Al3+, Fe3+, Ca2+, Mg2+, NH4+), buffering power, over the nutrient source for the plant. The quantity and nature of OM is highly dependent upon farming practices and climatic conditions and is found as both chemically stable humus (or passive OM) and partially decomposed plants, microbes and animal residues (or active OM).

Measures to increase the organic content are a very important part of good soil management in Mediterranean regions, especially in order to reduce vulnerability to erosion (European Soil Bureau, 1999). Practical measures are based on the incorporation of organic matter such as farm-yard manure, cover crops, pruning and processing residues, and soil tillage.

Plant availability of organic N is dependent on OM breakdown, which is difficult to estimate. The ratio of total organic carbon and total nitrogen (C/N) is the traditional guide to the nature of the organic matter present in the soil.

The basic premise behind this ratio is that organic carbon is the primary source of energy for soil microbes, but these also require nitrogen to multiply and utilise this energy. The microbes utilise soil carbon via respiration, with the consequent loss of carbon dioxide from the soil. As the active fraction of the OM is thus degraded, the C/N ratio drops until a steady state (the passive fraction) is finally attained. Interpreting this ratio is complicated, as it also depends on the nature of the OM. The passive fraction of the OM can have a C/N ratio that is 'medium'. Consequently, medium C/N ratio soils can have a wide variation in mineralisable N status, and this is a limitation when considering the C/N ratio in isolation.

Cultivation Techniques 43

Soil pH is one of the most common and important measurements in standard soil analyses (Hendershot et al., 2008b). The pH value expresses degree of acidity or alkalinity of the soil. It is important because it influences the chemical and physiological processes in the soil, and the availability of nutrients. Availability changes differently with pH levels: aluminium, copper, iron, manganese and zinc increase when the pH decreases; unlike magnesium that

Electrical conductivity (EC) is the ability of a material to conduct an electrical current and is commonly expressed in units of microSiemens per meter (µS cm-1). It is used to estimate the level of soluble salts. The measurement of EC in the soil water extracted from the field-water content is theoretically the best measure of salinity as it indicates the actual salinity level experienced by the plant root (Miller & Curtin, 2008). However, this measurement has not been widely used because it varies as soil-water content changes over time and so it is not a single-valued parameter. A soil is considered saline if the EC of the saturation extract exceeds 4000 µS cm-1 at 25°C. The soil EC varies depending on the amount of moisture held by soil particles. Consequently, the EC correlates strongly to soil particle size and texture

Soil water analyses can be organized into two main groups: analysis of storage properties and analysis of hydraulic properties. The water content of soil is part of the analysis of storage properties which refer to the soil's ability to absorb and hold water. Instead hydraulic conductivity is a hydraulic property which refers to the soil's ability to transmit or conduct water . It is more difficult for plants to absorb nutrient elements at low soil moisture

In order for plants to live, two key functions can be attributed to soil: habitability and nutrition. The function of habitability mainly depends on the physico-chemical characteristics of the soil. The function of nutrition depends on the factors that make nutrients bio-available to the plants, described above, determining the fertility of the soil as productive attitude. Biological soil functions depend on the micro-organic pattern, responsible for processes on the organic matter such as: mineralization, humification, nitrification, nitrogen fixation, symbioses, and parasitism. The agricultural management systems of soils, such as crop rotation, nutrient application, plant species, kind of tillage, and use of pesticides may have a strong impact on the composition of the soil microbial community. Maintenance of sustainable soil fertility depends greatly on the ability to harness the benets of rhizosphere microorganisms such as arbuscular mycorrhizal fungi (AMF), which form a symbiotic association with the roots of most plant families. Olive plants are known to form arbuscular mycorrhiza (Roldán-Fajardo & Barea, 1985; Briccoli Bati et al., 1992; Calvente et al., 2004), the most common mycorrhizal type involved in normal cropping systems, being considered as a key component in environmentally friendly

Mycorrhizae act as biofertilizers, bioregulators, and biocontrol agents (Lovato et al., 1996; Von, 1997). Arbuscular mycorrhizal fungi allow the plant to absorb greater quantities of

decreases when the pH decreases (Belsito et al., 1988; AA.VV., 1989; Jones, 2003).

and affects crop productivity.

**3. Soil management** 

levels, so nutrient element contents will be lower.

agro-biotechnologies (Jeffries & Barea, 2001).
