SESSION II - SOIL MANAGEMENT
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Lesson 5
Soil management under arid areas to increase water availability
by Francesco Angeletti, Irma Terracciano and Sergio Saia
Introduction to lesson 5
Introduction to lesson 5
Available water of a soil is the amount of water that the soil can store and that can be absorbed by plants. It corresponds to the difference between field capacity, intended as the maximum amount of water the soil can hold, and wilting point where the plant can no longer extract water from it. In the areas where precipitations are scarce, and evapotranspiration is high, available water result crucial for plants growth. The main factors affecting available water are: soil texture, soil structure, root and soil depth. Soil texture indicates the relative content of particles of various sizes such as, sand, silt and clay in the soil. The larger the particle size and the distance between them, the greater the water drainage. This is the case sandy soils. In clayey soils particles size is reduced and thus water drainage is slow. However, this last situation may not correspond to a great water availability for plants, because the strength necessary for roots to extract water from small pores may not be enough. Medium-textured like soils are those with the greatest available water holding capacity.Soil structure refers to how particles of sand, silt and clay are grouped together. When assembled, they form larger particles which are called aggregates. The spaces between aggregates provide medium and large pores, permitting water, air and roots movements through the soil. Poorly structured soils have strongly packed aggregates that do not allows root expansion and water and are low in water holding pores.The capacity of a plant to access available water on numerous soils is determined also by soil depth and rooting depth of crops. As an example, for crops with shallow root systems, such as onions, the available water below 60 cm is of little significance. By contrast, for crops with deep root systems, such as corn, the available water at depth is very important. In many agricultural soils there are subsoil barriers (compaction, acidity, salinity…) which avoid plant roots from accessing available water.To increase available water level of a soil, it is essential to achieve the following objectives:- increasing the portion of soil that can be explored by crop roots;- improving water storage in it;- enhancing soil water retention level;- reducing water losses. Tillage, when properly conducted, restores soil porosity and removes surface crust, consequently enhancing water infiltration and root expansion. However, in regions where precipitations are limited and soil tend to be loamy, minimum tillage or no tillage permit to obtain better results compared to conventional tillage. Minimum tillage is also useful in countering fissure presence in loamy soils that enhance evaporation.Good amount of organic matter in the soil is also important because, acting as a sponge, improves water retention. Organic matter content can be enhanced through the distribution of manure or plant residues, by green manuring or leaving crops residues on soil.Mulching consisting in covering soil trough straw, leaves or plastic sheets is useful in reducing soil water losses due to evaporation. Moreover, plant residues will contribute in increasing organic matter content. Wind breaking is also important. It reduces the amount of water lost in consequence of the wind action and it can easily be obtained using hedges. As well as cultivated plants weeds adsorb water from soil and transpire to realize photosynthesis, reducing therefore water available for crops. Weed control is another relevant tool for mitigating water losses.
In Depth
In Depth
5.1-Conservation agriculture outline in perennial crops5.1-Conservation agriculture outline in perennial crops
5.2 Conservation Agriculturehttps://www.fao.org/conservation-agriculture/in-practice/minimum-mechanical-soil-disturbance/en/
5.2 Conservation Agriculturehttps://www.fao.org/conservation-agriculture/in-practice/minimum-mechanical-soil-disturbance/en/
Soil porosity and roots
Soil fissures
Plant residues covering soil
Compacted loamy soil
Lesson 6
Soil inoculation with symbiontic microbes
by Nadia Massa, Guido Lingua and Daniela Campana
Introduction to lesson 6
Introduction to lesson 6
Arbuscular mycorrhizal fungi (AMF) and Plant Growth Promoting Bacteria (PGPB) are soil borne microorganisms that are beneficial for plants.AMF colonize plant roots forming specialized structures inside the root cells, called arbuscules, that are the site of the nutrient plant-fungus exchanges. AMF colonized plants are often more performant and more tolerant to biotic (e.g. pathogens) and abiotic (e.g. drought, salinity) stresses. Modern agriculture, due the massive use of fertilizers/pesticides and the mechanical soil tillage, pose a serious threaten to AMF survival. So, it may be necessary to re-introduce AMF in the form of inocula that are produced in pots filled with quartz sand or other substrates adding colonized roots or fungal spores in the presence of different plant species, like sorghum or clover. After 4-6 months of plant culture, the content of the pots and the plant roots, cut in small pieces, are carefully mixed and it is possible to use this material to inoculate other plants. The inoculum can be applied at seed sowing, at plant transplanting in the field or can be applied to plants already present.PGPB can favour plant growth in a number of ways that can be classified in direct and indirect mechanisms. While direct plant growth promotion occurs through increased acquisition of nutrients or modulation of the hormone level inside plants, indirect promotion consists in soil borne disease suppression. The release of PGPB in the environment is currently a quite common practice. Once candidate PGPB are isolated and identified, the strains are tested in vitro for their physiological traits. It is recommended to consider safety and health features of the strain. Then, their efficacy in vitro and in field trials need to be assessed and the procedure of bacterial inoculation is developed in order to ensure the bacterial survival and meet the farmer’s need. In our labs the procedure of inoculum preparation consists in a liquid or solid overnight culture of the bacterial strain containing 108 or 1011 CFU/ml (for experiment performed under controlled conditions and in open fields, respectively). For experiments performed under controlled conditions, we are used to inoculate a surface sterilized seed. Then, germinated seeds are dipped for 20 min in a bacterial suspension containing 108 CFU/mL in 0.1 M MgSO4 in order to favour the adhesion and the amount of bacterial cells on the treated seeds is measured by colony counting. If the experiment is performed in open field conditions the highly concentrated bacterial suspension is then diluted in water and distributed by drip irrigation on seedlings or adult plants.
Images
Images
🔎 6.1 Microscopic view of roots colonized by arbuscular mycorrhizal fungi. The vesicles (typical fungal structures) are visible (left side). The arbuscule is another characteristic fungal structure (upper right side). In the lower right position the extraradical mycelium can be observed.
🔎 6.2 Root nodules in bean (Phaseolus vulgaris) colonized by bacteria of the genus Rhizobium. Petri dish with rhizobia culture (lower part on the left). Microscopic view of rhizobia (lower part on the right).
Video Lesson
Video Lesson
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