Green manure is an ancient agronomic practice which represents, today as then, a valid tool for preserving and improving soil fertility. Modern agriculture, increasingly oriented towards satisfying the growing demand for products, has often ignored the need to maintain a balance between resource exploitation and soil regeneration, and in a similar context rediscovering traditional methods such as green manure can represent a viable option to ensure sustainable management of crops.
Soil fertility is an asset to be preserved
Soil fertility is its ability to support the development of crops, offering a favorable environment for plant rooting and microbial growth. Fertility, in fact, does not only depend on the chemical characteristics of the soil, but also on the physical and biological ones: a soil rich in organic substance will be capable of hosting an active microbial population, fundamental for the decomposition of organic residues and for the release of nutrients available for plants.
In recent decades, agricultural intensification has led to an impoverishment of organic substance in the soil, with negative effects on the microbial balance and, consequently, on crop productivity: in areas with a strong agricultural impact, a drastic reduction in the substance has been recorded organic, which in some areas has gone from 3.3% to 0.75% in about 30 years. The extent of such impoverishment has triggered a spiral of decline in soil biodiversity, which is becoming increasingly less fertile and less capable of supporting crops.
Green manure: a thousand-year solution for the soil
Green manure is an agronomic technique which consists in the sowing and subsequent planting of herbaceous crops, not for production purposes, but to enrich the soil with organic substance. This is a method used for centuries to regenerate the soil and improve its structure and composition. Among the species most used for green manure are legumes, plants that establish a symbiosis with bacteria of the Rhizobium genus, capable of fixing atmospheric nitrogen and transforming it into organic nitrogen, available for subsequent crops.
The most common legumes for green manure include clovers (Trifolium spp.), field bean (Vicia faba), vetch (Vicia sativa), fodder pea (Pisum sativum), and sweet clover (Melilotus officinalis). The use of these plants contributes to the increase in nitrogen in the soil and increases the availability of organic substance, which is fundamental for maintaining the active microbial population and promoting the growth of the main crops.
One of the most interesting aspects of green manure is the possibility of using mixtures of different species, each with specific characteristics that bring different benefits to the soil: plants with deep roots, for example, facilitate the penetration of the roots of subsequent crops, while other species , like cruciferous vegetables, release substances that combat soil parasites, such as nematodes and some pathogenic fungi.
Green manure in the vineyard
The application of green manure in vineyards is a particularly interesting practice. The vine, a symbolic crop of the Italian agricultural landscape, is able to adapt to soils with different pedoclimatic characteristics, but this does not mean that its root system cannot benefit from fertile and well-balanced soil. The fertilization of the vineyard, in fact, is not only based on the supply of nitrogen, phosphorus and potassium, but must aim to create a porous and well-structured soil, into which air and water can easily penetrate.
Green manure in the vineyard offers numerous advantages. Firstly, it helps to keep the inter-row grassed, thus reducing surface erosion of the soil, a particularly relevant problem in hilly areas where many Italian vineyards are located: grassing protects the soil from erosion caused by rain, reducing the runoff and limiting the loss of fertile surface layers. It is estimated that every year in Italy, around 10 tonnes of soil per hectare are lost due to erosion, a phenomenon that seriously compromises the long-term sustainability of crops.
Furthermore, green manure promotes the infiltration of rainwater, improving the water reserve of the soil and reducing the need for irrigation during periods of drought: in the vineyard, where irrigation is often limited to emergency use, this characteristic is particularly valuable. The choice of green manure species must be careful and aimed at not creating competition for water with the vine, and for this reason sowing is generally carried out in autumn, in order to take advantage of the winter rains.
Another important advantage of green manure is the ability to counteract the growth of weeds. The species used for green manure can establish competition with the spontaneous flora, limit the development of weeds and thus reduce the need for chemical interventions to control them. This aspect is of fundamental importance from a sustainable agriculture perspective, which aims to reduce the use of pesticides and promote the biological control of parasites.
Economic incentives for those who practice green manure
The practice of green manure also ensures economic advantages. Farmers who adopt green manure practices can in fact access the contributions provided for by the Common Agricultural Policy (CAP). The recent update of Ecoscheme 5, which will come into full force in 2025, provides incentives for those who allocate part of the land to crops of beekeeping interest and honey and nectariferous species: the funds are intended to promote biodiversity and encourage the presence of pollinating insects , crucial for many agricultural crops.
Farmers who choose to allocate at least 2500 m2 of their land to melliferous species, as indicated by the Ministerial Decree of 28 June 2024, will be able to receive up to 500 euros per hectare of arable land, an excellent opportunity for anyone who wants to combine economic interest with environmental sustainability: the choice of nectariferous plants increases biodiversity and also improves soil fertility, effectively promoting the biological control of parasites.
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