TECNICA 44 TECNICA ficazione. Viceversa, le attrezzature per la minima lavorazione tendono a rimescolare lo strato sul quale agiscono (con una profondità massima di solito non superiore a 15 cm), distribuendo il materiale vegetale, se presente, in maniera più o meno uniforme nell’intero orizzonte di intervento, superficie inclusa. Peraltro, il continuo passaggio del macchinario in campo, sempre più potente e prestazionale, ma anche progressivamente più pesante, comporta un effetto negativo sulla struttura del terreno – il compattamento – che provoca una riduzione degli spazi vuoti entro i quali circolano aria e acqua e impedisce l’espansione dell’apparato radicale delle piante. Le lavorazioni periodiche sono finalizzate proprio a ripristinare un’ottimale struttura del suolo, e giocoforza si interviene solamente sullo strato superiore (in inglese, “topsoil”), ma nulla si fa per migliorare la situazione nello strato sottostante, il “subsoil”, comunque esplorato dalle radici delle piante coltivate, che subisce quindi una degradazione progressiva. In aggiunta, la tipica azione di alcuni attrezzi, quali l’aratro e la zappatrice, portano alla formazione della cosiddetta “suola di lavorazione”, ossia uno strato di qualche centimetro fortemente compattato, collocato immediatamente sotto l’orizzonte lavorato, che costituisce un ulteriore impedimento al normale sviluppo dell’apparato radicale (v. box). La discissura Per risolvere i problemi descritti, occorre intervenire in profondità, cercando di ripristinare anche in quel caso una struttura fisica del terreno che permetta una corretta circolazione di aria e acqua. tion, structure and natural biodiversity, safeguarding it from degradation and erosion. The main difference with plowing is that the latter has the main purpose of inverting soil layers, burying deep into the surface soil rich in plant residues (and any additional inputs, such as organic matrices like manure, compost, and the solid fraction of digestate), in order to promote their decomposition and humification. Conversely, minimum tillage equipment tends to remix the layer on which it acts (with a maximum depth usually not exceeding 15 cm), distributing plant material, if any, more or less evenly throughout the entire intervention horizon, including the surface. Moreover, the constant passage of machinery in the field, which is increasingly powerful and high-performance, but also progressively heavier, has a negative effect on the soil structure - compaction - which causes a reduction in the empty spaces within which air and water circulate and prevents the expansion of the plants' root system. Periodic tillage is aimed precisely at restoring an optimal soil structure, but playfully, one intervenes only on the topsoil. Still, nothing is done to improve the situation in the layer below, the "subsoil," which is, in any case, explored by the roots of cultivated plants and which thus undergoes progressive degradation. In addition, the typical action of some implements, such as the plow and the hoe, leads to the formation of the socalled "soil pan," which is a layer of a few centimeters strongly compacted, placed immediately below the tilled horizon, which is an additional obstacle to the normal development of the root system (see box). Soil cracking To solve the described problems, it is necessary to intervene at depth, trying to restore even then a physical structure of the soil that allows proper air and water circulation. The purpose of soil cracking is, therefore, precisely to break up the sole that is generated by the plow and hoe: by cracking and loosening the soil in depth (without, however, remixing it and turning its horizons over), the aeration and, particularly, the percolation of meteoric water in rainy periods, as well as its capillary rise in drought periods, is promoted. This type of tillage becomes even more important if one decides to adopt a minimum tillage technique, both because the deep layers are no longer disturbed but are still subject to progressive compaction due to machinery traffic and because in the transition from the traditional to the minimum tillage technique it is necessary to break up the sole that has been created over time by repeated plow intervention. This is an operation that does not require annual periodicity but can be performed every 3-5 years or even less frequently whenever a reduction in crop productivity related to a degradation of the physical state of the soil is noticed. Subsoiling or chiseling? One of the three pillars on which conservation agriculture is based is the reduction of agrarian soil tillage, aimed at recreating the biological balances necessary for the development of viable, fertile agricultural ecosystems capable of generating environmental benefits. Hence, minimum tillage techniques are implemented, which, however, require deep periodic interventions. Tillage of the soil layers below the tilled soil is usually carried out with different equipment, which in the Italian language are defined in numerous ways (i.e., subsoiler, chisel, dissolver, decomposer, disassembler etc.), but traceable in good substance to two types, which in English are the chisel and the ripper or subsoiler. Bearing in mind that the literature in the field is by no means in agreement in defining the various implements since there are many models available with intermediate characteristics, the real difference lies in the disruption characteristics: the chisel coarsely dislodges and L’aratura (sopra) inverte gli strati di terreno e interra in profondità i residui colturali, mentre la minima lavorazione (sotto) rimescola lo strato su cui si interviene, distribuendo nell’intero orizzonte il materiale vegetale presente (superficie inclusa) Conventional ploughing (above) involves overturning soil layers and burying crop residues, whereas minimum tillage (below) remixes the tilled soil layer, incorporating the existing plant residues across the entire horizon, including the surface
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