The 6 fundamental operations on soil

1. Preparing soil for crops: breaking up and subsoiling

The first group includes all those operations leading to the cultivation of soil that has never been cultivated or that hasn’t been worked for many years.
The types of operation in question are breaking up and subsoiling, which are different yet share some characteristics.
Breaking up is carried out after clearing i.e. on uncultivated land or land that has never been cultivated. The operation breaks up the compactness of the soil to a depth ranging from half a metre to 150 cm. Ploughs pulled by agricultural tractors are used to break up the soil, although excavators are sometimes used.
Subsoiling, instead, involves working soil that has been previously used for a crop. The aim is to increase the softness of the soil so that roots can easily spread in depth. 
Subsoiling can be carried out using different techniques: hole, trench or total. The choice depends on requirements and the depth to be reached is usually around 80-100 cm.

2. Ploughing, tilling and levelling

Ploughing is the technique of breaking up soil and turning it so that everything above ground is sent under the soil, and vice versa. This is a highly important step, especially when dealing with compacted soils or soils that haven’t been cultivated for many years. If soil isn’t ploughed, there’s a risk of working only the surface without going deep down. The effect of ploughing is often “reinforced” by the green manure technique, an agricultural practice that consists of burying certain crops in order to maintain or increase soil fertility. Ploughing can be carried out using specific machines, each one with its own unique characteristics adapting to the soil in question.
Tilling is an operation on the soil that involves breaking up clods of earth and mixing the soil. In situations where the soil is soft, especially with certain types of crops, ploughing can be skipped and the soil can be directly tilled. Tilling is carried out around the time of transplanting vegetables and is intended to make the soil hospitable in order to optimise seedling growth. 
The last step is soil levelling, which is useful for avoiding water stagnation caused by unevenness or hollows. 

3. Sowing

Seeds are distributed in the soil according to various specifications for each species: technique, depth, distance, type of crop and climatic conditions.
Nowadays, sowing is done by machine using seed drills. These consist of a seed hopper, distribution heads and coulters, with the latter responsible for burying.
For many crops, the most common sowing method is row seeding. In this case, seed drills have scaled cylinders or drainage rollers that lead to coulters via elastic hoses.
Precision seed drills are also available, which hold the seed by suction in the holes of a distributor disc, which then releases seeds at regular intervals.