Seeding machines that work at high speed represent an important technological development not so much and not only because they reduce labour requirements, but above all because they improve the agronomic timeliness of the operation. However, to achieve this goal it is necessary to intervene on other technological features of the seed drill in order, for example, to reduce the weight of ancillary time on the working day.
The greatest advantage of increasing the forward speed of the seed drill is to be found in the improved timeliness with which it becomes possible to carry out the operation. The planting of the crop is in fact a delicate phase of the production process and has become even more so in recent years during which, especially in the Po Valley, there have been alternating springs characterised by cold spells, excess rain and prolonged drought. All these phenomena reduce the opportunities for sowing: increasing the work capacity therefore increases the possibility of finishing the operation within the time windows granted by the weather trend. This is an important advantage that makes it possible to plant the crop at the most suitable time, to choose hybrids or varieties that perform better, to anticipate certain delicate phenological phases by avoiding that they take place during the hottest and driest periods, and to harvest in the most suitable period. In medium and large farms and for specialised contractors, all this justifies the purchase of ultra-fast seed drills precisely because their higher purchase cost is reflected in the improved production performance of the crop.
The cost-effectiveness of these seed drills is also positively affected by the reduction of labour, especially in the context of contracting, where the freed up labour can be easily re-employed by expanding the range of services offered and the areas covered. At seeding time, in fact, in addition to the planting operations, the final soil preparation, fertilisation and weeding operations are also required.
Speed and precision
The increase in seeding speed must not be at the expense of precision. The analysis of quality can, for this operation, be traced back to three parameters: respect for row spacing, avoiding failures and double seeding, respect for seeding depth, and adequate soil compression around the seed so as to favour rapid and simultaneous germination. The first parameter directly affects the homogeneity of the crop’s growth, which is necessary in order to guarantee good plot production for crops such as maize, sorghum, sunflower, etc., which are not able to compensate with greater development (and production) for the greater availability of space (which, on the other hand, occurs to a certain extent in crops such as beet, soya and some vegetables). The other two parameters influence the homogeneity of seed germination: however, seeds that are too deep or, in spring sowings, too shallow, and not surrounded by soil may never germinate.
Increasing the forward speed also increases the speed of the seeding disc which selects the seeds. In fact, the angular speed of this disc is adjusted so that its tangential speed (measured at hole level) is equal to the forward speed. In conventional seed drills, the seed falls freely to the ground guided by the adductor tube, and along this path, bounces within the adductor occur to a variable extent and number, which modify its travel time even under laboratory conditions. This variability is directly proportional to the speed of the seeding disc. A variation in travel time from the sowing disc to the ground results in an alteration of the distance between the seeds. Let’s take an example: proceeding at 5 km/h, a difference in the descent along the adductor tube between two neighbouring seeds of just one hundredth of a second translates into a variation in the distance between the two seeds of 1.4 cm with respect to the set value; at 15 km/h this difference becomes 4.2 cm. If the difference in travel time becomes two hundredths, the variability in distance doubles. Therefore, it can be said that the increase in speed widens the variability in the travel time of the seed from the disc to the ground and that this has an even greater effect on the variability in the distance between seeds.
The field introduces another variable that amplifies this problem: the vibrations and jolts of the seeding unit during the course of work. This type of stress increases as seeding speed increases, and this worsens the seeding performance of the machine compared to what is observed in the laboratory. This explains why if pneumatic or mechanical seed transport systems are not used, speeds above 8-10 km/h are absolutely not recommended.
However, these speeds are only possible if the connection of the seeding element to the frame beam is mediated by an efficient articulated parallelogram capable of minimising the stresses transmitted to the seeding element and keeping it in the same position with respect to the ground. The parallelogram must allow to adjust the load and sensitivity to variations in the soil surface profile over a wide range of values.
Depth wheels also play an important role and must be evaluated in terms of number, position, size and material. The depth wheels of precision seed drills may be two (one on each side) or one of suitable width; the centre of the wheel must fall along the vertical line passing through the seed release point; in seed drills designed to operate on hard soil, it is often advisable to use only one metal wheel per element and of reduced width, rubber in other cases.
Seed-pressing wheels or other similar devices that operate within the furrow are important to prevent the seed from moving from the drop point or even out of the furrow after deposition.
The furrow closing tools must adequately compress the soil so that soil moisture can be transferred quickly and continuously to the seed, triggering its germination processes. They must therefore have a wide range of adjustments to make the device effective on both soil that tends to be wet and on soil that tends to be dry and or tenacious.
The furrow opener
Today, the double disc is by far the most widely used furrow opener in precision seed drills because it is rightly considered the most suitable tool for making the seeding furrow, by replacing the non-functional sickle bar. In fact, since the 1990s, a different way of managing the soil has progressively imposed itself, changing the very concept of the “seeding bed”. Even the architecture of the entire seeding body has been modified and made more technologically advanced precisely to adapt to the changed agronomic requirements. The seedbed, characterized by a layer of fine soil where any light tool was able to open the furrow and deposit the seed, has been replaced by a poorly tilled, rough soil, sometimes with crop residues mixed in the first few centimeters and present on the surface, or even by untilled soil. The seed drill with its organs has to deal with clods, crop residues, cover crops or even hard ground.
This change does not only concern companies that have chosen minimum tillage, but also concerns conventional management where, due to the reduction in the number of passes and in the intensity of individual operations, clods and lumps of different sizes are present on the surface that require more robust tools. This is exacerbated in soil management based on minimum tillage, which, by virtue of the cost savings they offer, has spread widely throughout Europe. In companies that have adopted conservation tillage systems, the crop residue covers more than 30% of the area and reaches even greater degrees of coverage when operating in no-till systems. In this case, the furrow opener must interact with untilled soil and crop residues that can be very abundant.
The disc coulter also reacts well to high speed by reducing friction, avoiding furrow depletion (a problem that tends to occur even at low speed with anchor coulters), and adapting to the state of the soil.
The working day
All of the above becomes a concrete and tangible advantage only when the seed drill has technological equipment that simplifies its use and when time wasting and waiting times are avoided by optimizing ancillary services, which have a significant impact on the working day. For example, the machine’s supply network (seed, fertiliser, geodisinfectant, diesel) must be efficient. The prior quantification of the doses distributed makes it possible to predict the points within the farm where the units for refuelling can be conveyed. Obviously, the autonomy of the seed drill, i.e. the amount of work it is able to do before stopping to refuel, has a positive effect on working time. Hence the importance of seed hopper capacity, microgranulator capacity and fertiliser capacity for localised fertilisation.
The adjustment and calibration phases of the seed drill, which generally take place at each seed change, and the fielding phases are also fundamental. On this aspect, electronics today offer considerable opportunities, because in addition to simplifying the initial calibration phase, it allows its effectiveness and suitability to be checked as it progresses and, at least partially, to be modified without interrupting the operation.
The “things to be done” with the fielding are different depending on the model: the most delicate ones concern setting and checking the seeding depth and the load on the seeding unit and on the furrow closer in particular, as well the adjustment of the position of the latter. These adjustments must then be updated during the working day, considering that they are strongly influenced by the soil texture and the degree of humidity, which can vary throughout the working day. Some seeding units are equipped with sensors that can modify the depth according to real-time readings of certain soil parameters related to its water content and texture.
In trailed seed drills, the availability of intelligent drawbars allows for better field closure, avoiding or limiting both waiting times and overlaps. In this respect, satellite guidance devices accompanied by seeding element closure systems allow the progressive interruption of seed delivery. In this case, in addition to saving product and respecting the investment per square metre, it also simplifies trajectories in the field and ultimately working time.
Quick and easy emptying of seed hoppers reduces the time wasted associated with the cleaning up at the end of the day or, more frequent with contractors, even when changing hybrids or varieties. A reduced road encumbrance makes it easier and therefore quicker to move between plots, which can be burdensome as in certain areas of high land fragmentation.
Lorenzo Benvenuti
