Maize seeding, a technological challenge

Planting is a key step for obtaining an optimum yield when cultivating maize. The mechanization industry creates increasingly advanced system for carrying out this operation in a scientific and economic way and with a planting layout in keeping with the need of the plants to be exposed to sunlight

Planting is a key step for obtaining an optimum yield when cultivating maize. The mechanization industry creates increasingly advanced system for carrying out this operation in a scientific and economic way and with a planting layout in keeping with the need of the plants to be exposed to sunlight

 

Maize has been an important human food resource since ancient times, then with the arrival of silage techniques, became one of the basic ingredients in the diet for livestock feed while in more recent times maize has been raised to a privileged energy crop status. 

Moreover, from a genetic point of view, significant benefits have been achieved under the agronomic profile, especially as regards the tenor of starch, type of fiber, the bearing of the plants and the like. All the while, the density of plantings, that is investments in the crop, have been growing steadily over time. Unlike most of the other common full field crops, maize, because of its tropical origins, photosynthesizes with C4 carbon fixation which means that carbon dioxide in the cells of the mesophyll is added to the three-carbon molecule creating a four-carbon organic acid. In these case, photosynthesis and the production of sugars can continue even at temperatures higher than those typical  of C3 (Calvin cycle) plants. What is fundamental, however, is that the quantity of solar radiation taken in is optimum, that the shade of adjacent plants be reduced to a minimum.

 

The first step

To ensure the best possible planting, maize seeds must be distributed uniformly in the furrow with a so-called precision seed drill with distributor heads and coulters capable of burying each seed at the point wanted with mechanical devices, now not common, or operated by pneumatics. Put to use in this latter case, is air pressure generated by a central fan, normally of a centrifugal type, powered by the tractor PTO. The Venturi air flow conveys the seeds to perforated disc coulters driven by one of the seeder wheels for the distribution of the seeds according to the forward speed. During the rotation of the disc, the combined effect of the coulter pressure, at 30-60 kg, and the mechanical separator/selector device, allows holding a single seed in each perforation and carry it until the upcoming furrow depression is reached. At this point, with the help of a small brush, the seed drops into the diffusor tube which plants it in a defined location.

The basic principle is the same for all models but there are many offers of variations on the theme aimed at improving the precision of seeding even at high speed. Following is a short panorama of classic pneumatic seed drills.

 

Two in one

The standard distance between rows is 70-75 cm and this is difficult to reduce, especially because of the typical work width of pneumatic drills mounted on tractors for the cultivation of maize and also the combined harvester header for harvesting grain standardized over time. Also to increase the density of planting beyond present values, the distance between rows cannot be reduced due to excessive root competition. A solution is a twin row technology, that is two rows 20-22 cm apart to form a binary. The distance between one pair of tows and the adjacent pair is 53-55 cm, the additional value to reach the 75 cm inter-row distance allowing harvesting with traditional machinery. In practice, on a strip of land of the same width where two rows had been planted, seeds are deposited in a quincunx geometric patter of five points arranged in a cross, with four of them forming a square or rectangle with a fifth at its center that is, staggering a pair, allowing the best reception of sunlight for the plants. This is not a new technique as it was proposed in the United States some decades ago. However, significant results were not achieved with the hybrids available in those times but today, on the other hand, fixed-ear varieties are available which develop fully aside from the density of seeding. Also of importance is the selection of a cultivar which does not reach excessive height and with leaf blades which grow vertically. In substance, twin rows which are staggered make it possible to increase the density of the layout while minimizing root competition and making it fully possible to deploy normal machinery. The only machine obviously required for operations is the seed drill. Though it appears simple to arrange for twin row planting by coupling two standard components it must be recalled that these must be synchronized for achieving the quincunx planting pattern. This operation is possible but only by greatly extending the length of the machine which gives it more bounce and thus increases the load on the lifter.

A specific solution is marketed by MaterMacc with their twin row vacuum precision planter. At the heart of the machine is the tried and tested Magisem vacuum metering unit with special technical components, most of which are patented, providing various advantages for the seeding system. A thin seal plate fitted close to the distributor disc stops the seeds from lodging in the disc to ensure no seed breakage by the distributor causing damage for germination and leading inevitably to failure. With the Magicsem, the seeds remain on the surface, floating on the disc, and when they drop there is no change in their trajectory with their regular uniform drop into the diffusor tube. Moreover, by dividing the seal plate to half the clearance of the disc hole different seed varieties can be distributed with the same disc on the same day with no need to chance the disc but only with the regulation of the selector to avoid double seeding. Another original construction feature developed by MaterMacc is the reduction of friction between the seal and the seeder disc by the introduction of a disc plate which rotates on bearings. This solution eliminates typical attrition to also reduce the power required for running the distributor. The disc does not rotate irregularly, in jerks, as is normally the case, but rotates smoothly to provide the advantage of a better distribution even at high speed. Thanks to the minimum power required for operating, as many as eight units can be activated with the power of a single wheel of the planter. The vacuum chamber is ample and located directly behind the distributor disc to ensure great uniformity of the depressions produced and allow speeds of more than 10 km/h with excellent precision in planting. 

The MS Twin is available in models for planting from 2 to 12 twin rows with row spacing from 70 to 75 cm and work width from 1.5 to 9.45 meters. The machines mount two seed hoppers independent for each twin unit, each with a 35 liter capacity. As standard equipment, the MS Twin planting units are provided with double disc coulters or, on request, openers. To guarantee perfect depth of planting each single units makes use of the torque of the wheels.

Room for electricity

Deviating power to one of the wheels of the precision planter to activate the disc allows it to effectively distribute in proportion to real forward speed. The transmission however requires a large number of gears and relays which need maintenance and for varying sowing spacing it is necessary to physically replace gears or use mechanical transmissions. Moreover, temporarily excluding sowing a single row is fairly complicated unless the depressions of a single unit are interrupted. An alternative solution has come along recently with which a single seeding unit is activated individually by a low-power electric motor linked by a belt, or seamlessly, to the distribution disc. A CPU receives a single of the speed of the machine via a high precision GPS device installed on the tractor powered by motors which vary the speed of rotation according to the forward speed. Though the system is technically more complicated due to the electrical connections, a sower of this type has many advantages. Above all, the spacing of the seeding along the row is continuously regulated during work and the absence of mechanical connections among the various distributors makes it possible to easily fine tune folding or telescopic closing seed drills.

One of the leading manufacturers which believes in this solution is Kverneland with the Optima e-drive pneumatic precision drill on the market. These machines are available with different configurations, from 6 to 12 rows, with folding, telescopic or fixed frames and with coulter discs or openers on which the HD sowing unit can be mounted, ideal for sod seeding thanks to its standard weight of 129 kg which can be increased to 229 kg. The e-drive version provides complete control and monitoring of the machine from the tractor cab in accordance with the ISOBUS standard with data entered and read out via the IsoMatch Tellus terminal. With e-drive each sowing unit is driven individually via an electric motor. Another interesting feature is the tramline switching function for switching off units individually allowing the exclusion of one or more for creating traffic patterns with pre-set spacing to facilitate passage of the tractor and sprayer. The e-drive can be coupled with Geo-Control/Geo-Seed allowing, with GPS RTK, sowing parallel rows or staggered for the quincunx pattern.

 

Universal seed drills

To date two types of seed drills were required for the cultivation of cereals, a precision planter for maize and a so-called universal or strip seed drill for autumn-winter cereals, also available in mechanical or pneumatic versions. Pöttinger in Austria has now combined the two types in one mounted pneumatic seed drill, the Aerosem available in two work widths of 3 and 4 meters. The seed drill combined with a rotary harrow can sow wheat, rye, oats and the like as well as maize and sunflower seed thanks to PCS, Precision Combi Seeding, with integrated mechanical seed separation and deflectors for ensuring the precise and steady flow of seeds to the coulter. The double disc coulter then creates a well-defined furrow for the seed to drop a short distance to the bottom with no bounce. The dosage is regulated in relation to the forward speed in a traditional mechanical way with a spurred wheel or electrically with pilot motors run by the CPU. The distance between rows for planting small-seed cereals is from 12.5 to 15 cm and for maize, sown one row every five or six, to achieve the classic inter-row space of 75 cm.