The rotary harrow: the Joker for soil preparation

Rotary harrows are a type of equipment very widely used for refining the soil but in some settings they can be used to great benefit as the only machine for preparing a seedbed or transplanting. The most recent models feature speed and the option of combined operations

Rotary harrows are modern farm machines frequently put to use in many settings but mainly for refining the soil after a traditional plowing for cultivation which require very fine superficial layers. Moreover, the harrow also performs mechanical control of weeds in orchards and vineyards in operations usually between rows and, in some cases, also on the soil under the rows with models equipped with suitable sensors. For full field harrowing, these machines can be put to good use for preparing the soil and second harvest seeding for the minimum tillage practice of totally replacing the traditional combination of plowing and harrowing.

In horticulture and floriculture, for protected or full field crops, recourse to the harrow has become systematic because operations on soil suitable for settings in which the crops are frequently approached require quick and accurate preparation of the seedbed and for transplanting.

From the technical and construction point of view, there is usually a distinction between the macro category of rotary cultivators models equipped with working parts which are solidly welded to the rotor and those with hinged tools which are mobile. But in both cases the machine can operate on the soil surface down to a maximum depth of 25-30 cm.

 

Correct soil conditions

The models produced by Italian manufacturers are also suitable for work on very clinging soil making it possible to carry out initial operations, without plowing, and leave an excellent mix of previous crop residues in the top layers of the soil. Crop operations can be very energy intensive, depending mainly on the texture of the soil, the level of humidity and compaction and, obviously, to the depth and scale of the work being performed.

In this latter case, the machine can make it possible to intervene for preparing a seedbed which is soft and uniform, also for size and profile.

Work on cohesive soil must be avoided because other than the excessive pulverization, there is a considerable increase in energy consumption and wear on the working tools. Work parameters must be systematically avoided when the soil is in a plastic condition because this causes excessive compression of the tools on clods and the non-worked lower layer.

Because these machines do not require great traction, which is sometimes even negative with equipment to “spring” the tractor, they can be hitched to two-wheel drive tractors as long as they are equipped with a PTO with sufficient power to correctly run the trailed machine. 

Models with different work capacities

The common feature of these machines is that they run rotating tools on horizontal axes off the tractor PTO, but the market offers many types of rotary cultivators starting with those equipped with small self-propelled hoes – also called “tillers” with drive wheels which differentiate these machines from cultivators coupled with harrows – and on up to machines with much greater work widths to couple on the tractor three-point hitch. These latter types begin with those of a width of about one meter and go up to folding models with a work width of up to six meters. The hoes are not equipped with support wheels on the soil but in some cases they can mount a rear roller which simultaneously controls the depth of work and levels and lightly compacts the refined soil.

 

Ways to operate

The work mechanism of the cultivator is linear, based on the principle of tilling, and is performed by a series of shaped tools which rotate at high speed causing the loosening of a “slice” of soil by advancing thanks to the rotary power of a drum fitted with the tools and a robust steel carter wrapped around for refining the soil.

Obviously the housing stops the materials broken up to be thrown to the outside of the machine which means that it is very dangerous to open the carter too wide, perhaps by temporary and unsafe measures, or even remove it. Though the possibility of clogging is reduced, the danger is great especially if the soil is riddled with rocks or stones.

The transmission of power off the PTO to the working tools is generally through a traditional card an drive shaft which is best equipped with an overpower protection clutch with kinematic drive chain. The rotary cultivator is equipped with a series of gears, replaced in smal­ler models by a more simple pulley or chain transmission, for transmitting power to the horizontal rotor.

The refining of the soil is in propor­tion to the speed of the rotor speed and inversely proportional to the speed of advance so a good idea is to use a machine equipped with a simple two or three speed transmission for getting the desired results for refining soil with various consistency by deploying maximum power available from the tractor. Maximizing the forward speed of the tiller is important in that the work capacity of these machines are negatively influenced by their typical values which is rather limited in this area. Some recent models are equipped, in addition to a front hitch, a rear three-point hitch and another transmission for coupling a seed drill for carrying out both operations with a single passage.  

BOX: Subsurface harrows

The machines for operations between the rows of vineyards are considered advanced, the difficulties involved in mechanical subsurface weeding are undoubtedly greater, especially if trunks are close together and low and more so when the operation is on a terraced steep slope and with soil subject to surface erosion.

The ingenuity of Italian manufacturers has, however, have designed and fine turned rotary inter-row harrows capable of effectively safeguarding the plants with, of course, the skills of the operation during performance. The most simple and economical cultivators which provide for the manual insertion of working parts between one plant and another from the tractor seat or, as an alternative there is a second operator, but recently the preference has been for models equipped with automatic feelers.

In any case, operations on single rows require double passages at low speed, usually at 1.5 to 2.5 km/h, due to limited work capability (5-6 h/ha), but this can be substantially increased by the use of “double” equipment operating on both sides during each passage.

From the construction point of view, all the working parts are similar and full field models, or those built for inter-row operations, are relatively miniaturized (for a maximum soil surface depth of 15 cm).

They are mounted on special frames equipped with scanners and operated hydraulically. For the obvious reason of providing a view of the work, the best machines are mounted on the front of the tractor.  

BOX: A single passage for making the seedbed

Compared to traditional operations for preparing a seedbed or for transplanting with typical passages repeated on the same plot, the use of a single harrow carries a number of advantages such as reducing work time and the resulting costs, facilitating operations on slopes, a good soil mix within the area worked, the degree to which the soil is refined with crop residues for transforming them more quickly into organic substances and efficient control of annual weeds.

Moreover, harrowing can work to ensure, without decay, the quality of deep humid soil kept dry on the superficial layer.

Especially for deep work, down to 25-30 cm, a single harrowing requires greater power, involves the risk of downgrading the soil structure if the degree of refining is excessive, entails high maintenance costs due to the frequent need to replace the working parts, inevitably creates a work hardpan which impedes excellent drainage and spreads perennial rhizomatous infestations of red weed and Johnson grass because the rhizomes are spread by the working parts for favoring multiplication.