As is well known, the application of the direct planting system for growing different crops has led to a need to design machinery compatible with this type of tillage. As a result, there are machines on the market for direct planting of wheat, soybeans, linseed, rice, and the like. In the particular case of rice, its cultivation holds a dominant position in the regional economies of vast areas of Argentina's coastal and northeastern regions, including Entre Rios, Corrientes, Chaco, Formosa and Santa Fe. This cultivation activity requires a technology developed in accordance with its different stages of production, of which one of the most important is planting.
Planting determines the number of plants and their distribution in the ground, in relation to their proper subsequent development. These factors in turn will dictate the final crop yield, which will determine the economic results of the operation.
After a thorough analysis of the supply of domestic and imported direct planting machines currently on the market, the conclusion may be reached that the technology in use is based on the incorporation of machinery designed for another type of crop such as wheat, linseed, and the like, and adapted for cultivation of rice with varying degrees of success. This adaptation is the result of mechanical ingenuity aimed at solving the specific problems brought about by the special characteristics of rice cultivation.
The observations, analyses and conclusions obtained on this subject have been made by official agencies of the Argentine republic such as INTA, intermediate institutions such as AAPRESID, planters' associations, cooperatives, mass communication media, specialized magazines, and the like.
These conclusions outline the problems existing today and may be summarized as follows:
The planting machines currently used in cultivation systems with conventional tilling were designed to operate in similar soil preparation conditions for the various crops. Therefore, the issues of functionality were worked out almost entirely under similar premises.
As a result of the incorporation of the direct planting system, which has the special feature (as is well known) of requiring no tilling prior to planting, problems arose which were intrinsic to this process and were not resolved satisfactorily by the machines used up to that time.
This situation caused concern in various sectors connected with that activity, and the industry responded by manufacturing specific machinery for direct planting.
After observing the machinery in action, it was concluded that one of the most significant problems was occurring in the system of loads on the furrow-opening disks and the wheels that compact the planting furrow.
The load systems currently in use are based on single, multiple or intercombined springs actuated by levers, which gauge the load selected for the various ground conditions.
These systems have the disadvantage of not having a constant load during variations of the stroke of the arms that hold the disks or compacting wheels and, in accordance with irregularities in ground relief, they often partially or even completely lose the loads or become fully compressed, bringing said loads to values that are intolerable for the function they are supposed to perform.
Let us assume that the machine encounters raised or undulated terrain. When the furrow-opening wheel is at the highest point, the compacting wheel may be in the air because the associated spring is not long enough to enable it to rest on the ground again. When the compacting wheel is passing over the highest part of the mound, the furrow-opening disk may be in the air, out of contact with the ground.
It has also been shown that the effects of unloading and overloading the furrow-opening disks sometimes prevent these components from performing their function, which should be exact as regards their capacity for making the planting furrow at a preestablished constant depth. This is because of the loss of contact or small loads on the ground when passing over low-relief terrain, or because of exaggerated furrow depths in the case of high-relief terrain. In the latter case, overloads can also cause wear and tear or failure of some components of the mechanism.
The above observations show that the load control systems used by the majority and known up to the present time do not ensure proper depth of the planting furrow, resulting in a significant decrease in agricultural performance.