How angle and speed affect losses in mechanized soybean harvesting

Every process of mechanized harvesting of plant species involves greater or lesser loss of product, both depending on the morphological characteristics of the crops and the construction structure of the agricultural machinery. Studies indicate that a significant portion of the grain losses that occur during mechanized harvesting of soybeans could be avoided, increasing the farm's profit.

To avoid excessive losses of soybeans, above one bag per hectare, researchers recommend some basic precautions, which begin with the selection of cultivars adapted to the region and the sowing season, in addition to the appropriate plant population. This is because a plant population above the recommended level, in addition to increasing the cost of purchasing seeds, can result in etiolated plants, which are very sensitive to lodging. A deficit in the plant population will result in smaller plants, with pods very close to the ground. In both cases, the harvester will have difficulty collecting all the material to be threshed, leaving part of the production in the field.

The harvester must be adjusted according to the plant architecture, morphological characteristics, grain water content, harvesting speed and acceptable level of seed damage. Harvesting time is also a relevant aspect, since a delay in harvesting can result in lower quality of the harvested product and a greater quantity of grains lost in the field.

Regarding mechanized soybean harvesting, one fact that is drawing the attention of producers is the angle at which the harvester moves in relation to the crop lines. Traditionally, the machine operator sought to move the harvester along the soybean crop lines (0º angle). However, many soybean cultivation areas are steep and require the construction of terraces to prevent erosion. In these areas, the existence of terraces imposes a new characteristic on the crop areas, which leads the producer to a difficult decision: whether to sow in a level manner following the terraces, which reduces the effective operational capacity of the tractor-planter combination, or to sow in straight and parallel lines, crossing the terraces. Whatever the decision, the way in which the crop treatments and mechanized harvesting of the area are conducted will also be affected.

In this context, researchers evaluated the losses in the mechanized harvesting of soybeans carried out with the harvester moving in the parallel, transverse and perpendicular directions (harvesting angles 0º, 45º and 90º) in relation to the sowing lines, at speeds of 5 km/h, 6 km/h and 7 km/h, in an experiment conducted in a 3x3 factorial scheme, with four replications, set up in a strip design. 

The research was carried out at Fazenda Lira, in the municipality of Querência-MT, in March 2018. The Bônus IPRO cultivar was sown in the area with a row spacing of 0,45 m and, at the end, a population of 261.600 plants/ha was verified, with an average plant height of 0,87 m and an average productivity of 3.420 kg/ha. A combined harvester of the SLC brand, model 6200, manufactured in 1986, with a radial threshing system and a 13-foot platform, with usual adjustments of the property, was used for harvesting.

To determine losses, a rectangular frame with an interior area of ​​2 m2 and a length equal to that of the cutting platform was used, according to the methodology described by Mesquita et al (1998). To determine losses occurring on the platform, the machine was put into operation in the desired direction and speed until the moment when harvesting was abruptly interrupted, turning off its systems. Then, the machine was moved back and the frame was assembled in front of it, in an area delimited by the tracks of the harvester's front tires and the plants that had not yet been harvested. Within the area delimited by the frame, all grains, pods and plants were collected to quantify the mass of lost grains. Total losses were determined by collecting all grains and pods present on the ground, in an area delimited with the same frame, assembled after the harvester had passed. Losses in internal mechanisms were determined by the difference between total losses and losses on the platform. The data were subjected to analysis of variance at 5% probability and their means were compared using the Tukey test.

When analyzing the results, the researchers observed that losses occurring during the soybean harvest presented statistical differences (p<0,05) both as a function of the harvesting angle and the harvester's movement speed, as well as the interaction between the factors, which suggests the need for greater attention to the details of adjustments during the harvest. 

The statistical differences observed for grain losses on the platform as a function of the harvesting angles (Table 1) possibly occurred due to the way in which the plants were distributed in front of the cutting bar and the platform reel, which resulted in a variation in the flow of material cut by the cutting bar and conducted to the threshing system.

When harvesting was carried out parallel to the crop rows (0º angle), it was observed that the plants accumulated in the same position in front of the cutting knives, and that practically all the plants in the crop row were cut in the same position on the platform and by the same knives on the cutting bar. In this same position, there was greater friction between the crossbars of the reel and the plants, causing the pods to be threshed before the material entered the harvester. However, when harvesting was carried out in the transverse direction (45º angle), the cut material entered the platform and was transported by the screw conveyor into the harvester in a more continuous and smooth manner, with all the knives on the cutting bar performing their function, without the formation of “piles” or “bushings” on the screw conveyor, and the material continued to the threshing system in the same way.

With the harvesting carried out perpendicularly (90º angle) to the crop rows, the flow of material into the harvester was more variable. There were alternating intervals of overloading the cutting bar when cutting a crop row and resting when passing through the row between rows. This intermittency in the cutting system also resulted in discontinuity in the flow of material conducted by the screw conveyor to the threshing system.

The greatest losses in the platform found at a speed of 5 km/h can be explained by the relationship between the speed of the harvester and the peripheral speed of the reel, which should be, on average, 20% higher than the machine's travel speed. In the study, the usual settings for the property were maintained, with the peripheral speed of the reel 50% higher than the speed of the harvester's travel at a speed of 5 km/h. When the machine's travel speed was increased, this proportion naturally decreased. Rotating the reel above the limit increases losses in the cutting platform because the crossbars of the reel hit the plants at a higher speed, causing the pods to open.

Table 2 shows a greater loss of grains in the internal mechanisms when the harvest was carried out at a 90º angle at a speed of 7 km/h, a condition in which synergy between the factors possibly occurred. In this combination of factors, the discontinuous flow of material due to the displacement angle, combined with the greater quantity of material processed due to the higher speed, may justify these losses. To reduce them, it is recommended to increase the rotation of the threshing cylinder and/or reduce the opening between the cylinder and the concave. 

Total grain losses in the field during mechanized soybean harvesting showed statistical differences depending on the displacement angle and displacement speed, as well as the interaction between these factors (Table 3). These losses are the result of the sum of losses in the cutting and collection platform and losses in the threshing, cleaning and separation systems, consequently influenced by the same factors. 

The results indicate that only harvesting carried out perpendicularly (90º) to the plant rows at the highest speed (7km/h) resulted in losses greater than the tolerable limit indicated by Embrapa (60kg/ha). Another important point is that the difference between the lowest and highest average grain loss was 53,75kg/ha, which highlights the importance of the producer paying attention to the working speed and harvesting direction during the operation.

The year the harvester was manufactured also caught the researchers' attention. The time the harvesters have been in use and the technology they use can be identified as factors that also affect grain losses. However, this study used a 32-year-old harvester that showed total grain losses within the acceptable limit. This allows us to state that the age of the harvester is not the main factor in generating losses, but rather the way the machine is operated in the field, as well as its adjustments and maintenance. 

Finally, the researchers concluded that it is possible to reduce grain losses and improve the harvesting process with simple adjustments made by the machine operator from the operating station. To this end, they recommend - in addition to general machine maintenance - systematic monitoring of losses in the field followed by immediate adjustments to the machine in order to match the travel speed with the rotation of the reel, as well as the opening and rotation of the threshing system with the humidity and flow of soybeans that will be processed, considering that increasing the travel speed increases the flow of plants collected. 

*By Vandoir Holtz, Jelvonei Darlan Lira e Andre Maller, from Unemat, and Matthew Prolo Massola, from UEG/UnUCET