Evaluation of seed drill tips

Evaluation of four types of furrowing rod tips shows the furrow profile of each of them and the best solutions for each type of planting.

In the direct seeding system, seeders are equipped with rod-type furrowers and/or discs. However, they can only be equipped with discs since the rod is more suitable for compacted soils, such as in places where there is integration between crops and livestock.

The seeding furrow plays an important role in crop germination and establishment. When opened by rod-type mechanisms, an interesting decompaction of the surface layer of the soil occurs, promoting a displacement of aggregates from the bottom of the furrow to the surface. However, when dry periods occur, the use of a furrowing rod can be negative, as greater soil exposure favors moisture loss. In this case, there is an advantage in using disc-type furrowers, which provide less soil exposure, maintaining straw coverage close to the furrow.

An important element of rod-type furrowers is the tip. Its angle of attack and width directly influence the quality of the groove. Therefore, it is essential to replace this component when wear is observed, as the change in its geometry, caused by friction with soil particles, results in grooves with a smaller area of ​​mobilized soil.

Various models of tips are offered on the market at different prices. However, technical information regarding the characteristics of the groove is scarce. Therefore, a study was carried out with the objective of evaluating the soil area mobilized by four different commercial models of furrowing rod tips, configured in the “guillotine” system, under three soil moisture conditions.

The experiment was carried out in the experimental area of ​​the Federal University of Fronteira Sul, Campus Cerro Largo (RS) between February and April 2015. The soil is classified as typical distroferric Red Oxisol (LVdf) with clayey texture. The area used for the study was managed with direct sowing of annual crops for 10 years prior to the trial.

Tests were carried out with four tip models (Figure 1) under three soil moisture conditions (22%, 26% and 30%). Tips number 1 and 2 are 53 mm wide, tip number 3 is 22 mm, and number 4 is 20 mm wide.

The design used was the DIC, (Entirely Randomized Design) with four replications, with each plot consisting of a furrow opened by the guillotine-type furrowing mechanism, composed of a straw cutting disc and furrowing rod as shown in Figure 2.

The tests were carried out using a tool holder for coupling the furrow opening mechanism and a New Holland model TL75 tractor with 57 kW (78 hp) of power. The tractor's travel speed was 1,39 m/s (5 km/h).

When characterizing the soil, the texture (clay, silt and sand), gravimetric humidity, density and resistance to penetration were assessed. To determine soil texture, five samples were collected at the working depth (0 to 100 mm) distributed across the experimental area. To determine gravimetric soil moisture, five samples were collected in each layer (0 to 50mm; 50 to 100 mm) under the different moisture conditions evaluated. Afterwards, the samples were transported in waterproof packaging to the soil mechanics laboratory at UFFS, where the weighing and oven drying methodology was used for 24 hours.

Soil density was evaluated by collecting five undisturbed samples at each depth (0 to 50; 50 to 100 and 100 to 150 mm), using metal rings with an internal volume of 200 cm³ following the methodology proposed by EMBRAPA (1997). Soil resistance to penetration was determined using a manual penetrometer, up to a depth of 300 mm at eight random points under the three humidity conditions.

The assessment of the area of ​​soil mobilized was carried out using a profilometer with an accuracy of 5 mm. This equipment consists of a metal structure 1,2 m high and 1 m wide, where a row of cylindrical rods is positioned transversely to the sowing furrow. In this way, the soil surface was copied to the equipment and the mobilized area was determined.

For statistical analysis, the Assistat software, version 7.7, was used using the Scott-Knott test at a 5% probability level.

RESULTS AND DISCUSSION

The granulometric evaluation of the soil showed values ​​of 56,3% clay, 33,3% silt and 10,4% sand. According to the Brazilian Soil Classification System, this soil is classified as clayey. The soil was friable between moisture levels of 0,22% (contraction limit) and 0,30% (plasticity limit).

Gravimetric moisture analyzes carried out during the tests indicated an increase in moisture as a function of depth for the drier soil condition, and an opposite effect in the wetter soil condition (Table 1). 

The average soil moisture content, at the furrowers' operating depth (0 – 100 mm), was 22%, 26% and 30% for the three conditions evaluated. It is noteworthy that these three moisture values ​​were within the soil's friability range, which is the condition indicated for determining the soil's resistance to penetration, as well as carrying out mechanical interventions, including direct seeding.

Soil density analyzes indicated an increase in compaction as a function of depth (Table 2), but did not reach values ​​considered critical in the literature. 

Studies indicate that density values ​​greater than 1,34 g/cm³ can harm root development in clayey soils. However, in the evaluations carried out, the average density, at the furrower's operating depth (0 – 100 mm), was 1,24 g/cm³. The lower density in the surface layers of the soil can be attributed to the large amount of roots and cultural remains remaining from the management system.

Soil resistance to penetration showed a significant variation depending on humidity, even within the soil's friability range. Average values ​​of 3,60 MPa were obtained when soil moisture was 22%; 2,09 MPa when soil moisture was 26%, and 1,75 MPa when soil moisture was 30% in the 0 to 300 mm layer.

The growth of plant roots is limited by the soil's resistance to penetration, however, there are divergences in the literature about what resistance would limit crop productivity, as this is a factor that affects plant development indirectly, and has great fluctuation over time, mainly depending on the moisture content present in the soil. According to CLARK et al. (1990, 2003) the roots exert a pressure of around 0,2 to 1,2 MPa during their growth. SILVA et al. (1994) points out a value of 2 MPa as restrictive to root growth. However, these values ​​may not represent harm to the crop, as long as water and nutrients are available.

The evaluations of the area of ​​soil mobilized indicated that tip 1 and 2, with wider wings, present greater soil mobilization in relation to models 3 and 4. Except in the condition of higher humidity, where tip 1 presented higher values ​​than the others, according to Table 3.

In the drier soil condition, the wing tips, models 1 and 2, mobilized a greater amount of soil, without differing from each other. Tips 3 and 4 obtained lower mobilized area results, with model 4 showing the lowest mobilization. In the intermediate humidity condition, nozzles 1 and 2 rejected and mobilized a greater amount of soil than models 3 and 4. In the wetter soil condition, nozzle 1 was the one that showed the greatest mobilization.

When varying the soil humidity, a similar behavior was observed between tips 1, 2 and 3 when increasing the humidity. However, it is noteworthy that model 4 presented a smaller area of ​​soil mobilized in the lower humidity condition. This shows that at lower humidity, within the soil's friability range, it is interesting to use wider tips to provide a greater area of ​​soil mobilized.

CONCLUSION

In the guillotine system, the geometric characteristics of the tips and soil moisture influence the amount of soil mobilized by the furrowing rod.

The tips, with wider wings, present greater soil mobilization in the sowing furrow both in drier and wetter soil situations.

Narrower tips mobilize less soil area, resulting in shallower furrows. Despite being narrower and theoretically exerting greater pressure on the ground, the absence of wings is a factor that limits the depth of the tip, especially in situations of lower humidity.

Marcos Antonio Zambillo Palma, Dailson Guimarães Dugato, Daiana Cristina Johanns, Adrik F. Richter, Rafael A. Kupske and Guilherme Welter de Oliveira, UFFS

Article published in issue 164 of Cultivar Máquinas.