Performance of a planter-fertiliser under reduced soil preparation: furrowers, speeds and depths when sowing maize 1

- The search to optimise agricultural systems by adapting mechanised sets for sowing maize, is essential for improving operational performance, energy efficiency and initial crop establishment. The aim of this study was to evaluate the performance and sowing quality of a planter-fertiliser for maize, in a dystroferric Red Latosol managed under reduced tillage, as a function of the type of furrower, depth of seed deposition and operating speed of the planter. The experimental design was completely randomised, in a split-plot scheme with three replications, where the plots represented the type of furrowing mechanism (shank or double-disk) and the subplots represented three displacement speeds (3.20, 5.15 and 7.32 km h -1 ) and two sowing depths (35 and 40 mm). The best sowing quality for second-crop maize, the lowest power requirement at the tractor drawbar, the lowest specific and hourly fuel and consumption time, and the lowest travel reduction ratio are achieved when the tractor-planter-fertiliser set is configured to use a double-disk at a sowing depth of 35 mm. The adoption of higher displacement speeds results in increased operational and effective field capacity, as well as a lower energy demand when the tractor-planter-fertiliser set develops speeds close to or greater than 7.32 km h -1 , irrespective of furrower type or soil depth


INTRODUCTION
Optimised planning for cultivating second-crop maize starts with the fi rst crop, choosing early-cycle soybean cultivars for clearing the area, followed by rapid planting of the maize crop (CORTEZ; ANGHINONI; ARCOVERDE, 2020).To do this, conservationist soil-management systems are adopted, such as no-till, reduced tillage or minimal cultivation, which consists in the minimum of soil turning and maintaining plant residue, with light scarifi cation and harrowing.This allows the maize to be rapidly planted in succession to the soya, with an increase in production potential and less risk of loss from frost and/or drought, especially due to a reduction in soil water availability and air temperature during the winter (CORTEZ; ANGHINONI; ARCOVERDE, 2020;VIAN et al., 2016).
In addition, correctly regulating the components of the planter-fertiliser is of fundamental importance to maximise operational performance, improve the quality and initial establishment of the crop, and reduce production costs (FRANCETTO et al., 2015).
Sowing quality is related to such operational factors as the furrowing mechanism of the planter-fertiliser, displacement speed, and sowing depth (SOUZA et al., 2019).When sowing maize, these settings are even more important due to productivity being strongly dependent on seed distribution by the planter (VIAN et al., 2016).
The type of furrowing mechanism together with furrowing depth can affect the speed of emergence index and the population of maize plants per hectare (SOUZA et al., 2019).Due to its role in turning the soil, the type of furrower influences the tractive force (TRICAI et al., 2016), with shanks possibly requiring greater tractive effort than discs (FRANCETTO et al., 2015;MILAGRES et al., 2016).
An increase in sowing speed can lead to a reduction in the quality of the longitudinal distribution of the maize seeds (CARPES et al., 2018;SOUZA et al., 2019) and seedlings (ALONÇO et al., 2015;CORTEZ;ANGHINONI;ARCOVERDE, 2020).This is due to the greater demand of the dispensing mechanisms, which can lead to fi lling errors, a fault or lack of seeds in the well of the mechanism, with less regular distribution and more gaps (CARPES et al., 2018;CORTEZ;ANGHINONI;ARCOVERDE, 2020).
The energy demand can also increase when increasing the speed of the sowing operation (SILVEIRA et al., 2013).The association between furrower type and planter speed is related to furrow depth and area of turned soil (MODOLO et al., 2012), factors that establish a relationship with energy demand (TRICAI et al., 2016).Therefore, factors such as the suitability and condition of the tractor-equipment set, depth of operation, type and condition of the soil, type and number of operations for preparing the soil, and the soil water content (FURLANI et al., 2013), show a relationship with fuel consumption in agricultural tractors, which represents one of the highest costs in agricultural operations.
Therefore, the aim of this study was to evaluate the performance and sowing quality of a planter-fertiliser for maize, in a dystroferric Red Latosol under reduced tillage, as a function of the type of furrower, depth of seed deposition and sowing speed.

MATERIAL AND METHODS
The experimental area is in Dourados, Mato Grosso do Sul, Brazil (22º14'S, 54º59'W, at an altitude of 434 m).The climate in the region is of type Am, tropical monsoon (ALVARES et al., 2013).The B2620 PWU hybrid maize cultivar was grown in a dystroferric Red Latosol, with a mean slope of 2%, comprising 60% clay, 15% silt and 25% sand in the 0 to 0.20 m layer.The area had been managed for ten years under a no-till system of soya and maize, and was now under spontaneous vegetation with a large infestation of annual weeds, especially Guinea grass (Panicum maximum Jacq.) and sourgrass (Digitaria insularis).
To incorporate the spontaneous vegetation, mechanical soil management was carried out fi ve days before starting the experiment (17/02/2017), using reduced soil preparation by means of heavy harrowing followed by levelling, using a harrow plough with ten discs, each 30" in diameter, a weight of 1,688 kg and working width of 1,530 mm, and a levelling harrow with 28 discs, 22" in diameter, with a weight of 786 kg and working width of 2,350 mm.The 0-0.20 m layer of prepared soil showed a density of 1.38 Mg m -3 , penetration resistance of 1.87 MPa, and water content of 0.24 g g -1 .
To carry out the fi eld trials, a New Holland model TL85E, 4x2 AFT tractor, with autopilot, a telemetry data collection system (Field Logger), 4.2 Mg total loaded weight including operator, 3,908 cm³ cylinder capacity, 64.8 kW rated engine power at 2,400 rpm, 56.7 kW maximum PTO power, drawbar height of 0.47 m, wheelbase of 2.35 m, 18.4-34 rear tires and 14.9-24 front tires.Coupled to the tractor was a PPSOLO speed box 4500 fi ve-row planter-fertiliser with a working width of 4,480 mm and approximate weight of 4.1 Mg equipped with a smooth disc-type straw-cutting mechanism, horizontal perforateddisc seed-distribution mechanism, channelled-rotor fertiliserdistribution mechanism, and adjustable compactor wheels.
The machine was adjusted for a distribution of 55,000 maize seeds per hectare, at a spacing of 90 cm between Performance of a planter-fertiliser under reduced soil preparation: furrowers, speeds and depths when sowing maize rows.The tractor engine was initially regulated to maintain a rotation of 2,000 rpm during the tests.
The experimental design was completely randomised in a split-plot scheme, where the plots comprised the type of furrowing mechanism (shank or double-disk) and the subplots comprised the three mean displacement speeds (3.20, 5.15 and 7.32 km h -1 ) and two mean sowing depths (35 and 40 mm), with three replications.Each experimental unit occupied an area of 90 m 2 .
After sowing, the depth of seed deposition in the planting row was measured along one linear metre with 4 replications, using a rule with a resolution of 1 mm, as described by Souza et al. (2019).
The percentage and speed of emergence index of the seedlings were evaluated in a 20-m length of planting row, with four replications (SOUZA et al., 2019).The emerged seedlings were counted daily over 17 days.The percentage of seedling emergence was determined by the total number of emerged seedlings at the last count divided by the number of seeds distributed during sowing (SOUZA et al., 2019).
The longitudinal distribution uniformity of the seeds was determined using the methodology described by Arcoverde et al. (2017) and Cortez, Anghinoni and Arcoverde (2020), considering the following spacing percentages: 'double' (DBL): ≤ 0.5 times the Xref; 'normal or acceptable' (NOR) (A): 0.5 < Xref ≤ 1.5; and 'gap' (GAP): > 1.5 times the Xref, where Xref is the value of the reference spacing calculated based on the setting of the planter-fertiliser for each operation.As the Xref was 0.20 m, values of less than 0.10 m were considered 'double', values greater 0.10 m and less than or equal to 0.30 m were considered 'normal" and, fi nally, spacing values greater than 0.30 m were considered 'gaps'.
The force and power required at the drawbar, and the fuel consumption of the tractor with the planter confi gured for transport were determined as a function of the displacement speed of the set.
The effective fi eld capacity was determined from the quotient of the sown area of each experimental unit and the time actually spent on each test (SOUZA; FERNANDES, 2020).Operational fi eld capacity was calculated using Equation 1, obtained as per the methodology of the American Society of Agricultural and Biological Engineers (2006).
The tractive force was determined using a Z-shaped load cell with a maximum capacity of 49.1 kN.The power required by the planter-fertiliser at the tractor drawbar was determined from the product of force and speed.The equivalent power of the tractor engine was determined using an effi ciency of 72% between the boom and the PTO (AMERICAN SOCIETY OF AGRICULTURAL AND BIOLOGICAL ENGINEERS, 2006), and a nominal engine effi ciency for a PTO of 87.5%.The energy consumed per hectare of sown maize was determined using Equation 2.
( 2 ) where, E ha -energy consumed per hectare of sown maize, kWh ha -1 ; W -power demanded by the set, kW.
Fuel consumption was determined using two model M-IIILSF41L0-M2 fl ow meters (injection pump and return), with a pulse-type output signal and resolution of 1 mL per pulse.The hourly consumption was calculated from the fuel consumption data and the time of each test (Equation 3).Specifi c fuel consumption was determined using Equation 4. Fuel density was 781.5 ± 2.5 g L -1 .
The travel reduction ratio resulting from drive-wheel slippage was determined based on the relationship between the number of turns of the tyres, as per Equation 5. A wheel with 32 teeth and an infrared sensor were installed at the tip of the rear axle of the tractor to measure the number of turns of the drive wheels.
( 5 ) where, n 0 -number of turns of the tractor drive wheels confi gured for the tractive regime of the planter-fertiliser; n 1 -number of turns of the tractor driving wheels operating to transport the planter-fertiliser; s -travel reduction ratio, %.
The data were submitted to analysis of variance with the mean values compared by Tukey's test at 5% probability.Regression analysis was carried out considering the significance of the coefficients, the coefficient of determination and a study of the phenomenon, at 5% probability.The SAEG 9.1 software was used for the analysis.

RESULTS AND DISCUSSION
Using the double-disk, the seedling speed of emergence index (SEI), emergence in the fi eld, acceptable spacing and number of gaps were greater, however using the shank resulted in fewer gaps (Table 1).Normal spacing occurs at a depth of 35 mm.When the soil is submitted to reduced tillage, the sowing speed does not affect the SEI, emergence in the fi eld or seed distribution.Souza et al. (2019) found that only from 7.2 km h -1 was there any effect on seed deposition, germination, SEI or seedling population.These authors found no effect from the furrower or depth.Bottega et al. (2014), also found a reduction in the acceptable spacing from 7.0 km h -1 .
It should be noted that the values for acceptable spacing (Table 1) were not considered satisfactory, as they were less than 60%, which is the minimum required for a quality mechanical planter (MIALHE, 1996).This contributed to the increase in faulty spacing, which may have been due to mechanical damage to the seeds from the action of the horizontal dispensing mechanism (BOTTEGA et al., 2018).Furthermore, as there was no effect from the sowing speed, the existence of any gaps when fi lling the holes with seeds may not have been noticeable due to a reduction in the time available at higher speeds (CORTEZ; ANGHINONI; ARCOVERDE, 2020).
The speed of emergence index, emergence in the fi eld and normal spacing demonstrate the better action of the double-disc furrower at smaller depths (Table 1), agreeing with Modolo et al. (2013) andTrogello et al. (2012).For Souza et al. (2019), in no-tillage maize, the furrowing mechanisms exert different behaviour over germination depending on the cutting depth of the soil and seed deposition.
There was an increase in effective and operational capacity, as well as in power, with the increase in speed, while force was not affected (Table 2).These results corroborate those of Cortez et al. (2018). However, Milagres et al. (2015) found that each increment of 1.0 km h -1 increased the planting row by 1.19 kN.Queiroz et al. (2017) point out that because power is a product of strength and speed, it is expected that the higher the speed, the greater the tractive power, to maintain constant strength.
The force required at the tractor drawbar was infl uenced by the interaction of depth of seed deposition and furrower type of the planter-fertiliser (Table 2), agreeing with the results obtained by Francetto et al. (2015), Milagres et al. (2015) and Tricai et al. (2016).
Table 1 -Summary of the analysis of variance and mean values for the speed of emergence index (SEI, seedlings day -1 ), emergence in the fi eld (SE, %), acceptable spacing (NOR, %), double spacing (DBL, %), gaps (GAP, %), effective fi eld capacity (FCe, ha h -1 ) and operational fi eld capacity (FCo, ha h -1 ) for furrower type (Fu), sowing speed (V) and sowing depth (P) The force at the drawbar seen while transporting the planter-fertiliser was 5.2 kN, equal to the effort required to overcome soil resistance to the rolling of the machine support wheels.
The effective fi eld capacity increased with the increase in the speed of the tractor-planter-fertiliser set (Figure 1).These results were expected, as fi eld capacity is a direct function of speed (FURLANI et al., 2008).
The values for operational fi eld capacity showed quadratic behaviour with an increase in speed (Figure 1).This result can be explained by the fact that an increase in speed reduces machine time while maintaining the manoeuvring and interruption times.Field production (AMERICAN SOCIETY OF AGRICULTURAL AND BIOLOGICAL ENGINEERS, 2006) varies with the speed of operation, differing from the results obtained by Amorim et al. (2019), who adopted a constant yield value of 75%.Santos et al.
(2021) adopted a constant value of 75% for yield, working with a speed of 4.5 km h -1 when sowing; while for the same speed in this study, a yield of 48.4% was achieved.
The power required at the engine and tractor drawbar to transport and pull the machine increased linearly with the increase in speed (Figure 2).An increase in speed entails greater energy demand to traverse the experimental unit in less time, thereby explaining the behaviour of the power values.Transportation power represents up to 69% of the power required at the drawbar during sowing tests, for this reason the less displacement lost in the fi eld, the better the planting system can be optimised, with a reduction in displacement costs.
Higher specific fuel consumption and a higher travel reduction ratio were seen when the shank furrower was used.The travel reduction ratio was lower at the lowest speed and at a depth of 35 mm.At higher speeds, less energy was consumed per hectare, despite showing the highest hourly fuel consumption and travel reduction ratio (Table 2).The values for the travel reduction ratio were similar to those found by Furlani et al. (2008) while sowing maize in a clayey Oxisol under conventional tillage.
Table 2 -Summary of analysis of variance and mean values for tractive force (Fb, kN), tractor engine power (Pm, kW), energy demand (EPH, kWh ha -1 ), hourly fuel consumption (Ch, L h -1 ), specifi c fuel consumption (Cs, g kWh -1 ) and travel reduction ratio (s, %) for the variables furrower type (Fu), sowing speed (V) and sowing depth (P) *Signifi cant at 5% probability by F-test.Mean values followed by the same letter do not differ by Tukey's test at 5% probability.SV -source of variation.DF -degrees of freedom For both furrowing mechanisms, an increase in hourly fuel consumption was seen with the increase in speed (Figure 3), the highest values being found when using the shank furrower.These results are related to the increase in travel reduction ratio with the increase in speed (Figure 4), responsible for raising the equivalent power of the engine, and refl ecting in increased fuel consumption.The hourly fuel consumption seen for transportation ranged from 3.7 to 11.2 L h -1 , which demonstrates that lower displacement speeds should be chosen, provided that the search for optimal yield allows for higher speeds to be adopted.
There was a linear increase in hourly fuel consumption with the increase in the travel reduction ratio (Figure 5).According to Furlani et al. (2008), the increase in hourly consumption is attributed to greater tractive force and power, in this study, to the equivalent power of the engine.
The force required at the drawbar, the power demand on the engine and the energy required to sow one hectare of maize showed higher values when the greatest depth was chosen, regardless of the furrower (Table 3).On the other hand, when the shank furrower was used at the shallowest depth, it showed similar results in terms of strength and power to those obtained using the double disc.At the greatest depth, only energy demand was affected by the type of furrower, with the double disk showing the highest value; the opposite was seen at the greatest sowing depth (Table 3).Francetto et al. (2015), Levien et al. (2011) andMilagres et al. (2015), evaluating different furrowers, found that shanks result in a greater demand for tractive force, and that when working at greater depths, there was an increase in the demand for force and power at the bar (GROTTA et al., 2009).
*Signifi cant at 1% by t-test Performance of a planter-fertiliser under reduced soil preparation: furrowers, speeds and depths when sowing maize Specifi c fuel consumption was reduced as the square root of the force increased (Figure 6).This shows that an increase in force affords better use of fuel within the adopted confi gurations for tractor engine acceleration during the seeding operation and its effective demand in the fi eld.
According to Levien et al. (2011), use of the shank furrower generally results in more soil being turned along the planting row than when using double discs, with less demand for tractive force and fuel consumption, as well as less slippage, thereby affording an increase in operational capacity.

CONCLUSIONS
1. Use of the double-disk instead of the shank furrower, regulated to deposit seeds at a depth of 35 mm, in addition to benefi tting the initial establishment of second-crop maize, allows the mechanised sowing system to be optimised in relation to an increase in operational performance and reduction in energy demand, when carried out in a dystroferric Red Latosol managed under reduced tillage; 2. When sowing maize, the adoption of higher displacement speeds results in an increase in operational and effective fi eld capacity, as well as a lower energy demand when the tractor-planter-fertiliser set develops a speed close to or greater than 7 km h -1 , irrespective of the type of furrower.

Figure 1 -
Figure 1 -Effective (FC E ) and operational (FC O ) fi eld capacity of the planter-fertiliser as a function of operating speed

Figure 5 -
Figure 5 -Hourly fuel consumption of the tractor engine for pulling the planter-fertiliser as a function of the travel reduction ratio

Figure 6 -
Figure 6 -Specifi c fuel consumption of the tractor engine to pull the planter-fertiliser as a function of the force required at the drawbar

Table 3 -
Mean values for drawbar force, engine power, energy required per hectare and specifi c fuel consumption for furrower type and sowing depth Mean values followed by the same lowercase letters in a column and uppercase letters on a line do not differ by Tukey's test at 5% probability ** Signifi cant at 1% and 5% by t-test