Comparative performance of six planter attachments in two residue management corn production systems

Field performance of six combinations of planter attachments on a conventional row-crop planter in two residue management corn production systems was evaluated. The management systems consisted of baled-out residue plots worked by a single pass of disc harrow (RMS1) or untouched residue plots worked by a single pass of chisel plow followed by a disc harrow (RMS2); both systems were planted by a row crop planter with one out of six attachments. Results revealed that both systems fell within residue cover limits defined for conservation farming. The winged chisel furrow opener preceded by a row cleaner equipped with treader wheels (WCRT) arrangement removed appreciable amounts of residues on the row for both systems, but more residues were removed for RMS2 plots. The WCRT pushed almost double amount of residue aside. In spite of higher initial residue in RMS2, chisel plowing and subsequent disc harrowing reduced more residues paving the way for planting in a more seeding depth. Higher percentage of emergence rate index was noticed for RMS2 plots. For both systems, the WCRT and chisel furrow opener preceded by a row cleaner (CR) showed the maximum and minimum quality of feed index, respectively. However this index was higher for RMS2 plots. The WCRT and CR arrangements had the minimum and the maximum multiple index values, respectively. However this index decreased significantly in RMS2 plots compared to RMS1 plots. The RMS2 treatments showed lower values of precision index, which is favorable. The results suggest that adoption of WCRT to planters in soil prepared under RMS2 is useful for a satisfactory conservation crop production system.

Palabras clave adicionales: abridor de surcos; agricultura de conservación; ruedas de acondicionadoras; sembradora en surcos; separador de residuos. Comparative performance of planter attachments that row-crop planter equipped with row cleaner followed by rolling coulter increased quality of feed index (QFI); the improvement amounted to 37.7%. Recently a farm machinery manufacturer introduced a row cleaner equipped with aluminum treader wheels claiming that the new combination prevents the row cleaner wheels trenching within soft soil and hence improving cleaner performance residue (Martin Company Inc., 2009-2010. Treader wheels provide traction to help keep the row cleaner turning in heavy residue (Martin Company Inc., 2009-2010. According to Needham (2009) adding aluminum treader wheels to row cleaner allows the unit to be carried across softer areas of the soil surface and contours of the ground without gouging.
No previous study has been undertaken to evaluate combinations of row cleaner and furrow opener with treader wheels. Therefore the main objective of this study was to evaluate field performance of six planter attachment arrangements in two residue management systems (RMSs) at two forward speeds considering the amount of residue after planting, seeding depth, emergence rate index (ERI), quality of feed, multiple, miss and precision indices.

Description of the row-crop planter & planter attachments used in this study
A single unit row crop planter simulating a typical four row crop planter was equipped with appropriate conservation farming tools to accomplish the treatment envisaged in this study. The seed metering system was adjusted for a theoretical seed spacing of 10 cm. Before field operation row-crop planter was calibrated in the laboratory.

Introduction
One of the important concerns encountering in conservation agricultural systems is non-uniformity in seed spacings and amount of residues retained when using conventional crop production systems in fields with previous residue. Siemens & Wilkins (2006) reported that both stand establishment and seedling dry weight in residue baled-out levels are significantly higher than those for untouched residue fields. A number of studies have found that conservation tillage compared to conventional tillage could increase soil water and minimize soil erosion, and soil temperature fluctuations (Triplett & Doren, 1977;Wall & Stobbe, 1984;Dick et al., 1991;Wagger & Denton, 1992).
Crop residues like wheat straw and corn stalk are considered as renewable biomass. Crop residues in a bio-refinery save greenhouse gas emission (GHG) and residue fossil energy demand (Cherubini & Ulgiati, 2009). Raoufat & Matbooei (2007) developed a star wheel row cleaner for residue management and cleaning crop residue on seed rows. They reported that the row cleaner removed 70% of wheat straw residue on the row band which resulted in a significant improvement in soil-seed contact. Straw residue with adequate amount of organic material has important function in terms of improvement in soil structure and stability (Morris et al., 2010). According to Erbach (1981) and Raoufat & Mahmoodieh (2005), to overcome the seed placement problems and improving seed indices in agricultural conservation systems row-crop planters should be equipped with rolling cultures. Sanavi & Raoufat (2006) found desirable values of emergence rate and seed spacing by equipping a conventional row-crop planter with a winged chisel furrow opener preceded by a row cleaner attachment arrangement. Fallahi & Raoufat (2008) evaluated field performance of a conventional row-crop planter with three types of planter attachment (plain rolling coulter, row cleaner and a row cleaner followed by plain rolling coulter) in three tillage systems (single pass of disc harrow, three passes of disc harrow and single pass of disc harrow followed by chisel plowing). They reported Abbreviations used: CR (chisel furrow opener preceded by row cleaner attachment); CRT (chisel furrow opener preceded by row cleaner equipped treader wheels attachment); DPA (number of days after planting); DR (double disc furrow opener preceded by a row cleaner attachment); DRT (double disc furrow opener preceded by row cleaner equipped treader wheels attachment); EMG (percentage of seeds planted emerged on the day); ERI (Emergence rate index); QFI (quality of feed index); RMS (residue management system); WCR (winged chisel furrow opener preceded by a row cleaner attachment); WCRT (winged chisel furrow opener preceded by a row cleaner equipped treader wheels attachment).
Chisel furrow opener used was fabricated from high-carbon steel plates 5 mm thick and with 30° rake angle. Edges sharpened winged chisel furrow opener cut residue on rows and push them aside. Winged chisel furrow opener was fabricated from high carbon steel plates 5 mm thick. The winged chisel with 30° rake angle and two 5 mm width bottom beveled wings which were downward 45°. The front blade could cut soil 25-30 mm deeper than the wings. Sharp edge winged chisel can be cutting and pushing more residue asides (Sanavi Shiri & Raoufat, 2006). Double disc furrow opener with two 350 mm diameter plain plates placed at a 30° angle to each other. Plates were made from 1.5 mm thick high-carbon steel and were sharpened to 14°. Furrow openers were bolted to the steel shank which was hitched to row-crop planter frame ( Fig. 1).
In agricultural conservation systems, row cleaners clean trash and residue on the row and are believed to improve seed spacing indices significantly. Row cleaner was made of two 25 cm diameter free rotating thin wheels placed at a 45° angle against each other. The row cleaner attachment was installed in front of the furrow opener to clean rows from previous residue. Row cleaner assembly comprised of a pivot joint and spring loaded link, providing suitable floatation.
The conical treader wheels were fabricated from aluminum with larger and smaller diameters of 200 and 170 mm, respectively. The treader wheels were fabricated in conical shape to promote residue removal to the row boundaries ( Fig. 1).

Residue management systems
The residue management systems consisted of baledout residue plots worked by a single pass of disc harrow (RMS1) or untouched residue plots worked by a single pass of chisel plow followed by a disc harrow (RMS2); both systems were planted by a row crop planter with one out of six attachments. The average amount of irrigated wheat residue before tillage operation for untouched and baled-out residue were 5.85 and 4.09 t ha -1 , however the amount of residues after tillage operations for non-baled and baled plots were measured and found to be 1.75 and 2.69 t ha -1 , respectively.
The disc harrow used was an offset 24 blade 90 cm in diameter with notched discs on the front gang and plain discs on the rear gang. Its working width and depth were 2.46 m and 10 cm, respectively. The spring loaded chisel plow used (9 shank, 20° rake angle) was equipped with curved shanks. Its working width and depth were 2.5 m and 20 cm, respectively.

Experimental design
A split-split-plot experiment arranged as a randomized complete block design was conducted with three replications. A conventional pneumatic row-crop planter equipped with one out of the attachment arrangements was used to plant in two RMSs (RMS1 and RMS2, see above) and two forward speeds. The splitlevel was furrow opener attachment arrangements, as chisel furrow opener preceded by row cleaner attachment (CR), chisel furrow opener preceded by row cleaner equipped treader wheels attachment (CRT), winged chisel furrow opener preceded by a row cleaner attachment (WCR) and winged chisel furrow opener preceded by a row cleaner equipped treader wheels attachment (WCRT), double disc furrow opener preceded by a row cleaner attachment (DR), and double disc furrow opener preceded by row cleaner equipped treader wheels attachment (DRT). The sub-split-level was plant forward speed in two levels (7 and 10 km h -1 ). The plots dimensions were 15 m × 3 m.
Field experiments were established in summer 2010 at the Agricultural Research Station, Shiraz University located in NW Shiraz, Iran (52°32' E, 36°29' N and 1810 m asl). Corn hybrid SC-704 with 1000 kernel weight of 250 g, emergence rating of 92% and purity of 98% was planted using a conventional pneumatic single seed type row-crop planter equipped with listers.

Measurements
Soil properties. Soil moisture and bulk density were measured by taking 20 soil samples at 0-20 cm of depth before tillage operations. The soil samples were weighted and dried in an oven at a temperature of 105°C for 24 h. The average moisture content and mean dry bulk density were 9% (db) and 14.3 kN m -3 , respectively. The soil was composed of 17.8% sand, 48% silt and 34% clay classified as clay-loam.
Residue measurement technique. In order to measure the quantity of wheat residue per unit area a 0.5 m × 0.5 m frame measuring system was used. Residue in frame was collected and dried in an oven at temperature of 105°C for 24 h. Then quantity of residue per unit area was calculated and found to be 0.25 m 2 . Quantity of residue before and after tillage operations were measured by taking 10 samples in each plot. Seeding depth. In order to measure seeding depth, a special tube was developed with one edge sharpened to help pull seedlings out of the soil. The seedlings were washed and the length of the mesocotyl was measured by a digital caliper. Since nodal roots typically grow approximately 2 cm below the soil surface, an extra 2 cm was added to obtain seed placement depth (Ritchie et al., 1993).
Emergence rate index (ERI). The ERI is an indication of how fast and uniform in time the crop emerges from the soil (Staggenborg et al., 2004). Erbach (1982) suggested the use of Eq. [1] for computing % ERI: where n is the emergence observation, EMG n is the percentage of seeds planted emerging on the day of the n th emergence observation and DPA n is the number of days after planting when the n th emergence observation was taken. The number of plants emerged in mid-6 m length of each row were counted after 3,4,5,7,9,12,14,17,20 and 25 days after planting and stopped when no further increased in emerged counts was observed.
Uniformity of seed spacings. For determining uniformity of seed spacings ISO standard (1984) was adopted as suggested by Kachman & Smith (1995 (1) a multiple, closer to the previous plant than the theoretical spacing; (2) a single, closer to the theoretical spacing than either the previous plant or a single skip; (3) a single skip, closer to a single skip than either the theoretical spacing or a double skip; (4) a double skip; and (5) a triple or more skips. The plant spacings which fall in the second region are considered as correct spacings. These measures are defined in the following sections: -Multiple index is the percentage of plant spacings that are less than or equal to half the theoretical spacing. Smaller value of multiple index indicates better planter performance than larger values.
-Miss index is the percentage of plant spacings that are 1.5 times larger than the theoretical spacing. Similarly, a smaller value of miss index indicates better planter performance than larger values.
-Quality of feed index (QFI) is the percentage of plant spacings that are more than half and less than or equal to 1.5 times the theoretical spacing. Greater values QFI is a sign of better planter performance than smaller values. In other words, QFI is a measure of how often the spacings are close to the theoretical spacing (Kachman & Smith, 1995). For example a QFI of 70% means that 70% of the spacings are not classified either as multiples or skips.
-Precision is a measure of the variability in spacing between plants after accounting for variability due to both multiples and skips. Smaller value of precision indicates better performance than larger values. The theoretical upper limit for precision is 50% and this distribution spacing would indicate that the theoretical spacing was incorrectly specified and, therefore, this theoretical level is unfavorable. A practical upper limit on the value of precision is 29%. While there is a theoretical upper limit of 50% on the precision, values consistently larger than 29% should be viewed with suspicion (Kachman & Smith, 1995).
In this research, the theoretical plant spacing was considered to be 10 cm, which is a common local practice. Therefore the multiple index is the percentage of spacings that are ≤ 5cm, the miss index is the percentage of spacings that are > 15 cm and QFI is the percentage of spacings that are > 5 cm and ≤ 15 cm.

Data analyses
Analysis of variance to detect significant differences and comparison of means were performed using SPSS package.

Surface residue after planting operation
Analyses of the variance of data on residue retained after planting operation as affected by various treatments and their interactions indicated that only interaction of RMS, attachment arrangement and forward speed significantly affected this index. No interaction was found between RMSs, attachment arrangement and forward speed.
According to McCarthy et al. (1999) at least 621 kg ha -1 of residues equal to 30% surface coverage is needed for small grain such as wheat to establish soil conservation tillage system. In the present study, the amount of residues retained before and after tillage and after planting operations on each row for all the treatments was more than 621 kg ha -1 (Table 1). It can be concluded that the treatments envisaged for the present study fall within residue cover limits defined for conservation farming practices.
Comparison of means of data on this index showed that for both RMSs, the mean values of WCRT retained the lowest amount of residue on the seed row after planting (Table 1). The winged chisel furrow opener preceded by a row cleaner equipped with treader wheels (WCRT) in RMS1 plots removed 20% of wheat residue on the row band as compared to similar plots worked with CR attachment (Table 1). Whereas, the WCRT arrangement in RMS2 plots removed 27% of wheat residue on the row band as compared to CR attachment ( Table 1). The reason is that the treader wheels rotation have pushed aside residue on the row, the subsequent winged-chisel has pushed further residue asides. Comparing the overall means of amount of residue retained indicated that for both RMSs, increase in forward speed from 7 to 10 km h -1 resulted in significant residue removal on the row band as seen in Table 1.

Effects on seeding depth
Analysis of variance of the data on seeding depth indicated that RMS, attachment arrangement and forward speed have significant effects on this index. No interaction was found between tillage and RMSs, type of attachment arrangement and speed levels as far as seeding depth is concerned.
Comparison of the means of seeding depth (Table 1) indicated that regardless of type of attachment, seeding depth increased from 4.37 to 4.93 cm as tillage operation increased in RMS2 treatments. Although RMS2 treatments were applied to a soil with higher initial residue, the chisel plowing and subsequent disc harrowing reduced the residue retained to average 950 kg ha -1 , which in turn can pave the way for planting in a more seeding depth.
Comparison of the data means on seeding depths (Table 1) indicate that for both RMSs, increase in forward speed resulted in less seeding depth, not necessarily in a significant manner. The reason may be less furrow opener penetration at a higher speed level.
For both RMSs, WCRT and CR attachment resulted in the highest and the lowest seeding depth, respectively (Table 1). Comparison of data revealed that WCRT treatment performed better in RMS2. This improvement in seeding depth may be due to fewer residues retained in this RMS.

Effects on emergence rate index (ERI)
Analysis of variance of the data on ERI indicated that RMSs, attachment arrangement and forward speeds have significant effects on this index. There was no significant interaction between RMSs, attachment arrangement and forward speed.
Higher soil temperature due to lower surface residue resulted in higher % ERI in RMS2 plots as compared to RMS1 ones; average improvement up to 14% was noticed (Table 1). Table 1 also shows that for both RMSs, WCRT and CR were associated with the highest and the lowest % ERI, respectively. Higher % ERI may be attributed to less residues retained due to rotation of row cleaner equipped with treader wheels and also sharpened edge winged chisel furrow opener which could remove further residue, resulting in a higher soil temperature (Table 1). This finding is similar to that of Wicks et al. (1994) who stated that higher surface residue cause further reduction in soil temperature and thus slow emergence. The higher % ERI for RMS2 plots may be due to fewer residues retained on the soil in this RMS.

Effects on seeding indices
Data on seedling spacings were used to calculate the following four indices of spacing. Comparative performance of planter attachments

Effects on multiple index
Analysis of variance of data on multiple index indicated that tillage and RMSs, attachment arrangement and forward speed have significant effects on this index. No interaction was found between RMSs, attachment arrangement and forward speed.
Comparison of the data means indicated that multiple index decreased in RMS2 plots as compared to RMS1 plots from 18.9% to 15.1%. That is for the plots worked under RMS2, only 15.1% of the plants were viewed as "dropped at the same time" as the previous plants (Table 1).
Further analysis indicated that increase in forward speed from 7 to 10 km h -1 , reduced % multiple index for both RMSs, which is desirable. In both RMSs, significant differences in % multiple index were noticed among attachment arrangements and WCRT and CR arrangements had the lowest and the highest multiple index values, respectively (Table 1).

Effects on miss index
Analyses of variance of data on miss index as affected by various treatments and their interactions indicated that only interaction of RMSs and attachment arrangement affected this index in a significant manner. Comparison of means of data on miss index indicated lower mean for RMS2 plots compared to those for RMS1 plots (Table 1). Fewer residues in RMS2 plots as a result of more tillage operations and less press wheel slippage are the possible causes of this improvement. Significant difference was also noticed on values of miss index for forward speed levels. Increasing forward speed from 7 to 10 km h -1 , resulted in increase in miss index for both  (Table 1). The high levels of the miss index could be due to a number of factors including the failure of the planter to drop the seed or the failure of the seed to germinate or produce a seedling. Other data indicated that plots with WCRT treatments had the least % miss index for both systems.

Effects on quality of feed index (QFI)
Analysis of variance of data indicated that the type of RMS had significant effects on QFI. Mean comparison of overall % QFI indicated that RMS2 treatments resulted in higher % of this index as compared to RMS1 treatments (Fig. 2a). The increase amounts to 16%, which is considerable. The reason may be more tilling operations in RMS2 plots resulting in less surface residue and as a result less wheel slippage. Comparison of the means of data also indicated that RMSs and attachment arrangements studied have significant effects on % QFI (Fig. 2b). Mean comparison of data on QFI for both RMS1 and RMS2 plots revealed that WCRT and CR arrangements have the maximum and minimum values of QFI for both systems, respectively (Table 1). The reasons for high values of QFI in WCRT plots are inclusion of rotation treader wheels which push residue on the row aside; furthermore, sharp edges winged-chisel also helps push more residue asides. Fewer residue on the row results in lower slippage in the planter press wheel which in turn results in higher % of QFI. The average QFI for the RMS2 plots were above 60%, indicating that more than two-third of the spacings was not classified as multiples or skips, whereas the average QFI for the RMS1 treatments was 53.4% (Table 1).
QFI increased for both RMSs when forward speed increased from 7 to 10 km h -1 , although this increase was not significant (Table 1).

Effects on precision of plants spacing
Analyses of the variance of data on precision index as affected by various treatments and their interactions indicated that only interaction of RMSs and attachment arrangement significantly affected this index. No interaction was found between RMSs, attachment arrangements and forward speed levels.
Comparison of the means of data indicated that reduction in precision values up to 40% was noticed in RMS2 plots as compared to RMS1 ones, which is desirable (Table 1). The reason may be more tillage operations in RMS2 plots, less press wheel slippage, and hence lower standard deviation of the seed spacings. Table 1 shows that significant differences were found among the values of precision index at different speed levels. Lower values of % precision were found at lower forward speed, this was true for both systems, which is desirable. The lower values of precision index may be attributed to fewer residues retained on plots prepared by RMS2.
Other comparison indicated that WCRT has the lowest value for precision for both RMSs. Further comparison indicated that WCRT and CR arrangement have the lowest and the highest precision indices for RMS1  Table 1). Columns with same lower or upper case letters are not statistically different at p = 0.05. Grey histograms: RMS1. White histograms: RMS2. and RMS2 plots, respectively (Table 1). The range of the precision index observed for the RMS2 treatments was roughly 12-32%, where similar data for RMS2 treatment were 9-22%, indicating that planter performance was close to the recommended value of 29% (Kachman & Smith, 1995). Therefore it can be concluded that in this study, the spacings were spread uniformly within the target range, however, RMS2 treatments showed lower values of this index, which is favorable. The study showed that both RMSs included in the present study fell within residue cover limits defined for establishing conservation farming practices and the WCRT arrangement successfully removes appreciable amounts of residue on the row for both systems, as expected more residues have been removed for RMS2 plots. Other results show that as the forward speed increases more residues are removed. In spite of higher initial residue level in RMS2 treatments, chisel plowing and subsequent disc harrowing reduced more residues paving the way for planting in a more seeding depth. For both RMSs, increases in forward speed resulted in less seeding depth. Generally QFI was higher for RMS2 plots. The WCRT and CR arrangements showed the desirable and the worst for both multiple and QFI indices, respectively. Increasing forward speed resulted in higher miss index for both systems, which is undesirable.
As final conclusions, the study suggests that addition of WCRT attachment arrangement to conventional planters in soil prepared under RMS2 is useful for a satisfactory soil conservation crop production system.