A Comparison of Drill and Broadcast Methods for Establishing Cover
HORTSCIENCE 49(4):441–447. 2014. on crop performance vary depending on a variety of factors (i.e., seeding rate, soil and seedbed condition, crop, sowing implement, A Comparison of Drill and Broadcast method, climate, post-seeding tillage, etc.) and the primary objective of growing the crop Methods for Establishing Cover Crops (i.e., grain, forage, weed suppression, pasture renovation, etc.), making it difficult to con- on Beds clude that one method is universally prefer- able. Part of the challenge of making such Eric B. Brennan1 and Jim E. Leap a generalization stems from the diversity of U.S. Department of Agriculture, Agricultural Research Service, U.S. implements that are used to broadcast the Agricultural Research Station, 1636 E. Alisal Street, Salinas, CA 93905 seed (i.e., centrifugal spreaders that fling seed horizontally across the soil vs. implements Additional index words. organic farming, planting method, rye, seedling establishment, attached to tractors or aircraft that drop the vegetable production, vetch seed vertically onto the soil) and whether and how the seed is incorporated into the soil. Abstract. Cover crop stands that are sufficiently dense soon after planting are more likely Ball (1986) noted that broadcasting is ‘‘an to suppress weeds, scavenge nutrients, and reduce erosion. Small-scale organic vegetable attractive technique for growing cereals farmers often broadcast cover crop seed to establish cover crops but lack information on cheaply by reducing fuel, machinery and the most effective implements to incorporate the seed into the soil. Experiments were labor in a wide range of soil conditions’’; conducted with winter- and spring-sown cover crops to compare drilling vs. broadcasting however, the dominance of drilling in mech- methods for establishing rye (Secale cereale L.) mixed with either purple (Vicia anized agriculture for more than a century benghalensis L., winter) or common vetch (V. sativa L., spring) on bed tops at a seeding (Heege, 1993) suggests that farmers prefer L1 rate of 140 kg·ha in Salinas, CA. Broadcast seed was incorporated with a rototiller, drilling. This preference is likely because of cultivator, or tandem disc. Cover crop stand uniformity was assessed visually, and cover the poor stands that can result from broad- crop emergence over time and seeding depth were measured. Stands were more uniform casting as a result of a variety of commonly after drilling or broadcast + rototiller incorporation compared with the other methods. cited broadcasting challenges such as vari- Cover crops emerged sooner and in higher densities after drilling compared with ability in seed distribution and seeding depth, broadcasting. The delayed emergence of broadcast seed was most apparent during the soil–seed contact, and predation of seed on cooler winter experiment, particularly with purple vetch. Most drilled seed emerged the soil surface. These challenges explain from 2-cm depth compared with the broadcast seed that emerged from up to 11-cm depth why extension publications typically recom- with the greatest variability after disc or rototiller incorporation. The data indicate that mend 20% to 50% higher seeding rates the cultivator and rototiller are preferable implements to incorporate broadcast seed on when broadcasting than drilling (Jeffers beds, but that 50% to 100% higher seeding rates for broadcasting than drilling are and Beuerlein, 2001; Kearney et al., 2006). needed. The practical implications for weed and soil management, and planting costs are To our knowledge, previous studies have discussed. not compared broadcasting vs. drilling methods for bedded production systems where high-value vegetables are rotated with Establishing a uniform and sufficiently hand-weeding, which can be cost-prohibitive cover crops. To address this information gap, dense cover crop stand as soon as possible if weed seedbanks are not carefully managed. we conducted a study that evaluated the after planting is a critical first step to enable Shade reduces seed production of many weed effectiveness of three secondary tillage im- the cover crop to provide desirable services species (Benvenuti et al., 1994; Chauhan, plements for soil incorporation of broadcast such as weed suppression, nitrate scavenging, 2013; McLachlan et al., 1995; Steinmaus and cover crop seed compared with drilled seed and erosion control. Weed management is Norris, 2002); therefore, planting strategies using legume–rye cover crop mixtures. Our challenging in organic systems, and it is well that hasten cover crop emergence and reduce study was motivated by the need for effective known that narrow rows and dense and spa- light penetration to understory weeds should strategies that will enable small-scale growers tially uniform crop stands are more competi- be a primary focus of cover cropping. without access to a drill to grow uniform and tive with weeds (Brennan et al., 2009; Mohler, Drilling and broadcasting are the two weed-suppressive cover crops on beds. In our 2000; Olsen et al., 2005, 2012; Weiner et al., methods to plant cover crops (Fisher et al., comparison of four planting methods, we 2001). Suppressing weeds that grow during 2011; Van Horn et al., 2011). In vegetable evaluated stand density at various times, seed winter cover cropping is particularly impor- and strawberry systems in the central coast depth, and visually assessed overall stand tant in tillage-intensive, high-value vegetable region of California, grain drills are com- uniformity. The implements evaluated rep- and strawberry production regions such as the monlyusedbymedium-(i.e.,100 ha) to resent those typically used in organic and central coast of California where many annual large-scale (greater than 200 ha) farms, conventional vegetable row cropping sys- weed species grow year-round and can add whereas smaller-scale organic farms with tems in California and were configured for large amounts of seed to the weed seedbank fewer resources often broadcast cover crop a 2.03-m wide bed system, which is a stan- (Boyd and Brennan, 2006; Brennan and seed onto the soil surface and incorporate it dard bed configuration here. Smith, 2005). Many vegetable crops require into the soil in a separate pass with a second- ary tillage implement. Although numerous Materials and Methods studies have compared broadcast vs. drilling Received for publication 21 Nov. 2013. Accepted of agronomic crops (Ball, 1986; Collins and Two field experiments were conducted in for publication 7 Feb. 2014. Fowler, 1992; Heege, 1993; Kiesselbach and a 0.24-ha field at the USDA-ARS organic We thank Darryl Wong and Damian Parr for Lyness, 1934; Oxner et al., 1997; Popp et al., research farm in Salinas, CA. The soil is a reviews of an earlier version of this manuscript. 2000), pastures or forage crops (Bartholomew Chualar loamy sand (fine-loamy, mixed, super- The U.S. Department of Agriculture (USDA) is an et al., 2011; Bellotti and Blair, 1989c; active, thermic Typic Argixerol). The field had equal opportunity provider and employer. Mention Edwards, 1998), and grassland restoration been cover-cropped for several years before of trade names or commercial products in this publication is solely for the purpose of providing (Larson et al., 2011; Yurkonis et al., 2010), the study. Field preparation included disc specific information and does not imply recom- relatively few such comparisons have been harrowing and ring rolling (i.e., cultipacking) mendation or endorsement by the USDA. done with cover crops (Fisher et al., 2011; as needed to incorporate previous cover crop 1To whom reprint requests should be addressed; Jeon et al., 2011; Kaspar et al., 2012). The residue and break up large clods. A global e-mail [email protected]. effects of these contrasting sowing techniques positioning system-guided tractor with lister
HORTSCIENCE VOL. 49(4) APRIL 2014 441 shovels was used to create slightly peaked to plant the cover crop mixtures at 140 kg·ha–1 way across the sampled bed top to avoid the beds that were 2.03 m wide and 20 m long. for all treatments in both experiments; this is edges and middle of the bed. Using a bed cultivator (PerfectaÒ II bedded a typical seeding rate for many legume–cereal Expt. 2. The cover crop was planted on 19 crop field cultivator; Unverferth Mfg., mixtures in California (Brennan et al., 2011; May 2011 and sprinkler-irrigated as needed Kalida, OH), the beds were then shaped to Brennan and Boyd, 2012a). The seeder has to germinate the seed. Cover crop emergence create uniform and level bed tops that a hydraulically driven seed agitator with was determined as in Expt. 1 at 12 and 19 were 1.5 m wide and 15 cm above the furrow brushes and is designed to plant high-density DAP. Like in previous studies (Olsen et al., bottoms. Bed shaping and planting operations leafy green vegetables such as lettuce in up to 2012), photographs were used as a simple and were performed with a tractor (Model 5525; 30 lines across a uniformly tilled, low-residue, effective way to characterize differences in John Deere, Moline, IL) with wheel spacing at finely aggregated, 1.5-m wide bed top. The crop spatial patterns and densities. Vetch 2.03 m that ran in the furrow bottoms between seeder was modified for our study by directing seed depth was determined at 21 DAP by the beds. These bed preparation procedures the 30 seed drop tubes into 10 planter shoes carefully hand-digging the seedlings in one were typical of those used to prepare beds for to replicate a standard seed drill spacing of 50 · 50-cm quadrat from each treatment plot. vegetable seeding in this region. 14 cm between seed lines; the remaining The seed depth of each uprooted seedling was The experimental design was a random- 20 shoes were removed from the seeder determined to the nearest mm by measuring ized complete block with five blocks of the during the study. The seeder has a rolling the length of the light-colored section of the four planting treatments for both experi- drum before and after the shoes to firm the epicotyl that had been below the soil surface. ments. The experimental unit was a set of seed bed and control seeding depth. For the This technique was facilitated by the hypo- three adjacent beds with the center bed used Drill treatment, the shoes were set to drill geous germination characteristic of vetch for data collection. The four treatments in- the seed at 1.9 cm below the bed surface. For whereby the cotyledons remain below ground cluded a drilled treatment (drill) and three the broadcast treatments, the planter was at the depth where the seed germinated. treatments where broadcast seed was incor- raised so that the shoes were 15 cm above Statistical analysis. Separate analyses porated with a power takeoff-driven roto- the bed top, allowing the seed to drop were conducted for each experiment using tiller (broadcast + rototiller), a bed cultivator uniformly from the shoes across the bed the MIXED procedure in SAS Version 9.3 (broadcast + cultivator), or a disc harrow top without the shoes or drums contacting (SAS Inst., Cary, NC). Within each experi- (broadcast + disc). Implement settings and the soil. This approach ensured that the ment, a separate analysis was conducted for details are in Table 1. The cover crops were same seeding rate was used for the drill the two dates that cover crop emergence was mixtures of 50% cereal rye (Secale cereale and broadcast treatments, like in a previous measured. In the analyses, planting method L., ‘AGS 104’) and 50% purple vetch (Vicia study comparing drilling and broadcasting was considered a fixed effect, and block benghalensis L.) for Expt. 1 and 50% rye and (Bartholomew et al., 2011). was considered a random effect. Data were 50% common vetch (V. sativa L.) for Expt. 2. Expt. 1. The cover crop was planted on checked to meet the assumptions of analysis Mixture percentages were by seed weight and 2 Dec. 2010 and was rain-fed. Emerged cover of variance and were transformed as needed, seed was from L.A. Hearne Seed Company crop plants were counted by species in two although back transformed means and 95% (King City, CA). 50 · 50-cm quadrats per treatment plot at confidence intervals (CIs) are presented. Re- A Sutton Seeder (Sutton Agricultural 14 and 47 d after planting (DAP). The quadrats ciprocal transformations were used for total Enterprises Inc., Salinas, CA) was calibrated were located approximately one-third of the cover crop density and rye density at 12 and 19 DAP in Expt. 2. Multiple comparisons between the treatments were controlled at Table 1. Three point implements and settings of four treatments for planting cover crops on beds in Expts. a familywise error rate of P # 0.05 using 1 and 2. Tukey-Kramer adjustments. The MEANS Treatment Implementsz Implement settings procedure was used to calculate 95% CI of Drill Sutton Seeder Seeder shoes set to drill seed at 1.9-cm soil the response variables to help the reader depth; tractor speed 5.15 km·h–1; seeder make practical inferences about the data. agitator speed 32 rpm; seed plate #22. Comparisons between treatment means with Broadcast + rototiller Sutton Seedery + rototillerx Tiller blades set at a soil depth of 10 cm 95% CI can be made using the ‘‘rule of eye’’ –1 below the bed top; tractor speed 2.6 km·h ; method whereby intervals that overlap with tractor engine speed 2000 rpm. a mean are not different, and intervals that Broadcast + cultivator Sutton Seedery + cultivatorw Adjusted to minimize soil dragging by spike tooth gang; rolling basket adjusted to overlap by half of one interval arm are the aggressive setting; tractor speed significantly different at P 0.05 (Cumming, 4.8 km·h–1; S tines and spike teeth adjusted 2009); however, such comparisons are not to a soil depth of 16 cm below the bed top. adjusted to control the familywise error rate Broadcast + disc Sutton Seedery + discv Disc blade depth set at a soil depth of 12 cm and this method is more robust when samples below the bed top, with the front disc gangs at sizes are 10 or more. In several figures we the second most aggressive setting (14 )and included the data points of each replicate rear disc gangs at the least aggressive setting –1 in addition to the mean and CI to illustrate (7 ); tractor speed 6.3 km·h ; center sweep the distribution of the data as suggested by between disc gangs set to the depth bottom of disc blades; furrow disc hillers (61-cm Drummond and Vowler (2011). diameter blades) set to maintain furrows. zAll implements were connected to the three-point attachment of a tractor (Model 5525; John Deere, Results and Discussion Moline, IL) with 2.03-m spacing between wheels. yFor the broadcast treatments, the Sutton Seeder broadcast seed 15 cm above the bed surface at the same Climate. During Expt. 1, the daily average tractor speed, agitator speed, and seed plate size as for the Drill treatment. air temperature ranged from 5 to 14 C with xJohn Deere (Model 680). an average of 10 C, and cumulative rainfall wPerfectaÒ II (Kalida, OH) ‘‘bedded crop field cultivator,’’ also commonly known as a bed harrow. was 121 mm; rainfall distribution was 4 to Included three gangs of S tines, a spike tooth leveling bar, rolling basket, and shovels that maintain the 5 mm weekly during the first 2 weeks and 28 furrows. to 50 mm weekly for Weeks 3 to 5. There was vLand Pride (Salina, KS) tandem disc (Model DH25) with 56-cm diameter notched discs. The disc was modified as follows for use on beds. A single 33-cm wide sweep was added in the center of the unit between no precipitation during Expt. 2, and daily the front and rear disc gangs to cultivate the center area missed by the discs. A bar was added behind the average air temperature ranged from 12 to rear gang to position a disc hiller in each furrow to maintain the furrows. A flat 61-cm diameter coulter was 15 C with an average of 13 C. A total of also mounted on the rear bar and ran at 20-cm depth in the bed center to reduce sideward movement of the 19 mm of sprinkler irrigation was applied in implement. a single irrigation event on the first day of
442 HORTSCIENCE VOL. 49(4) APRIL 2014 Expt. 2. The rainfall distribution during Expt. crop–weed competition (Fischer and Miles, on beds is less common than cover cropping 1 and irrigation application during Expt. 2 1973; Regnier and Bakelana, 1995). In future in unbedded fields; however, a bedded cover were ideal for cover crop germination. studies of this nature we encourage re- crop can minimize spring tillage if minimum Distribution of cover crop seedlings on searchers to consider using Morisita’s index tillage implements are used to incorporate the bed tops and furrows. The four planting of dispersion to provide a simple and robust residue into the bed in preparation for the methods resulted in cover crop stands with measure of crop spatial uniformity and ag- next vegetable crop (Fennimore and Jackson, visually distinctive patterns on the bed tops gregation like in previous studies (Kristensen 2003; Jackson et al., 1993). Furthermore, and furrows that were consistent across rep- et al., 2006; Olsen et al., 2012) and provide raised beds can improve winter drainage lications and experiments (Fig. 1). The drill insights into weed-suppressive potential of and help to aerate the crown and root system and broadcast + rototiller methods provided various sowing methods. (Kearney et al., 2006). the most spatially uniform distribution of Incorporating seed with the cultivator and Total cover crop density. Average total cover crop plants across the bed tops and disc resulted in more cover crop emergence cover crop densities (rye + vetch) during the seldom had cover crop emergence in the in the furrows than was observed in the other first 2 weeks after planting ranged from 151 furrows. In contrast, incorporating the treatments. Cover crop emergence in the to 302 plants/m2 in Expt. 1 and from 224 to broadcast seed with the cultivator or disc furrows can create management challenges 359 plants/m2 in Expt. 2 (Figs. 2A and 3A). tended to concentrate the cover crop seed at season end when the cover crop is termi- These densities were within the typical range into two to three strips on either side of the nated by mowing and incorporation because it of legume–cereal cover crops in the region bed top center. These strips were caused by can be more difficult to kill and incorporate (Brennan et al., 2009; Brennan and Boyd, the S tines on the cultivator and the tandem cover crops in the furrows than bed tops. 2012a; Brennan and Smith, 2005). In both disc blades. Concentrating crop plants into Ideally, shallow tillage can be used as needed experiments, there were consistently greater such dense clusters is undesirable because it to kill weeds that germinate in the furrows total cover crop densities in the drill than hastens intracrop competition and delays during the winter. In our region, cover cropping broadcast treatments during the first 2 weeks
Fig. 1. Photographs of 203-cm wide beds with a common vetch–rye cover crop mixture in Expt. 2, 13 d after planting with a drill, or broadcasting the seed on the soil surface and Fig. 2. Cover crop population densities at 14 and 47 d after planting (DAP) in a purple vetch–rye cover crop incorporated it with a rototiller, harrow, or disc. mixture that was drilled or broadcast and incorporated with a rototiller, a cultivator, or a disc. All Planting occurred on 19 May 2011. Each treatments were planted at 140 kg·ha–1 on 2 Dec. 2010. The mixture included 50% of each seed type by photograph shows a centered bed of each seed weight. Each round black or gray dot in the cluster of five dots is the mean of two quadrats for each treatment and a portion of the same treatment of the five replicates, and the open squares with error bars are the means ± 95% confidence intervals. on the beds to the right and left. An irrigation The relative position of each dot with each cluster is offset (i.e., jittered) around the mean to avoid pipe runs across the beds approximately one- overlapping data points with the offset sequence in order from replicates 1 (left) to 5 (right). Means that third from the top of each photograph. At the are significantly different based on a Tukey-Kramer familywise error rate of P # 0.05 are indicated resolution shown, the majority of green plants below each data cluster with different lower case letters for 14 DAP and different upper case letters for visible are cover crops rather than weeds; a few 47 DAP. ***There were significant treatment differences (P # 0.001) at the two measurement times; individual weeds are barely visible in the NS = nonsignificant and the actual P value is in parentheses. The percentage of rye and vetch plants is furrows of the of the drill and broadcast + shown above the x-axis for each cluster of data. Comparisons within planting treatment between the rototiller treatments. The color of photographs 14 and 47 DAP can be made using the ‘‘rule of eye’’ method whereby intervals that overlap with a mean was adjusted digitally to help visualize the are not different, and intervals that overlap by half of one interval arm are significantly different at cover crops relative to the soil. The pink, red, P 0.05 (Cumming, 2009). Note that the y-axis range of the total cover crop plot (A) is greater than the and white objects were plot flags. range for the rye (B) and vetch (C) plots.
HORTSCIENCE VOL. 49(4) APRIL 2014 443 Rye and vetch densities. Rye densities averaged across treatments were slightly lower during the first 2 weeks of experiment 1 (137 ± 15 plants/m2, mean ± 95% CI) than Expt. 2 (154 ± 21) and changed relatively little thereafter (Figs. 2B and 3B). In general, broadcasting produced lower rye densities than the drilling; however, the relative rank- ing of the broadcast treatments varied be- tween experiments; emergence was highest with rototiller incorporation in Expt. 1 vs. cultivator incorporation in Expt. 2. Purple vetch densities were approximately two or more times greater in the Drill (119 plants/m2) than broadcast treatments (33 to 63 plants/m2) at 14 DAP in Expt. 1 (Fig. 2C) and these densities increased in all treat- ments, particularly in the broadcast treat- ments that more than doubled by 47 DAP. Purple vetch densities differed little between broadcast treatments. It is interesting to note that purple vetch emergence was slower than rye emergence, but over time, purple vetch densities in the broadcast treatments were comparable to the drill treatment, whereas this was generally not the case with rye. This indicates that rye was more sensitive than purple vetch to planting depth. Broadcasting also reduced common vetch densities in Expt. 2 (Fig. 3C); however, the magnitude of the difference with the Drill Fig. 3. Cover crop population densities at 12 and 19 d after planting (DAP) in a common vetch–rye cover treatment was not as great as with purple vetch crop mixture that was drilled or broadcast and incorporated with a rototiller, a cultivator, or a disc. All in Expt. 1 (Fig. 2C). Furthermore, despite the treatments were planted at 140 kg·ha–1 on 19 May 2011. The mixture included 50% of each seed type slight increase in common vetch densities by seed weight. Each round black or gray dot in the cluster of five dots is the mean of two quadrats for between 12 and 19 DAP, the densities in the each of the five replicates, and the open squares with error bars are the means ± 95% confidence broadcast treatments were an average of intervals. The relative position of each dot with each cluster is offset (i.e., jittered) around the mean to 31% lower (52 fewer plants/m2) than in the avoid overlapping data points with the offset sequence in order from replicates 1 (left) to 5 (right). Drill treatment by 19 DAP. Means that are significantly different based on a Tukey-Kramer familywise error rate of P # 0.05 are Planting method had a clear effect on indicated below each data cluster with different lower case letters for 12 DAP and different upper case letters for 19 DAP. ***There were significant treatment differences (P # 0.001) at the two the proportion of the mixture components measurement times. The percentage of rye and vetch plants is shown above the x-axis for each cluster that emerged during Expt. 1, especially in the of data. Comparisons within planting treatment between the 12 and 19 DAP can be made using the ‘‘rule broadcast treatments. For example, the per- of eye’’ method whereby intervals that overlap with a mean are not different, and intervals that overlap by centage of purple vetch increased in all half of one interval arm are significantly different at P 0.05 (Cumming, 2009). Note that the y-axis treatments overtime; however, this change range of the total cover crop plot (A) is greater than the range for the rye (B)andvetch(C) plots. was relatively small in the Drill treatment (4%) compared with the broadcast treatments where it ranged from 16% with rototiller and (P # 0.001). For example, compared with the DAP in Expt. 1, the average total density cultivator incorporation to 27% with disc Drill treatment, there were 33% fewer seed- increased by 24 plants/m2 (8%) in the Drill incorporation. Research with mixtures in pas- lings in broadcast + rototiller and an average treatment compared with an average increase ture and restoration plantings has similarly of 50% fewer in the broadcast + cultivator of 91 plants/m2 (54%) in the broadcast reported that the percentage of the mixture and broadcast + disc at 14 DAP in Expt. 1 treatments (Fig. 2A). In contrast, between components that emerge and that make up (Fig. 2A). A similar pattern occurred in Expt. 12 and 19 DAP in Expt. 2, the increase in the stand differ in broadcast vs. drill plant- 2 where there were 26% to 38% fewer total densities was only 7% (20 plants/m2) ings (Bellotti and Blair, 1989a, 1989b, seedlings in the broadcast treatments than in averaged across treatments (Fig. 3A). We 1989c; Larson et al., 2011). Although le- the drill treatment at 12 DAP (Fig. 3A). attribute the greater change between mea- gume seed accounts for 90% of the seed Within the broadcast treatments, broad- surement dates in total cover crop densities weight in typical legume–cereal mixtures cast + rototiller had an average of 53 (35%) in Expt. 1 than Expt. 2 to the cooler temper- in this region, cereal biomass often repre- more total plants/m2 than the other broadcast atures during Expt. 1 that likely delayed sents 70% to 90% of the total final cover treatments at 14 DAP in Expt. 1; this general emergence of deeper-placed seed in the crop biomass (Brennan et al., 2009, 2011; pattern continued to 47 DAP. In contrast, broadcast treatments. Our results of delayed Brennan and Boyd, 2012b). Additional re- there were fewer differences in densities emergence of broadcast seed is consistent search is needed to determine if drilling vs. among broadcast treatments in Expt. 2; how- with previous studies with cover crops broadcasting planting method influences ever, there was consistently less variability in (Fisher et al., 2011) and perennial pasture the legume’s persistence in the mixture the broadcast + rototiller treatment at both grass (Bellotti and Blair, 1989b). It is im- and its ability to produce desirable services measurement dates (Fig. 3A). portant to note that the density differences such as nitrogen fixation. We speculate that In both experiments, the total densities between the broadcast + disc treatment broadcasting would reduce the amount of increased from the first to second measure- relative to the other treatments would likely legume biomass produced if the incorpora- ment date; however, the increase was most have been greater if we had collected data tion method delays emergence of the le- apparent in the broadcast treatments during from across the entire bed top rather just gume component relative to the cereal as Expt. 1. For example, between 14 and 47 one-third of the way across the bed. occurred in Expt. 1.
444 HORTSCIENCE VOL. 49(4) APRIL 2014 Crop crop seed depth. There were marked because even with the disc adjusted to its cultivator in beds with moderate amounts of differences in the seed depth of common least aggressive setting, it buried the seed previous crop residue because the rototiller’s vetch between planting methods (Fig. 4). As deeper in the bed than is optimal, left a rela- rotating tines would readily shred the residue. expected, drilling resulted in the most uni- tively deep groove with few cover crop plants Additional research is needed to determine if form seeding depth at 2 cm. In contrast, all in the bed center, and moved seed from the simple modifications to the cultivator would broadcast treatments had more variability in bed top into the furrow. reduce the strip pattern that it created. For seed depth, particularly where the broadcast Our study indicates that either the roto- example, we speculate that removing the S seed was incorporated with the rototiller or tiller or cultivator can be effective tools to tines and relying only on the spike tooth gang disc. Variability in seeding depth of various incorporate broadcast seed in some situa- and rolling basket may incorporate the seed sowing methods is problematic because crop tions. The rototiller has the potential to pro- more uniformly across the bed top. Further- emergence decreases linearly with increased duce the most uniform stand of a broadcast more, it would be useful to compare the variabilityinseeddepth(Heege,1993).The cover crop; however, it would require ap- effectiveness of other common cultivators that differences in seed depth between planting proximately twice the incorporation time of only have spike tooth tines and to evaluate methods help explain the lower densities and the cultivator, more attention to control seed these tools on a range of soil textures. delayed emergence patterns in the broadcast depth, and would also be less energy-efficient Although we did not measure weed sup- treatments (Figs. 2 and 3). Our data indicate because it requires use of a tractor’s power pression, it is likely that the drilled cover that of the three broadcast methods, the takeoff. The slower incorporation speed of crops had the greatest potential to capture cultivator placed the broadcast seed at a rel- the rototiller may also increase the chance of more light and thus suppress weeds because atively uniform depth that is most similar to seed predation by birds, particularly if the the drill produced denser and more spatially drilling the seed. The shallower seed depth same tractor is used to broadcast and in- uniform stands sooner after planting than in the broadcast + cultivator plots compared corporate, and there was more time elapsed occurred with any of the broadcast methods. with the other broadcast methods likely from broadcasting to incorporation. Further- It is well known that deeper seed placement explains a trend toward greater rye emer- more, the rototiller would be less suitable delays crop emergence (Tadmor and Cohen, gence of the cultivator incorporated seed than the cultivator for small-seeded cover 1968), which in turn delays competition (Fig. 3B). crops such as mustards that are less tolerant to between crops and weeds for light. Compar- Practical implications. This study pro- deeper planting depths than cereals and grain isons of drill and broadcast sowing methods vides the first information on the effective- legumes (Vicia spp.; pea, Pisum sativa L.) have seldom evaluated light interception by ness of drilling vs. broadcasting methods for used as cover crops. Deeper seed placement the sown plants, but Yurkonis et al. (2010) planting cover crops on raised beds and by the rototiller would likely be more prob- showed greater interception in drilled stands. illustrates the benefits of drilling over broad- lematic in clay-textured soils that are known In California, canopy closure by fall-seeded casting. Our findings indicate that the tandem to inhibit emergence from deeper depths cover crops within the first month after disc was the least suitable implement to (Mutz and Scifres, 1975). However, the planting is a good general predictor of weed incorporate broadcast seed into a raised bed rototiller would have advantages over the suppression (Brennan et al., 2009; Brennan and Smith, 2005). Our current study suggests that broadcast seeding rates should be 1.5 to two times higher than drilled rates to provide similar early-season densities. The rototiller and cultivator methods produced cover crop stands with opposite strengths and weakness in terms of planting depth and spatial unifor- mity that may influence weed suppression. For example, the more even distribution of cover crop plants on the bed top after the rototiller would likely enhance weed control relative to that after the cultivator; however, these bene- fits may not be realized if the rototiller delays cover crop emergence by burying the seed deeper below the soil surface. Several issues need to be considered when deciding if the benefits of drilling cover crops would justify investing in a drill-type planter. Although broadcasting is usually considered a labor-saving approach to plant large areas quickly, this is clearly not the case with the broadcast systems we evaluated where the seed was broadcast and incorporated one bed at a time with separate broadcast and in- corporation passes. Assuming the current hourly labor costs for a tractor operator in our region of $20 including benefits (Dara et al., 2012) and the travel speeds of the implements (Table 1), we estimate that com- pared with drilling, the time and hence labor costs of the broadcasting methods evaluated Fig. 4. The percentage of common vetch seedlings in Expt. 2 that emerged from various depths (A, C, E, would be 1.9, 2.1, and 2.7 times higher for the G) and average seed depth (B, D, F, H) with a drill or broadcast on the soil surface and incorporated disc, cultivator, and rototiller methods, re- with a rototiller, cultivator, or disc. The seeding rate was 140 kg·ha–1 for a common vetch–rye mixture that included 50% of each component by seed weight. Data were collected 21 d after planting (19 May spectively. These higher labor costs com- 2011). Horizontal bars in plots A, C, E, and G are mean ± 95% confidence interval. Plots B, D, F, and H bined with the need for 1.5 to two times show the seed depth of each of the five replicates (round dots) and the mean ± 95% confidence interval. higher seeding rates for broadcast cover crops The total number of seedlings that provided the data summed across the five replicates was 165 (drill), illustrate the potential savings that a drill can 147 (broadcast + rototiller), 101 (broadcast + cultivator), and 104 (broadcast + disc). provide as the acreage in cover crop increases.
HORTSCIENCE VOL. 49(4) APRIL 2014 445 The higher labor costs of the broadcast crop’s ability to provide important services eight years of organic vegetables: I. Cover crop systems we evaluated were largely the result such as weed suppression, nitrate scavenging, biomass production. Agron. J. 104:684–698. of the presence of beds that restricted us to and cover crop biomass production. Despite Brennan, E.B. and N.S. Boyd. 2012b. Winter cover use implements that retained the bed during the potential problems from deeper seed crop seeding rate and variety effects during eight soil incorporation of the seed. Although placement from broadcasting, several studies years of organic vegetables: II. Cover crop nitrogen accumulation. Agron. J. 104:799–806. cover crops are grown on beds and unbedded reported equivalent yields of drilled vs. broad- Brennan, E.B., N.S. Boyd, R.F. Smith, and P. fields in this region, cover cropping on beds cast stands of agronomic crops (Graham and Foster. 2009. Seeding rate and planting ar- can allow smaller areas to be cover-cropped Ellis, 1980; Popp et al., 2000). rangement effects on growth and weed sup- regularly and can potentially save time and In conclusion, our study shows the bene- pression of a legume–oat cover crop for organic reduce fuel use if the cover-cropped beds are fits of drilling vs. broadcasting methods for vegetable systems. Agron. J. 101:979–988. to be ‘‘recycled’’ into bedded vegetable crops establishing uniform cover crops on beds. Brennan, E.B., N.S. Boyd, R.F. Smith, and P. using minimum tillage implements (Jackson Drilling required less time than broadcasting Foster. 2011. Comparison of rye and legume– et al., 2002). because the broadcasting methods all used rye cover crop mixtures for vegetable produc- An important issue to consider when a second pass to incorporate the seed. The tion in California. Agron. J. 103:449–463. growing cover crops on beds involves choos- data suggest that at a given seeding rate, Brennan, E.B. and R.F. Smith. 2005. Winter cover crop growth and weed suppression on the central ing an effective implement to either drill or drilled cover crops had characteristics such as coast of California. Weed Technol. 19:1017– broadcast the seed onto the bed top. High- greater uniformity and faster emergence that 1024. density vegetable planters that are configured would likely increase their ability to suppress Chauhan, B.S. 2013. Shade reduces growth and for wide beds such as we used in our exper- weeds that emerge with the cover crop. The seed production of Echinochloa colona, Echi- iments can work well for cover crops with main problems with the broadcasting methods nochloa crus-galli, and Echinochloa glabres- small- (i.e., mustard) to medium- (i.e., small evaluated were delayed emergence and lower cens. Crop Prot. 43:241–245. grains and vetch) sized seed; such planters cover crop stands that were likely the result of Collins, B.A. and D.B. Fowler. 1992. A compari- typically cost U.S. $9000 for the basic greater variability in seeding depth. The best son of broadcast and drill methods for no-till model we used in our study. Standard pull methods to incorporate broadcast seed into seeding winter-wheat. Can. J. Plant Sci. 72:1001– or three-point-type grain drills can work well the bed were a rototiller or a cultivator with 1008. Cumming, G. 2009. Inference by eye: Reading the assuming that their planting width and drive tines and a rolling basket, preferably at 50% overlap of independent confidence intervals. wheel spacing fits well with the bed width; to 100% higher seeding rates than drilling. Stat. Med. 28:205–220. drive wheels that fit in the furrow between Additional research is needed to determine if Dara, S.K., K.M. Klonsky, and K.P. Tumber. 2012. beds are preferable to avoid potential prob- modifications to the cultivator would reduce Sample costs to produce fresh market broccoli. lems with drive wheel tracks on bed tops. its tendency to concentrate the seed in strips. University of California Cooperative Exten- Relatively inexpensive (i.e., U.S. $1000) sion, Davis, CA. Drummond, G.B. and S.L. Vowler. 2011. Show the drop-type broadcast spreaders with variable Literature Cited rate settings that are typically used for lime data, don’t conceal them. Clin. Exp. Pharma- and fertilizer application may also work for Arnott, R.A. 1969. Effect of seed weight and depth col. Physiol. 38:287–289. planting cover crops on bed tops but would of sowing on emergence and early seedling Edwards, L. 1998. Comparison of two spring seeding methods to establish forage cover crops require a second pass to incorporate the seed. growth of perennial ryegrass (Lolium perenne). J. Br. Grassl. Soc. 24:104–110. in relay with winter cereals. Soil Tillage Res. A centrifugal broadcast seeder could also be 45:227–235. used for planting cover crop on beds but Ball, B.C. 1986. Cereal production with broadcast seed and reduced tillage—A review of recent Fennimore, S.A. and L.E. Jackson. 2003. Organic would also place seed into the furrows. experimental and farming experience. J. Agr. amendment and tillage effects on vegetable It is unknown if the lower-density cover Eng. Res. 35:71–95. field weed emergence and seedbanks. Weed crop stands in the broadcast methods would Bartholomew, P.W., J.M. Schneider, and R.D. Technol. 17:42–50. compensate and produce the same final cover Williams. 2011. Pasture residue amount and Fischer, R.A. and R.E. Miles. 1973. The role of crop biomass as a drilled cover crop. Several sowing method effects on establishment of spatial pattern in the competition between crop previous studies from this region reported overseeded cool-season grasses and on total plants and weeds. A theoretical analysis. Math. that final biomass production was typically annual production of herbage. Grass Forage Biosci. 18:335–350. Fisher, K.A., B. Momen, and R.J. Kratochvil. 2011. unaffected by stand density differences Sci. 66:560–568. Is broadcasting seed an effective winter cover caused by altering seeding rate (Boyd Bellotti, W.D. and G.J. Blair. 1989a. The influence of sowing method on perennial grass establish- crop planting method? Agron. J. 103:472–478. et al., 2009; Brennan et al., 2009; Brennan ment. 1. Dry-matter yield and botanical com- Fulbright, T.E., A.M. Wilson, and E.F. Redente. and Boyd, 2012a). However, in contrast to position. Aust. J. Agr. Res. 40:301–311. 1985. Green needlegrass seedling morphology those previous studies in which lower den- Bellotti, W.D. and G.J. Blair. 1989b. The influence of in relation to planting depth. J. Range Mgt. sities were the result of lower seeding rates, sowing method on perennial grass establishment. 38:266–270. the reduced densities in the broadcast + disc 2. Seedbed microenvironment, germination Graham, J.P. and F.B. Ellis. 1980. The merits of and broadcast + rototiller treatments in our and emergence. Aust. J. Agr. Res. 40:313– precision drilling and broadcasting for the present study were the result of slower emer- 321. establishment of cereal crops in Britain. ADAS gence from deeper seeding depths. Seedlings Bellotti, W.D. and G.J. Blair. 1989c. The influence Quarterly Review. p. 160–169. that emerge from deeper depths often have of sowing method on perennial grass establish- Hadjichristodoulou, A., A. Della, and J. Photiades. 1977. Effect of sowing depth on plant estab- reduced vigor and reduced biomass and root ment. 3. Survival and growth of emerged seedlings. Aust. J. Agr. Res. 40:323–331. lishment, tillering capacity and other agro- production, fewer tillers, and reduced hy- Benvenuti, S., M. Macchia, and A. Stefani. 1994. nomic characters of cereals. J. Agr. Sci. draulic conductance (Arnott, 1969; Fulbright Effects of shade on reproduction and some 89:161–167. et al., 1985; Hadjichristodoulou et al., 1977; morphological—Characteristics of Abutilon- Heege, H.J. 1993. Seeding methods performance Kirby, 1993; Loeppky et al., 1989; Lueck et al., theophrasti medicus, Datura-stramonium l for cereals, rape, and beans. Trans. ASAE 1949; Mahdi et al., 1998; Mutz and Scifres, and Sorghum-halepense L pers. Weed Res. 36:653–661. 1975; Photiades and Hadjichristodoulou, 34:283–288. Jackson, L.E., I.R. Ramirez, I. Morales, and S.T. 1984; Redmann and Qi, 1992; Tischler and Boyd, N.S. and E.B. Brennan. 2006. Weed man- Koike. 2002. Minimum tillage practices affect Voigt, 1983); all of these characteristics would agement in a legume–cereal cover crop with the disease and yield of lettuce. Calif. Agr. likely reduce the crop’s ability to capture rotary hoe. Weed Technol. 20:733–737. 56:35–39. Boyd, N.S., E.B. Brennan, R.F. Smith, and R. Jackson, L.E., L.J. Wyland, and L.J. Stivers. 1993. limited resources (i.e., light, nutrients, and Yokota. 2009. Effect of seeding rate and Winter cover crops to minimize nitrate losses in moisture) and hence to suppress weeds. Addi- planting arrangement on rye cover crop and intensive lettuce production. J. Agr. Sci. tional research is needed to determine if these weed growth. Agron. J. 101:47–51. 121:55–62. potential problems with deeper planted seed Brennan, E.B. and N.S. Boyd. 2012a. Winter cover Jeffers, D.L. and J. Beuerlein. 2001. Arial and other have a negative effect on a broadcast cover crop seeding rate and variety effects during broadcast methods of seeding wheat. Ohio State
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