Preparing And Calibrating A No-Till Or Conventional Drill
Preparing and Calibratinga No-Till or Conventional Drillfor Establishing Forage or Cover Crops
AUTHORSDennis W. HancockProfessor and ExtensionForage Agronomist,Department of Crop andSoil SciencesBrian MaddyCounty ExtensionCoordinator, Troup CountyJulia GaskinSustainable AgricultureCoordinator, Departmentof Crop and Soil SciencesLisa L. BaxterAssistant Professor,Department of Crop andSoil SciencesDeidre D. HarmonAssistant Professor andExtension LivestockSpecialist, Departmentof Animal Science, NorthCarolina State University
CO N T EN TSINTRODUCTION. 1PARTS OF A DRILL. 1DRILLS METER A VOLUME OF SEED.3COUNTING SEEDS IN THE ROW.3ADJUSTING FOR PURE LIVE SEED. 6ADJUSTING FOR SEED COATS.7DRILLING SEED MIXTURES.8PREVENTATIVE MAINTENANCE. 10CALIBRATION PROCEDURES. 10ADJUSTMENTS FOR PROPER PLANTING DEPTH.12SUMMARY. 13
Preparing and Calibratinga No-Till or Conventional Drillfor Establishing Forage or Cover CropsParts of a drillThere are many moving parts on a no-till or conventional drill. Each brand and model has designelements that differentiates it from other drills on the market, but most have several key featuresin common. These key features are identified in Figure 1. On a no-till drill, the rolling coulter travelsahead of the opener and cuts a slot through the sod, residue, and soil, and then the double-diskopener widens this slot. Conventional grain drills are used when the seedbed is already preparedand the coulter is not needed to cut through residue or the soil surface. Therefore, conventional drillsdo not have the coulter assembly on the front.Figure 1.Schematic drawing of the typical parts on one row unit of a no-till drill. A conventionaldrill would have similar parts, but usually does not have the coulter assembly on the front of the drill.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops1
Seed is held in the hopper boxes that sit on top ofthe drill. Some drills have multiple hopper boxes.Most drills designed for use on pastures will havelarge and small hopper boxes. The large hopperbox would be used for planting crops that havemedium to large seed sizes (e.g., cowpea, pearlmillet, tall fescue), while the small hopper boxwould be used to plant small-seeded species(e.g., clovers, brassicas, crabgrass). Some drillsmay also have a “native grass box,” which is ahopper box that is specially designed to handlenative warm-season perennial grass species.Several of the native prairie grass species havefluffy appendages on their seed which interfereswith seed flow through the bottom of the hopper.So, native grass boxes have agitators within thebox that improves seed flow (Figure 2).Figure 2.Agitators in the bottom of native grasshopper boxes ensure that the fluffy appendages onthe seed of some native prairie grasses do not keepthe boxes from properly metering the correct rate.Unlike the planters that are used for row crops,seed drills do not separate and drop individualseeds. Instead, seed flowing out of the opening at the bottom of a hopper box is metered by theseed metering unit, which is opened a set distance for a given seed size and seeding rate (Figure 3).As a drive shaft turns, seed is metered out and dropped into the seed cup.As the drill travels across the field, a ground-driven wheel connected to a driveshaft turns and seedfrom a hopper box above the row units is metered into the seed cup. The seed then falls downthrough the drop tubes. The seed is dropped between or just behind the double-disks, placing theseed within the furrow opened in the soil created by the opener. The press wheel follows behindand closes the furrow and firms the soil around the seed. The weight of the drill compresses thedown pressure springs that force the press wheels against the soil surface.Figure 3.In the bottom of the hopper box (left), an opening allows seed to flow into the seed metering unit.When calibrating and setting a drill, consult the drill’s manual to ensure that the seed metering unit is opened tothe appropriate size and the driveshaft gearing is set to the appropriate settings. Usually, minor adjustments inthe size of the opening at the seed metering unit will fine-tune the metering to provide the desired seeding rates.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops2
Drills meter a volume of seedDrills actually meter out a volume of seed ratherthan a precise weight or number of seeds (seeinset “Counting seeds in the row”). Consequently,the weight of seed per bushel (or other measureof volume), the number of seeds per pound, thetarget seeding rate in pounds per acre, and theappropriate seeding depth are all key pieces ofinformation when setting up and calibrating adrill. Table 1 provides the typical values fordifferent forage and cover crops, but it is importantto note that seed sizes can vary considerablyfrom one seed lot to another. For this reason, it isimportant to calibrate, check, and adjust the drillfrequently to account for changes in seed size orother planting conditions.In the Southeastern U.S, variability in annualryegrass seed size is a common example ofwhy accounting for different seed sizes is crucial.There are several varieties of annual ryegrasson the market that are tetraploids, meaning thattheir plant cells contain four sets of chromosomes(4n) rather than the two sets of chromosomesfound in the more common diploid (2n) varieties.Consequently, tetraploid varieties have seed thatmay be up to 150% the size of diploid varieties(Figure 4). Even though the seeding rate is thesame (i.e., same pounds/acre), one will likelyneed to adjust the seed metering unit openingdepending upon whether they are plantinga diploid or tetraploid variety to ensure theappropriate seeding rate is being used.COUNTINGSEEDS INTHE ROWMost row cropsare planted withplanters thatsingulate seedbefore dropping itinto the furrow. For this reason, the accuracyand precision of a planter is determinedby how many seeds are counted in a setdistance of the row and the distance betweenthe seed. For example, a seeding rate forcorn of 33,000 planted on 30-inch centersshould result in approximately 19 seeds per10 feet of row, with 6.4 inches between seeds.Conversely, drills meter out a volume of seedwhich is more haphazardly distributed, soit is not as precise, and counting seeds perdistance of row may result in tremendousvariation. Calibrating a drill should bedone to ensure the recommended weightof seed is distributed per unit area.Evaluating the number of seeds per distanceof row is not a recommended approach toadjusting seeding rates or calibrating a drill.Figure 4.Varieties of annual ryegrass differ in seed size, which will likely require adjustments to conventional andno-till grain drills to maintain the same seeding rate. Each of these beakers contains 20,000 seed of their respectivevarieties. Note that the seed of tetraploid varieties takes up approximately 140-150% more volume as the diploidvarieties. Photo credit: Henry Jordan, UGA Statewide Variety Testing Program.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops3
Table 1. General seeding information for grasses and legumes used for forage and cover crops.ˇThese seeding rates assume the species will be planted as a monoculture. If multiple species areto be planted together, reduce the seeding rates proportionate to the number of species in the mix(i.e., if several species are to be planted together, divide the seeding rate listed here for each by thenumber of species in the mixture).SEEDING RATE (DRILLED)CROPSPECIESAPPROXIMATE TEST WEIGHT(pounds/bushel) (number seeds/pound)FORAGECROPCOVERCROP(pounds/acre) 00010-15nr¼-½FMillet, -20¼-½EForageSorghum5624,0006-815-20½-1GSorghum ss4043,00010-1515-20½-1ETall 060-100½-1GWheat6011,00090-12060-100½-1EUGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops4
Table 1. Continued.SEEDING RATE (DRILLED)CROPSPECIESAPPROXIMATE TEST WEIGHT(pounds/bushel) (number seeds/pound)FORAGECROPCOVERCROP(pounds/acre) afClover60400,0005-8nr¼-½FBall ½-1ECrimsonClover60150,00015-2515-20¼-½GHairy Vetch6016,00020-255-10½-1ERed 0015-20nr¼-½PSoybean602,80060-7540-60½-1ESunn Hemp6015,00020-4020-40½-1EWhite -¼EChicory--425,0004-5nr¼-½FForbs/Other:ˇ Adapted from University of Georgia Cooperative Extension Circular 814, “Planting Guide to Grasses and Legumes forForage and Wildlife in Georgia,” by Hancock and Lee (2017); the fifth edition of Southern Forages by Ball et al. (2015);and Common Grasses, Legumes and Forbs of the Eastern United States: Identification and Adaptation by Abaye(2010). Cover crop seeding rates adapted from Managing Cover Crops Profitably with data from JC Plant MaterialsCenter and MS Plant Materials Center and review by various Southeastern experts.‡Ratings are P Poor, F Fair, G Good, and E Excellent.* nr Not recommended as a cover crop.** These values are not listed in reference books and are highly variable in the available scientific literature.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops5
Adjusting for purelive seedSeed quality differs from lot to lot. Someseed lots may be relatively low in viableseed or contain more inert material or weedcontamination. Seeding rates, such as thosein Table 1, assume high quality seed and areusually listed on a pure live seed (PLS) basis.Thus, one should always ensure that theseeding rate being planted is corrected fordifferences in viable seed and purity. To adjustfor these factors, calculate PLS for each seedlot by multiplying the percentage of viableseed (percent germination) by the purity of theseed (percent pure). For example, the seedlot described on the certified seed tag seen inFigure 5 indicates 80% viable seed (percenttotal germination) and 95% pure seed.Therefore, this bahiagrass seed lot wouldhave 76% PLS (0.80 x 0.95 0.76). Thus, if therecommended seeding rate for this crop is10 pounds/acre, one would need to apply 13pounds/acre using this seed lot (10/76% 13).Several warm-season grass species naturallyproduce seeds that have a substantial amountof dormant seed. Dormant seed is live,viable seed and is likely to germinate, but itwill not immediately germinate because ofphysiological constraints. Usually, the dormantseed will germinate several days to a fewweeks after it is sown. The bahiagrass seedlot shown in Figure 5 has 20% dormant seed.It is not uncommon for 20- 60% of somewarm-season grass species to be classifiedas dormant seed. When calculating PLSwith seed lots containing dormant seed, thepercentage that is dormant is included withinthe viable seed percentage (i.e., percentgermination plus percent dormant seed).Figure 5.This bahiagrass seed lot (variety blurredintentionally) is 95% pure and has an 80% totalgermination, so it contains 76% PLS. Note that thisseed tag is blue, indicating certified seed. Usersshould buy certified seed whenever possible to ensuregenetic purity and the highest-quality seed product.Most annual species have high germinationrates and usually have low levels of inertmatter or weed seed. So, adjusting for PLSwhen establishing a cover crop or annualforage crops is usually impractical orunnecessary as long as the germination rateis 80% or greater.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops6
Adjusting forseed coatsMany seed suppliers will add a seedtreatment and/or coating to the seed(Figure 6). Seed treatments often includeinsecticides or fungicides that guard againstpest challenges to seed or seedlings butusually have no significant effect on seedweight or flow characteristics. In contrast,seed coatings involve the application ofliquid binders and powdered fillers that,when combined, coat the entire seed. Thesecoatings are designed to alter the flow rateof the seed; act as a carrier for microbialinoculants, insecticides, or fungicides; and/or enhance seed survival and seedlingdevelopment. Seed coatings that carryRhizobia inoculum for their specific legumespecies have proven effective and area convenient alternative to inoculatinglegumes just prior to planting. The benefitsof other seed coatings (such as thoseapplied to grass seed) are hotly debated.Some have demonstrated marginalimprovements in establishment success,occasionally even at lowered seedingrates. However, several trials conducted byunbiased third parties have observed littleor no improvement in establishment success.Certified-organic growers should pay closeattention, as most seed treatments andcoatings are prohibited materials. Organicgrowers should buy raw, untreated seedand inoculate legumes just before planting.Setting aside the questions of efficacy, seedcoatings are likely to influence the rate theseed is metered by a drill and can add aconsiderable amount of weight or volumeto the seed (usually 20-50%). Seedingrate recommendations like those in Table 1and settings in the owner manual of adrill assume uncoated seed. Therefore,the seeding rates will need to be adjustedto account for the weight of seed coatings.The amount of weight added by the seedcoating is reported on the seed tag asadditional inert matter (Figure 7).Figure 6.Alfalfa seed (top) is shown without acoating compared to a relatively light (30%) coating,and red clover seed (bottom) is shown without a coatingcompared to a heavier (50%) coating.Figure 7.This seed lot of crimson clover was coatedwith a 50% coating that included a fungicide treatment.With 49.85% purity and 85% germination, this seed lotcontains 42% PLS.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops7
By adjusting the seeding rate for PLS, one will account for the seed coating. For example, the seedlot of crimson clover depicted in Figure 7 reports 85% viable seed (percent total germination) and49.85% purity, which results in 42% PLS (0.85 x 0.4985 0.42). So if the recommended seeding ratefor this crop is 15 pounds/acre, one would need to plant 36 pounds of coated seed per acre using thisseed lot (15/42% 36). Consequently, one should evaluate the cost effectiveness of coated seed.Research is mixed as to whether or not the adjustment for coated seed to PLS is necessary. Somestudies indicate similar biomass production at only 50% of the PLS rate. In other words, if 15 lbs/ac isthe target PLS rate, planting 20 lbs of coated seed/acre provided similar biomass in those studies.Other studies do indicate that adjusting for PLS increases biomass. Producers have to weigh the riskof decreased biomass against increased seed cost using PLS adjustment.Drilling seed mixturesEstablishing forage or cover crop stands consisting of mixtures of several species has becomeincreasingly popular (although the benefits are often not apparent). From a practical standpoint, thiscan pose several challenges when the seed mixtures contain species that differ in seedling vigorand/or have seed of various sizes and shapes (Figure 8). When a slow-establishing species is pairedwith a quick-establishing species, one could expect the latter to dominate the former. In general,annual species are faster to establish than perennial species, so it is usually best to avoid plantingannuals and perennials simultaneously in a forage planting. Some perennial species may bemixed with annual species for cover cropplantings. In some instances, annuals canbe interseeded into perennials to increaseforage quantity or quality in certainseasons. This should only be done if theperennial species is well-established.When planting cover crops, annualspecies should be used. Mixturescan provide a variety of functions.For example, a mixture of legume andgrasses can improve weed suppressionover a pure legume stand while stillproviding nitrogen for the subsequent cashcrop. At the proper seeding rate, the grasscan serve as a nurse crop for the legume.Figure 8. Complex seed mixtures are sometimes usedo establish pastures or cover crops. Carefully choosingthe species used in the mix and accounting for differencesin seed size and shape is crucial to ensuring the correctseeding rate results.Grasses and legumes are often plantedsimultaneously using both the large andsmall hopper boxes on a drill. Use thelarge hopper box for the largest-seededspecies when planting such mixtures. For example, overseeding annual ryegrass and crimson cloverinto Bermudagrass in the autumn is a common practice. When doing so, it is best to use the largehopper box for the ryegrass seed and the small hopper box for the clover seed. An analogous covercrop situation would be planting oats and crimson clover with the oats in the large seed hopper boxand clover in the small seed hopper box. Regardless, one should calibrate both the large and smallhopper boxes independently to assure both are planting the appropriate seeding rates.UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover Crops8
Some complex mixtures of four or more species are sometimes used, particularly in cover cropmixtures. Some of these mixtures may differ considerably in seed size and rate. The first challengeis determining what size opening the seed metering unit should be set to as a starting point forcalibration. In general, it is best to start with the metering unit set to distribute the largest seed in themixture at the rate it would be drilled and adjust from there. For example, a summer annual mixmay contain sorghum-sudangrass, pearl millet, forage soybeans, and forage brassicas with a goalof planting 4, 3, 15, and 1 pound/acre, respectively. These seeds are of considerably different sizes,so one should begin the calibration with the seed metering unit opening set to distribute 15 pounds/acre of soybeans/acre. In this case, if the total weight of the seed mixture is equivalent to 23 pounds/acre at this setting, the drill setting will be set close to the appropriate setting. If not, calibration canguide the user
UGA Cooperative Extension Bulletin 1510 Preparing and Calibrating a No-Till or Conventional Drill for Establishing Forage or Cover C
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