Carrier: Seed Ratios and Planting Rates (page 3 of 9)
Bulky seed to fertilizer bulk ratios must be considered. Most bulky and less bulky mixes disperse well when the seed-fertilizer ratio does not exceed 1 : 20 (5 pounds of seed to 100 pounds of fertilizer). For less bulky seeds such as those of bromegrass, crabgrass, fescue, orchardgrass, ryegrass, and wheatgrass, more seed and less fertilizer can be used. A mixture of up to 20 pounds of seed to 100 pounds of bulk-weight fertilizer usually flows well with the less bulky seeds. When extremely bulky, rough-husked, or awned seeds are used, a lower ratio of seed to fertilizer, near 1 : 40 (5 pounds of seed to 200 pounds of fertilizer) may be needed. In all of these cases, the weight of the mixture equals the planting rate per acre. For example, 5 pounds of seed per acre and 100 pounds of net-weight fertilizer per acre would be applied for a total of 105 pounds per acre.

The bulk density of the seed-fertilizer mixture can be greater or less than that of wheat seed, which is 60 pounds per bushel. The relative bulk density is part of what influences equipment planting rate settings and mixture flow from the equipment. For example, a planting of 5 pounds of less bulky crabgrass seed to 100 pounds of fertilizer (18-46-0) per acre has a higher bulk density than wheat at about 65 pounds per bushel, 20 pounds of less bulky bromegrass seed to 100 pounds of fertilizer per acre has a bulk density of about 54 pounds per bushel because of the higher volume of low-weight seed, and 20 pounds of very bulky native grass seed to 200 pounds of fertilizer per acre has the lowest bulk density of the three, or about 45 pounds per bushel.

Because of bulk density and other factors, it is best to calibrate the drill with the mixture to be used so initial planting will be somewhat accurate. Drill manuals and other publications explain how to do that (Griffith, n.d.). To start calibration, set the drill or broadcast seeder for a readily flowable, less bulky seed-fertilizer mixture such as the crabgrass-fertilizer mixture at about 75 percent of the setting for wheat at the same rate per acre. Test and adjust the setting as needed. Settings for this type of mixture may range from near 75 percent to about 100 percent of the same setting for wheat seed.

Planting a mixture like that of the bromegrass example above may require a trial drill setting of 180 percent that for wheat at the same rate. The native grass mixture example may require a trial drill setting of 250 percent that of wheat at the same rate. The bulkier the seed and the lower the relative bulk density, the higher the relative setting must be.

Mixture distribution by individual drills is incredibly variable. Relative bulk density, fertilizer and seed characteristics, humidity, and other factors also influence distribution. Calibration is important, but actual field experience is more important because drills may behave differently during actual use than they do during calibration. Keep precise planting records of equipment settings, rates per acre, and planting conditions for future use. It is wise to indelibly record this information on the underside of the drill or fertilizer hopper lid for easy reference.