Biological Systems Engineering


Date of this Version



Chapter in PRECISION AGRICULTURE (1996), P.C. Robert, R.H. Rust and W.E. Larson (eds.), p. 693-702.


Copyright © 1996 ASA-CSSA-SSSA


The inherent variability of seed and fertilizer application from volumetric metering devices is not readily recognized. The Canadian Prairie Agricultural Machinery Institute (P AMI) suggests a maximum coefficient of variation (CV) of 15% among outlets for seeding grain or applying fertilizer. P AMI does not report down-the-row variability of individual outlets. Parameters that influence variability of volumetric measuring external fluted wheels such as rotational speed of the metering wheel, product delivery rate, seed size, and cell collection lengths were examined.

In the first study, external fluted wheel meters on four grain drills were tested for seed delivery variability for wheat and soybeans, both among the metering outlets and down-the-row for individual meters. Tests on two additional drills, one an air drill and the other with external fluted metering, used two sizes of soybean seeds and two travel speeds. For wheat, down-the-row CV ranged from 12.5 to 22.5% and the CV among metering units ranged from 12.5 to 21 %. For soybeans, the CV ranged from 15.5 to 41.5% with the air drill having the lower CV. A faster travel speed gave a lower CV for both drills metering soybeans.

In a second study, when metering wheat, the seeding rate variability due to cell size and seeding rate were evaluated. Each meter was evaluated with cells 0.48 or 0.96 m in length and seeding rates of 60, 80,90, and 100 kg/ha. The down-the-row CV ranged from 10 to 28% with 0.48 m length cells, and from 4 to 22% with 0.96 m length cells. Some of these CVs may be too high for a metering mechanism such as the fluted wheel to be used in SSCM.