The primary problem with stripper harvesters is the high foreign material content of the seed cotton delivered to the cotton gin. Modifications to the stripper harvester mechanism and proper machine adjustments based on plant characters and operating parameters can help reduce the amount of harvested foreign material to a more satisfactory level for ginning and textile processing.

Adjustable combing pans mounted under the stripper rolls of the harvester are designed to reduce seed cotton losses during harvest. Previous research by the author on various cotton stripper modifications indicated that improper adjustments of the combing pans may contribute to the foreign material problem. The objective of this study was to determine the effects of combing pan spacing on harvest loss and foreign material content of seed cotton. A reduction in the amount of foreign material collected by the cotton harvester can reduce ginning costs and help maintain lint quality. Also, a decrease in stick content in seed cotton could significantly reduce the chance of a grade reduction because of excessive bark in the ginned lint. Bark is a fibrous material from the stalk and limbs of the cotton plant that often becomes embedded in the lint of stripper harvested cotton.

The variables in this study were pan setting(I-1/4, 2-1/2, and 3 inches), stripper speed (3 and 6 mph), and plant height (24 and 30 inches). The cotton was harvested with a 2 row self propelled stripper which had 3 rubber paddles and 3 brushes per roll, synchronized brush to brush. The paddles were reduced to a 1 inch width to help reduce stick content in a manner consistent with earlier studies. Bur cotton samples were taken at the trailer and at the feeder apron in the gin, and lint samples were taken before and after two stages of lint cleaning.

Increases in pan spacing increased harvest loss for both tall and short cotton plants. The 3-inch pan spacing wasted significantly more cotton than did the 1 1/4 or 2 1/2 inch spacings for the taller cotton. The harvest loss for the 3 Inch spacing was significantly greater than the 1 1/4 inch spacing for the short cotton plant. Harvest speed had a significant effect on harvest loss when harvesting the tall cotton where the harvest loss was 50% greater. A similar increase in harvest loss with increased speed was found for the shorter cotton but in this case the loss values were not statistically different.

The effect of harvest speed and pan spacing on foreign material content was not as great as originally expected. Bur, stick and fine trash contents of cotton collected in the trailer were not significantly affected by either variable. This was true for both plant sizes. While harvesting tall cotton, however, there was a tendency for the wider pan spacings to decrease fine trash content at the 3 and 6 mph speeds and reduce stick content at the 3 mph speed.

There was no significant difference in the foreign material content of samples collected at the feeder apron. HVI data for samples taken before and after lint cleaning were not significantly affected by pan spacing or harvest speed. Grade reductions due to bark were greater for the short cotton harvested at low speed(3 mph) and with a narrow pan spacing(1 1/4 Inch) than for other test -combinations. For the tall cotton, the low harvesting speed and the 2 1/2 inch pan spacing produced the lowest bark count obtained in this study.