The route-sampling method of estimating crop production has been extended to soybeans in a preliminary survey which is reported here. In 1941, just prior to harvest, 67 fields in eight east central Illinois counties were sampled for yield, percent protein, percent oil and iodine number of the oil.
Protein percent, oil percent and iodine number of the oil can be estimated satisfactorily, but estimating yield is more uncertain pending the accumulation of information on adjusting for harvesting losses and other factors which cause the sample average yield to be too large.
The yield of seed per acre differed with the method of planting (width of rows), indicating for the season studied that soybeans should have been planted in rows about 2 feet apart. The iodine number of the oil was lower for fields with wide rows than for drilled fields. This was attributed to difference in date of planting rather than method of planting.
It was concluded that two subsampling units should be taken per field and that the optimum size of subsampling unit is approximately 7 square feet.
Other investigations have shown that after the pods are fully distended there is little or no change in yield or chemical composition, indicating that production and quality can be estimated well in advance of harvest.
Houseman, Earl E.; Weber, Charles R.; and Federer, Walter T.
"Pre-harvest sampling of soybeans for yield and quality,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 27
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol27/iss341/1