Influence of planting date on yield and other characteristics of soybeans grown in southeast Missouri

Maturity, yield, seed quality, percentage oil, percentage protein, and iodine number of the oil are reported for five varieties of soybeans planted April 20, May 10, June 1, June 20, and July 10 in nursery rows during the four-year period 1942 through 1945, at the Southeast Missouri Branch Experiment Station, Sikeston, Mo. The soybean varieties were selected to represent maturity groups commonly grown from the central Corn Belt to the northern Cotton Belt. These varieties differed in their response to the various planting dates. For the four year mean, the varieties X dates interaction was highly significant for yield, protein content, and iodine number, and was significant for oil content. This study shows that early maturity can be obtained only by planting early maturing varieties at an early date; whereas early planting of full-season varieties results in only slightly advancing the maturity date. If planting is delayed until the first week of July, the use of Dunfield or any other similarly early variety will result in only slightly earlier maturity than if a full-season soybean, such as Ralsoy, is planted. The average of the four years' yield data indicates that the best date of planting for each variety is later as the natural number of days required for maturity decreases. Ralsoy and S100 were superior in yield to any other variety tested regardless of the date at which they were planted. Ralsoy yielded highest when seeded from April 20 to June 1, but S100 yielded highest when planted from June 1 to July 10. Date of planting had little effect on the seed quality of Ralsoy and S100. However, the earlier plantings of Boone, Chief, and Dunfield were of inferior seed quality as compared to later plantings. Poor seed quality was associated with early maturity which resulted from early plantings of the naturally short season varieties. Oil content was not appreciably affected by date of planting except for the latest date. For all five varieties this last date of planting resulted in the lowest average oil content. Relatively high oil content for a given variety was obtained when the variety was planted within the optimum range for the best yields. Protein content had a tendency to vary inversely with oil content. Seed with the highest percentage of protein was usually obtained when yields were relatively low. The iodine number of the oil of all varieties showed a tendency to increase with lateness of planting.