Investigations with the castor-bean plant. II. Rate-of-planting and date-of-planting tests

Thirty-five rate-of-planting tests and 10 date-of-planting tests were conducted with the castor bean plant from 1941 to 1943 at various locations in the southern half of the United States. This early work on rate-of-planting was done with a known number of established plants rather than a known amount of seed planted since the latter introduced questions of viability, depth of planting, emergence, seedling diseases, and seed treatment. The number of plants per unit area is an important factor in determining yield, but with a given number of plants the present varieties adapt themselves readily to various spacings and arrangements. On the basis of yield and ease of hand harvest (number and size of racemes), the optimum number of plants appears to be about 5,000 per acre, which is roughly one plant each 2 1/2 feet in 40 or 42 inch rows. The spacing within the row can vary between 2 and 3 feet without greatly affecting yield or ease of harvest. Also, similar yields can be expected by using the equivalent number of plants in checked rows. On the basis of field observations with average quality seed of the common varieties in a good seedbed, this number of plants will be produced by seeding approximately 10, 8, and 7 pounds of the Conner, Doughty 11, and Kentucky 38 varieties, respectively, per acre. Comparison was made of yields from plantings made as early as March 25 (at Beeville, Texas) and as late as June 30 (at Columbia, Missouri). As would be expected with a plant having an indeterminate growth habit, the greatest yields were produced by the earliest plantings. It is not recommended, however, that planting be done extremely early because of the difficulty of seedbed preparation, the danger of freezing weather, and germination problems in cold soil. The optimum planting date in most of the region of adaptation appears to be a few days ahead of corn planting time for the particular area.