Effects of covering materials and incorporated herbicides on lettuce stands under three irrigation treatments

Current Cultural Practices in California lettuce require a thinned stand with single plants spaced 12 to 14 inches apart on a 40-inch double-row bed. The ideal situation would be to plant the precise number of seeds to obtain such a stand, but the many hazards to germination, emergence, and plant survival make it impossible to plant consistently to a stand. At present, it appears more practical to precision-plant fewer seeds than are now planted commercially—and then thin to the desired stand with a selective thinner. This is a progress report of work to develop such a planting system. Factors studied were irrigation techniques, chemical weed-control treatments, and the use of covering materials for soil-crust prevention. (Two planters were used, but no effort was made to compare the two machines.)