Abstract
'South Bay' lettuce (Lactuca sativa L.) seedlings were fertigated in floating styrofoam flats in nutrient solutions containing N at 0,15,30,45, or 60 mg-L-1. Increasing N from 0 to 60 mg-L"1 resulted in an increase in transplant shoot and root mass. The increase in shoot mass was much greater than for root mass in response to N rate, and resulted in lower values for root:shoot ratios. Relative growth rate, specific leaf area, leaf area ratio, and leaf mass ratio increased with an increase in applied N, suggesting improved transplant growth at higher N rates. Growth responses of lettuce transplant shoots and roots to applied N were consistent, regardless of season or stage of growth. Leaf tissue N always was increased by N rate applied. Lettuce head mass in the field at harvest was increased by pretransplant application with increased N. The heaviest heads were obtained from transplants grown with 60 mg-L-1 in the greenhouse. This work demonstrated that at least 60 mg-L1 N supplied via floatation irrigation, was required for improved transplant shoot and root growth in a peat + vermiculite mix low in NO3-N. Transplants grown with 60 mg-L1 N versus 15 mg-L1 N were bigger at transplanting and resulted in improved head mass at harvest.
