Phosphorus restriction: control of transplant growth

Control of tomato (Lycopersicon esculentum Mill.) seedling growth and heigh t during production in the greenhouse is critical for efficient subsequent transplanting and acceptable field performance. Height can be reduced by P fertilisation. Eliminating P from nutrient solutions severely restricted gr owth. When fed a 10 mg P L-1 in the nutrient solution, seedlings were 11 cm tall after 49 d of growth, but only 3 cm tall without P. Intermediate P re duced height within this range. Transplanting was simulated after 49 d of s eedling production by transferring the transplants to a temperature-control led root chamber in larger volume cells plus fertilisation with a complete nutrient solution. Transplant growth with a complete nutrient solution caus ed differential growth according to the prior P feeding regime. New root gr owth in the various treatments was dependent on root growth during the tran splant stage. However, shoot growth differed greatly among the P levels. Se edlings grown without any P during transplant production grew very slowly w ith only a 25% increase in leaf growth after 9 d. With the 2 mg L-1 feeding during transplant production of leaf dry weight increased over 200% during the 9-d period. In conclusion, seedling growth restriction can be achieved by P deprivation; the amount of P deprivation, however, affects subsequent seedling growth.