Phosphorus restriction: control of transplant growth
Control of tomato (Lycopersicon esculentum Mill.) seedling growth and height 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 growth. 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 reduced height within this range. Transplanting was simulated after 49 d of seedling production by transferring the transplants to a temperature-controlled root chamber in larger volume cells plus fertilisation with a complete nutrient solution. Transplant growth with a complete nutrient solution caused differential growth according to the prior P feeding regime. New root growth in the various treatments was dependent on root growth during the transplant stage. However, shoot growth differed greatly among the P levels. Seedlings grown without any P during transplant production grew very slowly with 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. Key words: Phosphorus, nutrients, tomato, transplant.