Interactions

Abstract

The effects of withholding nitrate, phosphate or potassium from young lettuce plants for short periods were studied in glasshouse experiments to examine the importance of continuity of nutrient supply on growth and development. The results showed that reductions in relative growth rate following interruption in the nitrate or phosphate supplies occurred when the N and P concentrations coincided closely with the critical levels of these nutrients in the plants. Withholding potassium, by comparison, reduced growth even when its internal concentration was still high. This was probably due to a decline in the total ionic concentration within the plants, rather than to a specific deficiency in potassium. The relative growth rate of all deficient plants recovered quickly when each of the nutrients was resupplied, but they were unable to compensate completely for any losses in growth which had previously occurred. There was no evidence of substantial treatment effects on maturity date in any of the experiments.

Key words:

• Nitrate
• phosphate
• potassium
• temporary deficiency
• yield