Nitrogen

Abstract

This work was performed in order to obtain information about the relation between plant N‐levels and yields by means in vivo nitrate reductase activity (NRA) determinations in leaves of tomato and cucumber. Plants were grown under glasshouse conditions in solutions containing different N‐levels.

At different growth stages, leaves were sampled and NRA, total N and growth were determined.

Ammonia and NO₃‐N have a considerable influence on the NRA by way of the feedback mechanism and NRA was affected by growth stage.

This, however, is dependent on nitrification conditions when soil is applied.

In our conditions, maximum NRA values associated with maximum yield were approximately 3.40 ‐ 3.70 μmol NO₂‐ formed (g fresh weight, hr)^‐1 for tomato and 4.50 ‐ 4.70 μmol NO₂ ^‐ formed (g fresh weight, hr)^‐1 for cucumber plants.

Key words:

• Tomato
• cucumber
• N‐total
• nitrate reductase
• yield