FATE AND EFFECTS ON YIELD COMPONENTS OF EXTRA APPLICATIONS OF NITROGEN ON SPRING WHEAT (TRITICUM-AESTIVUM L) GROWN IN SOLUTION CULTURE

Spring wheat (Triticum aestivum L.) was grown with daily additions of nitrate-N. The relative addition rate of nitrate-N was decreased stepw ise, and after 125 days of growth, 58 mg N plant(-1) had been introduc ed. The fate and effect of an extra addition of nitrate (20 mg N plant (-1)) at six different times during the ontogeny (37, 54, 66, 79, 94 a nd 108 days from sowing) on grain yield and grain protein concentratio n was investigated. The plants absorbed all or most of the extra nitra te at all stages of development evaluated. Dry matter production of bo th aerial vegetative parts and grains, but not roots, generally increa sed as a result of the extra nitrate addition. The increase in grain d ry matter was mainly an effect of an increased number of grains per pl ant. Extra nitrate applications had large effects on grain nitrogen co ntent at all stages, but the effect on main shoot and tiller ears vari ed depending on the time of application. Early applications, i.e. befo re anthesis, mainly led to increased yield with unchanged protein conc entration whereas late applications also led to increased grain protei n concentration. The largest effect on grain nitrogen concentration (2 5-30% increase) was obtained when the extra nitrate was applied late a fter sowing, i.e. less than four weeks before final harvest. As the ex tra dose of nitrate was labelled with N-15, it was possible to follow the movement of the extra nitrogen addition within the plant. Samples were taken at one and five days after N-15-addition and at final harve st. There were differences in the movement of N-15 depending on when i t was introduced. Generally, net movement of the N-15-labelled N into the grain increased with age at application until 94 days after sowing when a maximum of 90% of the added N-15 ended up in the grain.