NITROGEN UPTAKE IN RELATION TO WATER AVAILABILITY IN WHEAT

Nitrogen uptake and distribution in wheat (Triticum aestivum L.) are d ependent on environmental conditions and in particular on the water re gime. Under Mediterranean conditions, where high water stress at the e nd of the crop cycle is frequent, nitrogen uptake can be reduced, affe cting yield and quality of the grain. To disclose these relations a fi eld experiment was carried out in Central Portugal. Wheat was grown on a clay soil (Vertisol) at three water treatments: rainfed (W0), with 80 mm of irrigation (WI) and with 50 mm and 70 mm irrigations (W2). Al l treatments received 50 kg ha-1 of N prior to sowing and were top-dre ssed with 140 kg ha-1 of N, splitted in two applications, Kjeldahl N w as determined in green leaves (GL), yellow leaves (YL), stems (ST), ch aff (CH) and grain GR). N uptake after anthesis was 40% of the total i n W2, but was not noticeable in the other two treatments. N concentrat ions in the total above-ground plant dry matter, and in both YL and ST were not very different according to treatment, but water availabilit y increased grain-N concentration. It seems, therefore, that grain pro tein concentration and N uptake can be substantially increased by late irrigations.