NITROGEN UPTAKE IN RELATION TO WATER AVAILABILITY IN WHEAT

Nitrogen uptake and distribution in wheat (Triticum aestivum L.) are dependent on environmental conditions and in particular on the water regime. Under Mediterranean conditions, where high water stress at the end of the crop cycle is frequent, nitrogen uptake can be reduced, affecting yield and quality of the grain. To disclose these relations a field 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). All treatments received 50 kg ha-1 of N prior to sowing and were top-dressed with 140 kg ha-1 of N, splitted in two applications, Kjeldahl N was determined in green leaves (GL), yellow leaves (YL), stems (ST), chaff (CH) and grain GR). N uptake after anthesis was 40% of the total in W2, but was not noticeable in the other two treatments. N concentrations in the total above-ground plant dry matter, and in both YL and ST were not very different according to treatment, but water availability increased grain-N concentration. It seems, therefore, that grain protein concentration and N uptake can be substantially increased by late irrigations.