Ann. appl. Biol. (1983), 102,399406 Printed in Great Britain 399 Uptake and distribution of nitrogen in wheat plants supplied with different amounts of nitrogen after stem elongation BY PILAR PEREZ, R. MARTINEZ-CARRASCO AND L. SANCHEZ DE LA PUENTE Centro de Edafologia y Biologia Aplicada, Salamanca, Spain (Accepted 30 September 1982) SUMMARY The uptake of nitrogen and its distribution between shoots and between organs within shoots in wheat (Triticurn aestivum) was studied from the start of stem elongation to 28 days after anthesis in a glasshouse experiment with eight nitrogen levels between 0.1 and 12.8 mequiv./litre. There was no net uptake of nitrogen in plants supplied with 0.8 mequiv./litre or less; with more nitrogen the absorption increased linearly. Twenty to 44% of the total plant nitrogen was absorbed after anthesis, this fraction increasing with nutrient supply. The nitrogen allotted to the main shoot decreased until the onset of anthesis and increased thereafter at the expense of the tillers, except with 12.8 mequiv./litre, where nitrogen percentage in the main shoot decreased also after anthesis. Raising nitrogen supply increased the proportion of plant nitrogen recovered in the tillers. Nitrogen accumulated in the ear after emergence and by the 28th day after anthesis it contained between 52% and 73% of the total plant nitrogen. The ear of the main shoot had a higher proportion of shoot nitrogen than that of the tillers. The fraction of ear nitrogen supplied by retranslocation decreased from almost 100% with 0.8 mequiv. N/litre or less to nil with 12.8 mequiv./litre. Increasing nitrogen application decreased the fraction of total nitrogen allocated to the ear. INTRODUCTION The absorption of nitrogen by cereals has been said to take place mainly in the early stages of growth, with little uptake occurring after anthesis. Thus, Watson, Thorne & French (1958) found that 75% of final plant nitrogen was present in the plant at ear emergence, and other authors reported values of 90% at that stage or 83% at anthesis (Austin & Jones, 1975; Austin, Ford, Edrich & Blackwell, 1977). However, considerable uptake of nitrogen after anthesis was observed in healthy crops under favourable growing conditions (Spiertz & Ellen, 1978). The ability for continued absorption of nitrogen after anthesis might therefore be maintained, the actual uptake being dependent upon nitrogen availability and soil moisture. During development there is a relocation of nitrogen in the plant, both between tillers and between organs, with a large relocation from the stem and leaves to the ear (Austin & Jones, 1975). The shoots of a plant are interdependent, the relation between tillers and main shoot being probably regulated by apical dominance (Thorne, 1962a; Fletcher & Dale, 1974; Smith & Rogan, 1980). As late-emerged tillers obtain their nitrogen by the root of the main shoot and primary tillers (Rawson & Donald, 1969), the distribution of the nutrient will determine the actual amount of nitrogen allocated to each shoot. Nitrogen application, which has been shown to increase tiller survival (Aspinall, 1961; Thorne, 1962a, b; Bremner, 1969; Power & Alessi, 1978), might affect nitrogen distribution, but detailed studies of the mobilisation of the nutrient between shoots and its modification by nitrogen supply are scarce. The relocation of nitrogen to the ear may be controlled in part by the demand of the grains 0 1983 Association of Applied Biologists