Absorption and Re‐distribution of Nitrogen during Growth and Development of Field Bean, Vicia faba

The absorption of nitrate by field bean plants at different times of development was investigated to determine the distribution and subsequent utilization of N up to the maturity of the beans. Nodulated plants were grown in sand culture and pulse‐labelled with 15NO3 for 4 short periods during development. Whole plants were sampled at intervals until maturity and analysed for total nitrogen and 15N. There was a rapid increase in the bean dry weight and total N after fruit set and, at maturity, the beans contained about three times as much N as had ever been in the rest of the plant. Nitrate absorption continued steadily throughout plant development but nodule N fixation made a progressively greater contribution to the total N in the plant. Over a quarter of the total 15N absorbed was found in the roots immediately after each treatment and little of this was subsequently translocated upwards in spite of the large increase in shoot N taking place. Above ground the most powerful “sink” for recently absorbed and redistributed N was initially the youngest vegetative tissue. However after fruit set competition developed between the growing tip and the developing beans until at the later stages the beans became the more powerful. Quantitatively redistribution made only a small contribution to bean N.