Influence of nitrogen availability on seed nitrogen accumulation in pea

The final seed nitrogen concentration (the ratio of seed N and dry matter c ontent) is highly variable in pea (Pisum sativum L,) and N remobilization d uring seen filling may limit yield by restricting the seed filling period. This study was conducted to determine how seed N accumulation is regulated in pea. The effect of N availability and distribution on individual seed N accumulation rate at different nodes was investigated in three genotypes gr own in the field and glasshouse under various levels of N fertilizer, depod ding, and defoliation, The N content of vegetative plants parts (stems, lea ves, podwalls) and seeds from three mainstem nodes were regularly recorded. Plant N available to the seeds at a given time was assessed as the sum of the amount of N still available for remobilization in vegetative parts and the amount of N accumulated by the plant. The results indicate that the N a vailable in a plant at a given time can be considered as one common pool ac cessible to all seeds and equitably divided among them, Thus, the rate of i ndividual seed N accumulation was unaffected by intra-plant position of see ds, This rate increased with the amount of N available per seed until a max imum rate of individual seed N accumulation (43 mu g seed(-1) degree-day(-1 )) was reached. The relationship established between the rate of individual seed N accumulation and the plant N available per seed will be useful to i mprove models simulating yield and final seed N concentration in legumes.