Persian shallot (Allium altissimum Regel.) was grown under fully irrigated conditions in a 2-year-field experiment (2010 - 2012) in the northeast of Iran to study and determine (i) radiation and nitrogen-use efficiency, (ii) growth analysis, (iii) carbon partitioning,and (iv) biomass production under different rates of nitrogen and cultivated bulb weights. The field experiment was performed as a randomized complete block design with a factorial arrangement of four nitrogen levels (control (100), 200, 250, and 300 kg ha-1) and two levels of cultivated bulb weight (10 - 20 and 20 - 30 g) with three replications in both years of the experiment. Our results showed that increasing the nitrogen rate and bulb weight significantly enhanced Persian shallot production. Radiation-use efficiency (1.06 to 1.27 g MJ-1), maximum crop growth rate (8.3 to 11.2 g m-2 d-1), and maximum leaf area index (1.3 to 2.6) showed a positive correlation with nitrogen rate and bulb weight. Nevertheless, nitrogen-use efficiency (0.87 to 2.38 g bulb per g nitrogen) indicated a negative relationship with applied nitrogen rate. Moreover, increasing the nitrogen application rate increased the carbon allocation to above-ground organs. On the other hand, nitrogen limited conditions increased the carbon allocation to underground organs and carbon remobilization from stem and leaves to bulbs during the late growth season. Increasing the nitrogen application rate and bulb weight may be appropriate practices for enhancing Persian shallot production; however, evaluation of the impact of nitrogen on the quality of bulbs needs to be investigated.

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