Growth and nitrogen uptake of two broccoli cultivars

Dry weight (DW) accumulation and partitioning, and N uptake and allocation for two broccoli cultivars ('Parthenon' and 'Montecarlo') grown in a Mediterranean environment, were studied. Transplanting was done on 25 September 2008 (3.5 plants/m2) and harvesting on 29 January 2009. Plants were fertilized with 130 kg ha-1 of N. Starting from 21 days after transplanting up to commercial maturity of corymbs, eight destructive samplings were performed. At each sampling, fresh and dry weight of leaves, stems and corymbs were recorded. Kjeldahl-N concentration was also determined on dried aerial parts of the plant. Nitrogen uptake data for each cultivar were used for modeling the decrease in N concentration in the aboveground plant DW as affected by plant DW increase, by using the exponential curve: %N=aDW-b. In 'Montercarlo' maximum aerial DW accumulation occurred 15 days before the harvest (5.3 t ha-1), while in 'Parthenon' DW continuously increased up to the end of the growing cycle (5.0 t ha-1). The maximum corymb DW accumulation was reached earlier in 'Montecarlo' that in 'Parthenon'. 'Montecarlo' compared with 'Parthenon' showed higher stem DW and an earlier leaf senescence. No difference was observed in the harvest index (0.26) and in the corymbs fresh yield. Partial factor productivity index indicates that 85.7 kg of fresh product was obtained for each kilogram of N fertilizer. Nitrogen dilution curve fitted for 'Montecarlo' had a and b parameters slightly higher compared with 'Parthenon' curve. Total N uptake was higher in 'Montecarlo' than in 'Parthenon', while corymb N uptake was 74 and 71 kg ha-1, respectively. Total plant nitrogen use efficiency (NUEtotal), showed by the total aerial DW accumulation per unit of up-taken N (NUE total), was similar for both cultivars, whereas 'Parthenon' exhibited higher nitrogen efficiency in head production per unit of up-taken N (NUE yield) than 'Montecarlo'.