The Journal of Horticultural Science & Biotechnology
Vol. 79 No: 3
Growth analysis of broccoli in relation to fertilizer nitrogen application
I.M VAGEN, A.O. SKJELVAG and H BONESMO
Six field experiments with different planting dates over three years in the South of Norway were used to analyse biomass production of broccoli. N was applied at rates of 0, 120, and 240 kg ha-1. Mineralized N levels in soil before planting differed among the experiments. Crop biomass, leaf area index (LAI), and accumulated intercepted photosynthetically active radiation (PAR) increased with enhanced N rate. So did also radiation use efficiency (RUE), but not significantly from 120 to 240 kg ha-1. Thus, crop biomass increased to the highest N rate rather by more intercepted radiation than by enhanced RUE. RUE reached saturation level when the sum of applied N and Nmin in soil before planting was about 200 kg ha-1. There was a strong effect of N application on early plantings, when low temperature and possibly oversaturation of light were the most likely reasons for low LAI, RUE, and RGR at low or no N application. The plant N concentration decreased with increasing biomass over time. Of two alternative relationships of critical N concentration (Nc) suggested by Greenwood et al., the linear one, which gave the higher estimates, fitted better. Both equations were evaluated on the correspondence between a relative N concentration N/Nc = 1 and maximum relative values for: biomass, LAI, accumulated intercepted PAR, and RUE. However, a curvilinear function for Nc might produce a higher correlation over the whole range of plant N concentrations. RUE and accumulated intercepted PAR approached a saturation level at a lower relative N concentration than did biomass and LAI, suggesting that N was more limiting for biomass production than for PAR interception and RUE at N rates below the highest application rate. Incident radiation was fully intercepted at a low LAI, resulting in a low RUE.
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