Dynamics of nitrogen and dry-matter partitioning and accumulation in broccoli (Brassica oleracea var. italica) in relation to extractable soil inorganic nitrogen

Abstract

. 1999. Dynamics of nitrogen and dry-matter partitioning and accumulation in broccoli (Brassica oleracea var. italica) in relation to extractable soil inorganic nitrogen. Can. J. Plant Sci. 79: 277-286. The effects of six rates of N fertilization (0, 125, 250, 375, 500 and 625 kg N ha -1 ) on the dynamics of N utilization relative to extractable inorganic N in the soil profile were determined for broccoli in three growing seasons. The amount of pre-existing extractable inorganic N in the soil was lowest for the spring planting, followed by the early-summer then late-summer plantings. During the first 2 wk after transplanting, plant dry-matter (DM) and N accumulation rates were low, and because of the mineralization of soil organic N the extractable soil inorganic N increased over that added as fertilizer, especially in the top 30 cm. From 4 wk after transplanting until harvest, DM and N accumulation in the plants was rapid and corresponded to a rapid depletion of extractable inorganic N from the soil. At high N-fertilization rates, leaf and stem DM and N accumulations at harvest were similar among the three plantings. However, the rates of accumulation in the two summer plantings were higher before and lower after inflorescence initiation than those in the spring planting. Under N treatments of 0 and 125 kg ha -1 , total N in leaf tissue and the rate of leaf DM accumulation decreased while inflorescences developed. There was little extractable inorganic soil-N during inflorescence development in plots receiving no N fertilizer, yet inflorescence dry weights and N contents were ≥50 and ≥30%, respectively, of the maxima achieved with N fertilization. These results indicate that substantial N is translocated from leaves to support broccoli inflorescence growth under conditions of low soil-N availability. De quatre semaines après la mise en pleine terre jusqu'à la récolte, l'accumulation rapide de la m.s. et de N observée dans les plantes correspondait à une exportation rapide du N minéral extractible du sol. Aux taux de fumure N élevés, l'accumulation de m.s. et de N dans les feuilles et les tiges à la récolte était semblable quelle que soit la date de la plantation. En revanche, les taux d'accumulation observés dans les deux plantations d'été étaient plus élevés avant et plus bas après l'initiation de l'inflorescence que dans la plantation de printemps. En présence d'apports de N de fumure de 0 à 125 kg ha -1 , la teneur en N total des tissus foliaires et le taux d'accumulation de m.s. dans les feuilles diminuaient à mesure que l'inflorescence se développait. Dans les parcelles ne recevant pas de fumure N, il restait peu de N minéral extractible dans le sol durant la formation de l'inflorescence, bien que le poids sec et la teneur en N de cette dernière étaient, respectivement, supérieurs ou égaux à 50 et 30 % des maximums obtenus en présence de fumure azotée. Ces résultats laissent voir qu'en régime de faible disponibilité de N du sol, une quantité appréciable de N est soutirée des feuilles du brocoli pour subve...

Broccoli growth in response to increasing rates of pre-plant nitrogen. II. Dry matter and nitrogen accumulation

“…Nitrogen accumulation was limited during the first 2 wk after planting, after which nitrogen content increased rapidly until the heads were first visible (approximately 1 cm diameter). Magnifico et al (1979) and Bowen et al (1999) reported a similar pattern in nitrogen accumulation over time. This model could be used to develop improved nitrogen application strategies, such as a feed-on-demand system.…”

“…This differed from 2002, when at 14 d after planting, the rate of DM accumulation increased with high nitrogen rates but at 56 d after planting, the rate of DM accumulation was highest in the 0 kg N ha (1 plots. Magnifico et al (1979), Beverly et al (1986) and Bowen et al (1999) reported a similar pattern in DM accumulation over time, although values for DM varied among studies.…”

“…This decline reflects uptake of soil nitrogen by the broccoli crop, immobilization, and/or loss of nitrogen from the system. Bowen et al (1999) reported much higher soil NO 3 ( -N content at planting and an initial increase after transplanting in British Columbia with or without additional fertilizer nitrogen. This is likely due to differences in soil type and environment.…”

“…Bowen et al (1999) found that soil nitrogen increased during the first 2 wk after transplanting broccoli and then decreased rapidly. Residual soil NO 3 ( -N levels at harvest increased at higher rates of applied nitrogen fertilizer, with maximum levels ranging from 87 to 350 kg NO 3 ( -N ha (1 , depending on the rate of nitrogen applied and soil sample depth (Kowalenko and Hall 1987;Zebarth et al 1995;Thompson et al 2002b).…”

“…However, split applications were not effective in improving nitrogen uptake or nitrogen use efficiency in cauliflower (Brassica oleracea L. botrytis L.) (Everaarts et al 1996) or potato (Solanum tuberosum L.) (Zebarth et al 2004). Bowen et al (1999) concluded that split applications of nitrogen were not necessary for broccoli in British Columbia as the crop was efficient at taking up nitrogen and there was no evidence that nitrogen applied at planting was leached below the rooting zone of the crop during the growing season.…”