Plant Characteristics and Nutrient Composition and Mobility of Broccoli (Brassica oleraceavar.italica) Supplied with NH4+, NO3⊟or NH4NO3

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Abstract
Shelp, B. J. 1987. Plant characteristics and nutrient composition and mobility of broccoli (Brassica oleracea var. italica) supplied with NH+4, NO⊟3 or NH4NO3.—J. exp. Bot. 38: 1603–1618. The effects of varying NH+4, NO⊟3 or NH4NO3 concentration on the final plant characteristics, element composition, and accumulation of NO⊟3-N, NH+4-N and organic-N were evaluated in broccoli (Brassica oleracea var. italicacv. Futura and Premium Crop) plants cultured in vermiculite under greenhouse conditions supplemented with light. NH+4-grown plants were stunted and exhibited signs of marginal necrosis on the old leaves, accompanied by an accumulation of NH4. The tissue levels of N, P, Mn, Cu, Zn and B were generally increased by NH+4 versus NO⊟3 nutrition whereas the reverse was true for Ca; Mg and K were only slightly affected, if at all. These results are attributed to: changes in element availability resulting from reduced rhizosphere pH due to NH+4uptake rather than NO⊟3uptake; competition of Ca uptake by NH+4; and dilution of N by increased vegetative growth with NO⊟3-nutrition. The element concentrations of N, P or K were similar in all tissues whereas Ca, B and Mn were markedly less in the florets and young leaves compared to mature leaves; this supports literature indicating that the former elements are phloem-mobile whereas the latter are not. Assuming that the nutrient supply for mature leaves is delivered principally via the xylem stream, the data suggest that nutrients for developing leaves and florets are supplied predominantly in the phloem. If so, under our experimental conditions. Zn and Cu were also readily mobile in the phloem whereas Mg movement was restricted. NH4+ versus NO4+ J nutrition altered the distribution of these elements. The two broccoli cultivars tested under the greenhouse environment differed in NH+4 tolerance and in the distribution of K and Cu suggesting there was a genetic basis for cultivar variation in mineral acquisition and redistribution.

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