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Nutritional evaluation of kale (Brassica oleracea) diets:3. Changes in plant composition induced by soil fertility practices, with special reference to SMCO and glucosinolate concentrations
Published online by Cambridge University Press: 27 March 2009
Summary
Nitrogen (0, 150 kg N/ha), sulphur (0, 50, 150 kg S/ha) and molybdenum (0, 400 g sodium molybdate/ha) fertilizers were applied to kale sown in spring on soils either low (4 mg/kg, site L) or high (22 mg/kg, site H) in sulphate (SO4-S). The plots were harvested after growing periods of 100, 160 and 220 days. Dry-matter (D.M.) yields were determined on each occasion and comprehensive plant analyses carried out on material harvested at 160 days.
Nitrogen application increased both the D.M. yield and nitrate content of kale grown at both sites, and increased S-methyl cysteine sulphoxide (SMCO) content in kale grown at site H and in the plots receiving S fertilizer at site L. Glucosinolate content was unaffected by N application in kale grown at site H, but was higher in the absence than in the presence of N in kale grown at site L. Molybdenum fertilizer had no effect upon D.M. yield or upon any aspect of plant composition.
At site H, S fertilizer application produced a range of soil SO4-S values from 10 to 23 mg/kg on day 160 and had no effect upon either kale D.M. yield or composition. At site L, corresponding soil SO4-S values ranged from 4 to 9 mg/kg; as soil SO4-S was reduced, concentrations of plant sulphate declined first, followed by SMCO and then protein-S (% D.M.), with the reductions in SMCO and sulphate being more pronounced in the presence of N application. Glucosinolate and nitrate contents, and the yields of D.M. and protein N, were unaffected by restricting fertilizer S supply.
It was concluded that SMCO synthesis in kale is stimulated by the application of N when soil SO4-S values are high, but is progressively reduced as soil SO4-S declines below 9–10 mg/kg, particularly if N is applied at the same time to stimulate synthesis of plant protein and hence the incorporation of S into protein. Use of this technique to produce kales of low SMCO content for animal feeding is discussed, utilizing tests to define soils initially low in SO4-S. It was further concluded that sulphate and SMCO function as storage of S that is taken up in excess of requirements for plant protein synthesis, thus explaining their ease of manipulation by soil fertility practices.
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- Copyright © Cambridge University Press 1981
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