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22 April 2013 Sulfur limitation increases nitrate and amino acid pools in tropical forages
Fabiana Schmidt, Fabiano D. De Bona, Francisco A. Monteiro
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Increasing the supply of sulfur (S) to forage plants can change their nitrogen (N) metabolism, causing changes in the N : S ratio that can potentially affect forage production and quality. The present study was focussed on revealing how supply (low, intermediate, high) of S affects amino acid composition and concentrations of total S, total N, sulfate-S, nitrate-N, and soluble protein in the leaves of tropical pasture species.

Greenhouse experiments were conducted in ground quartz (inert solid substrate) culture to examine the effect of S supply in two tropical species: Panicum maximum cv. Tanzania (Guinea grass) and Stylosanthes guianensis cv. Mineirão (stylo). Because legumes have greater S requirement than do grass species, application levels of S varied according to the species. Guinea grass was grown with 0.10, 0.55, 1.00, 1.45, and 1.90 mmol L−1 of S, and stylo with 0.10, 0.70, 1.30, 1.90 and 2.50 mmol L−1 of S. Plants of both species were harvested on two occasions.

Low S availability (0.10 mmol L−1) caused a nutritional imbalance with N in Guinea grass and stylo plants, as shown by a high N : S ratio (>60 : 1), and high concentrations of nitrate-N and free amino acids in plant tissues. Increased S supply regulated the N : S ratio at values close to 20 : 1, which provided N and S concentrations more suitable for protein synthesis and optimum forage production for both forage species. Asparagine was the predominant amino acid present in S-limited Guinea grass, whereas arginine was more abundant in S-limited stylo. This result indicates that a limitation of S increases nitrate-N and free amino acids while decreasing plant growth rates and soluble protein concentrations in these forage species.

© CSIRO 2013
Fabiana Schmidt, Fabiano D. De Bona, and Francisco A. Monteiro "Sulfur limitation increases nitrate and amino acid pools in tropical forages," Crop and Pasture Science 64(1), 51-60, (22 April 2013).
Received: 29 September 2012; Accepted: 1 March 2013; Published: 22 April 2013
amino acid composition
N : S ratio
nitrate concentration
sulfur fertilisation
tropical forage species
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