Seasonal variations in chemical composition of pasture

Abstract

Seasonal variations in pasture herbage for total nitrogen (Nt), total sulphur (S,), the lltrogen/sulphur ratio «NjS),), non-protein nitrogen (Nnp) , total water-soluble carbohydrates (TWSC), and the Nt/TWSC ratio, were studied by monthly samplings at seveñ ites in the lower North Island. Trends in N, were similar in grass and clover components of the pasture, although clover levels were generally higher than grass levels. Highest concentrations occurred in late autumn to early spring, and lowest in summer, although the summer minimum was much more evident in grass than in clover. Monthly fluctuations were similar in grasses and clovers, suggesting possible random effects from urinary return of grazing sheep. Seasonal variations in St were not pronounced, but levels in grasses were generally higher than those in the corresponding clovers, reflecting the greater tendency of grasses to ,:ccumulate sulphate-sulphur where the soil sulphur supply is not limiting. However, (N/S) t ratios ranged from 7 to 16 in grasses, and from 14 to 21 in clovers, suggesting that the sulphur supply may have been barely adequate at some sites. Nnp levels were determined only in mixed herbages, and tended to follow Nt levels. Nnp comprised 16-20% of Nt, with little variation between sites. TWSC levels varied considerably between sites, and from month to month, which was not unexpected for a constituent known to show wide diurnal and seasonal fluctuations. The mean levels showed some indication of a minimum in late summer to autumn, and a maximum in winter. The N,/TWSC ratio was frequently above the reported uanger level of 0.3 (for spring grass pastures in the semi-arid ranges of western U.S.A.), but its significance as an indicator of a grass tetany hazard under New Zealand conditions is not known.355

A new conceptual framework for plant responses to soil metals based on metal transporter kinetic parameters

“…metalliferous mine sites, ultrabasic, ultramafic and serpentine geological areas [43]. Indicators that have been used previously to assess possible soil contamination include titanium (Ti) [48,[53][54][55][56][57], chromium (Cr) [43], aluminium (Al) [53,54], iron (Fe) [53,55,56], silicon (Si) [58] and scandium (Sc) [46].…”

“…Although Ti is present in soils, its accumulation in leaf tissues is uncommon, and leaf concentrations exceeding 100 mg.kg -1 DW are likely to be due to soil contamination [55]. Titanium has also been used as a soil contamination indicator in micronutrient analyses of wheat and rice [57], and pasture [58]. However, the use of Ti as a soil contamination indicator is valid only if the analytical sensitivity is similar for each of the…”

“…Under normal conditions, Cr concentration in plants is less than 1 mg.kg -1 DW [66] and it is considered to become toxic between 5 and 30 mg.kg -1 DW [62]. Aluminium (Al) indicates possible soil contamination in plant samples [57,58]. Ranging between 1 and 4% in soil [62], it is more abundant than Fe [67].…”

“…However, some metallophyte species may accumulate high concentrations of Al in their tissues without any signs of toxicity [54,69], such as Melastoma malabathricum L. (Al accumulator) which stores more than 10,000 mg Al.kg -1 DW in its leaves and roots [70]. Threshold concentrations between endogenous (absorbed by the plant) and exogenous (external contamination, such as by dust) Al have been identified as 70, 100 and 120 mg.kg -1 leaf DW for grass, clover, or other herbage, respectively [58], and Al concentration in leaves of most plant species as less than 200 [69]. Metson et al [58] found that there was a reasonable agreement between soil contamination estimated from Al and Fe values although in some cases, values resulting from Fe was significantly higher than those from Al.…”

“…Threshold concentrations between endogenous (absorbed by the plant) and exogenous (external contamination, such as by dust) Al have been identified as 70, 100 and 120 mg.kg -1 leaf DW for grass, clover, or other herbage, respectively [58], and Al concentration in leaves of most plant species as less than 200 [69]. Metson et al [58] found that there was a reasonable agreement between soil contamination estimated from Al and Fe values although in some cases, values resulting from Fe was significantly higher than those from Al. Yasmin et al [67] concluded that Fe contamination on milled wheat seeds can be corrected by adjusting the Fe concentrations based on the concentration of Al in the grain.…”