Nonstructural Carbohydrate Concentrations in Timothy as Affected by N Fertilization, Stage of Development, and Time of Cutting

Abstract

Forages with increased total nonstructural carbohydrate (TNC) concentrations improve the N-use effi ciency of dairy cows. Th is study determined the eff ect of time of cutting (0700 vs. 1500 h), stage of development (heading and anthesis), and N fertilization (30, 50, 70, 90, and 110 kg N ha −1 as NH 4 NO 3 ) on the fermentable carbohydrate concentration of timothy (Phleum pratense L.) grown in northern Ontario, Canada. Forage dry matter (DM) yield and concentrations of N, starch, sucrose, glucose, fructose, and fructans were determined. Concentration of soluble carbohydrates (SC) was estimated by the sum of sucrose, glucose, and fructose, while TNC was obtained by adding SC and starch. Nitrogen fertilization did not aff ect forage carbohydrate concentrations, but slightly increased DM yield. Forage had higher TNC, starch, sucrose, and fructose concentrations (+9 to 63%) but lower glucose concentration (-27%) when harvested at anthesis compared with heading. Concentration of high degree of polymerization (HDP) fructans was close to 0 at heading and increased to 64.3 mg g −1 DM at anthesis. Th e aft ernoon-cut forage had higher TNC (+53%), SC (+60%), and sucrose (+87%) concentrations than the morning-cut forage; this positive eff ect was greater when timothy was harvested at heading compared with anthesis. Starch and HDP fructan concentrations were similar for both times of cutting, whereas results for glucose and fructose were inconsistent. Delayed cutting during the day and an extended growth period increased timothy TNC and HDP fructan concentrations to an extent likely to improve the N use effi ciency of dairy cows.

Evaluating the genotype × nitrogen fertilization interaction on the nutritive value of the first crop in timothy (Phleum pratense L.) clones

“…Fructan is a polymer of fructose and is stored as an energy reserve in many cool-season grasses (Pollock and Cairns 1991), but the standard deviations and ranges of fructan content were small (Table 3). Increasing N fertilization rates did not largely decrease the WSC, mono-and disaccharide or fructan content of timothy genotypes (Table 3), which agreed with the report by Pelletier et al (2009) but disagreed with the reports by Tremblay et al (2005) and Okamoto et al (2011). Hence, selection for WSC content, which is the sum of all these, should provide stable improvement of the fermentation quality of silage at different N fertilizer application levels.…”

“…Hence, selection for WSC content, which is the sum of all these, should provide stable improvement of the fermentation quality of silage at different N fertilizer application levels. Increasing N fertilization rates did not largely decrease the WSC, mono-and disaccharide or fructan content of timothy genotypes (Table 3), which agreed with the report by Pelletier et al (2009) but disagreed with the reports by Tremblay et al (2005) and Okamoto et al (2011). This conflict seems to come from the N rates used in the studies.…”

“…Tremblay et al (2005) and Okamoto et al (2011) reported decreased WSC content and silage quality at higher N rates. In contrast, Pelletier et al (2009) reported that increasing N fertilization rates did not decrease timothy carbohydrate content. Conflicts also exist as for the extent of the change of timothy genotype ranking under varying N application levels.…”

Seasonal Trends in Nonstructural Carbohydrates in Cool‐ and Warm‐season Grasses

“…This was subsequently followed by a reduction in fructan concentration from 18 May to 8 July with the exception of Kentucky bluegrass, perennial ryegrass, and Sandberg bluegrass, which exhibited an increase in fructan concentrations from 18 May to 2 June (Table 4). Pelletier et al (2009, 2010) observed increased fructan concentrations in timothy and other grasses from early heading to anthesis and in summer regrowth forage compared to spring growth in grasses. In general, fructan concentration on 3 August continued to decline by the first sampling date of regrowth (15 September) except for perennial ryegrass, orchardgrass, meadow brome, and tall wheatgrass which experienced a 12, 23, 20, and 40% increase in fructan concentrations during that period (Table 4).…”

Cultivar, Harvest Date, and Nitrogen Fertilization Affect Production and Quality of Fall Oat

“…This response has been noted previously with respect to WSC (Van Soest, 1982) and more recently in Canada (Tremblay et al, 2005) for timothy ( Phleum pretense L.), especially when forages were harvested during the stem‐elongation or early‐heading stages of growth. In another study (Pelletier et al, 2009), total nonstructural carbohydrates within timothy forages were not affected by N fertilization rate; however, the researchers suggested that this may be explained on the basis of non‐limiting N nutrition. Generally, decreases in WSC in response to N fertilization can be viewed as a net negative with respect to energy density and digestibility.…”