Changes in water‐soluble carbohydrates relative to crude protein in perennial ryegrass in response to defoliation frequency

Abstract

The water‐soluble carbohydrate relative to crude protein (WSC:CP) ratio in perennial ryegrass (Lolium perenne L.) has been postulated as a useful indicator of nitrogen (N) use efficiency in grazing dairy cows. A mini‐sward study was conducted to quantify the effects of defoliation frequency based on leaf stage on the CP fractions and the WSC:CP ratio in perennial ryegrass. Defoliation frequency corresponded to the time taken by ryegrass to develop 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 leaves per tiller. Plant growth dynamics and plant nutritive parameters related to N use efficiency were measured. The results showed that perennial ryegrass plants that were defoliated more frequently had reduced herbage mass accumulation, leaf elongation rate and total lamina length than plants defoliated less frequently in both growth cycles. Extending the defoliation frequency from the one‐ to five‐leaf stage resulted in a decline in WSC content, an increase in CP and buffer soluble CP and a decline in the WSC:CP ratio. Given the defoliation frequencies tested here, we concluded that plants defoliated too frequently have a potential risk of low N efficiency use by grazing animals, due to a low WSC:CP ratio. The best nutritional quality balance occurs when plants were defoliated at the 3.0‐leaf stage during the first growth cycle and at the 2.0‐leaf stage during the second growth cycle.

In Vitro Fermentation Patterns and Methane Output of Perennial Ryegrass Differing in Water-Soluble Carbohydrate and Nitrogen Concentrations

“…The chemical composition of treatments is similar to values reported in autumn and spring for grass pastures in humid temperate regions [13,40]. However, the concentrations of WSC observed in this study for both cultivars, especially in the high sugar treatment (322 and 343 g/kg for autumn and spring, respectively) were greater than what is commonly reported for PRG pastures (74 to 243 g/kg) [41].…”

“…Furthermore, pasture management has a significant effect on WSC concentration and WSC to CP ratio. Increasing the defoliation frequency, e.g., going from three leaves per tiller to two leaves per tiller, decreases the WSC concentration, increases the CP concentration, and decreases the WSC to CP ratio [13]. Nitrogen fertilisation rate also affects these components; increases in the amount of N applied per hectare increases CP and decreases WSC concentrations, leading to a decrease in WSC to CP ratio [14].…”

The Effect of Drying Methods on Water-Soluble Carbohydrates and Crude Protein Concentrations and Their Ratio in Two Perennial Ryegrass Cultivars

“…Lower ratios were reported when perennial ryegrass cultivars not selected for greater WSC concentration were evaluated in the same temperate climate as the present study [33]. When perennial ryegrass cultivar Impact AR1 was harvested at the 3-leaf stage, the WSC/CP ratio ranged from 0.5 to 1.0 in the autumn-winter and spring-summer seasons, respectively, and when defoliation frequency was extended from one to the five leaf-stage, this ratio increased from 0.7 to 1.7 respectively in the spring-summer period [52]. Similar results were also found with cultivar Alto AR1, where the WSC/CP ratio in early (August-October) and late spring (November-December) was 0.45 and 1.11, respectively.…”

Validation of a critical nitrogen dilution curve for hybrid ryegrasses

“…The use of increasing amounts of N fertilizer to improve grass yield is well documented and past work summarized by Hopkins () indicates a linear phase of response followed by a plateau. In ryegrasses (Loaiza, Balocchi, & López, ; Marino et al., ; Martin et al., ; Pembleton, Rawnsley, & Burkitt, ), tall fescue (Errecart, Agnusdei, Lattanzi, Marino, & Berone, ; Greenwood et al., ) or naturalized pastures (Lobos‐Ortega, Alfaro, & Martinez‐Lagos, ), a positive yield response occurs when increasing the N‐fertilizer rates.…”