Effect of defoliation management, based on leaf stage, on perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under dryland conditions. 1. Regrowth, tillering and water-soluble carbohydrate concentration

A field study was undertaken between April 2003 and May 2004 in southern Tasmania, Australia to quantify and compare changes in herbage productivity and water‐soluble carbohydrate (WSC) concentration of perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under a defoliation regime based on leaf regrowth stage. Defoliation interval was based on the time taken for two, three or four leaves per tiller to fully expand. Dry‐matter (DM) production and botanical composition were measured at every defoliation event; plant density, DM production per tiller, tiller numbers per plant and WSC concentration were measured bimonthly; and tiller initiation and death rates were monitored every 3 weeks. Species and defoliation interval had a significant effect (P < 0·05) on seasonal DM production. Prairie grass produced significantly more (P < 0·001) DM than cocksfoot and ryegrass (5·7 vs. 4·1 and 4·3 t DM ha^?1 respectively). Plants defoliated at the two‐leaf stage of regrowth produced significantly less DM than plants defoliated at the three‐ and four‐leaf stages, irrespective of species. Defoliation interval had no effect on plant persistence of any species during the first year of establishment, as measured by plant density and tiller number. However, more frequent defoliation was detrimental to the productivity of all species, most likely because of decreased WSC reserves. Results from this study confirmed that to maximize rates of regrowth, the recommended defoliation interval for prairie grass and cocksfoot is the four‐leaf stage, and for perennial ryegrass between the two and three‐leaf stages.     

Changes in the physiology and feed quality of cocksfoot (Dactylis glomerata L.) during regrowth

Abstract A glasshouse study was undertaken to determine the physiological and morphological changes in cocksfoot (Dactylis glomerata L.) during regrowth after defoliation. Individual plants were arranged in a mini‐sward in a randomized complete block design. Treatments involved harvesting each time one new leaf had expanded (one‐leaf stage), up to the six‐leaf stage, with the plants separated into leaf, stubble (tiller bases) and roots. Stubble and root water‐soluble carbohydrate (WSC), stubble and leaf dry matter (DM), tiller number per plant and leaf quality (crude protein (CP), estimated metabolizable energy (ME) and mineral content) were measured to develop optimal defoliation management of cocksfoot‐based pastures. WSC concentration in stubble and roots was highest at the five‐ and six‐leaf stages. Mean WSC concentration (g kg^?1 DM) was greater in stubble than roots (32·7 ± 5·9 vs. 9·4 ± 1·5 respectively). There was a strong positive linear relationship between plant WSC concentration and leaf DM, root DM and tillers per plant after defoliation (Adj R² = 0·72, 0·88 and 0·95 respectively). Root DM plant^?1 and tiller DM tiller^?1 decreased immediately following defoliation and remained low until the three‐leaf stage, then increased from the four‐leaf stage. Tillers per plant remained stable until the four‐leaf stage, after which they increased (from 9·9 ± 0·5 to 15·7 ± 1·0 tillers plant^?1). Estimated metabolizable energy concentration (MJ kg^?1 DM) was significantly lower at the six‐leaf stage (11·01 ± 0·06) than at any previous leaf regrowth stage, whereas CP concentration (g kg^?1 DM) decreased with regrowth to the six‐leaf stage. Both the levels of ME and CP concentrations were indicative of a high quality forage throughout regrowth (11·37 ± 0·04 and 279 ± 8·0 for ME and CP respectively). Results from this study give a basis for determining appropriate criteria for grazing cocksfoot‐based pastures. The optimal defoliation interval for cocksfoot appears to be between the four‐ and five‐leaf stages of regrowth. Delaying defoliation to the four‐leaf stage allows time for replenishment of WSC reserves, resumption of root growth and an increase in tillering, and is before herbage is lost and quality falls due to onset of leaf senescence.     

Patterns of leaf and root regrowth, and allocation of water-soluble carbohydrate reserves following defoliation of plants of prairie grass (Bromus willdenowii Kunth.)

This study utilized leaf stage‐based defoliation intervals to describe the concentrations and contents of water‐soluble carbohydrate (WSC) and nitrogen (N) in stubble and root reserves and their effect on the regrowth of prairie grass (Bromus willdenowii Kunth.) plants. The priority sequence for allocation of WSC reserves during the regrowth period was also investigated. There were substantially higher concentrations of WSC and N in the stubble compared with the roots following defoliation, confirming the stubble as the primary site for energy storage, with roots playing a lesser role. However, high R² values for the relationships between WSC concentration in roots and regrowth variables suggested that plants of prairie grass were reliant on WSC reserves from the roots in addition to the stubble to meet the energy requirements of plants until adequate photosynthetic tissue had been produced. The sequence of priority for allocation of WSC reserves followed the order of leaf growth, root growth and tillering during the regrowth period. Although WSC reserves were identified as the primary contributor to plant regrowth following defoliation, there was also a strong relationship between stubble N concentration and regrowth variables.     

Effect of defoliation management, based on leaf stage, on perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under dryland conditions. 2. Nutritive value

A field experiment was undertaken between April 2003 and May 2004 in southern Tasmania, Australia, to quantify and compare changes in the nutritive value of perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under a defoliation regime based on stage of leaf regrowth. Defoliation interval was based on the time taken for two, three or four leaves per tiller to fully expand. At every defoliation event, samples were collected and analysed for acid‐detergent fibre (ADF), neutral‐detergent fibre (NDF) and total nitrogen (N) concentrations and to estimate metabolizable energy (ME) and digestible dry matter (DDM) concentrations. Amounts of crude protein (CP) and metabolizable energy (MJ) per hectare values were subsequently calculated. There was a significantly lower (P < 0·001) NDF concentration for perennial ryegrass compared with prairie grass and cocksfoot, and a significantly lower (P < 0·001) ADF concentration for cocksfoot compared with prairie grass and perennial ryegrass, regardless of defoliation interval. The CP concentration of cocksfoot was significantly greater (P < 0·001) compared with the CP concentrations of prairie grass and perennial ryegrass. The estimated ME concentrations in cocksfoot were high enough to satisfy the requirements of a lactating dairy cow, with defoliation at or before the four‐leaf stage maintaining ME concentrations between 10·7 and 10·9 MJ kg^?1 DM, and minimizing reproductive plant development. The ME concentrations of prairie grass (10·2–10·4 MJ kg^?1 DM) were significantly lower (P < 0·001) than for cocksfoot (as above) and perennial ryegrass (11·4–11·6 MJ kg^?1 DM) but a higher DM production per hectare resulted in prairie grass providing the greatest amounts of ME ha^?1.     

Interaction between water-soluble carbohydrate reserves and defoliation severity on the regrowth of perennial ryegrass (Lolium perenne L.)-dominant swards

A field-study was undertaken in Hamilton, New Zealand to determine if there was an interaction between water-soluble carbohydrate (WSC) reserve content and defoliation severity on the regrowth of perennial ryegrass-dominant swards during winter. Perennial ryegrass plants with either low or high WSC content were obtained by varying the defoliation frequency. At the third defoliation at the one-leaf stage and at the first defoliation at the three-leaf stage (harvest H₁), swards were mown with a rotary lawnmower to residual stubble heights of 20, 40 or 60 mm. All swards were then allowed to regrow to the three-leaf stage before again defoliating to their treatment residual stubble heights (H₂). Frequently defoliated plants contained proportionately between 0·37 and 0·48 less WSC in the stubble after defoliation, depending on the severity of defoliation. There was no interaction between WSC content and defoliation severity for herbage regrowth between harvests H₁ and H₂. Herbage regrowth was lower from swards containing low WSC plants compared with high WSC plants (2279 vs. 2007 kg DM ha⁻¹). Furthermore, swards defoliated to 20 or 40 mm had greater herbage regrowth compared with those defoliated to 60 mm (2266, 2249 and 1914 kg DM ha⁻¹ for swards defoliated to residual stubble heights of 20, 40 and 60 mm, respectively). Regrowth of perennial ryegrass was positively correlated with post-defoliation stubble WSC content within defoliation severity treatment, implying that WSC contributed to the defoliation frequency-derived difference in herbage yield. However, the effect of defoliation severity on herbage regrowth was not associated with post-defoliation stubble WSC content.     

The importance of water-soluble carbohydrate reserves on regrowth and root growth of Lolium perenne (L.)

This glasshouse study aimed to determine the relative importance of water-soluble carbohydrates (WSC) and current photosynthate on root and top regrowth of perennial ryegrass (Lolium perenne L.). Individual plants were arranged in one of two miniswards (Experiments 1 and 2) and underwent varying defoliation frequencies designed to obtain a gradient of WSC content at the final harvest of each treatment (H₁), when all treatments were defoliated. In Experiment 1, the plants were defoliated either three times at the one new leaf per tiller stage of regrowth (treatment 3 × 1), once at the two-leaf and again at the one-leaf stage (treatment 2, 1), once at the one-leaf and again at the two-leaf stage (treatment 1, 2) or once only at the three-leaf stage (treatment 1 × 3), up to H₁. Leaf and root growth and other parameters were assessed over 6 d after H₁ in sunlight, and over a 4-week period in darkness, and related to initial plant WSC content. In Experiment 2, plant defoliation treatments were: 3 × 1, 1, 2 or 1 × 3. Leaf regrowth was assessed for 36 d until the plants had three fully expanded new leaves per tiller. Leaf regrowth in both experiments was significantly related to stubble WSC (below 50 mm height). In Experiment 1, plants were almost fully reliant upon plant reserves for the first 3 d of regrowth, with reliance decreasing up to 6 d. When regrowth of plants was compared after 1 week in light or in darkness, it was estimated that one-third of leaf regrowth was due to plant WSC reserves and the remainder due to photosynthesis. However, the capacity to photosynthesize and to grow roots after H₁ was also significantly related to stubble WSC content. In Experiment 2, there was a significant difference (P<0·01) between defoliation treatments on leaf dry matter (DM) yield at 12 d (×1 leaf tiller^?1) of regrowth, and this was, as in Experiment 1, significantly positively related to WSC content in the stubble. However, after 36 d of regrowth, DM yield of plants defoliated at 2 or 3 leaves tiller^?1 up to H₁ were similar, and both were significantly higher (P<0·01) than regrowth of plants defoliated at the one-leaf stage. After defoliation, the period of reliance on WSC reserves may be substantially increased in situations of shading (canopy competition or cloud cover) or if the new regrowth shoot is removed by regrazing.     

Comparative defoliation tolerance of temperate perennial grasses

The defoliation tolerance of cultivars of four temperate perennial pasture grasses, perennial ryegrass (Lolium perenne, cv. Yatsyn1), phalaris (Phalaris aquatica cv. Australian), tall fescue (Festuca arundinaceae cv. Demeter) and cocksfoot (Dactylis glomerata cv. Porto), was determined under controlled conditions over a period of 12 weeks. Undefoliated plants were compared with defoliated plants, where only half of one leaf was left intact at the initial defoliation, and leaf regrowth was harvested every 3–4 d. The growth responses measured were plant tiller number, dry weight, relative leaf regrowth rate, root:shoot ratio, sheath:stem ratio and specific leaf weight. All species showed morphological adaptations that potentially increased their ability to tolerate defoliation (e.g. increased allocation to shoot at the expense of roots and lower specific leaf weights) but cocksfoot was found to be the most defoliation‐tolerant and perennial ryegrass the least. The adaptation that favoured cocksfoot most strongly was high sheath:stem ratio, which, it is proposed, allowed it to maintain photosynthesis and a level of carbon supply sufficient to support regrowth throughout the experiment. The strategy of perennial ryegrass which favours leaf growth and leads to rapid leaf turnover rates made it particularly susceptible to defoliation under the conditions of this experiment. This highlights the likely importance of defoliation‐avoidance responses in explaining the well‐known grazing resistance of this species. Phalaris and tall fescue showed responses that were intermediate between the other two species. The importance of defoliation‐avoidance mechanisms and implications for grazing management are discussed.     

Performance and quality of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) and mixtures of both species grown with or without white clover (Trifolium repens L.) under cutting management

There is increasing interest in tall fescue (Festuca arundinacea Schreb.) in Western Europe and elsewhere, mainly because of its better drought resistance and yield potential compared with perennial ryegrass (Lolium perenne L.). Important drawbacks of tall fescue, compared with perennial ryegrass, are its lower digestibility and voluntary intake. Mixtures of both species might combine the advantages of each, and species interactions may eventually lead to transgressive overyielding. We compared the agronomic performance of tall fescue, perennial ryegrass and tall fescue–perennial ryegrass mixtures, as pure‐grass swards or in association with white clover (Trifolium repens L.). Tall fescue–perennial ryegrass mixtures differed in the proportion and ploidy of the perennial ryegrass component. Yield, feed quality and botanical composition were measured in the 3 years after the sowing year. We found significant effects of ploidy of the ryegrass variety and of the proportion of ryegrass in the initial seed mixture on the botanical composition of the swards. Nevertheless, all swards were dominated by tall fescue at the end of the experiment. No overyielding of the mixtures compared with that of single‐species swards was found, but feed quality was intermediate between that of the single‐species swards. Mixed swards had better drought resistance than L. perenne and higher feeding quality than F. arundinacea swards.     

Soil moisture and growth of contrasting varieties of Lolium, Dactylis and Festuca species

Varieties of Italian, perennial and Italian × perennial ryegrasses, tall fescue and cocksfoot were used to determine the effects of soil moisture on grass growth. Weather conditions were monitored and herbage accumulation, leaf extension rate, leaf appearance rate and tillering were recorded under natural (control), covered and irrigated treatments.
Water deficit reduced crop growth rate in the spring and drought was the major factor influencing crop growth rates in all varieties during the summer. The ryegrasses appeared most sensitive to drought, and particularly poor recovery growth was exhibited by the Italian ryegrass RvP and the hybrid ryegrass Snowdon.
Leaf extension rate and leaf appearance rate were both reduced by increasing soil water deficit. Herbage accumulation was increased by irrigation when potential soil water deficits were greater than 100 mm. When water deficits were large, irrigation increased leaf extension more than leaf appearance or tiller number. Increasing moisture deficit had a greater effect upon tiller number than on leaf extension.     

Priority for allocation of water-soluble carbohydrate reserves during regrowth of Lolium perenne

A glasshouse study was undertaken to determine the priority within the perennial ryegrass (Lolium perenne L.) plant for leaf and root growth and daughter tiller initiation after defoliation, in relation to various levels of water-soluble carbohydrate (WSC) reserves at defoliation. Individual plants were arranged in mini-swards, and underwent varying defoliation frequencies and ambient temperatures before defoliation, and harvest heights at defoliation, to obtain a gradient of WSC content at H₁, the date when all plants were defoliated. Defoliation interval consisted of defoliating either three times at the one new leaf tiller^–1 stage (1-leaf stage) of regrowth, or once only at the 3-leaf stage, up to H₁, while night temperature in the week prior to H₁ was altered from 15°C to either 8 or 20°C. At H₁, plants were defoliated to a stubble height of either 20 or 50 mm. Plants were subsequently destructively harvested at days 4, 6, 8, 12, 18 and 27. Leaf and root extension and tiller dynamics were also measured. On a regrowth timescale, tiller initiation was most sensitive, root regrowth moderately sensitive, and leaf regrowth relatively insensitive to a decrease in WSC. The time of daughter tiller initiation also coincided with replenishment of stubble WSC levels. In contrast to this sequence of regrowth events following defoliation, the quantitative effects on growth were different, with elongation and survival of roots most affected by reduced WSC levels. A 30-fold difference in stubble WSC at H₁ between high and low WSC plants (1·52 vs. 0·05 mg tiller^–1) produced only a 4-fold increase in leaf dry matter (DM) after 27 d (2·2 vs. 0·6 g plant^?1), while tiller number plant^?1 increased 6-fold (138 vs. 23% increase in tiller number from H₁). Root elongation rate was 59 times higher in the high than in the low WSC plants (1·18 vs. 0·02 mm d^?1). From a pasture management perspective, the study confirms that defoliation, coinciding with the 3-leaf stage of regrowth and around a stubble height of 50 mm, optimizes persistence and productivity of perennial ryegrass. By allowing more rapid replenishment of WSC reserves, this optimal defoliation strategy enables a greater proportion of WSC to be allocated to maintain a more active root system, and promotes tillering, compared with more frequent and close defoliation.     

Regrowth dynamics and grazing decision rules: further analysis for dairy production systems based on perennial ryegrass (Lolium perenne L.) pastures

To support the further development of grazing practices for dairy production systems based on perennial ryegrass (Lolium perenne L.), allometric relationships among leaf‐stage categories and pseudostem were derived for perennial ryegrass tillers sampled from swards each month, from July 2008 to January 2010, within a dairy grazing‐system experiment in south‐west Victoria, Australia. The relative lamina mass of the first leaf that emerged on tillers following grazing (denoted L3) and the subsequent leaf to emerge (L2) was used as an indicator of the trajectory of regrowth. L2 was consistently 30–40% heavier than L3 during the period July–September (mid‐winter to early spring), but thereafter the difference between leaf stages lessened, and disappeared altogether in late spring. No substantial lag was observed in the rate of herbage accumulation during the early stages of regrowth of perennial ryegrass swards from 1500 kg DM ha^?1 post‐grazing. Therefore, grazing at any time in the period between emergence of the second and third leaves after the previous defoliation event should lead to high efficiency of pasture harvest under most conditions. The dry‐matter digestibility (DMD) and crude protein (CP) content of the most recently emerged leaf (denoted L1) declined sharply during spring, whereas the DMD and CP content of older leaves were more consistent. Decision rules for grazing management should include sufficient flexibility to account for interactions between leaf stage and time of year in relative lamina mass and nutritive value.     

In vitro rumen methane output of perennial ryegrass varieties and perennial grass species harvested throughout the growing season

The selection and feeding of perennial ryegrass (Lolium perenne L.) varieties (PRV) or perennial grass species (PGS) may affect enteric methane (CH₄) output because of changes in the fermentation dynamics in the rumen as a result of differences in herbage chemical composition. The objective of this study was to determine the effects of PRV and PGS harvested throughout the growing season on herbage chemical composition, and in vitro rumen fermentation variables and CH₄ output per unit of feed using a batch culture technique. Seven PRV (Experiment 1: Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella) and six perennial grasses [Experiment 2: perennial ryegrass (Navan), perennial ryegrass (Portstewart), cocksfoot, meadow fescue, tall fescue, timothy; defined as PGS], managed under a simulated grazing regime, were incubated for 24 h with buffered rumen fluid in two separate experiments. The CH₄ output per unit of feed dry‐matter (DM) incubated was not affected (P > 0·05) by PRV (range of mean values across PRV of 23·9–25·3 (SEM 0·41) mL g^?1 DM) or by PGS (25·6–26·6 (SEM 0·37) mL g^?1 DM). The CH₄ output per unit feed DM disappearing during the in vitro rumen incubation was not affected by PRV (33·9–35·1 (SEM 0·70) mL g^?1 DM), and although there was an overall PGS effect (P < 0·05; 37·2–40·3 (SEM 0·71) mL g^?1 DM), none of the paired contrasts between PGS were significant when analysed using Tukey adjusted comparisons. This outcome reflected either small‐scale or a lack of treatment effects on individual herbage chemical composition (e.g. 454–483 g NDF kg^?1 DM, 215–224 g CP kg^?1 DM and 94–122 g water‐soluble carbohydrate (WSC) kg^?1 DM across PRV; 452–506 g NDF kg^?1 DM, 208–243 g CP kg^?1 DM and 73–131 g WSC kg^?1 DM across PGS) and in vitro rumen fermentation variables. Hence, these results provide no encouragement that choices among the grasses examined, produced within the management regimes operated, would reduce enteric CH₄ output per unit of feed in vivo. However, the technique utilized did not take account of animal × PRV or PGS interactions, such as potential differences in intake between animals, that may occur under farm conditions.     

GRAZING MANAGEMENT FOR SEED PRODUCTION IN LEAFY STRAINS OF GRASSES

Leafy strains of five grasses were grown for seed and subjected to various cattle grazing treatments between October and April for three harvest years. The grasses were: S.143 cocksfoot, S.215 meadow fescue, S.170 tall fescue, S.59 red fescue and S.23 perennial ryegrass. All but S.59 red fescue (row crop) were studied as row and broadcast crops. The plots were sown under an arable silage crop and received top dressings of nitrogenous fertiliser every year. Yield of seed, and also quantity of herbage in winter, were measured.
October grazing in the seeding year reduced the first crop of seed in all species except ryegrass. Grazing in December improved the yield of meadow fescue throughout the experiment, and of cocksfoot, tall fescue and red fescue after the first year. Several factors might operate to bring about this effect; suggestions are made for further investigation. Repeated grazing from December to March tended to reduce vigour, and so to offset the advantage of removing autumn-grown herbage. Grazing at intervals from December to late April seriously reduced yield in all species. Tall fescue and red fescue, early flowering species, were most seriously affected, meadow fescue and perennial ryegrass least. Cocksfoot and tall fescue yielded more seed when grown in 2-ft. rows than when broadcast. Meadow fescue and perennial ryegrass did not. The yield of meadow fescue was less affected by adverse conditions than cocksfoot.     

Micronutrient concentrations in common and novel forage species and varieties grown on two contrasting soils

We investigated differences between forage species with regard to micronutrients that are essential to sustain livestock health. Five grasses (timothy, perennial ryegrass, meadow fescue, tall fescue and cocksfoot), three legumes (red clover, white clover and birdsfoot trefoil) and four forbs (ribwort plantain, salad burnet, caraway and chicory) were grown on one micronutrient‐poor/low pH soil and one micronutrient‐rich/high pH soil (outdoor pot experiment). In addition, six grasses (timothy, perennial ryegrass, meadow fescue, tall fescue, Festulolium hybrid and cocksfoot) and one legume (red clover) were field‐grown on the micronutrient‐poor soil. Of the twelve pot‐grown species, herbage of chicory, red clover and white clover generally had the highest micronutrient concentrations (maximum Co, Cu, Fe and Zn concentrations were 0·23, 9·8, 233 and 109 mg kg^?1 DM, respectively), except for Mo, which was highest in the clovers (10·6 mg kg^?1 DM), and Mn, which was highest in cocksfoot (375 mg kg^?1 DM). Soil type had the strongest effect on plant Mo and Mn concentrations. We also investigated differences in micronutrients between varieties, but they were generally few and negligible. The results indicate that choice of forage species is of major importance for micronutrient concentrations in herbage and that soil type exerts a major effect through pH. Forage of chicory, red clover and white clover generally met the requirements of high‐yielding dairy cows with regard to most micronutrients; therefore, diversification of seed mixtures so as to include these species could increase micronutrient concentrations in forage.     

THE EFFECT OF METHOD OF SOWING ON THE ESTABLISHMENT OF GRASS SEED CROPS

Methods used by growers to establish seed crops of perennial ryegrass, cocksfoot, timothy and meadow fescue have been examined. While satisfactory establishments were obtained by sowing perennial ryegrass broadcast, cocksfoot, timothy and meadow fescue should be sown in rows, especially if they are to be sown under a cover crop.     

Effect of dairy slurry application rate and forage type on production,soil nutrient status and nitrogen‐use efficiency

Seven forage types (diploid and tetraploid perennial ryegrass, Italian ryegrass and hybrid ryegrass, a low‐input mixture of perennial ryegrass, cocksfoot, timothy and meadow fescue, a mixture of perennial ryegrass and white clover, and monoculture of red clover) were sown in late July 2004. Each received one of four rates of dairy cattle slurry in three annual applications by trailing shoe, which supplied average nitrogen (N) inputs of 0·0, 114·9, 204·8 and 301·2 kg N ha^?1 annum^?1. Treatments were cut either three or four times annually over four years. Average dry‐matter yield (DM) response to slurry N was 15·6 kg DM kg^?1 N. Lowest recovery of slurry N was in the second application each year (after first cut). The data suggest that slurry applied to Italian ryegrass, and also to swards containing legumes on soils with high phosphorus content, will produce a lower DM response to slurry N and result in a lower slurry N recovery than on swards of perennial ryegrass or cocksfoot‐dominant low‐input mixtures. Apparent recovery of slurry N was low at the second cut, especially when first‐cut yields had been high. To maximize slurry N recovery, application to regrowths with potentially slow rates of growth or high legume content should be avoided.     

Forage quality of white clover (Trifolium repens L.) × Caucasian clover (T. ambiguum M. Bieb.) hybrids and their grass companion when grown over three harvest years

Interspecific hybrids between white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb.) have been developed to introgress the rhizomatous growth habit into white clover, to increase persistence and drought tolerance. The forage quality of T. repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids and companion grass, when grown in mixtures with an intermediate perennial ryegrass (Lolium perenne L.) under a cutting‐only management, was measured. In vitro dry‐matter digestibility (DMD), water‐soluble carbohydrate (WSC) and crude protein (CP) concentrations of the legume and grass fractions were measured throughout the growing season over three harvest years. Trifolium repens had a lower WSC but a higher CP concentration than the perennial ryegrass companion in all harvest years and at all cuts. The legume fractions from the BC1 and BC2 hybrid plots had a higher WSC and a lower CP concentration but an in vitro DMD value comparable with white clover throughout the growing season and in each harvest year. The grass fractions from the mixtures with the backcross hybrids had a higher WSC and a lower CP concentration than the grass fraction from the T. repens plots, in all harvest years and throughout the growing season. No difference in in vitro DMD between parental species and backcross hybrids was observed. The implications of these results for the development of these hybrids and animal performance are discussed.     

Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne L.): milk production from late-lactation dairy cows

Eight multiparous Holstein–Friesian dairy cows in late lactation were used to investigate the potential of using perennial ryegrass with a high concentration of water‐soluble carbohydrate (WSC) to increase the efficiency of milk production. After a pretreatment period on a common pasture, the cows were each given ad libitum access to one of two varieties of zero‐grazed grass continuously for 3 weeks. Treatments were: high sugar (HS), an experimental perennial ryegrass variety bred to contain high concentrations of WSC; or control, a standard variety of perennial ryegrass (cv. AberElan) containing typical concentrations of WSC. The two grass varieties were matched in terms of heading date. All animals also received 4 kg day^–1 standard dairy concentrate. Grass dry matter (DM) intake was not significantly different between treatments (11·6 vs. 10·7 kg DM day^–1; s.e.d. 0·95 for HS and control diets respectively), although DM digestibility was higher on the HS diet (0·71 vs. 0·64 g g^–1 DM; s.e.d. 0·23; P < 0·01) leading to higher digestible DM intakes for that diet. Milk yield from animals offered the HS diet was higher (15·3 vs. 12·6 kg day^–1; s.e.d. 0·87; P < 0·05) and, although milk constituent concentrations were unaffected by treatment, milk protein yields were significantly increased on the HS diet. The partitioning of feed N was significantly affected by diet, with more N from the HS diet being used for milk production (0·30 vs. 0·23 g milk N g^–1 feed N; s.e.d. 0·012; P < 0·01) and less being excreted in urine (0·25 vs. 0·35; s.e.d. 0·020; P < 0·01). In a separate experiment, using the same grasses harvested earlier in the season, the fractional rate of DM degradation, measured by in situ and gas production techniques, was higher for the HS grass than for the control. It is concluded that increased digestible DM intakes of the HS grass led to increased milk yields, whereas increased efficiency of utilization of the HS grass in the rumen resulted in the more efficient use of feed N for milk production and reduced N excretion.     

A COMPARISON OF BROADCAST AND WIDE-ROW SPACED GRASSES WHEN MANAGED FOR FOGGAGE PRODUCTION

A small-plot trial comparing perennial ryegrass, cocksfoot, timothy and meadow fescue sown broadcast and also in 21 inch rows was conducted at Auchincruive from 1954 to 1957. The cutting treatments were arranged so that measurement could be made of both summer and winter production.
Of the four species, cocksfoot was the most suitable for foggage production. Perennial ryegrass suffered severely from winter killing. Timothy and meadow fescue, although persistent, did not yield as much as cocksfoot.
Total dry-matter production over three years was higher from the cocksfoot rows than from the broadcast stand. For ryegrass and meadow fescue, broadcasting gave higher yields than row sowing while timothy showed no significant difference between sowing methods.
During the winter, all species showed a loss of dry matter. Losses for ryegrass, cocksfoot, timothy and meadow fescue were respectively 34%, 17%, 18% and 24%. Broadcast stands averaged 11% greater loss than the rows.     

Effects of continuous sheep stocking and strategic rest periods on the sward characteristics of binary perennial grass/white clover associations

Five binary perennial grass/white clover (Trifolium repens, cv. Menna) mixtures were evaluated over a 3-year period under continuous sheep stocking together with the imposition of a rest period for either an early or a late conservation cut; the experiment with plot sizes of 0·16 ha was replicated three times. The grass species and cultivars used were Merlinda tetraploid and Magella diploid perennial ryegrass (Lolium perenne), Prairial cocksfoot (Dactylis glomerata), Rossa meadow fescue (Festuca pratensis) and Goliath timothy (Phleum pratense). The greatest total lengths of white clover stolon developed in the meadow fescue (171·6 m m^?2) and timothy (151·9 m m^?2) associations compared with those in tetraploid perennial ryegrass (98·6 m m^?2), diploid perennial ryegrass (91·9 m m^?2) and cocksfoot (74·6 m m^?2) (s.e.d. 16·4, P < 0·001). On average, the proportion of white clover stolon that was buried was between 0·86 and 0·89 and this was more abundant in late than early season. Whereas timothy persisted, the persistence of meadow fescue was low under any of the managements tested and this was markedly reduced by the third grazing season. In the diploid perennial ryegrass sward, a late June to early August rest period for conservation enhanced white clover stolon length. An early April to late May rest period greatly reduced total white clover stolon length in both diploid perennial ryegrass and tetraploid perennial ryegrass associations (diploid perennial ryegrass-unrested 89 m m^?2, early rest 56·1 m m^?2, late rest 130·7 m m^?2; tetraploid perennial ryegrass - unrested 125·1 m m^?2, early rest 71 m m^?2, late rest 99·7 m m^?2; s.e.d. 19·19, P < 0·001). The numbers of white clover stolon growing points per unit stolon length were greatest when the sward was rested during late June to early August ?55·9 m^?1 stolon length compared with 45·7 m^?1 for an April to late May rest and 46 m^?1 in the absence of a rest (s.e.d. 2·59, P < 0·001). Likewise, the percentage of stolon above ground was greatest with the late June to early August rest ?15·78% compared with 10·61% for the April to late May rest and 7·69% for no rest (s.e.d. 1·569, P < 0·001). The complementary percentages of buried stolon indicate the important role this fraction has and the need to study stolon behaviour in grazing studies generally. It is concluded that, in relation to perennial ryegrass as a companion grass, meadow fescue and timothy allow better white clover development and cocksfoot less. However, other attributes have to be considered, for example the poor persistence of meadow fescue and the slower regrowth of timothy, both of which allow the invasion of weed grasses, or the lower acceptability of cocksfoot to livestock. The timing of the rest period before the conservation cut can influence white clover development considerably, but the effects differed with different companion grasses.