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.     

Radiation‐use efficiency for forage kale crops grown under different nitrogen application rates

Crop growth is related to radiation‐use efficiency (RUE), which is influenced by the nitrogen (N) status of the crop, expressed at canopy level as specific leaf N (SLN) or at plant level as N nutrition index (NNI). To determine the mechanisms through which N affects dry‐matter (DM) production of forage kale, results from two experiments (N treatment range 0–500 kg ha^?1) were analysed for fractional radiation interception (RI), accumulated radiation (R_acc), RUE, N uptake, critical N concentration (N_c), NNI and SLN. The measured variables (DM, RI and SLN) and the calculated variables (NNI, R_acc and RUE) increased with N supply. RUE increased from 0·74 and 0·89 g MJ^?1 IPAR for the control treatments to 1·50 and 1·95 g MJ^?1 IPAR under adequate N and water in both experiments. This represented an increase in RUE of 52–146% for the range of N treatments used in both experiments, whilst R_acc increased by 9–17%, compared with the control treatments. Subsequently, the total DM yield of kale increased from 6·7 and 8 t DM ha^?1 for the control treatments to ≥ 19 t DM ha^?1 when ≥150 kg N ha^?1 was applied. The DM yields for the 500 kg N ha^?1 treatments were 25·5 and 27·6 t DM ha^?1 for the two experiments. RUE increased linearly with SLN, at an average rate of 0·38 g DM MJ^?1 IPAR per each additional 1 g N m^?2 leaf until a maximum RUE of 1·90 g MJ^?1 IPAR was reached in both experiments. There were no changes in RUE with SLN of > 2·6 g m^?2 and NNI >1, implying luxury N uptake. RUE was the most dominant driver of forage kale DM yield increases in response to SLN and NNI.     

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.     

Modelling net photosynthetic rate of field-grown cocksfoot leaves under different nitrogen, water and temperature regimes

A simple multiplicative model using temperature, foliage nitrogen (N) concentration and water status was developed to predict the maximum photosynthetic rate (Pmax) of field‐grown cocksfoot (Dactylis glomerata L.) leaves when none, one, two or all the factors were limiting. The highest Pmax was 27·4 μmol CO₂ m^–2 s^?1 in non‐limited conditions, which was defined as the standardized Pmax value dimensionless (Pmax_s=1). Pmax_s increased 0·058 units per °C from 10°C to the optimum range (19–23°C) (Pmax_s=1) and then declined 0·077 units of Pmax_s per °C from 23 to 31°C. Pmax_s=1 was also measured from 59 to 52 g N kg^?1 dry matter (DM) foliage N. Pmax_s then decreased at the rate of 0·115 units per 10 g N kg^?1 DM from 52 to 26 g N kg^?1 DM, and 0·409 units of Pmax_s per 10 g N kg^?1 DM from 26 to 15 g N kg^?1 DM. For predawn leaf water potential (ψ_lp), Pmax_s=1 was measured from ?0·1 to ?1·2 bar but declined linearly at a rate of 0·078 units per bar of ψ_lp from ?1·2 to ?14·0 bar because of a linear decrease in stomatal conductance. An interaction between low N content (≤20 g N kg^?1 DM) and high temperature (>23°C) was also detected. Together, this multiplicative model accounted for 0·82 of the variation in Pmax_s.     

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.     

‘MaxClover’ grazing experiment: I. Annual yields,botanical composition and growth rates of six dryland pastures over nine years

Six dryland pastures were established at Lincoln University, Canterbury, New Zealand, in February 2002. Production and persistence of cocksfoot pastures established with subterranean, balansa, white or Caucasian clovers, and a perennial ryegrass‐white clover control and a lucerne monoculture were monitored for nine years. Total annual dry‐matter (10.0–18·5 t DM ha^?1) and sown legume yields from the lucerne monoculture exceeded those from the grass‐based pastures in all but one year. The lowest lucerne yield (10 t ha^?1 yr^?1) occurred in Year 4, when spring snow caused ungrazed lucerne to lodge and senesce. Cocksfoot with subterranean clover was the most productive grass‐based pasture. Yields were 8·7–13·0 t DM ha^?1 annually. Subterranean clover yields were 2·4–3·7 t ha^?1 in six of the nine years which represented 26–32% of total annual production. In all cocksfoot‐based pastures, the contribution of sown pasture components decreased at a rate equivalent to 3·3 ± 0·05% per year (R² = 0·83) and sown components accounted for 65% of total yield in Year 9. In contrast, sown components represented only 13% of total yield in the ryegrass‐white clover pastures in Year 9, and their contribution declined at 10·1 ± 0·9% per year (R² = 0·94). By Year 9, 79% of the 6.6 t ha^?1 produced from the ryegrass‐white clover pasture was from unsown species and 7% was dead material. For maximum production and persistence, dryland farmers on 450–780 mm yr^?1 rainfall should grow lucerne or cocksfoot‐subterranean clover pastures in preference to ryegrass and white clover. Inclusion of white clover as a secondary legume component to sub clover would offer opportunities to respond to unpredictable summer rainfall after sub clover has set seed.     

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.     

Net photosynthetic rate of cocksfoot leaves under continuous and fluctuating shade conditions in the field

Maximum light‐saturated photosynthetic rate (Pmax) and stomatal conductance (gs) of field‐grown cocksfoot (Dactylis glomerata L.) leaves in a silvopastoral system were measured at different times under moderate (850–950 µmol m^?2 s^?1 photosynthetic photon flux density, PPFD) and severe shade (85–95 µmol m^?2 s^?1 PPFD). Also Pmax and gs were measured after 30, 60 and 180 min of severe shade to determine the lag in the rise of photosynthesis rate from low to high irradiance levels (induction state). The highest Pmax and gs values obtained were 26·5 µmol CO₂ m^?2 s^?1 and 0·41 mol H₂O m^?2 s^?1 in non‐limiting conditions with full sunlight (1900 µmol m^?2 s^?1 PPFD). These values were defined as standardized dimensionless Pmax_s=1 and gs_s=1 for comparison of treatment effects. The Pmax_s under severe shade decreased by 0·004 units per minute from 1 to 180 min and reached a steady‐state of 0·37 units after 140 min. Under moderate shade, Pmax_s decreased by 0·002 units per minute from 1 to 120 min and reached a steady‐state of 0·76 units. The time required to reach full induction on return to full sun (Pmax_s=1) was 15 min after 30 min of severe shade and 37 min after 180 min of shade. Mathematical equations were derived to describe the changes in Pmax_s and gs_s under severe and moderate shade and during induction. The rate of change of gs_s was slower than for Pmax_s on entering shade and also slower during the subsequent induction process. This indicated other factors in addition to gs were operating in the reduction and increment of Pmax and a two‐step model to explain this is proposed. The defined photosynthetic responses of cocksfoot leaves to fluctuating light regimes could be used to develop quantitative predictions of Pmax for inclusion in a canopy photosynthesis model of silvopastoral systems.     

Effect of application timing and grass height on the nitrogen fertilizer replacement value of cattle slurry applied with a trailing‐shoe application system

This study investigated the effect of using a trailing‐shoe system to apply cattle slurry, under different conditions of grass height (low [LG]: freshly cut sward [4–5 cm height] vs. high [HG]: application delayed by 7–19 d and applied to taller grass sward [4–11 cm] height) and month of application (June vs. April), on the nitrogen fertilizer replacement value (NFRV) and apparent N recovery (ANR_S) of cattle slurry applied to grassland. NFRV was calculated using two methods: (i) NFRV_N based on the apparent recovery of slurry‐N relative to that of mineral‐N fertilizer; and (ii) NFRV_DM based on DM yield. The effect of applying slurry into HG swards, relative to LG swards, decreased the DM yield by 0·47 t ha^?1 (P ≤ 0·001), N uptake by 5 kg ha^?1 (P = 0·05), ANR_S by 0·05 kg kg^?1 (P = 0·036), NFRV_N by 0·05 kg kg^?1 (P = 0·090) and NFRV_DM by 0·11 kg kg^?1 (P < 0·001). It was concluded that the main factor causing these decreases with HG, compared with LG applications, was wheel damage affecting subsequent N uptake and growth of the taller grass sward.     

Yield and nitrogen concentration of above- and below-ground biomasses of red clover cultivars in pure stands and in mixtures with three grass species in northern Europe

Three red clover (Trifolium pratense) varieties differing in productivity and winter hardiness, Jokioinen, Betty and Ilte, were sown in a 2‐year (2003–2004) pot experiment in pure stands and mixtures with the grasses, timothy (Phleum pratense), tall fescue (Festuca arundinacea) and meadow fescue (Festuca pratensis). Grass growth dominated until fertilizer‐N, applied when the stands were sown, was depleted. Timothy was the least competitive of the grass species. Red clover variety Ilte produced the highest dry‐matter (DM) yields. Variety Betty yielded less, but allocated as much biomass to the root and stubble (soil‐bound) fraction as variety Ilte. Variety Jokioinen allocated least to the soil‐bound fraction. While the root structure and the starch concentration of the crown‐root area were similar in all varieties, the high ratio of soil‐bound: harvested fractions could be a key to the higher winter survival and higher DM yields of Betty under field conditions. At the end of the experiment, 3–5 g N pot^?1 (49–81 g m^?2) had been harvested and 0·7–1·5 g N pot^?1 (11–24 g m^?2) was left in the soil‐bound fraction, amounts depending on the red clover variety and grass mixture, with pure clover stands containing the highest N amounts. Because of the high N concentrations in the biomass of red clover, the proportion of red clover and conditions prevailing during canopy and root death in mixed stands are crucial for N mineralization and incorporation into new growth.     

Effects of cutting frequency on plant production, N-uptake and N2 fixation in above- and below-ground plant biomass of perennial ryegrass–white clover swards

Nitrogen (N), accumulating in stubble, stolons and roots, is an important component in N balances in perennial ryegrass–white clover swards, and the effects of cutting frequency on the biomass of above‐ and below‐harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N₂ fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range of 3000–7000 kg DM ha^?1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height but the different weather conditions between years had less effect on stubble and, in particular, biomass of roots. The biomass of roots of white clover was significantly lower than that of roots of perennial ryegrass and remained at a relatively constant level (200–500 kg DM ha^?1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2400 kg DM ha^?1 in the year of establishment to 10 200 kg DM ha^?1 in the infrequent cutting treatment and 6650 kg DM ha^?1 in the frequent cutting treatment by the end of the experiment, giving shoot:root ratios of 4·7–16·6 and 0·5–1·6 for white clover and perennial ryegrass respectively. Annual N₂ fixation was in the range of 28–214 kg N ha^?1, and the proportion of N fixed in stolons and roots was on average 0·28. However, as weather conditions affect the harvested DM production and the shoot:root ratio, care must be taken when estimating total N₂ fixation based on an assumed or fixed shoot:root ratio.     

Characteristics of baled silage made from first and second harvests of wilted and severely wilted forages

First and second harvests of lucerne (Medicago sativa L.), perennial ryegrass (Lolium perenne L.) and a lucerne–perennial ryegrass mixture [80 or 144 g kg^?1 dry matter (DM) of ryegrass] at the first and second harvests were cut and conditioned, wilted to 500 or 700 g DM kg^?1 then baled and stretch‐wrapped for silage on the same dates. Lucerne bales were denser (411 kg m^?3) than bales of perennial ryegrass (331 kg m^?3) (P < 0·05). After an 8‐month storage period, silage made from high DM‐content forage had a higher concentration of neutral‐detergent fibre (NDF) and was less digestible than that made from low DM‐content forage. Daily DM intakes by beef steers, when the silages of the second harvest were fed ad libitum, were 31·2, 31·2 and 22·3 g kg^?1 live weight for lucerne, lucerne–perennial ryegrass mixture and perennial ryegrass silages, respectively (P < 0·01), when the herbage had been wilted to 500 g kg^?1. In vivo digestibility of NDF in the lucerne–perennial ryegrass mixture silage (0·587) was significantly lower than that of perennial ryegrass silage (0·763) but higher than lucerne silage (0·518). Higher intakes of baled lucerne silage tended to offset its lower digestibility values. Lucerne–perennial ryegrass mixture silage had a higher DM and NDF digestibility than lucerne silage, indicating perhaps the presence of associative effects.     

Potential of imaging spectroscopy as tool for pasture management

The use of imaging spectroscopy to predict the herbage mass of dry matter (DM), DM content of herbage and crude fibre, ash, total sugars and mineral (N, P, K, S, Ca, Mg, Mn, Zn and Fe) concentrations was evaluated. The experimental system used measured reflectance between 404 and 1650 nm at high spatial (0·28–1·45 mm²) and spectral resolution. Data from two experiments with Lolium perenne L. mini‐swards were used where the degree of sward damage or N‐fertilizer application varied. Regression models were calibrated and validated and the potential reduction in prediction error with multiple observations was estimated. The mean prediction errors for DM mass, DM content and N, total sugars, ash and crude fibre concentrations were 235–268 kg ha^?1, 9·6–16·8 g kg^?1, 2·4–3·4 g kg DM^?1, 16·2–27·7 g kg DM^?1, 5·8–6·5 g kg DM^?1 and 8·4–10·4 g kg DM^?1 respectively. The predictions for concentrations of P, K, S and Mg allowed identification of deficiency levels, in contrast to the concentrations of Na, Zn, Mn and Ca which could not be predicted with adequate precision. Prediction errors of DM mass may be maximally reduced to 95–142 kg ha^?1 with 25 replicate measurements per field. It is concluded that imaging spectroscopy can provide an accurate means for assessment of DM mass of standing grass herbage. Predictions of macronutrient content and feeding value were satisfactory. The methodology requires further evaluation under field conditions.     

The effects of treating low dry-matter, low digestibility grass with a bacterial inoculant on the intake and performance of beef cattle, and studies on its mode of action

This experiment evaluated a bacterial inoculant based on a single strain of Lactobacillus plantarum as a silage additive. Three silages were harvested on 8 September 1989 from the second regrowth of a perennial ryegrass sward, which had received 167 kg N, 28 kg P₂O₅ and 45 kg K₂O ha^?1. Mean dry matter (DM) and water soluble carbohydrate concentrations of the herbages at ensiling were 148 g kg^?1 and 78 g.(kg DM)^?1 respectively. Herbages were treated with either no additive (C), formic acid (3·0 1 t^?1) (F) or the inoculant (3·0 1 t^?1) (I) and were ensiled in three 80-t capacity silos. For silages C, F and I respectively, pH values were 4·70, 3·77 and 4·47, ammonia-N concentrations were 192, 111 and 182 g (kg total N)^?1 and butyrate concentrations were 6·8, 1·8 and 7·1 g (kg DM)^?1. The silages were offered ad libitum and supplemented with 2·0 kg concentrates per head daily to thirty-six heifers (mean initial live weight 442 kg). For silages C, F and I, silage DM intakes were 12·7, 14·4 and 14·1 (s.e. 0·42) g (kg live weight)^?1, metabolizable energy intakes were 155, 166 and 172 (s.e. 5·1) kJ (kg live weight)^?1, and estimated carcass gains were 456, 519 and 518 (s.e. 28·1) g d^?1 respectively. A further 18 similar cattle were used in studies on the digestibility of the silages, and rumen degradation of each was estimated with three mature cattle. Inoculant treatment significantly increased crude fibre (P <0·01), neutral detergent fibre (P <0·01), modified acid detergent fibre (P <0·01), hemicellulose (P <0·05) and N digestibilities (P <0·05) and tended to increase N retention from the total diet. It is concluded that although treatment of herbage that was difficult to ensile with the inoculant did not improve silage fermentation, it significantly increased digestibility, especially of the fibre fractions, and silage DM intake and tended to increase animal performance to levels similar to those achieved with a well preserved formic acid-treated silage. Increases in silage DM and metabolizable energy intakes are likely to have been attributable to the effects of the inoculant on digestibility, especially of the fibre fractions.     

Chemical composition and nutritive value of leaves and stems of tropical weed Chromolaena odorata

Chromolaena odorata (Siam weed) has been classified as a weed plant in West Africa. Data from C. odorata foliage after 4, 6, 8, 10 and 12 weeks of regrowth showed that the leaf fraction had a crude protein content above 194 g kg^–1 dry matter (DM) and an average leaf to stem ratio of 2·1:1. Chemical analysis of the leaf fraction of an 8‐week‐old regrowth indicated a high crude protein content (258 g kg^–1 DM) and a high degradable nitrogen content (60·7 g N kg^–1 digestible organic matter), but low neutral‐detergent fibre (331 g kg^–1 DM), acid‐detergent lignin (53·1 g kg^–1 DM), total extractable phenolic (37·1 g kg^–1 DM), extractable tannin (0·72 absorbance at 550 nm) and extractable condensed tannin (1·4 g kg^–1 DM) contents. In sacco degradability analysis of the 8‐week‐old regrowth leaf sample showed a high 48 h organic matter (935 g kg^–1 DM) and crude protein (953 g kg^–1 DM) degradability. The leaf sample had an organic matter degradability of 670 g kg^–1 DM as estimated by cumulative gas production in vitro after 24 h incubation. There was little or no phenolic‐related antinutritive factors in C. odorata. Additionally, leaf samples had no effect on rumen protozoa activity estimated as the rate of [¹⁴C]leucine Selenomonas ruminantum bacterial protein breakdown. Data from this study suggest that C. odorata leaves are of high nutritive value and might have the potential to be used as a protein supplement to ruminants. There is need for further investigation to test whether C. odorata leaves may have any deleterious effect on the host animal.     

The response of manured forage maize to starter phosphorus fertilizer on chalkland soils in southern England

The impact of various starter phosphorus (P) fertilizers on the growth, nutrient uptake and dry‐matter (DM) yield of forage maize (Zea mais) continuously cropped on the same area and receiving annual, pre‐sowing, broadcast dressings of liquid and semi‐solid dairy manures was investigated in two replicated plot experiments and in whole‐field comparisons in the UK. In Experiment 1 on a shallow calcareous soil (27 mg l^?1 Olsen‐extractable P) in 1996, placement of starter P fertilizer (17 or 32 kg ha^?1) did not benefit crop growth or significantly (P > 0·05) increase DM yield at harvest. However, in Experiment 2 on a deeper non‐calcareous soil (41 mg l^?1 Olsen‐extractable P) in 1997, placement of starter P fertilizer (19 or 41 kg P ha^?1), either applied alone or in combination with starter N fertilizer (10 or 25 kg N ha^?1), significantly increased early crop growth (P < 0·01) and DM yield at harvest by 1·3 t ha^?1 (P < 0·05) compared with a control without starter N or P fertilizer. Placement of starter N fertilizer alone did not benefit early crop growth, but gave similar yields as P, or N and P, fertilizer treatments at harvest. Large treatment differences in N and P uptake by mid‐August had disappeared by harvest. In field comparisons over the 4‐year period 1994–97, the addition of starter P fertilizer increased field cumulative surplus P by over 70%, but without significantly (P > 0·05) increasing DM yield, or nutrient (N and P) uptake, compared with fields that did not receive starter P fertilizer. The results emphasized the extremely low efficiency with which starter P fertilizers are utilized by forage maize and the need to budget manure and fertilizer P inputs more precisely in order to avoid excessive soil P accumulation and the consequent increased risk of P transfer to water causing eutrophication.     

Performance of white clover/perennial ryegrass mixtures under cutting

Clover persistence in mixtures of two varieties of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover (Trifolium repens) varieties differing in leaf sizes was evaluated at two cutting frequencies. An experiment was sown in 1991 on a clay soil. The plots received no nitrogen fertilizer. In 1992, 1993 and 1994, mixtures containing the large-leaved clover cv. Alice yielded significantly more herbage dry matter (DM) and had a higher clover content than mixtures containing cvs Gwenda and Retor. Companion grass variety did not consistently affect yield or botanical composition. Cutting at 2 t DM ha^?1 resulted in slightly higher total annual yields than cutting at 1.2 t DM ha^?1, but did not affect clover content. In 1992 the mixtures yielded, depending on cutting frequency and variety, 10·6–14·6 t DM ha^?1 and 446–599 kg ha^?1 N, whereas grass monocultures yielded only 1·2–2·0 t DM ha^?1 and 25–46 kg ha^?1 N. From 1992 to 1994 the annual mean total herbage yield of DM in the mixtures declined from 12·2 to 10·5 to 8·7 t ha^?1, the white clover yield declined from 8·7 to 6·5 to 4·1 t ha^?1 and the average clover content during the growing season declined from 71% to 61% to 46%, whereas the grass yield increased from 3·4 to 4·0 to 4·5 t ha^?1. The N yield decreased from 507 to 406 to 265 kg N ha^?1 and the apparent N fixation from 470 to 380 to 238 kg N ha^?1. Nitrate leaching losses during the winters of 1992–93 and 1994–95 were highest under mixtures with cv. Alice, but did not exceed 10 kg N ha^?1. The in vitro digestible organic matter (IVDOM) was generally higher in clover than in grass, particularly in the summer months. No differences in IVDOM were found among clover or grass varieties. The experiment will be continued to study clover persistence and the mechanisms that affect the grass/clover balance.     

Effects of supplementation on the ingestive behaviour of grazing steers*

Herbage intake is usually depressed when beef cattle grazing abundant pastures are supplemented with energy-rich feedstuffs but relatively little is known about the effects of supplementation on the components of ingestive behaviour. An experiment was conducted to establish the effect of ground corn (Zea mays L.) on the ingestive behaviour of yearling Angus and Angus × Hereford steers (Bos taurus) (mean live weight (LW) of 323 kg) grazing autumn stockpiled Boone cocksfoot (Dactylis glomerata L.) using a tethered grazing system in which the experimental unit was the tethered steer and its grazing area (45 m²) for one grazing session. Herbage dry matter (DM) mass was 1662 kg ha^?1 and herbage DM allowance was 7–5 kg steer^?1 for each grazing session. Herbage DM intake was measured as the difference between herbage DM mass offered and refused. Grazing took place during two daily sessions each of about 2 h duration commencing at 08.00 and 14.00 h for 9 days. Ground corn (0, 1·5, 3·0 and 4·5 kg steer^?1) was fed each day at 12.00 h and had no significant (P < 0·05) effect on rate of DM intake, rate of biting or DM intake per bite. Mean DM intake was 6 2 kg steer^?1 d^?1 (87 mg (kg LW)^?1 min^?1). Steers averaged 4832 bites per grazing session, with a mean DM intake per bite of 644 mg (2·0 mg (kg LW)^?1) and a mean rate of 44 bites min^?1. Data obtained at the beginning and end of each grazing period on ingestive behaviour of one group of four steers (mean LW of 306 kg) fitted with oesophageal fistulae supported data for the two groups of normal steers and showed no response to supplementation. Mean values for rate of DM intake, DM intake per bite and rate of biting established for the fistulated cattle were 73 mg (kg LW)^?1 min^?1, 521 mg bite^?1 (1·7 mg (kg LW)^?1) and 39 bites min^?1, respectively.     

Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne L.). Evaluation in dairy cows in early lactation

Twelve multiparous Holstein–Friesian dairy cows in early lactation were used to investigate the potential of using perennial ryegrass (Lolium perenne) with a high concentration of water‐soluble carbohydrates (WSC) to increase the efficiency of milk production. Ad libitum access to one of two varieties of zero‐grazed herbage was given continuously for 3 weeks: treatment High Sugar (HS), an experimental perennial ryegrass variety (Ba11353) bred to contain a high concentration of WSC, harvested in the afternoon; or Control, a standard variety of perennial ryegrass (cv. AberElan), harvested in the morning. All dairy cows also received 4 kg d^?1 of a standard dairy concentrate. Dairy cows given the HS diet treatment consumed 2·8 kg dry matter (DM) d^?1 more than Control dairy cows (P < 0·01), and the DM digestibility of the diet on the HS treatment was significantly greater than that of the diet on the Control treatment (0·75 vs. 0·72; s.e.d. 0·010; P < 0·05). Excretion of urinary purine derivatives (PD) tended (P < 0·1) to be higher from dairy cows on the HS treatment, implying increased microbial protein flow to the duodenum, although there was no significant difference in the apparent efficiency of rumen fermentation of either dietary nitrogen (N) or DM expressed as a ratio to urinary PD. Milk yields and milk composition were not significantly affected by dietary treatment, although true protein yields of milk were higher (P < 0·05) from dairy cows given the HS treatment. The proportion of dietary N excreted in urine was significantly lower from HS cows, although the values were low for both treatments (0·20 g g^?1 vs. 0·27 g g^?1; s.e.d. 0·020; P < 0·05). It is concluded that increased DM intakes by dairy cows given the HS treatment led to increased milk protein outputs. With a proportional decrease in urinary N excretion, the use of perennial ryegrass with a high WSC concentration, in the context of the harvesting regime used in this study, may help to reduce N pollution from dairy systems into which it is incorporated.     

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.