STUDIES OF RESPONSE TO FERTILIZER NITROGEN

Fifteen out of 36 possible combinations of 3 cutting dates for hay, 3 rates of N application and 4 intervals between N application and cutting date were compared to study the effects of pre-harvest application of N on the N, P, K, Mg and Ca contents of the aftermath and the effectiveness of utilization of these elements. According to the method of calculation given by ARC (1), the control haycrop harvested on 16 June was deficient in N, Ca, P and Mg, and the aftermath which was given no further N after harvest was of low bulk, but adequate in mineral content. Earlier harvesting improved the quality of the hay, and increased the bulk and reduced the mineral content of the aftermaths. Applying 125.6 kg N/ha after harvest resulted in a satisfactory increase in bulk, plus an improved mineral content in the aftermath. Applying N before harvest resulted in increased uptake of N, K, Ca, P and Mg in the hay and in the increased percentage of N, K, and Ca in the DM of the hay. Very early application of pre-harvest N increased the percentage of Mg. The general effect of pre-harvest N on the aftermath was to reduce yield and uptake of N, K, Ca, P and Mg. Doubling the pre-harvest N raised the mineral uptake. Very early pre-harvest application resulted in low mineral uptake in the aftermath. The percentage of N, K and P in the aftermath was reduced by pre-harvest N applied at both levels and on both dates. Deferring the application of fertilizer N until 4 days after harvesting the hay crop produced the highest mineral contents in the aftermath, without reducing its bulk. Mineral uptake in the regrowths was linearly related to N uptake at 1.43 kg K, 0.34 kg Ca, 0.157 kg P, 0.006 kg Mg/kg N uptake.     

Forage yield and quality from intercropped barley, annual ryegrass and different annual legumes

Six annual legumes were evaluated as components of cereal-grass-legume intercrops in two experiments at two sites differing in elevation by 789 m. Barley (Hordeum vulgare L.) and Westerwolds rye-grass (Lolium multiflorum Lam.) were seeded on all intercrop plots. Dry-matter (DM) yield, crude protein (CP) and organic matter digestibility (OMD) were measured. DM yield and N content were used to estimate legume N fixation. Experiment 1 was conducted at both sites. At the lower site, Persian clover (Trifolium resupinatum L.) and annual alfalfa (Medicago sativa L.) accounted for 70% of the DM yield in harvest 1 (July), increased CP and OMD, but did not affect intercrop yield. They increased harvest 2 (August/September) intercrop yield by 263% and CP concentration by 65 g kg^?1 DM. They increased harvest 3 (October) yield by 275% and CP concentration by 78 g kg^?1 DM. Inclusion of striate lespedeza (Lespedeza striata) did not affect intercrop yield or quality. Annual legumes failed to establish at the higher elevation site and therefore had no effect on DM yield or forage quality. In Experiment 2, in which the performance of Westerwolds ryegrass was also compared with that of Italian ryegrass, and conducted at the lower site only, Persian clover and berseem clover (T. alexandrinum L.) increased CP of all three of the year's harvests. These two species contributed 29% of the DM yield in the first harvest (July) but did not affect total intercrop yield. They increased harvest 2 (August) yield by 313%. Persian clover increased harvest 3 (October) yield by 318% and berseem clover increased harvest 3 yield by 405%. Barrel medic (Medicago truncatula) and snail medic (M. scutellata) contributed 29% of harvest 1 yield, and increased both DM yield and CP content. Medics did not regrow. Aubade Westerwolds ryegrass contributed a greater percentage of the DM yield than did Maris Ledger Italian ryegrass at harvests 1 and 2. Ryegrass type did not affect total DM yield but did affect forage quality; intercrops containing the Italian ryegrass had higher CP at harvest 2 and higher OMD at harvest 3 than those containing the Westerwolds ryegrass. Over both experiments, at the lower elevation site, stands with Persian clover, berseem clover or alfalfa produced 80% of the yield of barley-ryegrass receiving 250 kg N ha^?1, and 165% of the yield of unfertilized barley-ryegrass. Berseem and Persian clover fixed about the same amount of N over the growing season; 188 kg N ha^?1 in Experiment 1 and 134 kg N ha^?1 in Experiment 2.     

STUDIES IN RESPONSE TO NITROGEN

The residual effects of 59, 118 or 177 kg N/ha applied to the primary growth of a ryegrass sward were measured in two successive regrowths as yields of fresh matter (FM), DM and digestible organic matter (DOM). The first regrowths (RGl) harvested on 12 June followed primary growth (PG) harvests 8, 12, 16, 23, 29, 45 and 57 days after applying N on 16 Apr. The second regrowths (RG2) were harvested on 12 Aug., 62 days after RGl and 119 days after applying N. Significant residual responses were shown in both regrowths which increased the annual responses substantially. Responses to the first increment of N, averaged over dates of primary growth harvests, were raised from 70.3 kg FM, 9.2 kg DM, and 5.6 kg digestible OM/kg N applied, for the primary growth, to responses for primary growth+2 regrowths of 140.8 kg FM, 22.5 kg DM and 13.9 kg digestible OM/kg N applied. For the second increment of N, negligible or negative primary growth responses of 19.0 kg FM, –0.68 kg DM and –0.68 kg digestible OM/kg N applied became 179.7 kg FM, 25.6 kg DM and 16.4 kg digestible OM/kg N applied for the sum of the 3 growths. There were significant differences between the residual responses obtained for different dates of PG harvest. When PG was harvested 8 days after applying N, primary response was low or negligible; residual responses were high, and the total responses were 21.0 kg DM/kg N applied for the first N increment and 31.0 kg DM/kg N applied for the second. Similar effects were observed for FM and digestible OM. Residual responses to the second increment of N were greatest where primary growth was harvested 23 days after N application. Similar residual responses followed the primary growth harvest 29, 45 and 57 days after N application hut the total responses were reduced. It is concluded that the very high residual responses to the second increment of N can only he explained in terms of increased availability of soil N.     

STUDIES IN RESPONSE TO NITROGEN

Regression equations have been calculated for the primary growth of a ryegrass sward as FM (fresh matter), DM, DOM and for uptake of N, K, P, Ca, Na and Mg after application of 59,118 or 177 kg fertilizer N/ha on 16 Apr. These have been used to predict changes in response with time, the responses in terms of time, the dates when specific yields of DM are attained, the different characteristics of herbages at specified yields of DM and the effects of changing harvesting interval on annual DM yield and uptake of minerals. DM and DOM show significant responses to 118 kg N/ha but no response to the next increment throughout the 57-day growth period. All other attrihutes, including FM, showed responses to 177 kg N/ha. Calculated response as days gained suggest that for short-interval grazing systems the use of even 118 kg N/ha is questionable. The reduction in annual DM production and the increase in N uptake when growth intervals are shortened are related to the form of their growth curves.     

THE EFFECT OF NITROGEN FERTILIZER AND CLIPPING FREQUENCY UPON THE YIELD AND IN VITRO DIGESTIBILITY OF INTERMEDIATE WHEATGRASS

The effect of rate of nitrogen fertilizer and clipping frequency on total production of dry matter (DM), in vitro digestible organic matter (DOM), and crude protein (CP) was investigated in the first harvest year of intermediate wheatgrass. The highest yields of DM and DOM, but not of CP, were obtained at the longest clipping intervals and at the higher rates of fertilizer application. Fertilizer failed to give satisfactory increases in yield even at very high rates of application when a 2-week clipping interval was used. The interaction between clipping frequency and fertilizer rate had a highly significant effect on yields of both DM and DOM. A sharp decline in percentage DOM that occurred with increasing length between clippings was offset to some degree by application of N fertilizer. A similar assessment of treatments was obtained from DOM and DM yield data when the grass was fertilized with N, but not when N was deficient. The CP data gave a different assessment of treatments from that obtained from either DOM or DM data.     

Intake, rumen fermentation, degradability and digestion kinetics in beef cattle offered autumn grass herbage differing in regrowth interval

The effects of a 10-d increase in regrowth interval (35 and 45 d) of a predominantly perennial ryegrass sward harvested in two periods in the autumn in Ireland on feed intake, rumen fermentation, in situ degradability and rumen digesta kinetics was examined using six ruminally cannulated Holstein–Friesian steers in three replicates of a 2 × 2 crossover design. The longer regrowth interval had a higher grass dry-matter (DM) yield of herbage by 615 kg DM ha⁻¹ and a lower crude protein (CP) concentration of herbage by 27 g kg⁻¹ DM. There was no effect of regrowth interval on DM intake, rumen pH, total volatile fatty acid concentration or the molar proportions of acetate, propionate or butyrate in the rumen but the concentration of rumen ammonia (NH₃-N) was lower on the longer regrowth interval. The longer regrowth interval had a lower apparent total tract digestibility of DM, organic matter (OM), N and neutral-detergent fibre (NDF). There was no effect of regrowth interval on the in situ degradability of DM, OM, N or NDF. The passage rates ( k _p) of DM and OM were higher while the rate of digestion ( k _d) of DM and NDF was lower with the longer regrowth interval. The results indicated that, although increasing the regrowth interval by 10 d in autumn reduced the apparent digestibility of the grass herbage, there was no adverse effect on DM intake, rumen fermentation pattern or in situ rumen degradability. The reduction in rumen NH₃-N concentrations, reflecting the lower herbage CP concentration in herbage for the longer regrowth interval, may potentially reduce nitrogen excretion to the environment.     

In vitro total and methane gas production as influenced by rate of nitrogen application, season of harvest and perennial ryegrass cultivar

The effects of rate of inorganic nitrogen (N) fertilization (0, 80 or 160 kg N ha^?1 per regrowth), season of harvest (regrowths 1, 2 and 3) and perennial ryegrass (Lolium perenne L.) cultivar [classified as having either a normal or elevated water soluble carbohydrate (WSC) concentration genotype] on in vitro gas production and digestibility were assessed. Increased N fertilizer application significantly decreased total gas production (TGP), methane (CH₄) production and organic matter digestibility (OMD). The results suggest that the decreases in TGP and CH₄ production were associated with a restriction in organic matter (OM) fermentation and an altered crude protein (CP) to structural carbohydrate ratio rather than a modification in the stoichiometry of fermentation. Season of harvest only significantly (P < 0·05) altered in vitro OMD and CH₄ production at 8 h, despite altering the chemical composition of the herbage. Cultivar effects on all measured in vitro parameters were not significant presumably because the elevated WSC concentration trait was not expressed strongly in the study.     

The impact of supplementation with Rhagodia preissii and Atriplex nummularia on wool production,mineral balance and enteric methane emissions of Merino sheep

The Australian perennial shrubs, oldman saltbush (Atriplex nummularia) and rhagodia (Rhagodia preissii), can complement the diets of sheep grazing moderate‐quality cereal residues. We compared liveweight change, organic matter digestibility, nitrogen and mineral balance, wool growth and methane emissions of Merino wethers offered oaten hay (OMD 622 g kg^?1 DM; N 9.74 g kg^?1 DM) with and without shrub biomass (substituted at 25% of OM). Diets were fed at restricted levels for 1 month. Substituting hay with shrub biomass significantly decreased liveweight loss, increased clean wool growth and increased apparent absorption of phosphorus compared to the hay alone. Substitution of hay with both saltbush and rhagodia led to over 23% greater clean wool growth. Nitrogen balance and apparent digestion of organic matter, calcium and magnesium did not vary significantly between animals on the diets. Wethers on the rhagodia and hay diets had similar enteric methane emissions, while animals offered the saltbush diet had significantly higher emissions (L/OM intake). When methane is expressed in terms of wool growth, animals on the rhagodia diet produced 26% less methane for every gram of wool.     

STUDIES OF RESPONSE TO FERTILIZER NITROGEN

The uptake of N was measured in 2 successive regrowths harvested on 12 June and 13 Aug. following harvests of primary growths 8, 12, 16, 23, 29, 45 and 57 (12 June) days after applying N at 59, 118 or 177 kg N/ha on 16 Apr. Residual responses were obtained to both increments of N, leading to high apparent recoveries of fertilizer N, especially to the higher increment. This increased availability of soil N when high rates of N are applied is shown to vary with date of harvest of primary growth, reaching a maximum equivalent to 151% apparent fertilizer N recovery 23 days after N application. In the second regrowth, percentage N in the herbage showed a negative response to N applied to the primary growth. This appears to reflect a reduction in available soil N brought about by its increased availability and uptake in primary growth and first regrowth. The possibilities of improving the efficiency of fertilizer N by exploiting soil N are considered against the possible reduction in available N for future regrowths.     

The effect of date of primary growth harvest and levels of nitrogen and potassium fertilizers on the dry matter production of timothy (Phleum pratense)

Scots timothy was harvested three times a year for 3 years under four harvesting patterns and at all combinations of three levels of application of nitrogen and four of potassium. Harvesting patterns, H1, H2, H3 and H4, comprised cutting primary growth on 27–29 May or 14, 28 or 42 d later followed by cutting a first regrowth 8 weeks afterwards and a second regrowth on 15–16 October. N treatments, N0, N1 and N2, involved annual totals of 0,108 and 216 kg ha^-1 N in three equal doses. K treatments, K0, K1, K2 and K4, involved annual totals of 0, 54, 108 and 216 kg ha^-1 K also in three equal doses. Mean herbage DM yields in successive years were 8·90, 9·54 and 9·61 t ha^-1 containing92·4%, 93·1% and 94·5% timothy, respectively. Systems H3 and H4 had 24% higher yields than H1 and H2. The superiority of the late systems derived from higher yields of primary growth. Mean response to 108 kg ha^-1 N at 36·7 kg DM per kg N was significantly higher than the response to an additional 108 kg ha^-1 N. Response in primary growth to successive increments of 36 kg ha^-1 N averaged 53·9 and 27·5 kg DM per kg N. The first regrowth gave linear responses up to 72 kg ha^-1 N. The possibility is discussed of more effective use of N by increasing the proportion applied to regrowth. Response to K was low except in the third year when there was a marked response at N2. It was calculated that to maintain soil potash it is necessary to apply 23·9, 47·7 and 86·6 kg ha^-1 fertilizer K for each harvest at N0, N1 and N2 respectively.     

Differences in the nitrogen use efficiency of perennial ryegrass varieties under simulated rotational grazing and their effects on nitrogen recovery and herbage nitrogen content

Eight varieties of perennial ryegrass (six new varieties and two old ones) grown at five levels of applied fertilizer (100, 200, 300, 400 and 500 kg of N ha^–1) were cut monthly during two growing seasons (March to October in 1997 and 1998) and their herbage dry‐matter (DM) yield and nitrogen (N) content were determined. Herbage leaf content and the N content of young fully expanded leaves were also measured in 1997, and monthly recovery of applied N was determined in both the first and second harvest years by using ¹⁵N. The rank order of varieties was similar for annual yield of DM and N at all five fertilizer levels. Proportional differences between varieties in DM yield were greatest in the first cut of each year, the late‐heading candidate variety Ba12151 out‐yielding the old late‐heading variety S23 by more than 70%. However, differences in annual DM yield were much more modest than in early spring yield, up to 10% in 1997 and up to 21% in 1998. The relatively small differences in total annual DM yield were attributed to only a small proportion of the applied N being recovered during a single regrowth period, most of the remainder becoming available for uptake in subsequent regrowth periods. There were small but highly statistically significant differences among varieties in the N content of their leaves, leaf N content being inversely related to yield of DM and N. This lends further support to the hypothesis that the metabolic cost of protein synthesis and turnover is a key factor controlling genetic variation both in leaf yield and in annual DM and N yield under frequent harvesting. Seasonal variation in herbage N content was much greater than differences among varieties in mean N content over all harvests. In May of both years at all applied fertilizer levels, herbage N content fell below the 20 g N kg^–1 DM level required by productive grazing animals.     

Use of regrowth for forage in seed crops of meadow fescue(Festuca pratensis Huds.)

Different procedures for autumn management in crops of Festuca pratensis grown for seed, in particular the possibility of combining seed production with the production of forage in autumn, were examined in eleven experiments conducted between 1993 and 1996 at various locations in south-east Norway. Methods without intensive use of regrowth, such a nitrogen (N) fertilizer application (40 Kg N ha^?1) on 10 the September, either separately or preceded by cutting on the same date, generally stimulated the subsequent number of reproductive tillers and seed yield compared with untreated plots (no N, no cuting). However, cutting before N fertilizer application on 10th September tended to have a nagative effect on seed yield in 1995–96, when a mild autumn was followed by a winter with extremely low temp ratures and no, or very little, snow cover. Maximizing regrowth, by the application of 80 kg N fertilizer ha^?1 immediately after seed harvest, never impaired seed yield when a forage harvest was taken on 10 September but did so in 1995–96, when a forage harvest was delayed to 10 October. Additional N (40 kg ^?1) after a forage harvest did not significantly affect seed yield, although negative and positive tendencies were observed after harvesting in September and October respectively. When forage harvesting was delayed from 10 September to 10 October, the average yields of dry matter (DM) increased, but the forage quality, especially the crude protein content, decreased. As a result of the high yields of DM obtained (on average 2250 kg ^?1 in September and 2610 kg^?1 in October), use of regrowth may be of essential economic value for seed growers of Festuca pratensis.     

THE YIELD RESPONSE OF A TALL FESCUE/WHITE CLOVER SWARD TO NITROGEN RATE AND HARVESTING FREQUENCY

A series of eight fertilizer N rates, ranging from 0 to 377 kg N/ha per year, at increments of 53.8 kg N, was applied to a S170 tall fescue/SlOO white clover sward. The annual rates were split into 8, 6 or 4 equal dressings for harvests at intervals of 3, 4 and 6 weeks, respectively, over a 24-week growth period from March to September, in each of two years. Residual harvests were taken 6 weeks later in October. Curves relating annual herbage yields to N rate were fitted to tbe data. Total herbage DM responses to 108 kg N/ha were small because of the typical white clover yield N rate interaction, but were almost linear from 108 to 323 kg N/ha at all harvesting frequencies. Tbe decline in rate of response at tbe bigher N application levels was less marked with frequent than with infrequent defoliation. Tall fescue DM responses were substantially linear from 0 to 323 kg N/ha. For the first and second years, relative DM yields of total herbage for harvesting frequencies of 3, 4 and 6 weeks were 100:108:120 and 100:111:131, respectively. Total herbage CP response curves were similar to those for DM, but continued to rise more steeply to the highest N rate tested, 377 kg N/ha. Tall fescue CP responses were linear from 0 to 377 kg N/ha. Harvesting frequency did not markedly influence CP yields. Total herbage DM yield was 14% less in the second year compared witb the first. The decline was due to a reduction in white clover, attributed mainly to the effect of repeated N applications, also the subsidiary effects of companion grass and weather.     

STUDIES OF RESPONSE TO FERTILIZER NITROGEN

The effects of 59, 118 or 177 kg N/ha were measured on 7 occasions from 8 to 57 days after application to a perennial ryegrass sward in terms of changes in composition. The first increase Dt of N significantly raised percentages of CP, non-protein N, K, P, Ca, Na and Mg and significantly depressed percentages of DM, OM and OM digestihility. The second increment of N resulted in a further rise in the percentages of CP, true protein, non-protein N, K, P, Ca, Na and Mg; the percentages of DM and OM were further depressed but OM digestihility was not significantly depressed. Percentages of P and Na showed increased responses for the more mature herbage; while percentage non-protein N showed a more marked response in younger herbage. As herbage matured percentages of OM and Na rose, the latter only from days 16 to 45. All other attributes showed falling percentages to levels which could be inadequate for a 500 kg dairy cow yielding 15 kg milk. CP percentage reached this critical level (1.4% N) at days 37, 45 or 56 given 59, 118 or 177 kg N/ha; P percentage became critically low (< 0.36%) at days 27, 35 or 38, respectively; Mg percentage fell to the critical level (0.12%) at days 23, 35 and 46. Na percentage showed the reverse trend, being deficient (< 0.13%) in the earliest samples and becoming satisfactory from days 23 or 27 at 118 and 177 kg N/ha but it remained inadequate at 59 kg N/ba.     

Effect of harvest time on yield and pre-harvest quality of semi-leafless grain peas (Pisum sativum L.) as whole-crop forage

The aim of the work was to study changes in the yield and nutritional characteristics of whole crop semi-leafless field pea over two growing seasons in the Po plain, Italy. Samples of two cultivars (Baccara and Sidney) were collected from flowering to grain maturity. The developmental stage, yield, dry matter (DM) content, crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), starch, water soluble carbohydrates (WSC), gross energy (GE), organic matter digestibility (OMD) and the net energy for lactation (NE_L) were determined at each harvest. The forage characteristics were regressed on the growing degree days (GDD) with 4.4 °C as the base temperature. The DM yield increased with advancing maturity from 0.5 to 8.91 Mg ha⁻¹, while the CP decreased from 261 to 159 g kg⁻¹ DM. During the whole growth cycle the GE, OMD, NE_L and milk forage units (milk FU) were almost steady. No differences were observed between the cultivars for any of the measured parameters. At grain maturity, the crop produced over 4.0 Mg ha⁻¹ DM of grain. The CP, starch and WSC of the grain did not show any differences between the cultivars or years. The data showed that the nutritive quality of the forage of the semi-leafless grain pea harvested as a whole crop for ensiling purposes did not diminish with maturity and could help improve the self-sufficiency of dairy farms, in terms of home-grown protein forages.     

Age of regrowth as a factor affecting the nutritive value of hay of kikuyu grass (Pennisetum clandestinum) offered to lambs

The changes in chemical composition of hay of kikuyu grass ( Pennisetum clandestinum ) harvested at 50, 70 and 90 d of regrowth, and its effect on intake, digestibility, fermentation and microbial protein synthesis in the rumen (Experiment 1) and oxygen uptake by portal-drained viscera (PDV) (Experiment 2) were evaluated. The experiments were carried out with Polwarth × Texel crossbreed lambs with a mean live weight (s.e.m.) of 35(3·0) kg housed in metabolic cages. Organic matter (OM), neutral-detergent fibre (NDF) and nitrogen (N) intake, as well as rumen ammonia-N concentration, decreased linearly with age of regrowth ( P  <   0·05). Acid-detergent fibre (ADF) and indigestible NDF intakes were similar for all treatments. Apparent digestibility of organic matter (OM), NDF and N, as well as true digestibility of OM, microbial protein synthesis in the rumen, N retention, pH of rumen fluid and sugars, amino acids and peptide concentrations in rumen fluid were similar for all treatments. Age of regrowth also did not affect the kinetics of passage of the particulate phase through the digestive tract nor oxygen uptake by PDV. Heat production by PDV represented an average of 0·039 of digestible energy (DE) intake. Increasing the age of regrowth of kikuyu grass from 50 to 90 d did not affect digestibility nor the efficiency of DE use by PDV tissues of lambs but it reduced the nutritive value of the hay due to a lower intake of OM. Intake of hay appeared to be most limited by the ADF and indigestible NDF concentrations of the hay.     

STUDIES IN RESPONSE TO NITROGEN

Data are presented demonstrating the effects of applying fertilizer N at 59, 118 or 177 kg/ha on 16 Apr. on uptake of K, P. Ca, Mg and Na in primary growth (PG) harvested 8, 12, 16, 23, 29, 45 and 57 days afterwards, and residual effects in two successive regrowths (RG1 and RG2) harvested on 12 June and 13 Aug., respectively. Significant residual responses as uptake of K, P, Ca, Mg and Na were shown in RG1 and RG2 after all dates of harvesting PG. The residual responses compensated for poor uptake in PG. Thus, low uptakes to the second increment of N were followed by high residual responses in both regrowths; and low uptakes in PG harvested shortly after applying the fertilizer N were followed by high residual responses. Averaged over the seven dates of PG harvest, the sum of responses (PG+RG1+RG2) to the second N increment was greater than total response to the first increment in P and Mg, considerably greater in Ca and Na and slightly lower in K. These marked residual responses to the second N increment were most noticeable where PG was harvested 23 days after applying fertilizer N and became less marked as date of PG harvest was advanced. Percentage K, P, Ca, Mg and Na in DM of the PG and of RG1 increased as N application was raised. By RG2, the residual effects of fertilizer N on percentage K. P and Mg were reversed to give reduced percentages with increased N application to PG. indicative of deficiencies in availability of these elements. The application of 177 kg N/ha to PG resulted in the release of additional soil N and of other mineral elements which could lead to their depletion.     

Effect of seed rate of red clover and of companion timothy or tall fescue on herbage production

Tetraploid red clover (cv. Hungaropoly) was sown at seed rates of 6,12 or 18 kg ha^?1 alone and in mixture with timothy (cv. Scots) at 2, 4 or 6 kg ha^?1 or with tall fescue (cv. S170) at 6,12 or 18 kg ha^?1. Two ‘silage’ crops and an ‘aftermath grazing’ crop were harvested in 2 successive years. In harvest years 1 and 2, total herbage production levels of 11.12 and 7.47 t dry matter (DM) ha^?1 respectively were obtained from pure-sown red clover compared with 11.84 and 8.78 t DM ha^?1 for red clover-timothy and 12.23 and 9.64 t DM ha^?1 for red clover-tall fescue. Corresponding red clover production levels were 10.93 and 5.30 t DM ha^?1 (red clover swards), 8.04 and 3.131 ha^?1 (red clover-timothy), and 6.42 and 109 t ha^?1 (red clover-tall fescue). Total herbage organic matter digestibility was improved by the timothy companion grass but not consistently by the tall fescue, whereas crude protein (CP) concentration was decreased by the addition of either grass. Increased seed rate intensified these effects, as well as the general effect of the companion grass in depressing red clover DM, digestible organic matter (DOM) and CP production. Total herbage DM, DOM and CP were not markedly affected by increasing red clover seed rate but red clover DM, DOM and CP were increased as red clover seed rate was raised, due to increases in the red clover component. The potential for silage cropping of red clover swards was confirmed but there was advantage in sowing a companion grass. Taking yield and quality parameters into consideration, timothy proved a better companion than tall fescue. A seed rate of 2 or 4 kg ha^?1 timothy and 12 kg ha^?1 red clover proved the most satisfactory.     

Dry-matter yields and crude protein and rumen-degradable protein concentrations of three Arachis pintoi ecotypes at different stages of regrowth in the humid tropics

Well‐established stands of three ecotypes of Arachis pintoi (CIAT 17434, 18744 and 18748) were harvested from replicated plots (three blocks, each containing three plots for each ecotype) during the two dominant seasons (dry and wet) of the low altitude, humid tropics of Costa Rica. Each plot was further divided into six subplots so that, within each season, samples corresponding to 4, 6, 8, 10, 12 or 14 weeks of regrowth could be collected. For each harvest, dry matter (DM) yield of the leaf, stem and whole plant, and the leaf:stem ratio, were recorded. Samples of the whole plant were analysed for crude protein (CP), rumen‐degradable (RDP) and rumen‐undegradable protein (RUP) concentrations. DM yield of the leaf, stem and whole plant increased with advancing period of regrowth but the effects of period of regrowth varied somewhat among ecotypes and across seasons. Generally, DM yield was greater during the wet than during the dry season. The greatest difference between ecotypes for stem and total DM yields was evident during the dry season. In general, DM contents were low in the whole plant, leaf and stem samples (<220 g kg^?1) and increased with increasing period of regrowth. Increases in leaf:stem ratio were most dramatic during the dry season with greater periods of regrowth, although the ratio was fairly constant during the wet season. Whole‐plant CP concentration was relatively high after short periods of regrowth (up to 279 g kg^?1 DM) but declined with longer periods of regrowth; the relative decline was much greater during the dry season. The RDP concentration was relatively constant during the wet season (mean 115 g kg^?1 DM), but declined with longer periods of regrowth during the dry season (range 194–111 g kg^?1 DM). In general, the concentrations of RDP, on a CP basis, were greater during the dry season and ranged from 590 to 700 g kg^?1 CP. Season, ecotype and period of regrowth all exerted an effect on RUP concentrations.     

The effect of herbage allowance on daily intake by Creole heifers tethered on natural Dichanthium spp. pasture

Two experiments were carried out in Guadeloupe to estimate the organic matter intake (OMI) and digestibility (OMD) of a Dichanthium spp. sward, grazed by tethered Creole heifers [mean live weight (LW) 202 ± 2·0 kg], at three daily herbage allowances. Experiment 1 examined herbage allowances of 16, 25 and 31 kg of dry matter (DM) d^–1 on a fertilized sward at 21 days of regrowth whereas, in experiment 2, lower allowances of 11, 15 and 19 kg DM d^–1 were examined on the same sward, which was unfertilized and grazed at 14 days of regrowth. In each experiment, the herbage was grazed with three groups of two heifers in a 3 × 3 Latin square design. Sward characteristics were described before grazing. OMI was calculated from total faecal output, and OMD was predicted from the crude protein (CP) content of the faeces. The amount of herbage defoliated by the heifers was also estimated on tillers selected at random.
Organic matter intakes were on average 26 g and 19 g OM kg^–1 LW, and OMD values were 0·740 and 0·665 for Experiments 1 and 2, respectively, and were not affected by allowance. In Experiment 1, the herbage quality was high [0·50 of leaf and 116 g CP kg^–1 organic matter (OM)] for a tropical forage, whereas in Experiment 2, the quality of the herbage (0·27 of leaf and 73 g CP kg^–1 OM) was lower. These differences were reflected in differences in intake and digestibility in the two experiments.
The experimental tropical Dichanthium spp. swards can have intake characteristics similar to those of a temperate sward.