An evaluation of potassium and nitrogen fertilization of grassland, and date of harvest, on fermentation, effluent production, dry-matter recovery and predicted feeding value of silage

The effects of levels of application of potassium (K) fertilizer, and its interactions with both nitrogen (N) fertilizer and the growth interval between fertilizer application and harvesting on ryegrass herbage yield and chemical composition, and the fermentation, predicted feeding value, effluent production and dry-matter (DM) recovery of silage were evaluated in a randomized block design experiment. Twenty plots in each of four replicate blocks received either 0, 60, 120, 180 or 240 kg K ha^?1, each at either 120 or 168 kg N ha^?1. Herbage from the plots was harvested on either 24 May or 8 June and ensiled (6 kg) unwilted, without additive treatment, in laboratory silos. Immediately after harvesting, all plots received 95 kg N ha^?1 and were harvested again after a 49-day regrowth interval. From the primary growth, herbage DM yields were 6·31, 6·57, 6·74, 6·93 and 6·93 (s.e. 0·091) t ha^?1, herbage K concentrations were 15·5, 16·2, 19·1, 22·4 and 26·1 (s.e. 1·06) g kg^?1 DM and herbage ash concentrations were 57, 63, 71, 73 and 76 (s.e. 0·9) g kg^?1 DM, and for the primary regrowth herbage DM yields were 2·56, 2·73, 2·83, 2·94 and 2·99 (s.e. 0·056) t ha^?1 for the 0, 60, 120, 180 and 240 g K ha^?1 treatments respectively. Otherwise, the level of K fertilizer did not alter the chemical composition of the herbage at ensiling. After a 120-day fermentation period the silos were opened and sampled. The level of K fertilization had little effect on silage fermentation and had no effect on estimated intake potential, in vitro DM digestibility (DMD), DM recovery or effluent production. Increasing N fertilizer application increased silage buffering capacity (P < 0·05) and the concentrations of crude protein (P < 0·001), ammonia N (P < 0·01) and effluent volume (P < 0·01), and decreased ethanol concentration (P < 0·05) and intake potential (P < 0·05). Except for the concentrations of lactate and butyrate, delaying the harvesting date deleteriously changed the chemical composition (P < 0·001) and decreased intake potential (P < 0·001) and DMD (P < 0·001) of the silages. It is concluded that, other than for K and ash concentration, increasing the level of K fertilizer application did not alter the chemical composition of herbage from the primary growth or the resultant silage. Also, the level of K fertilizer application did not affect predicted feeding value, DM recovery or effluent production. Herbage yield increased linearly with increased fertilizer K application. Except for acetate and ethanol concentrations, there were no level of K fertilizer application by level of N fertilizer application interactions or level of K fertilizer application by harvest date interactions on silage fermentation or predicted feeding value. Increasing N fertilizer application from 120 to 168 kg ha^?1 had a more deleterious effect on silage composition and feeding value than increasing K fertilizer application from 0 to 240 kg ha^?1. Delaying harvesting was the most important factor affecting herbage yield and composition, and silage composition and had the most deleterious effect on silage feeding value.     

The effect of timing and rate of potash application on the yield and herbage composition of grass grown for silage

Replicated field trials were carried out at 23 sites in England and Wales between 1986 and 1988 examining the response of first-cut grass silage to different levels of early winter- or spring applied potash on dry matter (DM) yield and herbage composition. Residual effects at the second cut were measured. In 1986/87 and 1987/88, the effect of additional potash at second cut was examined. Yield responses at first cut were measured at 13 sites (P<0·05). Optimum potash rates (K-opt) ranged from 0 to over 160 kg ha^?1, the highest rate tested. The mean rate of response up to K-opt at responsive sites was 10·4 kg DM (kg K₂O)^?1. Herbage K% increased with potash rate regardless of the requirement for maximum economic yield. Increasing potash rate reduced herbage Mg% by less than 0·020% which was less than the effect of soil Mg level. An increase of 50 mg 1^?1 in soil Mg (0-7·5 cm depth) increased herbage Mg by 0·034%. Early winter application of potash was generally as effective as spring application though it gave slightly lower herbage K and higher herbage Mg concentrations. Offtake of potash (K₂O) at first cut was on average 12 kg ha^?1 more from spring than from early winter application. Herbage analysis for N:K ratio was the best indicator of potash requirement. Regression analysis of the N:K ratio of herbage in control (nil potash) treatments against K-opt at first cut gave an r² value of 51·4% (***). For herbage total K%, r² was 39·7% (**) and for soil K (0-7·5 cm depth) it was 21·3% (*). Taking account of soil K below 7·5 cm depth was important at some sites, particularly those with a history of arable cropping and associated soil cultivation. Residual effects of a single early winter or spring application were measured, but additional potash applied for second cut was generally more effective. Optimum rates of potash for second cut were not determined.     

Herbage intake and milk production by grazing dairy cows 1. The effects of variation in herbage mass and daily herbage allowance in a short-term trial

Twenty-four British Friesian cows were allocated between six grazing treatments (two levels of herbage mass x three levels of daily herbage allowance) in a balanced change-over design with four periods of 12 d each at monthly intervals. Herbage OM mass ranged from 3790 to 5770 kg ha^-1 measured to ground level and daily herbage DM allowances were 30, 60 and 90 g per kg animal live weight. Herbage OM intake was lower at high than at low herbage mass (24·6 vs 26·3 g per kg LW), and was 26·9, 26·6 and 22·9 g per kg LW respectively at daily herbage DM allowances of 90, 60 and 30 g per kg LW. Milk yield was not affected by herbage mass but was depressed at the low herbage allowance.     

Effect of continuous stocking by sheep at four sward heights on herbage mass, herbage quality and tissue turnover on grass/clover and nitrogen-fertilized grass swards

The effects of continuous stocking by sheep at sward surface heights (SSH) of 3, 5, 7 and 9 cm in grass/clover (GC) and nitrogen-fertilized grass (GN) swards were examined in relation to herbage mass and quality, clover content, tiller density and rates of herbage production and senescence in two periods in each of three grazing seasons (1987-89). The GN swards received a total of 300 kg N ha^?1 each year in six equal dressings from March; GC swards received a single dressing of 50 kg N ha^?1 in March each year. Herbage mass measured from ground level increased linearly with SSH with overall mean herbage masses of 0·89, 1·38, 1·78 and 2·12 t OM ha^?1 (s.e.m.0·024, P < 0·001) at SSH of 3, 5, 7 and 9 cm respectively. GN and GC swards had mean herbage masses of 1·58 and 1·51 t OM ha^?1 (s.e.m. 0·051, NS) respectively. Mean N content of herbage on GN swards was greater than that on GC swards and declined with increasing SSH. Crude, fibre (CF) content of herbage was similar for both sward types and increased with increasing SSH. Clover content of GC swards remained low throughout the experiment, ranging from 0·002 to 0·074 of herbage mass. However, from tissue turnover rates it was estimated that its contribution to herbage production was in the range of 0·049–0·219 of net herbage growth. Total growth increased with increasing SSH in both sward types, with maximum growth rates in GN swards of 143 and 130 kg DM ha^?1 d^?1 and in GC swards of 88·2 and 85·4 kg DM ha^?1 d^?1 in Periods 1 (up to early July) and 2 (after July) respectively. Senescence rates ranged between 13·3 and 50·1 kg DM ha^?1 d^?1 and tended to be higher in Period 2 than in Period 1. Net production increased with increasing SSH in Period 1, while in Period 2 net production declined at SSH above 6·5 cm. The increased net herbage production in taller swards was not associated with greater utilized metabolizable energy production at sward heights above 5 cm.     

Effect of cultivar and seed rate of perennial ryegrass and strategic fertilizer nitrogen on the productivity of grass/white clover swards

Four cultivars of perennial ryegrass (intermediate diploid cv. Talbot and tetraploid cv. Barlatra, and late diploid cv. Parcour and tetraploid cv. Petra) were each sown at 10,20 and 30 kg ha^-1, all with 3 kg ha^-1 of white clover cv. Donna. Herbage productivity was measured over 3 harvest years, 1982–84. under two annual rates of fertilizer N (0 and 150 kg ha^-1); the 150 kg ha^-1 rate was split equally between March and August applications. Fertilizer N increased total herbage DM production; the 3-year means for the 0 and 150 kg ha^-1 N rates were 8·04 and 8·91 t ha^-1, respectively. In successive years, total herbage responses to N (kg DM (kg N applied)^-1) were 6·6, 35 and 72 (overall mean, 58). Mean white clover DM production over the 3 years was reduced from 4·48 t ha^-1 at nil N to 2·82 t ha^-1 at the 150 kg ha^-1 rate, a fall of 37%. Grass seed rate did not influence total herbage production or white clover performance. The two intermediate perennial ryegrass cultivars had a marginal advantage in total herbage production over the two late cultivars, but white clover content and production were higher with tetraploids than diploids. It is concluded that the value of increased herbage production from strategic use of fertilizer N has to be weighed against its depressive effect on white clover performance; application of 75 kg ha ha^-1 N in both spring and autumn was excessively high if maintenance of a good white clover content in the sward is an objective. There is considerable flexibility in the grass: clover seed ratio in seeds mixtures. Modern highly-productive perennial ryegrass varieties do not differ substantially in compatibility with white clover but tetraploids permit better clover performance than diploids.     

Responses of herbage P,Ca, K and Mg content and Ca/P and K/(Ca + Mg) ratios to long‐term continuous and discontinued cattle grazing on a rough fescue grassland

Herbage minerals affect performance of grazing cattle. We investigated the response of herbage P, K, Ca and Mg contents and Ca/P and K/(Ca + Mg) ratios to long‐term stocking rate, continuous vs. discontinued grazing practice, and sampling year. Cattle had been stocked at 2·4 and 4·8 animal unit months ha^?1 since 1949. Exclosures were installed in April 1998. Herbage samples were collected near peak herbage mass in 2001, 2003, 2008 and 2012 and analysed for mineral content. Mineral contents were similar between the two stocking rates, but were lower (P < 0·05) under discontinued than continuous stocking, with the exception of similar P contents. The content of P and K in herbage was higher and the content of Ca and Mg was lower (P < 0·05) in years with greater precipitation and lower temperatures. Herbage mineral content, with the exception of P, exceeded minimum recommended levels for cattle. Given the low P content in herbage (0·74–1·19 g kg^?1) and high Ca/P ratios during the dry and hot year (of 2001), a dietary P supplement should be considered for cattle grazing rough fescue grassland in drought years. The low K/(Ca + Mg) ratios (<2·2) suggest there is little risk of grass tetany in cattle grazing on this grassland.     

Determining the critical plant test potassium concentration for annual and Italian ryegrass on dairy pastures in south‐western Australia

Potassium fertilization in intensive grassland systems is particularly important on sandy soils with limited K storage capacity. A 3‐year plot experiment was conducted in south‐western Australia to determine the critical K concentration in herbage dry matter (DM) of annual and Italian ryegrass required to achieve 0.95 of the maximum yield, under best‐practice grassland management. A factorial design was employed with eight fertilizer K rates (range 0–360 kg ha^?1 year^?1) and two ryegrass species replicated four times, on a sandy soil site managed over 7 years to deplete mean soil Colwell K concentration to 42 mg/kg. Herbage was defoliated six times per year at the 3‐leaf stage of regrowth. Herbage DM yield, macronutrient and micronutrient concentrations were measured at each defoliation. Dry‐matter yield increased significantly (p < .001) with increasing levels of K fertilizer in all 3 years and the effect was curvilinear, while 0.95 of the maximum herbage DM yield was achieved at an annual K fertilizer application rate of 96, 96 and 79 kg/ha respectively. At these K fertilizer application levels, the mean K concentration of herbage DM over the 3 years was derived to be 11.4, 12.7 and 11.2 g/kg respectively. Sodium, magnesium and calcium concentrations of herbage DM all declined significantly (p < .001) as the K concentration increased. Grassland producers on sandy soils should target a K concentration in herbage DM of 16 g/kg for annual ryegrass and Italian ryegrass‐dominant swards to ensure K availability is not limiting herbage production.     

Cattle and sheep grazing effects on soil organisms, fertility and compaction in a smooth-stalked meadowgrass-dominant white clover sward

This experiment was carried out to improve understanding of sward and soil responses to cattle and/or sheep rotational grazing of low-input (no N fertilizer), natural swards dominated by smooth-stalked meadowgrass (Poa pratensis) syn. Kentucky bluegrass and based on white clover (Trifolium repens). Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S), Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg dry matter (DM) ha^?1. Plants in sheep-grazed swards regrew more quickly and accumulated more herbage (8·28 compared to 5·35 t DM ha^?1 for cattle-grazed swards, unadjusted for rejected area) than in other treatments. After 2 years, soil in sheep-grazed areas contained 0·25% N, 5·7 kg available P ha^?1, and 379 kg K ha^?1, compared to an average of 0·19, 3·9, and 179 respectively for the same soil nutrients in cattle-grazed treatments. Besides differences in manure distribution and sward rejection, differences in soil compaction among treatments also may have affected soil organisms and thus plant growth. After 2 years, soil bulk densities (g cc^?1) were 1·37, 1·37, 1·27, and 1·12; soil penetrometer measurements (kg cm sec^?1 sec^?1) to 20-cm soil depth were 9·8, 9·3, 9·5, and 6·7; soil nematodes per 100 g of soil were: 5333, 8705, 2810, and 15208; soil rotifers per 100 g soil were: 288, 242, 715, and 33; and earthworms m^?2 (and their biomass (g m^?2)) were 262 (205), 157 (162), 344 (409), and 294 (343) for C, CT, CS, and S treatments, respectively.     

The effects of autumn closing date on sward leaf area index and herbage mass during the winter period

The provision of grass for early spring grazing in Ireland is critical for spring calving grass‐based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha^?1), leaf area index (LAI) and tiller density (m^?2) during winter and early spring. Thirty‐six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments – 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha^?1) and LAI (by approximately 0·86 units) in mid‐February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R² = 0·78). Herbage mass increased by approximately 1000 kg DM ha^?1 as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m^?2). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid‐October; swards required for grazing after mid‐March can be closed during November.     

Influence of cutting regime and fertilizer application on the botanical composition,yield and nutritive value of herbage of wet grasslands in Central Europe

The changes in dry matter (DM) yield, botanical composition and nutritive value of herbage to ruminants of two wet grasslands, Arrhenatherum elatius grassland (Experiment 1) and a Molinia caerulea fen meadow (Experiment 2), in which a range of cutting and fertilizer treatments were imposed in 1999, were assessed after 4–7 years of treatment imposition. Both experiments had a split‐plot design with four replicates. In Experiment 1 the three main‐plot cutting treatments were two cuts with a delayed first cut, three cuts and four cuts during the growing season of each year. In Experiment 2 the cutting treatments were two cuts with a traditional harvest time, two cuts with a delayed first cut and three cuts. The four sub‐plot fertilizer treatments were an unfertilized control, application of a phosphorus and potassium (PK) fertilizer, application of a nitrogen (N) and PK fertilizer to the first cut only (N₁PK) and application of PK plus N applied to each of two, three or four cuts (N_c PK). Application of fertilizer influenced yield and botanical composition of herbage more than the cutting treatments while the opposite occurred for nutritive value of the herbage. Application of fertilizer increased the proportion of tall grasses in Experiment 1 and forbs in Experiment 2. The proportion of Equisetum palustre, present only in Experiment 1, was reduced from 0·33 to less than 0·01 by increased cutting frequency together with the NPK fertilizer treatments. In Experiment 1 diversity of vascular plants was negatively affected only by the four‐cuts treatment while on both wet grasslands other cutting and fertilizer application treatments had no effect. Changes in DM yield of herbage caused by the cutting and fertilizer application treatments were similar for both vegetation types with DM yield increased significantly by fertilizer application but only slightly or not reduced by increasing the cutting frequency. Nutritive value of herbage was positively correlated with cutting frequency and was most influenced at the first cut.     

Productivity of beef cattle grazing Brachiaria brizantha cv. Marandu with and without nitrogen fertilizer application or mixed pastures with the legume Desmodium ovalifolium

The use of forage legumes to contribute biologically fixed nitrogen (N) to pastures is an alternative to increase beef cattle production in tropical regions. The objective was to compare the impact of the introduction of a legume with that of N fertilizer application on forage and animal production in Brachiaria pastures. This two-year study assessed three pasture treatments: (1) mixed Marandu palisadegrass (Brachiaria brizantha [syn. Urochloa brizantha] cv. Marandu) and the legume “ovalifolium” (Desmodium ovalifolium) cv. Itabela (Mixed), (2) Marandu palisadegrass pastures with 150 kg N ha⁻¹ (Fertilized), and (3) Marandu palisadegrass without N fertilizer (Unfertilized). Rotational stocking with a variable stocking rate was used with a target herbage allowance of 1.0 kg forage kg body weight⁻¹. The pre-grazing green herbage mass was similar for Fertilized and Mixed pastures, with 54% and 63% more mass than Unfertilized pasture, respectively (p < .001). Cattle that grazed the fertilized pasture had the greatest average daily gain (ADG; p = .017). The stocking rate and liveweight gain per area were greatest for the Fertilized and Mixed pastures (p < .001 and p < .001, respectively). No differences between treatments were found for DM forage intake (p = .555). Organic matter digestibility was lowest (p < .001) for the Mixed pasture. The inclusion of the ovalifolium legume in the Marandu pasture had the same impact on beef cattle production as annual fertilization with 150 kg N ha⁻¹. The potential and environmental benefits of ovalifolium are discussed.     

Nitrogen recovery and loss in a fertilized elephant grass pasture

Limited information is available regarding the recovery and loss of fertilizer nitrogen (N) applied to intensively managed tropical grass pastures. An experiment was carried out in Brazil to determine the fertilizer‐N recovery and ammonia volatilization loss in an elephant grass (Pennisetum purpureum, Schum.) pasture fertilized with 100 kg N ha^?1 as urea or ammonium sulphate, labelled with ¹⁵N, in late summer (LS) or in mid‐autumn (MA). Herbage mass was highest and litter mass was lowest in LS (P < 0·05). The N concentration of herbage was highest in autumn (P < 0·05) and the total N content in soil was lower in LS than in MA (P < 0·05), reflecting the high N uptake capacity of the grass. Proportionately higher ¹⁵N recovery in litter mass (P < 0·05) was observed in autumn (0·094) than in LS (0·0397) and the ¹⁵N recovery in herbage was 0·046 higher for ammonium sulphate‐fertilized pastures (P < 0·05; proportionately 0·243 for ammonium sulphate and 0·197 for urea). Around 0·60 of the fertilizer‐¹⁵N recovered was retained in soil and in non‐harvestable fractions of the plant. The NH₃ volatilization loss was higher in LS and most of the N loss occurred soon after fertilizer application. Urea and ammonium sulphate fertilizers were equally effective in sustaining herbage dry matter yield in the short term. However, the use of ammonium sulphate, rather than urea, would be preferable for LS applications when the objective is to reduce NH₃ volatilization losses.     

Dietary cation–anion difference of Timothy (Phleum pratense L.) as influenced by application of chloride and nitrogen fertilizer

The effectiveness of forages to prevent post‐calving hypocalcaemia, when used as a feed source for non‐lactating dairy cows, can be predicted by the dietary cation–anion difference (DCAD). Three to four weeks before calving, the ration of non‐lactating dairy cows should have a DCAD around ?50 mmol_c kg^?1 DM. In an experiment, swards, based on Timothy (Phleum pratense L.), were used to (i) evaluate the impact of two types (CaCl₂ and NH₄Cl) and four application rates of chloride fertilizer per season (0, 80, 160 and 240 kg Cl ha^?1) in combination with two N application rates (70 and 140 kg N ha^?1) on mineral concentrations and DCAD in the herbage, and (ii) determine the economically optimal rate of chloride fertilizer (Cl_op) for DCAD in herbage. Chloride and N fertilizers were applied in the spring and, after the first harvest in 2003 and 2004 at four locations that differed in K content of their soils. Two harvests were taken during each year. Averaged across N‐fertilizer application rates, harvests and locations, the highest rate of chloride fertilizer increased chloride concentration in herbage by 8·5 g kg^?1 dry matter (DM) and decreased DCAD in herbage by 190 mmol_c kg^?1 DM to values as low as ?9 mmol_c kg^?1 DM. Both types of chloride fertilizer had the same effect on chloride concentration and DCAD in herbage and had no effect on DM yield. When no chloride fertilizer was applied on soils with a high content of available K, application of N fertilizer increased DCAD in herbage by 47 mmol_c kg^?1 DM at both harvests. Herbage DCAD was lower in summer than in spring by 47–121 mmol_c kg^?1 DM depending on the location. Application of chloride fertilizer can effectively lower the DCAD of Timothy‐based herbages; the economically optimal rate of chloride fertilizer in the spring varied from 78 to 123 kg Cl ha^?1, depending on soil K and chloride contents and expected DM yield.     

Allowance-intake relations of cattle grazing vegetative tall fescue†

Herbage allowance is one of the important pasture factors in the determination of intake by grazing livestock. Ingestive behaviour of 12 adult Angus cows (Bos taurus) was measured over a range of allowances (0·25 to 0·72 kg dry matter (DM) per 100 kg live weight (LW) for a 1-h period) of vegetative tall fescue (Festuca arundinacea Schreb.). A balanced change-over design was used to estimate direct, residual and permanent effects of herbage allowance on rate of DM intake, rate of biting and herbage DM intake per bite. In Experiment 1, herbage DM intake per meal increased linearly from 0·68 to 1·72 kg (100 kg LW)^?1 as DM allowance increased from 0·25 to 0·72 kg (100 kg LW)^?1 h^?1. Cows grazed at ·30 kg (100 kg LW)^?1 h^?1 and stopped grazing when the sward was reduced to a height about 10 to 12 cm above the soil surface, approximately defined by the tops of pseudostems. In Experiment 2, herbage DM intake rates of 0·29, 0·47 and 0·42 kg (100 kg LW)^?1 h^?1 were recorded as cows grazed allowances of 0·43, 0·70 and 0·90 kg (100 kg LW)^?1 h^?1 for most of the 1-h grazing period. Limiting herbage DM allowances in Experiment 2 were associated with small reductions in rate of biting and herbage DM intake per bite as allowance declined. Sward DM density (>5 cm) was an important variable in the determination of herbage DM intake rates at lower herbage allowances.     

An evaluation of the effects of rate of nitrogen fertilization of grassland on silage fermentation, in-silo losses, effluent production and aerobic stability

A factorial experiment was carried out to evaluate the effects of level of nitrogen (N) application to grassland and subsequent treatment of the herbage at ensiling with formic acid on the rate of silage fermentation, dry-matter (DM) recovery, aerobic stability and effluent production. Herbage from the primary regrowth of predominantly perennial ryegrass swards received either 72 (LN), 126 (MN) or 180 (HN) kg N ha^?1. The herbages were harvested and yield estimated after a 50-day regrowth interval. After storage for 24 h in polythene bags, the herbages were ensiled, unwilled, in laboratory silos (6 kg capacity) either untreated (UT) or treated with formic acid (F) at 3 ml (kg herbage)^?1. Three silos per treatment were opened and sampled on days 1, 3, 6, 15, 50 and 105 after ensiling. The mean herbage yields for the LN, MN and HN swards were 5.2, 6.3 and 6.2 (s.e. = 0.27) t DM ha^?1 and there was no carryover effect of nitrogen treatment on the yield of a subsequent 22-day regrowth harvested on 2 September. As level of fertilizer N application increased, concentrations in the herbage at mowing of crude protein, nitrate and ash increased, DM decreased and water-soluble carbohydrate and in vitro DM digestibility remained unchanged. Increasing the rate of N fertilizer to the sward resulted in higher silage pH (P< 0.001) and ammonia N concentrations (P <0.001) at each time of sampling. Increasing the rate of fertilizer N increased effluent output (P < 0.001) and DM recovery (P < 0.001). Aerobic stability was improved (P <0.001) by use of high rates of N fertilizer application. Formic acid treatment restricted fermentation and increased effluent output (P <0.001) but had no effect (P > 0.05) on DM recovery. It is concluded that the rate and extent of pH decline was reduced with increasing N application, associated with increased buffering capacity and decreased DM concentrations of the herbage at ensiling. However, increasing the level of N fertilizer applied increased DM recovery and effluent output, and improved aerobic stability of the resulting silages.     

The effect of sward height and its direction of change on the herbage intake, diet selection and performance of weaned lambs grazing ryegrass swards

Abstract Four sward height treatments were imposed by continuous variable stocking using at least ten Suffolk × Greyface lambs per plot from late July to late August: constant 3·5 cm. constant 6·0 cm. 3·5cm increasing to 6·0 cm and 6·0 cm decreasing to 3·5 cm. The treatments were established on two swards given fertilizer N applications over the season of 97 and 160 kg N ha^?1 respectively. Animal density was greater on the high fertilizer treatment, at the lower sward height and especially on the decreasing height treatments. Liveweight change of lambs was higher (P <0·001) on the 6-cm than on the 3·5-cm treatments (+159 vs-13g d^?1 and was also higher (P <0·001) on the increasing than on the decreasing sward height treatments (+92 vs-26 g d^?1). Herbage organic matter intake (OMI), measured on two occasions in the experiment, was greater (P <0·001) on the 6·0 cm than on the 3·5-cm sward heights whereas values for the increasing sward height treatments were much greater than those for the decreasing sward height treatments. There was little difference in the organic matter digestibility of the diet between treatments. Diets were composed largely of lamina, although there was more pseudostem and dead herbage in the diets of Iambs grazing the decreasing than the increasing sward height treatments at the end of the experiment. Bite mass was closely related to OMI but the treatment and period differences were relatively greater than for OMI. Bite mass was more closely related to the depth of the lamina layer (sward height-pseudostem height) than it was to sward height. There was evidence that pseudostem acted as a barrier to defoliation on these short swards and also that the proportion of youngest leaf in the diet was positively related to sward height and to increases in sward height. Sward height and especially the direction of change in sward height, together with associated stock density, were potent influences on lamb growth rate. This was a consequence of differences in herbage intake, which was strongly influenced by bite mass.     

Effect of a stay-green locus on the dry-matter yield, nitrogen yield and shoot density of perennial ryegrass

A rare stay‐green allele transferred from meadow fescue (Festuca pratensis L.) to perennial ryegrass (Lolium perenne L.) has improved both the colour of turf and the nutritive value of herbage. In this study its effect on shoot density and forage yield was assessed. Equivalent populations of perennial ryegrass were constructed with and without the stay‐green allele, following eight generations of backcrossing to perennial ryegrass. The stay‐green population, the normal population and the cv. AberStar were compared over two harvest years (2005 and 2006) in a field experiment with six application rates of N fertilizer (100, 200, 300, 400, 500 and 600 kg ha^?1 annually). There were no significant interactions between level of N fertilizer and population in any of the traits measured. The mean annual dry‐matter (DM) yield over all populations and fertilizer levels was 6·45 t ha^?1 lower in the second harvest year. Mean annual DM yields over all fertilizer levels of the normal population were higher than, or equal to, AberStar while those of the stay‐green population were significantly (proportionately 0·10–0·13) lower than the normal population. In 2005, the mean total yield of N in the herbage of the stay‐green population was 0·09 lower than that of the normal population and the mean concentration of N over all harvests was 1·5 g kg^?1 DM higher. The shoot density of the stay‐green population after the last harvest in November 2006 was 0·18 lower than that of the normal population (3689 and 4478 shoots m^?2 respectively).     

Herbage intake and N excretion by sheep grazing monocultures or a mixture of grass and white clover

In 1988 and 1989, swards of grass (G0), while clover (C0) and grass/white clover (GC0) receiving no N fertilizer, and a grass sward supplied with 420 kg N ha^?1 (G420), were grazed by non-lactating sheep to maintain a sward surface height of 6 cm. Herbage organic matter (OM) intakes averaged between 1200 and 1700 g OM ewe^?1 d^?1. For treatments G0, C0, GC0 and G420 respectively, the ewes' live weight gain was 102, 112, 100 and 110 g d^?1 and changes in body condition scores were +0·28, +0·52, +0·36 and +0·44 units season^?1. However, the effect of treatment was not significant for either variable. There were similar levels of output of faecal N ewe^?1 but significantly more urinary N ewe^?1 was excreted on treatments C0 and G420, where the concentrations of N in herbage laminae were also higher. For example, in 1989, total daily N excreted was 39·7, 64·4, 44·0 and 63·3 g N ewe^?1 for G0, C0, GC0 and G420 respectively. Taking into account the mean daily stocking rates, which were 19·4, 26·6, 27·2 and 36·5 ewe ha^?1, the total faeces and urine returns over the season were 161, 358, 249 and 484 kg N ha^?1 for each treatment respectively. The herbage OM intakes ewes^?1 d^?1 measured in September and October were similar for C0 and G420, and so the intake of herbage OM ha^?1 d^?1 was related to stocking rate, i. e. the estimated herbage intake ha^?1 over the growing season for the white clover monoculture was 73% of that for N-fertilized grass. Excretal nitrogen returns to the pasture from grazed mono-cultures of clover were high, and similar to those from a grass sward receiving 420 kg fertilizer N ha^?1. Consequently potential losses of N to the environment are high under these management systems.     

Manipulation of herbage production by altering the pattern of applying nitrogen fertilizer

The redistribution of herbage production during the growing season to synchronize herbage supply with feed demand by livestock by altering the application pattern of a range of nitrogen (N) fertilizer rates was studied. Application rates of N were 50, 150 and 250 kg N ha^?1 per annum and patterns were with 0·60 of N fertilizer applied before June (treatment RN) and with only 0·20 of N fertilizer before June (treatment IN). Treatments were imposed in a cutting (simulated grazing) experiment (Experiment 1), which was conducted for 2 years and a grazing experiment (Experiment 2) which was conducted for 3 years. In both experiments, herbage production was reduced in April and May and increased in the June–October period on treatment IN relative to RN, but annual herbage production was not significantly affected except in the third year of Experiment 2, when treatment RN had significantly (P < 0·05) higher herbage production than treatment IN. Crude protein (CP) concentration of herbage was lower in April and May on treatment IN than treatment RN. However, CP concentration of herbage was rarely below 150 g kg^?1 DM and so it is unlikely that livestock productivity would be compromised. On treatment IN, concentrations of CP in herbage were higher in the late summer than on treatment RN, which may increase livestock productivity during July and August when livestock productivity is often lower. Altering the strategy of application of N fertilizer did not affect in vitro dry matter digestibility of herbage.     

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.