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.     

Influence of sward condition on leaf tissue turnover in tall fescue and tall wheatgrass swards under continuous grazing

Two experiments were carried out on a tall fescue sward in two periods of spring 1994 and on a tall wheatgrass sward in autumn 2001 and spring 2003 to analyse the effect of sward surface height on herbage mass, leaf area index and leaf tissue flows under continuous grazing. The experiment on tall fescue was conducted without the application of fertilizer and the experiment with tall wheatgrass received 20 kg P ha^?1 and a total of 100 kg N ha^?1 in two equal dressings applied in March (autumn) and end of July (mid‐winter). Growth and senescence rates per unit area increased with increasing sward surface height of swards of both species. Maximum estimated lamina growth rates were 28 and 23 kg DM ha^?1 d^?1 for the tall fescue in early and late spring, respectively, and 25 and 36 kg DM ha^?1 d^?1 for tall wheatgrass in autumn and spring respectively. In the tall fescue sward, predicted average proportions of the current growth that were lost to senescence in early and late spring were around 0·40 for the sward surface heights of 30–80 mm, and increased to around 0·60 for sward surface heights over 130 mm. In the tall wheatgrass sward the corresponding values during spring increased from around 0·40 to 0·70 for sward surface heights between 80 and 130 mm. During autumn, senescence losses exceeded growth at sward surface heights above 90 mm. These results show the low efficiency of extensively managed grazing systems when compared with the high‐input systems based on perennial ryegrass.     

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.     

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 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.     

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 3. Sward characteristics and animal output, years 4–8

Results for years 4–8 of a long-term grazing experiment on swards of a diploid perennial ryegrass (Lolium perenne), var. Contender (D swards), a tetraploid ryegrass, var. Condesa (T swards) and Condesa with S184 white clover (Trifolium repens) (TC swards), direct sown in May 1987, are presented. The swards were continuously stocked with sheep from 1988 to 1990, as previously reported, and for a further 5 years, 1991–95, at a target sward surface height (SSH) of 4–6 cm. Control of sward height was successfully achieved by variable stocking, except in 1993 when paddocks were set stocked and the resulting mean SSH was 9·3 cm. Grass swards received on average 160 kg N ha^?1 year^?1; grass/clover swards were mainly not fertilized with N with the exception that they were given 30 kg N ha^?1 as a remedial mid-summer application during a period of low herbage mass on offer in 1994 and 1995. Mean white clover content of the swards fell from 18·2% of herbage dry-matter (DM) in 1992 to 8·5% in 1993, whereas stolon lengths fell from 120 to 58 m m^?2. A return to lower sward heights in 1994–95 resulted in an increase in white clover content to 12·8% by the final sampling in August 1995. Perennial ryegrass content of the grass swards remained high throughout (mean 96·7% in 1995). Perennial ryegrass tiller densities recorded in August 1991, 1993 and 1994 showed consistently significant (P < 0·001) sward differences (3-year mean 16 600, 13 700 and 10 100 perennial ryegrass tillers m^?2 for the D, T and TC swards). In 1994, the year after lax grazing, a low perennial ryegrass tiller density (9100 m^?2) and low white clover content (mean 4·3%) in the TC swards resulted in a much lower herbage bulk density than in the grass swards (April–July means 72, 94 and 44 kg OM ha^?1 cm^?1 for the D, T and TC swards). There was a consistent 40 g d^?1 increase in lamb liveweight gain on the TC swards over the T swards, except in 1994. In that year there was a reduction in lamb liveweight gain of 33 g d^?1 on the TC swards and a significant increase in ewe liveweight loss (117 g d^?1) associated with low herbage bulk density despite optimal sward height. Lamb output (kg liveweight ha^?1) on TC swards reflected white clover content, falling from a similar output to that produced from grass given 160 kg N ha^?1, at 18% white clover DM content, down to 60% of grass + N swards with around 5% clover. A 6% greater output from the T than the D swards was achieved mainly through higher stocking rate. The experiment demonstrated a rapid, loss in white clover under lax grazing, and showed that the relationship between performance and sward height is also dependent on herbage density. High lamb output from a grass/clover sward was only achieved when the clover content was maintained at 15–20% of the herbage DM.     

Effects of date of autumn closing and timing of winter grazing on herbage production in winter and spring

Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [≤2 livestock units (LU) ha^?1], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn‐closing dates and four winter‐grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north‐east. Closing swards from grazing in early and mid‐September (north‐east and south of Ireland respectively) provided swards with >2 t DM ha^?1 and a proportion of green leaf >0·65–0·70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of >230 g kg^?1 DM and dry matter digestibility (DMD) of >0·700. The effects of autumn‐closing date and winter‐grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn‐closing date in the north‐eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0·34 t DM ha^?1 and delaying winter grazing reduced the herbage mass in late March by up to 0·85 t DM ha^?1. The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha^?1. The effects of imposing treatments in successive years did not follow a consistent pattern and year‐to‐year variation was most likely linked to meteorological conditions.     

Some effects of applying undiluted silage effluent to grassland

Two small-plot experiments were carried out to assess the influence on herbage dry matter (DM) production, chemical composition and soil fertility status of applying undiluted silage effluent at a range of application rates and intervals after a silage cut. In the first experiment, in 1990, silage effluent was applied at 25, 50, 100, 150 and 200 m³ ha^?1 1, 8, 15 and 22 d after a silage cut in August. In the second experiment, in 1991, silage effluent was applied at 7, 14, 21, 28, 35, 42, 49, 75, 100, 125 and 150 m³ ha^?1 1, 4, 8, 15, 22 and 29 d after silage cuts were taken from different sites in May, July and August. An untreated control and an Inorganic fertilizer treatment were incorporated in both experiments. The immediate effects of the treatments on herbage yield, chemical composition and soil nutrient status were assessed 6–8 weeks after the initial application; residual effects on herbage and soil fertility were measured at a subsequent harvest. Compared with the untreated control, herbage yield increases were obtained with increasing rates of effluent application. Although there was evidence that higher yields could be obtained from earlier applications, up to 50 m³ ha^?1 of effluent could be applied up to 15 d after taking a silage cut with little damage to the sward. Delaying the timing of application, and increasing the application rate, increased the proportion of the sward which was damaged; this reached a maximum of 0·84 when the highest application rates were applied 29 d after a silage cut. The increase in the proportion of dead herbage in the sward, associated with increasing rate of effluent application, reduced the quality of the herbage harvested in Experiment I. In Experiment 2 the N, P and, in particular, the K content of the herbage increased with increasing rate of effluent application, whereas the effect on Mg content was variable with contents generally being less than 2·0 g kg^?1 DM. Apparent recovery of nutrients applied in the effluent was both low and variable ranging from 0·58 to ?0·03 for N, 0·10 to ?0·005 for P, 0·34 to ?0·02 for K and 0·21 to ?0·002 for Mg over both experiments. Effluent had little effect on soil pH, whereas P and, in particular, K contents increased with increasing rate of effluent application. There was evidence that effluent had a beneficial effect on both herbage yield and chemical composition at the residual cut, the extent depending upon rate and time of effluent application.     

The effect of sowing date and nitrogen on the dry‐matter yield and nitrogen content of forage rape (Brassica napus L.) and stubble turnips (Brassica rapa L.) in Ireland

Two field experiments were conducted at Teagasc, Moorepark, Ireland, to determine the effect of sowing date and nitrogen application on the dry‐matter (DM) yield and crude protein (CP) content of forage rape and stubble turnips. The first experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) on forage rape DM yields. The second experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) over two soil sites (fertile or nitrogen depleted) on forage rape and stubble turnip DM yields. A delay in sowing from 1 to 31 August characterized a 74·5% decrease in forage rape DM yield, while stubble turnip DM yield decreased by 55·5%. Forage rape DM yields increased positively up to 120 kg N ha^?1 at the first two sowing dates over both sites. In contrast, stubble turnips showed less response beyond 40 kg N ha^?1 on site 1 in the first two sowing dates, while DM yield increased positively up to 120 kg N ha^?1 on the less fertile site. The results indicate that the optimal sowing time for forage rape and a stubble turnip in Ireland was early August.     

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.     

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.     

Dietary cation–anion difference and cadmium concentration in grasses fertilized with chloride

High dietary cation–anion difference (DCAD) of grass herbage increases the occurrence of hypocalcaemia of dairy cows. Application of chloride fertilizer reduces DCAD of herbage but it could increase cadmium concentration in herbage. This study includes an experiment conducted in Australia and in Canada. A glasshouse experiment in Australia evaluated the effect of four rates of chloride application (0–240 kg ha^?1) on values of herbage DCAD and cadmium concentration of above‐ground plant material of timothy (Phleum pratense L.) and phalaris (Phalaris aquatica L.), harvested 6 weeks after sowing and grown on two soils that had received cadmium either as a contaminant in superphosphate (soil + Super) or in sewage biosolids (soil + Bio) along with respective control soils (soil 0 Super and soil 0 Bio). Application of chloride fertilizer decreased values of herbage DCAD by 349 mmol_c kg^?1 dry matter (DM). Herbage DCAD values were highest on the 0 Bio soil (739 mmol_c kg^?1 DM) and were not different among the three other soils. Species did not differ in herbage DCAD values. Cadmium concentration in the above‐ground plant material was highest on the +Bio soil treatment (1·67 mg kg^?1 DM) and was lower for the three other soil treatments. Above‐ground plant material of phalaris had a higher cadmium concentration than that of timothy. Application of chloride fertilizer did not affect cadmium concentration in above‐ground plant material, despite the high cadmium content of the soil on the +Bio treatment. The field experiment in Canada evaluated the effect of four rates of chloride application (0–144 kg ha^?1) on cadmium concentration of a timothy‐based grass sward grown on four sites with soils of different potassium content. Application of chloride fertilizer increased cadmium concentration of herbage at two of the four sites but the maximum increase in cadmium concentration was only 0·025 mg kg^?1 DM. Chloride fertilizer can be applied to decrease forage DCAD with minimal risk of increasing Cd in the food chain.     

Effects of autumn and spring defoliation management on the dry‐matter yield and herbage quality of perennial ryegrass swards throughout the year

A small‐plot experiment was conducted in south‐west Ireland to investigate (i) the effects of pre‐closing regrowth interval and closing date on dry‐matter (DM) yield and sward structural and composition characteristics, during the autumn–winter and spring opening periods, and (ii) subsequent carryover effects. The study used a randomized block design with a factorial arrangement of treatments (4 closing dates × 2 opening dates) with a split plot (two pre‐closing regrowth intervals). The long pre‐closing (LPC) interval began on 9 August, and the short pre‐closing interval (SPC) started on 15 September. The autumn closing dates were as follows: 1 October (CD1), 15 October (CD2), 1 November (CD3) and 14 November (CD4). Plots were defoliated again on 1 February (EOD) or 1 March (LOD). On the LPC treatment, herbage yield increased from CD1 (2463 kg DM ha^?1) to CD3 (3185 kg DM ha^?1). On the SPC treatment, herbage yield was similar for CD3 and CD4, indicating a ceiling in herbage accumulation. For each 1‐d delay in closing date between CD1 and CD4, the opening herbage yield was reduced by 10 kg DM ha^?1. Herbage quality decreased as the closing date was delayed; DMD and CP decreased by 0·06 and 12 g kg DM^?1, respectively, between CD1 and CD4. The EOD resulted in increased leaf and decreased dead proportions over the LOD treatments. A balance between autumn CD and spring OD needs to be achieved to ensure a sufficient supply of high‐quality grass in spring.     

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.     

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.     

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.     

Effect of plant spacing and nitrogen fertilizer levels on the growth,dry‐matter yield and nutritive quality of Columbus grass (Sorghum almum stapf) in southwest Nigeria

A field experiment was conducted in 2006 and 2007 to determine the agronomic performance and nutritive value of Sorghum almum for introduction in the derived savannah area of Nigeria. The experiment was arranged in a 2 × 4 factorial design with 2 plant spacings (0·5 × 0·5 m and 1·0 × 1·0 m) and 4 nitrogen (N) fertilizer levels (0, 60, 120 and 180 kg N ha^?1). Plant height, tiller number, leaf proportion, biomass yield and nutritive value of the herbage were evaluated as part of the search for alternatives (especially drought tolerant) to local forages for dry season feeding of ruminants. Herbage yield data were tested for linear, quadratic and cubic trends to identify the optimal fertilizer levels for both spacings. Spacing × N interactions (P < 0·05) were observed for plant height and tiller number in both years. Agronomic performance was marginally better in 2007 compared with 2006. The maximum dry‐matter (DM) yield of 3500 and 3740 kg ha^?1 for the more dense row spacing (0·5 × 0·5 m) was achieved at N fertilizer levels of 144 and 149 kg N ha^?1 for 2006 and 2007 respectively. For the less dense (1·0 × 1·0 m) row spacing, the maximum DM yield of 3020 and 3240 kg ha^?1 was achieved at 51 and 97 kg N ha^?1 for 2006 and 2007 respectively. The crude protein content of the grass ranged from 61 to 89 g kg^?1 DM, while the neutral detergent fibre (NDF) content ranged from 700 to 734 g kg^?1 DM. The ability of S. almum to persist into the second year in this region is seen as a promising index as persistence is one of the characteristics of a good forage plant. Considering the exorbitant price of N fertilizer, less dense row spacing with N fertilizer rate in the range of 50–100 kg N ha^?1 is hereby recommended for this region.     

Nitrogen fertilizer application and developmental stage affect silage quality of timothy (Phleum pratense L.)

Crop composition at harvest affects the ensiling process and the resulting silage quality. The objectives of this study were to determine: (i) the effect of annual N‐fertilizer application (0, 60, 120 and 180 kg N ha^?1) and developmental stage (stem elongation, early heading, late heading and early flowering) on the ensiling properties and silage quality of the spring regrowth of timothy (Phleum pratense L.) at two sites for 1 or 2 years, and (ii) the relationship between ensiling properties of the forage and the quality of the resulting silage. Laboratory silos with wilted forage at approximately 350 g dry matter (DM) kg^?1 of fresh matter were prepared at each harvest and opened 150 d later for silage analysis. Higher rates of N‐fertilizer application decreased the concentration of water‐soluble carbohydrates (WSC), increased the buffering capacity (BC) and nitrate concentration, and decreased the ratio of WSC:BC, primarily in the early stages of development. The ensiling properties of timothy were, therefore, less favourable when high rates of N fertilizer were applied. Silage pH generally increased with increasing rates of N‐fertilizer application; this increase was particularly evident at the first three developmental stages at one site in 1 year. Non‐protein N (NPN) and soluble N concentrations of the silages increased with increased rates of N‐fertilizer application at the first three developmental stages but decreased at early flowering. Ammonia‐N concentration in the silages increased by 0·85, 0·56 and 0·67 when rates of N‐fertilizer application were 60, 120 and 180 kg ha^?1, respectively, compared with that when no N fertilizer was applied. Significant correlations between the composition of the forage ensiled and silage quality variables were found at sites in individual years but, when all data were combined, WSC concentration and BC, and their ratio in the forages, were not correlated with pH, and soluble‐N and ammonia‐N concentrations of the silages, and were weakly correlated with NPN and free amino acid‐N concentrations of the silages. Silage quality was reduced by increased N‐fertilizer application, primarily at the early developmental stages, and this can be attributed to a reduction in WSC concentration and an increase in BC of the forage. Water‐soluble carbohydrate concentration, BC, and their ratio, however, were poor predictors of silage quality.     

Spring and autumn establishment of Caucasian and white clovers with different sowing rates of perennial ryegrass

The effect of sowing date (SD) and sowing rate of perennial ryegrass (PRG) on the establishment of Caucasian and white clovers in New Zealand was assessed. Clovers were sown in spring on 24 September (SD1) and 9 November (SD2) 1999, and in autumn on 4 February (SD3) and 31 March (SD4) 2000. On each date, clovers were sown with 0, 3, 6 or 12 kg ha^?1 of PRG. Total herbage dry matter (DM) production up to 6 November 2000 was 13–16 t DM ha^?1 for SD1 and SD2 when sown with 3–12 kg ha^?1 of PRG, and 7–10 t DM ha^?1 for sown clover monocultures. For SD3 and SD4, total herbage production was 6–9 t DM ha^?1 with PRG, while total herbage production of clover monocultures was 5·4 t DM ha^?1 for SD3 and 2·6 t DM ha^?1 for SD4. By 6 November 2000, white clover contributed proportionately more than 0·15 of herbage mass when sown with 3–12 kg ha^?1 of PRG on SD1, SD2 or SD3, but less than 0·09 when sown on SD4. The proportion of Caucasian clover never exceeded 0·09 of herbage mass in any of the swards. White clover was successfully established in spring and in autumn with 3–12 kg ha^?1 of PRG provided the 15‐mm soil temperature was above 14 °C. None of the combinations of Caucasian clover and PRG provided an adequate proportion of legumes during the establishment year. This unsuccessful establishment of Caucasian clover with PRG was attributed to its inability to compete for available light as a seedling due to slow leaf area expansion from secondary shoot development and a high root:shoot ratio. Alternative establishment strategies for Caucasian clover may include the use of slow establishing grasses, cover crops and temporal species separation.     

Effect of grazing management on herbage protein concentration,milk production and nitrogen excretion of dairy cows in mid‐lactation

The objective of this experiment was to use diurnal and temporal changes in herbage composition to create two pasture diets with contrasting ratios of water‐soluble carbohydrate (WSC) and crude protein (CP) and compare milk production and nitrogen‐use efficiency (NUE) of dairy cows. A grazing experiment using thirty‐six mid‐lactation Friesian x Jersey cows was conducted in late spring in Canterbury, New Zealand. Cows were offered mixed perennial ryegrass and white clover pastures either in the morning after a short 19‐day regrowth interval (SR AM) or in the afternoon after a long 35‐day regrowth interval (LR PM). Pasture treatments resulted in lower pasture mass and greater herbage CP concentration (187 vs. 171 g kg^?1 DM) in the SR AM compared with the LR PM but did not affect WSC (169 g kg^?1 DM) or the ratio of WSC/CP (1·0 g g^?1). Cows had similar apparent DM (17·5 kg DM cow^?1 d^?1) and N (501 g N cow^?1 d^?1) intake for both treatments. Compared with SR AM cows, LR PM cows had lower milk (18·5 vs. 21·2 kg cow^?1 d^?1), milk protein (0·69 vs. 0·81 kg cow^?1 d^?1) and milk solids (1·72 and 1·89 kg cow^?1 d^?1) yield. Urinary N concentration was increased in SR AM, but estimated N excretion and NUE for milk were similar for both treatments. Further studies are required to determine the effect of feeding times on diurnal variation in urine volume and N concentration under grazing to predict urination events with highest leaching risk.