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.     

POTENTIAL PASTURE PRODUCTION IN THE UPLANDS OF WALES

Resown S23 perennial ryegrass pastures showed considerably greater response to the application of fertilizer N (0·1075 kg N/ha per year = 0–960 Ib N/ac) at 305 m O.D. than the native Festuca ovina/Agrostis tenuis and Molinia caerulea dominant communities on identical brown earth and peaty gley soils. Ryegrass DM production during 1967–70 increased with N application rates up to 538 kg N/ha per year (480 Ib N/ac) on the acid-brown earth, while on the extremely N-deficient gley soil yield responses were recorded up to 1075 kg N/ha (960 Ib N/ac). Percentage N recovery by ryegrass, bowever, although improved by grazing and re circulation, was less than under lowland conditions and the response to N during the growing season was also lower, exceeding 20 kg DM/kg N from applications in May, June and July only. The recovery of N by Festuca/Agrostis and Molinia in 1968–70 ranged from 3% and 2% at 938 kg N/ha to 14% and 9% at 117 kg N/ba per year, respectively. The respective maximum average DM yields recorded were 29 t/ha and 2.2 t/ha from the native communities and 70 t/ha and 62 t/ha from the corresponding resown pastures (2610, 1950, 6250 and 5520 Ib/ac). The results are discussed in relation to the strategy of land improvement in upland areas.     

THE EFFECT OF NITROGEN AND STOCKING RATE ON THE OUTPUT OF PASTURE GRAZED BY BEEF CATTLE

An experiment was conducted in two successire years to measure the effect of two levels of fertilizer N, 50 and 300 kg/ha (45 and 270 Ib/ac) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and 4 at the higher level. The responses per kg fertilizer N were approximately 1 kg liveweight gain, 20–24 Meal ME and 8–9 kg DM. Maximal yields of about 1000 kg gain/ha (890 Ib/ac) and 19,000 Meal ME/ha (7700 Mcal ME/acre) were recorded. Animal performance was similar on the low and the high N pastures. There was evidence that the chemical quality of pasture was lower on the low N pasture in the first year, but there was no difference in the second year. The numbers of dung pats per ha and the refusal of herbage due to fouling were reduced by Increasing the stocking rate.     

POTENTIAL PASTURE PRODUCTION IN THE UPLANDS OF WALES

The DM and N contribution of S184 white clover in mixed ryegrass/clover swards was recorded at Pant-y-dwr Hill Centre (305 m) for 4 years, 1967–70. By direct comparison with fertilized grass swards it was estimated that the clover N contribution on peaty gley soil averaged 100 kg N/ha per year (89 Ib N/ac) under cutting and 98 kg N/ha (87 ib/ac) under grazing with faecal return. On more fertile acid brown earth the corresponding contributions were 81 and 90 kg N/ha (72 and 80 Ib/ac). Full replacement of clover by N fertilizer would require average annual applications of 268, 229, 156 and 128 kg fertilizer N/ha, respectively (239, 204, 139 and 114 Ib N/ac).     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS

In an experiment described earlier (13), the N content of Italian ryegrass in spring reached a high value one or two weeks after applying N and then fell quickly at first and then more slowly. After 10 weeks average N content (in DM) was 0.6% from an application of 25 lh N/ac (28 kg/ha), 0.9% from 75 lb N (84 kg/ha), and 12% from 125 lb N (140 kgJha). Nitrate-N content fell more abruptly and tben remained fairly constant. Percentage nitrate–N (in DM) fell below 0.10% during the second week after an application of 25 lb NJac, during the third week after 75 lb N, and during the fifth week after recciriag 125 lb N. The yield of N increased during the first 5 or 6 weeks, remained fairly constant for 3–5 weeks, and then hegan to fall. During the ninth and tenth weeks, the crop lost an average of 9 lb N/ac per week (10 kg/ha) after an application of 75 Ib N/ac and 12 lb N/ac per week (13 kg/ha) after 125 Ib N.     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS.

Residual response to an initial application of nitrogen was measured in 3 years and was found to be quite large, e.g. a response of 8 Ib DM per extra Ib N at the first harvest, when applying 125 Ib N/ac (140 kg/ha) rather than‘75 Ib (84 kg/ha) and allowing 6 weeks' growth, was increased to 21 Ib DM when yield from residual cuts was taken into account. Response was large in relation to the amount of N estimated to have been left behind after the first harvest. Marginal recovery of N, already quite high at the first harvest, was increased to a little over 90% when yield from residual cuts was taken into account Recovery, however, was lower than this when 10 weeks' growth was allowed before the first harvest, and it seems that, in this case, some N may have been lost from the system. A supplementary experiment suggested that the residual effect of N on DM yield could be obscured to some extent by fresh applications of N.     

THE DISPOSAL OF COPPER-ENRICHED PIG-MANURE SLURRY ON GRASSLAND

Cu-enriched pig-mannre slurry was applied to grassland at two rates, 5000 and 10,000 gal/ac (56,000 and 112,000 I/ha), on three occasions, supplying a total of 5.4 Ib/ac (6.1 kg/ha) and 10.8 Ib/ac (12.2 kg/ha) Cu, respectively. At the higher rate, soil Cu extractable with EDTA increased from 24 ppm to 7.3 ppm Cu in samples taken to a depth of 3 in. (7.5 cm) and Cu in herhage DM increased from 9.1 ppm to 21.2 ppm Cu (mean of 5 cuts). Much of the additional Cu in the herhage was thought to be derived from external contamination. In other tests, leafy herbage sampled a few hours after applying slurry contained 338 ppm Cu in the DM. Samples of soil and herbage were taken in 1969, 1970 and 1971 from farm grassland that had received Cu-enriched pig-manure slurry each year; levels of Cu increased in the soil, Cu levels in herbage were variable and appeared to be affected by the rate of grass growth. The evidence suggests that there is at present littie risk of Cu toxicity following applications of Cu-enriched pig-manure slurry; the greatest risk to susceptible stock would appear to be by ingesting either grazed or conserved herbage contaminated with slurry. To avoid possible hazards from a build-up of Cu in the soil, a maximum annual application of ahout 8.5 Ib/ac (9.5 kg/ha) Cu is suggested until more is known on the availability of Cu in slurry to crops and grass.     

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.     

THE EFFECT OF CUTTING HEIGHT AND NITROGEN LEVEL ON THE YIELD, IN VITRO DIGESTIBILITY AND CHEMICAL COMPOSITION OF ITALIAN RYEGRASS SWARDS

Three cutting heights, 2±5, 7±6 and 12±7 cm (1, 2±5 and 5 in.) and three levels of fertilizer N, 168, 280 and 392 kg N/ha (150, 250 and 350 Ib N/ac) were imposed on a sward of Italian ryegrass (Lolium multiflorum) cv. Irish. Lowering the cutting height and increasing the level of applied N increased the yield of herhage DM. Increasing the level of applied N had a greater effect on the chemical composition of the herbage than altering the cutting height     

AMMONIA AS A SOURCE OF NITROGEN FOR GRASS SWARDS

Aqueous ammonia was injected to a depth of 10 cm into small grass plots in late winter at rates equivalent to 200 and 400 kg N per ha. The effect on yield of DM, seasonal distribution of yield and uptake of N in the herbage was compared with that of single or split applications of ammonium nitrate. Two levels of supplementary irrigation were given in summer. The method of injection minimised damage to the sward and loss of ammonia by volatilization.
Aqueous ammonia and ammonium nitrate (single application) gave similar yields of dry matter, uptake of N and distribution of yield over the season. Ammonia was no more effective than ammonium nitrate under dry conditions. A single application in February of 200 kg N/ha as ammonium nitrate gave a greater total annual yield than the same quantity of N as ammonia or as a split dressing of the solid fertilizer. At 400 kg N/ha, split application gave the highest yields. The uptakes of N in the harvested grass was similar, in each irrigation treatment and at each level of N, for the three methods of applying N, The apparent recovery was low.
Aqueous ammonia, efficiently injected, was a satisfactory form of N for grass at the first cut, but it did not provide a continuing supply of N for crops harvested later in that season.     

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 APPLICATION TO PASTURE ON BEEF PRODUCTION

Five grazing experiments each lasting 2 or 3 years were made between 1955 and 1967, all starting in the first year of ryegrass/cocksfoot/clover or ryegrass/clover leys. A high and a low rate of N, 235 and 45 Ib/ac on average (263 and 51 kg/ha) were compared for beef production. High- and low-N treatments gave mean clover contents for the grazing season of 8 and 24 % on a dry-weight basis, respectively. High N consistently gave a smaller liveweight gain/animal than low N, on average 1±92 and 2±08 Ib/day (0±87 and 0±94 kg/day), respectively. Liveweight gain/ac was 20% greater for high N than for low N, and in terms of net energy the production from high- and low-N, respectively, was 18,500 and 15,000 MJ/ac (45,700 and 37,100 MJ/ha). Data from these experiments, together with published results, were used to calculate a regression of liveweight gain response on N rate and an equation was derived from this to express the output in terms of profit. At 1971 prices profit was maximal at λ0±9/ac (λ2/ha) with 112 Ib N/ac (125 kg N/ha); it was considerably greater at 1973 prices when higher rates of N were justified.     

FURTHER COMPARISONS BETWEEN A RIGID ROTATIONAL WYE COLLEGE' SYSTEM AND OTHER SYSTEMS OF GRAZING FOR MILK PRODUCTION

In two 20-week grazing experiments, a rigid rotational system of grazing termed the ‘Wye College’ system was compared with a flexible paddock-grazing system in 1972 and with strip grazing and set-stocking in 1973. Eight spring calved Ayrshire cows were used on each treatment at a stocking rate of 5 cows/ha (2 cows/ac). The mean daily milk yields per cow were 17·7 and 17·0 kg(39·0 and 37·5 Ib) on the Wye College and the paddock systems, respectively, in 1972; and 17·9, 17·7 and 16·4 kg (39·4, 38·9 and 36·2 Ib) on the Wye College, strip, and set-stocking systems in 1973. The average annual output of milk varied from 11,500 kg/ha (1030 gal/ac) on the set-stocking system to 12,500 kg ha (1120 gal/ac) on the Wye College system, but none of the differences was significant. The most rapid decline in daily milk yield occurred on the set-stocking system in August and September as the amount of available herbage declined. This system requires further investigation. It is concluded that the Wye College system, with its rigid and pre-determined grazing cycle was as effective as either a one-day paddock or a daily strip-grazing system in producing high yields of milk.     

THE EFFECT OF LEVEL OF PROTEIN IN SILAGE ON THE INTAKE AND PRODUCTION OF DAIRY COWS

Two silages of contrasting protein content were compared in a 16-week winter-feeding experiment with 12 Ayrshire cows. One silage contained 8.2% DCP in its DM and the other 15.9% DCP. The silages were fed ad lib . with a supplement of either barley or barley plus groundnut cake. The DM digestibilities of the low and high protein silages were 74 and 67%, respectively, and the calculated S.E.s 56 and 47. Silage and total DM intakes were highest in the treatments containing low protein silage and in those containing groundnut. The mean daily milk yields for the treatments with and without groundnut were 35.4 and 32.s5 Ib (16.1 and 14.8 kg), respectively, with the high-protein silage, and 38.1 and 35.0 Ib (17.3 and 15.9 kg) with the low-protein silage. The S.N.F. contents of the milk were low and averaged 8.26 and 8.34% on the high- and low-protein silage treatments, respectively, and were not affected significantly by the supplements. It is concluded that the low-protein silage was superior to the high-protein silage as a feed for cows, and that the digestibility of the silage DM was a truer indication of quality than protein content.     

THE EFFECT OF FERTILIZER NITROGEN AND WHITE CLOVER ON HERBAGE PRODUCTION

The effect of a range of N rates on herbage production from grass/white-clover and grass swards was investigated in two long-term grazed experiments. The mixed sward yielded more than the grass swards over the range of fertilizer rates tested which were 0–120 lb N/ac (134.5 kg/ha), but the response of the mixed sward to fertilizer N was less than that of tbe grass sward. Tbis was due to the direct and indirect effect of clover, which was considerable with no fertilizer N but decreased witb increasing rates of application. However, clover was not completely suppressed by N at eitber site and contributed to berhage yields at all N rates. Rate and time of N application and the amount of clover in tbe sward affected tbe seasonal distribution of DM yields. The mid-season decline was less marked at bigb- tban at intermediate-levels of N supply.     

RED CLOVER SILAGE FOR MILK PRODUCTION

Nine wilted silages made from tetraploid red clover were fed in four winter-feeding experiments to 32 Ayrshire cows. The DM content of the silages averaged 23±5% (range 15±8–27±1) and contained an average of 19±6% crude protein, 14±2% digestible crude protein and 52±0% digestible organic matter. The pH values varied from 4±0–6±2, depending on the DM content and mechanical treatment of the crop, and the rate of application of formic add. The silages were fed ad lib.with supplementary concentrates and the average daily intakes of silage DM ranged from 16±0–24±0 Ib/cow (7±3–10±9 kg). The highest daily intakes were obtained with double-chopped silage containing 24–26% DM with a pH of 4±0. Although the red-clover silage had a high content of N and apparently provided a balanced ration with the addition of barley, yields of milk were increased significantly by substituting 1 Ib (0±4 kg) groundnut cake for 1 Ib barley in the daily ration of the cow. The silage contained oestrogenic compounds but the breeding pattern and fertility of the cows were not affected adversely. The tetraploid red clover produced approximately 9000 Ib DM/ac (10 100 kg/ha) in the 1st-harvest year and it is concluded that a safe and highly palatable silage with high intake characteristics can be made if the clover is wilted to about 24% DM, double chopped, and formic acid is applied at the rate of 0±5 gal/ton.     

THE EFFECT OF HEAVY DRESSINGS OF SLURRY ON FORAGE MAIZE PRODUCTION

Cow slony was incorporated into land at levels equivalent to 0, 125, 250 or 500 t/ha (0, 50, 100 or 200 tons/ac) shortly before sowing maize (INRA 200). Quantity and quality determinations were made on the crop at 73, 93, 115 and 137 days after plant emergence. The slurry dressings delayed the emergence of maize plants. The 250 t/ha (100 tons/ac) treatment gave a significant increase in DM yield at the final harvest, but 500 t/ha (200 tons/ac) tended to depress yields of the whole crop and of the ear. There was no significant effect on the percentage DM of the crop. Slurry applications increased the level of E and nitrate-N in the plants, but depressed Mg. Crude protein and in vitro digestibility were not affected.     

THE EFFECT OF NITROGEN, STOCKING RATE AND GRAZING METHOD ON THE OUTPUT OF PASTURE GRAZED BY BEEF CATTLE

An experiment was conducted in 1971 and 1972 to study the effects of two levels of fertilizer N (50 and 504 kg/ha) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and three at the higher. In addition to rotational grazing, set-stocking and an integrated grazing-conservation system were included. The responses/kg N were approximately 1 kg live-weight gain, 19–24 Meal ME and 8–9 kg DM. Maximum yields of 1200–1300 kg live-weight gain/ha and 25,000–27,000 Meal ME/ha were recorded. Productivity of set-stocked pasture was similar to rotational grazing at the high N level, but lower at low N. The integrated system yielded comparable results to high-N rotational grazing. Performances and herbage intakes per animal reflected the stocking rates imposed.     

POTENTIAL PASTURE PRODUCTION IN THE UPLANDS OF WALES

Study of the growth of heavily fertilized swards of S23 perennial ryegrass (Lolium perenne) at a hill and a lowland centre in mid-Wales during 1968–69 demonstrated that lower productivity in the uplands could only be partially attributed to a shorter growing season and poorer summer growth conditions. Comparison of yields with potential transpiration estimates indicated that winter damage had an important bearing on production during the following year. In 1969, the adverse combination of a mild autumn and a severe winter led to a spring tiller density which was less than 25% of normal at the hill centre. With an annual fertilizer input of over 500 kg N/ha (480 lb N/ac) total DM production in 1968 and 1969 was 10.6 and 4.4 t/ha at the upland site compared with 14.8 and 10.1 t/ha in the lowlands (9450, 3920, 13,190 and 9000 lb/ac).     

THE INTAKE OF DRINKING WATER BY GRAZING DAIRY COWS. THE EFFECT OF WATER AVAILABILITY

In a 16-week grazing experiment with six spring-calved Ayrshire cows, drinking water was available to the animals in three different ways, and the effect on milk prodnction was studied. The water was available from a water howl in the cowshed for 2.8 h/day in Treatment A, from a trough in the field for 21.2h/day in Treatment B, and from hoth sources for a total of 24 h/day in Treatment C. The cows on all treatments were grazed in individual plots of intensively-managed perennial ryegrass, stocked at the rate of 1 cow/0.22 ha (0.54 ac). The mean daily intakes of drinking water were 10.1, 15.3 and 15.5 kg (2.23, 3.37 and 3.42 gal)/cow, and the mean daily milk yields were 17.0, 17.2 and 16.8 kg (37.5, 37.9 and 37.0 lb)/cow in Treatments A, B and C, respectively; milk yields were not significantly different The herbage had an average DM content of 17.3%, and contained 19.6% crude protein and 66.5% digestible organic matter in the DM. The weight of water drunk was significantly and positively related to the DM percentage of the herbage, the air temperature and the daily hours of sunshine, and negatively related to daily rainfall. It is concluded that when dairy cows are grazing leafy herbage of high digestibility as their sole feed, the time during which drinking water is available may safely be restricted.