In 1992 and 1993, eight rates of 15N-labelled fertilizer (0–245 kg ha−1) were applied to winter wheat growing on the Ropsley long term field trial where eight different N amounts had been applied annually since 1978. The fate of the labelled N in the crop and topsoil (0–23 cm) was determined at harvest in the year of 15N application and in the first and second residual years.

By harvest in the second residual year, 60–77% of the original labelled application had been recovered in the crop and topsoil with 23–40% lost. These losses virtually all occurred within the first two growing seasons; there was no significant loss during the second residual year. Significant changes in the 15N balance were observed at N applications in excess of the range 140–175 kg ha−1 which suggested a marked decrease in the efficiency of N use and an increase in residual labile N in the soil at harvest. At low N applications (<175 kg ha−1), a positive added nitrogen interaction (ANI) was observed: 40–50% of this was a residual ANI due to the short or long term effect of applying N fertilizer, and the remainder was probably an apparent ANI due to pool substitution in the immobilization process. At large N applications (>175 kg ha−1) a negative ANI was observed: large N applications resulted in a net suppression of soil N uptake due to substitution by fertilizer for a limited plant N demand.

Results of an experiment conducted during the summer seasons of 1990 and 1991 in North West India revealed that a Spanish semi-spreading type groundnut cultivar ICGS 1 produced 93% higher pod yield than a Valencia bunch type MH 2. Application of chlormequat chloride (CCC) to both cultivars at 0·5 ml/l water enhanced yield by 17%. An input of 13 kg P/ha increased the pod output significantly over control.

Six plant species were compared in terms of their physical breakdown when eaten by sheep and when macerated: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). In two experiments at Aberystwyth in 1985 and 1986, the species were artificially dried and fed to lambs as the total diet. In another experiment in 1987, they were fed fresh, in 1·5 min meals, to yearling sheep.

Perennial ryegrass was more difficult to break down than the dicotyledonous species, judging by the particle size distribution in macerated and in chewed material and in the rumen contents and from the rather long time the sheep spent eating and ruminating per 100 g dry matter (DM) intake and the rather high fibrosity index. The width of some of the smaller ryegrass particles in the rumen was such that they must have contained only a single vein. Spurrey was readily broken down by macerating and by chewing and a relatively short time was spent eating and ruminating per 100 g DM intake. The shape of spurrey particles in the rumen was quite similar to that of stemmy ryegrass particles and the fibrosity index of spurrey was high. The breakdown of chickweed was similar to that of spurrey, but the fibrosity index of chickweed was lower. Accumulation of DM in the caecum appeared particularly pronounced in sheep fed ribwort or dock. The dock particles in the rumen typically had a low ratio of length to width and it seemed that dock particles did not need to be reduced in size as much as ryegrass particles before passing out of the rumen.

Excessive applications of liquid pig manure (LPM) could result in nutrient accumulation in the soil, thereby increasing the potential for plant nutrient losses through movement in groundwater. The objective of this work was to measure the concentrations of total carbon (Ct), total nitrogen (Nt), total phosphorus (Pt) and Mehlich-3 extractable-P (PM3) with depth in a Le Bras silty loam soil growing maize (Zea maize L.) under reduced tillage conditions. The soil was fertilized annually with various rates of LPM (0, 30, 60, 90 and 120 m3/ha) in four completely randomized blocks since 1979. In autumn 1992, twenty soil plots were sampled in increments of 20 cm to a depth of 1·0 m and analysed for total C, total N, total P and Mehlich-3 extractable-P. LPM application rate (R), soil depth (D) and the interaction R × D had highly significant (P<0·001) linear effects on Ct, Nt, Pt and PM3 concentrations throughout the 100-cm depth profiles. At all depths, Ct, Nt, Pt and PM3 contents increased with increasing rates of LPM application. The zone of maximum accumulation of Ct, Nt, Pt and PM3 concentrations occurred at the first 0–40 cm depth. A significant relationship was found between soil organic matter and Nt, Pt and PM3. Differences in N and P concentrations between manure rates are due to manure and maize. The increase in PM3 was generally greater for soil samples with high Pt content. Results from this study indicate that long-term application of a high rate of LPM leads to greater total C, N and P concentrations in the soil profile.

The effectiveness of 20 strains of Rhizobium leguminosarum bv. trifolii was evaluated with Trifolium semipilosum and T. burchellianum grown in a Vertisol soil in the glasshouse at the International Livestock Research Institute (ILRI) in Addis Ababa. Several effective strains were identified for both species. In T. semipilosum, inoculation significantly increased nodule DM and root N yield over the uninoculated control; Ethiopian Rhizobium isolates outperformed isolates from other sources for shoot DM and N yield. In T. burchellianum, contrast analysis revealed that there was no significant response to inoculation, although one effective strain was identified. Inoculant strains failed to overcome the competitive dominance of indigenous strains as reflected in mean nodule occupancies by inoculant strains of 15 and 7% in T. semipilosum and T. burchellianum, respectively. The 20 strains showed variable persistence following a 5-week drought period; only two of eight (T. semipilosum) and six of eight (T. burchellianum) strains were recovered from nodules on seedlings planted in the soil following the drought period. Overcoming the constraints of low nodule occupancy and variable persistence will require further understanding of the competitive interaction and the factors affecting access to nodule infection sites if superior Rhizobium–clover combinations are to be identified and developed.

The fatty acid composition of the plasma free fatty acid and adipose tissue triacylglycerol fractions was determined in lean and fat selection lines of Texel-Oxford and Scottish Blackface sheep at the 6th year of divergent selection. The mean proportion of 18[ratio ]2n-6 in the triacylglycerol of subcutaneous backfat was 1·3-fold higher in the phenotypically fatter sheep in the fat lines than in the phenotypically leaner sheep in the lean lines. Regression analysis indicated a positive relationship between this fatty acid and backfat depth whereas the proportion of 18[ratio ]1n-9 in the tissue triacylglycerol was negatively related to fatness. The proportions of 18[ratio ]2n-6 and of other polyunsaturated fatty acids in the plasma free fatty acid fraction were much higher than in adipose triacylglycerol. For the Scottish Blackface sheep in the fed state, the mean proportion of 18[ratio ]2n-6 in plasma free fatty acid (measured on all sheep) was 1·4-fold greater in the fat line than in the lean line. Regression analysis indicated a positive relationship between the plasma content of this fatty acid and backfat thickness whereas the proportion of 18[ratio ]1n-9 in plasma free fatty acid showed a negative relationship with fatness. The relationship between the plasma proportion of 18[ratio ]2n-6 and fatness was not observed after 48 h of fasting; instead, the plasma proportion of 18[ratio ]0 was found to be positively related to fatness in the fasted state. In summary, this paper shows how plasma and adipose tissue fatty acid profiles differ, and it quantifies the effects of selection on the plasma profiles. Possible reasons for the difference in fatty acid profiles between adipose tissue and plasma are discussed in the paper. It is suggested that plasma 18[ratio ]2n-6 levels during the early post-weaning growth period should be investigated as indicators of future fatness.

Studies were conducted from 1993 to 1995 in Southern Spain to determine the feasibility of controlling broomrape (Orobanche crenata Forsk.) in broad bean (Vicia faba L.) and lentil (Lens culinaris L.) by treating seeds with imazethapyr and imazapyr. In the broad bean, soaking for 5 min in 0·01–0·1% herbicide solutions or coating at 20–40 g ha−1 (seed sowing rate 160 kg ha−1) with imazethapyr (Pursuit-10) did not affect seed germination and crop growth, and resulted in 60–80% broomrape control. Furthermore, broad bean seeds treated with imazethapyr followed by an additional late post-emergence application of imazapyr (Arsenal-25) at 5 g ha−1 resulted in excellent broomrape control (>95%). Similarly, lentil seed treatments with imazapyr by coating seeds at rates equivalent to 5–10 g ha−1 or by soaking for 5 min in 0·25% solutions did not affect germination or crop growth, and controlled 85–95% of broomrape. As a result, with broomrape-efficient herbicide treatments, crop biomass/seed yield increased as compared to broomrape-infested, non-treated controls. Herbicide seed treatments with imazapyr in broad bean and with imazethapyr in lentil were less well tolerated and were less effective in controlling broomrape than treatments with imazethapyr and imazapyr, respectively.

Rice, a cash crop, was grown in the alluvial valley bottom (fadama) of an inland valley region of central Nigeria. The main staple crop, maize, was grown on the adjacent upland areas. Both oxen and manual labour were used for initial cultivation (ploughing and harrowing for rice and ridging for maize). Times spent were 94·3 and 315·2 h/ha respectively for rice and 28·2 and 65·5 h/ha for maize. Plots cultivated by animal traction (AT) produced more weeds and required more time for weeding than manually cultivated ones. Thus although animal traction saved time at the most critical time of year, it did not save time overall. Total time values were 1045 and 1064 h/ha for rice using animal traction and manual cultivation respectively. Corresponding values for maize were 654 and 484 h/ha. Type of cultivation had no significant effect (P > 0·05) on yields of crops (4·50 and 4·55 t/ha, AT/manual, for rice and 1·60 and 1·83 t/ha for maize). Not weeding the plots reduced rice yields to 2·78 and 2·83 t/ha for ox and manual cultivation respectively and to virtually zero for maize.

Annual liveweight gain of beef cattle (steers) grazing grass pasture fertilized with 200 kg N/ha was compared over a period of 7 years (1989–95) with that of steers grazing grass/white clover pasture given no artificial N fertilizer at North Wyke, Devon, UK. Nitrogen lost by leaching over the ensuing winter drainage periods was monitored from both pastures. Nitrogen leaching loss from the fertilized pasture over an extended period of 13 years (1983–95) is also reported.

The average annual liveweight gain of the steers grazing the grass/clover pasture (0·81 t/ha) was 19% lower than that of the steers grazing the N-fertilized grass pasture (1·00 t/ha). The average annual loss of nitrate-N by leaching in winter drainage from the grass/clover pasture (13 kg/ha) was only 26% of that recorded from the fertilized grass (50 kg/ha). A possible reason for this difference may arise from the previous history of the grass/clover pasture which had been ploughed in 1982, causing a flush of N mineralization and consequently greater immobilization of N in the soil in subsequent years.

Losses of N each winter by leaching measured over a 13-year period from the fertilized grass were highly correlated (P<0·001) with the preceding summer's soil moisture deficit, with the highest losses following dry summers. The nitrate-N concentration in the drainage water exceeded the European Union limit in drinking water (11·3 mg/l) in the initial 25 mm of drainage during 11 of the 13 autumns. The average loss of N each winter (53 kg/ha) was equivalent to 26% of the fertilizer-N applied annually. Immediate losses of N by leaching of fertilizer applied in early spring and throughout one very wet summer (1993) were minimal.

Rice was grown in an inland valley (fadama) region of central Nigeria. Plots were cultivated using oxen either in the dry season or at the beginning of the wet season. Around 25% more time was required for dry season cultivation but this enabled an average saving of 53·5 h/ha during the most critical time of the year at the beginning of the wet season. Total time for all operations during the year was similar (2075 and 2150 h/ha for dry and wet season respectively) of which most was spent on weeding (1388 and 1527 h/ha). Weeding time could be reduced by the application of pre-emergence herbicide to 1042 and 1247 h/ha for dry and wet season cultivation respectively. Grain yields were 4·0, 4·8, 4·2 and 4·6 t dry matter/ha for dry season/no herbicide, dry season/herbicide, wet season/no herbicide, and wet season/herbicide respectively. Similarly, straw yields were 4·8, 7·0, 5·7 and 7·4 t/ha. None of the differences in yield was statistically significant.

Glasshouse and field experiments were conducted in 1993 at the International Livestock Research Institute (ILRI) in Addis Ababa to identify effective combinations of Trifolium semipilosum genotypes and Rhizobium leguminosarum bv. trifolii strains and to investigate the effects of waterlogging of Vertisols on the response of clover to inoculation. In the glasshouse, the Rhizobium strain ILCA372str produced nearly ten times as much nodule DM, three times as much shoot DM, five times as much root DM, and twice as much plant N on cv. Safari as it did on accession ILCA7609 under normal watering conditions. This spontaneous streptomycin-resistant mutant strain performed better than its parent strain. Shoot DM and N yields of this combination were, however, only 55 and 71%, respectively, of the corresponding N-fertilizer (150 kg N ha−1) treatment. Waterlogging reduced nodule DM by 33%, shoot DM by 41%, root DM by 25% and N yield by 33%, and responses of both plant genotypes to inoculation and to N fertilizer were reduced. In the field, there were no significant differences in nodulation, plant DM and plant N between seed and soil inoculation methods. Dry matter and N yields of Safari inoculated with strain ILCA372str were at least twice as high as those produced by any other strain or N fertilizer supplied at 100 kg N ha−1. Waterlogging during early establishment in the field probably reduced the availability of N fertilizer to the plants. Further field testing of the Safari-ILCA372str combination is recommended, particularly in combination with broad-bed and furrow (BBF) technology to drain Vertisols.

In order to assess relative thermal sensitivity between the day and the night, vaginal temperature (Tv), heat production (HP), heart rate (HR), respiration rate (RR), skin surface temperatures (from which mean skin temperature (Ts) was calculated) and standing time were measured at environmental temperatures (Te) of 23, 28, 33 and 38°C during the day (11.00–15.00 h) and during the night (23.00–03.00 h) using four Holstein heifers. Both Tv and mean body temperature (Tb) were greater during the night than during the day, increased with increased Te, and the rate of increase of both Tv and Tb with increased Te was greater during the night (P<0·05). Estimated mean HP was similar during the night and during the day, and HP did not increase with increased Te. Respiration rate was greater but not significantly different at night compared to during the day, and increased with increased Te. Mean skin temperature was similar between day and night, and increased with increased Te. The amount of time engaged in standing activity was greater but not significantly different during the night than during the day and standing activity increased with increased Te. The results suggest that thermal sensitivity is lower during the night than during the day, and consequently the greater night responses of Tv and Tb, over day responses, are a requirement for the maintenance of heat balance.

The Cu, Zn and Mn status of 44 fields from the Canterbury region of New Zealand under winter wheat was investigated in Spring 1993. Micronutrient status was assessed using EDTA, DTPA and HCl as extractants. The Mn status of soils was generally high and unaffected by soil development. However, when samples were separated according to soil series, it was found that extractable Cu and Zn levels in both the 0–15 and 15–30 cm soil layers generally decreased with increasing soil development (increasing soil age and annual rainfall). Twenty-three percent of fields had EDTA-extractable Cu levels <1 μg g−1 whilst 34% had EDTA-extractable Zn levels <1 μg g−1.

Twenty-two of the soils were used in a glasshouse experiment in which wheat was grown in the soils with or without the addition of added Cu and/or Zn. Plant dry matter responses to added Cu were recorded in soils with extractable Cu levels <1·1 μg g−1 EDTA, 0·4 μg g−1 DTPA and 0·9 μg g−1 HCl. Responses to added Zn occurred in soils with extractable Zn levels <0·8 μg g−1 EDTA, 0·25 μg g−1 DTPA and 1·4 μg g−1 HCl. Significant linear correlations were found between EDTA-, DTPA- and HCl-extractable Cu and Zn and Cu and Zn uptake respectively by wheat. Correlation coefficients were closer for Cu than for Zn uptake. It was concluded that many sites on the more strongly developed soils of the Canterbury Plains are potentially deficient in Cu and/or Zn and that these can be identified using conventional micronutrient soil tests.

Maize was grown in the upland areas surrounding an inland valley in central Nigeria in a randomized block experiment using six cultivation techniques (manual cultivation with a hand hoe (MC); ploughing in both directions to throw up a ridge (DPL); single ploughing with the seed placed on the ridge (SPL); ridging with a wooden, single tine, locally made ‘bush’ plough (BPL); single ploughing with the seed placed in the furrow (FPL) and ridging with a conventional ridger (RID) with or without pre-emergence herbicide (PEH) with two replicates. Initial cultivation times ranged from 29 to 70 h/ha (BPL<RID<SPL<FPL<DPL<MC). Total weeding time ranged from 220 to 512 h/ha (MC<DPL<RID<FPL<BPL<SPL) with PEH and from 431 to 763 h/ha (MC<SPL<DPL<RID<FPL<BPL) without PEH. Ox cultivation techniques were associated with higher weeding times and larger weed burdens. Total times for all field operations were 568–758 h/ha (MC<FPL<DPL<BPL<SPL<RID) with PEH and 791–870 h/ha (BPL<MC<SPL<DPL<RID<FPL) without PEH. Thus, although ox cultivation saved time at the most critical time of year (cultivation and planting), it did not save time overall.

Amongst the ox cultivation techniques, work inputs were 6·3–34·1 MJ/ha (BPL<FPL<SPL<RID<DPL) and draught forces 387–1377N (BPL<DPL<FPL<SPL<RID).

Yields of maize cobs were 2·55–4·0 t/ha (SPL<FPL<MC<RID<DPL<BPL) with PEH and 1·65–3·55 (RID<BPL<FPL<DPL<MC<SPL) without PEH. Except for SPL, PEH was associated with increased yield especially when used with ox cultivation.

As regards crop yield, time inputs and work input, there was no advantage to be gained from using a separate (and expensive) ridger for maize compared with a locally made plough or the plough also used for the main cash crop (rice).

At 1992 prices, the cost of PEH was about the same per ha as the price of labour saved on weeding, but additional benefits associated with PEH use were the avoidance of mid-season labour bottlenecks and an overall increase in crop yield.

The phosphorus fertilizer requirements and long term productivity of nitrogen-fertilized Gatton panic (Panicum maximum cv. Gatton) pastures, grazed by lactating dairy cows, were evaluated over 7 years. Cows grazed at 2·6 cows/ha on pastures that received annually 100 or 300 kg N/ha at each of 0, 22·5 or 45 kg P/ha. Phosphorus treatments were applied as single superphosphate, balanced for calcium by applications of gypsum.

The soil had an initial available soil phosphorus content of 40 mg/kg (bicarbonate extraction). At zero P fertilizer (0P), extractable soil P declined at the rate of 1·9 mg/kg each year; at 22·5P it was maintained close to the original level while at 45P it increased at 6·6 mg/kg each year. Increased P fertilizer caused significant (P<0·01) increases in plant P concentration from year 2 onwards. In years 6 and 7 there was significantly less green pasture and leaf on offer in 300N pastures at 0P than with 22·5P and 45P. There was no influence of rate of P fertilizer at 100N on pasture quantity on offer in any year. There were clear trends at 100N of decreasing total pasture and green dry matter (DM) on offer over the 7 years, but not at 300N.

Cows at 300N consumed more leaf in the diet in autumn and winter than at 100N. Leaf was 55–60% of the diet in summer and autumn, but decreased to 21% (100N) and 37% (300N) in winter. Dead material in the diet was always higher at 100N. Pasture leaf percentage and leaf yield were the best individual predictors of leaf percentage in the diet. Diet P selected from pasture was reduced by the higher rate of N fertilizer in each season. Estimated P concentrations of the diet selected from pasture for summer, autumn and winter averaged 0·30, 0·38 and 0·28% DM for 100N and 0·19, 0·24 and 0·18% DM for 300N treatments, respectively.

The response to P fertilizer was dependent on the rate of N fertilizer applied. The critical bicarbonate extractable soil P level for this soil type, below which pasture responses occurred, was 30 mg/kg at 300N. The critical level at 100N was not reached, but was <23 mg/kg P.

Three glasshouse experiments were conducted between 14 September 1993 and 9 January 1996 at the Plant Growth Unit, Massey University, Palmerston North, New Zealand. Experiment 1 studied the effects of cutting height on the regrowth and biomass allocation of chicory (Cichorium intybus L. cv. Grasslands Puna), Expt 2 investigated the biomass allocation and root carbohydrate reserves of three chicory cultivars (Puna, PG90 and Orchies) in response to defoliation, and Expt 3 studied the morphological characteristics and persistence of Puna under extreme defoliation.

Cutting height had no significant effect on accumulated secondary leaf and stem masses in Expt 2, but affected secondary leaf mass in Expt 1. However, cutting height significantly reduced root size after two cuttings in both Expts 1 and 2. Three severe cuttings (removing all shoots including visible buds >5 mm on crown) killed 73% of plants, whereas 96% plants survived under lax cutting (100 mm) in Expt 3. Orchies had the highest total reducing sugar concentration in its taproot (56·6%), whereas PG90 had the lowest (32·1%). Therefore, Orchies was the most persistent but had the slowest growth rate, and PG90 the least persistent with the highest growth rate. The performance of Puna was intermediate.

It is concluded that the persistence of Puna would be more sensitive to cutting frequency than cutting intensity due to its medium level of root carbohydrate reserves. In contrast, PG90 could be defoliated frequently, but not closely. However, Orchies with its thick taproot was insensitive to cutting intensity and would also be insensitive to cutting frequency due to its larger root carbohydrate reserves. It is suggested that to improve the persistence and enhance the leaf production of Puna by plant breeding the emphasis should be on increasing taproot size without unduly prejudicing herbage production.

Thirty-two N'Dama heifers were offered ad libitum Andropogon hay plus 10·2 g/kg liveweight (LW) groundnut hay (GNH) (L) or 10·2 g/kg LW GNH and 3·9 g/kg LW groundnut cake (GNC) (H). After 4 weeks on the diets, half of each group were infected intradermally with Trypanosoma congolense clone (ITC 50) (LI and HI). Peak parasitaemia occurred 6–8 days after infection and started to decrease c. 56 days later. No differences in parasitaemia were observed between LI and HI animals. Packed cell volume (PCV) fell in all treatments (by 5·4, 13·8, 3·7 and 9·4 units after 49–63 days post-infection (p.i.) for the L, LI, H and HI groups respectively) and significant effects of infection and diet were observed. GNH and GNC intakes were maintained during the trial; however, infected animals had a decreased intake of Andropogon hay. LI animals lost significantly more weight during the experimental period than the non-infected controls (−71·4 v. −13·7 g/day). Meanwhile, HI animals gained less weight compared with the H group (52·2 v. 167·6 g/day). Weight losses appeared to be due to decreased food intake. In the period 54–68 days p.i., plasma concentrations of albumin were lower and plasma protein was higher in infected animals. Plasma cholesterol concentrations were also lower in infected animals 54–68 days p.i. Plasma urea concentrations were higher in supplemented animals but were not affected by infection. The results showed that animals on a higher plane of nutrition showed less severe clinical signs of infection. However, for all the parameters considered, the magnitude of the difference between groups on different diets was similar for both infected and control animals, suggesting that mechanisms of resistance were not affected by the planes of nutrition considered.

Results are reported from three experiments conducted at the Dairy Research Institute, Ellinbank, Australia during 1992/93 which examined the composition and kinetics of the gas in the rumen headspace of lactating dairy cows grazing white clover/perennial ryegrass pastures. Before grazing, rumen headspace gas was composed of carbon dioxide 65%, methane 31% and nitrogen 4% whereas, after one hour of active grazing, the headspace gas was composed of carbon dioxide 76%, methane 22% and nitrogen 2%. The composition of headspace gas was not affected by antibloat capsules (which release 250 mg/day of monensin). The headspace gas from bloated cows contained slightly less (P<0·01) carbon dioxide and slightly more nitrogen than that from non-bloated cows.

A novel technique which employs ethane as a tracer to measure rumen headspace volume and the kinetics of the rumen headspace gases is described. The tracer technique was used in two experiments in which the influence of grazing, antibloat capsules and bloat on the rumen headspace volume and the kinetics of the headspace gases were examined. It is concluded that our ethane tracer technique provides a simple and inexpensive way to estimate methane production by grazing ruminants.

Field trials were conducted at six sites throughout Ireland in 1992, 1993 and 1994, to assess the efficiency of utilization of N in cattle slurry treated with nitric acid. Slurries were left untreated or were acidified to pH 5·5 with 12 m nitric acid immediately prior to spreading. Slurries were either band-spread or splashplate-spread using an automated tanker system. The efficiency of N (NH+4-N+NO−3-N) in slurry for grass production (Eff-N%) was measured by comparing N offtake values with those from a range of rates of inorganic fertilizer N (ammonium nitrate/calcium carbonate) treatments. Slurry was applied at rates (13–28 m3/ha) which supplied N (NH+4-N+NO−3-N) below the highest inorganic fertilizer treatment. In all experiments, untreated cattle slurry was compared with nitric acid-treated cattle slurry at the same rate of application. The Eff-N% values for unacidified or acidified slurries were highly variable by both spreading methods. The effect of spreading method depended on whether or not the slurry was acidified. On average the Eff-N% value of the band-spread unacidified slurry (59%) was significantly higher than the Eff-N% value of the splashplate-spread slurry (37%). For acidified slurry, the average Eff-N% value of the band-spread slurry (85%) was not significantly different from the Eff-N% value of the splashplate-spread slurry (81%). The overall average Eff-N% value of the acidified slurry was 83% which was significantly less than 100%. Cattle slurry acidified with nitric acid to pH 5·5 was more variable and less efficient than inorganic fertilizer N under the soil and climatic conditions tested.

The phosphorus fertilizer requirements and long term productivity of nitrogen-fertilized Gatton panic (Panicum maximum cv. Gatton) pastures, grazed by lactating dairy cows, were evaluated in a 7-year experiment. Cows grazed at 2·6 cows/ha on pastures that received annually 100 or 300 kg N/ha and each of 0, 22·5 or 45 kg P/ha. Cows received no energy supplements in years 1–3 and were offered molasses at 3·5 kg/day from year 4 to year 7. Cows grazed their experimental paddocks from the start of the wet season until they started to lose weight in the dry season.

In years 6 and 7 there was significantly less green pasture and leaf on offer in 300N pastures at 0P than with 22·5P and 45P. This was reflected in a reduced milk yield by cows at 300N/0P in these two years. There was no influence of rate of P fertilizer at 100N on milk yield in any year. Lactation milk yields at 300N in years 6 and 7 averaged 3930, 4310 and 4610 kg/cow (P<0·05) for 0P, 22·5P and 45P, respectively. Nitrogen fertilizer increased milk yield in each year (P<0·01) except the first. Milk yields at 100N and 300N averaged 2860 and 3320 kg/cow respectively in years 1–3 and 3720 and 4290 kg/cow in years 4–7.

The milk yield responses to P fertilizer were related to the greater amounts of pasture and green leaf on offer, which led to a higher proportion of leaf in the diet, and the response to P fertilizer was dependent on the rate of N fertilizer applied. Phosphorus intakes were estimated to be below that of published requirements for cows producing this quantity of milk. An annual model of P flow between plant, animal and soil pools demonstrated that at 100N/22·5P more P was returned to the soil as excreta (15·7 kg P/ha) than with 300N/22·5P (7·1 kg P/ha). The major pathway of return of P to the soil at 300N was through plant litter. Soil organic P was the largest, but least exploited, pool of phosphorus.

This study has illustrated how the demand for phosphorus by the plant in grazed pastures is modified by the input of N fertilizer, is poorly predicted from plant analysis and published standards for animal requirements, and indicates that a response in milk production may be mediated through the effects of P on leaf growth and not on dietary P content.