From 1985 to 1987, 20 experiments were carried out on shallow chalk soils, in which soil N reserves were expected to be small, to assess seasonal variations in the response of winter cereals to applied fertilizer N, and to relate these responses to measurements of soil mineral N (SMN), temperature and soil moisture deficits (SMD).

Soil mineral N measured in autumn varied from 21 kg/ha (1986) to 73 kg/ha (1985), while SMN in spring ranged from 19 kg/ha (1987) to 91 kg/ha (1985), these values were typical of soils in long-term arable rotations. Estimates of apparent net N mineralization (AM) during the growing season were small at c. 26 kg/ha and suggested large seasonal variation. The small AM is considered to be due to the shallow topsoil drying out during the growing season. Whole crop N offtake without fertilizer N was only c. 40kg/ha. Crop N offtake, grain yield without fertilizer N and AFR (apparent recovery of fertilizer N) could not be reliably predicted by regression on SMN in autumn, SMN in spring or AM. Little or none of the variation in crop yield could be accounted for by regression on accumulated temperature over winter, maximum SMD in April to July or mean temperature in April to July.

Despite optimum grain yields being only moderate at 6·59 t/ha for winter wheat and 6·78 t/ha for winter barley, response to applied fertilizer N was large, between 3·77 and 5·38 t/ha. In consequence the requirement for fertilizer N (c. 240–250 kg/ha) was also large, but differed little between seasons. This large requirement is concluded to be a result of limited fertilizer recovery and mineralization of soil N during the growing season.

Twenty-six experiments were carried out in England and Wales from 1983 to 1985 to compare urea and ammonium nitrate (AN) as N top-dressing for cereals over the range 100–300 kg/ha N. Most of the experiments were sited on chalky or other soils of pH>7·0 where the greatest differences in effectiveness were expected.

The results showed that while relative N offtake in grain was 2·5% greater from AN, there was no difference in grain yield. Splitting the main N application increased N offtake from urea but not from AN. Overall, urea effectiveness from a single application at GS 31 increased with increasing rainfall on the day of application, but was not increased by subsequent rainfall. On chalk soils, urea effectiveness increased with increasing cumulative rainfall up to the fifth day after application. There was little effect of rainfall on urea effectiveness when the dressing was split. Although grain yield was unaffected by the type of fertilizer N applied, grain N concentration was usually less from urea.

The fertilizer N requirement for optimum yield (Nopt) wassimilar for both fertilizers. Splitting the main N application had no effect on yield or Nopt. We concludethat urea is a satisfactory source of N for cereals.

Although it has been generally recognized that the difference in yield potential amongst wheat cultivars released in different eras is related to differences in their reproductive sink strength, there have been few investigations about changes in source–sink ratios as a consequence of wheat breeding. In the present study, two field experiments, in which plots were fertilized and irrigated and lodging and diseases were prevented, were carried out with seven cultivars (including a commercial hybrid) representing different periods of plant breeding in Argentina from 1920 to 1990. The cultivars were defoliated during post-anthesis to analyse the response of grain weight at particular positions within the spike (which have intrinsic differences in potential size).

Individual grain weight was virtually unaffected by defoliation in the old cultivars, but modern cultivars exhibited a significant reduction in individual grain weight for several positions within the spike, although this reduction was small (c. 15%) and many grains were unaffected. In addition, no relationship was found between individual grain weight in the controls and its reduction due to defoliation.

We concluded that if the source–sink ratio is further reduced, the grain yield of modern wheats will be simultaneously limited by the source and the sink. Future breeding should therefore attempt to improve simultaneously both sink and source strengths.

A field experiment was carried out at Lumle Agricultural Research Centre (LARC) farm, Nepal, during the winter seasons of 1992/93 and 1993/94 in order to study the profitability of intercropping wheat (Triticum aestivum L.) with tori (Brassica campestris var. toria) and pea (Pisum sativum L.). A sole crop of wheat planted at 120 kg seed ha−1 was compared with sole crops of tori and of pea planted at 8 kg ha−1 and 60 kg seed ha−1, respectively, wheat+tori mixed-intercropped at 120[ratio ]6, 120[ratio ]4 and 120[ratio ]2 kg seed ha−1and wheat+pea at 120[ratio ]45, 120[ratio ]30 and 120[ratio ]15 kg seed ha−1.

Results over the two seasons showed that the intercropping of wheat+pea was profitable in terms of overall grain yield, land advantage, monetary advantage, economic return and meeting the dietary requirements of the subsistence farmers, although the sole crop of pea gave the highest net return. Mixing pea with wheat did not reduce wheat yields in either year except when pea was sown at 45 kg seed ha−1, which reduced wheat yield significantly in the first season. For wheat+pea intercropping, sowing pea at 30–45 kg ha−1 was the most profitable. The wheat+tori intercrop did not perform as well and was not as profitable as either sole crop. Intercropping of tori had a negative effect on wheat yield at all seed rates in the first year.

Seventy-seven adaptive research trials were conducted, with the participation of local farmers, on their fields during the 1993 and 1994 wet seasons (southwest monsoon seasons) in the warm subhumid tropical zone on the west coast of India. The objective of the trials was to compare the agronomic and economic benefits of an improved management consisting of placing urea briquettes containing diammonium phosphate (UB–DAP) by hand (56 kg N/ha and 14 kg P/ha) after controlled transplanting using a modified 20×20 cm hill spacing with two other practices: (i) the current management system, consisting of random transplanting and two split applications of prilled urea (PU) and a basal application of single superphosphate (SSP) and (ii) the farmers' traditional management practices, involving random transplanting and broadcasting of fertilizers. In spite of marked variations in rainfall distribution patterns during the 1993 and 1994 seasons, the improved management using UB–DAP increased grain yields by 2·14 t/ha (89%) in 1993 and 1·23 t/ha (45%) in 1994 over traditional management practices and by 1·56 t/ha (52%) in 1993 and 0·83 t/ha (27%) in 1994 over the current management system. These additional yields were obtained at a 28–36% lower plant population density (25 hills/m2v. 35–39 hills/m2). The use of a modified 20×20 cm spacing could reduce by up to 50% the labour normally required for the conventional placement of UB by hand about 1 week after transplanting using the standard 20×20 cm spacing (8–10 workdays/ha). The estimated value: cost ratios for the improved management ranged from 4·9 (1994) to 8·6 (1993) and increased further when the savings in seed input were considered. Stochastic dominance analysis of the yield data suggests that the improved management of UB–DAP could be risk-free and therefore would be preferred over the other two managements by rice farmers and policy makers.

Male sterile combinations made from interspecific crosses between the polima CMS line of Brassica napus and varieties of B. chinensis were backcrossed to BC3. Twenty-six selfing lines from B. chinensis were tested for their ability to either maintain complete sterility or to restore fertility in crosses with the polima male sterile line. Results show that four of these hybrids were completely male sterile and two were fertile. The sterility of the B. chinensis with polima cytoplasm was much more stable than male sterile lines with B. campestris and B. chinensis cytoplasm, which were sterile before full flowering but progressively became fertile as flowering proceeded. The results suggest that polima cytoplasm could be a suitable male sterile-inducing allocytoplasm for B. chinensis, as both maintainers and restorers are available, and could supply a reliable pollination control system for hybrid seed production in this species.

Over three growing seasons (1989 to 1991) perennial ryegrass swards were cut at regular 3-week intervals or changed to a 2, 4, 5, 6, 7, 8 or 9-week regrowth interval in the early (April to mid-June), mid (late June to mid-August) or late season (late August to mid-October) at the Agricultural Research Institute of Northern Ireland. Fertilizer was applied according to the length of the regrowth period to supply the equivalent of 2·2 kg N/ha per day with an annual rate of 416 kg N/ha.

Lengthening the regrowth interval by a single 6-week interval increased the annual yield of herbage DM and digestible organic matter (DOM) from 10·13 to 11·15 and from 6·73 to 7·47 t/ha respectively. The effect increased with increasing length of regrowth period and was greatest in the early part of the season. In swards cut on a regular 3-week regime there was no significant difference in organic matter digestibility (OMD) throughout the season (mean 69·4%), whereas N concentration increased steadily throughout the season, ranging from 25·6 g/kg DM in April to 41·8 g/kg DM in October.

During the variable regrowth periods, the greatest response in DM and DOM yield to increasing length of regrowth interval was obtained in the early part of the season in spite of a rapid fall in OMD. There was little to be gained by lengthening the regrowth interval beyond 6 weeks in mid-season, due to low and declining herbage OMD. However, in the late season period, the rate of decline in herbage OMD tended to decrease after week 5 and so the rate of decline in DOM accumulation was reduced, making length of regrowth period in the late season less critical.

The treatments imposed had little effect on yield of herbage N (range 293–354 kg N/ha).

Moringa oleifera grows throughout most of the tropics and has several industrial and medicinal uses. The objective of this study was to evaluate the potential of different morphological parts of this tree as animal feed. The crude protein (CP) content of leaves, soft twigs and stems was 260, 70 and 60 g kg−1 respectively. About 64, 79 and 67% of the total CP present in the leaves, twigs and stems respectively was found to be degradable after 24 h in the rumen. The protein insoluble in acid detergent fibre (ADIP), considered unavailable to animals, in these samples was 30, 150 and 170 g kg−1 respectively. About 87% of the total CP was in the form of true protein in the leaves (60 and 53% in twigs and stems respectively). The leaves had negligible amounts of tannins (12 g kg−1), and trypsin and amylase inhibitors, lectins, cyanogenic glucosides and glucosinolates were not detected. The saponin content of the leaves was 80 g kg−1 as diosgenin equivalent, which did not show any haemolytic activity. The phytate content of the leaves was 21 g kg−1. Tannins, saponins, cyanogenic glucosides and glucosinolates were detected in twigs and stems but the concentrations were negligible. Trypsin and amylase inhibitors were not detected in twigs and stems. Phytate contents of both twigs and stems were c. 30 g k−1. In leaves, amounts of all the essential amino acids were higher than the amino acid pattern of the FAO reference protein and comparable to those in soyabeans. The CP and lipid contents of the kernel were 370 and 420 g kg−1 respectively, and the CP of the meal (fat-free) was 610 g kg−1. The kernels and meal are extracted with water and the extract is used for the purification of water in some developing countries. The residues left after water extraction of kernels and meal (designated as extracted-kernel and extracted-meal) had a CP content of 350 and 700 g kg−1 respectively and all of this CP was in the form of true protein. After taking into account the ADIP contents in these samples, c. 38 and 69% of the total protein was calculated to be available in the post-rumen in extracted-kernel and extracted-meal respectively. The pepsin digestibility of these samples was 91 and 84% respectively. The sulphur-containing amino acids in kernel proteins were present at higher concentrations than those specified in the amino acid pattern of the FAO reference protein but other essential amino acids were deficient. Amongst the antinutritional factors mentioned above, glucosinolates and phytate were present in appreciable amounts (65·5 μmol/g and 41 g kg−1 respectively) in meal. Haemagglutination activity was also detected in the meal. The extracted-meal was virtually free of all the antinutritional factors examined except for phytate (67 g kg−1). The leaves of Moringa oleifera and the residue obtained after the recovery of oil and coagulants can be good sources of proteins for animal feeds.

Four experiments were carried out in Lelystad, The Netherlands in 1994, in which perennial ryegrass wilted to 421–568 g dry matter (DM) kg−1 was ensiled with and without an inoculant containing Lactobacillus plantarum and Enterococcus faecium strains in 1-litre capacity laboratory silos. Treated silages showed a markedly increased rate of pH decline. The final pH of treated silages was reached 20–30 days after ensiling, whereas acidification of control silages continued during the full 180-day ensilage period. After 180 days ensilage, treated silages showed significantly (P<0·001) lower pH, DM loss and ammonia-N concentrations and significantly (P<0·001) higher lactic acid concentrations than control silages in all experiments. Concentrations of ethanol and acetic acid were significantly (at least P<0·05) lower for the treated silages, except for acetic acid in one experiment and ethanol in another. Butyric acid was not found in any of the silages. One of the control silages (ensiled at 517 g DM kg−1) contained ethanol as the major fermentation product indicating that alcoholic fermentation had taken place, probably by yeasts. Treated and untreated grasses used in the first experiment (432 and 442 g DM kg−1, respectively) were also used to produce silages in two 40-t capacity clamp silos. Similar to the laboratory silos, the treated silage had a higher lactic acid concentration and lower pH and ethanol, acetic acid and ammonia-N concentrations than the untreated silage.

The phosphorus (P) balances and 32P kinetics of 15 Droughtmaster heifers were studied in mid and late pregnancy and early and late lactation to compare their P absorption coefficients and their P endogenous faecal losses with those of growing cattle. The heifers continuously grazed three paddocks of tropical pasture for a year to provide a range of P intakes.

The daily dry matter (DM) and P intakes of the heifers were generally much higher during lactation (17–26 g DM/kg LW and 11–40 mg P/kg LW) than during pregnancy (10–16 g DM/kg LW and 6–22 mg P/kg LW), due in part to the heifers calving at the beginning of the wet (pasture growing) season. Plasma inorganic P levels decreased as the experiment progressed and were very low (<30 mg/l) in all treatments in late lactation. Milk and milk P secretion were high in early lactation (4·0–5·5 l/day and 12–16 mg P/kg LW per day) so the heifers were in more negative balance during lactation than during pregnancy.

The coefficient of P absorption was similar to that previously observed in growing cattle consuming forage diets and it was concluded that 0·75 was the appropriate value to use in the estimation of requirements. Endogenous faecal losses ranged from 7 to 17 mg/kg LW and were related to P intake or DM intake plus plasma inorganic P. Comparison of the regressions with those from the larger data set for growing cattle showed that the endogenous faecal losses were similar and there were no special faecal endogenous losses in breeding cattle.

The productivity of grazing sheep was assessed under 7-year-old rubber at the Rubber Research Institute of the Malaysia Experimental Station at Sungai Buloh near Kuala Lumpur between October 1988 and May 1990. The sheep were Dorset × Marlin crossbred lambs and they grazed planted leguminous cover crops and naturally occurring species at a range of stocking rates.

In the immature rubber trial, presentation yields of forage declined with time regardless of stocking rate. In the mature rubber trial, presentation yields of forage were low (<1000 kg/ha) due to low light transmission. High stocking rates (>6 sheep/ha) resulted in a decrease in the proportion of palatable species, namely Pueraria phaseoloides, Paspalum conjugatum, Asystasia gangetica and Mikania micrantha and an increase in the proportion of the less palatable species such as Calopogonium caeruleum and Cyrtococcum oxyphyllum.

Daily liveweight gains ranged from 100 g/lamb per day at 4 sheep/ha to 70 g/lamb per day at 14 sheep/ha in the immature rubber trial. Only the lowest stocking rate of 2 sheep/ha was continuously sustainable in the mature rubber trial. The estimated maximum liveweight gain that could be achieved under immature rubber was 266 kg/ha per year at a stocking rate of 13·2 sheep/ha.

The productivity and persistence of 91 accessions of grasses, legumes and broad-leaved weeds were evaluated under young rubber at the Rubber Research Institute of Malaysia Experimental Station at Sungai Buloh near Kuala Lumpur. The species were chosen from world collections for their reported shade tolerance. Two small plot experiments were conducted from 1989 to 1990 and regular harvests were used to assess yield and persistence. The soil at the site was acidic (pH 4·7) and infertile, and light transmission declined from 65 to 20% in Expt 1 and from 90 to 50% in Expt 2.

Pattern and cluster analyses were used to allocate accessions to groups with similar yield responses. Grasses which demonstrated both high yield and persistence of yield were Brachiaria decumbens MARDI accession, B. humidicola cv. Tully and Panicum maximum cvs Gatton, Riversdale and Vencedor. High yielding and persistent legumes were Stylosanthes scabra cv. Seca and S. guianensis CIAT 184. Survival of species monitored one year after completion of the experiment indicated the good longer term persistence of grasses Stenotaphrum secundatum, Panicum laxum, Paspalum notatum, Paspalum wettsteinii, Brachiaria humidicola and Panicum maximum cv. Vencedor, and legumes Arachis repens and A. pintoi.

The interrelationship in metabolism between dietary selenium (Se) and copper (Cu) was investigated in sheep receiving a diet with or without sodium bicarbonate (NaHCO3). A sheep finishing diet, containing 0·3 mg Se/kg DM and 7·4 mg Cu/kg DM, and supplemented with 1·0 mg Se (as Na2SeO3) and/or 15·0 mg Cu (as CuSO4) and/or 40 g NaHCO3 per kg feed, was fed to young ewes for a period of 64 days. Hepatic Cu concentration and net accumulation were not affected by NaHCO3 supplementation. Furthermore, no evidence was found in blood, tissues or faeces to show that NaHCO3 influenced Se metabolism. However, hepatic Cu concentration was raised from 354 to 422 mg/kg DM (P<0·05) when the diet was supplemented with 1 mg Se/kg DM, independent of the level of dietary Cu. Furthermore, hepatic Cu retention was significantly (P<0·05) influenced by a Se × Cu interaction, namely when the diet was supplemented with 15·0 mg CuSO4 or 1·0 mg Na2SeO3 /kg DM or both, 0·084, 0·081 and 0·088 of the dietary Cu respectively was retained in the liver, compared to 0·047 in the sheep on the basal diet. In addition, supplementation with Se and Cu together increased hepatic Se concentration to a greater extent (P<0·001) than when Se alone was added to the feed (3·65 v. 5·17 mg Se/kg DM respectively). The concentration of Se in both muscle tissue and in rumen bacteria was raised (P<0·001) by Se supplementation, but more so (P<0·05) in both cases when Cu was not added to the diet. Interactions between Se and Cu were not influenced by NaHCO3 supplementation in the conditions of this study.

The extent to which condensed tannins (CT) in Lotus corniculatus were able to affect protein degradation and the nutritive value of pasture were evaluated at Palmerston North, New Zealand in 1992 in an indoor feeding trial with sheep and using in vitro incubations. The feeding trial involved three groups of seven young wether sheep held indoors in metabolism crates for the 32-day experimental period with one group fed freshly cut ryegrass/clover pasture (Pasture group) whilst the other two groups received a mixture of c. 37% freshly cut Lotus corniculatus and 63% pasture (dry matter (DM) basis). One of the latter groups was given twice daily oral drenches of polyethylene glycol (PEG) to bind with and remove the effects of the CT (PEG group) whilst the remaining sheep (Tannin group) were not drenched. Intakes of sheep given the mixed diets were constrained to that of the pasture group. The CT concentration in the lotus was 26·1 g/kg DM so that the mixed diets contained c. 10g CT/kg DM. Effects of CT on digestion and sheep performance were minimal. Apparent digestibility of N was lower in the Tannin group (76·4%) than PEG (79·8%) or Pasture (79·4%) sheep (P<0·001), but there were no differences in DM digestibility (75%) or wool growth from mid-side patches. Rumen ammonia and soluble protein concentrations appeared to be similar in PEG and Tannin sheep and volatile fatty acid (VFA) concentrations were similar in all groups (100 mmol/l).

For incubations in vitro, several ratios of Lotus corniculatus: pasture were used to determine the effects of CT on precipitation of soluble proteins and the net yield of ammonia and gas with and without PEG. Homogenates of Lotus corniculatus leaves and pasture showed that 50% of soluble protein was precipitated by 1·3% CT in homogenate DM and there was a substantial decrease in in vitro degradation to ammonia when lotus leaf accounted for 33% or more of DM with pasture. This work emphasises the need for caution when extrapolating from in vitro to the in vivo situation and suggests that 1% CT from Lotus corniculatus may be insufficient to affect the nutritive value of fresh forages for sheep.