Six white clover genotypes that were easily distinguishable from each other on the basis of leaf lamina marks and morphology were grown at Lodi, Italy, during 1990 and 1991 in dense swards, under field conditions and a mowing regime, as (i) pure stands, (ii) a complex mixture of all genotypes, (iii) binary mixtures of each genotype with each of two ryegrass varieties, and (iv) complex mixtures of all clover genotypes in binary association with each grass variety. The grass components were of known, different vigour. The study assessed both intergenotypic and interspecific interference and related dry matter yield responses to morpho-physiological traits of the clovers, and also determined whether a high level of morpho-physiological heterogeneity conferred a yield advantage on clover populations.

Greater heterogeneity (i.e. a complex mixture of clover genotypes) did not produce higher clover yields either in the presence or absence of interspecific interference from grass; thus, the use of blends of varieties or the development of varieties with a fairly high degree of heterogeneity was not recommended for short-term meadows in environments with relatively low spatial and temporal variability. Interactions for yield occurred between clover genotypes and the presence or absence of intergenotypic interference (P<0·001), and between clover genotypes and the presence or absence of interspecific interference from the grass variety characterized by greater vigour and aggressiveness (P<0·01). The variance of the former interaction tended to be consistently larger than that of the latter interaction, indicating that competitive effects were greater between clovers than between the clover and grass components. A lower Spring [ratio ] Summer yield ratio and taller canopy tended to confer a competitive advantage under intergenotypic interference. Relatively better performance under interspecific interference was related to higher stolon density, suggesting that selection for this trait may increase the general ecological compatibility of large-leaved white clover types grown with vigorous grass companions.

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.

Maize kernels were soaked for 16 h in solutions containing the growth regulators BAS 106.W at 40 or 80 mg/l, PP333 at 80 or 160 mg/l, or BNO 0184 at 100 or 150 mg/l. The plant growth regulator (PGR)-treated kernels and water-soaked controls were sown in planting trays, and seedling transplants were raised in a glasshouse for 24 days. When they were planted in the field, the PGR-treated plants were significantly shorter than controls, with average plant heights (measured from soil level to uppermost leaf collar) of 4·7 cm (BAS 106.W, 40 mg/l), 3·7 cm (BAS 106.W, 80 mg/l), 6·1 cm (PP333, 80 mg/l), 8·0 cm (PP333, 160 mg/l), 6·4 cm (BNO 0184, 100 mg/l), 7·1 cm (BNO 0184, 150 mg/l) and 11·0 cm (controls). The dwarfing of PGR-treated transplants was mainly due to shortened leaf insertions of the lower leaves. Shoot weights were little affected by PGR-treatment, since decreased plant heights were partly compensated for by thicker stems and broader leaves. PGR effects on leaf numbers were negligible. At crop maturity, PGR-treated plants and controls showed similar grain weights and harvest indices. A partial leaf removal treatment at planting using untreated seedlings was associated with rapid crop establishment in the field and like the PGR treatments, it had no significant effect on final yield. It is suggested that a PGR-treatment with a short term dwarfing effect would facilitate the production and handling of maize seedling transplants and may improve establishment and early growth in the field.

In 1989 and 1990, small, medium and large seed tubers, cv. Désirée, were planted 38 cm apart in experiments designed to measure the effects of different combinations of neighbouring plants on the yield and size of tubers from individual plants. Total yield, ware yield (> 150 g), numbers of tubers and numbers of stems increased as seed tuber size increased. Also, decreasing the size of seed tubers decreased the numbers of tubers in all sizes except those > 200 g. Competition from the two neighbouring plants on either side in the same row (first neighbours) increased as the size of seed tubers increased and with all seed sizes yields decreased. For example, plants from large seed benefited from small seed planted as neighbours whereas, with plants from small seed, yield was decreased with neighbouring plants from large seed. Numbers of stems and tubers were not affected by neighbouring plants. Also yields were not affected by the two plants adjacent to the first neighbours (second neighbours) or by the size of seed tubers planted in adjacent rows. Competition from first neighbours also affected tuber size distributions and, with small seed, increasing the competition decreased the number of tubers > 150 g and increased numbers < 50 g. Medium and small seed planted as neighbours of large seed increased numbers of tubers > 150 g. When yields from plants produced by seed of each size with similarly sized seed planted as first neighbours (uniform populations) were compared with mixed populations, yields were always greater from the mixed populations of different seed sizes planted alternately than from the means of uniform populations. Therefore in the mixed populations, there were larger gains from the larger seed than losses from the smaller seed.

Growth, shoot water relations and root hydraulic conductivity were studied in tomato plants (Lycopersicon esculentum cv. INCA9) subjected to different salt concentrations in the root medium. Two experiments were carried out at Instituto Nacional de Ciencias Agrícolas (INCA), Cuba, during May and June 1995. In the first experiment, plants were grown for 13 days in a nutrient solution with 0 or 100 mM NaCl. In the second experiment, the hydraulic conductivity was measured on roots submerged in nine different concentrations of NaCl up to 200 mM. The effect of temperature treatments between 0 and 50 °C on root hydraulic conductivity was also examined. Shoot growth, leaf water potential, leaf stomatal conductance, leaf relative water content and root hydraulic conductivity values decreased more rapidly in the treated plants than in control plants. A strong correlation was found between the root hydraulic conductivity and leaf water parameters, indicating that water flow through the roots was the main factor controlling shoot water relations.

Many biological experiments and almost all quantitative genetic studies draw conclusions from differences between families. Such differences are caused as much by heritable as by non-heritable sources. This paper investigates the impact of seed quality on the expression of quantitative variability among 20 highly inbred lines of Nicotiana rustica using ten seed categories representing different pollination times, seed sizes, seed positions in the capsule and seed maturity. Analysis of variance revealed that while the mean performance of the inbred lines remained more or less the same across all the seed categories, their individual performances differed widely, showing a highly significant interaction between lines and seed categories. This interaction accounted for up to 12% of the total variation and was largely attributable to late pollinations and immature seed. Seed categories were also the main source of heterogeneity among the within-line variances, but only immature seed lowered the correlation between the inbred means. In general, seed quality affected the developmental characters much less than the traits measured at or after flowering, and the expression of genetic variation was not critically affected by seed size or position. Immature seed, on the other hand, generated the highest level of unreliability in the comparative performance of lines and such seeds should therefore not be used in quantitative genetic experiments under any circumstances. Further implications of seed quality effects on the interpretation of genetic components are discussed in detail.

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).

Forages produced in the north central interior of British Columbia are low in percentage crude protein (CP). Growing lucerne (Medicago sativa L.) should increase forage percentage CP, but many of the soils are considered too acidic for this species. The objective of three field experiments, conducted at the Prince George experimental farm, was to evaluate management practices that might accommodate the growth of lucerne on acid soils without the expense of liming. Experiment 1 compared three legume species (lucerne, alsike clover (Trifolium hybridum L.) and red clover (T. pratense L.)), preinoculated lime-coated seed (GNRTM, Grow Tec Ltd, Nisku, Alberta), and soil liming on root nodulation and forage dry matter (DM) yield. Experiment 2 compared lucerne genetic lines, seed preinoculation and soil liming on root nodulation and forage DM yield and percentage CP. Experiment 3 compared lucerne rhizobia genetic strains, seed preinoculation and soil liming on root nodulation, forage DM yield and percentage CP.

For effective nodulation, lucerne required seed preinoculation, whereas alsike clover and red clover did not. Lucerne persisted longer than alsike or red clover. In Expts 2 and 3, the combination of lime and preinoculation increased lucerne DM yield by 136% and %CP from 9·2 to 15·4. The addition of lime alone increased lucerne DM yield by an average of 130% and %CP from 9·2 to 16·3. With preinoculation alone, lucerne DM yield increased by 100% and %CP increased from 9·2 to 12·7. Although using preinoculated lime-coated seed alone is not as effective as lime alone, coated seed may be the preferred method, based on ease of application and cost. Neither the six lucerne lines nor the three rhizobial strains evaluated resulted in improved root nodulation under acidic conditions.

In 74 experiments carried out in England from 1990 to 1994, cereal test crops were grown on sandy soils prone to nitrate leaching, following cereals, sugarbeet and potatoes. Measurements were made of the effects of the previous crops on soil mineral N, and on N recovery by the cereal test crop.

Soil N supply in autumn (SNSa) was greater following potatoes (c. 100 kg/ha N) than following sugarbeet or cereals (c. 60 kg/ha N). However when potato crops to which organic manures had been applied were excluded, mean SNSa after potatoes was only c. 60 kg/ha. Soil N supply in spring (SNSs) following sugarbeet and potatoes was similar and at c. 56 kg/ha, c. 10 kg/ha greater than following cereals. Seasonal differences in SNSs were related to excess winter rainfall and soil water-holding capacity. Modelled leaching losses gave good agreement with overwinter changes in SNS (r=0·87), although SNSs was usually greater than predicted by the model. This discrepancy was considered to be due to overwinter mineralization, which was estimated from the intercept of the regression lines to be c. 40 kg/ha following cereals and potatoes, and c. 50 kg/ha following sugarbeet.

Apparent net mineralization (AM) of N during the test crop growing season was c. 37, 53 and 63 kg/ha following cereals, sugarbeet and potatoes respectively. However, AM was c. 24 kg/ha N greater if the preceding potato crop had been given organic manures, but there was no difference in AM following manured and unmanured sugarbeet crops.

Nitrogen offtake by the cereal test crop without fertilizer N (NoffN0) was c. 15·20 kg/ha greater following potatoes and sugarbeet than following cereals. The greater N offtake following potatoes is considered to be due to mineralization of organic manures applied to the potato crop, while the effect following sugarbeet appears to be due to mineralization of sugarbeet residues. At harvest, SMN was c. 38 kg/ha and similar for all three previous crops. It is concluded that mineralization of sugarbeet residues has taken place more quickly on these sandy soils than previously reported on soils of greater clay content. Only potatoes grown with organic manures leave greater N residues than cereals.

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.

The effects of short-term waterlogging during the vegetative, reproductive and total growth phases were investigated in four cultivars of cowpea (Vigna unguiculata L. Walp) in relation to their controls in a pot experiment conducted at the University of the West Indies, St. Augustine, in 1989. All cultivars were able to recover completely and produce near to normal yields, when waterlogging was confined to the vegetative period. Recovery growth was affected in cultivars waterlogged during the total growth phase and the plants were significantly smaller (P < 0·05) in vegetative dry matter (60–80% of the size of their respective controls) even at maturity. Recovery growth was affected, to a greater extent, in cultivars possessing a small mainstem[ratio ]branch ratio. Yield development in the waterlogged plants was affected by accelerated leaf senescence and consequent reduction in the reproductive period. As a result, yields in all the cultivars tested were significantly smaller (P < 0·05) than their respective controls and varied between 54 and 60% of the controls. Plants waterlogged during the reproductive phase were not significantly different (P < 0·05) in vegetative dry matter from the controls, but showed root degeneration and accelerated leaf senescence in all but one cultivar (Local Red). Yield reduction, however, was significant (P < 0·05) only in IT-83S-898. Possible criteria for selecting plants tolerant to waterlogging are discussed.

In field trials in 1987/88 near Pangbourne, England, wheat (Triticum aestivum) and field beans (Vicia faba) were grown in an organic farming system as sole crops and additive intercrops. The sole crops were grown at 25, 50, 75, 100 and 150% of the recommended density (RD) for conventionally grown crops. The intercrops consisted of all density combinations of wheat and beans from 25 to 100% RD in a factorial experiment. The grain yield of sole cropped wheat and beans increased significantly as their density was increased. The highest yield of both was achieved at 100% RD, indicating that the conventional recommendation was the optimum when applied to organically grown crops. Land equivalent ratio (LER) values for the intercrops were significantly greater than 1·0 when the wheat was sown at > 5% RD and beans at > 50% RD. The highest LER of 1·29 was achieved when wheat and beans were both sown at 75% RD. There was resource complementarity, expressed as relative yield total (RYT) > 1·0, in all of the density combinations. There was a significant decrease in resource complementarity with increasing wheat and bean density. The nitrogen content of the wheat grain and whole plant biomass was significantly increased when the density of beans in the intercrops was increased; this was reflected in a significant increase in grain protein at harvest. The total amount of N accumulated by the wheat, however, decreased with increasing bean density due to a reduction in the biomass of wheat. Beans also showed a significant increase in %N as the density of the other component increased and a decrease in total N accumulation due to reduced biomass. All of the intercrops accumulated more N than the sole cropped wheat, but did not exceed that accumulated by sole-cropped beans. The biomass of weeds was greater under beans than under wheat. Weed biomass in intercrops was significantly reduced when the density of wheat and beans was increased, resulting in a lower weed biomass in the intercrops than was achieved in either the sole cropped wheat or beans. The N content of weeds was significantly reduced with increasing wheat density but was significantly increased with increasing bean density. The total amount of N accumulated by weeds per unit area was reduced significantly by increasing the density of both components. The levels of disease on the wheat were low, but mildew (Erysiphe graminis) increased significantly as bean density increased. The incidence of chocolate spot (Botrytis fabae) increased significantly with increased bean density. The experiment demonstrated that it was possible to harvest the crop with a combine harvester and the wheat and beans can be planted separately mechanically, therefore this system is suited to mechanized agricultural systems.

Five British hill sheep breeds and their crosses were compared on a hill farm in a common environmental and husbandry system in 1974 in Peeblesshire, Scotland. A home-bred Scottish Blackface stock was maintained, and ewes were crossed with rams of each of the five hill breeds, North Country Cheviot, Derbyshire Gritstone, Exmoor Horn, Swaledale and Scottish Blackface. The crossbred female progeny were then mated half to homebred Blackface rams and half to rams of the paternal breed. This was reversed in later generations to form a continuous criss-crossing system. The performances of the crossbred ewes and of the crossbred lambs were compared, and the effects of the breeds and the average heterosis were estimated. A total of 5579 ewe and 6516 lamb records were available for comparison over an 8-year period from 1977 to 1984. Some 20 rams per breed were used over this period. The Swaledale crosses had substantially higher output and efficiency than any of the other crosses, while the Derbyshire Gritstone and Exmoor Horn crosses were generally inferior. There was appreciable heterosis for most traits, that for fleece weight and for litter weight at weaning being the highest. The heterosis for output per ewe exposed and efficiency of lamb production are positive and significant. The results support greater use of the Swaledale and of a crossbreeding system with Blackface to exploit heterosis in harsh hill farm conditions.

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.

Water balance components under wheat were assessed by employing two simple models, differing in their structure and data requirements, namely the soil-plant–atmosphere–water (SPAW) model of Saxton (1989) and the water balance model (WBM) of Arora et al. (1987). A few modifications based on the SPAW model procedure for the estimation of green canopy were used in a modified WBM and its performance was also tested. Soil water loss (the sum of interception evaporation, soil evaporation, plant transpiration and deep drainage) from sowing to harvest, simulated with the WBM, modified WBM and the SPAW model, had a close correspondence with the measured sum of profile water depletion, rainfall and irrigation for values ranging between 18·3 and 42·7 cm. Estimates of drainage with the WBM and modified WBM using empirical coefficients were greater than those calculated using the SPAW model for situations where the upward flow of water into the root-zone was negligible. Estimates of soil water evaporation using the WBM and modified WBM were invariably smaller than those using the SPAW model. A comparison of simulated and measured soil water storage and a correlation analysis of simulated transpiration with measured biomass at harvest showed that the performance of the WBM was the most realistic of the three models. However, it requires the input of leaf area index values to infer green canopy for each water supply regime. In the absence of this information, the modified WBM and SPAW models are more useful for assessing water balance components in cropped soils.

Urediospores of U. viciae-fabae (broad bean rust) germinated well in the range 5–26 °C, with fastest germination at 20 °C. Exposure to 30 °C gave poor germination and damaged the spores. Infection of Vicia faba leaves depended on a moisture film. At 20 °C some infection occurred with only 4 h leaf wetness, but longer wet periods up to 24 h gave increased infection. At lower temperatures, the infection process was slower and final pustule numbers were smaller. Spore germination was delayed by daylight and by all artificial light sources that contained far-red (700–800 nm) wavelengths. The delay was increased at higher light intensities. When spores were subjected to alternating periods of light and darkness, it was found that 40 min of darkness was sufficient for the irreversible induction of germination at 20 °C.

Two experiments were carried out at Mt. Cotton, The University of Queensland, from November 1992 to July 1993, to study the effect of extent of digestion or feed type (grass or legume) on particle kinetics in the rumen. Small (0·5–1·18 mm) Yb-labelled grass or legume particles, either digested or undigested, were injected into the rumen of sheep fed on different diets, and their retention time in the reticulo-ruminal compartment measured. In Expt 1, four intact wethers were fed on either pangola grass hay, chaffed lucerne hay, pelleted lucerne hay or commercial pelleted concentrate. Digested particles from the faeces of animals fed on pangola or lucerne and undigested material from the same diets were wet-sieved and the fraction 0·5–1·18 mm collected, labelled with Yb-acetate and injected into the animals together with a solution of Cr-EDTA. Faecal samples were taken and analysed for marker concentrations. In Expt 2, four similar animals, fitted with duodenal and ruminal cannulae, were fed on different proportions of pangola grass hay and lucerne hay, and Cr-EDTA and the above mentioned labelled particles were injected through the rumen cannula. Samples were taken from the duodenum and analysed for marker concentrations.

The results indicated that diet characteristics rather than extent of digestion or particle type had the greatest influence on rates of passage of both liquid and particulate phases. Different proportions of pangola and lucerne did not result in marked differences in either the volumes of rumen contents or the rates of passage of the solid phase marker but altered the rates of passage of Cr-EDTA. Increasing the proportion of legume increased intake and decreased retention time markedly, with no additive effects on digestibility.

Particles of the same small size escaped with the same fractional passage rate within each diet, irrespective of type (grass or legume) or status (undigested or digested), indicating identical kinetics within each rumen type.

It was concluded that rumen conditions as influenced by diet type have most influence on water and particle kinetics and that extent of digestion of the small particles used in our experiments was not important. Particles of legume or grass of the same size behaved similarly within a diet type.

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.

Nitrogen (N) fertilizer not used by the crop can increase the risk of nitrate leaching into the groundwater. In two growing seasons, 1990/91 and 1991/92, the relationships between N fertilization and yield, N uptake by the grain and the N leaching in the subsequent percolation period were investigated in a multifactorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape – winter wheat – winter barley, and effects of soil tillage (minimum tillage without ploughing, conventional tillage), application of pig slurry (none, application in autumn, application in autumn and in spring), mineral N fertilization (none, 80 or 200 kg N ha−1 to oilseed rape and 120 or 240 kg N ha−1 to cereals) and application of fungicides (none, intensive) were all tested. In each year, the rotation and the treatments were located on the same plots. Mineral N fertilization and fungicide application increased yield and N uptake by grain or seed in all crops. In contrast, the application of slurry, especially in autumn, had only small effects on yield and N uptake. Nitrogen losses by leaching (measured using porous ceramic cups) were affected mainly by the year and the crop. In 1992/93, averaged over all factors, 80 kg N ha−1 was leached compared with 28 kg N ha−1 the previous year. Oilseed rape reduced N losses, whereas under winter wheat up to 160 kg N ha−1 was leached. Due to a lower N-use efficiency, autumn applications of slurry increased N leaching, and mineral N fertilization of the preceding crop also led to higher N losses.

Since the amount of leached N depends both on the nitrogen left by the preceding crop (unused fertilizer N as well as N in residues) and on N uptake by the subsequent crop, it is not possible to apportion the N losses to any particular crop in the rotation. The cropping sequence, together with its previous and subsequent crops, must also be considered.

To minimize leaching, N fertilization must meet the needs of the growing crop. In order to improve the efficiency further, investigations must be conducted in order to understand the dynamics of N in the plant–soil system in conjunction with the weather and crop management practices.

Individually-penned Matebele does were randomly allocated to three dietary treatments during gestation (0·66, 0·50 and 0·33 MJ ME/kg metabolic weight) and subsequently offered either 0·95 or 0·6 MJ ME/kg metabolic weight during lactation in Gwanda, south west of Zimbabwe, in 1990. The diets offered consisted of veld and lucerne hay and maize grain in proportions of 0·56, 0·24 and 0·2, respectively.

Reducing the amount of energy consumed from 0·58 to 0·26 MJ ME/kg metabolic weight in the last 7 weeks of gestation resulted in does suffering a net loss in body weight (−2 kg) and body condition score, although it had no significant effect on the birth weight of single kids.

Reducing feeding in the first 15 weeks of lactation from 0·95 to 0·59 MJ ME/kg metabolic body weight only had minor effects upon liveweight and body condition score change of the does and had no effect on the growth of kids. Amount of feed offered in lactation had a positive effect upon milk yield and there was a trend for yields to increase proportionally to pre-partum dietary intake. Diet had no effect upon milk composition. It was concluded that the benefits of supplementary feeding are small and may not justify the extra costs entailed in smallholder systems.