The recovery of nitrogen ‘retained’ through cover crop uptake, delayed ploughing and immobilization by straw was assessed in a spring cropping rotation on a chalk loam in Eastern England (1989–96). The effect of annual cover cropping on yield of the subsequent spring crops and on the soil N balance was also investigated. The recovery of retained N was in part dependent upon cover crop management. Late August-sown cover crops which were incorporated in February/March tended to reduce spring crop yields and crop N offtake. Adverse effects on soil N supply, seedbed conditions and soil water reserves were not in evidence and so an allelopathic effect from the decomposition of the rye cover crop, previously reported by others, may be responsible for the reduction in yield of spring crops. When the cover crops were drilled later and their early destruction was followed by a short fallow period, spring crop yields and N offtake were increased. The soil N balance indicated that over the course of the experiment there was a positive N input to the system due to continuous cover cropping. This input may be held as immobilized organic N, in which case it could be made available to subsequent crops over a number of years or lost via other routes. Nitrate concentrations in drainage water increased with the number of years under cover cropping.

The effects of weather and nitrogen application rate on bread volume, protein concentration and gluten strength were investigated in spring and winter wheats in Sweden during 1990–96. The investigation was carried out in wheats containing the high-molecular-weight (HMW) glutenin subunit combinations 2+12 or 5+10.

The results showed that a warm (c. 20°C mean dry temperature) and dry grain-filling period, as during 1994 and 1995, led to high gluten strength. As a relatively gentle dough mixing is normally applied in Sweden when baking bread, excessively high gluten strength results in low bread volumes. Wheat cultivars containing HMW glutenin subunits 5+10 generally had higher gluten strength than those containing subunits 2+12. However, not all the cultivars containing subunits 5+10 showed overstrong gluten properties, whereas some cultivars containing subunits 2+12 were overstrong during 1994 and 1995. Different cultivars produced the highest gluten strength in different years. Generally, cultivars containing HMW subunits 2+12 gave higher bread volumes than those containing subunits 5+10. This is probably due to the Swedish baking method, where the dough is given a relatively gentle mixing for a fixed period of time.

Increased fertilizer rates led to increased protein concentration and decreased gluten strength. However, during certain years, for example 1994, the gluten strength was only decreased slightly by increased fertilizer rates, particularly in cultivars containing HMW glutenin subunits 5+10.

Three pot experiments were performed at the University of Wales, Bangor, Gwynedd, UK during 1993 to determine if differences in the competitive ability of three annual weeds (Chenopodium album L., Sinapis arvensis L. and Phalaris minor Retz.) were related to their relative effects on leaf growth, gas exchange and nitrogen uptake of spring wheat (cv. Alexandria). In all experiments, wheat density (316 plants m−2) was similar to that in a commercial crop and five weed density treatments (between 0 and 600 plants m−2) were tested. Measurements of gas exchange were made on fully expanded, attached wheat flag leaves on four occasions between emergence and complete senescence in the control and highest weed density treatments. High weed density resulted in a lowering of net photosynthetic rate due to stomatal and non-stomatal factors. Lamina area and stomatal density of wheat flag leaves were decreased, and specific leaf area was increased by weed competition, but the effects on these variables were smaller than on net photosynthesis. Weed density did not affect wheat plant height, but dry weight, grain yield and total N-uptake were decreased with an increase in density of all weed species. The rank order of competitive ability of the species (C. album>P. minor>S. arvensis) was unaffected by weed density and was the same irrespective of whether it was based on the % decreases in wheat grain yield or in total plant dry weight. Averaged over the four measurements made during the grain-filling period there were only small differences between the weed species in their effects on net photosynthetic rate. However, when these were combined with effects on flag leaf area, there were larger differences in calculated net photosynthetic productivity, which were related to differences in the effects of weeds on grain yield. Differences in the competitive ability of weeds were not related to differences in their effects on wheat flag leaf lamina area, specific leaf area, stomatal density or total nitrogen uptake. Differences in competitive ability between weed species were not related to differences in weed plant height, dry weight or nitrogen uptake. It was concluded that the observed effects of weeds on wheat were due either to shading, or to competition for a nutrient other than nitrogen.

The productivity of eight forage maize cultivars (Zea mays L.) in response to N was investigated in a 3-year field experiment located in Northern Germany. Nitrogen fertilizer applications were zero, 50 and 150 kg N/ha given each year shortly after sowing. Each cultivar was grown on the same plot, beginning in 1993, following the ploughing up of a 2-year old grass sward, to which slurry had been added. Plants were sampled regularly for dry matter (DM) production and N uptake. A non-linear regression equation was used to compare the data. Growth analysis and N uptake characteristics (maximum crop growth rate, duration of maximum crop growth rate, period until maximum crop growth rate, maximum N uptake rate, duration of maximum N uptake rate, period until maximum N uptake rate) which derived from the function were used to compare the cultivars.

The cultivars DM yield and N uptake were highest in 1993 and declined in the next two years partly due to a decrease in soil N mineralization following the ploughing of the grass sward and partly due to the drier weather conditions during the summers of 1994 and 1995. Duration of the maximum crop growth rate was greater during the cool year of 1993. In contrast, maximum crop growth rate was at its highest in the dry vegetation period of 1995. A significant N×cultivar interaction for growth analysis characteristics (P<0·05) was found in 1995. Cultivars with a high maximum crop growth rate (above the average value of the eight cultivars tested) and a short duration of maximum crop growth rate (below the average) accumulated more DM than those genotypes which showed an inverse relationship.

Increasing N yield was determined by increased maximum N uptake rather than by a greater duration of maximum N uptake. A significant N×genotype interaction for N uptake parameters (P<0·05) was found in 1994 and 1995. With some exceptions, cultivars with a high maximum N uptake rate (above average) accumulated more N per unit area compared to those genotypes which had low uptake rates. The exceptions had a longer duration of uptake, which could not, however, compensate for the lower rate. Maximum N uptake rate occurred earlier and duration of maximum N uptake rate increased compared to the start and duration of maximum crop growth rate. Especially in 1995, the amount of N taken up before the day of maximum crop growth rate accounted for 71% of total N uptake. The N uptake rate and the amount of accumulated N until the day of maximum crop growth rate were highly correlated with DM yield.

This result indicates the availability of genotypic variability in crop growth and N uptake rate to assist the improvement of DM yield by selection.

A natural rock phosphate, ‘Kodjari” (RP), sparingly soluble, indigenous to Burkina Faso, and a commercial single superphosphate (SSP) fertilizer were studied at Farako-Bâ in the Northern Guinea Savannah (NGS) and at Oipasse in the Sudan Savannah (SS) regions of Burkina Faso. A 3-year crop sequence either of cowpea, maize and sorghum or of cowpea, sorghum and sorghum was used, respectively, in the NGS and SS regions. The sorghum crop in the third year was not fertilized with any phosphorus (P) source. The objectives of the research were to study the direct and residual effects of the P fertilizers on soil fertility improvement in order to boost agricultural productivity in both regions.

Cowpea daylength-insensitive cultivars, in both regions, and maize and sorghum in the NGS and SS regions, respectively, responded more strongly to SSP than to RP fertilizer treatments. The optimum rate of SSP and RP source was 21·8 kg P/ha and 43·6 kg P/ha, respectively, for cowpea in both regions. The optimum rates of phosphorus fertilizer applied in the second year to maize in the NGS and to sorghum in the SS region, in addition to the optimum rate of P applied to cowpea the previous year, was 10·9 kg P/ha of SSP or 43·6 kg P/ha of RP, and 21·8 kg P/ha of SSP or 43·6 kg P/ha of RP, respectively. Both P sources had significant residual effects for up to 2 years. The agronomic effectiveness of RP relative to SSP, in the year of application of both fertilizers, was greater for cowpea than for maize in the NGS region and similar for cowpea and sorghum in the SS region; it increased markedly for the two subsequent cereal crops in both regions. Cowpea fertilization with both P sources proved, therefore, to be effective in improving the soil fertility and boosting the productivity of cereal crops in the 3-year crop sequence.

Cowpea and sorghum grain crops, fertilized with 26 kg of phosphorus (P) per ha from either a P-soluble (SP) or a slightly P-soluble fertilizer (Kodjari, a natural rock phosphate (RP) indigenous to Burkina Faso), and cowpea and crotalaria (Crotalaria retusa) green manure crops, either unfertilized or fertilized with 26 kg P/ha from RP; were studied for their effects as preceding crop treatments for maize. The experiment was conducted in semi-arid West Africa (SAWA) at Farako-Bâ in Burkina Faso in 1983–86. Nitrogen (N) and soluble P fertilized and unfertilized subtreatments, applied to maize the following year, allowed the effects of the preceding crop treatments in improving soil fertility and the direct effects of P and N fertilizers applied to the maize crop to be assessed. Maize productivity was increased both by P fertilization and by soil improvements following cowpea and crotalaria; N fertilization in excess of 60 kg N/ha was not beneficial. Cowpea grain crop treatments, especially when fertilized with a P-soluble source, maximized maize yields, whereas cowpea and crotalaria green manure treatments were either similar to the cowpea grain treatment fertilized with RP or were intermediate between the latter and the sorghum treatment fertilized with SP. Sorghum, regardless of the source of P-fertilizer used, appeared not to be a suitable preceding crop for maize in SAWA.

The interaction between headbugs (Eurystylus sp.) and grain mould (GM) on sorghum was examined in field trials carried out at Samaru, Nigeria in the 1995 and 1996 wet seasons. The results obtained show that in all three sorghum cultivars tested, insect damage increased the number of fungal colonies associated with the grain. This resulted in lower germination, 1000-grain mass and yield in such treatments. Insect damage also altered the relative abundance of the common fungal flora species as, following insect damage, Fusarium moniliforme (≡Gibberella fujikuroi), Phoma sorghina and Curvularia lunata (≡Cochliobolus lunatus) were the most common fungi in decreasing order of frequency as against the normal order of P. sorghina, F. moniliforme followed by C. lunata. These results are the first clear evidence of interactions between headbugs and GM in Nigeria.

Tissue flow measurements of leaf material in Lolium perenne (perennial ryegrass), Agrostis capillaris or Poa annua, and Trifolium repens (white clover) were made at three upland sites in Scotland (Hartwood, Sourhope and Fasque) in 1992/93 to determine if there were differences in seasonal growth, senescence and losses to herbivory between species in their response to more extensive sward management. The measurements were made monthly from May until October in established predominantly perennial ryegrass/white clover swards receiving three different treatments. One treatment received a conventional annual fertilizer application of 140 kg N/ha plus maintenance P and K and was grazed by sheep at a sward height of 4 cm (4F), whereas the other two treatments were unfertilized and grazed to maintain a sward height of 4 cm (4U) or 8 cm (8U).

Significant sources of the variation in leaf appearance, increase in green lamina/petiole length (leaf extension), senescence and losses to herbivory were attributable to site, sward, species and date of measurement. The rate of leaf extension for all three measured species was less in 4U than 4F swards, and less in 4U than 8U swards. Leaf extension of L. perenne exceeded that of the other species, even in unfertilized swards, but rates of leaf appearance were less. There was some evidence in spring of a reduction in net growth as a consequence of removing fertilizer inputs and maintaining a sward height of 4 cm. Species differences in the losses of leaf tissue to herbivory were dependent on sward management. In the 4F treatment, leaf loss to herbivory from L. perenne tillers was greater than that from either A. capillaris, P. annua or T. repens in May, June and September. In the 4U treatment more leaf tissue was also lost from L. perenne than from T. repens. In contrast, there was no difference between grass species in losses to herbivory in either unfertilized sward. The responses of species to changes in fertilizer and grazing management were similar at three sites of differing fertility. The results are discussed in relation to plant competition and species dynamics in extensively managed swards.

In NW Europe a major limitation to the yield of sugarbeet is development of the foliage canopy in May and June, too late to capture much of the available solar energy. This problem could be solved if the crop was sown during autumn so that the seedlings survived the winter and developed a large leaf canopy in early spring. This has led to a search for mechanisms to control flowering so that plants remain vegetative after the winter. However, there has been no serious attempt to estimate the effect of advanced canopy development on the likelihood of water stress. This study has used a combination of modelling of growth to predict yield of rainfed crops and an analysis of the literature to examine the likely consequences for pest and disease incidence if autumn sowing could be achieved without bolters. Compared to spring sowing, a potential yield advantage averaging 26% could be achieved, but this is likely to be overturned by any one of several beet-specific pathogens. For example, beet yellows virus would become more difficult to control and this has the potential to halve yield. Downy and powdery mildew and beet cyst nematode would be more expensive to control. The change from spring to autumn sowing would not allow harvest to be significantly earlier; this would be prevented by dry, strong soil conditions. Nevertheless, the increased emphasis on autumn work on arable farms would be costly.

Three successive experiments, of similar design, were carried out during 1986–88 at Mount Derrimut, Australia. Mature Merino ewes were mated to Poll Dorset rams and then allocated to either a control group (C) or a treatment group (R). Ewes from each treatment were slaughtered 60, 70, 100 or 140 days post-conception and the development of their foetuses was compared in terms of body size and muscle characteristics. In Expts 1 and 2, some ewes were allowed to lamb and the progeny in each group were slaughtered after reaching a body weight of 35 kg, for comparison of growth rates, muscle characteristics and meat quality.

In each experiment, treatment extended from mating to day 70 of pregnancy and, during this period, both groups were housed. Ewes in group C were kept as one group and fed ad libitum and ewes in group R were individually penned and fed a restricted ration of the same diet as that given to group C in order to achieve a steady loss of body weight. In Expt 1, this loss was 8 kg but, in Expts 2 and 3, feed intake was controlled according to condition score and, during this period, group R ewes lost 25–35% of their body weight at mating. After day 70, all ewes were kept grazing and were offered supplementary feed at rates sufficient for a steady increase in ewe body weights.

Foetuses in group R were lower in body weight (P<0·05), crown-rump length (P<0·05) and girth (P<0·01). However, birth weights and mean ages of the 35 kg lambs at slaughter did not differ significantly between treatments.

There were no significant differences between treatments for the semitendinosus (ST) and semimembranosus (SM) muscles in total muscle weight, DNA content, protein content, nor in the ratios of muscle weight[ratio ]DNA and protein[ratio ]DNA. However, there were significant differences between experiments, which indicated that cell size in the ST and SM muscles was lower in Expt 2 than in Expt 1.

In day 70 foetuses, the cross-sectional area of α fibres was greater (P<0·05) in group R than in group C but by day 140 the difference was no longer significant. At day 70, there was also a positive correlation (r=0·65, P<0·01) between the cross-sectional area of β fibres and the number of α fibres surrounding each of them. There were no significant differences between treatments at any age in the percentages of βR, αR and αW fibres.

Meat from group R lambs was more tender than that from group C lambs as indicated by significantly lower means in the SM muscle for adhesion (P<0·01) and Warner–Bratzler Peak Force (WB PF) measurements (P<0·05).

Although some effects of nutritional restriction were found, severe feed shortage in early pregnancy in sheep is unlikely to have significant effects on the production of prime lamb meat provided that adequate nutrition is available during late pregnancy and post-natal growth.

An experiment was carried out in Northern Ireland in 1994 to examine the effects of ensiling grass on the partitioning of nutrients between lean and fat deposition in lambs using the comparative slaughter technique. The six treatments consisted of: (1) unsupplemented grass silage; (2) grass silage supplemented with concentrates, concentrates constituting 250 g/kg total dry matter intake (DMI); (3) grass silage supplemented with concentrates, concentrates constituting 500 g/kg total DMI; (4) unsupplemented grass which had been conserved by freezing; (5) pre-frozen grass supplemented with concentrates, concentrates constituting 250 g/kg total DMI, and (6) pre-frozen grass supplemented with concentrates, concentrates constituting 500 g/kg total DMI. A total of 84 Dutch Texel×Greyface (Border Leicester×Blackface) lambs, consisting of 42 males which were initially 35 (s.d. 4·8) kg liveweight and 42 females which were 33 (S.D. 2·6) kg liveweight, were used. The silage was well preserved as indicated by its low pH (3·8), low concentration of ammonia (60 g/kg total nitrogen) and high concentration of lactic acid (129 g/kg DM). The grass had a higher pH (5·2) and higher WSC concentration (129 g/kg DM) and lower concentrations of lactic (33 g/kg DM) and acetic acids (6 g/kg DM). Ensiling had no significant effect (P>0·05) on empty body and carcass weight gains. Animals offered unsupplemented silage had significantly lower protein (P<0·001) concentration in the carcass gain and significantly higher lipid and energy (P<0·001) concentrations than animals offered unsupplemented frozen grass. However, there was no effect of forage type on chemical composition of carcass gains when 50% forage was offered. It is concluded that ensiling had no effect on empty body or carcass weight gains, but did increase carcass fatness when unsupplemented forages were offered.