The effect of a range of one-year set-aside treatments on soil mineral nitrogen (SMN), during the set-aside period and in a following wheat crop were studied in a phased experiment at five sites from 1987 to 1991. Ground cover options permitted under the UK government's ‘set-aside’ scheme, including natural regeneration, autumn sown Italian ryegrass (Lolium multiflorum), spring-sown legumes and cultivated fallow, were compared with a control treatment of continuous cereals managed with fertilizer inputs. In the first of three phases in this experiment, an uncultivated fallow (kept weed-free) and autumn-sown forage rape (Brassica napus) were included as extra treatments. There were large differences in total SMN (0·0–0·9 m) between sites, ranging from 16 to 205 kg N/ha, reflecting differences in soil type, which ranged from clays to sands, and previous cropping husbandry. Differences in SMN between set-aside treatments during the first winter of the set-aside year were small, but increased during the following summer. Amounts of SMN were greatest after cultivated fallow (46–178 kg N/ha) and least after ryegrass (26–111 kg N/ha). Natural regeneration and spring sown legumes were more variable in their effect on SMN. Compared to continuous cereals, there was a build up in SMN during bare fallow, but a reduction under ryegrass, prior to returning to wheat cropping in the autumn after set-aside. SMN results suggest there was an increased nitrate leaching risk for bare fallow and natural regeneration set-aside, compared to sown ryegrass covers, in the winter following ploughing out of set-aside. This risk could be minimized by earlier sowing of winter cereals following set-aside or sowing with winter oilseed rape rather than cereals to maximize crop nitrogen (N) uptake, during the autumn growth period.

Averaged across five sites, residual SMN supply in the spring of first test year cereal crops for all set-aside treatments was similar to that for continuous cereals, suggesting over-winter losses by N leaching or immobilization. The low residual N fertility after rotational set-aside suggested that following crop N recommendations should be the same as for continuous cereals. Amounts of SMN were less each year in spring than in the preceding autumn in both the set-aside and first test cereal crops. The results suggested that a ryegrass cover appeared to be the most environmentally favourable option for rotational set-aside management, as it minimized the amount of readily leachable N both during and immediately after the set-aside period.

Two pot experiments were performed to study the effects of three pre-emergence herbicides (terbutryn/terbuthylazine, trietazine/simazine and prometryn) and a post-emergence herbicide (bentazone) on nodulation, symbiotic nitrogen fixation, growth and yield of pea (Pisum sativum L.) grown in perlite under nitrogen-free conditions. All pre-emergence herbicides decreased nodulation, total nitrogenase activity, net photosynthesis, leaf area, root and shoot dry weight, nitrogen content and seed yield of peas. The effects of herbicides increased with increase in rate of application. Of the herbicides tested, terbutryn/terbuthylazine and trietazine/simazine had the greatest adverse effects. Pea plant biomass (root plus shoot) was correlated with plant nitrogen content but not total nitrogenase activity. The results of the experiments suggested that the decreased growth of herbicide-treated plants was due to direct effects of the herbicides on peas and not due to indirect effects of the herbicides on rhizobia.

This study was carried out at the University of Ankara, Faculty of Agriculture, Field Crops Department experimental field during 1994–1996. Two flax (Linum usitatissimum L.) cultivars having two different flower colours were used as the study material. The cultivar with white flowers was used as a receptor and the violet coloured cultivar was used as a donor.

Average cross-pollination ratio was 1·81% in 1994 whereas it was 0·93% in 1995. The highest cross-pollination was obtained from third experimental design as 4·85% in 1994 and 3·21% in 1995. There were differences among the experimental designs in respect to cross-pollination. The results of this research showed that cross-pollination ratio decreased when distance between donor plants increased.

A glasshouse experiment in 1997 at Wye College, University of London, investigated the uptake of 35S-SO4 at two growth stages. When labelled S was applied at growth stage 24 on 20 January only 14% of available sulphur was detected in the plant parts. There was a progressive increase in uptake into the newly emerged leaves. The leaves, which emerged after the application of the radiolabelled sulphur solution was complete, imported sulphur from other parts of the plant. At final harvest the ears had become a major new sink and had imported 68% of the labelled sulphur.

When labelled sulphur was applied on 7 March at growth stage 41–45, an average of 93% of available sulphur was taken up during the 3 days exposure period. The major portion was quickly translocated and recovered from the aerial parts. At final harvest 53% appeared in the grain. The experimental results demonstrated that sulphur reserves can be remobilized to developing sinks. It is suggested that sulphate ions can be retained as a reserve pool by the plant until they are required by actively developing sinks.

The composite effects of two irrigation frequencies (one irrigation at crown root initiation stage and five irrigations at five critical physiological stages of wheat), eight nutrient treatments consisting of N, P and K either applied alone or in combinations at the recommended doses (N:P2O5:K2O at 120:60:40 kg/ha) on population and dry weight of weeds and on the growth, nutrient uptake and yield of wheat were investigated. Observations on the components of the weed population and their biomass made at 60 DAS did not reveal any significant difference between the high and low frequency irrigation. Among the nutrient treatments, the N-treated plots (N, NP, NK and NPK) had a higher population and biomass of grass weeds, whereas sole P and K application or their combination produced the greater growth of broad-leaved weeds. However, the overall weed competition was significantly higher in the P- and K-treated plots than in the N-treated plots. The NP, NPK, NK and N treatments produced significantly higher values for dry weight, crop growth rate, leaf area, number of tillers, nutrient uptake, number of ear-bearing tillers, protein content and grain yield than the other treatments. Weeds in unweeded control plots did not significantly affect wheat growth (CGR, dry weight, tillers/plant) and uptake of the nutrients except of the P at 60 DAS. However, the number of ear-bearing tillers, grains per ear and yield were significantly higher in the weed-free plots than in the unweeded control treatment.

Sorghum hybrids are generally considered to be drought tolerant based on their yield performance in multi-locational trials. The present study was undertaken to test this hypothesis. A short duration hybrid, CSH–6, a long duration hybrid, CSH–9, their common male parent and both female parents were evaluated in the field in India under both rainfed and irrigated conditions during the rainy seasons of 1986 and 1987. Due to the low rainfall received in these years, the unirrigated treatments experienced severe water stress during the vegetative and post-anthesis periods. The hybrids produced more leaf area and dry matter than their parents even under water stress. The values for the physiological traits examined either resembled those of one of their parents or were intermediate between them. The hybrid CSH–6 produced more grain than its female parent under rainfed conditions but, due to the severe water stress, neither CSH–9 nor its parents exhibited panicle emergence. The results suggest that crop phenology is very important for the production of grain yield under severe water stress. Given knowledge of rainfall characteristics and probable periods of drought within specific regions, it should be possible to breed phenologically and physiologically adapted hybrids for specific environments.

Infection of pearl millet by downy mildew [Sclerospora graminicola (Sacc.) Schrot.] has been shown to be influenced by soil pH, soil bulk density, soil moisture content and addition of farmyard manure and nitrogen fixing bacteria. A pH value of 8·5 allowed disease to develop the most, with increases in acidity to pH 7·5 producing 70% reduction in disease. Higher soil bulk density and moisture content also led to reductions in disease but the effects were not as marked as for pH. The addition of farmyard manure to soil or the addition of Rhizobium, Azospirillum or Azotobacter inocula as combined seed and soil treatment also reduced disease with the best effects being from a cluster bean isolate of Rhizobium and from Azotobacter chroococcum. Assessment of rhizosphere microorganisms associated with the resistant and susceptible varieties of pearl millet showed that, overall, the fungal population was lower in the resistant varieties but that it was increased in both susceptible and resistant varieties by infection with downy mildew. Bacterial and actinomycete populations were also lower in resistant varieties but in this case downy mildew infection decreased the rhizosphere populations of both groups.

Dehydrogenase activity of rhizosphere soil was higher in susceptible varieties but was decreased in both variety types by infection with S. graminicola.

The results are discussed with reference to possible mechanisms to explain the observed effects.

From 1990 to 1992, diet selection and nutrient intake of Zebu cattle grazing Sahelian pasture were studied in Central Mali. Forty-five intact males and 12 oesophageally fistulated animals were separated into three groups of 15 intact and 4 fistulated animals. The control group (C) grazed natural pasture only, while the moderately supplemented group (M) additionally received 0·8–1·5 kg OM/day of crop by-products during the dry season (November–June) and the first month of the rainy season. The third group (H) was highly supplemented with 1·2–2·7 kg OM/day in the dry season and 0·8–1·2 kg OM/day in the rainy season. Oesophageal extrusa was collected during 5 consecutive days at intervals of 4–5 weeks. Samples were analysed for contents of organic matter (OM), crude protein (CP) and neutral detergent fibre (NDF). Digestible organic matter (DOM) and metabolizable energy content (ME) were calculated from in vitro gas release. Intake of organic matter (IOM) of the fistulated animals was determined from faecal organic matter excretion (FOM) and extrusa DOM content. Intake of CP (ICP) and ME (IME) were calculated from IOM and the respective nutrient contents of extrusa samples.

Extrusa CP, DOM and ME contents did not differ significantly between the three groups either in the dry or in the rainy season. The CP content was c. 230 and c. 197 g/kg OM during the rainy season, and declined to values [les ]70 and [les ]95 g CP/kg OM at the end of the dry season of 1990 and 1991, respectively. Average DOM and ME contents were c. 668 g DOM and c. 9·9 MJ ME/kg OM during rainy seasons. At the end of the dry seasons, these values decreased to <550 g DOM and <8·0 MJ ME/kg OM. Per kg of metabolic body mass, IOM of group C was c. 89 g/day during the early dry season. It was accompanied by a daily ICP of 8–10 g and by an IME of 691–765 kJ/day. Due to a higher nutrient content in the selected diet, energy intake was slightly increased and protein intake was significantly higher during the rainy than during the dry season, although IOM was only 77–81 g/day. At the end of the dry season, unsupplemented animals ingested <70 g IOM/day and the concomitant CP and ME intake were <6 g CP/day and <500 kJ ME/day, respectively. Feed intake from pasture was stimulated by a moderate supplementation, but reduced by a high supplementation. The results indicate that on slightly degraded Sahelian rangeland, the nutrient intake of cattle is in the first place limited by biomass availability and only secondly by the quality of the vegetation.

The growth of body mass and changes in empty body composition of three groups of 15 male Zebu cattle (Bos indicus) grazing natural pasture were studied in the Sahelian zone of Mali from 1990 to 1992. The control group (C) grazed natural pasture only, whereas the moderately supplemented group (M) received 0·8–1·5 kg OM/day of crop by-products during the dry season and the first month of the rainy season. Group H (high) was supplemented at 1·2–2·7 kg OM/day in the dry season and at 0·8–1·2 kg OM/day in the rainy season. Applying the deuterium dilution technique, empty body composition was measured at the beginning and end of the rainy season and in mid-dry season, using seasonal factors to correct for fill of the gastrointestinal tract (GIT). Energy retention was calculated from the contents of empty body protein and fat.

During the 2 years of study, body mass gains were 143 kg (S.E. 4·9) for group C, 196 kg (S.E. 5·8) for group M and 251 kg (S.E. 6·0) for group H. Total GIT fresh matter content accounted for 166 g (S.E. 4·6) per kg of fasted body mass (FBM) in the dry season and increased to 228 g/kg FBM (S.E. 2·9) at the beginning of the rainy season (P[les ]0·001). Throughout the period of study, the proportion of protein in the empty body varied between average values of 156 g/kg and 179 g/kg, and the proportion of empty body fat ranged from 124–257 g/kg. For all body components, the effect of supplement treatment over time was significantly different between unsupplemented and supplemented animals (P[les ]0·001). From linear regressions between metabolizable energy intake and energy retention the maintenance requirement of grazing cattle was determined at 732 kJ ME/kg0·75/day for the dry season and at 522 kJ ME/kg0·75/day for the rainy season.

It is concluded that the methodological approach yields useful results on empty body composition and energy requirement of Zebu cattle in extensive management systems.

The relationship between liveweight at mating and calving probability was examined in cattle grazing subtropical pastures in a 4 year study. The aim was to establish whether breed type, lactation, protein meal supplements, and/or pasture quality affected the relationship. Cows (n=242) of Hereford (H), Brahman (B) and Brahman×Hereford (BH) breed types were selected as maiden heifers, 20–;27 months of age, and grazed pastures of low digestibility (D), (0·45–0·62) and medium (D, 0·47–0·67) quality which are typical of subtropical grassland areas. The maiden heifers were supplemented with cottonseed meal (D, 0·67, 61 g nitrogen/kg) at 0, 750 or 1500 g/day for 130 days and mated during 90 days in the first year of the study and as cows in the following three years. There were 633 mating records of cows collected during the study.

A generalized additive model was used to describe the relationship between calving probability and mating liveweight. There was no relationship between mating liveweight and calving probability when the model included the main factors. At the mean herd mating liveweight of 430 kg the calving probability (predicted mean±S.E.) of B cows (0·59±0·034) was less than that of H (0·74±0·029) or BH cows (0·81±0·026). There were significant reductions in calving probability with lactation and from medium to low pasture quality. Calving probability was not increased significantly in BH cows by supplementation but was for B and H cows. On low quality pastures, lactation reduced predicted calving probability from 0·77 to 0·54 for non-supplemented H cows and from 0·61 to 0·35 for non-supplemented B cows. The reductions were smaller in H and B cows when supplemented at 1500 g/day. On medium quality pastures the effect of lactation and supplementation on the calving probability of cows was less than for those grazing low quality pastures.

In order to learn more about some of the reasons for differences between forage plant species in nutritive value, plant parts of three contrasting species, Onobrychis viciifolia Scop., Spergula arvensis L. and Lolium multiflorum Lam., were examined. In vitro digestibility was recorded in milled and in chopped (1 cm lengths) material, neutral detergent fibre (NDF) and lignin were recorded in milled material and the proportions of thick-walled, thin-walled and epidermal cells and the thickness of the cell walls were recorded in cross-sections. Early harvesting was compared with later harvesting in each of two years. The plants were grown in a heated glasshouse in spring-summer.

In O. viciifolia the petioles had much higher concentrations of NDF and lignin, a higher proportion of thick-walled cells and generally thicker cell walls than the leaflets, but the petioles were, if anything, slightly more digestible than the leaflets. The leaflets of O. viciifolia had cell walls of similar thickness to those of Trifolium repens and Medicago sativa. The leaves of S. arvensis had generally thin cell walls and a high proportion (0·84) of thin-walled cells. The stems of S. arvensis had high concentrations of NDF (633 g/kg) and lignin (94 g/kg) and a high proportion of thick-walled cells, but the walls of these cells were not particularly thick (1·4 μm). The leaflets and petioles of O. viciifolia and the stems of S. arvensis were much less digestible than the leaf blades or leaf sheaths of L. multiflorum. L. multiflorum leaf blades and leaf sheaths were low in lignin (16–18 g/kg) and had rather thin cell walls; the sheaths were lower in NDF than the blades and tended to be more digestible than the blades, despite thicker epidermal cell walls.

Sixteen sheep were continuously fed diets based on straw, straw and barley grain, or NaOH-treated straw, each with adequate minerals and with or without additional urea (7·3 g N/day for the straw and straw and barley diets; 14·4 g N/day for the diet containing NaOH-treated straw) infused intra-ruminally. [14C] tracers were used to measure the rate of irreversible loss (i.e. synthesis) of plasma urea and its transfer to the rumen and to the remainder of the gastrointestinal tract in 4–6 sheep per treatment. [15N] tracers were also used to make these measurements in four sheep fed the straw, straw and barley and straw and barley with intra-ruminal urea infusions. Inclusion of the barley grain in the diet increased digestible organic matter intake by c. 70%. Replacing the straw with a greater amount of NaOH-treated straw increased digestible organic matter intake by 43% in the absence of additional urea, and by 65% when urea was infused intra-ruminally. Rumen ammonia concentrations were 37 and 31 mg N/l when straw or straw and barley diets respectively were provided and were reduced to 3 mg N/l when treated straw was given to the sheep. These concentrations exceeded 223 mg N/l when urea was infused intra-ruminally. Rate of irreversible loss of plasma urea measured using [14C]urea ranged from 3·7 g N/day in sheep given the treated straw diet to 16·8 g N/day when urea was infused intra-ruminally, while this rate was correlated with plasma urea concentration. In the three diets where it was measured, rate of irreversible loss of [15N]urea was on average 0·73 of the rate of irreversible loss of [14C]urea. Measurements made with 14C and 15N tracers of plasma urea transfer to the rumen were similar. This transfer measured with 14C tracers ranged from 1·4 to 2·4 g N/day for the three diets without additional urea, while providing urea by intra-ruminal infusions reduced the transfer to 1·1–1·4 g N/day. Transfer of plasma urea to the rumen was not changed by the higher digestible organic matter intake associated with either inclusion of barley grain in the diet or provision of a greater amount of more highly digestible NaOH-treated straw. These studies indicate that plasma urea transfer to the rumen is not always increased by greater organic matter fermentation in the rumen.