In research into competition between individual cultivars of one perennial grass species sown in mixtures, fixed matrix designs have been widely used because of difficulties in identifying the components inanatural sward.Extrapolation of results from such fixed designs to the sward situation is often difficult in any but the short-term context.

This paper describes the principles, requirements and use of an electrophoretic technique together with a mathematical concept which can be used to distinguish certain perennial ryegrass cultivars when sown in mixtures. Such methods have useful implications for the study of sward composition and competitive ability of ryegrass cultivars sown in mixtures. The number of samples required to study selected 2-way cultivar mixtures using this method is indicated.

Field experiments were carried out in the early and late growing seasons in the rainforest zone of Nigeria to determine the responses of yield, components of yield and nutrient contents of cow pea to magnesium fertilizer. Yield and components of yield studied were not significantly increased by Mg application but N, P and Zn concentrations were significantly increased, while Mn concentration decreased significantly with applied Mg.

Yield was positively correlated with the micronutrient (Zn, Fe, Cu, Mn) concentrations of cow pea. A level of 0·43 m-equiv/100 g of exchangeable Mg or 15% Mg saturation appears adequate for successful cow-pea production in a typical forest zone within the humid tropics.

A pot experiment studied the effect of gypsum and green manuring on equilibrium soil solution pH, pE, Mn concentration and Mn equilibrium in three sodic soils. Submergence decreased soil solution pH and increased Mn concentration in all the soils. Addition of gypsum with green manure further decreased soil solution pH and increased Mn concentration. Maximum Mn concentration in all the treatments was observed at 4 weeks of submergence in Kaheru soil and at 6 weeks of submergence in Jagjitpur and Langrian soil followed by a decline up to 12 weeks. In spite of wide variations in pH, pE and Mn concentration in soil solutions, the solubility of Mn after peak values appeared to be mainly controlled by the MnC03-Mn2+ system irrespective of the treatments, and the Mn2O3-Mn3O4 system appeared to operate after 2 weeks of submergence in the control and gypsum-treated soils.

The nutritive value of diets predominantly of dried cassava (Manihot esculenta Crantz.) tubers supplemented with protein concentrates, and roughage were measured in three experiments using steers.

In Expt 1 the digestibility of diets of dried, chipped cassava tubers and tops (80:20) or rolled sorghum grain and cotton seed hulls (80:20), supplemented with 4 or 8% groundnut meal and urea, was determined. The apparent digestibility coefficients of organic matter (OM) of the cassava diets with 4 or 8 % groundnut meal (0·77 and 0·80, respectively) were significantly (P < 0·01) higher than grain diets with 4 or 8% groundnut meal (both 0·74). The digestibility of starch in the cassava diets was significantly (P < 0·01) higher than in the grain diets (1·00, 0·99, 0·94 and 0·93, respectively). There were no significant differences in the digestibility of the N component (0·62 and 0·61 v. 0·58 and 0·59, respectively). The N retained (g/day) was lower (P > 0·05) with cassava (7·8 and 6·8 v. 11·1 and 10·5, respectively) and was utilized (g/100 g apparently absorbed N) less efficiently (P > 0·05) (18 and IS v.28 and 27, respectively).

The high apparent digestibility of the cassava diet suggests that cassava could replace cereal grain in intensive finishing diets. The N retention data suggest that groundnut meal is no better than urea as a N source.

In Expt 2, 15 steers with a mean initial weight of 173 kg were individually fed pelleted diets of sorghum grain, cassava plus urea or cassava plus meat and bone meal (90 concentrate: 10 roughage). The cattle fed the grain diet ate significantly (P < 0·01) more OM (4·3 v. 3·4 kg/day), grew faster (P < 0·01) (1·21 v. 0·85 kg/day) and slightly more efficiently (P > 0·05) (3·6 v. 3·8 kg/kg) than cattle fed cassava with urea. Cattle fed cassava with meat and bone meal were intermediate between the two treatments for intake and daily gain (3·7 and 1·06 kg/day, respectively) but had the best feed conversion (3·5 kg/kg). The acetic/propionic acid ratio was similar on all three diets (1·2, 1·6 and 1·4:1, respectively), but the ratio of propionic/butyric was significantly (P < 0·01) different (5·8, 2·7 and 2·7:1, respectively).

In Expt 3, 15 other steers with mean initial weight of 195 kg were individually fed pelleted cassava diets with 0, 5 or 10% fishmeal (82 cassava: 18 roughage). The intake of OM (4·2, 4·5 and 4·7 kg/day, respectively), daily live-weight gain (0·98, 1·27 and 1·32 kg/day, respectively) and feed conversion (4·3, 3·7 and 3·7 kg/kg, respectively) were all better in cattle fed cassava with fishmeal. The proportions of volatile fatty acids in the rumen fluid were similar to that recorded in cassava fed cattle in the earlier trial.

It is concluded that cattle fed high energy diets based on dried cassava tubers can perform well. Although feed intake and daily gain of cattle fed cassava may be lower than for cattle fed grain diets, the conversion of food to live-weight gain should be similar or better.

Two experiments examined the effect of improving the distribution of the pigeonpea plants in sorghum-pigeonpea intercropping by having an alternate row arrangement of the two orops (SP) instead of the two sorghum: 1 pigeonpea row arrangement (SSP) that was studied earlier. One experiment was under conditions of good moisture supply (a deep Vertisol site in the high rainfall year of 1978) but the other experienced early moisture stress and had much lower end-of-season soil moisture storage (an Alfisol site in 1979). In 1978 the proportional sorghum yield was not affected by row arrangement (86 and 85% of the sole crop yield for the SSP and SP treatments respectively). Under the drier Alfisol conditions of 1979, the proportional sorghum yield was lower, probably because of the increased competitive ability of the drought resistant pigeonpea, and it was adversely affected by the alternate row arrangement (72% for SSP and 60% for SP).

Compared with the SSP arrangement, the SP arrangement increased the level of light interception by the intercropped pigeonpea immediately after the sorghum harvest from 30 to 48 % in 1978 and from 44 to 60 % in 1979; the total energy intercepted during the whole post-sorghum period was increased by 23 and 12 % in the 2 years, respectively. However, these improvements in canopy cover were associated with only small increases in total dry matter of the intercropped pigeonpea at final harvest, from 69 to 74 % of the sole crop in 1978 and from 60 to 65 % in 1979. The increase in seed yield was even less than that in total dry matter in 1978 (from 90 to 93% of the sole crop) but similar in 1979 (71 to 76%); the value of this increase in 1979 was insufficient to offset the decrease in sorghum yield. None of the increases in total dry matter or seed yield of pigeonpea reached significance. It is concluded that with a good moisture supply alternate rows could be an alternative to the 2 sorghum: 1 pigeonpea arrangement, though it offers no additional yield advantage. With poorer moisture supply, alternate rows are not a worthwhile option because of the risk of reducing sorghum yield to an extent that cannot be offset by the small increase in pigeonpea yield.

Spring-barley straw or maize silage were the major components in mixed diets of compound and forage fed to yearling dairy heifers. With straw, rolled barley was fed either alone or with fishmeal, soya-bean meal, protected soya-bean meal, whey + urea or Ewoplua (a product made from whey and rich in lactosyl urea). With maize silage the rolled barley was fed either alone or with fishmeal, whey + urea or Ewoplus.

When straw was included in the diet fishmeal and protected soya-bean meal increased live-weight gain, and all the supplements increased nitrogen retention. When maize silage was fed, only fishmeal increased live-weight gain although all the supplements increased digestibility. Concentrations of rumen NH3-N were increased by all the supplements, when fed with straw, and also by maize silage when fed without an N supplement or with fishmeal. Small changes were noted in total and molar proportions of VFA.

Calculated ME intakes suggested a more efficient use of energy for growth from maize silage than from straw, except when the straw diet was supplemented with fishmeal.

Two experiments were conducted with eight rams in a latin-square design of four treatments with different lucerne hay (LH): maize grain (MG) ratios: 100:0, 80:20, 50:50 and 20:80. In Expt 1 the amount of food offered was restricted to 1 kg/day. In Expt 2 the rams were offered 1·5 kg/day, which was about the maximum amount the animals in the 100% LH treatment were able to consume. Animals were kept on each treatment for 4 weeks; during the final 8 days the faeces were oollected and weighed for each animal and analysed for dry matter, organic matter (OM), crude fibre and δC

The values of δC in LH, MG and different faeces samples were used for direct determination of LH and MG digestibilities of mixed diets in the different treatments.

The increase of MG in the ration and the decrease of LH improved the digestibility of total OM. The effect of MG was more pronounced at the low than at the high level of consumption. At the low level of intake, an increase in the amount of MG in the ration did not affect the digestibility of LH, and MG digestibility was close to the extrapolated value. At a food intake level 1·5 times that of Expt 1, the addition of grain to more than 50 % of the ration caused a marked depression in digestibility of LH.

Results of the δC method were discussed in comparison with calculated values of LH and MG digestibilities and with whole ration crude-fibre digestibility.

Leaching in a salt-affected, permeable, sandy loam soil was evaluated under continuous and intermittent ponding conditions in 2 × 2 m (S1), 4 × 4 m (S2) and 6 × 6 m (S3) plots. The soil contained large amounts of soluble salts throughout the profile to the water table, chiefly chlorides and sulphates of sodium, calcium and magnesium. The leaching curves did not differ significantly between Slf Sa and S3 plots under continuous ponding but did under intermittent ponding. The leaching efficiency decreased sharply with increased plot size. The leaching efficiency in Sj plots was significantly greater with intermittent than with continuous ponding, but the reverse was true in S3 plots. The displacement of the resident soil solution in S1 plots under intermittent ponding was nearly piston-like. With increased plot size, it tended to deviate from this behaviour. The leaching curves from S3 plots (this size being reasonable in farmers' fields) were compared with those obtained from numerical solution of a simplified steady-state salt transport model. The model also included a source term, solubility rate constant, for the slightly soluble salts present in the experimental soil. The pore water velocity was estimated from field capacity and time-averaged infiltration rate. The effective dispersion coefficient and solubility rate constant were estimated by a least-squares minimization technique. A reasonably good agreement was obtained between simulated and experimental leaching curves. For practical purposes, this simple model may be adequate to predict leaching in salt-affected soils similar to the one under consideration.

From the progeny of a cross between the winter wheat varieties Norman and Talent early and late F5 lines were selected in the field. These selections and the two parental varieties were grown in controlled environment cabinets to assess their sensitivity to photoperiod and vernalization.

The F5 selections and Norman and Talent were also grown in field trials, at the Plant Breeding Institute in Trumpington, and at The Murrays Experimental Farm of the Scottish Crop Research Institute, near Edinburgh.

Norman was more sensitive to photoperiod and vernalization than Talent. The early F5 lines were relatively insensitive to photoperiod and/or vernalization. The late lines were sensitive to both photoperiod and vernalization. Differences in date of ear emergence among the selections were found which were independent of photoperiod and vernalization sensitivity. This variation in ear emergence, described as earliness per se, was similar under controlled environment conditions and in the field, and was also shown to be similar in magnitude to that due to differences in sensitivity to photoperiod and vernalization. Both sources of variation can be exploited to modify time of ear emergence under field conditions in Great Britain.

Disks of hard wheat (Triticum durum Desf.) leaves subjected to rapid desiccation over 4 h showed noticeable changes in the shape of the in vivo chlorophyll fluorescence induction curves. In drought-sensitive varieties (such as Claridoc), water stress resulted in a strong inhibition of the slow fluorescence induction transients. In particular, the fluorescence quenching rate was markedly decreased in water-stressed leaf disks. In contrast, leaves of drought-resistant varieties (such as Aouedj) showed only minor changes in chlorophyll fluorescence. The results of this investigation suggest that the slow transient of the in vivo chlorophyll fluorescence induction phenomenon may provide a simple method for selecting drought-tolerant wheats.

Two trials were conducted to study the seasonal variation in oestrous activity over the year in Suffolk (S) or mutton Merino (M) temperate breeds, and their crosses with the local Ossimi (O) sheep under the prevailing subtropical conditions. In the first trial, groups of S, 75% S, 50% S, and O were used and the second trial involved groups of M, ¾M, ½M, ½M and O. The incidence of oestrus was measured by teasing with vasectomized rams. Suffolk ewes had a restricted period of oestrous activity (August–January) whereas M had a longer breeding season (August–March) with high incidence of long and double cycles. Local O showed irregular oestrous activity almost around the year, with particular decline in April. In both trials, all crosses had better oestrous activity than the pure parents, with the 50% S and the ½M having the best performance in the two trials, respectively. The period from September to February seemed to be the period of normal cycling activity in all breed groups, whereas the period from March to May was associated with marked breed-group variation in oestrous activity. Normal cycle length of the S was significantly (P < 0·01) shorter than the local O (16·0 v.17·7 days) and was more consistent than other breed groups. In the two trials, normal cycle length of the cross-breds was ranked between the two purebred parents.

In the 350–600 mm seasonal rainfall ecological zone in northern Syria three-course rotations are commonly practised under rainfed conditions. The precipitation regimes at three sites in this ecological zone have been examined. These have been shown to exercise a powerful influence on crop management, and an enhanced understanding of the effect of precipitation on crop productivity would therefore assist in the development of improved strategies of agronomic and rotational management. Considerable variability has been demonstrated in characteristic elements of the precipitation regime at the selected sites and this has indicated the unsoundnesa of applying general management recommendations to the ecological zone as a whole.

A model of reproductive performance in dairy herds is described. The model relies upon no empirical relationships but is constructed from a series of simple stochastic processes involving only three principal parameters: ovulation detection rate, pregnancy rate and embryo loss rate. The model shows how the complex interactions between these parameters and management policy concerning the definition of the service period are generated.

Experiments were conducted between 1978 and 1981 to investigate the effect of autumn and spring sowing on emergence, winter survival, growth and yield of combining peas (varieties ‘Frimas’, ‘Filby’ and ‘Vedette’). Effects of growth regulator PP 333 (Paclobutrazol, ICI pic) application and defoliation on winter survival of Filby were also investigated. Field emergence of autumn-sown Frimas (winter hardy) was less than Vedette or Filby but percentage winter survival was greater. PP 333 application, but not defoliation, increased percentage winter survival of Filby sown in September. Total dry-matter production and photosynthetic area of autumn- compared with spring-sown crops varied considerably between seasons. Yield data indicated that autumn-sown crops produce similar seed yields to spring sowings when winter survival is adequate. November sowings matured 2–4 weeks before March-sown crops, depending on variety and season. Optimum sowing dates were mid-November and early March. Large seed-yield reductions occurred when sowing was delayed until mid-April.

Pure and mixed swards of Centrosema pubescens (centro), Pueraria phaseoloides (puero) and Brachiaria mutica (para grass) established under a 12-year-old mango plantation were sampled at 6-week intervals for 2 years to determine crude-protein (CP) content, dry-matter (D.M.) and CP yields and apparent digestible energy and apparent digestible crude-protein (DCP) contents. Daily dry-matter intake (DMI) and apparent digestible energy and digestible crude-protein intakes (DEI and DCPI), as well as live-weight gain (LWG) by 11·5 kg penned West African cross-bred weaner lambs, were also determined.

The pure legumes were better than the mixed swards in respect of CP (mean: 22·1, 18·8, 14·4 and 13·8% for centro, puero, centro-para grass and puero-para grass respectively) and DCP (mean: 16·2, 13·4, 10·4 and 10·0% respectively) contents, and daily DMI (mean: 50·8, 49·7, 41·8 and 41·3 g/kg W0·75 respectively), DEI (mean: 562, 531, 418 and 410 kj/kg W075 respectively) and DCPI (mean: 8·09, 6·55, 4·04 and 3·94 g/kg W0·75 respectively). On the other hand the legume-grass mixed swards, especially puero-para grass, were superior to the corresponding pure-legume swards with regard to D.M. yield (mean: 11·90, 7·69, 7·13 and 4·54 t/hafor puero-para grass, centro-para grass, puero and centro respectively) and CP yield(mean: 1·62,1·09, 1·32 and 0·99 t/ha respectively). The pure-legume stands gave the highest LWG per lamb (mean: 45·7, 3·89, 2·63 and 25·3 g/day for centro, puero, centro–para grass and puero-para grass respectively) but it was estimated that the legume-grass mixed swards would give higher returns in terms of lamb LWG on forages harvested per unit sward area than the corresponding pure-legume cover.

It was concluded that legume-grass covers would be preferred to all-legume covers if livestock were to be integrated into tree crop farming systems. However, the choice of companion grass would have to be given proper consideration as shade-intolerant grass species, such as para grass, would detract from profit maximization.

Involvement of plant genotype, stage of development of plant and seed, fertilizer and irrigation in frost tolerance of oil-seed Brassica spp. were examined. The number of apparently frost-killed or undeveloped seeds has been used to assess tolerance. Three B. campestris L. genotypes namely Span, Torch and Bell showed considerable tolerance of frost. Very young and also nearly mature seeds were less affected by freezing than seeds at an intermediate stage of development. The amount of nitrogen fertilizer applied had no effect, but the unirrigated orop was injured by frost more than the irrigated one.

To evaluate the effects of chronic environmental heat stress during mid-gestation on gravid uterine and foetal metabolism, mature Hereford cows were assigned to control (n = 8) or heat stress (n = 5) treatments beginning on day 100 of gestation. Uterine and umbilical blood flows were estimated by the steady-state diffusion procedure on day 169 ± 4 of gestation. Oxygen (O2), glucose, lactate, α-amino nitrogen and urea nitrogen concentrations were determined for uterine and umbilical blood samples collected during this procedure. Foetuses and foetal fluids were collected on day 174±4.

Uterine and umbilical blood flows were reduced and foetal weight also was less for heat-stressed than for control cows. In addition, foetal liver weight as a proportion of foetal weight and total foetal liver RNA and protein were less for heat-stressed cows. Uterine and umbilical arterial–venous concentration differences in metabolites were similar between the two groups. Uterine, foetal and utero-placental uptake or secretion rates of the metabolites measured in this study were reduced in the heat-stressed cows, primarily because of differences in blood flow. Thus, chronic heat stress during mid-gestation had an adverse effect on foetal development resulting, at least in part, from decreased uterine and umbilical blood flows, which led to a reduction in uterine, utero-placental and foetal nutrient uptake or secretion rates.

On 13 pastures grazed by beef cattle live-weight gain (range, 0·34–1·12 kg/head/day) was significantly correlated with non-green grass content of pasture. In turn, non-green grass in pasture was not significantly correlated with non-green grass in oesophageal extrusa. Live-weight gain was largely explained (adjusted R2 = 0·91) by non-green grass content of pasture, cell-wall content of green-grass leaf and pasture dry matter on offer in a quadratic model. The quadratic form was best understood in terms of pasture growth with which non-green grass content of pasture was significantly and negatively correlated.

The influence of physiological state (pregnant, lactating, dry) on body composition and fat partitioning in Friesian cows has been examined. A total of 20 cows, four per physiological state, were slaughtered and their left half carcasses dissected into individual muscles, bones and fat depots. All body parts, including the internal organs and fat depots, were weighed at slaughter.

Muscle tissue and the internal organs showed some weight changes, consistent with a redistribution of tissue towards the udder and gut, and mobilization of muscle, but the major changes in weight associated with changing physiological state occurred in total body fat.

Intermuscular fat made the greatest absolute contribution to changing fat weight, but subcutaneous fat showed the greatest proportional change with changing physiological state. The order of depletion of fat depots during fat loss was approximately the reverse of the order of development found during developmental growth.

The distribution of subcutaneous fat between seven defined regions of the carcass was not affected by differences in total fatness in different physiological states. This, and the high correlation found between fat depth and total body fatness, confirms the view that measures of subcutaneous fat depth, e.g. by ultrasonics, should be useful predictors of the energy status of cows in varying physiological states.