A field experiment was made during the rainy seasons of 1968 and 1969 on a sandy loam soil to study the response of Sorghum hybrid CSH–1 to phosphorus in relation to content of water-soluble phosphate in fertilizers. Triple superphosphate, dicalcium phosphate, rock phosphate (200-mesh), nitrophosphate and mixtures of triple superphosphate with dicalcium phosphate and rock phosphate in 3:1, 2:2 and 1:3 ratios were studied. The amounts of phosphorus applied were 30 and 60 kg P2O5/ha. Phosphorus application significantly affected dry matterproduced, plant height, days to 50% bloom, number of grains per ear, thousand-grain weight, stover and grain yield. Triple superphosphate and 3:1 triple superphosphate/dicalcium phosphate mixture were the most effective while rock phosphate and 1:3 triple superphosphate/rock phosphate mixture the least. Differences among sources were more marked in 1968 and at the higher amount i.e. 60 kg P2O5/ha. The response of sorghum to phosphorus was considerably lowered when the water solubility waa below 50% in triple superphosphate/dicalcium phosphate mixtures and below 75% in triple superphosphate/rock phosphate mixtures. Relative effectiveness was assessed by calculating ‘superphosphate equivalents’ and ‘multiple regressions’. Using superphosphate equivalents dicalcium phosphate, nitrophosphate and rock phosphates were 47–53%, 35–56% and 3–25%, respectively, as effective as triple superphosphate.

In two experiments with potatoes the effects of plant population (from 13 to 59 stems/m2 in 1969 and 18–111 stems/m2 in 1970) and harvest date (from mid-June till late August/early September) on the yields of tubers and particularly those of canningsize (2–4 cm) were studied in the cv. Maris Peer.

Yields of canning-sized tubers increased linearly with increases in the number of mainstems over the range 13–64 stems/m2. The response was similar for harvests made at different stages of growth except for the period of 2–3 weeks after tuber initiation when the effect of plant population on yields was small. For crops grown at low plant populations yields of canning-sized tubers rose to a maximum early in the season and then declined with further growth of the crop. Progressive increases in plant population resulted in maximum yields at progressively later stages in the growth of the crop. The period over which it would have been possible to harvest crops having an acceptable quality and each giving their maximum yield was 4–6 weeks in 1969 and 3–4 weeks in 1970.

There was no effect of seed tuber size per se on total tuber yields or yields of tubers in size grades. In both years at least twice the weight of large (over 66 g) as opposed to small seed (22 and 27 g) was required to establish the same stem population/m2. The production and use of small seed suitable for canning potato production is discussed.

Samples were prepared to simulate the populations which would be obtained from the random interpollination of known numbers of inbred lines. This was done by mixing together seed of a vigorous and a less vigorous genotype in calculated proportions. The less vigorous represented the inbred component which would result from selling and sibbing within the constituent lines, while the more vigorous represented the hybrid fraction. The difference in yield between the two genotypes was comparable with the level of enhancement which could be expected in the hybrids as a result of heterosis. Root yields of these populations in the field suggest that depression due to the presence of inbred individuals in a synthetic variety may be predicted by a mathematical model. Yields calculated from the model to allow for various levels of compensation enabled the order of magnitude of the compensation to be estimated. However, the presence of quite small numbers of less vigorous individuals was detectable. Given the limitations imposed by the assumptions necessary to simulate these varieties, the optimal number of lines for an open-pollinated variety may be predicted.

The yield results are reported for the final 3 years of a 6-year experiment in which twenty-one rates of nitrogen fertilizer ranging from 0 to 800 lb/acre (897 kg/ha) were applied annually on S. 23 perennial ryegrass swards with and without S. 100 white clover. The long-term effects of the treatments on herbage yields are discussed using the results from all 6 years. Four-parameter exponential curves fitted to the herbage yield data from each year show that the response pattern for the pure-grass sward remained relatively constant over the years although the mean annual yields varied slightly. The response of dry-metter yield to nitrogen rate on this sward was almost linear between the 0 and 300 lb nitrogen/acre (336 kg/ha) rates, then it decreased progressively, becoming non-significant about the 500 lb/a ere (560 kg/ha) ra te. Crude-protein yield responded almost linearly up to the 600 lb/acre (673 kg/ha) rate. The average yield responses over the 6 years for the pure-grass sward with nitrogen rates between 0 and 300 lb/acre was 27–8 lb dry matter (range 25·8–29·8 lb) and 4·2 lb crude protein (range 3·8–4·8 lb) per lb of nitrogen applied. At high nitrogen rates the yield curves for the grass and clover sward were similar to those for the pure-grass sward but at low rates the grass and clover sward gave a lower response to nitrogen and a greater yield at each nitrogen rate. The yield response to nitrogen rates between 0 and 300 lb/acre applied on this sward increased from 13·1 lb dry matter/lb of nitrogen in the first year to 20·2 lb in the sixth year. The difference in yield between the grass and clover and the pure-grass swards given no nitrogen fertilizer decreased from 4850 lb dry matter/acre (5440 kg/ha) to 2370 lb/acre (2660 kg/ha) over the same period. Within each year the yield difference between the two swards decreased with increasing nitrogen rate reaching an insignificant value at a rate of about 350 lb/acre (392 kg/ha) in the first year declining to 150 lb/acre (168 kg/ha) in the sixth year. On average the weight of nitrogen required annually on the pure-grass sward to give the same herbage yield as the grass and clover sward receiving no nitrogen was 125 lb/acre (140 kg/ha) on a drymatter basis and 195 lb/acre (219 kg/ha) on a crude protein basis.

Fistulated cross-bred sheep were given, by means of continuous feeders, concentrate diets containing chromic oxide (Cr2O3). Dry-matter digestibility coefficients predicted from the faecal concentration of Cr2O3 were compared with those obtained by total collection of faeces, and the concentration of Cr2O3 in spot samples of faeces taken at different times of day was compared with that in faeces bulked over an 8-day collection period. The rate of flow of digesta from the abomasum and the partition of digestion between the stomach and intestines, calculated from the concentration of Cr2O3 in samples of abomasal digesta, were compared with values obtained using two markers, one of which remained in solution while the other was adsorbed by particulate matter.

Récovery of Cr2O3 in the faeces ranged from 91 to 101% and predicted dry-matter digestibilities were similar to those obtained by total collection. There was no diurnal variation but there was marked random variation in the concentration of Cr2O3 in spot samples of faeces. Cr2O3 was shown to behave independently of the particulate matter in digesta and, as a single marker, it significantly underestimated the flow of digesta from the abomasum relative to the double marker method. Cr2O3 thus overestimated digestion in the stomach and underestimated digestion in the intestines. It was concluded that Cr2O3 was not a satisfactory marker for studies of the flow of digesta and hence the partition of digestion within the gastro-intestinal tract when digesta samples are taken from a simple cannula.

The effects of environment and genotype on growth and yield of cotton were studied in three experiments done at Namulonge, Uganda, from 1966 to 1969. Treatments were date of sowing, variety, fertilizer, plant population and water. Variety BPA66 sown in June at 4–10 plants m-2 outyielded other varieties, sowing dates and population densities. Compound fertilizer at l.25 t ha-1 increased yield by 15% and irrigation increased yield by 38%. The soil water deficit (CSWD) was calculated from meteorological data, and the relative water content (RWC) of the plants was measured. CSWD did not affect growth until a critical value (CD) was reached, which increased from 20 to 50 mm as the crop aged. When CD was reached RWC was s0·094 at dawn and 0·83 at 1400 h. Growth stopped when CSWD > CD, except while any rain, insufficient to make CSWD < CD, was being consumed. Days while such rain was being consumed and days when CSWD < CD were added to give the effective numbers of growing days which accounted for differences in numbers of mainstem nodes caused by sowing date and spacing, and for differences in plant dry weight and leaf area caused by sowing date. Variation in light transmitted by the crop canopy depended on leaf area index (L) alone; spacing, fertilizer and CSWD had no independent effects. The measured extinction coefficient was 1.1 compared with 0·9 predicted by de Wit's (1965) model. Measured value of crop growth rate (C) agreed with values predicted by the de Wit model for the vegetative phase. Spacing and fertilizer only affected C through L. During the reproductive phase C became much less dependent on L, and the form of the relationship changed. Some varieties including BPA66 had a greater net assimilation rate. Maximum C was expected when L ~ 3, but L was seldom > 2. Crops sown at current and previously recommended spacings had sparse canopies and did not fully use light available for dry matter production.

The actual transpiration of corn (Zea mays L.) was determined by hydraulic lysimeters, by the inflow-outflow method and by use of a neutrone probe. Two irrigation treatments were used; wet and dry. Under the wet treatment, 740, 858, and 743 mm of irrigation water was used during the seasons 1968, 1969, and 1970 respectively. Under the dry treatment, amount of irrigation water used was 560, 627, and 565 mm during the seasons 1968, 1969 and 1970, respectively. Ratios of actual transpiration (Et) to Penman's estimate of potential evaporation (Eo), evaporation from a Class-B pan (EpB), global radiation (Rg) and net radiation (Rn) were calculated. Values of Et measured by the different methods are in good agreement. Seasonal averages of Et, were 6·2 and 4·9 mm/day under wet and dry treatments, respectively. The Et/Eo, Et/EpB, Et/Rg and Et/Rn ratios increased with leaf area index (L.A.I.) and reached their maximum values when L.A.I, reached its maximum value of 1·03 under wet and 0·92 under dry treatment. The empirical coefficient (f = Et/Eo) under wet treatments was found to be higher than that given by Penman for short grasses and about the same as that obtained by Boumans et al. (1963) for golden-gram (Phaseolus aureus) in Iraq for the months August and September. The empirical coefficient Kb in the Blaney–Criddle formula was greater than the value given by Blaney and Criddle for an arid climate, and less than the value obtained by Boumans et al. for golden-gram in Iraq. It was further found that water use efficiency for grain production was greater under dry than under wet treatments.

Twenty-two Finnish Landrace × Blackface ewes suckling either single, twin, triplet or quadruplet lambs were maintained indoors during a 12-week lactation period. Milk production was estimated at weekly intervals by hand milking following oxytocin administration. Milk was collected from each ewe in four similar volumetric portions which were retained in order of withdrawal and analysed for maj or constituents. Weighted volumes of milk from each of the four portions were bulked to give a single sample for analysis. Estimated mean total milk production over a 12-week period from parturition was 134, 205, 212 and 218kg for single-, twin-, triplet- and quadruplet-suckled ewes respectively. Most of the difference in total yield between multiple-suckled groups of ewes occurred during the first 3 weeks of lactation, and the data indicate that the number of lambs born, or the total weight of concepta, influences the initial quantity of milk available to the lambs. Regression analysis showed significant evidence for difference between the linear components of the regression of milk yield, fat, protein, lactose and Gross Energy on the stage of lactation for all suckling groups. The concentration of all constituents other than lactose and ash was higher in colostral milk, but was significantly higher only in respect of fat, protein and Gross Energy. Substantial differences found between suckling groups in respect of fat and protein, content of the milks indicate an influence on these constituents due to the number of lambs suckled. The mean growth rates of the triplet- and quadruplet-suckled groups of lambs were each significantly lower than each of the single- and twin-suckled groups. The food intake of the ewes in relation to shape of lactation curves and consequent lamb growth is discussed.

A significant interaction between genotype and cutting height was found in an experiment conducted to investigate regrowth from cutting heights of 2 cm and 5 cm above ground level in two contrasting genotypes with fast and slow rates of leaf appearance. There was, however, no evidence that production of herbage above the initial cutting height was increased by raising the height of cutting. This observation, and the difference between the genotypes, can be explained not only in terms of differences in the proportion of total above-ground parts harvested, but also in the scale of losses of leaf tissue by death.

Two experiments axe described which investigated the effect of two row widths, 68·6 cm and 137·2 cm, on the total and graded yields of three potato varieties, Majestic, Up-to-Date and King Edward, grown at a wide range of seed rates.

Numbers and yield of small (< 3·81 cm) tubers were reduced by wide rows but effects were less on larger tubers and yields of large tubers (> 5·08 cm) were even increased by wide rows at high seed rates. Row width had least effect on King Edward, which produced the most tubers.

The results suggest that much wider rows than have hitherto been used for potatoes may be justified and lead to only small reductions in ware yields.

The dietary and individual factors influencing the utilization of digestible nitrogen in the dry cow were studied with numerous rations fed to Friesian cows kept in metabolism stalls.

Urinary nitrogen excretion and nitrogen balance were above all influenced by the level of digestible nitrogen intake. They are also correlated to metabolizable energy and digestible potassium intakes.

Endogenous urinary nitrogen, estimated by extrapolation, was 30·6 mg N/kg body weight/d or 0·169 W0·73 g/d with the rations meeting approximately the energy maintenance requirements of the cow.

The changes in diet accounted for 80% of the variability of nitrogen balance.

A method was worked out for calculating the body condition of the cow from the live-weight variations.

The changes in body condition accounted for 11% of the variability of nitrogen balance.

Red cell GSH concentrations were measured in 83 pure-bred and 65 cross-bred Tasmanian Merino sheep. A bimodal distribution was found; 40% of sheep had mean GSH values of 27·3 ± 1·2 mg and 60% had 92·2 ± 1·5 mg/100 ml red cells. Family data are limited, but they suggest that this difference is under genetic control, the gene for low GSH levels being dominant to that for high. Unlike GSH-low type Finnish Landrace sheep, GSH-low type Merino sheep do not have lower than normal red cell sodium and potassium concentrations.

The growth of the progeny from self-pollination was studied in seven cultivars of Lolium perenne and five cultivars of Lolium multiflorum. All cultivars otLolium perenne showed a reduction in the dry weight of the selfed progeny after one generation of inbreeding, although only four of these attained statistical significance. By contrast the reduction in Lolium multiflorum was less marked with only one cultivar showing a significant reduction on inbreeding. An analysis of the growth of two of the Lolium perenne cultivars which showed reduced vigour in progeny from self-pollination suggested that a lower germination rate and a slower development of leaves in the seedling were two factors which resulted in reduced weights in inbred progeny. The possible effect of the environment in which the inbreds were produced on seedling performance is discussed.

Intact barley coleoptiles subjected to high temperature stress of 46°C for up to 4 h showed a significant decrease in their growth rate, and in the final length attained by the coleoptiles before exsertion of the true leaves within. These effects of high temperature were progressively more pronounced with increase in duration of stress. Excised wheat coleoptile sections also experienced a similar growth retardation due to heat stress. This heat-induced growth retardation could not be prevented by exogenous applications of 0·5–100 ppm indole-3-acetic acid or 0·5–5 ppm gibberellic acid; nor by dilute aqueous solutions of calcium chloride, cobalt nitrate or zinc sulphate. The agronomic significance of heat-induced coleoptile stunting is briefly discussed.

Two experiments are described in which the possible yield benefits of mixing maize and beans were examined under intensive farming conditions. A ‘replacement series’ of pure maize, two-thirds maize/one-third beans, one-third maize/two-thirds beans and pure beans was used at four plant populations. A high level of nitrogen was applied on the maize to eliminate the effects of nitrogen transfer from the beans.

Yields of the mixtures were up to 38% higher than could be achieved by growing the crops separately. It is concluded that this occurred because the mixtures achieved a greater utilization of environmental resources; it is suggested that, because of the marked height differences of the two crops, an increased utilization of light was probably a major contributing factor. The need for high populations in mixtures is indicated, partly because the largest yield increases were achieved at high populations and partly because the mixtures required a higher population pressure to produce their maximum yield.

The maize was found to have the higher relative competitive ability, and this increased with increase in plant population pressure. It is suggested that this was probably due to the shading effect which the maize had on the beans. The effects of a change in relative competitive abilities, or in relative selling prices, on the optimum proportion of two species in a mixture are also considered.

In a randomized block 3x2 factorial experiment 72 Large White type and Large White x Landrace pigs were restrictedly fed to 160 lb (72–5 kg) live weight on diets (as wet mashes) containing high levels of maize, wheat or barley in either ground meal or ground flaked forms. A further five groups of six litter-mate Large White type hog pigs per group were used in digestibility and nitrogen balance studies. The diets of meal were formulated to be iso-nitrogenous and to contain similar levels of lysine and for each cereal similar levels of protein and vitamin/mineral supplements were included in the flaked diets. There were no significant cereal x processing interactions for any of the parameters studied. Overall, flaking improved digestibility and this was reflected in a higher (P >0-05) digestible energy content of the flaked diets (3402 kcal/kg air dry weight) compared with the meal diets (3334 kcal/kg air dry weight). The digestible energy contents of the maize, wheat and barley diets were significantly different (P < 0-001) at 3477, 3431 and 3195 kcal/kg air-dry diet respectively. Nitrogen retention, growth rate and efficiency of food conversion were all significantly poorer for the flaked, compared with the meal based diets. The nitrogen retained from the wheat-based diets was significantly lower than that retained from the maize- and barley-based diets. Growth rates of pigs given the wheat- and barley-based diets were similar but taken together were significantly (P < 0-05) better than those obtained from pigs given the maize-based diet. Efficiency of food conversion followed a similar pattern but the differences were not statistically significant.

An experiment is described in which the possible yield benefits of mixing dwarf sorghum and beans were examined under intensive farming conditions. A ‘replacement series’ of pure sorghum, two-thirds sorghum/one-third beans, one-third sorghum/twothirds beans and pure beans was used at four plant populations. A high level of nitrogen was applied to the sorghum to eliminate the effects of nitrogen transfer from the beans.

Yields of the mixtures were up to 55% higher than could be achieved by growing the crops separately. As with some earlier maize/beans experiments (Willey & Osiru, 1972), it is concluded that these yield increases must have been due to a greater utilization of environmental resources. It is suggested that the main factors which made this possible were probably the different rooting depths of the two crops and their different growth cycles.

In agreement with the earlier experiments, mixtures which consisted of two-thirds sorghum/one -third beans gave greatest yield increases at high populations and also had a higher optimum population than the pure stands. However, no such trends were apparent in the mixtures which consisted of one-third sorghum/two-thirds beans.

For both species intra-specific competition was greater than inter-specific competition. In contrast to the earlier maize/beans experiments, the relative interspecific competitive abilities of the species changed with change in the initial proportions of species in the mixtures. In the two-thirds sorghum/one-third beans mixtures the sorghum was the more competitive species, whilst in the one-third sorghum/two-thirds beans mixtures the bean was the more competitive species. Also in contrast to the maize/beans experiments, these relative competitive abilities were not affected by change in theoverall plant population pressure.

In a randomized block 3x2 factorial experiment 72 Large White type weaner pigs were individually and restrictedly fed, from 501b (22–7 kg) to approximately 1601b (72–7 kg) live weight, iso-nitrogenous (16% crude protein) maize-based diets (as wet mashes with 2:1 ratios of water to dry food) containing 0–15%, 0–22% or 0–29% tryptophan and either 0–85% or 0–97% lysine. Overall, for the period in its entirety and in the period from the start to 110 lb (50–0 kg) live weight, the diets containing 0–22% and 0–29% tryptophan gave a similar performance. Together they gave a significantly superior performance compared with that obtained from the diets containing 0–15 % tryptophan. Pigs fed the diets containing 0–85 % lysine converted their food better and grew faster than pigs fed the diets containing 0–97 % lysine. These differences were significant (P <0–05) for both parameters in the period from 110 lb (50–0 kg) live weight to the finish of the experiment at 1601b (72–5 kg) live weight and significant (P <0–05) for efficiency of food conversion in the overall experimental period.

Six mature rams were used in a 6 × 6 latin square experiment. They were put on a high concentrate ad lib. diet. Voluntary food intake was measured on the rams which received the following treatments: control, thiouracil, sodium acetate, thyroxine, sodium acetate plus thiouracil and sodium acetate plus thyroxine. Acetate was infused intraruminally at the level of 6·2 g/kg W0·75 per day for 4 successive days. Thyroxine was injected subcutaneously at the level of 0·3, 0·6, 0·9 and 0·9 mg/kg W0·75/day successively. Thiouracil was given orally as the propionyl derivative at a level of 0·03, 0·06, 0·06 and 0·06 g/kg W0·75/day successively.

Respiration rate, pulse rate and rectal temperature were measured before and 1 h after dosing. A period of at least 25 days was allowed between the trials. All the results were calculated as feed intake (g dry matter)/kg W0·75.

Injection of thyroxine, sodium acetate and both together inhibited food intake significantly. Thiouracil showed no significant effect on feed intake but it relieved part of the depression caused by acetate. Pulse rate showed significant differences between treatments but rectal temperature and respiration rate did not change significantly. The results are discussed in the text.