Eight soil Mn tests, namely, CH3COONH4-, Mg(NO3)2-, H3PO4-, hydroquinone-, 3m-NH4H2PO4-,1·5m-NH4H2PO4- and EDTA-extractable Mn and total Mn were evaluated for their ability to predict Mn uptake by maize (Zea mays L.) on 63 soils of diverse origin. Regression equations were derived by comparing Mn uptake with each test in combination with pH. The best prediction of Mn uptake was provided by a combination of CH3COONH4-extractable Mn and pH; 52·9 % of the variability in Mn uptake was accounted for by these two variables. EDTA and H3PO4-extractable Mn were superior to the other soil Mn tests in predicting Mn uptake.

The effect of soil properties on the extractability of soil Mn by each extractant was analysed statistically. Only with hydroquinone-extractable Mn did the soil variables investigated account for a major portion of the variability in the Mn test. The soil variables most often correlated significantly with the Mn test were pH and total Mn. Organic carbon and clay contents were significant only in determining EDTA- and Mg(NO3)2-extractable Mn, respectively.

Analysis of 21 years' cotton yield data from factorial experiments at three sites in the Sudan Gezira established that yields were significantly increased by nitrogenous fertilizer, that close spacing outyielded wide spacing and that variety X1730A (L type) outyielded variety MSDS (a Sakel type). The effect of nitrogen varied depending on variety and spacing and there were also marked variations from year to year in the effects of nitrogen, spacing, variety and some of the interactions. Year-to-year variations in the overall level of yield were very pronounced and accounted for more than half of the total variance at each site. Causes of year to year variation and the mechanism of the treatmenteffects will be discussed in subsequent papers.

The adaptation of the ruminal flora of sheep to the hydrolysis of biuret has been successfully demonstrated. Bi-weekly measurements of biuretolytic activity of ruminal ingesta were made before, during and after the supplementation of biuret to poor, medium and high-quality rations. Generally no activity was found prior to biuret feeding, but an almost immediate response to biuret feeding occurred which increased progressively with the number of days the animals were fed biuret. The time required to reach maximum activity on very low, medium and somewhat higher protein diets were found to be 15, 30 and 70 days approximately. The supplementation with starch in addition to biuret was found to increase biuretolytic activity. Since neither protein nor starch was found to have any direct effect on biuretolytic activity in vitro, a change in numbers of biuretolytic organisms in the ingesta is discussed as a likely mechanism for the adaptation and de-adaptation of the ruminal flora. A stoichiometric conversion of biuret-N to NH3-N by active ingesta was demonstrated in vitro but was not reflected by the nitrogen levels in vivo. The activity of the ingesta was greatly reduced by straining.

At three sites in the Sudan Gezira the variations in seed cotton yields between 1941 and 1961 were due, in the main, to variations in insect pest damage and, at one site only, to a downward trend in soil nitrogen level.

At each site seed cotton yield was predetermined by total plant top dry weight before the opening of the first cotton bolls. The cotton crop was sown in August. At Turabi in the northern Gezira and at the Gezira Research Station in the south-central Gezira, variations in plant growth up to early October had little effect on subsequent yield. The yield was determined by growth during October, November and December; the total top dry weight at the end of December was much more important than the pattern of growth by which this weight was attained. At these sites yield was much more closely dependent on the amount of leaf recorded as free from pest and disease damage than on total leaf weight. Damage due to jassid (Empoasca lybica), thrips (Caliothrips spp.) and leaf curl accounted for 69% of the year to year yield variation at Turabi. Damage due to jassid and thrips accounted for 56% of the year-to-year variation at the Gezira Research Station.

Severe pest damage was associated with low July plus August rains and high temperatures during the growing season but was not found to be dependent on leaf nitrogen levels.

At Hag Abdulla in the southern Gezira, there was a general downward trend in yields over the years as well as variation from year to year consequent on variations in thrips damage. The downward trend inyields was associated with a trend to lower soil nitrate and plant nitrogen levels which resulted in anearlier cessation of leaf growth in recent years than hitherto.

Variation in the level of pest attack accounted for 61% of the year-to-year variation in nitrogen response at Turabi, while at Hag Abdulla the response to nitrogen was determined by the deleterious effect of thrips and by a trend to increasing response as natural soil nitrate levels declined.

Gezira commercial crop yields were closely correlated with those of the appropriate experimental plots for the years considered (r = 0·859 for the S-type crop, 0·736 for the L-type crop) inspite of some differences in cultural practice. This suggests that the major causes of variation were the same in both cases and that adequate protection against insect pests should do much to prevent the recurrence of seasons of extremely low yield with their serious economic consequences.

Eight feeding trials on cattle showed that the response in live-weight gain was curvilinear when protein or energy level was varied independently in rations based on poor quality roughages to which cereals and groundnut were variously added to give a range of protein and energy intakes. Live-weight gain was increased by 0·12 lb/day for each 0·1 lb additional digestible crude protein/day at levels of intake below 0·7 lb/day and by 0·03 lb/day at higher levels. It was increased by 0·4 lb/day for each additional 0·1 lb starch equivalent daily/100 lb live weight at total intakes below 0·9 lb daily/ 100 lb and by 0·2 lb/day at higher levels. Over the range 0·5–2·0 lb digestible crude protein daily and 0·7–1·2 lb starch equivalent daily/100 lb live weight the effects of these nutrients were additive.

A Latin square nitrogen balance trial demonstrated that a portion of the nitrogen from a protein supplement was retained in the body despite the excretion of the greater part of it in the urine and a further part in the faeces. Nitrogen retention was increased by a supplement of readily available energy through a decrease in urinary nitrogen loss. Nitrogen balance was not increased by a supplement of a fibrous energy source because this induced an increase in faecal nitrogen loss.

In a further feeding trial milk yield was found to be affected in a similar manner to growth. At a yield of 30 lb/day the response per lb starch equivalent added to the diet was 0·5 lb milk including 0·05 lb solids not fat and to an increase of 0·1 lb digestible crude protein daily it was 0·25 lb milk including 0·025 lb solids not fat.

The environmental and genetic control of reproductive growth was studied in S. 170 a variety of Festuca arundinacea Schreb. The variety had induction requirements for short days and low temperatures before inflorescence production could occur, but some genotypes became induced with only short-day treatments. Low temperatures and short days in controlled environment rooms were less effective in bringing about induction than winter conditions in an unheated glasshouse. Only non-additive genetic effects could be shown to be significant in the control of induction requirements. Field studies showed that all inflorescence characters were subject to genetic and genetic x environmental control, and they also indicated that seed weight per inflorescence and seed fertility were most likely to show a response to selection. Diallel analysis under glasshouse conditions showed that the seed fertility and 1000 seed weight of the parental crosses were subject to maternal control, but these effects were not detectable in the next generation. Genetic control of seed fertility and 1000 seed weight in the diallel progeny was mainly additive.

The use of tritiated water to estimate total body-water content of animals experiencing recovery from under-nutrition was studied.

The time for equilibration of tritiated water (TOH), given intraperitoneally, with total body water (TBW) was determined in rabbits and in rats. As judged by the specific activity of blood water, equilibration had occurred by 76–125 min in the rabbit and did not appear to be affected by the plane of nutrition. However, between slaughter groups the specific activity of water obtained from the liver 180 min after injection of TOH was significantly different from the specific activity of water simultaneously obtained from the blood plasma. It is concluded that the liver is not a suitable tissue to use for testing achievement of equilibration.

As judged by the specific activity of blood water compared to that of water from the whole body macerate, equilibration in mature rats either in stable body condition or undergoing rapid compensatory growth occurred in less than 60 min.

A trial comparing TOH-space (corrected by 3% body weight) and actual TBW (by desiccation) was conducted on thirty rabbits which experienced under-nutrition followed by compensatory growth.

Prior to under-nutrition the agreement between actual and estimated TBW was satisfactory and within 2·3%. During compensatory growth the agreement was poor— the TOH values over-estimating actual TBW by about 12%.

A trial with mature rats confirmed the findings with rabbits. For rats in stable body weight the mean estimated TOH-space for fourteen animals was within 1·2% of the actual TBW. For fourteen rats undergoing compensatory growth the mean estimated TOH-space (corrected by 3% body weight) overestimated actual TBW by 6·2%.

Preliminary field studies were carried out to obtain an understanding of the progress of dry-matter accumulation in maize and its end-point at harvest. Dry-matter accumulation and its partition between morphological parts was affected, at various stages of growth, by competition. For maximum total yield per unit area of land, early and rapid development of leaf area was needed to exploit the relatively high net assimilation rate early in the season. This leaf area should persist as long as possibleto maximize leaf area duration. A high total plant yield, and high yield of the important ear component, by the individual plant, was obtained at a plant population of about 40000 per acre. The photosynthetic area of the ear made no significant contribution to cob weight.

Complete diets were given ad libitum to dairy cows over a whole lactation in order to study the voluntary intake of food, lactation performance and efficiency of feed conversion. The effect of including four levels 16, 24, 32 and 40 % of coarsely milled barley straw in the loose mix was studied for diets based mainly on barley or on sugar beet pulp, using a double 4 × 4 Latin square design.

The results confirmed that cows can perform normally when given complete diets for extended periods. Dry matter and digestible energy intake was depressed at the higher levels of straw inclusion and milk butterfat content at the lowest level. The net efficiency of conversion of metabolizable energy (M.E.) into milk was higher at the higher levels of straw. It is concluded that complete diets for the self-feeding of dairy cows should contain a minimum of about 24 % of coarsely milled straw and that estimated metabolizable energy intake and production were depressed by including straw at higher levels.

There was no measurable competition among plants before the four-leaf stage of growth. Competition among plants after the four-leaf stage reduced their average weight and their capacity to store assimilates in the ear after anthesis. As competition intensified total dry-matter yield at lower plant populations approached progressively the yield at the highest plant population. Total whole plant yield per unit area showed an asymptotic response to increase in plant population. Ear yield per unit area showed a parabolic response.

On a unit leaf area basis, the top three leaf laminae apparently contributed about 66% more to cob (rachis + grain) dry weight than the three adjacent leaf laminae immediately below them.

Ear weight per plant was reduced, either (a) by increasing plant population, or (b) by partial defoliation, or (c) by both treatments. In situation (c), i.e. where high plant populations were partially defoliated, cob weight per plant was apparently determined by the amount of available assimilates, and not by ear storage capacity.

The components of yield were studied in a local strain of field beans (Baladi) and two Egyptian varieties (Rebaya 40 and Giza 1). Although no significant differences between varieties were detected in yield per plant, there were differences in components of yield. The Egyptian varieties produced heavier seeds but less pods and seeds than the local strain. The higherpod number in Baladi resulted from a capacity to produce more pods per stem rather than from anability to produce more stems per plant.

Correlations between yield and other plant characters and between components of yield were computed. The path-coefficient analysis was employed to partition the correlation coefficients and to compare the relative importance of the primary yield components in predicting yield. Pods per plant showed the highest correlation with yield and selection for high yield can be based on it. Seed weight was negatively associated with pod number and seeds per pod but the r values were too low to be of predictive value. Multiple correlations indicated that 95–98% of the variability in yield was accounted for by the components pod number, seeds per pod and seed weight.

Results of genetical tests in the Sudan are consistent with those of Arnold (1963), who was unable in Tanzania to transfer the bacterial blight intensifier gene, B6, as a separate entity to local cotton. Confirmation was obtained of the presence of B2 in Mwanza Local. The high resistance of UKBR selections from Mwanza Local was found to result from the interaction of B2 with a gene, or complex of genes, occupying the same locus as B6, or closely linked to it. This B6-type gene was obtained by exerting steady selection pressure over a number of years and gradually increasing resistance; it therefore reveals that during the last 50 years blight resistance in African Uplands has evolved per se. Whether all of Knight's (1957) B genes have arisen in such a way, or by point mutation, is conjectural.

The objective of the investigations reported in this paper was to examine the possibility of using plasma free fatty acid concentrations as a means of estimating food requirements for maintenance purposes in sheep. Estimates derived in these investigations are considered to be less satisfactory than those based on live-weight change. It is concluded, however, that the technique merits further consideration, and that, with more precise knowledge of FFA concentrations in maintenance-fed sheep and of the FFA: food intake response curve, it could provide a useful alternative means of estimating maintenance requirements.

Competition among maize plants in the vegetative stage of growth was postponed by application of nitrogen to the seed bed and by maintaining soil moisture near field capacity. The amount of available nitrogen was a critical factor in determining the effect of the competitive balance between nitrogen and light on maize yield. The supply of either affected the capacity of the crop to utilize the other, but ultimately light became the dominant factor.

Soil moisture deficits of up to 1.0 in from field capacity, in the early stages of vegetative growth, did not reduce dry-matter accumulation and uptake of nitrogen, but in the absence of weed competition and post-planting cultivation soil moisture losses in the early stages of crop growth may be small.

In 1966, maize responded quicker to surface applied than to deep-placed nitrogen and utilized the surface applied nitrogen for dry-matter accumulation more effectively.

Provided that there was initially an adequate supply of nitrogen in the seed bed, there appeared to be no advantage to total yield from application of nitrogen top dressings to maize. In the West Midlands, under conditions of adequate nutrient and soil moisture supply, the optimum plant population for commercial production of forage maize was about 40000 per acre.

Eighty-nine lactating sows, which had farrowed at least once before, were given 140 injections with 2000, 1800 or 1500 i.u. pregnant mare serum hormone. Seventy sows served as controls. 124 injections with 2000 i.u. P.M.S. were followed by 113 oestrus reactions and 88 pregnancies, and 16 injections with 1800 or 1500 i.u. by eleven instances of oestrus and six of pregnancy.

Oestrus occurred in 69% of the positive reactors on the 5th day after injection, and in the rest either earlier or later. The interval between the P.M.S. injection and the onset of oestrus was similar to that between weaning and oestrus in the controls.

The difference between the pregnancy rate of 71% following injection with 2000 i.u. P.M.S. and that of 83% in the control sows from the first oestrus after weaning was found to be statistically highly significant.

Mean litter size and weight were not affected by different time intervals between farrowing and P.M.S. injection, nor were there any statistically significant differences in size and weight of litters at birth or at weaning at 8 weeks of age between those of hormonally treated sowsand the controls.

The shortening of the farrowing interval by P.M.S. injection had no after-effect on the sizeand weight of litters subsequently obtained with or without hormone application.

Injections with 1800 or 1500 i.u. P.M.S. were followed by a reduced pregnancy rate, but the few litters thus obtained were similar in mean size and weight to those obtained with 2000 i.u.or those of the controls.

Sows that did not come on heat or become pregnant following P.M.S. injection came into heat at the same times after weaning of their litters as the control sows.

The shortening of the farrowing interval by an average of 22 days was considered to be of sufficiently high economic value to warrant the introduction on the farm where the experiment wasconducted of the routine application of 2000 i.u. P.M.S. to all gilts and sows on the 28th day after farrowing.

A subclinical calcium or phosphorus dietary deficiency on many hill pastures and a relationship between this and the premature loss of permanent incisor teeth are postulated. The effects of small individual supplements of calcium (12 g calcium carbonate suspended in water) or phosphorus (13 g monosodium phosphate in solution) supplied three times a week between mid-February and the end of May to Scottish Blackface ewes which grazed reseeded pasture in April and May were compared with those of no mineral supplement and with those of no mineral supplementon hill pastures throughout.

Neither supplement had any significant effect on the number or weights of lambs born or reared on reseeded pastures. Both resulted in significantly greater ewe live-weight gain during the treatment period, in a significant improvement in the firmness and permanence of the incisor teeth, and in significantly higher serum Ca levels during lactation. All effects increased with advancing age.

The use of hill pastures during late pregnancy and early lactation without any mineral supplement could result in significantly poorer ewe live-weight gain during the treatment period depending on season. This was also associated with significantly lighter single lambs at 6 weeks and with slower deterioration of the incisor teeth.

It is suggested that minerals lost from the body during lactation on reseeded pastures are not replaced during the autumn recovery period on hill pastures and that a gradual depletion occurs throughout life, leading possibly to demineralization of the alveolar bone and premature loss of the incisor teeth. It is suggested that this is indicative of a higher mineral requirement for maintenance of the permanent dentition than is necessary for normal acceptable growth andreproductive performance. Mineral content of hill herbage may therefore be too low to supply requirements at the levels of OM intake normal on hill pastures.

The digestibility of fats differing in glyceride structure has been investigated, the fats used being natural lard, interesterified lard and beef tallow. Natural lard was found to be better digested than interesterified lard which in turn was better digested than beef tallow, the differences being the result of differences in the digestibility of the saturated fatty acids. The digestibility of palmitic acid was found to be dependent upon its positioning within the glyceride molecule, absorption being greatest when it was esterified in the β-position. The positional distribution of stearic acid was thought not to be the factor limiting the extent of its absorption in the given circumstances. The fats did not differ in their effects upon growth performance or carcass composition and differences in the digestibility of the fats were not reflected in the quality of the carcass backfat. It was demonstrated that increasing the nutrient density of diets through the addition of fat, together with careful regulation of nutrient intake, resulted in improved growth performance and carcass composition.

Flocks of 9-month-old Merino and Border Leicester & Merino sheep were sampled over the full range of body weights present within flocks. Six pairs of ewes and wethers of equal body weight were taken. The sheep were weighed and slaughtered after a 36 h fast. Total weights of blood, skin, head, feet, internal organs and carcasses were obtained for each animal. Each component was analysed for ash, crude protein, ether extract and total energy. Half of each carcass was dissected into bone, muscle, fat and waste.

The compositions of the sheep were compared by regression analyses of weights of body components on empty body weight (EBW) between the four groups and by means of percentages of EBW. There were highly significant linear relationships between both fresh and dry weights of body components, carcass components, and chemical components with EBW; moisture content was not related to EBW. Rates of change with EBW in weights of body components, or in amounts of ash, crude protein, ether extract and energy were the same for all groups of sheep with the exceptions of bone and skin ether extract (EE) weight. However, intercepts of regression lines frequently differed, indicating that body composition differed between groups at the same EBW.

All groups had the same dry weight of blood, internal organs and muscle, weight of ether extract, and total energy in the whole body at the same EBW. Border Leicester × Merinos had lighter skins with less wool, but their carcass weights were higher than Merinos. There were other differences between breeds in the chemical composition of individual components. Wethers had heavier head + feet weights and carcass bone than had ewes. There were also some sex differences in chemical composition of body components. In general, there were fewer sex than breed differences in body composition. The breed differences cannot be explained on the basis of early and later maturing types.

A total of 512 pigs were given from 50 lb live weight one of 16 diets, i.e. with 4 lysine levels at each of 12, 14, 16 and 18% protein, at one of 4 levels of intake. They were killed at 100, 150, 200 or 250 lb live weight.

Live-weight gain was not improved significantly by increasing the protein level above 16, 14, 12and 12%, respectively, for the 50–100, 100–150, 150–200and200–2501bstages. However, conversion of feed to live-weight gain was improved significantly during the 50–100 lb stage by increasing the protein to 18%. Gain in lean meat and in the efficiency of conversion of feed to lean meat were improved by increasing the above protein levels slightly.

Live-weight gain was not improved significantly by increasing the lysine level above 1·04, 0·74, 0·70 and 0·59%, respectively, for the 50–100, 100–150, 150–200 and 200–250 lb stages. However, conversion of feed to live-weight gain was improved significantly during the 50–100 lb stage by increasing the lysine level to 1·22%. Raising the lysine level at each level of protein had no significant effect on the rate and efficiency of lean meat gain.

Live-weight gain was significantly improved by increasing the level of feed intake almost to ad libitum levels for the 50–100, 100–150 and 150–200 lb stages. There was a suggestion of a similar effect in the 200–250 lb pigs although it was not statistically significant. Conversion of feed to live-weight gain was improved in the 50–100 lb pigs only by increasing the level of feed intake: in the older pigs increasing the level of feed intake caused a worsening in feed conversion ratio. Increasing the level of feed intake gave a significant improvement in rate of lean meat gain but a significant worsening in the efficiency of conversion of feed to lean meat during all stages up to 200 lb.

Interaction effects of these factors and sex, on growth performance, are described.

On three occasions in May—July one half of a ryegrass pasture was grazed intensively by cattle and the other was mown. In August and September these areas, designated fouled (F) and clean (C) respectively, were each strip-grazed by two groups of five cows. One group on each area had a herbage allowance of 11·4 kg dry matter per cow per day (C11 and F11) and the other 20·4 kg (C20 and F20).

Before the August-September grazing the fouled area had 2·8% of its surface covered by faeces. After this grazing 23 % of the F n area and 34 % of the F20 area were classified as having been rejected by the cows. However, the upper parts of the sward on these rejected areas were in fact grazed. There were only small differences in N and soluble-carbohydrate contents between the herbages offered and rejected.

Organic-matter digestibility (%) and intake (kg/cow per day) for the four groups were: C11, 73·0 and 10·5; C20, 74·9 and 11·7; F11 , 74·4 and 9·6; F20, 77·0 and 10·6. The C11 cows consumed all the herbage allowed to them, but the F11 rejected 13%. Digestible organic matter intake was affected more by grazing intensity than by fouling; this was the case also for milk yield, milk composition and the live-weight change of the cows.