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.

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.

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.

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.

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.

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.

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.

Eighty Friesian heifers were used to study the effect on milk production of two fixed levels of intake at two stages of the lactation. The rations were estimated to contain 7·9 and 6·2 kg starch equivalent per day, with adequate protein content. The heifers were allocated at random to these two levels of intake for weeks 1·9 of lactation and re-allocated at random to them for weeks 10–18 of lactation. Apart from minor variation the heifers were all fed alike for the remainder of the lactation.

The higher level of feeding increased yields of milk and milk solids and solids-not-fat content in each period but had a smaller effect in mid- than in early lactation, a trend which was shown to continue further into later lactation. It also conserved body reserves.

There was a residual effect in weeks 10–18 from the level of feeding in weeks 1–9 of lactation. This was directly additive to the effects of the current level of feeding. Those animals which had received the higher level of feeding in weeks 1–9 yielded more milk of higher solids-not-fat content than those which had had the lower level of feeding in weeks 1–9. The former group gained less live weight. The effect on milk production over the full lactation from additional feeding in early lactation was three times that observed in early lactation itself. Additional feeding in mid-lactation did not have a residual effect.

The absolute output of milk per unit of food over the 18-week period was greatest for that group which had received the lower level of feeding throughout, followed by the group which received the higher level of feeding in weeks 1–9 only. This superiority was achieved at the expense of body reserves. There was a negative regression of live-weight change on milk production.

Estimated intakes of metabolizable energy agreed closely with requirements for milk production as indicated by the Agricultural Research Council (1965).

Records have been analysed from a small herd in which early weaning was practised. Piglets were weaned when average weight was 7–8 kg, at about 30 days old. Decreased feeding of sows, followed by a short period of fasting, was practised at weaning.

Mean duration of suckling was 31·5 days and mean interval from weaning to oestrus 6·0 days. 93% of sows conceived to service at the first or second heat period. Mean farrowing interval for all sows was 159·7 days (151·9 days for those holding to the first service). Corresponding annual farrowing frequencies, calculated from these figures, are 2·29 and 2·40.

Litter sizes at birth and at weaning were 10·7 and 9·3; corresponding weights of piglets were 1·74 and 7·99 kg. With increase of litter sequence there was a significant decrease of weaning weights; however, there was also an increase in size of litter weaned. Seasonal changes of piglet weight were also found. Early weaning can be considered a useful way to increase production.

Individually-penned adult Merino wethers were fed for 16 weeks on a basal diet of ground, pelleted oat straw or Phalaris straw. Urea was supplied either in a salt-urea block containing 30% urea, or as crystalline urea incorporated into the pellets. A commercial mineral supplement was given during the first 8 weeks, but this was replaced with a laboratory-prepared mineral mix during the second 8 weeks.

Urea supplementation significantly reduced live-weight loss. Over the 16 weeks control sheep lost a mean of 14·5 kg, and supplemented sheep 8·7 kg body weight. Most of this response to urea occurred during the second half of the experimental period.

Food intakes of all sheep increased over the first 2 weeks and then fell. In the unsupplemented groups, levels of intake then remained fairly low, whereas in the sheep fed urea food intakes rose over the final 6 weeks of the experiment. There was a significant linear regression of live-weight change on food intake only with the urea-fed sheep. Intakes of urea-N from the blocks were extremely variable between individual sheep and between periods within sheep; in most cases, however, they appeared to be adequate, as this type of supplementation gave results similar to those obtained by mixing urea throughout the roughage.

There was no significant effect of urea on total wool growth during the experimental period, although wool growth in the supplemented shepp showed a rise towards the end of the experiment. Wool growth in any 4-weekly period was closely related to food intake and live-weight change during that period.

Adult Merino wethers were fed for 16 weeks on diets of oat straw mixed with urea and pelleted (A); oat straw pellets, with access to a salt block (B); oat straw pellets, with access to a salt-urea block (C); Phalaris straw mixed with urea and pelleted (D); and Phalaris straw pellets (E). A commercial mineral supplement was given during the first 8 weeks, and a laboratory-prepared complete mineral supplement supplied during the second 8 weeks. During the fifth to eighth weeks (period I), and the thirteenth to sixteenth weeks (period II), digestibility and balance studies were conducted on sheep from each treatment.

Digestibilities of organic matter (O.M.) and cellulose were generally increased by the addition of urea, but only in one comparison, between diets A and B, was the difference significant. Urea did not significantly affect water intake in relation to food intake.

Urea increased nitrogen (N) intake, faecal and urinary N excretion, and N balance, these effects being more pronounced in period II. All sheep were in negative N status in period I; five of the 12 urea-fed sheep were in positive N status in period II. In diets B and C water intake and urine output were positively related to salt intake, but in no diet was there a significant relation between urinary N excretion and total output of urine.

Sulphur balances (excluding wool) were generally positive and did not improve significantly in period II despite higher sulphur intakes. However, a corresponding increase in the intake of phosphorus, from 0·5 g/day to about 2·0 g/day, brought nearly all sheep from negative to positive phosphorus balance. With the urea diets there was a significant, negative relation between urinary N excretion and phosphorus balance.

Intakes of sodium, potassium, calcium and magnesium appeared to be sufficient in both periods.

It seems likely that the improved response to urea which occurred during the experiment was due to the change in mineral supplementation rather than to adaptation to urea.

The competitive ability of two natural populations of Dactylis glomerata, one from Norway and the other from Portugal, was investigated by growing them in monoculture and together in a mixed sward under different temperature and light regimes. At 7 °C and 8 h photoperiod, the performance of the prostrate Norwegian population grown in mixture with the erect Portuguese population was suppressed as compared with its performance in monoculture. However, at 30 °C and 16 h photoperiod, when the growth habits of these two populations were reversed in comparison to those at 7 °C, the dry weight per plant of the erect Norwegian population was significantly greater in the mixed sward than in monoculture. The dry weight per plant of the Portuguese population did not differ significantly in the two types of sward at either temperature. The results are discussed in relation to competition for light.

Various rates of nitrogen fertilizer were applied in early and late spring to two densities of winter wheat to examine their effects on grain yield and its components. A severe attack of ‘sharp eyespot’ (Rhizoctonia solani) allowed an assessment of the effects of the treatments on the incidence of this disease.

The disease level was much higher where nitrogen was applied early and increased with increase in nitrogen up to 120 units applied; it was slightly higher at the higher density. Grain yield was slightly greater where nitrogen was applied late; early application gave more, but smaller, ears. Main shoots produced at least 70% of the grain in the high-density plots but less than 50% at the low density. Tillers appearing after early March contributed little to grain yield at the higher density but substantially at the lower one. Tillers produced after early April died without heading. In general, the chances of survival of a tiller diminished with delay in the time of its appearance, but some early tillers died while later ones survived and produced ears. The chances of survival of later tillers were greater at low density and high rates of nitrogen.

An experiment was done to see if three varieties of wheat (Jufy I, Yeoman and Cappelle) of widely different tillering propensities differed in their response to early spring application of nitrogen; and, concurrently and conjointly, to assess the effects of unproductive tillers on the growth of productive shoots.

None of the varieties responded to the higher of two levels of nitrogen. The presence of a large number of unproductive tillers appeared to have only a transitory effect on the growth of productive shoots; the latter were able to grow rapidly after the death of tillers and caught up with productive shoots which had been subjected to much less inter-tiller competition.

Suppressed development of edible portion in carcasses from cattle fed hay during the early feeding period (216–340 kg live weight) was followed by compensatory growth during the intermediate (341–409 kg live weight) and final (410–454 kg live weight) periods. However, when silage in the early feeding period was followed by corn concentrate in the intermediate period, no increased ‘edible portion’ development was achieved beyond that produced by continuous silage. The final feeding period (corn concentrate) resulted in a decline in ‘edible portion’ percentage in cattle that previously received concentrate in the intermediate period whereas those that previously received silage remained at about the same percentage.

Cattle fed hay during the early period had less (P > 0·01) carcass weight, less (P > 0·01) fat cover, and more (P > 0·01) reticulo-rumen weight than those fed corn silage for the same period, regardless of slaughter weight.

In the heavy (409 and 454 kg) slaughter groups, cattle fed silage in the early period had higher (P > 0>05) marbling scores than those fed hay. Feeding silage in the intermediate period resulted in lower colour (P > 0·01) and firmness (P > 0·01) scores in the longissimus dorsi muscle than feeding concentrate at that time. The dietary regimes used in these studies resulted in widely varying growth rates among treatments with consequential differences in the average age of the animal groups at slaughter. Therefore, the treatment effects observed seem to be easily explicable on the basis of age differences.

Studies were conducted on the quantity and distribution of fat in 104 half-sib Angus steers which had received various combinations of hay, corn silage, and corn concentrate. Groups were slaughtered at live weights of 216, 284, 340, 409, and 454 kg. The weights of mesenteric, cod, pelvic, kidney and total excess carcass fat were determined. Four linear measurements of subcutaneous fat, three cross-sectional area measurements of intermuscular fat, and the intramuscular fat in seven muscles were observed. The results showed that the feeding regimes had marked influences on the quantity and location of fat, particularly during the early feeding period (216–340 kg live wt.). Feeding hay during this period generally resulted in less fat deposition than feeding corn silage, but the suppression of intramuscular fat deposition was not evident until the animals were subsequently fed higher energy rations to heavier weights (409 and 454 kg). The results indicated that it may be possible to design dietary regimens that suppress waste fat but allow intramuscular fat to be deposited.

The results described above imply that one might influence the deposition of intramuscular fat by proper design of the diet in the early feeding period. Although this possibility exists, it is noted that quantities of chemically extractable fat are not identical with quantities of marbling fat and hence changes in the former may not alter the visible quality of the meat.

The effects of several dietary regimens on the fat-free mass and the dry-matter, ash and potassium-40 content of selected bovine muscles were estimated. Muscle data from 104 half-sib Angus steers were secured at several stages of growth and after several feeding regimens. The results indicated that a hay diet, by comparison to a higher energy silage diet in the early feeding period (216–340 kg live weight), suppressed the fat-free weight, reduced the dry-matter content and increased the ash content of several muscles. These effects of early diet were reversed, however, when the animals were subsequently fed higher-energy rations and slaughtered at heavier weights (409 and 454 kg live weight). Data on potassium-40 gamma emissions by composite muscle samples confirmed the existence of age- or weight-associated decreases and suggested possible dietary influences on potassium levels in bovine muscles. The trends in these data indicated that low dietary energy (hay feeding) in the early feeding period delayed the decline in muscle potassium that normally accompanies maturation.

Results of grain analyses for the content of nitrogen, oil and husk are presented from trials in the F1 and F2 generations of four subject varieties, Condor (Avena sativa), Sierra, Avon and Anita (A. byzantina), nine tester varieties, mainly of north-west European origin and the 36 crosses between them.

Yield of grain crude protein per unit area was positively correlated with grain yield, but nitrogen content of the grain, expressed as a percentage of dry matter, was inversely related to grain yield in both trials. Although the highest values for grain nitrogen content were invariably associated with low grain yields, the highest yielders had average or slightly better than average values for nitrogen content.

Analysis of straw samples from the F2 trial revealed considerable differences between varieties and crosses in the proportion of the total shoot nitrogen (grain + straw) ultimately found in the grain. The proportion of total shoot nitrogen translocated to the grain was positively correlated with the ratio of grain yield to straw yield. High grain yielders took up more nitrogen per unit area from the soil and translocated relatively more nitrogen to the grain from the vegetative tissues than did varieties with low grain yields.

Yields of grain oil were highly positively correlated with yields of grain per unit area but there was no significant regression of oil content on grain yield in either trial. In the F2 trial, oil yield per unit area was positively correlated with oil content of the grain. The variety Avon and its crosses had consistently high oil content.

There was no correlation between yielding ability and husk content of the grain, and some of the highest grain yields were associated with low mean husk contents. High husk content of the grain tended to be associated with stiffer straw.

The results are discussed in relation to improving grain quality in the breeding of new varieties of oats.

Nineteen experiments were made between 1964 and 1967 on fields where previous sugar beet crops showed symptoms of magnesium deficiency. None, 2·5 or 5 cwt/acre kieserite or 20 cwt/acre dolomitic limestone were tested in a factorial design with none or 3 cwt/acre agricultural salt (crude sodium chloride), and 0.8 or 1.2 cwt/acre nitrogen as ‘Nitro-Chalk’. Additional plots tested kainit (7 cwt/acre) and a large dressing of potash (2 cwt/acre) as muriate of potash.

Kieserite and dolomitic limestone increased sugar yield and the most effective dressing was 5 cwt/acre kieserite, which gave 3·1 cwt/acre more sugar than the crop without magnesium fertilizer. Agricultural salt and the larger dressing of nitrogen were profitable, and neither interacted with magnesium on average; the large dressing of potash also increased yield. The magnesium in the kainit increased yield slightly, but the dressing tested supplied too little to satisfy the crop's requirement of magnesium.

Each year in late summer the percentage of plants showing magnesium-deficiency symptoms was recorded, and a sample of twenty-four plants harvested from each of the magnesium treatments and analysed. All the magnesium fertilizers increased the concentration of magnesium in leaves, petioles and roots, and also decreased the number of plants showing deficiency symptoms.

The magnesium concentrations in plants grown without magnesium differed widely and were related both to the yield response to magnesium fertilizer and to the percentage of plants with deficiency symptoms. Both relationships showed a similar ‘transition zone’ from deficiency to adequate supply, for leaves this was 0·2–0·4% Mg, for petioles 0·1–0·2 Mg and for roots 0·075–0·125 % Mg in the dry matter.

Purified diets prepared from finely ground constituents such as starch, casein, gelatine, cellulose, etc., are not readily acceptable by poultry. This is probably due to their powdery nature, for Coates, Kon & Shepheard (1950) found that chicks grew faster when fed a granulated purified diet than when this was fed unprocessed. Granulation was accomplished by mixing the diet with about a third of its weight of water, pressing the resulting paste through a no. 8 sieve and drying the granules at 40 °C.