K+ uptakes from forty-four arable soils from England by 1 cm portions of the roots of intact onion seedlings during 10 days growth were measured. A single-split-root arrangement was used, enabling the determination of uptake by known surface area of the root. Transpiration was restricted to make K+ diffusion in the soil the predominant supply mechanism. These were compared with calculated values using separately determined K+ diffusion coefficients in the soils.

Two methods were followed, namely (a) measuring K+ diffusion to a hydrogen form of cation exchange resin paper and calculating diffusion coefficients assuming total depletion of the (ammonium acetate) exchangeable K+ at the resin paper: soil boundary; and (b) deriving diffusion coefficients from estimated values of the impedance factor and the measured K+ buffer power of each soil, for 50, 60, 90 and 100% depletion of the initial soil solution K+at the root:soil boundary. None of the predictions adequately accounted for the observed uptake. Calculations of the root:soil boundary concentrations showed a wide range of depletion. Soils with initial soil solution K+ in the range 0.04–0.4 μmoles/ml were depleted of the solution K+ to near zero or even less. A negative concentration of K+ in solution indicates the probable contribution of non-exchangeable K+. When the initial soil solution K+ was more than 0.4 μmoles/ml, the uptake of K+ could be accounted for by 30–85 % depletion at the root:soil boundary.

Partial and multiple regression of the measured uptake on the initial exchangeable K+ content and the initial soil solution K+ concentration were calculated. A simple relationship between the uptake and the exchangeable K+ content accounted for about three-quarters the variance. The uptake was less closely associated with the K+ in solution or its ratio to Ca2+ + Mg2+ in solution. These correlations are discussed from the diffusion point of view and in relation to the usually reported correlations from pot experiments.

Potato yield response to K+ fertilizer additions in field experiments are examined in relation to the supply of K+ by diffusion in the soils. When K+ uptake by 1 cm portion of onion root from the unfertilized soil exceeded l.2 μmoles/10 days, yield response to K+ addition became erratic and occasionally negative.

Populations derived from a diallel set of crosses involving five inbred Upland varieties were tested for bacterial blight resistance at Wad Medani in the Sudan and at Namulonge in Uganda. Four of the varieties carried a known B gene for resistance; no B gene was present in the fifth, which was used as a susceptible parent. The importance of genotype/environment interaction was emphasized and it was found that the B genes did not maintain the same dominance relationships at the two sites.

The Reba gene, B9L, segregated as a gene or ‘effective factor’ of large effect but Mendelian segregation was not discernible in hybrid populations not involving Reba. Most of the genetic variance was accounted for by additivity and dominance. Although statistical analysis failed to reveal epistasis there was a strong interaction in the B2 × B6 cross.

At Namulonge, where it was possible to test for leaf and boll resistance, the proportion of dominant and recessive alleles was the same for both phases of the disease.

The incidence of swayback among lambs in two flocks, previously reported, was reanalysed by a specially developed modification of the probit analysis technique in order to allow for the joint complications of an all-or-none trait and a large number of possible classifications for the animals in each flock. The form of analysis described yields predictions of the probability of swayback among lambs for the given circumstances.

Breed and sire within breed each affected the probability appreciably even when allowance for live weight of ewe and lamb was made. The effects of live weight, though significant in each flock, were not consistent in direction between the flocks. Other significant factors affecting swayback incidence were the manner of rearing the lambs, week of birth, and, in one flock, the sex of the lamb.

Gestating female pigs received either a low or a high intake per day of diets containing either a low or high protein concentration. A change in the composition of both diets occurred after 2 years, when the protein quality of the high protein diet was improved and the energy content of both diets was increased. Vitamin A determinations were carried out on 245 piglet livers and 32 pairs of kidneys and lungs at birth from 47 sows. The livers, kidneys and lungs of 16 sows were also analysed for vitamin A after approximately 4 years on experiment. Vitamin A was detected at birth with antimony trichloride in the liver of the piglet, but not in the kidney or lung. The sow's kidney was found to contain only small amounts and lung tissue only traces.

A dietary vitamin A level of 4800 i.u./kg during the breeding life of healthy sows, or 8600 i.u./day during gestation, was adequate from the point of view of both a constant storage in piglet livers at birth over eight to ten parities and a relatively high concentration remaining in sow livers after that period. This conclusion is in line with recommendations of the Agricultural Research Council (1966).

As a consequence of differences in both the condition of the sows and in their responses in the two periods, the results for each period are presented separately. In the first 2-year period, when the sows received a relatively low intake of dietary protein during gestation (between 248 and 317 g protein/sow/day), and a low energy intake; that is, when protein was used for energy production, the liver vitamin A storage of the piglet at birth was increased by raising either the daily protein intake during gestation to 352 g, or the food intake from 1·8 to 2·3 kg/sow/day. Liver vitamin A and N concentrations were negatively correlated with liver weight, but increasing dietary protein concentration raised liver weight and its vitamin A content. Liver vitamin A per piglet was not affected by litter size.

A conclusion may not be drawn concerning the contribution of dietary energy to the differences in response between periods, because in addition to dietary changes other differences occurred between periods. Nevertheless, in the second 2-year period, when energy intake during gestation was adequate for normal growth and development, a difference of 150 g in protein intake/sow/day (363 g against 208 g) had no effect on liver weight or its vitamin A content. Furthermore, there was no significant treatment effect on total protein or albumin concentrations in the serum of the sow.

The intensive finishing of steers on simple rations of 10% sorghum stubble and 90% sorghum grain plus urea was investigated. Fine grinding of the grain resulted in a lower mean daily intake, but a significantly greater efficiency of conversion of feed to carcass weight gain (P < 0·01) than coarse grinding the grain. Coarse chaffing of the stubble significantly reduced the intake of the stubble in comparison with hammer milling, but had no significant effect on rate of body weight gain, total feed intake or efficiency of feed conversion.

The addition to the ration of either 1 mg of selenium, or 200 mg vitamin E, 200 mg vitamin E and 100 mg vitamin K per day had no significant effect on rate or efficiency of body or carcass weight gain. Seven out of 32 steers which were not injected with 3 million i.u. of vitamin A at the start of the experiment exhibited nyctalopia. None of the 32 steers which received the vitamin A injection had hepatic vitamin A concentrations less than 33 μg/g. Vitamin A injection did not have a significant effect on the rate of body weight gain (mean ±S.E. 1·3 ± 0·03 kg per day), efficiency of feed conversion (10·4 ± 0·16 kg D.M. per kg carcass weight gain), or time to attain slaughter weight (133 ± 3 days). Drenching twice with thiabendazole had no significant effect on rate of body weight gain.

Effects of N as ‘Nitro-chalk’, P as superphosphate, and K as KCl and K2SO4 on ‘available’ P, K and Mg were examined over 14 years. The area was under grass/clover regularly cut 6 times a year.

Soil pH was maintained by annual applications of ‘Nitro-chalk’ supplying an average of 4 cwt CaCO3 and 174 lb N per acre. Superphosphate supplying 43 lb P per acre per annum increased available P (modified Morgan method) appreciably even on plots where more than this quantity was taken off in herbage. Applied N also consistently increased available P. It was thought that this was because P in the root system was rapidly mineralized. Applied K consistently reduced available P because of increased uptake in cut herbage, with no apparent increase in root P for mineralization.

The amount of available K in soils which received no added K was fairly constant over the period for a given N treatment. About 40 lb/acre/annum of K was released by weathering.

There was a very marked interaction effect between rates of N and K fertilizers on available soil K, the large increase in available K where K fertilizer but no N was applied being considerably reduced with increasing N rates. These effects directly reflected uptake of K in cut herbage.

Residual values of applied P, K and Mg on the respective ‘available’ nutrients were considerable and persistent.

Available Mg was reduced by increasing rates of fertilizer N and by fertilizer K.

The potential digestibility of cellulose is defined as the maximum digestibility obtainable when the conditions and duration of digestion are not limiting factors. Techniques for measuring potential cellulose digestibility were examined and the relationship between potential cellulose digestibility and in vivo cellulose digestibility was explored for a range of grasses.

Cellulose digestibility was found to reach a maximum value after 5 days incubation in vitro. No further cellulose was digested when the residues from an initial incubation for 6 days were incubated with a second rumen liquor inoculum. The values measured after a single incubation of 6 days duration were similar to cellulose digestibility coefficients measured by the suspension of ground forage samples in nylon bags in the rumen for 6 days. Plant factors appear to limit further digestion and the residue from prolonged digestion in vitro consisted only of lignified and cutinized tissue. Potential cellulose digestibility measured by either of the above techniques was higher than cellulose digestibility in vivo. The difference varied between forages and when the difference was large, the digestibility of cellulose in faeces was high.

It is suggested that measurements of the potential digestibility of cellulose in feed and faeces may be of use in estimating the digestibility of grazed herbage.

Variety, sowing date, irrigation water and plant spacing were the variables in five experiments over three seasons in southern Arabia. The results are used to develop the idea that morphological change and increase in dry weight—two aspects of the growth of cotton which are often studied separately—must be linked to explain or predict crop performance.

A straight line related the number of flower buds counted at any time to the number of mainstem nodes on a plant. The mainstem was therefore a simple parameter for the effect of age, temperature and water on the development of plant structure. The relationship was explained by a model in which fruiting branches compete with one another. The structure of the crop plants, as measured by the types and number of nodes, developed along a course in time determined by variety and spacing at a rate dependent on temperature. The rate decreased with age, but was independent of the quantity of water available, until a critical amount had been used, when development stopped abruptly.

Accumulated day degrees accounted for the differences between dates of sowing in the subsequent production of nodes. This relationship was consistent with work on temperature elsewhere. Date of sowing effected the position of the first fruiting branch in the variety Bar XL 1 but not in Wild's Early. The position of the first fruiting branch and spacing affected the number of vegetative branches. Wider spaced plants produced flower buds faster only because they had more fruiting branches, a result in turn of more vegetative branches. The ratio between the mean rates of production of nodes on vegetative branches, and on fruiting branches were varietal constants and agreed with results elsewhere in contrasting conditions.

Variety, water and spacing were treatments in two experiments with cotton in 1963 and 1964 in which fruiting points, flowers and bolls were counted and the dry weights and leaf areas of plants were measured at intervals during the season.

Until leaf-area index, L, started to decrease, the equation described how dry weight, W, changed. The equation gave smoothed estimates of crop growth rate, C, which were consistent with estimates of photosynthesis made with de Wit's (1965) model. The relationship between G and L conformed to , derived from Beer's Law, rather than C = aL — bL2 derived from the linear regression of E on L. When L > 3 the crop appeared to use most of the available light, so that C approached a maximum. Treatments initially affected dry-matter production through the numbers and types of branches and nodes, which in turn affected the sinks available and thus the proportion of dry matter reinvested in new leaf. This initial period, when growth was simple to describe in conventional terms, was denned as the vegetative phase of growth.

The start of the reproductive phase of growth overlapped the vegetative phase. The change from one to the other was completed when the rate of dry weight increase of the bolls, CB, equalled C. This indicated that the sink formed by the bolls had increased sufficiently in size to use all the assimilates available for growth. Sink size increased as the crop flowered and was estimated from the product of the number of bolls and the growth rate of a single boll.

When CB equalled C, bolls were shed which prevented the size of the sink to increase beyond the ability of the plant to supply it with assimilates. This agrees with Mason's nutritional theory of boll shedding. Because of the crop's morphology and because age decreased the photosynthesis of the crop, the size of the sink inevitably increased out of phase with the supply of assimilates. The extent to which this was so determined when CB equalled C. It is postulated that environment, genotype and agronomic practice affect yield according to whether they increase or decrease the extent to which the sink size and the supply of assimilates are out of phase.

The biological and economic performance of a cotton crop are examined. The effects of variety, water, sowing date and spacing on crop performance are considered in relation to their effects on crop growth, which had been studied previously, or noted in the literature. Suitable varieties and agronomic practices are discussed. An empirical relationship between available water, dry matter production and yield of seed cotton is evaluated physically and biologically on the basis of Penman's and de Wit's work, and practically in the light of commercial yields and rates of watering.

1. Three methods, based on treatment with neutral detergent or acid detergent, or involving ultrasonic disintegration, are described and compared for the direct estimation of undigested dietary nitrogen in individual samples of sheep faeces. Estimates of the true digestibility of the nitrogen in several sheep diets derived from analyses performed with these methods agreed well with each other, and were in accord with published estimates, derived by extrapolation techniques. Two other methods, based on treatment with phenol–acetic acid–water, and lysozyme–trypsin, respectively, were found to be unsuitable for such estimates.

2. The quantitative distribution of nitrogen between undigested dietary residues, bacterial residues, endogenous debris residues and the water soluble fraction was determined chemically. It was concluded that 57–81% of the non-dietary faecal nitrogen was associated with bacterial material.

3. Indirect evidence suggested that most of the bacterial nitrogen in faeces originated in the rumen.

Increases in nitrite in ten gamma-irradiated soils have been investigated under aerobic conditions up to 7 days after treatment over the range 0·25–2·5 Mrad. The formation of nitrite showed significant correlations with the percentage of soil inorganic carbon and incubation time, and over 100 ppm nitrite-N accumulated within 3 days in Broadmoor series, which contained the most inorganic carbon. Only the very acid series failed to produce nitrite, but formation and persistence was poor in all soils below pH 7.

Leaching with ammonium or nitrate ions after irradiation suggested that microbial reduction of nitrate was the mechanism responsible for nitrite accumulation, rather than inhibition of nitrite oxidation.

Thirty-eight experiments were made on commercial farms to determine the fertilizer requirement of sugar beet grown with farmyard manure (F.Y.M.). They were in two groups; the first (1961–3), with uniformly applied F.Y.M., tested the value of additional fertilizer—nitrogen, phosphate and potash, with and without agricultural salt (crude sodium chloride). The second (1964–7) tested the value of fertilizer N and agricultural salt with and without F.Y.M.

The average economic optimum dressings of fertilizers with F.Y.M. were 0·6 cwt/acre N, 0·3 cwt/acre P2O5, 0·5 cwt/acre K2O, with agricultural salt which largely replaced the need for potash. Chemical analyses of samples of F.Y.M. used in the second group of experiments gave no reliable guide to the requirement of additional nitrogen or sodium. With adequate P2O5 and K2O, the F.Y.M. increased sugar yield at all except one site, on average equivalent to the increase from 0·3 cwt/acre N. Agricultural salt increased yield economically at most sites except on the silts round the Humber and the Wash. No clear relationship was found between soil analysis for sodium and sugar yield response to agricultural salt, but where the exchangeable soil sodium was less than 25 ppm Na, a response was likely.

Of eight experimental fertilizers (with %N; %P2O5; %K2O ratios of 2:1:1) obtained, four contained triple superphosphate and four mono-urea phosphate; all contained muriate of potash. In the first four, urea supplied either 100, 66, 33 or 0% of the total N (ammonium nitrate supplied the remainder); in the second four, urea and ammonium nitrate supplied only the balance of the N, but in the same proportions.

For barley, each fertilizer was combine-drilled to give 0·5 or 1·0 cwt N/acre. In 1965, much rain fell after drilling, early growth was not harmed and yields from each fertilizer were the same. In 1966, dry weather followed sowing and all fertilizers checked growth; those containing urea killed many plants and diminished yields. Also, yields from the fertilizers containing urea phosphate were larger than from those containing superphosphate; thus urea phosphate was safer than urea alone. For kale, the fertilizers were broadcast in May to give 1·25 or 2·50 cwt N/acre. None seriously diminished plant number and yields from all were similar.

Increasing the proportion of urea in the fertilizers greatly increased %N in the barley grain in 1966, but not in 1965. The crops recovered more N from ammonium nitrate than from urea.

Forty-two Persian Blackhead ewes were used to investigate the effect of three prenatal planes of nutrition 6 weeks before lambing on birth weights and weights at 4 and 12 weeks after birth of their progeny. Nutritional regimes were: good grazing with concentrate supplement (high), good grazing without supplement (medium) and poor grazing without supplement (low). Pastures used were rotationally grazed Pangola grass. High-plane ewes gained significantly more weight during the last 6 weeks of gestation than ewes of the other two groups. Ewes nursing twin lambs lost significantly more weight than ewes nursing singles during the first 4 weeks of lactation. Birth weights of male single lambs and lambs from mature ewes were significantly affected by the prenatal plane of nutrition of the ewe. Lambs from mature ewes weighed significantly more than lambs from maiden ewes and male lambs weighed significantly more than females. Live-weight gains to 4 weeks were significantly affected by prenatal plane of nutrition in all cases. Type of birth was an important factor affecting growth rate and maturity of the ewe less so. Male lambs gained more weight than females during this period. Similar tendencies were apparent during the growth period of 4–12 weeks after birth although rate of gain was lower.

Colchicine induced 64-chromosome white clover was compared at a number of centres with control material (2n = 32), as spaced plants and in broadcast plots with and without companion grasses.

The chromosome-doubled material generally conformed to the well-known reaction of polyploids; the plants were later flowering, had thicker petioles and stolons, broader leaflets and spread less vigorously. Yield of green matter of spaced plants was much less, and in broadcast plots the gross yield (grass + clover) and that of the clover fraction was 7% less than in comparable S. 100 plots. The Finlay-Wilkinson analysis indicated that the chromosome-doubled form did not respond to improved conditions to the same extent as did the control varieties. The presence of grass in the mixture partly compensated for low clover yield, but was insufficient to increase total yields to that of S. 100 controls.

The effect of maturity on the nutritional quality of hay from two alfalfa varieties and four grass species was studied. Each hay was harvested at six different stages of growth, chopped in 4–6 cm lengths, and fed to sheep in quantities of 10% in excess of voluntary intake. The relationship between intake (Y) and digestibility (X) of dry matter was best expressed by regressions of the form: Y = a + b1X + b2X2. The rate of intake declined 1·5 g daily per kg0·75 of body weight per unit decrease in digestibility percentage, and was the same for both alfalfa and grass hays. However, the intake of alfalfa hay was about 10% higher than that of the grass hays of similar digestibility. No differences in the relationship between intake and digestibility (P < 0·05) were observed between the two alfalfa varieties or between the four grass species. When the nutritional quality was expressed as voluntary intake of digestible organic matter daily per kg0·75 of body weight, and time of harvest as day-number of the year, the difference in quality between the six kinds of hay was very small or absent at the beginning of the season (immature to prebloom) and increased toward maturity (dough stage to seed ripe). The decline in quality of alfalfa hay was slower than that of grass hay, and ceased at the mature to overripe stage. On the average, voluntary intake of digestible organic matter declined 0·29 g daily for each day delay in harvest time; this decline varied from 1·2% of the daily intake of digestible organic matter in the beginning of the season to 0·6% at the mature stage. Time of harvest ‘accounted for’ 77–89% of the variation in the quality of the hays. The confounded effect of maturity and leanness on the nutritional quality of the hays was expressed best by concave, second degree polynomial regressions. On the average a unit decline in percent leaves corresponded to a decline of 0·58 g and 0·73 g respectively in the daily intake of digestible organic matter from alfalfa and grass hay. This varied from over 1 g early in the season to less than one tenth of a gram late in the season. The confounded effect of leafiness and growth stage ‘accounted for’ over 75% of the variability in nutritional quality. The relationship between intake and digestibility of the alfalfa and grass hays was used to illustrate how voluntary intake of metabolizable energy (percent of requirement for maintenance) from hay of pure or mixed species may be predicted from in vitro digestibility.

Determinations were made of the available-water capacities and moisture release characteristics of six soils of different texture from Rothamsted, Woburn and Saxmundham. The amount of available water retained in the surface foot of soil ranged from 1·59 in in a sandy loam to 2·75 in in a silt loam under permanent grass. With one exception soils which had received additions of farmyard manure had significantly higher available-water capacities than unmanured soils.

In the course of an experiment designed to study the effects of calcium and phosphorus supplementation on the performance of Scottish Blackface hill ewes, with particular reference to the premature loss of permanent incisor teeth (Gunn, 1969), blood samples were taken from 40 ewes on ten occasions per year over a 4-year period. These were drawn equally from a control and three treatment groups. The control group followed the existing pattern of ewe management on the farm in question by utilizing improved pastures in the spring and early summer, and the treatment groups were a calcium dosed group (12 g calcium carbonate) and a phosphorus dosed group (13 g monosodium phosphate), both of which received the same management, and an undosed group run permanently on the hill. Details of the management and feeding are given in a previous paper (Gunn, 1969). It is sufficient to say here that mineral dosing took place three times per week between mid-February and the end of May and no minerals except salt were added to the concentrated ration fed to all groups at the rate of 10 oz (283 g)/head/day from mid-February to early May. Lambing commenced at about the end of the first week in April.