The influence of three rates of each of N, P and K fertilizers on the availability of native and applied Mn to wheat was studied in a field experiment on an alluvial soil of the Indo-Gangetic plain. Increasing dressings of N as ammonium sulphate resulted in consistently higher yields and Mn uptake by the crop. Concentration of Mn in the grain increased with increasing N dressings when native Mn and Mn fertilizer supplied this nutrient but it was unaffected inplants sprayed with Mn. Adding P as superphosphate tended to lower the concentration of Mn in the grain when relying on native or applied Mn but it significantly enhanced the crop yield and total Mn uptake. Applying K as muriate of potash slightly depressed Mn uptake by plants. Potassium had a more pronounced effect in the absence of P fertilizer. The concentration of Mn in thestraw was not significantly affected by N, P and K fertilization.

The progression of sprouting was observed in water-yam (Dioscorea alata) and whiteyam (D. rotundata) tuber pieces planted in moist sawdust. Soon after planting, white callus-like protuberances (sprouting loci) were seen on the tuber surface, followed by the appearance of one or more differentiated shoot buds on the sprouting locus. Sprouting loci appeared more readily on the upper and lower parts of each tuber piece than on the sides. Large tuber pieces sprouted more rapidly, had larger and more numerous sprouting loci, and gave rise to more shoot buds than small tuber pieces.

Anatomical examination showed that the shoot bud resulted from the activity of a layer of meristematic cells lying close to the tuber surface. Extensive cell divisions commenced in this layer after planting, and some of the resulting cells soon differentiated into the shoot bud.

From 1969 to 1971, 743 animals (indigenous Zebu and European dairy cattle, lactating or dry cows and heifers) received oestrous cycle synchronization treatments at government-owned and private ranches and farms in the Tanzanian highlands (West Kilimanjaro); 445 matching animals served as controls. Treatment schedules consisted of chlormadinone acetate (CAP) given daily for 14 days (10 mg/day) orally; or a single CAP injection (50 mg) followed by 4 or 5 days of oral treatment (10 mg/day) 9–12 or 11–15 days later. In addition, some groups received either estradiol valerate (5 mg) together with the CAP injection, or 10 mg/day mestranol from day 11 to 15, together with CAP; one treatment group received 1000 i.u. of HCG after the last CAP medication and were inseminated 12 and 24 h thereafter. Animals were either inseminated or bred naturally. With all treatment schedules, good synchronization, unimpaired fertility and consistently a significant reduction of anoestrus was achieved. Oestrogen treatments had no effects; treatment with 1000 i.u. of HCG was unsuccessful. Management factors, food supply and phase of reproductive life had significant impacts on treatment success and fertility. Synchronization can be used successfully under a wide range of management conditions to unfold existing potentials of artificial insemination in Bos indicus and Bos taurus in the tropics.

Wether sheep were fed on six forage diets, namely, (1) barn-dried low-N hay, (2) barndried low-N hay plus urea infused intraruminally at 12·6 g/24 h, (3) dried sainfoin, (4) dried lucerne, (5) fresh red clover and (6) dried and pelleted red clover. The proportions of amino acids in the diet and in samples of digesta from the duodenum and ileum were determined.

The relative proportions of individual amino acids in the duodenal digesta showed little variation despite the differences in intake and the variation in the proportions of amino acids in the feeds. Only the proportions of methionine, lysine, 2:6 diaminopimelic acid (DAPA) and aminoisobutyric acid (AIB) showed significant (P < 0·01) variation with respect to diet. In the ileal digesta the proportions of methionine, leucine, tyrosine, phenylalanine, glutamic acid, proline, glycine, alanine, AIB and DAPA showed significant variation by diet.

With all diets except lucerne the quantity (g/day) of total amino acids presented at the duodenum was higher than the quantity ingested. There was no correlation between the quantity of total amino acids presented at the duodenum and the quantity disappearing within the small intestine.

The duodenal digesta contained a significantly higher (P < 0·001) proportion of essential amino acids than did the ileal digesta. This difference was most marked with the diets which supplied a low amino acid intake.

With all diets there was little apparent absorption of DAPA in the small intestine.

Welsh mountain sheep were subjected to a number of stressful treatments including minor surgical interference, restrictive handling and adrenaline administration. A decline in plasma calcium concentration was consistently observed following treatment, and this was accompanied by the elevation of plasma NEFA levels. There was a highly significant negative correlation between these changes.

Subcutaneous adipose tissue taken by biopsy from adrenaline-treated sheep showed an increase in calcium concentration which was significantly correlated with the depression of plasma calcium concentration.

In vitro incubation of omental fat with adrenaline showed there was an uptake of calcium by adipose tissue from the medium, which was dependent on time and log dose of adrenaline.

The results are discussed in the light of the possible effect of calcium transport into adipose tissue on calcium homeostasis during periods of severe calcium loss.

Sixteen factorial experiments made from 1969 to 1971 on Northern Ireland pastures measured effects on yield of 0, 180 or 360 kg of N, 0, 30 or 60 kg of P and 0, 150 or 300 kg of K/ha/year both with and without 138,000 1 of slurry/ha.

Without slurry, pasture yield was almost always substantially increased by nitrogen, slightly by potassium and hardly at all by phosphorus. There was a slight positive interaction between nitrogen and potassium, but no other interactions. Response to nitrogen was not linear and therefore was lower than has been obtained in many British trials.

Slurry sharply reduced response to nitrogen and virtually eliminated response to phosphorus and potassium. The NH4-nitrogen content of slurry gave an adequate measure of its effect on pasture yield. The nitrogen, phosphorus and potassium contents of the most concentrated slurries were 15, 29 and 36 times respectively those of the most dilute batches. Hence considerable imprecision is brought into a fertilizer programme when slurry is applied.

As manuring on individual fields can never be precise, the fertilizer phosphorus and potassium needed for grassland is best assessed by considering the farm as a whole. A nutrient balance can show if the farming system is gaining or losing phosphorus and potassium. The amounts of fertilizer phosphorus and potassium needed are those which cover any deficits on the farm as a whole.

Herbage samples from 16 trials testing the effects of N, P and K fertilizers and slurry on grassland were analysed for % N, P, K, Ca, Mg and Na. The data were examined to see if a fertilizer policy designed for optimum yield should be modified after taking pasture mineral content into account.

The correct fertilizer nitrogen policy appears to be to apply nitrogen for the desired yield and to disregard any effects on mineral content. The correct fertilizer policy for phosphorus and potassium is to steer a middle course between depleting soil reserves and accumulating undesirable excesses. The quantities of phosphorus and potassium which should be applied to cut grass to maintain the status quo in the soils are discussed. The amount of phosphorus and potassium added in slurry must be allowed for in this calculation. As the amount of slurry available depends upon the farming system, an effective fertilizer policy for phosphorus and potassium can only be devised by studying the farm as a whole.

At the first cut, the slurries provided on average 115 kg NH4-N/ha, 114 kg K/ha and 86 kg P/ha. Slurry potassium was somewhat less than half as effective as fertilizer potassium in increasing % K in the herbage at the first cut. Furthermore, the herbage recovered only 0·8 kg of the 86 kg of slurry phosphorus. In the short term, slurry was only just over 10% as effective as fertilizer phosphorus, presumably because much phosphorus in it is organically bound.

Twenty-three shorn, adult Merino sheep weighing 22·6–63·1 kg were killed and total skin surface area and eight regional skin surface areas measured after skinning. Bodyfat content (1·9–43·6% of body weight) was estimated from the tritiated-water space and body dimensions were recorded before slaughter.

Body weight was the best single measure for predicting total area and regional areas, and little advantage was gained by using multiple regressions incorporating body weight, fat content and body dimensions. Proportional surface areas of all regions except the neck were significantly related to body weight; positively for the trunk, and negatively for the ear, lower leg, upper leg and head. Equations relating regional surface area (% total area) to body weight are presented.

The effects of low protein and low Ca intakes during pregnancy on the chemical composition and histological appearance of selected bones of ewes and lambs is reported. Twenty-eight 6½-year-old Blackface ewes were used in a 2 x 2 experiment in which semi-purified diets containing 11·8 and 6·0% crude protein and 1·2 and 0·11% Ca in the dry matter were offered in amounts designed to induce a level of undernutrition typical of that experienced by hill sheep in winter. In addition, six sheep were killed in early pregnancy as controls, and a further six were offered, during pregnancy, a conventional diet containing 16% crude protein and 1·9% Ca in the dry matter at levels which prevented energy undernutrition. Ewes and lambs were killed at parturition and the tibias, 3rd ribs and 3rd and 4th lumbar vertebrae removed for chemical and histological examination.

The degree of mineralization of the organic matrix (ash:organic-matter ratio) of the bones at the beginning of pregnancy was poor and it increased in all groups during pregnancy largely irrespective of protein or Ca intake, but especially in the wellnourished sheep. The density of ash in the whole bone (ash:volume ratio) increased in the well-nourished and high-protein groups but did not change in the low-protein groups. These differences were attributable to the effect of protein nutrition on the density of the bone organic matrix (organic matter:volume ratio). Matrix density of the bones of the well-nourished groups increased while that of the low-protein groups decreased.

The histological data essentially confirmed this picture and showed that trabecular or cancellous bone from the tibial head and vertebrae of the low-protein and to a lesser extent the high-protein sheep was porotic, but microscopic assessment conflicted with the chemical findings in that histologically Ca intake appeared to affect bone quality in the vertebrae.

There was considerable variation in the histology of individual lamb bones which was independent of maternal nutritional experiences, but the overall size of the bones was determined by maternal protein nutrition.

Growing wether sheep in metabolism cages were fed a low phosphorus diet (0·75g P/day) supplemented with 1·75 g P/day as either a magnesium phosphate (20·0% Mg, 18·5% P) or a calcium magnesium phosphate (16·1% Ca, 6·0% Mg, 18·5% P). In addition, the magnesium phosphate provided 1·87 g Mg/day and the calcium magnesium phosphate 0·57 g Mg/day. In each case comparisons were made with equivalent amounts of phosphorus and magnesium supplied as dicalcium phosphate (26·5% Ca, 16·0% P) and magnesium oxide (60·0% Mg).

All the supplements resulted in similar positive phosphorus retentions of between 0·77and 0·92 g P/day compared with a daily loss of 0·17 g P/day for the low phosphorus diet. Calcium retentions were higher (1·40 and 1·70 g Ca/day) whendicalcium phosphate rather than the magnesium phosphates (1·16 g Ca/day) were given. Magnesium retentions were increased from 0·1 g Mg/day (unsupplemented) to 0·3–0·4 gMg/day and were similar for both magnesium oxide and the magnesium phosphates.

Blood phosphorus and magnesium concentrations were increased to a similar degree by all forms of supplementation.

Estimates of genotypic and phenotypic variances and covariances were determined for yield and yield components in ten field beans varieties grown at two locations over three seasons.

Substantial amounts of genotypic variance were obtained for yield/plot, 1000-seed weight and number of pods/plant. Variability in number of seeds/pod and much of the variation in yield/plant was attributable to environmental effects and their interaction with the varieties. Seed yield/plot was closely and positively correlated with number of pods/plant and yield/plant, while it was closely and negatively correlated with 1000-seed weight.

The implications of these correlations for selection are discussed.

In each of the crops studied, weeding increased grain yield, weeding 2 weeks after sowing being better than weeding either four or eight weeks after sowing and weeding two and four weeks after sowing being better than weeding either two and eight weeks or four and eight weeks aftersowing. Weeding thrice (two, four and eight weeks after sowing) was significantly superior to all the other weeding treatments. Weeding increased leaf area index, dry weight of side and mainstem and number of mature pods at harvest in green gram and cowpeas. In sorghum, apart from increasing leaf area index, it also increased the length of ears and grain weight per unit lengthof ear. The weeding treatments affected grain yield in cowpeas and green gram due totheir influence on leaf area development, development of the main and side stems and on the number of mature pods produced at harvest. The effect of the weeding treatments on grain yield of sorghum was due to their influence on leaf area development, length of ear and grain weight perunit length of ear.

Results from 10 field experiments are reported. Inra 200, the standard variety in official maize grain trials in Britain, was grown in six of the trials; comparative information was obtained on a range of competitive commercial hybrids and an experimental, early flowering, hybrid. The final plant densities most commonly involved ranged from 5 to 20 plants/m2, with extremes of 2 and 30 plants/m2. The effects of spatial arrangement were also considered in multifactorial or systematic designs; in general, yields increased slightly with more even spacing but no evidence was adduced that spacing, within the limits likely to be encountered in commercial practice, would significantly modify interpretations of density effects.

In all varieties tested, a satisfactory model for the response in yield of grain to changes in plant density was 1/y = a + bx + cx2, where y = grain yield/plant and x = density. Estimated parameter values, however, were not the same for all varieties and significant genotype × density interactions were obtained.

Grain yield/unit area in Inra 200 was maximal at densities of 8–10 plants/m2, but the response curve did not have a pronounced peak; differences in average yieldat densities ranging from 6 to 14 plants/m2 were less than 6%, and yield at 20 plants/m2 was about 80% of the maximum. Other flint × dent hybrids grown commercially for grain in northern areas (Anjou 210, L.G. 11, Warwick SL 209) reached maximum grain yield/unit area at lower densities (6–8 plants/m2), and the decline in yield with increasing density was much more marked than in Inra 200. In contrast, an earlier flowering, shorter growing, experimental hybrid (ARC 51 A) did not reach maximum yield until density was raised to 14 plants/m2, and was even more tolerant of high plant densities than Inra 200. With increasing plant density the number of ears/plant declined, falling below 1–0 in Inra 200 at densities in excess of 10 plants/m2, and averaging about 0–8 at plants/m2. Over the range 6–20 plants/m2 shelling percentage was reduced by no more than 4%, but water content of the ear (grain plus rachis) increased significantly with density. In the very early hybrid, ARC 51A, the difference in water content of the ear at 6 and 20 plants/m2 was less than 3%, but in Inra 200 it averaged about 8% and in varieties less tolerant of high densities it was often ofthe order of 15%. These results could be related to the delaying effects of increasing density on time of silk emergence. Relatively, time of pollen shed was little affected by density changes. In Inra 200 the difference in time between mid-anthesis and mid-silk was about 7 days more at 20 plants/m2 than at 6 plants/m2 while in Anjou 210 and Kelvedon 59A the comparable increase was 14 days.

The practical significance of the findings is discussed in relation to current grain and silage maize production practices, and to future breeding and testing programmes in Northern Europe.

In five experiments made at Rothamsted from 1966 to 1970 ‘Nitro-Chalk’ (ammonium nitrate–calcium carbonate mixture, 21% N) was broadcast for grass cut for silage, either in a single dose in spring or divided equally for three cuts. The ‘Nitro-Chalk’ was used to evaluate anhydrous ammonia (82% N) in 1966, anhydrous ammonia and aqueous ammonia (approximately 26% N) in 1967, 1968 and 1969, and anhydrous ammonia, aqueous ammonia and aqueous urea (18% N) in 1970. All these fertilizers were applied to give 125, 250, 375 and 500 kg N/ha, except in 1968 when 250, 375, 500 and 625 kg N/ha were given.

Anhydrous ammonia gave smaller yields (of dry matter) than the other N fertilizers except in 1968, a wet year, when it was at least as good as ‘Nitro-Chalk’, but slightly less good than aqueous ammonia. Yields were larger with autumn- than with springinjected aqueous ammonia and larger with either, than with equivalent single doses of ‘Nitro-Chalk’. Yields with aqueous ammonia were also larger than with ‘Nitro-Chalk’ divided equally for three cuts when more than 375 kg N/ha was tested, but smaller with less. Aqueous urea was as good as a single dose of ‘Nitro-Chalk’ but less good than divided ‘Nitro-Chalk’ in 1970, the only year it was tested. ‘Nitro-Chalk’ divided equally for three cuts gave larger yields than when a single dose of up to 375 kg N/ha was given, but with more N than this a single dose was better.

Apparent recovery of N was least from anhydrous ammonia and differed little between autumn and spring injection in 1968, the only year when a valid comparison was possible. Apparent recoveries of N from autumn and from spring-injected aqueous ammonia and from ‘Nitro-Chalk’ broadcast in a single dose differed little, nor did the proportion of the N recovered at each cut. Recovery from ‘Nitro-Chalk’ broadcast in three equal amounts was more uniform, but little larger.

Judged by yield, no more than 375 kg N/ha was justified; grass given this amount of N either as aqueous ammonia or as ‘Nitro-Chalk’ removed approximately 29 kg of N, 3 kg of P (7 kg P2O6), 26 kg of K (31 kg K2O) and 2 kg of Mg (3 kg MgO) per tonne of dry matter produced.

Variation of cotton yields from year to year has been a major problem in the Sudan Gezira for a long time. Previous studies indicated involvement of pest attack, soil nitrogen levels and lengths of growing season in this and suggested that adequate control of these factorswould lead to consistently high yields. Factorial experiments to test this hypothesis, comparing plots sown in early or late August, with or without frequent insecticide spraying and with orwithout nitrogenous fertilizer were therefore carried out at each of five sites in the Sudan Gezira and the first five years’ results are presented.

There were large, positive responses to nitrogen, spraying and early sowing at all sites. Nitrogen and spraying interacted positively, i.e. the response to nitrogen was much greater on sprayed plots and the response to spraying much greater on fertilized plots. Where plots were sprayed, early sowing also increased the response to nitrogen.

Treatment responses varied from year to year in such a way that the optimum combination resulted not only in much higher average yields but also in greatly improved stability of yield from year to year. The average yields, and the response to nitrogen on sprayed plots, were up to the levels which previous regression studies had estimated would be obtained in the absence of serious pest attack and were similar to peak yields in earlier years. During the course of theseexperiments commercial crop practice has changed towards earlier sowing, heavier nitrogen dressing and more frequent spraying, with apparently beneficial effects on yield and consistency of cropping.

The effects of the sowing date of cotton and application of nitrogenous fertilizer to it on the incidence of insect pests were investigated over a 5-year period. Response to frequent insecticide spraying was also determined and the results were related to previously reported interactions between nitrogen, sowing date and insecticide application in their effects on yield and its year-to-year variation. Numbers of jassids (Empoasca lybica de Berg) and whiteflies (Bemisia tabaci Genn) were considerably greater on the fertilized plots. The pattern of pest population change over the season varied with sowing date and also from year to year as did the relative numbers of jassids and whiteflies. Effects of spraying on the yield obtained under different agronomic treatments and in different years were clearly related to effects on numbers of insect pests.

In a 3-year field experiment, calcined magnesite, Epsom salt, magnesium ammonium phosphate and magnesian limestone gave only small and non-significant increases in yield of a mixed sward but increased the concentration of magnesium in the herbage at all 11 cuts. Magnesianlimestone increased plant magnesium concentrations less than calcined magnesite, magnesium ammonium phosphate or Epsom salt, all of which had a similar effect; each increment of calcined magnesite gave additional increases in magnesium concentration.

Concentration of magnesium in the plant dry matter increased as each season progressed and was linearly related to exchangeable magnesium. At an exchangeable soil magnesium of 1·4 m-equiv./100g soil, Mg concentrations doubled between the first and last cuts. Changes in magnesium concentrations caused by increasing the exchangeable soil magnesium from 0·7 to 1·4 m-equiv./100g soil were less than the seasonal effects.

A study was conducted to determine root development in a stratified and mixed sandy soil in the Sahara sands of Libya. Lucerne (Medicaqo sativa L.), millet (Pennisetum typhoides Burn.)> wheat (Triticum activumL.), grain sorghum (Sorghum bicolor L.), and several other crops were grown on soil that varied in depth to the stratified layers. Root depth and growth were measured by excavating along a representative root at intervals until the crop was mature or until no further root penetration into the subsoil occurred.

Trial plantings showed that none of the root systems of the plants tested could penetrate the stratified layers to any important extent, even with the application of adequate water and fertilizer, although all the layers were sufficiently porous to allow surplus water to drain through them freely. However, a few roots of lucerne, sudangrass, grain sorghum, and millet penetrated 2—3 cm into these layers, and many roots, especially of lucerne, grew into any natural cracks that occurred in these layers. If the compacted layer was loosened by cultivation, all the crops tested rooted normally in the loosened zone.

Three experiments were made, in which two, four and three sheep were given rations in which increasing amounts of linseed oil fatty acids or Unseed oil were incorporated.

Although the changes in the rumen fermentation patterns were similar in all sheep, in some sheep the lipid metabolism in the rumen appeared abnormal, inasmuch as there was considerable accumulation of palmitic and smaller amounts of myristic acid.

It was concluded that the increases in the concentration of palmitic acid were due to an increased rate of its synthesis in the rumen, and an attempt was made to calculate these rates approximately.

The significance of these results within the context of rumen fermentation, methanogenesis and its inhibition were discussed.

In oven-dried whole plants from three regrowths of four varieties of Panicum maximum, leaf and stem of normal and stunted oats at three stages of first growth, leaf and stem of rape and the whole plant of millet, cell wall ranged from 14 to 77% of the organic matter. In vitro digestible cell wall ranged from 13 to 46% of the organic matter and was closely related to the cell wall (residual standard deviation, ± 2·5). In 16 legume hays the average in vitro digestible cell wall was 22·1% of the forage organic matter compared with an average value of 20·5% found previously from in vivo digestibility experiments with legumes. An unsatisfactory feature of the in vitro digestibility determination was that in silages and low quality grass hays, the digestible cell wall was low relative to known in vivo values for these forage types. The separate determinations of cell wall and in vitro digestible cell wall would add to the confidence that can be placed on estimates of in vivo digestibility from laboratory measurements. Often, the determination of cell-wall content is sufficient for this purpose.