ALBERT

Beschreibung: It is now generally recognized that the pH of a silage is the best single criterion of its quality. In other words, it is regarded as the best single guide to the type of fermentation that has taken place in the mass in the silo and thus serves to indicate the degree of success achieved in the ensilage process, whatever the crop or its stage of growth. For instance, in the case of silages, made with or without molasses, where the pH is at or below 4·0, the silage would be deemed to be of ‘excellent’ quality, that at 4·0-4·5 would be designated ‘good’, that at 4·5–5·0 only ‘moderate’, and at or above the latter figure the silage would be classified as ‘bad’. To get a complete picture of the chemical changes that have taken place and to assess the feeding value of a silage is quite a different matter and is not the object of the present note.

Beschreibung: Experiments on evaporation from freely drained soils are described. Under isothermal conditions characteristic winter field behaviour is obtained, even when the air drying power is greater than its normal English midsummer value. Characteristic summer field behaviour is obtained when the rapid drying of a thin surface layer is achieved, either by using an extremely high air temperature under ‘isothermal’ conditions, or by raising the surface temperature by means of radiation—the normal method in nature. The effect of a high salt concentration in the soil water is shown to lead to greater evaporation losses and to a tendency for the salt to concentrate in the more salty patches.It is suggested that mulching will only be beneficial during the isothermal part of the year, i.e. when soil surface and air temperature are approximately equal, and that it will have little effect on water conservation where the soil will be self mulched by the action of summer sunshine. The cause of this self-mulching action is briefly considered in the light of our limited knowledge of soil water dynamics; it appears to depend on the existence of a dual mechanism of water movement in soils—as liquid and as vapour—the rates of movement being very different functions of moisture content and moisture gradient.

Beschreibung: 1. Calcium and phosphorus balance experiments with pullets during which the plasma alkali reserve of the birds was followed are described. Evidence is produced in support of the view that the onset of reproductive activity in the pullet is accompanied by an increase in plasma alkali reserve, as well as of calcium retention, provided the ration contains adequate calcium carbonate.2. These high levels of plasma alkali reserve tend to decrease with the beginning of laying, but apparently the plasma alkali reserve of laying birds tends in general to remain higher than that of the non-laying bird or of cocks.3. The possible bearing of these observations on bone mineral composition and Ca/P retention ratios is discussed.4. It is shown that on a cereal ration moderately low in calcium, where the apparent digestibility, of phytic acid phosphorus is of the order of 40–70%, it was not possible to correlate apparent digestibility with the calcium metabolism of shell formation. When the same ration was supplemented with 5% calcium carbonate, so that the apparent digestibility was of the order of 9–25%, then it was possible under circumstances of intense laying to detect a slight increase of apparent digestibility in association with laying.

Beschreibung: An account is given of artificial insemination of 733 grade cows in Kenya from January 1936 to August 1939. 76·8% of the cows inseminated calved, with an average of 1·88 inseminations per conception. The different doses and dilution of sperm used gave very similar results, as did two inseminations, compared with one insemination, in a single heat period.

Beschreibung: The experiments conducted at Ottershaw Park in the years 1937, 1938 and 1939 indicate that for a well-drained sandy loam, under a considerable range of moisture-supply conditions, main-crop potatoes do not respond in the absence of weeds to ridging-up, or to deep or frequent inter-row grubbings, by any increase in yield or in the percentage of ware. The crop showed successful powers of adaptation to a range of contrasting inter-row tillage treatments.The potato crop showed considerable sensitivity to weed competition in the early stages of growth. This indicates that it is of great importance to maintain the crop in a weed-free condition during this early period.Inter-row tillage operations on this type of soil should, therefore, be designed to destroy weeds and to provide moderate cover for the tubers. Intensification of such tillage beyond these limits is not of direct benefit to the plants.No moisture-conservation effect of any importance was produced by a 3 in. soil mulch during dry weather, even when the water-table lay within 4 ft. from the surface.A significant upward movement of water from the water-table to the surface soil was observed, but this was limited to a vertical distance of approximately 4 ft. for the soil type described. Beyond this limit the surface soil was apparently unaffected by the depth of the water-table.These results may not be applicable to heavier soil types. It is probable, however, that they would hold good for most sandy loams.The results indicate the desirability of carrying out further experiments on contrasting British soil types, especially in the important potato-growing areas.

Beschreibung: 1. Blood copper data are reported on ninety-four sheep divided into four experimental groups on a “border-pining” hill-side in Northumberland in 1940, in comparison with more extensive findings reported in 1939.2. The mean value for comparable sheep was 0·080 mg. % in 1940 as compared with 0·086 mg. % in 1939, the overall range, 0·013–0·210 mg.%, being even wider than before.3. Variations between animals comprising a group were as wide as between groups, and blood levels were not affected by moderate variations in Cu intake. Only in young sheep was there any evidence that a mineralized cake supplement, containing copper sufficient to double the natural grazing intake, had any elevating effect on blood copper.4. Variations between values for the same individuals in 1939 and in 1940 were as wide as between different individuals in either year. Over 25% of the sheep showed Cu levels in 1940 falling within ±0·01 mg. % of their 1939 values, but nearly 20% showed figures differing by more than ± 0·05 mg. %, irrespective of differences in group treatments.5. The significance of the figures, for normal. Northumbrian ewes is discussed in relation to those reported for Derbyshire ewes bearing lambs affected with “enzootic ataxia” or “swayback”.

Beschreibung: Evidence is adduced to show that sowing the fertilizer in restricted zones or bands gives higher yields of swedes, sugar beet and mangolds than broadcasting and harrowing in fertilizers.Sowing fertilizer in bands at one or both sides of the seed is the most satisfactory method of application. The bands should be about l½ in. from the seed and an inch or so below it. Placing the bands much further away than 1½ in. gives inferior results.Sowing fertilizer in bands at both sides of the seed involves risk of bad sowing, as, on bad seed beds, clods may jam between the fertilizer coulters even if they are staggered. Sowing fertilizer in a single band at the side of the seed obviates this difficulty and sometimes gives higher yields. It is recommended that for swedes, mangolds and sugar beet, complete fertilizers should be sown in one band about 1 in. below and distant laterally about 1½ in. from the seed.On soils very deficient in one or more nutrients, sowing fertilizer in a band below, but not in contact with the seed, gives very good results, but on most soils it is likely to lead to a poor stand of plant and low yields.Sowing fertilizers in the drills in contact with the seed gives good results on soils acutely deficient in one or more nutrients, but it can only be recommended for specific fertilizers in restricted areas (e.g. super-phosphate can be used in this way for swedes on some soils in Wiltshire and Dorset) since it involves serious risk of impaired germination.

Beschreibung: 1. Biological trials have been carried out to determine the efficacy of petroleum ether as solvent for the extraction of pyrethrum flowers for analysis. 95% of the toxic material was extracted from flowers one year old after only 3 hr. percolation. An extraction period of 8 hr. with petroleum ether is suggested.2. A method of preparing colourless extracts of pyrethrum and analytical data for such extracts are given. They are shown to be of value for the preparation of concentrates of the pyrethrins. The preparation of a colourless concentrate containing 93% of total pyrethrins, as determined by a modified Seil method, is described.

Beschreibung: It has been shown that a diet supplying, in addition to barley meal, weatings and 2% of lucerne meal, 5% of fish meal up to 90 lb. live weight, 2% from 90 to 150 lb. and no protein-rich food from 150 lb. to slaughter at about 200 lb. live weight, will give almost as good results, from the standpoints of mean daily live-weight increase and efficiency of food conversion over the whole period as one that provides 10% of fish meal from weaning to 150 lb. and 5% of a protein-rich food such as ex. soya bean meal from 150 to 200 lb. live weight. The small differences noted in the present trial were not statistically significant. It is true that the reduction of the fish meal supply to 5% or less retards to a significant extent the rate of growth up to 90 lb. live weight, but this initial setback, according to the results of this and the writers' previous investigations, tends to be wiped out during the later stages of feeding.Further, a diet supplying, in addition to cereal, weatings and a small proportion of lucerne meal, as little as 2% of fish meal up to 90 lb. live weight and no protein-rich food at all thereafter has been shown to give results that are not seriously inferior, particularly when viewed against the background of wartime conditions, to those obtained on the standard diet. In this treatment, the protein required for growth beyond 90 lb. live weight was supplied by a diet of barley meal and weatings reinforced by 2% of lucerne meal.

Beschreibung: An investigation of the problem of propinquity has shown that the yield of any unit of 6 in. of drill row of wheat is significantly affected by the number of plants in adjacent units. The “competition correlation”, which measures the intensity of this effect, is greatest with medium plant densities, and low and often insignificant for units of high or low plant density.Competition is primarily underground for water, soil nutriments and soil air; of these, competition for water is most important in determining yield.

Beschreibung: Natural drainage periods, i.e. periods between consecutive cessations of flow of the Rothamsted 20 in. drain gauge, were selected for the months of June, July and August. All periods of from 2 to 13 days were taken.A curvilinear relationship between the difference of rainfall and drainage (deficit) and rainfall was established.Residuals from this curve showed no appreciable correlation with the mean air temperature, but there was some slight evidence that the deficit was increased by a decrease in relative humidity or an increase in wind velocity.The residuals showed little correlation with drainage during the previous 3 weeks.

Beschreibung: 1. In metabolism experiments undertaken to study the channels of elimination of copper under varying conditions, the rabbit was chosen as experimental animal for convenience of manipulation. This choice, although not defeating the main objects of the work, accidentally added valuable informationon the little-known habit of “physiological faecal refection”in this animal.2. On a normal diet of bran and oats, containing the usual traces of copper, the rabbit is in copper equilibrium, excreting as much in faeces and urine as is taken in the food. Urinary elimination is of the order of 0·07–0·38 mg. per litre, but this is very subsidiary to faecal elimination of about 2·5 mg. per 100 g. of dry matter, which may account for even more than 96 % of the total food copper.3. Increase of food copper is not reflected by material increase of urinary output, the higher quantities appearing almost entirely in the faeces. Of 50 mg. of copper or nearly 200 times the normal food intake, as the dissolved sulphate dried on to the food, only 0·1 mg. appeared in the urine, the remainder being slowly excreted in the faeces over the unexpectedly long period of 4 or 5 weeks.

Beschreibung: A micro-pipette for the ultra-mechanical analysis of soils is described. The sources of error in the usual centrifugal methods are discussed and the new method is shown to be simple, accurate and capable of being adopted as a routine method even in the most moderately equipped laboratories. The treatment of the soil with alkaline permanganate to destroy humus does not affect the inorganic soil colloids.

Beschreibung: Calcification on 1% of controlled cod-liver oil was less satisfactory than on 1% of genuine cod-liver oil as judged by radiography at 5 weeks old. Growth rates were not significantly different.⅔ of 1% of the genuine cod-liver oil promoted calcification as satisfactorily as (and significantly better on one diet than) 1% of controlled oil. The mean tarso-metatarsal distances on ⅔ of 1% of controlled oil were too wide for the calcification to be regarded as normal. It has thus been shown that satisfactory growth is no criteria of adequate calcification and bone structure.From the age of 6—16 weeks, ⅔ of 1% of controlled cod-liver oil mixture was not adequate, as demonstrated by radiographic examination, for optimal calcification; but using the criteria of naked eye examination and weight, no significant difference would have been found between genuine cod-liver oil and the controlled mixture. These birds showing subnormal calcification could not be expected to stand up well to the strain of laying, which puts heavy demands upon the calcium metabolism.

Beschreibung: 1. The accurate measurement of the amount of bone, muscle and fat in the bodies of meat animals is of considerable importance in all technical studies relating to carcass quality. Chemical analysis and laboratory dissection of complete animals are associated with disadvantages which preclude their extensive use. Material derived from nutritional experiments has provided the opportunity for statistical investigation of the possibility of using sample joints and carcass measurements as indices of the composition of bacon pigs of 200 lb. live weight. The extent and nature of the variation in the composition of the pigs concerned adds to the significance of the results obtained.2. The total weight of bone, muscle and fat in the bacon-pig carcass can be estimated with a high degree of accuracy from the respective weights of these tissues in either the loin or the leg. The combination of these two joints provide even higher correlations in each case than either one alone. In all cases the correlation coefficients approach unity and are strongly significant at the 1% point. For the combined joints the values of r for bone, muscle and fat respectively are +0·9444, + 0·9765 and +0·9750. Regression functions have been developed for the purpose of estimating carcass composition from these joints.

Beschreibung: Five inbred Large Whites from the same strain as used by McMeekan (1940) were reared on a High Plane of nutrition to approximately 330 lb. live weight at which one was killed as a control. The rest were put on to a submaintenance diet of straw and water and killed successively at roughly equal intervals in live weight between 330 and 200 lb. The weights of blood, organs and offals were determined and the carcasses were jointed and completely dissected into their constituent tissues. The total weights of each and the weights within the various joints were recorded.(1) Organs. The early-maturing organs, brain, eyes, etc., continued to grow. Other organs like the heart, liver, lungs, etc., suffered a greater or less degree of atrophy which was probably determined by a suspension of their functions.(2) Carcass composition. The tissues of the carcass were affected in reverse order to their development, i.e. fat most, muscle less and bone least. Bone continued to grow in the earlier stages of submaintenance.

Beschreibung: 1. Study of the automatic records shows:(a) There is a seasonal change in the drainage response after rain which can be almost wholly ascribed to viscosity changes arising from seasonal changes of soil temperature (p. 77).(b) Evaporation occurring after a fall of rain has no measurable effect on the drainage response to that rain (pp. 78, 87).(c) The maximum drainage rates for the 20 in. gauge are much larger than those for the deeper gauges. The maxima change seasonally and are again primarily dependent on viscosity (p. 78).(d) There is no marked change in the field capacity of the gauge during the year. The air-filled pore space at field capacity may change by about 15% of its average value (p. 81).

Beschreibung: The discrepancies between nursery plots and field plots, found by previous workers when investigating yield problems with wheat, are discussed. The reason for these differences is given, and the true optimum plant density identified.It is shown that the intensity of competition for water and soil nutriments influences the optimum plant density, and that a high intensity of competition is associated with a low optimum plant density. A summary of literature is given, and the varying values for the optimum seed rates in different parts of the world interpreted in the light of water and soil nutriment supplies.

Beschreibung: The haemoglobin values for the blood of clinically normal cows and ewes over England and Wales are very similar, with a mean value around 11·5 g. per 100 ml. Although the extreme range is wide, about 8–17 g., the distribution of values is such that the common normal range may be taken as 9·5–13·5 g. per 100 ml. There is no striking difference in age groups.Metabolic disorders such as ‘milk fever’ and ‘grass tetany’ in cows and ‘pregnancy toxaemia’ in ewes have no specific effect on haemoglobin level. Chronic hypoglycaemic ketosis of the dairy cow leads to progressive anaemia in which levels down to 6 g. per 100 ml. were found. Border or Northumbrian ‘pining’ of sheep is accompanied by an even more pronounced progressive anaemia, values as low as 3·2 g. per 100 ml. being encountered.It is a pleasure to acknowledge the technical assistance of Mr F. J. Salt and the direction and interest of Dr H. H. Green in the main programme from which the protocols were drawn.

Beschreibung: By growing peas in water cultures with carefully regulated amounts of manganese, the effects of a deficiency of this element have been studied.Complete absence of manganese produces a mottling of the younger leaves and death of the growing tip as previously reported. The plant does not reach the flowering stage.Small amounts of manganese, insufficient for normal requirements, enable increased growth and seed formation. The seeds show marsh spot lesions, the severity of the lesions being greater at the lower manganese concentrations.Normal growth and sound seed are produced when sufficient manganese is present in the nutrient solution.Marsh spot results from a partial deficiency of manganese, the amount available to the plant being sufficient for its normal vegetative requirements but not for healthy seed production.

Beschreibung: Any conclusions drawn from the foregoing results will of course apply only to the necessarily limited range of soils in one county. This range is limited geologically and the Aberdeenshire soils belong largely to the class of light to medium acid soils of low base status. The results for these soils indicate that:(a) The occurrence of grass sickness is not confined to soils of any particular geological origin.(b) The range of textural conditions in the soils examined is a wide one covering loams, sands and peaty types with a few moderately heavy soils. There does not appear to be any relationship between soil texture and the incidence of grass sickness.(c) The soils examined all fall into the class of acid soils and in only a very few—about 5 to 10%—could the addition of lime be considered unnecessary from the general agricultural point of view. As against this there are no striking abnormalities in the ratios of exchangeable or readily soluble cations in the soils, which might serve as a clue to the occurrence of grass sickness. Although little is known of the actual magnesium, manganese and strontium requirements of hay and pasture plants, the range of values covered in the soils examined is sufficiently wide to make it very unlikely that there is any relationship between the incidence of grass sickness and the magnesium, manganese or strontium contents of the soil. In view of the relatively widespread acidity in the soils examined, the possibility of a relationship between the occurrence of grass sickness and soil acidity has to be borne in mind. It would be of value to find out if grass sickness occurs to an appreciable extent on limestone soils, or on soils which have been systematically limed and which have pK values in the neighbourhood of 7.(d) The majority of the soils are, from the general agricultural point of view, somewhat low in readily soluble or available potash and phosphate, but against this about 30% of the soils have satisfactory phosphate contents and about 20% of the ordinary surface soils and 46% of the top 2 in. samples, in which occur the bulk of the plant roots, have satisfactory potash contents. It does not appear likely therefore that the occurrence of grass sickness is to be related directly to the phosphate and potash contents of the soil. As far as reserves of the common plant foods are concerned there is likewise no abnormality which could account for the disease.

Beschreibung: 1. A study of the length of the rachilla in barley shows that it is a varietal character, although strongly affected by environmental factors.2. Rachilla length as a varietal character is affected by the density of the ear and the type of hairs or bristles borne on the rachilla.3. In six-row barleys the length of the rachilla of the lateral spikelet is greater than that of the corresponding median spikelet.4. In the absence of any of the complicating factors mentioned above, rachilla length is inherited as a straightforward quantitative character with an intermediate F1 and no signs of segregation in the F2. The number of major factors when the extremes of length are hybridized appears to be in the neighbourhood of four.5. Hybridization of “Archer” and “Chevallier” type parents has given “dominance” of length and a possible heterotic effect. Long rachilla in these crosses appears to be linked with the “Chevallier” rachilla type.

Beschreibung: 1. Some preliminary observations on the carbonic anhydrase activity of the hen's oviduct are reported.2. It is suggested that the carbonic anhydrase activity of the uterine epithelium is higher than that of the remaining oviducal tissues, and that this activity may play a part in shell secretion.

Beschreibung: 1. These researches were undertaken in order to analyse and define with precision the causes of infertility in a heath soil at Wareham Forest, Dorset.2. The presence of substances actively inimical to growth has been confirmed and the origin of the resulting toxicity established.3. A new technique for biological analysis, the nutrient-agar-film method, makes it possible to estimate the relative degree of toxicity in any given sample, thus facilitating development of methods of laboratory control for elimination and redistribution of the factor or factors responsible.4. It has been proved that the toxic substances are of biological origin and that they operate directly by inhibiting fungal growth. The resulting biological inertia is exemplified by almost complete cessation of cellulose decomposition. Following upon this inertia are indirect effects of a secondary character on growth of the higher plants, in the case of trees restricting root growth, impeding mycorrhiza formation, and curtailing supply of nutritive requirements.5. Justification for the use of organic composts for relieving the observed infertility under field conditions has been provided by laboratory experiments proving that removal of toxicity and profound alteration of the organic substrate and soil bionomics follow addition of compost. Changes so induced are self-propagating and the effects on growth persistent.6. The bearing of these results on fertility in other natural soils and in cultivated soils is discussed.

Beschreibung: 1. Experiments have been carried out to determine the relation between the moisture content of artificially dried grass and the relative humidity of the surrounding atmosphere. This relation is given by a smooth curve. At relative humidities which are typical of outdoor winter conditions in the British Isles (80–90%) the equilibrium moisture content lies between 18 and 30%.2. The rate of moulding is directly related to the relative humidity and therefore to the moisture content of the dried grass. For reasonably safe storage a relative humidity of 67 % should not be exceeded. This corresponds to a moisture content of roughly 13 %. Even this low value does not confer absolute immunity from mould growth.3. The importance of extending storage trials over long periods is stressed. In one instance storage for 300 days was required before mould growth occurred. Neglect of this fact may account for the widely held view that a relative humidity of 70–75 % provides safe storage conditions.4. Attempts to detect mould growth at an early stage by plating methods proved unsuccessful. It is shown that the two earliest and most reliable indications of mould growth are (i) the appearance of visible mycelium when the product is examined under a low-power objective, and (ii) the detection of a musty smell.

Beschreibung: 1. The degree of dispersion on shaking of the heavy clay Gezira soil has been studied in relation to its initial moisture content when it is added to the water. A minimum dispersibility was found at about 7% initial moisture content. Such behaviour is different from that found with certain English soils by Puri & Keen.2. Spontaneous dispersion was studied using the same soil, and by this method it was found that the dispersion decreases with increasing moisture content over a range of zero to 9% moisture.3. This relation between dispersion and water content is discussed in relation to possible effects in the field of practice. Attention is drawn to possible seasonal and daily differences in the effect of rainfall.

Beschreibung: 1. An account is given of the distribution of four separate boulder clays, which form the parent materials of the soils of eastern Kincardineshire.2. The mineral composition of the fine sand fractions of the boulder clays is given.3. The boulder clays, notwithstanding colour similarities, have been shown by mineralogical examination to be distinct.4. The middle boulder clay, largely influenced by rocks of Old Red Sandstone age, is shown to have a higher proportion of ferromagnesian silicate minerals than soils from glacial drifts similarly derived elsewhere in Scotland.

Beschreibung: Failures of cereal crops are occasionally reported, the seed having been dressed with an organo-mercury seed disinfectant and the failures attributed to the dressing. It should be noted, however, that prior to the introduction of the organo-mercury seed dressings similar crop failures had often been recorded, and in many cases failure had been attributed to the dressing which had been applied, or alternatively, to the conditions under which the treated grain had been stored.Reduced germination during storage is common to all agricultural and horticultural seeds, but although the interaction of the factors involved is complex it is generally recognized that for satisfactory germination to be maintained over the maximum period of storage the following conditions should be observed:(1) The seed should be of relatively high initial germination.(2) The moisture content of the seed should approximate to the average for that kind.(3) Storage temperature and humidity should both be relatively low and not subject to wide fluctuation.(4) Ventilation should be adequate.

Beschreibung: The digestibility coefficients of old barley straw fed with a basal ration of oats, bran and maize to two adult horses and of the same straw after treatment by Beckmann's method were ascertained. The coefficients of the nitrogen-free extractives and the crude fibre of the untreated straw were 33·23 and 38·24 respectively and of the treated straw 54·14 and 63·71. There was a reduction in the digestibility of the small quantity of protein and fat.Taking into account the 14·5% of dry matter lost during treatment, the starch equivalent value of the treated material was somewhat higher than that of poor quality meadow hay.The digestibility coefficients were considerably lower for an immature horse previously maintained entirely on fresh grass.

Beschreibung: Pot experiments were made with red clover and with soy beans to determine how far the number of nodules developed was a specific character of the strain of Rhizobium supplied.The number of nodules per gram of root was found to reach a limit specific to each strain. This limiting equilibrium was attained regardless of the size of the root system or the age of plant at which the culture was first supplied, provided enough time were allowed for the limit to be reached.When two different strains were applied to the root surroundings in succession, the final number of nodules was determined by the limit specific to the strain in contact with the roots while these were making most of their growth. In clover this was the second and in soy beans the first applied strain.

Beschreibung: 1. Some recent developments of mineral balance studies on laying fowl are discussed and applied to the interpretation of the average results of twenty-six balance experiments with pullets.2. Several of the experiments are re-examined in detail from the same standpoint.3. A tentative hypothesis covering the relations between the calcium metabolism of shell formation and the calcium-phosphorus metabolism of bone is put forward on the basis of this reconsideration of available data. It is suggested that some degree of mobilization of skeletal calcium is a normal feature of shell formation in the fowl, the fraction of bone mineral material mobilized always having a higher Ca: P ratio than the skeleton as a whole, although the actual ratio may vary with the calcium in the diet and with the form in which the calcium is provided.

Beschreibung: The total nitrogen and carotene have been determined in sixty-three samples of white clover, cocksfoot, rye-grass and timothy taken at different times during the growing season from various localities.Except for rye-grass, there was more carotene in the leaves and stems than in the heads or flowers. A late dressing of ammonium sulphate increased the carotene content of rye-grass by 55 and 17% in the leaves and heads respectively. The effects of lime and slag on the carotene content of cocksfoot and rye-grass were much less marked and there were no obvious effects due to environment.The predominant factor in determining both nitrogen and carotene, which were very closely related, was stage of growth. Grazing effected important increases in both constituents.

Beschreibung: The results obtained from artificial insemination of high grade Merino sheep in Kenya are given and discussed in relation to the season of the year, time of insemination during oestrus, the number of inseminations in each oestrous period and the degree of dilution of sperm.

Beschreibung: 1. The results of a six-year cultivation rotation experiment are given. The rotation used was wheat-mangolds-barley and the seed-beds for these were prepared either by ploughing, using a rotary cultivator or a tractor-drawn grubber.2. The yields of these crops were barely influenced by the depth of ploughing, a 4 in. depth giving throughout the six years just about the same yield as an 8 in. depth. The mangold crop was possibly a little larger on the deeper ploughed plots.3. The mean yields of the seed-beds prepared with the tractor drawn grubber or cultivator followed by harrows etc. were lower than the ploughed seed-beds for all the crops, and this was particularly so on those seed-beds prepared by only one grubbing down to 4 in. depth.4. The mean yields on the seed-beds prepared by the rototiller were lower than on the ploughed seed-beds for wheat and mangolds. If the seed-bed was prepared by rototillage to a depth of 8 in. by going over the land twice, the yield of barley was the same as on the ploughed seed-beds, but was definitely less on the seed-bed rototilled only once to 4 in.5. Seed-beds prepared by the rototiller or grubber have only a small residual effect on the crop yields in the following year.6. It is concluded that the primary function of ploughing is weed control, and that it is only advisable to omit ploughing either if the land is already fairly clean or if the crop will be hoed very early on in its development.7. For wheat and mangolds differences in weed infestation of the seed-bed were probably of greater importance than differences in tilth in so far as the crop yield was concerned. The reverse may have been true for barley.