Experiments were made to compare the practices of planting yam at the onset of the dry season (November) or at the beginning of the rains (February). Setts were also planted in February after pre-sprouting either outdoors from November/December, or indoors without water from November. Comparisons were also made between plots that were harvested first in mid-season and again at the end of the season (doubleharvesting), and plots that were harvested only at the end of the season (singleharvesting).

Setts that were pre-sprouted outdoors had low percentage emergence, produced weak plants, and yielded poorly whether double-harvested or single-harvested. Setts prepared and planted in the field in November emerged over a very long time, and attained half-maximum emergence only 10–19 days earlier than setts prepared and planted in February. Whether in double-harvesting or in single-harvesting, tuber yield/sett for the November planting was significantly greater than for pre-sprouted plantings, but not greater than for the direct February planting. The first harvest of the November planting had more mature tubers and a higher percentage of marketable tubers than the others. In all treatments, single-harvesting resulted in slightly greater yield than double-harvesting, but the differences were not significant. Each second-harvest tuber from double-harvesting was more amorphous in shape, more woody, and had more eyes (buds) on it than the single-harvest tuber. It is concluded that for efficiency of land utilization, February planting is preferable to November planting, and that singleharvesting is likely to be more economical than double-harvesting.

1. Sixty-two commercial sows with a history of sterility were served either less than 7 days or between 12 and 21 days before slaughter and the ovaries examined at autopsy. Thirty-eight sows had apparently normal ovaries and twenty-four abnormal ovaries. Of the sows with normal ovaries, seven out of ten served within 7 days of slaughter were pregnant, but only four out of twenty-two served between 12 and 21 days were pregnant. Two sows were not served because they did not come into oestrus. Of the sows with abnormal ovaries only one out of nineteen which had been served was pregnant. Thus in sows with apparently normal ovaries it is suggested that the main cause of sterility is embryonic mortality, whereas in sows with abnormal ovaries the main cause is lack of fertilization.

2. Sterility associated with cystic ovaries was studied in inbred sows and the oestrous cycle in such sows was found to be irregular, usually with an abnormally long dioestrous interval. There were no cases of nymphomania associated with cystic ovaries.

3. The ovaries of ten sterile sows were examined by successive observational laparotomies. In some cases cysts were present together with apparently normal ovulations and it is suggested that the cysts developed from follicles which failed to rupture. In other cases cyclical growth and regression of cysts occurs without ovulations, whereas in others where the cysts are very large (30-50 cm. in diameter) the cysts may be permanent structures. Sows with large multiple cysts frequently show no signs of oestrus and it seems likely that the breakdown in the ovulation process starts with irregular ovulations and tends to proceed towards the development of these large multiple cysts.

4. Intravenous injections of Prolan (l.h.) had no effect on the ovarian cysts. Implantation of stilboestrol tablets reduced the cystic condition but the treated sows did not come into oestrus although corpora lutea were found in the ovaries at autopsy. Intramuscular injections of stilboestrol also reduced the cystic condition and in one case a sow actually became pregnant.

5. No response was obtained to p.m.s. injections in sows in which the ovaries had reverted to an infantile condition.

6. Cystic ovaries were produced by subcutaneous injections of progesterone and these closely resembled those found in sterile sows. The ovaries of gilts with progesterone-induced cysts tended to revert to normal after the cessation of the injections but the fertility of the gilts was low due to failure of fertilization.

7. Preliminary attempts to graft ovaries met with little success probably due to immunological reaction against and imperfect vascularization of the grafts. Further attempts were postponed pending the results of trials with sheep using a different grafting technique.

8. Evidence as to the effect of fatness in causing sterility in gilts was obtained from the records of the National Pig Breeders' Association. Two overfat experimental gilts which did not come into oestrus were found to have apparently normal ovaries at autopsy and a third came into oestrus and was mated after a period on a submaintenancediet, but though it ovulated normally the ova were unfertilized.

Rice was grown in an inland valley (fadama) region of central Nigeria. Plots were cultivated using oxen either in the dry season or at the beginning of the wet season. Around 25% more time was required for dry season cultivation but this enabled an average saving of 53·5 h/ha during the most critical time of the year at the beginning of the wet season. Total time for all operations during the year was similar (2075 and 2150 h/ha for dry and wet season respectively) of which most was spent on weeding (1388 and 1527 h/ha). Weeding time could be reduced by the application of pre-emergence herbicide to 1042 and 1247 h/ha for dry and wet season cultivation respectively. Grain yields were 4·0, 4·8, 4·2 and 4·6 t dry matter/ha for dry season/no herbicide, dry season/herbicide, wet season/no herbicide, and wet season/herbicide respectively. Similarly, straw yields were 4·8, 7·0, 5·7 and 7·4 t/ha. None of the differences in yield was statistically significant.

1. Dry-meal diets based on whitefish meal or soyabean oil meal, balanced in respect of minerals, and containing 28, 23 or 18% crude protein were given to pigs from 10 to 25 lb., and similar diets containing 18% crude protein were given from 25 to 40 lb. From 40 to 100 lb. and from 100 lb. to bacon weight all pigs were given the same diets with 16% crude protein and 14% crude protein, respectively.

2. From 10 to 25 lb. live weight the results showed that:

(a) With diets based on whitefish meal there was an improvement in growth rate of 11% (P < 0·05) and an improvement in feed conversion efficiency of 14% (P < 0·001) when the level of crude protein was increased from 18% to 23%. Growth rate and feed conversion efficiency were not improved further by increasing the level of crude protein from 23 to 28%.

(b) With diets based on soyabean oil meal, feed conversion efficiency and growth rate were not improved by increasing the protein in the diet from 18 to 23%, and performance was similar to that on the 18% protein diet based on whitefish meal. Pigs fed on the soyabean diet containing 28% protein were unthrifty and grew very slowly; some showed gastric ulceration.

(c) Consumption of the diets containing 18% crude protein was 8% higher (P < 0·05) than consumption of the other diets.

(d) Apparent digestibility of the dry matter of the diets, as measured by the chromic oxide marker method, rose as the pigs grew older, and apparent digestibility of the dry matter and crude protein of the diets based on soyabean oil meal was consistently lower than when whitefish meal was the main supplementary source of protein.

A simple model of vernalization, originally developed to quantify the vernalization response of fieldgrown carrots, was fitted to previously published experimental results for winter wheat cv. Norin 27. The optimum temperature for vernalization indicated by the model was c. 5·2 °C, as this induced the fastest progress to final leaf appearance, expressed as the reciprocal of number of days from sowing to final leaf. This rate decreased linearly with temperature rise or fall on either side of the optimum, extrapolating to zero at –4·8 °C (Tmin) and 26·6 °C (Tmax). When all the treatment temperatures and durations were expressed as vernalizing degree days > –4·8 °C (V °C d), there was a linear increase in post-treatment development rate with increasing vernalization up to c. 275 V °C d. Ending the effective treatment duration for vernalization at the estimated time of initiation of the final leaf primordia brought many of the data points closer to the linear trend which described the rest of the data.

Effects of using leaf number, which is linearly related to thermal time, instead of days as the unit of time to compensate for temperature differences in the original experiment were examined. Unvernalized plants had the potential to produce 18 leaves before flowering and therefore rates were expressed as the fraction of the potential total leaf number that each new leaf represented. All plants were assumed to have an initial development rate of 1/18 per leaf. This rate was assumed to increase linearly with time during the vernalizing treatment periods and then remain constant after treatment until the final leaf appeared. Leaf numbers reported from the original experiment were used with these assumptions to estimate the rate at the end of each treatment. The relationship between these rates and treatment temperatures was similar to that for rates based on post-treatment durations. There was an optimum temperature c. 5·5 °C and Tmin and Tmax of –5·1 and 18·8 °C estimated by extrapolating the decreasing linear trends to the base rate of 1/18. When plotted against V °C d calculated from these temperatures, the rates from the full data set were well represented by the model line which had been fitted to the data from just one treatment duration.

The paper examines the statistical properties of criteria currently used to determine the distinctness of herbage varieties and suggests alternatives.

The spatio-temporal variation of leaf chlorophyll content is an important crop phenotypic trait that is of great significance for evaluating crop productivity. This study used a soil-plant analysis development (SPAD) chlorophyll meter for non-destructive monitoring of leaf chlorophyll dynamics to characterize the patterns of spatio-temporal variation in the nutritional status of maize (Zea mays L.) leaves under three nitrogen treatments in two cultivars. The results showed that nitrogen levels could affect the maximum leaf SPAD reading (SPADmax) and the duration of high SPAD reading. A rational model was used to measure the changes in SPAD readings over time in single leaves. This model was suitable for predicting the dynamics of the nutrient status for each leaf position under different nitrogen treatments, and model parameter values were position dependent. SPADmax at each leaf decreased with the reduction of nitrogen supply. Leaves at different positions in both cultivars responded differently to higher nitrogen rates. Lower leaves (8th–10th positions) were more sensitive than the other leaves in response to nitrogen. Monitoring the SPAD reading dynamic of lower leaves could accurately characterize and assess the nitrogen supply in plants. The lower leaves in nitrogen-deficient plants had a shorter duration of high SPAD readings compared to nitrogen-sufficient plants; this physiological mechanism should be studied further. In summary, the spatio-temporal variation of plant nitrogen status in maize was analysed to determine critical leaf positions for potentially assisting in the identification of appropriate agronomic management practices, such as the adjustment of nitrogen rates in late fertilization.

Little information is available on the phenotypic performance of perennial ryegrass varieties when exposed to grazing conditions on commercial grassland farms. Grass varieties are classically evaluated in mechanically defoliated plot systems which, although designed to mimic grazing conditions, do not fully capture the range of stresses or interactions that a sward is subjected to under commercial settings or over any period longer than 4 years. The evolution of technology in the form of PastureBase Ireland has led to agronomic data of individual paddocks being made available for analysis over multiple years. Data used in the current study consisted of dry matter (DM) production and ground score data across a 7-year period from ten perennial ryegrass varieties grown as monocultures in 559 paddocks on 98 commercial farms. The results demonstrated how perennial ryegrass variety is associated with a range of agronomic performance traits on commercial farms; including total and seasonal DM production, grazing DM production and number of grazing events. Varieties with the highest total DM production also had the highest spring and mid-season DM production; autumn DM production was associated with the interaction between variety and year. The highest producing variety in the study, AberGain, produced 1342 kg DM/ha/year more than the mean of all other varieties. Variety differences manifested themselves as swards aged, with some varieties increasing in total DM production while others reduced in total DM production. The current work provides a basis for the consideration of on-farm variety assessment in the composition of future variety evaluation protocols.

A probabilistic crop forecast based on ensembles of crop model output (CMO) estimates offers a myriad of possible realizations and probabilistic forecasts of green water components (precipitation and evapotranspiration), crop yields and green water footprints (GWFs) on monthly or seasonal scales. The present paper presents part of the results of an ongoing study related to the application of ensemble forecasting concepts for agricultural production. The methodology used to produce the ensemble CMO using the ensemble seasonal weather forecasts as the crop model input meteorological data without the perturbation of initial soil or crop conditions is presented and tested for accuracy, as are its results. The selected case study is for winter wheat growth in Austria and Serbia during the 2006–2014 period modelled with the SIRIUS crop model. The historical seasonal forecasts for a 6-month period (1 March-31 August) were collected for the period 2006–2014 and were assimilated from the European Centre for Medium-range Weather Forecast and the Meteorological Archival and Retrieval System. The seasonal ensemble forecasting results obtained for winter wheat phenology dynamics, yield and GWF showed a narrow range of estimates. These results indicate that the use of seasonal weather forecasting in agriculture and its applications for probabilistic crop forecasting can optimize field operations (e.g., soil cultivation, plant protection, fertilizing, irrigation) and takes advantage of the predictions of crop development and yield a few weeks or months in advance.

Progress in politics and science often happens by serendipity, and an unforeseen effect of the 2001 foot and mouth epidemic will be its impact on bovine tuberculosis in three areas. Cattle TB will be much worse, increasing the risk to public health, and ‘the highly emotive and complex issue’ of badgers and TB may be resolved after 30 years controversy. A critical reappraisal of these three areas is worthwhile.

A field experiment conducted for two cropping seasons (1976–7 and 1977–8) showed that a fodder crop of Egyptian clover (Trifolium alexandrinum) increased the grain yield of a subsequently grown maize crop. Lathyrus (Lathyrus sativus) and peas (Pisum sativum) were less effective in this regard.

The effect of undersowing on a spring oat crop with four long-term ley mixtures was investigated. Ryegrass, cocksfoot, timothy and general-purpose mixtures were used; broad red and white clovers were included in all mixtures and two levels of nitrogen applied, no nitrogen (n0) and Nitro-Chalk at 3 cwt./acre.

1. Panicle number was reduced by all the undersown mixtures except when cocksfoot was the only grass sown (mixture B).

2. The weight of individual grains was slightly reduced by undersowing with a ryegrass-dominant general-purpose mixture (D) in the absence of Nitro-Chalk, and there was also an indication of a lowering of the total number of grains per panicle when Nitro-Chalk was applied.

3. All the herbage mixtures reduced the percentage of kernel at both nitrogen levels under the ryegrass-dominant mixture (A), but only at one level of nitrogen when cocksfoot (mixture B) or timothy (mixture C) were the only grasses sown.

1. A survey was made of swede fields in Cumberland and it was found that more than half the gross acreage was affected with Brown Heart to a greater or lesser extent.

2. The water-soluble boron content of soils from affected and non-affected fields was determined. In general the boron content of fields showing Brown Heart was less than 0·30 parts per million.

3. There is a close association between soil texture and the incidence of boron deficiency, a greater proportion of cases occurring on light soils.

4. Recent liming rather than the actual pH. level of the soil appears to be correlated with the occurrence of Brown Heart in the field.

5. It would appear that some prediction of the possibility of Brown Heart occurring might be made from a knowledge of the ‘available boron’ content of the soil taken in conjunction with such factors as the soil-texture and liming history of the field concerned.

Two group-feeding and one individual-feeding experiments were made for 112 and 182 days, respectively, with 76 cross-bred and eight Zebu bulls. Simmental, Friesian and Jersey sire breeds were mated to three Ethiopian Zebu breeds, namely Boran, Horro and Barca, while Zebu bulls were included for comparison purposes in Expt 3. The trials were conducted in confinement at Holetta Research Station, located at 2400 m elevation and having a mean maximum temperature range of 18·7–24 °C. In the group-feeding trials (Expts 1 and 2) a common diet was fed, consisting of native hay (30%) molasses (20%) and a concentrate supplement. In the third experiment, two diets containing 30 and 50% native hay were supplemented by concentrate and fed individually to eight Simmental and eight Friesian cross bulls, while eight Zebus served as a control.

The average daily gains, feed intake and conversion did not differ markedly between Simmental and Friesian crosses, but lower values were generally found for Jersey crosses. Cross-breds outgained Zebus, consumed more feed and converted it more efficiently to live-weight gain. Performance differences were noted between the Zebu breeds as well as some evidence of sire × dam breed interactions. Significantly higher gains were achieved with the low than with the high roughage diet.

The existence of a high degree of variability in all production traits of dairy cattle in tropical countries has been demonstrated. Evidence has been adduced to show that this is due largely to increased environmental variability than to any great inherent differences between animals. The conclusion is drawn that, despite minor differences, the genetics of milk production in tropical dairy cattle is fundamentally very similar to that in European stock.

Continuous records of the temperature of potatoes stored in clamps were made in 1942–3 (one clamp) and in 1943–4 (three clamps). In the first year, the temperatures at various positions in the clamp coverings were also recorded.

The temperature at the middle of the potato heap showed a drift with time similar to that of mean air temperature. Deviations of mean air temperature from smooth trend, lasting for about a week, had no effect on the temperature of the potatoes; longerperiod deviations were reflected in the temperature of the potatoes after a lag of about a week. The difference in weekly mean temperature between potatoes and external air averaged about 1–5° C. in 1943–4. In 1942–3 it was greater, increasing to over 20° C. in April, because bacterial rotting of the potatoes following blight infection increased the rate of heat production and caused the clamp to collapse at the end of April.

1. Waksman's simplified scheme of fractionation was used in attempts to trace the organic transformations occurring in some tropical samples of composts, soils and peats.

2. It was found that a useful partition of the nitrogenous substances into hydrolysable and resistant fractions could be effected by boiling with 5 per cent sulphuric acid for 6 hours.

3. Two profile layers of a black calcareous Trinidadian clay soil were compared with two horizons of a prairie soil examined by Waksman & Stevens. The surface layers of both soils were found to be similar in chemical characters, but the lower subsoil layers of the Trinidadian soil gave evidence of a more advanced and profound degree of organic decomposition.

4. Serial soil samples, taken from eight undisturbed natural profiles representative of humid tropical soil types occurring in Jamaica and Trinidad, were similarly examined.

In continuation of earlier work (2) on the destruction of annual weeds in cereal crops some thirty-four replicated experiments have been carried out during 1934 and 1935 in widely different localities. Besides sulphuric acid, nitric acid, ammonium and sodium hydrogen sulphates and ammonium thiocyanate were tested, while the effect of a wetting agent was also studied.

In every experiment the solution was applied by means of a knapsack sprayer at the rate of 100 gallons per acre. In general at the time of spraying the weeds were in the seedling stage, and the cereal crop not more than 6 in. high. Counts of the weed density were made in order to estimate the degree of control, while in the majority of the trials the yield of the cereal was determined.

Sulphuric acid at a concentration of 9·2 per cent. (1 gm. H2SO4 per 100 c.c.) gave a 90 per cent. control of Brassica arvensis (average of nine experiments) and when a 13·8 per cent, strength was used it gave a 95 per cent, control of Raphanus raphanistrum (average of eight experiments). Nitric acid at equivalent concentrations was slightly but significantly more effective in three out of nine trials for the eradication of these two species. Ammonium hydrogen sulphate (21·6 per cent.), sodium hydrogen sulphate (23·6 per cent.) or ammonium thiocyanate (3–10 per cent.) did not, on the whole, compare favourably with sulphuric acid. Decreasing the concentrations of sulphuric acid by a third resulted in a less effective destruction of Brassica arvensis or Raphanus raphanistrum. This loss of efficiency at the lower concentrations was not corrected by the addition of a wetting agent (Agral 1 at 0·1 per cent.); similar results were obtained for nitric acid.

Maize and cowpea were grown at various replacement ratios (100/0, 67/33, 50/50, 33/67 and 0/100) in field experiments. The experiments were carried out during the early growing seasons of 1977 and 1978 at Ibadan in the rainforest zone of Nigeria. A maize cultivar (FARZ 17) and three cowpea cultivars (Ife brown, New Era and TVu 4557) were used.

Maize sown alone gave a greater yield than all mixtures. The yield of New Era cowpea was no less when grown in mixture with maize than when grown alone; indeed when grown in a 50/50 mixture it was significantly greater.

It has been shown that in this trial the increase in milk yield of the nine cows considered as a herd is within the limits normally expected in the case of thrice-daily milking.

The increase in the case of the heifers is below expectation, and the probable reasons for this are indicated.

The effect of three 8-hour intervals on butter-fat percentage has been studied, and it is shown that as far as the individual cows are concerned there is little difference between the number of low fats produced under thrice milking at equal intervals and twice milking at unequal intervals in the case of the herds specified. It is shown that the reason for the bulk milk of the thrice-milked cattle maintaining a high standard of fat percentage at each milking is that each individual cow maintains a fairly high level consistently at one specific milking, and that this is not the same milking for each cow.