The 15N isotope was used to compare the uptake and recovery of NH4 + and NO3 – nitrogen by ryegrass growing in soil under controlled simulated spring conditions when the temperature of the root was appreciably lower than that of the shoot. A preference was shown for NH4 + N over N03 – N, particularly at low soil temperatures. The limited uptake of NO3 – does not appear to be due to an inhibitory effect of the NH4 + ion. Ryegrass not only absorbed less N from NO3 – but also translocated a lower percentage of the total nitrogen taken up, to the shoots, the difference being greatest at low soil temperatures.

The results give increasing support for the recommendation that early spring nitrogen should be applied in the NH4 + form. However, the preferential uptake and translocation of NH4 + ions would be of agricultural importance only if it led to an increase in dry-matter production.

The possibility of utilization of leaf wax by N2-fixing micro-organisms on the leaf surface of plants was examined. Chloroform and n-hexane extractable wax could be isolated in significant amounts, ranging between 0·13 and 6·83 g/kg fresh weight from leaves of rice cv. IR·26, wheat cv. Sonalika, jute cv. JRO 632, pigeon pea, Ficus benghalensis, F. religiosa, Eichornia crassipes, Calotropis procera and Cocos nucifera. Pigeon pea and coconut leaves were very rich in wax. The utilization of leaf wax was studied by observing the growth of micro-organisms in Burk's N-less DN2 medium containing 0·025% yeast extract and jute or coconut leaf wax as the sole C source. A 2·fold increase in growth was observed as compared with the control containing no wax. The most growth was exhibited by Pseudomonas azotogensis, P8. azotocolligans, Xanthobacter flavus, Azotobacter paspali 23A and Klebsiella pneumoniae Kupbr2. Utilization of wax components was studied by comparing the amounts of acetylated alcohols and methyl esters of fatty acids in leaves inoculated with those untreated with bacteria after separation of the components by gas chromatography. A strain of K. pneumoniae KUP4, the association of which very remarkably improved the growth of jute plants, was found to utilize particularly C10–, C13– and C16– saturatedfatty acids and C15–, C18–, C25–, C26– and C27– fatty alcohols. It is suggested that leaf wax may act partly as an energy substrate for growth of N2-fixing micro-organisms on the leaf surface.

Results are reported from experiments carried out in three seasons in an environment with mild winters and early springs in which the date of sowing of winter oil-seed rape was varied from early September to early December. Consistently high seed yields were achieved in the late sowings and, in two of the three seasons, delaying sowing beyond early September resulted in significant yield increases. The pattern of dry-matter accumulation and changes in leaf area index were affected to a large extent by sowing date, but no significant effect on total dry-matter production at final harvest was found. Numbers of axillary inflorescences per plant and, in two of the experiments, numbers of fertile pods/m2, were reduced by late sowing, but large increases in numbers of seed per pod were found in each experiment. Mean weight per seed was reduced when sowing was delayed but there was no consistent effect on oil content. Differences were found between cultivars in the extent to which delayed sowing produced increased yields. It is suggested that early spring growth, delayed flowering and reduced reflexion of radiation during flowering were important factors leading to the high yields achieved by late sowings. No interactions were found between sowing date and plant population density for any yield component in one experiment.

The effects of nitrogen applications, ranging from 0 to 25 g N/m2, on the nitrogen uptake and growth of the potato crop was studied in an experiment in both 1983 and 1984. Nitrogen uptake was substantially increased by fertilizer application. At high rates of nitrogen application, the crops took up more than was needed to satisfy their immediate requirements for growth. Initially, this extra nitrogen appeared predominantly in the form of soluble protein in the leaves and nitrate in the stem, with reduced-nitrogen in the tubers becoming a large component during tuber bulking. Application of 25 g N/m2 increased the partitioning of nitrogen to the foliage compared with the tubers.

Tuber yield was considered to be a product of four processes: radiation interception, conversion of intercepted radiation to dry matter, partitioning of dry matter between tubers and the rest of the plant and regulation of tuber dry-matter contents. Maximum tuber yields at final harvest were achieved with 15 g N/m2 in both years. Yield increases were due to increased radiation interception, while the photosynthetic efficiency of the canopy and the dry-matter contents of the tubers were little affected. Increases in light interception, in response to nitrogen, were partially offset by a concomitant decrease in the proportion of the dry weight partitioned to the tubers, particularly during the initial period of tuber bulking. The effect of nitrogen application on tuber yield was, therefore, dependent on the date of harvest.

The results are presented for a 4-year experiment in which three cutting frequency treatments and four nitrogen fertilizer rates were applied on plots sown with perennial ryegrass and one of three varieties of white clover. The cutting frequencies were three, five and tencuts each year, and the nitrogen rates were 0, 150, 300 and 450 kg/ha annually. Two medium-large leaf clover varieties Blanca and Sabeda were compared with the medium-small leaf Aberystwyth S. 100. Comparison of the present results with those from an earlier experiment (Reid, 1978) suggests that, on average over the clover varieties, the inclusion of white clover in the ryegrass sward results in smaller effects of nitrogen application rate and cutting frequency. Decreasing the number of cuts from ten to five gave a marked increase in the dry-matter yield of mixed herbage and of clover at all nitrogen rates, but the decrease from five to three cuts had little additional effect. These results suggest that white clover may be more suited to conservation systems than previously thought, but for optimum production the interval between cuts should not exceed about 5 weeks. The medium-large leaf varieties of white clover did not appear to be in any way superior to the medium-small leaf varieties for conservation systems.

The ley-farming system (integrated cereal and livestock production in which cerealsrotate with self-regenerating pastures) is considered to be of great potential benefit to north Africa and west Asia. In the colder parts of this region (of which north Syria is typical) its application is limited by poor adaptation of commercial medic cultivars (mainly Medicago truncatula and M. littoralis). An extended selection programme hag identified M. rigidula as adapted to the soils and climate of the region but nothing is known of its adaptation to the ley-farming system itself.

An experiment which included 23 selections of M. rigidula and one each of M. rotata and M. noeana was conducted over 3 years during which herbage production, seed yield, and the fate of seeds were observed during the 1st year when pastures were established, the 2nd year when wheat was sown, and the 3rd year when the pasture regenerated. Of the 400–800 kg seed/ha produced in the 1st year an average of 87% remained in the soil in spring of the 3rd year. The weight of seed regenerating in the 3rd year varied from 30 to nearly 170 kg/ha, and herbage production, especially in winter, depended heavily on the number of regenerating seedlings. The most productive regenerating pastures produced nearly 2 t/ha of dried herbage by 1 January, and more than 6 t/ha for the whole growing season.

The results showed that there was sufficient residual and newly produced seed at the end of the 3rd year to be sure that subsequent regeneration would result in similar herbage yields in the 5th year, and that the pasture was assured of long-term persistence. The significance of this for livestock production is discussed, and it is concluded that the results should encourage further investigation of grazing management and socioeconomic factors seen as constraints to introducing the ley-farming system to north Syria.

In field investigations in a sandy-loam soil, probit percentage seedling emergence of commercial and aged seed lots of spring wheat (Triticum aestivum L., cv. Timmo) was a positive linear function of probit percentage laboratory germination and mean soil temperature and a negative linear function of percentage soil moisture content over the ranges 12·1–15·5% moisture content and 7·0–11·0 °C. In a laboratory investigation using the same soil a similar form of relationship was observed in six lots over a range of constant soil moisture contents between 10 and 18% and at constant soil temperatures of 8 and 20 °C. In all cases there was no interaction between any of these determinants of seedling emergence.

Linear relationships between the mean rate of seedling emergence in the field (i.e. reciprocal of mean emergence time) and probit percentage laboratory germination and mean soil temperature were shown, but there was no obvious effect of mean scil moisture content between 12·1 and 15·5% on rate of field emergence. Seed lots of different percentage laboratory germination had the same base tsmperature for emergence (1·9 °C): differences between seed lots in mean emergence rate were due to different thermal time (day-degree) requirements for emergence; the thermal times required were a function of probit percentage germination in a standard laboratory test. The implications of these results in providing better advice on sowing rates are discussed.

Four experiments are reported which studied the effects of date of sowing on the development of winter and spring barley. The first three experiments (1979–80, 1980–1, 1982–3) were carried out at Trefloyne, Tenby and used the varieties Sonja (winter) and Jupiter (spring). The final experiment (1983–4) was carried out in Cambridge using the varieties Igri (winter) and Triumph (spring). A wide range of dates of sowing (August-June) was used and there were considerable differences in temperature between seasons.

In both Sonja and Igri, delaying sowing from August to mid-February reduced the number of mainstem leaves but further delay in sowing increased the number of leaves. In Jupiter, delaying sowing until late October had little effect but further delay consistently reduced the number of leaves. In Triumph, delaying sowing reduced final number of leaves over the whole range (October-May).

In all experiments rate of leaf emergence was characterized by long periods when leaves emerged linearly with time, despite considerable variation in temperature. The only consistent changes in rate of leaf emergence occurred shortly after each equinox, rates slowing in the autumn and increasing in the spring. Rates of leaf emergence were similar in different seasons and sites for similar periods despite differences in temperature.

Initiation of spikolet primordia proceeded linearly with time for most dates of sowing. For winter varieties rates of spikelet initiation increased with delay in sowing provided emergence occurred before the spring equinox. Further delay in sowing decreased the rate of spikelet initiation. In contrast in Jupiter and Triumph the rate increased with each delay in sowing. During periods of low temperature, rate of spikelet initiation slowed but frequently increased to faster rates in succeeding increasing temperatures. Such increasing temperatures had no effect on rate of initiation of later-sown treatments which had not experienced the low temperatures. Effects on spikelet initiation were found when no effects on leaf emergence could be detected.

Initiation of spikelet primordia in all varieties appeared to begin when a fixed number of leaves (different in some varieties) had emerged and end when a fixed number of leaves were left to emerge. Delaying sowing in winter varieties until February and in Jupiter over the whole range reduced the number of leaves emerging during spikelet initiation and was the developmental mechanism through which large differences in date of sowing became small differences in date of anthesis (and grain maturity).

Attempts to relate development to temperature were unsuccessful and the major influence on development appeared to be daylength. Number of emerged mainstem leaves was the most consistent measure of development over sites, seasons and varieties and for winter varieties was influenced by the direction of change of daylength at emergence. Two positive linear relationships between number of leaves and daylength at emergence were found for the periods from summer to winter solstice and from spring equinox to summer solstice. The slope of the latter relationship was greater than the former. For the period from winter solstice to spring equinox a negative linear relationship between number of leaves and daylength at emergence was found. In Triumph number of leaves decreased with decreasing daylength in the autumn and decreased further with increasing daylength. The effects in Jupiter were less clear but there was evidence of the effect of both daylength at emergence and direction of change on number of leaves.

In view of the control of number of leaves exercised by daylength, close negative linear relationships between time from sowing to anthesis and date of sowing were found. The significance of the results for relating agronomic practice to development is discussed.

A study was made in rabbits on the effects of energy intake during pregnanoy on pup birth weight and survival, and on doe body composition and milk output in the ensuing lactation. In addition the experiment examined the effects of varying crudeprotein intakes during lactation on the rate of fat loss of does and the resultant energetic efficiency of milk production.

Forty-seven multiparous cross-bred does were used. They were offered one of two diets in pregnancy, either diet HE (14·8 MJ digestible energy (DE)/kg D.M.) to appetite or diet LE (12·9 MJ DE/kg D.M.) at maintenance levels. After parturition seven does on each treatment were slaughtered and their body composition analysed (control groups). In lactation the remaining does were evenly allocated to receive either diet LE (195 g crude protein (CP)/kg D.M.) or diet HP (240 g CP/kg D.M.) to appetite. Litter sizes were standardized to six pups and litter growth rates were used as an indirect estimate of milk production. Does were then killed, at random, on day 9 or day 18 of lactation to give an estimate of changes in body composition as lactation progressed.

Does offered diet HE during pregnancy had higher carcass fat levels at parturition than their counterparts offered diet LE (496 cf. 370 g/kg carcass D.M. respectively). Litter size was unaffected by dietary treatment during pregnancy but litter weights at birth were significantly greater in HE does (442 cf. 398 g respectively). Pup mortality at birth, however, was also much higher in these animals (28 cf. 9% respectively). Voluntary food intake in early lactation (day 1—9) was depressed by feeding diet HE during pregnanoy. Milk composition was affected by pregnancy diet, with does offered diet HE producing milk containing significantly higher fat levels (HE 123 g fat/kg milk cf. LE 105 g fat/kg milk).

Doe carcass composition changes revealed that fat was usually mobilized in early lactation and gained as lactation progressed independent of dietary treatment. The protein content of the fat-free dry matter appeared to be relatively unaffected by the dietary treatments imposed. The data were used to derive an estimate of the partial efficiency of dietary energy utilization (fc) for milk output and maternal tissue gain. The line of best fit was described by the equation ER = 0·65 (±0·17) MEI-1–25, where ER = milk energy output + carcass energy change and MEI = metabolizable energy intake in MJ.

Samples of pig feed, infested to various known amounts with Acarus siro L., were scanned using an NIR analyser. Visual inspection of the spectra of infested feed did not indicate the presence of mites, but principal components derived from these spectra were correlated with the number of mites. Examination of the spectrum of Ringer solution, and of principal components for both infested feed samples and for mites scanned in isolation, indicated that in infested samples mite haemolymph caused the absorbance maximum for water to be shifted towards the visible end of the spectrum. Simpler calibration models, of the type used by current commercial NIR analysers, were developed which were able to detect and quantify economically significant levels of mites in infested pig feed.

The amylolytic activity of the cytoplasmic fraction prepared from 14 single species of rumen ciliate protozoa and two natural mixed populations has been determined using five different assays. All the protozoa contained an a-amylase and the major product of amylose digestion was maltose. The highest activities were found in Eremoplastron bovis, Diploplastron affine, Ophryoscolex caudatus and Polyplastron multivesiculatum grown in vitro on grass and wholemeal flour and the lowest in Ostracodinium obtusum bilobum and Diplodinium pentacanthum under all growth conditions and in cultured Entodinium bursa and E. caudatum. The maximum activities depended on the substrate and with Eremoplastron bovis varied from 2·3 (with starch grains) to 48·8 (with amylose) μtmol maltose produced/mg protein per h.

The distribution of amylase between various rumen fractions has been determined at three times after feeding in sheep containing no ciliate protozoa or seven different protozoal populations. A method to give maximal release of the enzyme from mixed rumen bacteria was devised and three different assay methods were compared. The total rumen amylase varied by up to 2·6 times and was highest in animals that contained only Entodinium caudatum or natural A- or B-type populations. The distribution of amylase activity between rumen fractions varied considerably with the various protozoal populations, that in the protozoal cytoplasm being highest in animals containing Epidinium ecaudatum caudatum (46–53%) and the natural A- and B-type populations (35–57 %) and lowest in the animals containing no protozoa (3–11 %) or only Ostra-codinium obtusum bilobum (6–21%). The reverse was true for the activity in the bacterial fraction which contained little activity in animals with natural A- and B-type populations and over 58% of the total activity in an animal containing only Entodinium caudatum. The lowest activities in all fractions were obtained 1·5 h after feeding. Comparatively little activity was found in the plant debris or clarified rumen fluid fractions from any animal. Using results obtained previously the ratios of carboxymethylcellulase to amylase activities have been calculated and shown to be highest in the protozoal cyto-plasmic fraction of Diplodinium pentacanthum and Ostracodinium obtusum bilobum and lowest in Entodinium spp., Diploplastron affine and Eremoplastron bovis.

The major portion of nitrogen nutrition of flooded rice is met through the mineralization of organic forms of N present in soil. This is true even when fertilizer nitrogen is added. The mineralization of organic matter under waterlogged conditions is governed mainly by the prevailing chemical and biological conditions. In recent years, attempts have been made to characterize the products of hydrolysis of soil organic nitrogen (Asami & Hara, 1970; Shinde, 1978; Subba Rao & Ghosh, 1981). Information on different fractions of nitrogen in waterlogged rice soils is scanty.

Two experiments are reported which investigated the effects of time and method of crop defoliation and of extending the interval between defoliation and harvest on the relationship between dry-matter percentage and tuber size in Pentland Crown potatoes.

Differences in average tuber dry-matter content between seasons and treatments were large, but the relationship between tuber dry-matter percentage and tuber size was always negatively quadratic. The dry-matter content of tubers of all sizes invariably decreased after defoliation, by about 0·6 % on average for each week that harvest was delayed in 1983 and 0·3 % in 1984. The largest decrease was from 22·7 to 16·7 % over the 10-week period following mechanical defoliation in mid-August 1983. In 1984, chemical defoliation in mid-August gave a smaller decrease than the mechanical method (0·25 and 0·38%/week) but their effects were similar when carried out in mid-September. Water uptake was the main factor responsible for the decrease because evidence showed that fresh weights of tubers increased proportionally following defoliation whilst dry weights remained virtually constant.

Natural senescence was late in both seasons experiments so that the crops foliage was still mostly alive when defoliation occurred, even in September and early October. Thus, the relatively large effects of late defoliation may have been greater than might be expected where haulm senescence is already well advanced by this time and water uptake has almost ceased. Nevertheless, the decline in dry-matter percentage which may occur between defoliation and harvest can be extremely important where potatoes for processing are concerned. It could make them unacceptable for particular outlets and should be considered when defoliation and harvesting programmes are planned.

A field experiment comprising four rates of application of atrazine (0·25, 0·50, 0·75 and 1·0 kg/ha), three times of application (pre-emergence, 10 days after emergence and 20 days after emergence) and two additional treatments of unweeded and weedfree-crop was conducted at the National Dairy Research Institute, Karnal during the rainy seasons of 1979 and 1981. Application of atrazine at 0·25 and 0·5 kg/ha preemergence and 10 days after emergence gave effective control of weeds and resulted in green and dry fodder yields of sorghum similar to weed-free conditions. It was noted that pre-emergence application of the atrazine at 1·0 kg/ha showed a phytotoxic effect on sorghum and resulted in significant reduction in green and dry fodder yields compared with 0·5 kg atrazine/ha.

There is evidence from solution culture studies that ammonium nitrogen is taken up by grass preferentially to NO3-N at low temperatures (Clarkson & Warner, 1979). In addition NH4 ions are less subject to leaching losses or denitrification (Ryden, 1982). It has been speculated therefore that ammonium N could be the best form of nitrogen for early grass, especially in wet springs. Field experiments have studied the efficiency of different nitrogen forms at the first application over a number of years (McAllister et al. 1965; Van Burg, Dilz & Prins, 1982). The yield response has tended to be variable and may have depended on climatic and soil conditions. Investigations of climatic effects on fertilizer efficiency have often necessitated long-term field studies, but it is proposed that the importance of rainfall in particular could be investigated by means of a short-term irrigation experiment. This paper reports such an experiment using irrigation to simulate a wet spring while keeping other conditions the same for all treatments.

An experiment with 36 high-yielding spring-calving cows studied the effect of 1 or 6 kg/day of concentrates offered to cows on either continuously stocked grazing or rotational strip grazing. A 4 × 4 latin-square design with periods of 3 weeks duration was adopted.

Mean yield was 29 kg/day of fat corrected milk (FCM). The continuously stocked cows had higher milk yields, consumed more herbage organic matter, grazed longer, with bites of smaller size and responded less in total intake to the higher level of concentrates than the strip-grazed cows. The higher concentrate treatment increased milk yields but reduced fat contents so that the average response was 0·26 kg FCM/kg concentrate. There was no difference in response to concentrate allowance between grazing treatments.

The differences recorded between grazing systems were attributable mainly to differences in green herbage allowance, which was greater with continuous grazing.

Many pigs are given their diets in cubed or pelleted form and the process of pelleting has been shown to increase nutritive value. The reasons for increases in nutritive value following pelleting of a diet are uncertain but reductions in crude fibre and improved apparent digestibility of gross energy and dry matter (D.M.) may be involved (Lawrence, 1971, 1976, 1979). As rapeseed meal (RSM) is higher in crude fibre and, in general, of lower digestible energy value than soya-bean meal (SBM), it was thought possible that the beneficial effect of pelleting could be greater in RSM than in SBM diets.

In the last two decades significant progress has been made in understanding the factors and processes affecting the K requirement of crops. Simultaneously analytical techniques to study the behaviour of K in soil have been developed, on the understanding that soil controls the supply of nutrients to crop plants by adsorbing and sometimes fixing nutrients. As in solution culture, the concentration of K in the soil solution governs the uptake of K by plants. The soil matrix serves as a reservoir from which the soil solution is replenished. Monitoring K status of the soil solution under fixed crop sequences can provide a useful basis for improving fertilizer recommendations. Kconcentrations in the soil solution have, therefore, been measured on a soil in which a number of crops have been grown in fixed annual sequences in field experiments.

Nitrogen fixing, free-living, organisms like Azotobacter and Azospirillum are known to increase the nodulation and efficiency oiRhizobium (Krasilinikov & Korenyakov, 1944). The beneficial effect of incorporation of Azotobacter with Rhizobium may be due to the production of auxins (Vancura & Macura, 1960) and prolonged survival of Rhizobium in the presence of a large amount of polysaccharide gums (Krasilinikov & Korenyakov, 1944). In green gram (Vigna radiata L. Wilczek), because of high temperature and unavoidable soil moisture stress during hot and dry summer months (April-June), survival of the seed-inoculated Rhizobium is very poor (Lai, Dubey & Chandra, 1983). In the present study attempts were made to improve the efficiency cf Rhizobium as an inoculant by the use of Azotobacter chroococcum and Azospirillum brasilense.