Four inexperienced operators used a Smith's Essem Metatest ultrasonic grader and a Philips Sonatest instrument to estimate the thickness of tissue overlying the M. longissimus dorsi at three sites over the tenth intercostal space of live steers. They also measured skin fold thickness over the central site using a micrometer. Suprafascial (selvedge) and total carcass fat were measured at corresponding sites on the chilled carcasses.

The residual standard deviations from multiple and simple regressions of suprafascial and total carcass fat thickness on the ultrasonic readings of different operators, using both instruments over the three sites with and without a measurement of skin thickness were compared.

The following conclusions were drawn. Use of a constant distance from the midline of the live animal to locate the site for ultrasonic point measurement would lead to errors in estimating fat thickness at a specific anatomical location. If the edge of the M. 1. dorsi is palpated to locate the measurement site, estimates of carcass fat thickness with a residual standard deviation of 2·5 mm are possible by relatively inexperienced operators using single point reading ultrasonic instruments. Fat deposition between the fascial sheath and the underlying M. 1. dorsi is a source of inaccuracy when estimating carcass fat cover particularly at sites closer to the midline and on fatter animals.

Using the Metatest instrument, fat cover could bo estimated in the live animal with an accuracy similar to that reported by other workers using the Scanogram. Using the Sonatest instrument the estimates were generally slightly less accurate especially at the most lateral site. Inclusion of a measurement of skin thickness gave a very slight but consistent improvement in accuracy of estimation of carcass fat cover.

In studies of the seasonal distribution of nitrogen fertilizer dressings on grassland using conventional experimental designs it is usually not possible to separate the true effects of an individual fertilizer dressing on the yield at a particular cut from the residual effects of previous dressings. An experiment is described which was designed to allow separation of the direct and residual effects, with certain restrictions, for a system involving five cuts and five possible fertilizer dressings per season on perennial ryegrass swards. From the results obtained over two harvest years on swards on two adjacent sites equations were derived relating the dry-matter and crude-protein yields of herbage to the rate of nitrogen application at five dressings in the season. Predictions of yield distribution patterns from the equations are compared with observed yields from various sequences of nitrogen dressings included in previous experiments at this Institute. Examples are also given of the prediction of sequences of nitrogen dressings required to obtain certain patterns of yield distribution.

Field experiments on ryegrass leys at Rothamsted in 1981, 1982 and 1983 examined the eifects of injected aqueous urea and of broadcast prilled urea applied alone or with one of several nitrification or urease inhibitors, on yields and N, K, Ca and Mg uptakes. Aqueous urea, prilled urea or ‘Nitro-Chalk’ were applied as single 375 kg N/ha dressings, and prilled urea or ‘Nitro-Chalk’ as three 125 kg N/ha dressings. The nitrification inhibitors etridiazole or nitrapyrin were injected with aqueous urea, but dicyandiamide (DCD) was broadcast with prilled urea. Neither the urease inhibitor hydroquinone nor the nitrification inhibitors slowed the rate of urea hydrolysis. Neither hydroquinone nor DCD diminished volatilization losses of ammonia from broadcast urea which ranged from 8 to 25 kg N/ha; they were less than 4 kg N/ha from injected urea or broadcast ‘Nitro-Chalk’. Nitrapyrin, etridiazole and DCD effectively inhibited nitrification. DCD, and to a lesser extent hydroquinone, increased yields and nitrogen uptakes from a single broadcast application of prilled urea given either in winter or in spring. However, these yields were still smaller than those given by injected urea or by divided dressings of urea, whether or not an inhibitor was used. The inhibitors did not increase yields with divided broadcast dressings of urea, which were slightly smaller than those with equivalent dressings of ‘Nitro-Chalk’. Inhibitors did not consistently increase yield when injected with aqueous urea. Inhibitors applied with injected or broadcast urea slightly increased K uptakes, and slightly decreased Ca and Mg uptakes.

Recent studies on maize in Nigeria showed that the new ‘FARZ series’ of maize, which were specially bred for high yield, respond to high density treatments (Lucas, 1981; Remison & Lucas, 1982). The optimum maize grain yields were obtained by these workers at density treatments 6·6 and 5·3 plants/m2. Prior to the release of these varieties, optimum grain yields were obtained between 3·7 and 4·3 plants/m2 (Fayemi, 1963; Chinwuba, 1967).

It is well known that the uptake of fertilizer-N by crops is relatively inefficient, often amounting to less than half the quantity applied. Some becomes unavailable by combining with soil organic matter and some is lost from the system by surface runoff, leaching, denitriiication or ammonia volatilization. Most research has shown urea to be less effective than other sources of N when applied under conditions where ammonia volatilization becomes significant, especially when broadcast on the surface of alkaline and calcareous soils. Devine & Holmes (1964) found that ammonium sulphate was less effective than ammonium nitrate for wheat on a calcareous soil. Nitrogen recovery by wheat and barley tended to be similar for various N-fertilizers but further recovery in the following year was highest from calcium nitrate followed by ammonium sulphate and ammonium nitrate (Alessi & Power, 1973). On the other hand the efficiency of nitrate-N for flooded rice is less than that of ammoniacal fertilizers, owing to denitrification and leaching. Sarkar et al. (1978) found that rice grain yields with ammonium sulphate were significantly higher than with urea whereas Narain & Datta (1974) reported that urea and ammonium sulphate were equivalent and gave significantly higher yields of rice than ammonium nitrate. Therefore, yield responses to different sources of N vary depending upon soil, crop, climate and management factors; the study reported here was initiated to provide information on the relative performance of various N carriers applied to wheat and rice in the Punjab.

Crop residues, consisting of cereal stovers and hays made from the vegetative parts of grain legumes, are important dry-season feeds for ruminant livestock in the Savannah Zone of West Africa (van Raay, 1975; McCown, Haaland & de Haan, 1979; Jahnke, 1982). With the increasing demand on land to produce more crops and animal products, traditional systems are under pressure. There is need for a reliable means to quantify the supply of feed from various sources and to monitor the type, quantity and quality of crop residue available to livestock.

The changeover from fertilizers containing calcium or ammonium sulphate to those containing little or no sulphur has led to the occurrence of sulphur deficiency in many areas of the world (McNaught & Christoffels, 1961). In the United Kingdom, it was thought that even in the absence of fertilizer sulphur, atmospheric inputs were sufficient to ensure an adequate supply for crops. Recent work in the north of Scotland has shown that this is not so, that many soils in the area are low in sulphur, and yield responses have been obtained following application of sulphur to grass (Soott et al. 1983; Scott, 1984). The purpose of the present experiments was to extend the work to cereals, in particular to examine the response to added sulphur of the grain yield of winter barley, and to measure the effect of sulphur on the chemical composition of plants.

Vegetative multiplication of potato is used routinely to produce disease-free seed tubers and to multiply new potato varieties for trials. The conventional methods of vegetative propagation using virus-tested stem cuttings allow production of 800–900 plants from a single plant in 3 years (Hussey & Stacey, 1981). Use of in vitro propagation allows much more rapid rates of multiplication of new varieties of potatoes (Wooster, 1984). Axillary buds taken from a few tubers can be multiplied to 500 plants within 4 months by repeated subculturing of nodal cuttings on artificial media in sterile conditions.