The effect of infrequent drinking on nitrogen metabolism was studied in Bedouin goats, a breed herded in the extreme deserts of the Middle East. The goats were given water either daily or only once every 4 days, while being maintained on roughages of different quality: lucerne hay (19% protein), Rhodes grass (10% protein) or wheat straw (3·7%). On lucerne hay and Rhodes grass the goats kept their body mass constant, whether given water daily or only once every 4 days. When on wheat straw the body mass was maintained constant only when given water once every 4 days. Infrequent drinking was found to hamper considerably the food intake of the goats when fed on high quality roughage. When on the wheat straw, the nitrogen intake of the goats (only 12% of that recorded when fed lucerne hay and given water daily) was, however, not affected by the drinking regime. Infrequent drinking improved nitrogen digestibility on all the diets, but more so on those of low quality than on the lucerne hay.

When tested on the low quality feeds, urea excretion was low and urea retention and recycling were maintained at high rates. Infrequent drinking had no adverse effect on these capacities.

The absolute and relative growth of the liver, kidney, heart and lung-and-trachea were studied for 64 female, 64 castrated male and 64 intact male indigenous Nigerian pigs between birth and 672 days of age. Highly significant (P < 0·001) sex and age influences were obtained for the absolute and relative weights of the liver, kidney and heart. At 280 days of age, the four organs on average weighed 28 times their birth values; the terminal weights averaged 1·31 times their values at 280 days. Organ growth became stabilized after 280 days.

The allometric equation: Y = aXb, transformed to its linear form log Y = log a + b log X, was employed to examine the relationship between organ weight and body weight. The growth coefficients 6 obtained ranged from 0·787 for kidney to 0·850 for lung-and-trachea and were similar to values reported in the literature. The accompanying highly significant R2 values strongly indicate that the functions of these organs are related to overall metabolism, which in turn is strongly dependent on body size.

Intercropping has been recognized as an important farming practice, particularly under rainfed conditions, for its greater stability in production, equal distribution of labour throughout the growing season and greater diversity of food and income sources. Evidence for higher productivity from intercropping through more efficient use of resources has been demonstrated (Andrews, 1972; De & Singh, 1979; Willey & Natarajan, 1978). Groundnutpigeonpea intercropping, which is prevalent in semiarid conditions of India on alfisols, does not produce good yields because of the traditional practice of having low pigeonpea density. Also, unsuitable genotype and poor arrangement of the crops often prove to be disadvantageous.

A field trial was conducted during 1982–3 and 1983–4 on a loamy sand soil to study the effect of magnesium application to the soil and in foliar spray in relation to various levels of nitrogen on the growth and yield of wheat. Results indicate that wheat responde significantly to magnesium application only at the higher level of nitrogen. At the higher level of N (120 kg/ha), the response of wheat to magnesium application (10 kg/ha) to the soil and in foliar spray was 56 and 68 kg grain/kg Mg, respectively. However, the corresponding values at a low level of N (60 kg/ha) were only 14 and 15 kg grain/kg Mg. Magnesium at the higher level of N increased the chlorophyll content of leaves, leaf area index, interception of photosynthetically active radiation, number of ear-bearing tillers and number of grains per ear. The higher level of magnesium (20 kg/ha) did not result in extra beneficial effect compared with the lower level of Mg (10 kg/ha). Maximum interception of photosynthetically active radiation by the wheat canopy coincided with the attainment of maximum leaf area index and chlorophyll content of leaves at 90 days after sowing.

Sugarcane is usually grown after paddy in tropical and subtropical India; this rotation is adopted when sugarcane is planted in October (autumn planting). Soil puddling is required for paddy, but puddling disturbs the soil structure and impedes development of roots beyond the puddled layer. Adverse effects on growth and yield of sugarcane are therefore expected, but contrary to such expectations, sustained or increased yields of cane after paddy have been observed (Alvarez & Snyder, 1984; Anon. 1984; Snyder el al. 1986). It appears that certain other soil factors overcome the harmful effects of adverse soil physical conditions. Therefore, the present study was undertaken to investigate such factors.

In field experiments with potato conducted from 1981 to 1983 on acid hill soils of Simla, a technique was developed to work out the relative contribution of soil and fertilizer nutrients to potato production. The locations accounted for more variation in tuber yield than the fertilizer effects. The value of soil tests in explaining the variation due to locations was modified by years. On average, nitrate, organic carbon and available K explained 59, 25 and 41% of the variation. The response to fertilizer N was significant in all yea s and to K was significant in 1982 only, but that to fertilizer P was not significant in any year. The fertilizer doses of N and K were calculated both from the soil test based regression equations and the fertilizer response equations. The dose of N varied from 129 to 133 kg/ ha in different years but the response per kg N at the economic dose varied from 0·05 to 0·13 t/ha.

Potato (Solanum tuberosum L.) is propagated vegetatively using the tuber because it rarely survives from the true seed. Under normal conditions, potatoes left in the air or dry soil will produce sprouts but not roots. Large and vigorous sprouts are indicators of rapid emergence and relatively early maturity.

The control of eyespot (Pseudocercosporella herpotrichoides (Fron) Deighton) is most effective after application of carbendazim (Hampel & Lücher, 1973; Taylor & Waterhouse, 1975) or prochloraz (Marshall & Ayres, 1986) at growth stages (GS) 30–31 (Zadoks, Chang & Konzak, 1974), although some control occurred after applying prochloraz with carbendazim at GS 37–49 (Marshall & Ayres, 1986). Growers in the U.K. are advised to apply eyespot fungicides only when severe disease is expected. This forecast is usually made at GS 30, and spraying is recommended when two or more leaf sheaths have been penetrated on at least 20% of shoots (Anon. 1985). However, subsequent weather conditions may result in severe eyespot developing when no spray was recommended, or may not favour eyespot and result in fungicide being wasted.

The effect of artificially applied urine on clover performance in a perennial ryegrasswhite clover sward grazed by sheep was examined during summer. Sheep urine or deionized water (51/m2) was applied to areas (2·70 × 1·25 m) which were protected from subsequent excretal return by graze-through cages. Grass and clover populations, nitrogen-fixing activity, soil nitrogen and soil pH were monitored over the following 90-day period.

Urine reduced clover population density, stolon length and dry weight but had little effect on number of grass tillers. Nitrogen-fixing activity of clover was reduced initially to less than 30% of control values, perhaps owing to high levels of soil inorganic nitrogen inhibiting fixation, although osmotic effects due to the high salt concentration in urine cannot be discounted. The lower levels of activity at later dates were due largely to reduced clover in urine-treated areas. Soil pH (0–5 cm) was increased by about 0–5 units 3 days after urine application, with a smaller increase in the 5–10 cm horizon. Recovery of urine nitrogen in the soil mineral N pool was at best 27% of the added nitrogen.

The results are discussed in terms of the significance of urine-affected areas in determining a patchy distribution of clover in grazed swards; the role of animals in the transfer of fixed N from clover to grass is considered.

Jute (Corchorus capsularis L.) is grown in the tropics. It is next only to cotton in importance as a fibre crop. Adequate supplies of plant nutrients, especially N, are essential for its vegetative growth. Response to applied N varies from region to region. In a light-textured soil with low cation exchange capacity (CEC), part of the applied N is generally lost mostly under rainfall (Engelsted & Russel, 1975) and the rest is manifested in the form of residual effect (McEwen, 1970). Such losses can be reduced by using slow-release N fertilizers or by coating the urea granules by paraffin wax, resin, gum, lac, or with a nitrification inhibitor (Prasad, Raj ale & Lakhdive, 1971). There is little information on the use of these products on jute. Mondal, Dohary & Pal (1977) reported that coated urea is better than uncoated ones. The current programme was designed to give a better picture.

Morrison et al. (1972), Hsia, Fuller & Koh (1974), and Ho & Khoo (1977) showed that sprinkling can alleviate the adverse effects (Straub et al. 1976) of high ambient temperature on feed intake and growth of pigs. Vajrabukka, Thwaites & Farrell (1986) demonstrated that pigs need to be thoroughly wet by sprinkling at least once every 60 min if high evaporative rates are to be maintained, but little is known of the relative benefits of different sprinkling regimes for pigs growing at high temperatures.

Cassava (Manihot esculenta Crantz) is a carbohydrate staple and cash crop for about 800 million people in the tropics. As food, its use is influenced by its content of potentially toxic cyanogenic glycosides that release hydrocyanic acid when enzymatically hydrolysed (Conn, 1969). Cyanide plays important role in the protection of cassava plants from attacks by animals and insect pests. The glycosides are synthesized mainly in leaves and translocated to all parts of the cassava plant (Bediako, Tapper & Pritchard, 1981). De Bruijn (1973) noted more than a 100% increase in the HCN content of stem bark above the incision after ringing, especially during the first 2 days, and a continued increase for at least 2 months. However, when leaves were removed, no such increase was observed. De Bruijn (1973) observed that younger plants showed a greater increase (165%) than older plants (65%). Leaf HCN did not increase after ringing, whereas root HCN decreased by about 20% in 2 weeks. The literature on cyanogenic glycoside translocation is relatively recent and limited. Consequently, the exploitation of the supposed direct relationship between leaf HCN and root HCN in the selection of low HCN clones in cassava breeding programmes needs to be carefully assessed. The assessment is complicated because the methods used by different workers for the determination of HCN vary in their efficiency. Thus, Cooke, Howland & Hahn (1978) found no correlation (r2 = 0·13) between leaf HCN and root HCN among 108 clones, yet over 88000 genotypes have been screened by analysis of leaf HCN, and leaf analysis has been used routinely in cassava improvement for 9 years (Hahn, 1983). Hahn also reported the range of HCN concentration within each leaf-picrate class (1 = 80, 2 = 80−200, 3 = 200 mg/100g fresh weight) but the ranges within each of these classes were too wide to enable effective selection for low HCN clones.

There has been considerable research on techniques for artificial insemination of sheep with frozen ram semen (Maxwell, 1984). Acceptable pregnancy rates were reported following ‘two-step’ dilution and freezing of semen in P.V.C. ‘ministraws’ (Colas, 1975; Colas & Guerin, 1981); however, other workers have obtained poor fertility following cervical insemination with semen frozen in straws (Maxwell, etal. 1980; Tervit elal. 1984).

Brown planthopper, Nilaparvata lugens (Stal), is one of the most serious insect pests of rice (Oryza sativa L.) throughout Asia. Introduction of resistant varieties could be an effective means of minimizing losses from the pest. Several hundred rice cultivars resistant to the pest have been identified and the genetics of resistance has been analysed. Studies have shown that the genes for resistance to brown planthopper, bph-4, and to green leafhopper, Glh-3, are linked (Sidhu & Khush, 1979). Ideka & Kaneda (1983) reported that bph-2 for brown planthopper resistance was linked with the gene d2 for dwarfness. The present study sought to ascertain relationships between resistance to brown planthopper and tungro virus and grain characteristics.

It is estimated that only 35–50% of the potential yield of field lettuce crops is harvested (Gray, 1978c). A major contributory factor is the failure to establish full, uniform plant stands. Erratic lettuce emergence has been attributed to inadequate soil moisture, soil crusting, and high (> 25 °C) soil temperature (Hemphill, 1982).

Urea can be an inefficient nitrogen source, compared with ammonium nitrate, on calcareous soils (Ernst & Massey, 1960) and under dry conditions (Murphy, 1978) as a result of ammonia volatilization. However, the interaction between factors which can affect the performance of urea is not clearly understood. The risk of ammonia volatilization would appear to be higher on light soils with a low cation exchange capacity than on heavier soils (Fenn & Hossner, 1985). Field trials in the Netherlands indicated that a minimum of 5 mm of rain must fall within 2 days of application to give good dry-matter yields with urea (Van Burg, Dilz & Prins, 1982). In addition ammonia volatilization has been affected by initial soil moisture content in some studies (Fenn & Escarzaga, 1977) but not in others (Gasser, 1964).

Bollworms (Heliothis zea Boddie and H. virescens F.) are serious cotton pests. During 1980, the cotton crop in U.S.A. suffered an 8·73% loss due to insect pests; 3·07% of this loss was due to the damage caused by bollworms. This 8·73% loss in cotton production occurred despite control measures adopted by cotton growers at an average cost of $36.27 per acre (Anon. 1981). Four plant characteristics impart varying degrees of host-plant resistance against bollworms in cotton (Maxwell, 1977). The bollworm moths exhibit an oviposition nonpreference towards glabrous and nectarless cottons. Presence of high gossypol and ‘X-factors’ in plant parts detrimentally affects the growth and survival of bollworm larvae. The ‘X-factors’ are unknown chemical substances that impart host-plant resistance against bollworms in cotton. This resistance was shown to be heritable by Lukefahr et al. (1974).

The problem of drought presents a challenge to plant breeders as breeding is a major method by which yield improvement can be obtained in drought-prone areas. The plant responses to drought and the nature of drought resistance have received the attention of several workers (Kozlowski, 1968; Kramer, 1969; Levitt, 1972). There are reports in the literature which show that yield and drought resistance are controlled by separate genetic entities. Breeding thus requires identification of definite drought resistance attributes and their transfer to high-yielding and agronomically acceptable cultivars.