Soils derived from Gault Clay in the eastern region of England are notorious for giving very variable yields of wheat. Whereas in recent years yields on other soil types have increased remarkably, largely owing to the use of high-yielding varieties and increased use of nitrogen (e.g. Holbrook, Osborne & Ridgman, 1982), yields from Gault Clay soils have remained at much the same level as the best crops of 30 years ago.

Effects of seven levels of N application and three seeds mixtures were studied on two sites for 4 years. One seeds mixture comprised perennial ryegrass (Lolium perenne L.) and two comprised perennial ryegrass with white clover (Trifolium repens L.). One site (Trefloyne) was 24 m above sea level on deep soil and the other (Pwllpeiran) was 328 m above sea level on relatively shallow soil. The plots were cut seven times per year.

White clover grew very strongly at Trefloyne in the first 2 years, fixing 350 kg N/ha/year where no N was applied; the clover declined very markedly during the 3rd year and there was very little in the sward in the 4th year; quite large quantities of clover were harvested in the 1st year even where 600 kg N/ha were applied. At Pwllpeiran the yields of clover were never high, but the clover persisted well where no N was applied. At Trefloyne the indirect contribution of the clover (in increasing the yield of grass) was greater in the first than in the second half of the year; clover was later than grass to grow strongly in the spring, but the extra grass growth compensated for this, so that the seasonal distribution of total herbage yield was similar on a grass-clover sward receiving no fertilizer N to that on a grass sward receiving six applications of N per year. At Pwllpeiran, on the other hand, the indirect contribution of the clover tended to be greater in the second than in the first half of the year where no N was applied.

The olover was similar to grass in phosphorus and potassium content and higher than grass in calcium and nitrogen. The clover was higher in nitrate-N content than grass grown without clover, at low levels of applied N, and increased the nitrate-N content of the grass growing with it.

Water consumption at Trefloyne was greatest on swards which contained olover and on the swards without clover which received at least 400 kg N/ha/year. The effect of clover on soil water was apparent particularly in the lower horizons of the soil.

In earlier papers, it has been demonstrated that many features of the production system in the lowland tropics affect the growth and development of pigeon pea differentially depending on the prevailing conditions (Tayo 1982 a, b, c, 1983 a, b). It has also been noted that when plant size is reduced as a consequence of reduced soil moisture, slight variations in production input tend to have a more significant effect on crop performance (Tayo, 1983b).

Several laboratories are currently using the rapid excreta collection assay desoribed by Sibbald (1979), or a modification thereof, to measure digestibility of amino acids (AA) in feedingstuffs for poultry. The use of faecal or excreta collection assays to measure utilization of dietary AA has been frequently questioned because of the unknown effects of gut micro-organisms on AA excretion. These effects may be large with swine (Holmes et al. 1974) and thus many researchers have used ileal digesta collection to measure AA digestibility with pigs (Zebrowska, 1978). The question on significance of microbial effects is less clear with poultry. Some studies with germ-free chicks suggested that influence of the hindgut microflora on digestibility of protein and AA was significant (Salter & Coates, 1971; Elwell & Soares, 1975), whereas others indicated that these effects were small and probably negligible (Salter, Coates & Hewitt, 1974; Salter & Fulford, 1974). More recently, Parsons, Potter, Brown, Wilkins & Bliss (1982) concluded that microbial fermentation in the hindgut may have a significant effect on AA excretion by poultry, but to a much lesser extent than swine.

India is the second largest litchi producing country in the world after China (Syamal & Mishra, 1984), yet the number of litchi cultivars grown in the country is quite small compared with mango (Mangifera indica). In mango most of the choicest Indian cultivars have been obtained from chance seedlings (Singh, 1960) grown in the past without any definite aim in mind. Litchi, as a result of crosspollination (Chaturvedi, 1965), is a highly heterozygous fruit, and as such, its seedlings, like those of mango, exhibit a wide range of variation which helps in the selection of new desired types. It has, thus, been emphasized that litchi should be grown in bulk from seeds to introduce genetic variability (Kumar & Thakur, 1981). Kadman & Slor (1974), encouraged by excellent success in grafting, have also stressed the need for raising plants through seeds for rootstocks.

Water buffaloes (Bubalus bubalis) are reared in many tropical and subtropical countries for meat and milk production and to serve as draught animals. The improvement of milk yield in water buffaloes has been handicapped by the absence of physiological data that may provide means of rapid genetic improvement. Endocrine function is known to vary with lactation intensity. Thyroid hormones seem to have a stimulatory effect on the metabolic rate and, consequently, on the productivity of dairy animals (Lenon & Mixner, 1957; Picha, Pichova & Karasek, 1970; Swanson, 1972). Anderson (1969) also reported an increase in thyroid activity in lactating cows and rats, although other investigators (Johnson & Vanjonack, 1976; Hart et al. 1978; Hart, Bines & Morant, 1979) reported that lactation induced a decline in plasma thyroid hormones. None of these studies performed measurement of plasma thyroid stimulating hormone.

Rice is the major food crop grown on black soils of southern India and these soils have problems of high zinc fixation due to high clay content, high pH and dominance of smectite minerals causing zinc deficiency problems. The addition of zinc fertilizers to these soils has often been ineffective as the element is transformed to unavailable forms particularly under flooded rice conditions. Studies on the distribution of fertilizer zinc among different pools of soil zinc (Viets, 1962) could be useful in formulating methods of zinc application for higher efficiency of utilization. An attempt was therefore made to study the transformations of added zinc in soils in field experiments conducted in a rice-rice sequence involving the use of 65Zn as a tracer.

Java citronella (Cymbopogon winterianus Jowitt) is an important perennial aromatic grass cultivated in different parts of India. The steam-volatile essential oil from the citronella herb is widely used in perfumery, in manufacture of deodorants and mosquito repellent creams and in flavouring beverages. Systematic cultivation of this crop is being taken up and application of large quantities of N fertilizers was found to increase yield (Narayana et al. 1975; Bommegowda, 1978; Singh, Pathak & Bodoloi, 1980; Prakasa Rao et al. 1983). However, the efficiency of N utilization by this crop was found to be quite poor (Prakasa Rao et al. 1983). No systematic data are available in India on the effect of harvest season and N fertilizers on the principal constituents of citronella oil. Therefore the present experiment was made with two objectives: (i) to determine the effect of harvest season and N fertilizers on the essential oil concentration and the principal constituents of the oil which determine the oil quality, and (ii) to determine the effect of neem cake, an indigenous cheap material which is reported to have nitrification inhibitory properties, on the herb and essential oil yields of citronella.

The potential for twice-yearly lambings by tropical sheep is well recognized (Brown, Cameron & Ngere, 1972; Goode, Linnerud & Tugman, 1980; Osinowo, 1982). In order for ewes to lamb every 6 months the rebreeding interval must be 33 days or less. Factors affecting rebreeding in post-partum ewes have been reviewed (Hunter, 1968a, b Van Niekerk, 1979).