A study designed to investigate the effect of K nutrition on the yield, components of yield and on macro- and micronutrient concentration of maize showed no significant effect of K on yield in forest alfisols derived from basement complex rocks and in savannah alfisols derived from sandstones in the tropics. Potassium addition significantly decreased lodging, but had little influence on cob length, ear weight, shelling percentage or moisture content.

Ear-leaf N and K were significantly increased, while Ca and Mg were decreased by K application. All the micronutrient concentrations (Zn, Fe, Mn, Cu) were significantly increased by K application in the forest and savannah zones. Yield was positively correlated with ear-leaf N on both soils.

The effects of season and altitude on floral initiation of two Trifolium repena L. cultivars, Haifa and California Ladino, were tested in the area of Ayacucho, Peru (2730 m, 13° S), with regard to their seed production potential. Specific effects of daylength at a constant temperature (20 °C) were examined in growth chambers.

In Ayacucho, the proportion of inflorescence-bearing nodes was found to be lowest between December and June (Haifa 10–20%, Ladino 0–10%) and highest in August (Haifa 30%) and September–October (Ladino 15%). Late in the cool season, floral initiation of Ladino, but not that of Haifa, increased strongly at a high altitude (3250 m). In growth chambers, Haifa initiated few inflorescences and Ladino none in a 10 h daylength. In 16 h, the floral initiation of Haifa was very limited but Ladino formed many inflorescences. Floral initiation of Haifa was most pronounced and lasted longest after a daylength shift from 10 to 13 h.

It is concluded that seasonal and altitudinal variations in low temperature were the main factors influencing floral initiation in the region of Ayacucho. Haifa is considered to be an intermediate-day plant, suited for seed production in the region because of its marked and early flowering. Ladino was classified as a quantitative longday plant, unsuitable for seed production at this low latitude because of its retarded floral response to low temperature.

During 1899–1964 various levels of 0·5 M sodium bicarbonate-soluble P had been established in an experiment on a sandy clay loam (pH 6·5–7·0) at Saxmundham, Suffolk. Modification made between 1965 and 1968 widened the range of soluble P values to 3–67 mg/kg. Relationships between these soluble P values and yields of potatoes and sugar beet in 1969–74 and cereals in 1970–7 were assessed. Responses by potatoes and sugar beet to freshly applied superphosphate were also determined at each level of soluble P. Residual effects of these dressings and responses to fresh superphosphate between 1974 and 1976 were measured by barley. Two amounts of N were tested on spring barley in 1976–7 and two cultivars of winter wheat were grown in 1977 and yields related to soluble P.

Relationships between yields and soluble P were described by an asymptotic regression equation. This model represented the measured yields well for all crops except barley, in one 4-year-period, when there were insufficient data at low soil P values and a linear regression model was fitted. The asymptotic model was used to estimate plateau yields each year and soluble P values at which yields were less than plateau values by one standard error. Average plateau yields, and associated soluble P values were: potatoes, 43 t/ha and 25 mg P/kg; sugar (from sugar beet) 6·8 t/ha and 20 mg P/kg; spring barley, given 63 kg N/ha, 4·7 t/ha and 25 mg P/kg; barley given 94 kg N/ha, 5·3 t/ha and 33 mg P/kg; winter wheat, 6·5 t/ha and 20 mg P/kg.

The model was further used to estimate responses to dressings of superphosphate at three levels of soluble P (9, 15 and 25 mg/kg) in the soils. Yield responses to 55 kg P/ha were 3·9, 2·1 and 1·8 t tubers/ha and 1·1, 0·3 and 0·0 t sugar/ha, for potatoes and sugar beet respectively, at the three levels of soluble P.

On impoverished soils (soluble P < 10 mg/kg) even the largest fresh applications of broadcast superphosphate did not raise yields to those achieved on enriched soils (soluble P > 25 mg P/kg) in the absence of fresh phosphate.

Soluble P in the soils accounted for much of the within-year variation of yields and estimated reliably and quantitatively the value of phosphate residues derived from both superphosphate and farmyard manure which had been applied in varying amounts and at different times between 1899 and 1976.

In a 3-year study, maize (Zea mays L.) sown on 11 November or 1 December produced longer ears, higher grain yield per plant and greater grain yield per hectare than maize sown on 21 October. However, 100-kernel weight was greater when the crop was sown on 21 October and 11 November than on 1 December. There were no differences in yield characters or grain yield between cultivars or between row orientation. The sowing dates, maize cultivars and row direction had no influence on the number of ears per plant.

The sweat rates, skin and rectal temperatures and other components of the heat budgets of cattle were measured in Kenya and in England. Mean sweat rate (Ec) was more closely related to mean skin temperature (T8) than to rectal temperature. The results were described by an exponential relationship between T8, (°C) and Ec (mg/m2.sec) of the form Ee = E0 exp (T8, — T0)/B, where T0 and B are parameters (both with units of °C) which describe the sweating response of the animal, and E0 is 1 mg/m2.sec. T0 was 30·8 °C for a single Bos taurus in England and 33·8 °C for five animals in Kenya suggesting that chronic acclimatization to a hot environment resulted in the cattle being able to tolerate a higher mean skin temperature. The effect of species (Bos indicus cf. B. taurus) was small compared with the effect of acclimatization, although the mean value of B was significantly higher for B. indicus (1·58 cf. 0·94 °C) indicating that the physiological mechanism controlling sweat rate in B. indicus was less sensitive to skin temperature.

A field experiment was made during the rainy season of 1982 and 1983 at the Indian Agricultural Research Institute, New Delhi to study the relative efficiency of prilled urea, urea supergranules (USG) and USG coated with neem cake and DCD. Prilledurea was applied at 60, 120 and 180 kg N/ha, while the other sources of N were applied only at 120 kg N/ha. Nitrogen was added to rice in a single application 20 days after sowing (20 DAS) or in two applications, half 20 DAS and the rest at panicle initiation. Response of rice to prilled urea was linear up to 180 kg N/ha, the highest dose in the present study. Two applications produced more rough rice and straw and resulted in higher nitrogen uptake and apparent recovery than a singleapplication. Neem-cakecoated USG was superior to prilled urea in respect of panicle characters, rough rice and straw yield, nitrogen uptake and apparent nitrogen recovery. Coating USG with DCD also showed some advantage. Uncoated USG was only slightly better than prilled urea.

Practical systems for the artificial insemination of sheep have been available for many years (reviewed by Maxwell, 1984). The traditional method is to separate from the flock ewes exhibiting a natural oestrus as identified by ‘teaser’ rams, and inseminate these ewes with freshly collected and diluted semen. The ewes are generally inseminated by suspension of the hindquarters over an elevated rail and deposition of the semen within the first fold of the cervix using a plastic pipette, speculum and headlamp (the cervical insemination method, Salamon, 1976).

Boron (B) nutrition problems of cacao (Theobroma cacao L.) in Nigeria deserve continuous attention in view of the fact that more cocoa-growing areas showing B deficiency are being brought to light. Omotoso (1975) examined plant tissue B and B extractable by hot water in relation to the appearance of B deficiency symptoms on cacao leaves and found that B deficiency symptoms had no direct relation to hot-water-soluble (HWS) B in the Nigerian soils studied. Omotoso (1975) then suggested further investigations to identify soil properties that can improve the capacity of HWS B to predict cacao uptake of B.

In recent studies of variability in carrot (Umlauf, 1978; Dowker & Gray, 1985) it was concluded that increasing the genetic uniformity of the seed populations did not bring about a detectable reduction in the variability in embryo sizes, the spread of emergence or seedling weight. In these experiments, however, only broad comparisons were possible since the seed sources used were not obtained from crops grown under identical cultural conditions or harvested at the same stage of maturity, both of which affect variability in the subsequent crop (Gray & Steckel, 1983). The purpose of the present experiment was to examine the influence on variability of the greater genetic uniformity of an F1-hybrid compared with an open-pollinated cultivar, when both were sown under identical conditions.

A number of methods have been developed for synchronization of oestrus in sheep (reviewed by Maxwell, 1984), but the most successful have been based on the suppression of the oestrous cycle by treatment with a polyurethane progestagenimpregnated intravaginal sponge (Robinson, 1965). A precise synchronization of oestrus and ovulation for artificial insemination (A.I.) is obtained following a 12- to 14-day treatment with the intravaginal sponge and an injection of pregnant mares serum gonadotrophin (PMSG) at sponge removal (Robinson & Smith, 1967). This allows a single fixed time A.I. to be performed on all ewes without the need for detection of oestrus.

In a long-term experiment on a boulder-clay soil Ralph & Ridgman (1981) found that the response of potatoes to freshly applied K fertilizer was independent of the amount of K that had been applied during the preceding 10 years. The greatest yield was obtained from plots which had received the greatest amount of K during the preceding 10 years together with the optimum amount of freshly applied K (120 kg K/ha in this case) and the addition of an extra 60 kg K/ha to plots which had received less K previously did not increase the yield. Similar benefits from residual K had been reported by Johnston, Warren & Penny (1970). In view of the continuing disagreement about the need for applying K to cereals on boulder-clay soils it was decided to attempt to quantify these effects more precisely.