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.

Poor quality underground irrigation water occurs in most arid and semiarid regions. This water contains not only excessive amounts of soluble salts but also fluoride (F) from traces to 30 mg/1 in India, but usually the concentration of F is below 5 mg/1 (Gupta, 1979). The effect of F on plants is not well known but plants accumulate it when it is present in the soil or applied through irrigation water. Singh, Chhabra & Abrol (1980) found that soil-applied F at 50 mg/kg was toxic to rice and 32 mg/kg tissue content of F was toxic to wheat. Paliwal (1972) found that F content in berseem increased from 18·1 to 52·7 mg/kg when the crop was irrigated with F contaminated water. He further found that 10 mg F/kg inhibited germination and growth of wheat seedlings, and whilst low concentrations of F may not be toxic to plants they may be hazardous to animals continuously fed on fodders containing fluoride.

The effect of fluoride-rich saline water on the yield and F content of fodder oats has therefore been determined.

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.