Six soil series differed in water-soluble, exchangeable and nonexchangeable K. Significant positive relationships were observed between exchangeable K and water-soluble K. A highly significant positive relationship was found between the K saturation of the cation exchange complex and water-soluble K in the individual soil series, and when the six series were pooled; K saturation, therefore, may predict water-soluble K in a range of tropical soils. Potassium desorbed in 35 min by electroultrafiltration (EUF) may serve as a measure of exchangeable K in predominantly kaolinitic tropical soils. In soils with appreciable amounts of mica, longer K extraction by EUF (up to 70 min) may indicate the reserves of nonexchangeable K.

A balance experiment was carried out using four young lactating goats in a Latin square design, fed with perennial ryegrass (Lolium perenne) from plots that had received 377 kg K/ha (diet 1); 63 kg K plus 377 kg Na/ha (diet 2); 188 kg K plus 188 kg Na/ha (diet 3) or no fertilizer (control diet 4).

The apparent availability of Mg was high in all the grass diets (0·355–0·469); it was significantly depressed (P < 0·05) when the intake of K was high (diet 1); but was not significantly different when a high intake of K was accompanied by a high intake of Na (diet 3).

There was a significantly lower (P < 0·05) apparent availability of Na in diet 4 and a significantly higher (P < 0·05) apparent availability of K in diet 3. There were no significant differences in the apparent availability of Ca.

The plasma Mg concentration was not significantly affected by any dietary treatment but did decrease temporarily when diets were changed.

There were no significant effects on mineral concentrations in the milk.

Ten dairy cows were allocated into three groups according to milk productivity (four high, four intermediate and two dry cows, respectively). Heat production and heart rate, but not rectal temperature, were significantly different (P < 0·05) between groups. Heat production increased during feeding in the morning and in the afternoon and reached a peak 3 h later. Minimum heat production was observed in the early morning before feeding. The diurnal pattern for heart rate reflected that of heat production. These results suggest that cooling dairy cows during hot summer days is most effective at feeding time and 3 h afterwards.

The effects of shade (50% of ambient light transmission) on the quality of established swards of buffalo grass (Stenotaphrum secundatum) and kikuyu grass (Pennisetum clandestinum) were examined at Wollongbar Research Station, northern New South Wales. Sarlon cloth was used to shade plots of the two species, after cutting to 8 cm, from November 1985 to March 1986. Herbage was harvested from shaded and adjacent unshaded plots for chemical analyses and for feeding as dry chaff to penned sheep at the University of Queensland research farm at Mt Cotton.

Shade markedly decreased the voluntary feed intake (VI) of P. dandestinum by 30·7% over the two harvests while VI of S. secundatum was not significantly affected. Shade had no effect on the in vitro and in vivo digestibility of P. clandestinum herbage but marginally increased that of S. secundatum. These shade effects resulted in a 14·2% increase for S. secundatum and a 34% decrease for P. clandestinum in the intake of digestible dry matter of shaded compared with unshaded herbage.

The reduced VI of the shade-grown herbage of P. clandestinum was associated with a higher proportion of stem (21 v. 8% for unshaded herbage), a lower proportion of leaf (48 v. 54%), and a lower concentration of total nonstructural carbohydrates (TNC) (0.9 v. 2.1%). In S. secundatum, there were similar, but smaller, changes in proportion of stem and TNC percentage in shade-grown herbage but, in contrast to P. clandestinum, these potential detriments to VI were offset by an increase in proportion of leaf and a decrease in the proportion of dead material. Average moisture content of shaded herbage (76%) was higher than that of unshaded herbage (70%). Nitrogen and potassium concentrations in plant tissue were higher in the shaded herbage.

The higher yielding capacity and maintenance of nutritive quality of shaded S. secundatum compared with shaded P. clandestinum indicates the potential usefulness of S. secundatum for plantation agriculture.

White clover genotypes selected for frost tolerance and susceptibility were pair-crossed in various combinations with unselected genotypes of Grasslands Huia. Progeny lines and parent genotypes were artificially frosted at −8°C and scored for percentage of leaves damaged. Progeny from crosses between frost-tolerant genotypes were less damaged by frost than progeny from crosses involving either susceptible genotypes or unselected Grasslands Huia genotypes. Heritability estimates for frost tolerance or susceptibility were high, ranging from 0·75 to 0·93, depending on method of calculation. Removal of leaf-size effects from scores of frost damage reduced heritability estimates to 0·54–0·73. It was concluded that, because heritability for frost tolerance was high, selection for this character and incorporation of frost tolerance into agronomically suitable but frost-sensitive cultivars by breeding would be successful.

seventeen maize (Zea mays L.) genotypes (unimproved local varieties, improved open-pollinated composites, hybrids and F1 varietal crosses) were compared on a 1–5 scale for taste when eaten as boiled green maize. Significant differences were obtained between and within genotypic groups. Differences within the open-pollinated composites and the varietal crosses were highly significant. Using mean score ratings as an index for selection, the three genotypes TZB, BN59 × 1K8149SR-BC2 and TZESR-W × 1K8149SR-BC2 were identified as having the best taste, with mean scores of 3·6, 4·3 and 3·5, respectively.

The response to shade in growth and nutritive quality of buffalo grass (Stenotaphrum secundatum) was compared with that of two other stoloniferous grasses, mat grass (Axonopus compressus) and kikuyu grass (Pennisetum clandestinum). The grasses were grown outdoors in Brisbane, Australia, in soil in pots over two growing seasons in 1985/86. Treatments in the first season (Expt 1) were shading at 0 (full sun), 42, 59 and 68% with moderate N (two spaced applications of 50 kg/ha) and, in the second season (Expt 2), 0 and 59% shade with high (50 kg/ha every 2 weeks) and low (5 kg/ha every 2 weeks) N.

Unusually for tropical grasses, the top yield of all species was higher under shade than in full sun, except for S. secundatum at high N in Expt 2. S. secundatum and A. compressusshowed an increase in top yield up to 68% shading whereas P. clandestinum reached a maximum at 42% shading. Shade increased shoot:root ratio and specific leaf area in all species but had little effect on leaf:stem ratio and the proportion of dead material in the tops. Stubble yield (stem bases and stolons) was reduced under shade but to a much smaller extent than root yield. S. secundatum and A. compressus had similar morphological characteristics. Their yield was lower than that of P. clandestinum in Expt 1 (autumn growth) but was similar to that of P. clandestinum in Expt 2 (summer growth). These grasses had a higher leaf:stem ratio and lower proportion of dead material in tops than P. clandestinum.

Shade generally increased herbage nutritive value through an increase in N concentration and drymatter digestibility. The latter response was somewhat variable and mostly small (1–3% units). Under shade, the general trend was towards a decrease in total nonstructural carbohydrates, cell-wall content and insoluble ash, and an increase in lignin content. A. compressus was higher in digestibility and soluble carbohydrates than the other grasses.

S. secundatum was not clearly superior in response to shade and its nutritive quality was lower than that of A. compressus.

The nitrate nitrogen content of the soil (0–90 cm) was measured immediately after the harvest of winter wheat at eight sites in central and eastern England in 1987 and 1988. On average, 50% of the total nitrate detected was in the 0–30 cm, 30% in the 30–60 cm and 20% in the 60–90 cm soil horizon. Although soil nitrate N increased with the amount of N fertilizer applied, it was not a linear relationship. There were small nonsignificant increases in soil nitrate up to the optimum fertilizer rate for yield but, once the optimum was reached, further addition of fertilizer increased nitrate contents significantly.

Therefore, applying the correct quantity of N for high grain yield did not significantly increase soil nitrate residues after harvest compared with the no-fertilizer treatment. This emphasizes the importance of applying the appropriate rate of N for each crop, because applying too much is not only uneconomic but also significantly increases the amount of mineral N which could be subsequently leached over the winter.

Four adult swamp buffaloes (Bubalus bubalis) and four adult Brahman cattle (Bos indicus), maintained in climate rooms, were provided ad libitum with a pelleted NaOH-treated barley straw ration (10·7 g N/kg dry matter) supplemented with sulphur, minerals and vitamins and 0, 14·5 or 22 g urea/kg. The animals were given each diet when housed at 32 °C and, in addition, were given the urea unsupplemented diet at 22 °C. All animals received all treatments for periods of 21 days, measurements being made during the last 8 days, after the animals had been given single doses of two nonabsorbable markers (Cr-fibre and Co-EDTA). Intake, digestibility and gastro-intestinal passage rate were low on the unsupplemented N-deficient (10·7 g N/kg dry matter) diet at both temperatures. Urea supplementation to provide diets of 17·3 and 20·7 g N/kg dry matter was associated with increased intake and digestibility of the feed and increased rate of passage of digesta through the gut.

Despite differences in respiration rate and plasma thyroxine (T4) and triiodothyronine (T3) concentrations at the two temperatures, no effects of temperature on intakes and digestion of the unsupplemented diet were seen. Differences between species were seen in respiration rate at 32 °C and plasma T4, which were higher, and mean retention time of Cr in the gut at 22 °C and water intakes, which were lower, in Brahman cattle than in buffaloes. There were no significant species differences in response to dietary urea supplementation.

Field experiments were conducted in two wet and two dry seasons in 1984–86 to evaluate efficiencies of different urea-based fertilizers, and methods of application, for irrigated rice. Response to applied N was significant in all seasons. In the wet season, use of dhaincha (Sesbania aculeata) green manure and urea (Dh + U), reduced zone placement of urea supergranules (USG), surface application of laccoated urea (LCU) and prilled urea in three split doses (PU-split) gave similar results, and all were better than basal broadcast application of urea coated with neem (Azadirachta indica) cake (NCU) or prilled urea (PU-basal). In the dry season, USG was significantly superior to PU-basal, NCU and (Dh + U). Nitrogen uptake by rice was greatest 15–30 days after transplanting (DAT), followed by a second peak during the reproductive phase of the crop. Ammonium-N in the soil decreased sharply up to 30 DAT, more slowly up to 60 DAT and then increased slightly. Ammonium-N in the soil was higher with USG, (Dh + U) and PU split than with other treatments, especially in uncropped conditions.

In order to determine the accuracy of controlling the time of maturity of a cauliflower crop by regulating the planting date, a series of transplantings of the variety White Fox was grown on a range of sites over 3 years and sampled throughout growth.

The time from transplanting to maturity and the time from curd initiation to maturity were both quadratically related to the time of transplanting but there were marked differences in the relationships between years. Differences between years in the time taken to reach maturity tended to increase with later transplanting; for example, cauliflower crops transplanted in May took between 77 and 94 days to mature, while those transplanted in July matured in as few as 67 or as many as 106 days. These differences resulted from a combined effect of the time taken to satisfy the vernalization requirement and the duration of curd growth, both of which are temperature-mediated and therefore subject to seasonal and annual variation. Differences in the vernalization requirements of different cauliflower crops are illustrated by the number of leaves formed before curd initiation, which varied from 22·5 to 37·3.

Variation in the time to maturity between crops transplanted at similar times of the year, in the same and different years, resulted in large deviations from planned production programmes and it is suggested that a complementary technique to aid crop marketing would be prediction of the time of crop maturity. However, the data collected in this study show that predictions based on the duration of crop growth from transplanting or curd initiation are unlikely to be sufficiently accurate and it is argued that predictions should be based on changes in curd dimensions with time.

The effects of winter shearing, 8 weeks before lambing, on ewe and lamb live weight changes over the first 30 days of lactation were studied in Reading between February and March 1984. Differences in ewe body condition score (BCS) and plasma concentrations of glucose, nonesterified fatty acids (NEFA), 3-hydroxybutyrate, growth hormone (GH), insulin, cortisol and thyroxine between shorn and unshorn groups of ewes were measured over the same period.

Lambs from shorn ewes grew, on average, 20% faster than those from unshorn controls even though both groups of lambs were of similar mean birth weight. There was no difference in maternal feed intake between shorn and unshorn groups, and ewe live weight and BCS decreased between the day of lambing and day 30 of lactation in all ewes. Plasma samples taken at hourly intervals for 24 h on days 12 and 27 of lactation demonstrated that shorn ewes had significantly lower plasma concentrations of insulin than unshorn controls; on day 27 of lactation, higher circulating concentrations of GH were recorded in the shorn group. There were no differences in the plasma concentrations of glucose, NEFA, cortisol or thyroxine between the two groups of ewes. It is concluded that metabolic adaptation by shorn ewes to the cold environment of a British winter during early lactation results in endocrine changes in ewes which are likely to increase the partition of nutrients towards milk production. This results in a higher lamb growth rate than in lambs reared by unshorn controls.

Tissues of maize grown under different temperature regimes showed remarkable differences in anatomical and chemical properties and in vitro digestibility. A high temperature regime (12 h at 30 °C and 12 h at 24 °C) resulted in decreased cell wall thickness, cell diameter and cell wall yield, doubled lignin content and decreased in vitro digestibility, compared with plants grown under a low temperature regime (12 h at 18 °C and 12 h at 12 °C). A reduction in intensity of staining for lignin was observed in plants grown at 30/24 °C. Cell wall digestibility was thought to be limited by an indigestible cell wall layer between the secondary walls of adjacent cells. The use of lignin staining was of limited value for predicting cell wall digestibility. High temperatures probably affect physiological processes leading to lignin formation and deposition.

A technique has been developed for the measurement of pituitary hormone secretion rates in conscious sheep. The technique involves the continuous and simultaneous sampling of blood from the carotid artery and jugular vein and the measurement of cephalic blood flow by an indicator dilution technique. Veno-arterial differences in hormone concentrations multiplied by cephalic blood flow gave average secretion rates which were measured after single or repeated large doses of luteinizing hormone releasing hormone (LHRH) and thyrotrophin-releasing hormone (TRH) at various times in the reproductive cycle.

An induced mutant of rice, designated M41, resistant to several races of bacterial leaf blight, obtained after irradiation with thermal neutrons, was crossed with the original variety, Harebare. Test crosses revealed that the resistance of M41 to the Japanese races I, II, III and IV is controlled by a single recessive gene, considered to be different from four previously identified dominant resistance genes of japonica-type varieties and from three recessive genes in indica-type varieties for resistance to Philippine races. The gene in M41 was tentatively designated xa-nm(t).

In a field experiment at Lucknow in 1985/87 and 1986/88, the ‘new’ N carriers urea super granules (USG), neem-cake-coated urea (NCU) and dicyandiamide-treated urea (DCD) and the traditional source of N, prilled urea (PU), were used to supply 150 kgN/ha to the plant crop (first crop after planting) of the cultivar Col 148. The ratoon crop was fertilized at 0 and 150 kgN/ha with PU over all the plant crop treatments. In both plant and ratoon crops, N application increased cane yields but decreased quality: differences in yield resulting from use of the new carriers were not significant, though the fertilizers tended to increase the final plant population density. Uptake and recovery of N were significantly greater using USG, NCU and DCD than using PU. The direct effect of N was 184 kg cane/kg of N applied to the ratoon crop but residual and cumulative effects of N applied to the plant crop on yield and quality of the ratoon crop were small. Adequate direct application of N is therefore suggested for increasing the yields of ratoon cane.