Urea (supplying 15 kg N/ha) applied to winter wheat (Triticum aestivum) at flag leaf emergence and again at ear emergence improved grain yield in only two, but increased grain nitrogen (N) in four out of five experiments. The size of the improvements in yield and nitrogen content differed over varying sites and seasons but were not affected by cultivar or propiconazole (250 g a.i./ha) plus tridemorph (500 g a.i./ha) fungicide applied with the urea. Breadmaking quality was assessed on grain from one site in 1985 and in 1986. The beneficial effects on loaf quality of urea and fungicide applied separately were reduced when they were applied as a mixture. In 1986 this negative interaction was associated with effects on sodium dodecyl sulphate (SDS) sedimentation volume, flour sulphur content (S), N/S ratio and dough resistance. The effect of urea also interacted with cultivar on SDS sedimentation volume in 1985 and dough resistance in 1986.

The effect of cowpea green manure (CGM) and farmyard manure (FYM) on phenological events in maize grown with different rates of nitrogen (N) was evaluated at Ludhiana, India in 1988–89 as part of a long-term experiment on sandy loam. Tasselling (T), anthesis (A), silking (S), maturity (M) and appearance of leaves were recorded in 1988 and 1989 from plots of maize manured with cowpea and FYM and grown at 0, 75 and 125 kg N/ha. Time to phenological events was calculated in terms of calendar days and growing degree units (GDU).

Phenological events in maize were significantly advanced by CGM, FYM and N. The occurrence of T, A and S with CGM was earlier by 60·5, 84·5 and 114·5 GDU, respectively, than without it and the end of each of the growth stages T, A and S was advanced by 81·0, 99·0 and 78·5 GDU, respectively. Maturity was earlier than in the control by 65·0 GDU. Leaf emergence occurred earlier after organic manuring. Farmyard manure advanced development less than CGM. Changes in phenological events due to N followed the same pattern of changes as those found with organic manures. Time from sowing to onset of T, A, S and M, and the interval between T, A, S and M were significantly correlated with yield and yield-related characters. Desirable changes in the timing of phenological events are thus one of the factors contributing to the improvement in productivity caused by organic manures. Calendar day was found to be as accurate an index as GDU for evaluation of the effect of cultural practices on phenological events.

Growth and aflatoxin production of Aspergillus flavus in preharvest maize grown in Texas, USA in 1989 were determined after treatment with chitosan, Bacillus subtilis and Trichoderma harzianum. Individual or combined control treatments were applied at the milk stage of ear development, 48 h before or after kernel inoculation with an aflatoxigenic isolate of A. flavus. Single and combined treatments reduced A. flavus growth and aflatoxin production. Toxin accumulation was significantly (P < 0·05) reduced, in some instances to non-detectable concentrations by single pretreatments. Either B. subtilis or chitosan as independent treatments applied 48 h before inoculation with A. flavus inhibited aflatoxin production.

Two experiments, each involving a set of six sweet potato clones, the first set developed in sites differing in altitude, and the second in sites differing in soil type, were done at three locations in 4 years in Cameroon. Data obtained were subjected to analyses of variance to determine the presence of genotype × environment (G × E) interactions, and to joint regression analyses to measure the performance of clones across environments. The first experiment produced higher yields and contained more stable clones than the second. In both experiments, mean yields were almost twice as high in 1984 (21·1 t/ha) as in each of the other years (c. 11·0 t/ha), and highest at Nyombe (18·0 t/ha). In Expt 1, the G × E interaction mainly concerned interaction with location, whereas in Expt 2 it concerned interaction with years.

Clones 1611 (Expt 1) and 048 (Expt 2) yielded above average and gave linear regressions significantly above unity (b > 1·0) for most traits, indicating specific adaptation to high-yielding environments and hence below average stability. Clones 1112, 1639 and TIbl (Expt I) yielded above average and had regression slopes equal to unity (b = 1·0), indicating average stability and thus general adaptability. Clones TIb2 (Expt 1) and 1487 (Expt 2) produced below average yields (b < 1·0), indicating specific adaptation to low-yielding environments. Since sweet potato is grown mainly for human consumption in Cameroon, a preferred clone must have stable marketable yields. Only clones 1112, TIbl and 1639 could be considered desirable for release to growers.

Experiments were carried out between 1983 and 1987 in a cool but dry environment in Tasmania to evaluate the growth, development and yield of chinoli compared with the Brassica napus cultivar, Marnoo. In 1983/84 chinoli plants became large, with many pods, but then lodged at the stage of peak pod development. Seed yields were less than half those of the B. napus lines and only slightly better than that of B. campestris, ‘Jumbuck’. In subsequent experiments, lodging was either delayed or completely eliminated, either by the application of plant growth regulators, particularly PP333, or by using low populations or late sowing. However, these remedial measures were all associated with lower seed yields. Early flowering before the achievement of adequate plant size and then the setting of a large number of pods resulting in few seeds in each were identified as the main reasons for the low seed yields in chinoli. Irrigation after anthesis increased numbers of seeds/pod and thus gave better seed yields, but still not as high as those of Marnoo.

A Brassica napus line that produces flowers with virtually no petals (Apetalous) was compared for its physiological significance with Marnoo, a related cultivar bearing conventional yellow petals. Experiments between 1984 and 1987 used different growth regulators, plant population densities and irrigation treatments. Apetalous allowed 30 % more short-wave radiation to reach the base of the inflorescence, and reflected only half as much radiation as Marnoo at peak flowering. This allowed leaves to persist and remain active for longer. Apetalous then consistently retained more seeds/pod, each of greater mean weight, at all heights within the crop canopy, resulting in substantially greater yields than Marnoo in most instances. At the highest population density, it retained productive secondary branches, whereas Marnoo had none. Irrigation after flowering increased the yields of both lines by allowing more seeds/pod to be retained, particularly at lower heights in the canopy. In Apetalous, however, even without irrigation, yields remained high. Apetalous does have larger flower parts, other than petals, which could contribute to the larger pods and seeds. This, combined with lower plant populations than Marnoo in some experiments, could have explained some of the effects seen, but the characteristic is worthy of further study in a range of genetic backgrounds and environments.

Chinoli (Brassica campestris subsp. oleifera × subsp. chinensis), Marnoo and Apetalous (B. napus), with contrasting morphological characters, were compared over four seasons in Tasmania in 1985/86 and 1986/87. The total water use estimated from a depth of 70 cm increased in proportion to irrigations. Before irrigation all the crops had a similar pattern of moisture extraction but differences between the lines, and due to irrigations, emerged after the irrigation treatments. The genotypic differences were clearer in the winter sowing of 1986/87, when the growing season was longer. Apetalous, when unirrigated, extracted a greater amount of water from the lower, wetter regions of the soil profile, particularly in the longer winter sowing when its water use was the same as in the treatment receiving one irrigation. With consistently higher stomatal conductance, Apetalous used more water than chinoli or Marnoo. It also maintained a higher turgor at lower osmotic potentials, suggesting a greater degree of drought tolerance than found in the short duration chinoli which, although it had a lower water use, also gave lower seed yields.

In 1984 and 1985, the growth of axillary buds of Brussels sprouts plants was studied at Cockle Park, Northumberland, UK. Bud growth commenced in late September or early October and continued at all nodes until the final harvest in December. Total bud yield increased at a broadly constant rate until late November but at a decreasing rate thereafter. Plants produced c. 100 nodes with buds ≥ 5 mm diameter. The largest buds were c. 40 mm diameter and 25 g fresh weight. Bud size increased from the base of the stem upwards to between the 20th and 40th nodes and then decreased towards the apex. Nodes 20–40 (20% of the total) produced c. 40–45% of total bud yield. The size profile of leaves along the stem followed a similar pattern to the buds and the largest buds were in the axils of the largest leaves. There were close relationships between bud fresh weight and size, bud fresh weight and size, bud fresh weight and volume and log10 bud fresh weight and log10 bud size (r2 ≥ 0·995). The density of buds was c. 0·8 and bud fresh weight doubled for each 5 mm increase in bud diameter.

Current photosynthesis of the leaf canopy was apparently the major source of assimilates for bud growth. A C14 tracing experiment suggested that growth of individual buds was mainly supported by their subtending leaves. There was no evidence of re-translocation of dry matter from dying leaves or the stems to buds or of substantial production of dry matter by the buds themselves. Rates of bud photosynthesis were only about 10% of the rate of leaves. The continued increase in bud fresh weight and size at the lowest nodes when leaves were senescing rapidly and after they had abscissed was probably mainly the result of water uptake rather than dry matter accumulation.

The objective of this study was to identify traits related to growth and yield response under drought stress in the field which would show less variation than yield itself. Experiments were conducted in 1987, at Durango, Mexico and at Michigan, USA. Twenty-six dry bean genotypes were sown under supplementary irrigation and terminal drought stress. Plant samples were taken at 50% flowering, mid-pod-filling and physiological maturity. At both sites, leaf expansion rate and crop growth rate at mid-pod-filling were greatly reduced by drought stress, resulting in significant reductions in total dry matter (DM) above ground and seed yield at physiological maturity. Because of differences in the timing and intensity of the drought stress, the yield components were affected differently at each location. Total DM content at physiological maturity, harvest index and number of pods/m2 were the only traits positively correlated with yield under stress at both locations. In order to evaluate a group of genotypes for adaptation to drought on the basis of seed yield, the genotypes should be grouped according to their phenological characteristics to stress them evenly.

The median concentration of phosphorus and potassium in a total of 867 samples of wheat and barley straw at harvest in England in 1986–88 was 0·07% P and 1·00% K in the dry matter. Variation was significant between years and between crop species. The concentration of potassium in wheat and barley straw increased with increasing rate of applied nitrogen at 60% of the sites where this was tested. The results have been incorporated into practical recommendation systems for farmers.

In 1989 three experiments with up to three different treatments each were carried out in North Germany to determine the ammonia flux densities after the application of liquid slurry using the micrometeorological mass balance method.

In Expts 1 and 2, pig slurry was applied with a conventional surface spreader to wheat stubble. The results demonstrated the influence of meteorological conditions and that of incorporation on the extent of ammonia volatilization. In comparison to warm and windy conditions, NH3 losses decreased from 56% of the NH4-N applied to wheat stubble to 42% during a cool and rainy period. When slurry was incorporated immediately into the soil, ammonia losses were significantly reduced to 20 and 10%, respectively, of the applied NH4-N. The highest losses (67% NH4-N) were found when slurry was applied during warm weather on wheat stubble covered with chopped straw. Soil cultivation of the wheat stubble before the application of slurry diminished the ammonia emission from 42 to 28% of the NH4-N.

In Expt 3, cattle slurry was applied to rape. It was found that compared with a conventional surface spreader the ammonia volatilization was reduced from 68 to 58% of the NH4-N when an alternative distribution system consisting of drag hoses was used for the application.

The nutritive value of taro leaf (Colocasia esculenta) silage, with or without various crop or crop byproducts as additives, was evaluated in two experiments in Western Samoa in 1988 and 1989. In Experiment 1, laboratory silos were used to assess the quality of eight taro leaf silages which were either ensiled fresh or wilted overnight. Taro leaf ensiled alone was poorly preserved with a pH of 5·4 and high concentrations of ammonia-N and volatile fatty acids. In contrast, silages with crop byproduct additives rich in water soluble carbohydrates (WSC), mainly molasses, ripe banana or papaya pulp, were of high quality with pH levels of c. 4 and low concentrations of volatiles. Copra meal, although low in WSC, was able to produce a satisfactory silage when added to taro leaf through its ability to restrict fermentation.

Despite only a small increase (14·2%) in silage dry matter (DM) content, wilting of taro leaves resulted in silage of significantly higher quality than that made from fresh leaves. Most of the benefit of wilting was attributed to better fermentation conditions rather than a restricted fermentation.

Two of the better silages from Experiment 1, taro/molasses and taro/banana, were prepared on a larger scale in earth pits and fed to goats in a second experiment. Both silages were highly palatable and digestible; DM intakes of 47 and 63 g/kg W0·75 per day and organic matter digestibilities of 69·0 and 74·9% were recorded for the banana and molasses silages, respectively.

It was concluded that taro leaf is a suitable forage for ensilage, and when combined with additives rich in WSC, a forage of high nutritive value can be produced.

Optimum applications of N fertilizer, Nopt have been related successfully to the amount of mineral N in the soil, Nmin in some parts of Europe but not always in the UK. If there is a body of mineral N, QN, that ultimately lessens the need for N fertilizer, it will not remain constant in its amount or its position. Mineralization will add to QN, while the nitrate component of QN will be leached downwards.Also, part of QN will be taken up into the crop where it will continue to lessen the need for fertilizer N but will be safe from leaching. A computer model was used to simulate these processes for 23 experiments, covering five sites and five years, in which N opt had been estimated. From these simulations we derived trial values of QN that took account of mineral N to a series of depths on a series of dates. For each date we used the trial values to find the depth for which Nopt was best correlated with QN andassumed that this was the depth, dL, of the lower boundary of QN on that date. Thus dL was a collective value for all 23 experiments. The value of dLincreased throughout the winter and the spring and was very closely related to the cumulative average drainage through 0·5 m soil at Rothamsted. By 15 April, dL, was 1·66 m, a depth that was compatible with observations by others that winter wheat can remove mineral N to a depth of at least 1·5 m. We inferred two likely reasons why Nmin may fail as a predictor of Nopt in the UK: insufficient depth of sampling, and too wide a spread of sampling dates. The values of Nopt were shown to be related satisfactorily to the values of QN computed, without any measurements of mineral N, for appropriate depths on single dates.

Three change-over experiments with yearling cattle examined the effects on voluntary intake and digestibility of treating barley, oat and wheat straws with NaOH. Increases in intake due to the NaOH treatment were: with barley straw 31 %, oat straw 9% and with wheat straw 1 %, and the corresponding improvements in digestibility were 36, 13 and 24%. A further three experimentswith yearling heifers and steers measured the effects of supplements on the responsein feeding value to NaOH treatment of wheat straw. Increasing the daily supplement of rolled barley from 10 to 3·4 kg led to a decrease in voluntary intake of treated straw from 4·6 to 3·6 kg organic matter (OM), while including urea, to increase the concentrationof nitrogenin a beet pulp supplement from 19 to 24 gN/kg dry matter (DM), gave an increasein intakeof straw from 3·4 to 4·8 kg OM. Providing more than c. 15 gN/kg dietary DM did not lead to a significant increase in voluntary intake or digestibility. In a further experiment, isonitrogenous supplements of rolled barley and soyabean meal, or rolled barley and fishmeal, led to similar intakes and digestibilities of treatedstraw. The variation in response to NaOH treatment is discussed.

Twenty-four Bos indicus cows of the Mashona/Nkone breeds, 36 dairy crossbreds (Mashona/ Nkone x Friesian), 48 Holsteins, 42 Friesians and 25 Jerseys were used to study the effect on milk production of sometribove (500 mg), a prolonged release formulation of bovine somatotropin (BST). BST was administered at 14-day intervals by subcutaneous injections into the ischio-rectal fossa which lies lateral to and on either side of the anus (tailhead). With the exception of the Bos indicus cows, which received seven injections of BST, all other treated cows received eight.

The administration of BST to Bos indicus cows, significantly (P < 0·05) increased milk yield from 0·45 to 1·75 kg/cow per day, and extended lactation. These effects combined to increase total milk production during the 14-week trial from 226 kg for the control group to 993 kg for the group treated with BST. With dairy crossbreds the use of BST significantly (P < 0·01) increased milk yield from 8·6 to 11·0 kg/cow per day. Milk composition for Bos indicus and dairy crossbreds wasunaffected by the administration of BST

BST significantly (P < 0·05) increased milk yield in Jersey (+ 2·9 kg/day), Friesian (+ 3·6 kg/day) and Holstein (+ 2·7 kg/day) cows. Bodycondition of treated cows tended to be slightly lower than that of the control cows at the end of treatment.

Cows remained in excellent health throughout all the trials. Farmers commented on how easy the injection was to give in the tailhead site, and on the complete absence of any adverse injection site reaction.

Breeding records over 12 years (1977–89), involving 455 West African Dwarf does derived from an original population of 133 breeding does, were used to examine the influence of dam age on the incidence of multiple births and perinatal reproductive wastage due to abortion and neonatal deaths. The animals were semi-intensively managed in two goat research units at the University of Ibadan Teaching and Research Farm.

The regression results showed that the variable component, multiple births, increased (P < 0·01) linearly with advancing age of the doe, while the incidence of abortionsand neonatal deaths increased (P < 0·01) exponentially with doe age. Graphs plotted from the regression results indicated a sharp increase in the incidence of abortion and neonatal deaths between the ages of 6 and 7 years. This suggests that the practice of keeping these animals for longer than necessary, especially in rural areas of the country where they are mostly reared and kept for prestigious reasons, should be re-evaluated. Therefore it is recommended that to maintain an economically viable production system, does should be culled between the ages of 6 and 7 years and the provision of replacements planned accordingly.

Maiden 18-month-old Cashmere does (JV=254) were inseminated laparoscopically with frozenthawed semen after treatment with Controlled Internal Drug Release devices and pregnant mare's serum gonadotrophin (PMSG) in the breeding season of 1989 in Tasmania. Kidding rates(does kidded/inseminated) were not statistically different after the insemination of 1, 5 or 25 × 106 motile spermatozoa (50·0, 55·8 and 56·4%), andfor semen frozen by the pellet or straw methods (56·8 and 50·8%). The fertility results suggest that the critical threshold may not have been reached at 1 × 106 frozen-thawed motile spermatozoa.