Lesion development and growth of Xanthomonas malvacearum (E. F. Smith) Dowson were followed in seedlings of different cultivars of cotton (Gossypium hirsutum L.) after inoculation of hypocotyls. There was a close relationship between numbers of the parasite and length of hypocotyl lesion. Disease development could be accurately determined by measurement of lesion length from 2 to 3 days after inoculation until growth of the parasite ceased. Growth patterns of the parasite in vivo took the form of a distinct period of exponential (phase 1) growth followed by relatively little, if any, further increase in numbers (phase 2 growth). The duration of phase 1 growth was related to host resistance and environmental factors.

The post-weaning growth, frame size and body condition of Hereford (H × H), Brahman × Hereford (B × H), Simmental × Hereford (S × H) and Friesian × Hereford (F × H) heifers were evaluated on three pasture systems in each of five years. One group of heifers was grown from weaning (at 8 months of age) to 18 months on the high-pasture system, which included supplementation with grain, while the other two groups were grown to 30 months on pastures of medium or low quality. Pasture effects were large compared with differences between years, with average daily gains between weaning and 18 months of 552, 275 and 97 g/day on high, medium and low pastures, respectively. Genotype had a significant effect on all measurements. Pasture × genotype interaction was significant in most instances. While crosses grew faster and were heavier than H × H on all pastures, S × H were heaviest by 18 months on high pasture, with B × H heaviest at all ages up to 30 months on both medium and low pastures. There was little difference in live weight between B × H and F × H on high pasture, or between S × H and F × H on medium pasture, whereas F × H was heavier than S × H on low pasture. There were concomitant differences in measures of skeletal size, but when adjusted allometrically to a common live weight, pasture effects were removed, while differences between genotypes remained. At a common live weight F × H had the largest height, length and pelvic area, but shared the lowest body condition with S × H. Pelvic height was greatest among B × H heifers, but this cross had similar body length, condition and subcutaneous fat cover to H × H. The pattern of genotype × pasture interaction observed in this study was similar to that observed by Darnell, Hearnshaw & Barlow (1987) for growth rate among contemporary steers located in different environments.

Published data are used in support of a hypothesis that equal amounts of digestible cell walls and digestible non-cell walls do not contribute equally to the energy value of forages. The relationship between the concentration in the organic matter of metabolizable energy (kcal/g organic matter) determined at the maintenance level of feeding, and the percentages of cell wall and digestible cell wall in the forage organic matter is defined by:

This equation derived from published data on 12 grasses appears to be applicable to both grasses and legumes.

Forty-one experiments were carried out in England and Wales between 1983 and 1985 to compare ammonium nitrate and urea as N top dressings for multicut silage.

The results showed that relative dry matter yields from the two fertilizers differed considerably between sites. However, compared with ammonium nitrate, there was a mean yield decrease with urea of 2% at the first cut and 5% at the second cut. Mean herbage N contents and apparent N recoveries were lower with urea than with ammonium nitrate at both the first and second cuts. It appeared, at least for first-cut dressings applied in early spring, that urea effectiveness increased with the amount of rain falling within 3 days of fertilizer application. The effect was much less obvious at the second cut.

Urea effectiveness was not markedly reduced on soils of high pH or light texture, where higher ammonia volatilization losses might have been expected.

At Mount Derrimut Field Station from 1982 to 1985, growth and body composition was studied in three groups of wethers from the same flock. A control group (C) and a restricted group (R) were housed from the age of 1 day until slaughtered. The first slaughter was at the age of c. 1 year (reported elsewhere) and the second at the age of c. 3 years. Apart from the first 36 days, when group R was fed a severely restricted ration, both groups were fed a high quality diet ad libitum throughout the experiment. At the end of the second year, a group of 2-year-old wethers (G) was introduced, to compare the growth of these sheep with those in groups C and R. Group G sheep were reared on their dams, kept as grazing animals and killed at the second slaughter.

At the age of c. 3 years there was no significant difference between groups C and R for mean fleece-free body weights, but the sheep in group G were significantly lighter (P<0·01) in spite of reaching mature size for grazing sheep in the general flock.

After the age of 7 months there was no significant difference between groups C and R in rate of wool production. Rate of wool production in group G sheep was not significantly different from that of sheep in the other groups except during the last 6 months, when they produced significantly less wool (P<0·05).

Regression analyses for surface and X-ray measurements against fleece-free body weight (independent variable) showed no differences between groups C and R, except for width of metacarpal (X-ray measurement). In this case, the regression coefficients were different (P<0·01) but, at slaughter, actual bone measurements were the same. Both X-ray measurements and those at dissection showed that the metacarpals of group G were significantly (P<0·05) longer and narrower, and had a narrower cortex, than those in the other two groups (P<0·05).

There were no significant differences between groups C and R in mean weight and chemical composition of the parts and tissues examined; however, the carcass fat content of sheep in group G was significantly less (P<0·01) than in the other two groups. The sheep in group G had higher weights (P<0·01) for the brain, the digestive tract (DT), kidneys and liver than those in groups C and R.

Cell size in the semitendinosus muscle, as indicated by the protein[ratio ]DNA ratio, increased (P<0·01) between the first and second slaughters. There were no differences between groups in protein[ratio ]DNA ratios, but the DNA and protein contents were significantly higher (P<0·05) in the kidneys and liver in group G than in the other groups. Although the weights of the semitendinosus muscle were heavier (P<0·01) in groups C and R than in group G, on a fat-free basis, there were no significant differences between treatments in muscle weight or in DNA and protein contents.

It is concluded that sheep will make a complete recovery after a severe nutritional check in early post-natal life if given the opportunity to do so. Even though large differences in body weight may develop between sheep, this appears to have little effect on mature skeletal dimensions. However, at maturity, with grazing sheep that grow relatively slowly, the metacarpals are likely to be narrower and longer than those of the same genotype fed to grow faster. Even with sheep fed ad libitum throughout life, the use of X-ray and surface measurements in young sheep at a particular body weight are unlikely to be useful for the accurate prediction of mature body weight.

Grass silage (21.0 % D.M.) was given ad libitum to sheep together with supplements of rolled barley, dried-grass pellets or dried-grass wafers at 12 and 25 g organic matter (OM)/kg0·75.

Intake of silage was greater with supplement at 12 g/kg0·75 but total intake of OM and digestible organic matter (DOM) increased with increasing supplement. Intake of OM was higher with the pellet supplement than with other supplements. Intake of DOM, however, did not differ between the pellet and barley treatments, but was lower with wafers.

Concentrations of ammonia and total volatile fatty acids and the molar proportions of butyric and higher volatile fatty acids were higher when silage was supplemented with barley than with dried grass. Mean rumen retention times of silage and of supplement were highest in the barley-supplemented treatments. Dried-grass wafers were retained longer than dried-grass pellets. Supplement treatments did not differ significantly for eating and ruminating times, rumen fluid volume and pH, digestion rate in the rumen and nitrogen retention.

At the low supplement rate silage consumption may have been controlled by factors associated directly with the silage, whereas at the high rate intake was limited either by physical factors or by the potential energy demand of the animals.

The correlation between sorption and mobility of potassium in illitic soils has been used to compare K leaching in profiles under different fertilizer treatments in longterm experiments. Estimates of potassium saturation of the cation exchange capacity in 15 cm soil layers to a depth of 225 cm indicated maximum leaching of K in unfertilized soils. Application of N, P and K increased K uptake by plants, reduced K saturation and thus its leaching.

The prospect of climate change has revived both fears of food insecurity and its corollary, market opportunities for agricultural production. In Australia, with its long history of state-sponsored agricultural development, there is renewed interest in the agricultural development of tropical and sub-tropical northern regions. Climate projections suggest that there will be less water available to the main irrigation systems of the eastern central and southern regions of Australia, while net rainfall could be sustained or even increase in the northern areas. Hence, there could be more intensive use of northern agricultural areas, with the relocation of some production of economically important commodities such as vegetables, rice and cotton. The problem is that the expansion of cropping in northern Australia has been constrained by agronomic and economic considerations.

The present paper examines the economics, at both farm and regional level, of relocating some cotton production from the east-central irrigation areas to the north where there is an existing irrigation scheme together with some industry and individual interest in such relocation. Integrated modelling and expert knowledge are used to examine this example of prospective climate change adaptation. Farm-level simulations show that without adaptation, overall gross margins will decrease under a combination of climate change and reduction in water availability. A dynamic regional Computable General Equilibrium model is used to explore two scenarios of relocating cotton production from south east Queensland, to sugar-dominated areas in northern Queensland. Overall, an increase in real economic output and real income was realized when some cotton production was relocated to sugar cane fallow land/new land. There were, however, large negative effects on regional economies where cotton production displaced sugar cane. It is concluded that even excluding the agronomic uncertainties, which are not examined here, there is unlikely to be significant market-driven relocation of cotton production.

In order to learn more about the digestibility, breakdown when eaten and physical structure of stovers and straws, seven diets were compared in one experiment and eight in another. The diets in the first experiment were: the upper and lower parts of lucerne (Medicago sativa) hay, the leaves, upper stem and lower stem of maize (Zea mays) stover and the leaves and stem of sorghum (Sorghum vulgare) stover. The diets in the second experiment were: the upper and lower parts of lucerne hay, the leaves, stems and whole stover of millet (Setaria italica), wheat (Triticum aestivum) straw, rice (Oryza sativa) straw and sweet potato (Ipomoea batatas) haulm. The diets were examined for in vitro digestibility in three forms: milled, chopped (1 cm lengths) and chewed (by cattle). The lengths and widths of the chewed particles were recorded in both experiments. Aspects of the morphology and vascular structure of plant parts of the diets and of chewed particles were recorded in the second experiment.

The in vitro digestibility of chopped or chewed plant material was lower (by 11 and 12 percentage units, respectively, on average) than that of milled material. The difference between chewed and milled material in in vitro digestibility was smaller with leaves (5 percentage units, on average) than with stems (18 percentage units, on average) in maize, sorghum and millet. Digestibility of chewed material was similar to or lower than that of chopped material, except with the leaves of maize, sorghum and millet. Millet stover had higher in vitro digestibility than wheat straw or rice straw, whether the diet was milled, chopped or chewed.

The thinnest stem internode vascular bundles recorded (0·14 mm) were in wheat. The percentage of stem internode cross-sectional area occupied by vascular bundles was in the range 6–8 for lucerne, millet, wheat and rice. The mean numbers of veins or vascular bundles per chewed particle were in the range 6–23. The mean length of the chewed particles varied from 10 mm with the upper stem of maize to 18 mm with sorghum stem and maize leaves. The mean width of the chewed particles varied from 1·8 mm with rice straw to 5·4 mm with maize leaves.

It is suggested that the low digestibility of mature plant tissue such as stovers and straws is not particularly due to thick vascular strands or to a high proportion of vascular tissue, but rather to a high proportion of cell wall and incomplete and delayed access by rumen microorganisms to much of the cell wall.

Sheathed filamentous bacteria, Leptothrix spp. and Gallionella spp., were observed in ochre samples from sites in England and Wales. Thiobacillus ferrooxidans was found in acidic samples (pH < 4·0) and in ochre from drainage water of near neutral pH suggesting that it can contribute to ochre formation over a wide range of drainage water pH, Heterotrophic bacteria capable of growing in artificial media of low pH and complexdegrading heterotrophic bacteria were also isolated. Some ochre deposits could be described as either pyritic or filamentous but the majority of samples fell between these extremes and had various combinations of T. ferrooxidans, sheathed filamentous bacteria and other heterotrophic bacteria.

Two 1-year experiments are described in which a single dressing of 120 lb N/acre (134 kg/ha) was applied to a grass sward as anhydrous ammonia (82% N), ammonium nitrate (34·5% N) or sulphate of ammonia (21% N) at various dates from December to April. The pattern of primary growth from each of the treatments was recorded from early April until mid-June by frequent sampling of the herbage to determine the dry matter and crude protein yields. At every date of fertilizer application from late January to mid-April the growth rate of the herbage was markedly lower with anhydrous ammonia than with ammonium nitrate. With the December applications the spring growth rate of herbage from the anhydrous ammonia treatment was similar to that from the ammonium nitrate treatment. Applications of sulphate of ammonia gave results almost identical with those obtained from ammonium nitrate. The calculation of the dates on which a yield of 2000 lb dry matter/acre (2242 kg/ha) would have been available for dairy cow grazing showed clearly a delay of 12–15 days where anhydrous ammonia rather than ammonium nitrate was applied. The response to anhydrous ammonia was improved by applying it early in the year but solid nitrogen fertilizers, applied either early in the season or when growth was starting, gave higher yields of herbage than anhydrous ammonia.

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.

Effects of N as ‘Nitro-chalk’, P as superphosphate, and K as KCl and K2SO4 on ‘available’ P, K and Mg were examined over 14 years. The area was under grass/clover regularly cut 6 times a year.

Soil pH was maintained by annual applications of ‘Nitro-chalk’ supplying an average of 4 cwt CaCO3 and 174 lb N per acre. Superphosphate supplying 43 lb P per acre per annum increased available P (modified Morgan method) appreciably even on plots where more than this quantity was taken off in herbage. Applied N also consistently increased available P. It was thought that this was because P in the root system was rapidly mineralized. Applied K consistently reduced available P because of increased uptake in cut herbage, with no apparent increase in root P for mineralization.

The amount of available K in soils which received no added K was fairly constant over the period for a given N treatment. About 40 lb/acre/annum of K was released by weathering.

There was a very marked interaction effect between rates of N and K fertilizers on available soil K, the large increase in available K where K fertilizer but no N was applied being considerably reduced with increasing N rates. These effects directly reflected uptake of K in cut herbage.

Residual values of applied P, K and Mg on the respective ‘available’ nutrients were considerable and persistent.

Available Mg was reduced by increasing rates of fertilizer N and by fertilizer K.

The present study aimed to evaluate the effects of chitosan instead of microbial inoculants on fermentation profile, losses, chemical composition, in vitro degradation, and aerobic stability of sugarcane silage (SS). Forty experimental silos (PVC tubes with 28 cm i.d., 25 cm height) were used in a randomized block design to evaluate the following treatments: (I) Control (CON): SS with no additive; (II) LB: SS ensiled with 5.0 × 105 colony forming units (CFU) of Lactobacillus buchneri (NCIM 40788)/g as-fed; (III) LPPA: SS ensiled with 1.6 × 105 CFU of L. plantarum and 1.6 × 105 CFU of Pediococcus acidilactici/g as-fed; and (IV) Chitosan (CHI): SS ensiled with 6 g/kg dry matter (DM) of chitosan. Microbial inoculation of SS reduced (P ≤ 0.05) silage pH relative to CON and CHI treatment. The LPPA decreased ammonia-nitrogen and LB decreased (P ≤ 0.05) ethanol content and increased acetic acid content relative to other treatments. The LPPA-silos had higher (P ≤ 0.05) gas losses and lower (P ≤ 0.05) DM recovery than other treatment silos. Consequently, LPPA reduced (P ≤ 0.05) DM and non-fibre carbohydrates and increased (P ≤ 0.05) neutral detergent fibre (NDF) silage content compared to other treatments. Treatments did not affect (P ≥ 0.212) DM and NDF in vitro degradation and silage pH after aerobic exposure. However, LB reduced silage temperature after aerobic exposure. Thus, LB reduces alcoholic fermentation and improves SS aerobic stability. Inoculation of LPPA reduces DM recovery and negatively affects SS chemical composition. Although CHI positively affects SS conservation relative to CON, it shows higher gas losses and decreased SS temperature after aerobic exposure compared to LB.

Detailed information on the timing of terminal spikelet formation, anthesis, maturity and the rate of leaf appearance is crucial to the predictive accuracy of the AFRCWHEAT2 growth simulation model for wheat. To obtain appropriate data under different growing conditions for two spring wheat (Triticum aestivum L.) cultivars (cvs Minaret and Canon), a main field experiment was conducted comprising eight sowing dates between mid-March and late June 1994; data from single sowings of Minaret in 1992 and 1995 were also included in the analysis. Minaret is the focus of a major European study of the impact of climate change factors on the growth and development of wheat, and data of the type reported here were essential to support the modelling aspects of the project involving AFRCWHEAT2.

The accumulated thermal time from emergence to critical developmental stages was similar for all sowings of both cultivars, even though biomass was greatly reduced in the later sowings. Although final leaf numbers were comparable for all sowing dates, the rate of leaf appearance was correlated with the rate of change of day length at crop emergence in Minaret. The unmodified AFRCWHEAT2 model did not predict the timing of critical growth stages and leaf numbers well, but removal of the vernalization and photoperiod factors from the developmental sub-model greatly improved the accuracy of such predictions. These results strongly suggest that fixed quantities of thermal time may be employed successfully to predict the timing of critical developmental stages of these spring wheat cultivars over a range of sowing dates, geographic locations and climatic conditions, since development appeared to be a linear function of temperature.

Despite removing the photoperiod and vernalization functions, the model consistently over-predicted final leaf number because leaf production by the model continued until 1·8 phyllochrons before anthesis, as compared to the three phyllochrons actually recorded for Minaret. AFRCWHEAT2 could therefore be further modified to reproduce more accurately the smaller number of leaves typical of these spring cultivars.

In two experiments, each involving 200 pullets, sunflower meal as a protein concentrate was compared with high quality fish meal, at two levels of protein intake. Since production was not reduced by the low protein intakes, it was concluded that the quality of the protein in sunflower meal was satisfactory for egg production. When 25% of sunflower meal was included in the mash, the consumption of mash was not reduced but the birds appeared to be unable to maintain high egg production and to maintain body weight at the same time. From this it was concluded that such percentages of sunflower meal gave an undesirably high fibre content and too low an energy value to the diet.

1. The effect of three factors (nitrogen level, time of nitrogen application and weed control) and their interactions on three different plant densities of winter wheat have been measured. Data concerning the growth, development and yield have been examined.

2. Plant populations of 104,000, 155,000 and 281,000 per acre produced on the average of all treatments 21·3, 22·4 and 23·2 cwt. grain per acre, respectively.

3. An increase in nitrogen fertilizer to the 2 cwt. sulphate of ammonia per acre level increased the grain yield of all populations. This response followed an increase in the number of tillers and an increase in the percentage of tillers producing ears. There was no significant interaction between nitrogen level and plant density. The nitrogen content of the grain increased with nitrogen level.

4. Time of nitrogen application did not affect the grain yield, although it did cause considerable differences in the growth and development of the plants. There was no significant interaction betweentime of application and plant density. The late application of nitrogen produced a lower yield of straw and a higher nitrogen content in the grain.

5. Weed control increased the grain yield of all plant populations, this increase following an increase in the number of ears per plant. There was a significant interaction between weed control and plant density. Weed control raised the yield of the low plant population by 3·9 cwt. per acre compared with 0·9 and 2·0 cwt. for the medium and high populations. Weed control also increased the nitrogen content of the grain.

6. The only other interaction concerning grain yield which was significant was that of weed control with time of nitrogen application. Weed control increased the yield of the early and late applications but inexplicably reduced the yield of the intermediate date.

7. It is concluded (a) that the experiment provided no evidence that the yield of a thin stand of winter wheat can be increased further by altering normal nitrogen fertilizer application or by altering the time of application of the fertilizer; (b) that for good results weed control is essential where the plant population is low.

Commercial Celery Cultivars Varied in their response to inoculation by celery mosaic virus. The most severe symptoms occurred in self-blanching cultivars, but a high level of resistance was found in some non self-blanching cultivars such as Solid White and Fordhook. The resistance in these cultivars was confirmed in glasshouse tests.

The K balance, the difference between K added as fertilizer or farmyard manure (FYM) and K removed by the crops, was calculated for soils from the Classical and Ley-Arable experiments at Rothamsted and for the Woburn Ley-Arable experiment, for the duration of each experiment. Linear regressions on K balance accounted for 78% of the variation in exchangeable K (Ke) and for 83% in K uptake by ryegrass (KP) in the Classical experiments, for 56 and60% respectively in the Ley-Arable experiments at Rothamsted, and for 39 and 6% in the Woburn Ley-Arable experiment.

Regressions of Ke and Kp on K balance suggested that, in the Rothamsted Ley-Arable experiments, rather more than half of the K balance remained extractable by ryegrass from the plots with a rotation of crops, and apparently all of the K balance from those under continuous grass. About one-fifth of the K balance remained extractable by ryegrass from the soils in the Rothamsted Classical experiments and soils given FYM retained K slightly better than other soils. With all soils about half the K extractable by ryegrass was exchangeable to ammonium acetate.

The plots with FYM or under continuous grass contain more organic matter than other plots in the same experiments. The following possible effects of increasing the organic matter content of the soils were investigated by calculating the multiple regressions of K, and KB on K balance with either percentage of organic C, total CEC, or organic CEC:

(1) loss of K decreased by increasing the water retention and lessening leaching;

(2) improved K retention by increasing the total cation exchange capacity (CEC) available for K absorption;

(3) improved K retention by a mechanism arising from the different selectivities of clay and organic matter for K relative to Ca.

In the Classical experiments, where organic matter usually increases because of FYM additions, effect (2) seems the most probable, perhaps because the K given in the FYM was already absorbed by organic exchange sites. In the Ley–Arable experiments, where the K was given mainly as soluble K fertilizer and the organic matter develops mainly under grass, effects (1) or (3) seemed to operate, probably simultaneously.

The Woburn Ley-Arable experiment had no continuous grass plots, the soils differed little in organic matter content and no deductions could be made.

The influence of weight of stakes planted on subsequent cassava yields and the stability of yields was investigated in a 4-year study (1986–90) in Nigeria using two cultivars (TMS30572 and TMS91934). Harvest yields were dependent on the weight of stakes planted and an optimum weight of 875 kg/ha for both cultivars was established; which corresponds to an average stake weight of 88 g. Cultivar TMS30572 consistently outyielded TMS91934 (P <0·05). Tissue analysis of 25 cm long stakes from the mainstem and from the primary and secondary branches of both cassava cultivars showed differences in the amounts of food reserves stored in the stakes. More carbohydrate was found in each of the three stakes of the mainstem than in the stakes from the primary and secondary branches of both cultivars. The yields of each cultivar for the three growing seasons did not vary significantly, which suggests that sustainable high root yield appears to be achievable and is greatly aided by the appropriate management of the stakes.