In a field experiment where winter wheat and winter barley were sown on the same date, the patterns of root growth of the two species were similar, with a few roots reaching a depth of at least 120 cm. Roots senesced sooner in barley, in association with earlier maturity of the shoots and grain. The number of shoots and leaf area index of the barley were greater than for the wheat, but rates of dry-matter production until anthesis of the barley were similar in both species. The grain yield of wheat was about 10% heavier than for barley. Where chlormequat had been applied in early December at the 3- to 4-leaf stage, when shoot apices of both species were still vegetative, root density of the winter wheat in the following March and April was slightly greater than for untreated plants, but the difference disappeared later. For winter barley there was no effect of chlormequat on root growth until July when root length tended to be greater at depth after the chlormequat treatment. The chlormequat treatment significantly shortened stem length, but did not significantly affect the number of shoots, crop dry weight or grain yield of either species.

Oestrous activity of three flocks of Ossimi, subtropical fat-tailed ewes was detected by teaser rams over a calendar year. The flocks were raised at north Delta, mid-Delta and middle Egypt.

The two Delta flocks showed irregularity in percentage of ewes coming into oestrus monthly, with a marked decrease in March, April and May, April being the lowest. On the other hand, the mid-Egypt flock showed consistent oestrous activity throughout the year, with small fluctuations.

The three flocks showed month-to-month variation in incidence of oestrus per ewe, with lower activity in the spring months. Neither of the two Delta flocks showed real regular oestrous activity in any month throughout the year, with high ewe variation. Some ewes showed regular activity throughout the year (16–20 cycles), whereas some others showed only 4–7 cycles per year.

There were two periods of the year with high frequency of anoestrus. The more intense was March–May while fewer ewes had an anoestrous period in July–August. This was the case in the three flocks but with varying intensity.

A period of more than 1 year of detecting oestrus affected oestrous performance of the ewes and should be avoided.

Rations for dairy cows are often formulated using predictions of voluntary feed intake calculated from regression equations. The accuracy of the predictions of dry-matter intake by seven equations is investigated. Comparisons are made when live weight is taken to be the observed weekly mean (MLW), the observed live weight after calving (CLW) or an estimated breed weight accompanied by a notional pattern of live-weight change (BLW). Data recorded on a British Friesian dairy herd at the Grassland Research Institute fed mostly silage ad libitum and various supplements are used. The mean square prediction error (MSPE) is calculated for each week and summarized over the whole experimental period.

The least MSPE's are 2·1, 2·8 and 2·4 (kg D.M.)2 for comparisons using MLW, CLW and BLW respectively. The Ministry of Agriculture, Fisheries and Food (1975) equation involving only live weight and milk yield performs well and would be useful when only the limited measurements of live weight and milk yield are available, but the more complex equations of Vadiveloo & Holmes (1979) and of Lewis (1981) give consistently the best predictions. The importance of using the original definitions of the variables when applying a predictive equation is illustrated. Even so, the large errors found in the predictions of intake points to the need for further research.

Field experiments to study the effect of pre-sprouting, cutting seed and seed soaking in plant regulators on the number and size of seed tubers and yield of potatoes were conducted during the autumn crop seasons of 1978–9 to 1980–1. At the same seed rate, cut seed produced significantly more sprouts and stems, seed-size tubers and seed yield than the whole seed without affecting the aggregate yield. Similar effects were recorded with soaking whole non-dormant tubers in 10 mg GA 3/1 solution for 15 min before planting. Soaking whole non-dormant seed in 0·5% thiourea solution for 1 h increased the number of sprouts and seed-size tubers, giving increases in seed yield of 2·26, 2·73 and 2·65 t/ha over soaking seed in water in the three consecutive years. The corresponding increases in aggregate yield were 1·79, 1·48 and 1·60 t/ha. Soaking cut seed in solutions of 10 mg GA 3/1 and 0·5% thiourea singly or in combination had an adverse effect on the yield of potatoes.

The amounts and rates of release of the different categories of soil K were measured on 21 soils from field experiments in England, Wales and West Germany using a calcium saturated cation exchange resin. The soils contained various amounts of exchangeable, fixed and matrix K; some contained no fixed K at all. These amounts could be qualitatively related to the clay contents of the soils.

Regression analyses of K removed at harvest by spring barley, winter wheat, field beans and sugar beet, grown in the field experiments, were made on the quantities measured by the Ca-resin method and on K exchangeable to M ammonium acetate (EK). The Ca-resin method proved a better predictor of K availability than EK for all four crops. A multiple regression of the amount and rate of release of exchangeable K, and the rate of release of fixed K, as measured by Ca-resin, gave the best correlation with K removed. The contribution of fixed K to the regression increased with the demand of the crop for K and with the length of time the crops had been grown without K fertilizer. For the cereals, fixed K appeared to be either completely available or unavailable depending on whether its rate of release exceeded a critical value characteristic of each crop.

The Ca-resin method is probably the best method available for measuring K reserves. It is, perhaps, too laborious for routine soil analysis, but could be used to characterize the long-term K release properties of a soil.

Working rules for determining plot size and number of plots within a block in field experiments are proposed based on the value of the intrablock correlation (ρ), which can be obtained from the analysis of variance of a randomized-block experiment. The method uses Binns' (1982) equation to relate this correlation to Smith's (1938) empirical law. The rules are: (1) if ρ is greater than 0·5, use an incomplete block design or reduce the plot size in order to increase the number of replications; (2) if ρ is less than 0·1, an increase in plot size is effective; (3) if ρ is between 0·1 and 0·5, an increase in plot size and a decrease in the number of plots per block may be helpful in combination.

A nutrient indexing survey of the soils and rice crop was conducted on 300 fields of four villages in some floodplain areas of Ludhiana. The soils are, in general, alkaline in reaction, highly calcareous, medium in organic matter and mostly heavy in texture. Soil analysis (DTPA extraction) indicated that about 27% are deficient in available zinc. Leaf analysis indicated the concentration of N, Zn, Cu, Fe and B to be below their critical levels in 27, 25, 93, 39 and 6% of the samples respectively: the low levels of Cu(l–3 μg/g) are considered as a ‘hidden hunger’ as the crop lacked any visual Cudeficiency symptoms.

Correlation studies indicated the absence of any relationship between the micronutrient status of the soils, assessed by DTPA extraction, and leaf content. Consequently leaf analysis is recommended for evaluating the nutritional disorders of lowland rice.

Chemical compositional (protein, fat, ash and water) changes in the fleece-free empty body, carcass, viscera and ‘remainder’ components of Corriedale wether sheep were measured by serial slaughter of animals following five different growth paths.

The composition of sheep, after losing up to 34% of body weight over 18 weeks at 125 g/day, was significantly different from a continuously growing control group at the same body weight, but the actual differences in the weights of tissues were small. At the end of weight loss all treatment sheep contained more fat and protein, and less water than controls.

The different growth paths followed during weight loss led to differences in the proportions of protein, fat, ash and water lost and to differences between the three body components in the relative contribution made by each.

The periods of weight loss led to changes in the relative growth coefficients for chemical constituents during realimentation, particularly those of fat and ash which were reduced, and of water which was increased.

The response to realimentation differed between body components, particularly the carcass and viscera. Above the body weight at which weight loss was imposed the realimented sheep did not differ in chemical composition from the continuously ad libitum fed controls when compared at the same weight.

In four consecutive experiments, plasma uric acid (PUA), hepatic xanthine dehydrogenase (XDH) and body-weight gains (WG) of broiler chickens were measured under varying dietary methionine, protein and energy. In Expt 1, increases in WG with increasing dietary methionine peaked at 0·60%, a level where the initial decreases in either PUA or XDH reached a minimum. PUA and XDH in broiler finishers (Expt 2) decreased between 0·26 and 0·50% dietary methionine while WG improved between 0·26 and 0·50% methionine. XDH in the 18% protein and 0·68% methionine + cystine (MC) diet combination for Expt 3 was 66·4 μtmol/10 min/total liver weight, a value higher than either the 43·5 or 46·5 μtmol/10 min/total liver weight, respectively obtained in the 21% protein + 0·68% MC and 24% protein + 0·68% MC diet combinations. Both PUA and XDH, however, increased with increasing dietary protein when MC was either 0·76 or 0·84% diet. XDH in Expt 4 decreased between 11·7 and 13·4 MJ ME/kg diet that contained either 0·76 or 0·84% MC, tending not to vary between 13·4 and 15·1 MJ ME/kg diet. This enzyme activity remained essentially similar between 11·7 and 15·1 MJ ME/kg diet that contained 0·68% MC.

Three trials were conducted over two cropping seasons, on portions of the production fields of the Nigerian Sugar Company sugar-cane estate, Bacita, to evaluate the efficacy of several herbicide mixtures for weed control in sugar cane using the varieties Co. 957 and Co. 1001. With a broad spectrum of weeds, early post-emergence applications of diuron + hexazinone (2·0 + 0·7 kg a.i./ha) followed by hexazinone + paraquat (0·5 + 0·3 kg a.i./ha) about 8 weeks after the first application gave satisfactory weed control that resulted in high cane yields. Addition of glyphosate to the mixture for the first application or its substitution for paraquat in the second application, or both, resulted in increased suppression of nutsedge. This was, however, more phytotoxic to the sugar-cane plants. Addition of pendimethalin to either diuron or hexazinone improved the control of grass weeds. Hexazinone-based mixtures were found to give longer-lasting weed control than the diuron-based mixtures. Both diuron and hexazinone were generally more selective on Co. 957 than on Co. 1001. The degree of weed infestation between 6 and 12 weeks after planting was inversely related to cane yield.

Metal contents are reported of the soils from a field experiment in which two rates of various organic manures, including sewage sludge and sludge compost, were applied from 1942 to 1961. Changes in the concentrations of some elements in the sludges during the 20 years are also presented.

The percentage recoveries of the added metals Zn, Cu, Ni, Pb, Cd and Cr in the topsoil varied from 71 to 96%. In 1960, extractability of the metals from the soils by 0·05 M-EDTA was 50% of the aqua regia-soluble total metals. This figure did not vary greatly with metal or with the type of organic manure that was applied.

In Expt 1 the efficiency of absorption of phosphorus in feedingstuffs was compared within four sets of 18-month-old, chimaera-derived triplets; 12 feedingstuffs were evaluated in four balance trials with 32P. Seven diets consisted of a P-rich ingredient mixed with a low-P basic diet and five of hay or pelleted dried grass or lucerne. The P ingredients tested were the protein-rich meals, rape, soya-bean, maize gluten, fishmeal and rice bran, and the cereals, barley and wheat.

Sets of triplets absorbed dietary P with different (P < 0·001) efficiencies; the mean values were 0·72, 0·63, 0·76 and 0·79. The availability of P differed (P < 0·001) between diets, highest values being seen with the fishmeal (0·80), barley (0·78) and wheat diets (0·78) and the lowest with rice bran (0·63) and a perennial ryegrass hay (0·64). There was no evidence for an age effect on efficiency of absorption.

Endogenous faecal excretion was positively related to intake (P < 0·001) and negatively related to efficiency of absorption of dietary P. Plasma concentration was positively related (P < 0·001) to both intake and, between sets, to the efficiency of absorption.

Significant urinary excretion of P generally occurred when the efficiency of absorption was greater than 0·70. Two members of a set which absorbed P with high efficiency and excreted low volumes of urine died from urethral obstruction caused by calculi.

In Expt 2 an estimate of the variation in the concentration of P in plasma of 48 ewes on a barley-based diet was assessed and the values for three of the chimaera sets fell within the top quartile.

Safety factors were calculated from the animal and plant variations in the efficiency of absorption of dietary P and used to determine dietary allowances for different classes of sheep.

The ruminal metabolism of lactic acid was investigated in vivo under normal feeding conditions in four sheep each adapted to one of the following diets: high-concentrate, intermediate, high-roughage containing 65, 43 or 10% maize meal and molasses respectively, or lucerne hay. A continuous basal turnover of ruminal lactate (0·01–0·02 mmol/1/min) was found which increased 10- to 40-fold immediately after feeding when production exceeded utilization and lactate accumulated in the rumen. This was followed by an increase in utilization rate which removed the accumulated lactate. Both lactate and glucose turnover were related to the amount of readily fermentable carbohydrate in the diet. Approximately 8, 6·5, 5 and 2·5% of the total VFA was formed through lactate on the high-concentrate, intermediate, high-roughage and lucerne hay diets respectively.

Rumen microbial counts of total culturable, glucolytic, amylolytic and lactateutilizing bacteria, and of ciliate protozoa were also performed on the four sheep. Numbers of micro-organisms in all groups were highest on the high-concentrate diet and lowest on the two roughage diets. The proportions of the predominant genera from the different metabolic groups of bacteria differed, although in most cases the same organisms were present in the rumen on all diets. The succinate pathway was found to be quantitatively more important in the conversion of lactate to propionate in the rumen. Although the numbers of lactate-utilizing bacteria increased as the amount of RFC in the diet increased, their metabolic activity was actually lower. Reasons for this finding are discussed, together with factors influencing the regulation of lactate production and utilization in the rumen.

Four trials were carried out to investigate the effect of inter-plot competition on seed yield and plant height of field beans using experimental designs balanced for neighbours. One trial tested four varieties ranging in final height from 25 to 100 cm and sown in four-row plots with 30 cm spacing between rows and one blank row between plots. When grown between plots of a dwarf variety, the plot yield of the tallest variety was increased by 20% compared with its pure stand yield: a complementary reduction in yield was shown by the dwarf variety when grown between plots of the tall. The effect on the yield of the inner rows of the plot was somewhat smaller than that of the outer rows but still significant. Another trial with six commercial varieties differing in final height by less than 15 cm showed no differential effects of inter-varietal competition on yield. In two trials with six varieties of widely differing heights planted with 50 cm spacing between rows, but no gap between plots, plot yield was strongly affected by the neighbouring variety in the trial with single-row plots, while yields from the four-row trial showed a large interaction between variety and inner and outer row position, again indicative of inter-variety competition. The yield response to competition could be described by a common linear regression on the excess height of plot neighbours: there was little evidence of varietal differences in sensitivity or aggressiveness.

Plant height showed a positive response to height of plot neighbours in all four trials, whilst in the single-row trial, the ratio of grain yield to total dry-matter production (harvest index) was negatively related to excess height of neighbours.

The results suggest that, when testing varieties differing in height by more than 20 cm, at least two buffer rows, e.g. six-row plots with the centre two rows harvested, are required to obtain a true comparison of pure-stand yield. Alternatively, when this procedure would result in an unacceptable use of resources, one of the statistical models adapted in this paper may be used to adjust variety yields for pure stands.

Heterosis and combining abilities for yield, bollworm resistance, fruiting efficiency and photosynthesis were studied in a five-parent diallel involving cotton (Gossypium hirsutum) strains differing in their resistance to the bollworm complex (Heliothis zea and H. virescens).Substantial magnitudes of useful heterosis (over the commercial cultivar ‘Coker 304’) were observed for yield and other agronomic characters. Useful heterosis for yield ranged from 1 to 32·7%. The highest yielding hybrid was Coker 304 × PD 695. The strain PD 695 is moderately resistant to bollworms.

All the hybrids having at least one resistant strain as their parent suffered less damage from bollworms than Coker 304. The resistant strains (BW 76–31, PD 695 andred leaf cotton) had desirable general combining ability (GCA) effects for bollworm damage. Relative yield (yield without protection expressed as percentage of yield with protection) was used as a measure of bollworm resistance. The high gossypol strain BW 76–31 had desirable GCA effects for relative yield, bollworm damage to buds, number of live worms and for bolls per plant. The fruiting efficiencies and photosynthetic rates of some bollworm-resistant strains were similar to those of a high-yielding, moderately susceptible cultivar.

Combining-ability analysis indicated BW 76–31 to be a desirable parent for use in hybridization programmes for improving agronomic performance, fruiting efficiency, photosynthetic rate and bollworm resistance. It was also observed that bollworm-resistant cottons do not always have lower fruiting efficiencies and photosynthetic rates and it might be possible to combine this resistance with high yields.

Plants of the Cucurbita pepo L. cultivars Cinderella, Cobham Bush Green and Gold-rush were inoculated with six strains of cucumber mosaic virus (CMV) from different geographical areas and known to differ in pathogenicity and virulence. The cv. Cinderella showed high resistance to all strains, cv. Cobham Bush Green was moderately resistant and cv. Goldrush was highly susceptible particularly to the CMV–SEV strain which caused necrotic symptoms.

Sixty families of each of two tomato triple test crosses (S 120 × EC 61747 and EC 31513 × Pusa Ruby) were raised in completely randomized blocks in two replications with two fertilizer levels. Perkins & Jinks' (1971) analysis was used to detect and measure the interactions of additive, dominance and epistatic effects of genes with micro- and macro-environments for flowering time, maturity period, number of branches, final height, number of locules, number of fruits per plant, yields per plant and weight per fruit. Additive and dominance gene effects were almost equally sensitive to micro- and to macro-environments. The j and l type epistasis was more sensitive to the environments than the i type epistasis.

A series of experiments in Tasmania examined the growth, development, yield and components of yield of new Australian oil-seed rape cultivars from Victoria and Western Australia. The highest yields obtained were around 5·5 t seed/ha, from an autumn sowing with supplementary irrigation. Spring sowings with irrigation or autumn sowings without produced up to 4 t/ha. The Victorian lines with Japanese parentage clearly outyielded the Western Australian cultivars or Midas, a widely grown Canadian cultivar. When autumn sown, the Victorian lines grew more rapidly at low temperature, which under conditions of later stress contributed to a high yield relative to the other cultivars. However, the most consistent feature from both autumn and spring sowing was high rates of seed survival, up to near the potential number of around 30 per pod, giving very large numbers of seeds per m2. While individual seeds in the Victorian lines, particularly Marnoo, were smaller than in Midas, oil content remained high except under extreme stress in the later stages of seed development.

To ascertain the inheritance of seed shape and resistance to Ascochyta blight and to incorporate resistance in commercial cultivars, crosses were made between cv. Kinnauri, a round-seeded resistant source and commercially important cvs Bonneville, Lincoln, GC 141, and Selection 18, highly susceptible to disease but wrinkled-seeded. The F1, F2 and F3 data indicated that seed shape and resistance to Ascochyta blight is determined by two independently inherited genes. Round seed and disease resistance are dominant over wrinkled seed and susceptibility. Commercially desirable lines have been selected which combine the resistance gene of Kinnauri with wrinkled seed from susceptible commercial cultivars, and which also possess high pod yields and other desirable characters.

The effect of sowing date on root growth of high-yielding crops (8–1 It grain/ha, 85% D.M.) of winter wheat (Triticum aestivum L. cv. Hustler) was measured at Rothamsted and Woburn in 1980 and 1981. Roots were sampled by coring on five occasions and changes in root dry weight and length were determined. The average growth rate between March and June was about 1 g/m2/day (200 m/m2/day), over 5 times that measured between December and March. Increases in root weight or length with time were generally exponential to anthesis when the crops had 101–172 g root/m2 (20–32 km/m2). September-sown wheat had more root than October-sown wheat at all times, but whereas early differences in length were maintained throughout the season, root weights converged between March and June. Overall, there was no significant difference in root dry-matter production between sites at anthesis, but there was a substantial difference between years. Differences in root growth between crops were reduced by plotting the amount of root against either the number of days from sowing or accumulated thermal time. Using che latter, root growth between December and June was reasonably linear although there was some indication of a lag below 500 °C days. Regression equations obtained for the relationships between root growth and accumulated thermal time also fitted previously published data and may provide general descriptions of root growth with time.

Roots of September-sown crops reached 1 m depth by December but those of October-sown crops were not detectable at this depth until April. For most crops the distribution of roots with depth was reasonably described by an exponential decay function, with over 50% of the roots in the top 20 cm of soil at all times. At Woburn in 1981, a plough-pan restricted roots to the upper soil horizons for most of the season but apparently had little effect on the total amount of root produced. For one of the experimental crops an empirical mathematical function describing the distribution of roots with depth and time is presented.

Using the data from this and previously published studies, the relationship between grain yield and the amount of root at anthesis was investigated. Total root length was positively correlated with grain yield but nonetheless similarly yielding crops could have different-sized root systems. Total root dry weight was poorly correlated with grain yield.