Single chromosome substitution lines of hexaploid wheat were developed using a variety resistant to difenzoquat, Chinese Spring, as donor and a susceptible variety, Sicco, as recipient, and were used to identify chromosomes carrying genes which modify the responses of these varieties. It was found that chromosomes 3B and 5D from Chinese Spring might act to reduce the amount of damage caused by the herbicide in the presence of the allele for susceptibility at the Dfql locus. The intermediate response to the herbicide, which is shown by some commerical varieties, was also investigated using a backcross reciprocal monosomic analysis. In these varieties, the allele at the Dfql locus determining the reaction to the herbicide was shown to be similar to that of the susceptible variety Sicco. It is, therefore, probable that the responses of intermediate varieties are due to the effects of modifier genes increasing resistance.

Six experiments were carried out over 2 years (1985 and 1986) in commercial spring barley crops on calcareous soils in Hampshire. Herbicides increased grain yield by 0·05–1·21 t/ha, and fungicides by 0·01–0·68 t/ha. Herbicide use affected each of the yield components ears/plant, grains/ear, 1000-grain weight and harvest index in one or more cases but the effects were not consistent between experiments or consistently related to yield increases. Fungicide use had little effect on yield components other than 1000-grain weight, which was significantly increased in all experiments. There were no significant herbicide × fungicide interactions. Large differences in yield were recorded between field edge (headland) and midfield plots, with headland plots outyielding the midfield in two of the three experiments where this effect was considered.

The effects of fungicide use were accounted for by associated increases in the green lamina area of the flag leaf and second leaf at the late milk stage of grain development. This is consistent with previous work. Differences in yield response to herbicide between sites were linearly related both to weed numbers early in the season and to weed biomass at harvest. Weeds did not always directly replace crop biomass; in some experiments the combined dry matter production was greater when herbicide was not used. However, the results indicate that, where a diverse weed flora composed of species of moderate to low competitive ability is present, simple weed counts may provide a useful indication of potential yield loss.

It is concluded that headland areas can often be as productive as the rest of the field, but a greater understanding of the factors involved is needed if this potential is to be realized.

While the relative advantage of hybrids over open-pollinated varieties has long been established for temperate sorghums in developed countries, similar information for semi-tropical sorghums used in Africa and India is relatively scant, especially under conditions of drought stress. This study compared 23 hybrids with 21 open-pollinated varieties, all developed in India and/or Southern Africa. Materials were field-tested under conditions of stored soil moisture at two levels of drought stress (dryland or one supplemental irrigation) at Bet Dagan, Israel in 1989.

Irrespective of the water regime, grain yield and harvest index increased and leaf area index decreased with a shorter growth duration of the genotypes. Hybrids were earlier, had a larger leaf area index, more than double the harvest index and produced more grain compared with varieties. In spite of their longer growth duration, varieties were less water-stressed than hybrids, as judged by their midday leaf water potential, relative water content and the extent of leaf rolling. The relatively poor plant water status of the hybrids could be partly ascribed to their larger leaf area index. Hybrids produced more biomass per day than varieties under low stress while varieties produced more biomass per day than hybrids under high stress. Thus, in terms of plant water status and mean daily biomass production, varieties were more drought resistant than hybrids. However, the physiological superiority of the varieties under drought stress did not result in a higher grain yield because of their inherent relatively poor harvest index, typical of the tall and late African sorghums. The superior physiological resistance to drought stress of these varieties could be translated into a yield advantage under drought stress if their potential harvest index is improved.

Two varieties of Italian ryegrass (Lolium multiflorum Lam.), Tribune and RvP, were cut in each of 2 years, ensiled and individually fed, ad libitum, to dairy cows. In one year, two rates of supplementary concentrate feeding were compared and, in the other year, two types of concentrate and a silage-only diet. Tribune silage was more digestible, in vitro, and was lower in neutral detergent fibre and fibrosity index than RvP silage. There was no difference between the varieties, however, in the cows’ intake of silage. On the silage-only diet, the cows fed Tribune produced a higher yield of milk solids than did those fed RvP; on the other diets, there was no significant difference between varieties in the yield or composition of milk.

The same two varieties were compared when grazed by herds of dairy cows in spring, summer and autumn of the first harvest year on six farms and in the second harvest year on four of the farms. Tribune persisted much better than RvP, in numbers of plants and tillers/m2 and in ground cover, and the herbage was more digestible than that of RvP. Milk yield/cow was c. 0·6 kg per day higher when grazing Tribune than when grazing RvP.

Pastures of Digitaria decumbens (pangola grass) previously oversown with Lotononis bainesii at Mount Cotton, south-east Queensland, Australia, were grazed by sheep for 3 years (1985–87), using a factorial combination of seasonal variations in stocking rate.

Lotononis behaved as a short-lived plant with a mean half-life of 4·2 months (range 1·6–10·3); rate of mortality was positively related to initial seedling density. The proportion of lotononis remained very low for the first 2 years of the experiment, when conditions were unsuitable for large-scale seedling regeneration, which was also limited by the hardness of the seed reserves. Subsequently, lotononis regenerated well in treatments which combined the following features: (i) light grazing (5 sheep/ha) during the main flowering period of spring-early summer, (ii) heavy short-duration grazing in mid-summer to create a ‘gap’ and (iii) medium or heavy (18 or 27 sheep/ha) grazing during late summer-autumn to reduce competition from pangola grass.

The ecological niche of lotononis and the possible use of complementary pastures are discussed.

Sprout emergence in the potato variety Estima was investigated in controlled environment and field experiments. The effects of temperature, physiological age, planting date and soil moisture were examined in controlled environments and the results were compared with the emergence of physiologically young and old seed in field experiments with different soil types, planting dates and planting depths.

Elongation of sprouts could be described by a lag period of slow growth followed by a period of rapid linear growth. The lag period was shorter with increase in temperature up to 20 °C and sprout length at planting up to c. 10 mm. The lag period was slightly reduced by warming seed at 10 °C before planting, compared with planting seed directly from cold storage. The rate of linear growth increased with temperature up to 20 °C but was similar for young and old seed at different planting dates. The rate of growth was lower in dry soil than in soil near to field capacity, particularly at high temperatures.

The observed date of emergence in the field was usually later than predicted, particularly with shallow planting, but prediction was improved by accounting for soil moisture. The use of this model should give more accurate estimation of emergence for farm operations and crop growth models than existing equations.

The effects of weed competition, harvest date and cultivar on sweet potato (Ipomoea batatas(L.) Lam.) yield and components of yield were investigated in three factorial experiments planted during the wet seasons of 1984 (Expt 1) and 1986 (Expts 2 and 3) in the tropical lowlands In Expts 1 and 2, the commencement of regular hand-weeding (every 14 days) was delayed for varying lengths of time following planting. In Expt 3, the duration of hand-weeding from planting onwards was varied. The main competing weed species following planting were Cyperus rotundus, C. brevifolius, Euphorbia geniculata and Portulaca oleracea. After canopy closure, E. hirta, Imperata cylindrica, Eleusine indica, Sida rhombifolia, Mollugo pentaphylla and Mimosa invisa were the predominant weeds to emerge and persist. Cultivars differed in their sensitivity to weed competition. In L431 both mean marketable root tuber weight and number of tubers/plant were severely reduced. However, in L44, tuber number was more sensitive than tuber weight: marketable tuber weight was significantly reduced only by prolonged weed competition (no weeding until 56 days after planting (DAP)). In Expts 1 and 2, delaying the commencement of weeding beyond 14 DAP significantly decreased vine weight, total yield and mean number of tubers/plant. In Expt 3, prolonging regular weeding until 14 DAP and longer significantly increased total and marketable tuber yield and mean number of tubers/plant.

Effects of weed competition in the early part of the season during the first 28–42 DAP substantially reduced crop production in the later part of the growth cycle (after 110 DAP). This was probably due to a partial suppression of vine growth early on, which reduced tuberous root initiation and thus limited the number of root tubers that could develop in the later stages of crop growth. Hand-weeding during the period 28–42 DAP also appeared to have a detrimental effect on tuber initiation as a result of mechanical root disturbance at this sensitive period of root differentiation. There was also a trend towards lower yields when the crop was regularly hand-weeded after 56 DAP, probably due to disturbance of the vine canopy.

The critical period for weed competition commenced at or before 14 DAP, possibly as early as 7 DAP, and did not continue beyond 56 DAP. In order to avoid weed competition and the detrimental mechanical effects of hand-weeding, an optimum hand-weeding programme for sweet potato in the tropical lowlands of will probably involve (i) keeping the crop weedfree for the first 14–21 DAP; (ii) no crop disturbance during the period of maximum tuberous root initiation (from c. 21–28 DAP until 42–56 DAP); (iii) clean weeding at c. 56 DAP; and (iv) minimal or no weeding after 56 DAP. Weeding during the period 7–14 DAP is particularly important.

Potassium concentrations in various plant parts of cotton (Gossypium hirsutum L.) at different growth stages were determined in field experiments in Punjab, India, in 1987, for plots fertilized at sowing and flowering, and these were compared with the final seed cotton yield. The optimum time of sampling for predicting relative yield depends on the time of K fertilizer application: if applied at sowing, plants should be sampled before the peak flowering stage (70 days after sowing, DAS); if applied at flowering (50 DAS), plants should be sampled 90–115 DAS. Critical K concentrations (% K. in dry matter) in the plant parts measured at different growth stages were 3·26 in the petioles of the third leaf from the top at flower initiation; 0·69 and 0·90 in blades and petioles of a lower leaf (first or second healthy leaf from the bottom of plant) respectively, and 2·60 in the petioles of the third leaf (young, fully mature leaf from the top of the plant) at peak flowering stage; 0·85 in blades of the third leaf, 0·53 and 0·50 in blades and petioles of a lower leaf, respectively, at the boll development stage; 0·70 and 2·85 in blades and petioles of the third leaf and 0·68 in petioles of a lower leaf at boll opening stage.

A 50–fold increase in peach tree growth over a 98-day spraying season resulted in a 64 and 96% reduction in nigrosine dye deposit in the periphery and centre of the tree, respectively. Drift from spraying of adjacent rows made a significant contribution (18–39%) to the total chemical deposit in the tree periphery in four of six applications. Drift between rows was not a factor in centre tree deposit, except for a 38% contribution in the initial application. A variable reduced application rate of methyl parathion, calculated using a regression equation, resulted in a more uniform deposit throughout the season than a full application rate, providing comparable control of Oriental fruit moth with c. 50% less insecticide.

15N-labelled fertilizer was applied, in spring, to winter wheat crops in nine experiments in eastern England over a period of 4 years. Five were on Batcombe Series silty clay loam, two on Beccles Series sandy clay loam (with a mole-drained clay subsoil) and two on Cottenham Series sandy loam. In three of the experiments, different rates of fertilizer N were applied (up to 234 kg N/ha); in the others, a single rate (between 140 and 230 kg/ha) was used.

Recovery of fertilizer N in the above-ground crop (grain, chaff, straw and stubble) ranged from 46 to 87% (mean 68%). The quantity of fertilizer N retained in the soil at harvest was remarkably constant between different experiments, averaging 18% where labelled N was applied as 15NH415NO3, but less (7–14%) where K16NO3 was applied. Of the labelled N present in soil to a depth of 70 cm, 84–88% was within the cultivated layer (0–23 cm).

L70 = 5(± 1 63) + 0·264(±00352) R3

accounted for 73% of the variation in the data where: L70 = percentage loss of fertilizer N from the crop: soil system, defined as percentage of labelled N not recovered in crop or in soil to a depth of 70 cm at the time of harvest; R3 = rainfall (in mm) in the 3 weeks following application of N fertilizer.

There was a tendency for percentage loss of fertilizer N to be greater when a quantity of N in excess of that required for maximum grain yield was applied. However, a multiple regression relating loss both to rainfall and to quantity of N applied accounted for no more variance than the regression involving rainfall alone. In one experiment, early and late sowing were compared on the first wheat crop that followed oats. The loss of N from the early-sown crop, given fertilizer N late in spring, was only 4% compared with 26 % from the later-sown crop given N at the same time, so that sowing date had a marked effect on the loss of spring-applied fertilizer N.

Uptake of unlabelled N, derived from mineralization of organic N in soil, autumn-applied N (where given) and from atmospheric inputs, was < 30 kg/ha on a low organic matter (0·08% total N) sandy soil but > 130 kg/ha when wheat followed potatoes or beans on soil containing c. 0·15 % total N. Unlabelled N accounted for 20–50% of the total N content of fertilized crops at harvest. About 50% of this unlabelled N had already been taken up by the time of fertilizer application in spring and the final quantity was closely correlated with the amount present in the crop at this time. Applications of labelled fertilizer N tended to increase uptake of unlabelled N by 10–20 kg/ha, compared to controls receiving no N fertilizer. This was probably due to pool substitution, i.e. labelled inorganic N standing proxy for unlabelled inorganic N that would otherwise have been immobilized or denitrified.

When 15N is used to trace the fate of N fertilizer applied in spring to winter wheat crops, some is not recovered in the crop or the soil and has to be presumed lost. In 13 experiments made from 1980 to 1983 on three widely differing soils, these losses ranged from 1 to 35%. We partitioned them between leaching and denitrification by using models to estimate the loss by leaching, talcing into account the N absorbed by the crops, and subtracting this loss from the total loss to obtain the apparent percentage loss by denitrification, LDN. An analysis of variance showed that LDN increased significantly with the quantity of N applied, so the study considered LDN values for a standard N application of 150 kg/ha subsequently. Regressions showed that LDN was better related to the wetness of the soil during the 3 weeks after fertilizer application than to the corresponding amount of rain, as would be expected for denitrification. Values of LDN could not, however, be satisfactorily related to soil temperature, probably because the range of temperatures was too narrow. The apparent losses by denitrification were, on average, nearly twice as large as those by leaching, but the ratio varied greatly between experiments.

Moisture movement through soil under trickle irrigation was studied in the laboratory at the Central Soil Salinity Research Institute, West Bengal, in 1988/89. Using a cylindrical flow model, the finite difference technique was used to compute the 2-dimensional moisture distributions and wetting front advancements in soils with clay contents ranging from 22·1 to 51·8%. Seven-day cyclic irrigations, each day having one on-cycle (infiltration) with a constant trickle discharge of 0·3 litre/h for 12 h and one off-cycle (redistribution) for 12 h, were used with two water qualities, EC 0·15 and 0·64 S/m. Moisture distributions were measured in artificially packed soil columns 60 cm high and 56 cm in diameter. The degree of agreement between the theoretical and observed values was expressed by Relative Error Percent (REP), defined as the difference between the two, divided by the observed value and expressed as a percentage. The mean REP ranged from 0 to 30, 62·5% of the values falling in the range 0–10, 22·5% from 10 to 20, and 15% from 20 to 30, irrespective of soil texture, water salinity or the irrigation cycle used. It was concluded that the theoretical data closely matched the experimental results. The wetting front in the soil columns was defined as the minimum detectable increase in moisture (10-3 cc/cc) from the initial content, and its advancement was calculated over the entire period of on-off cycles. This model was also used to calculate, for one soil, the theoretical moisture distribution under trickle irrigation with simultaneous loss by evaporation, which is an essential component of field moisture balance.

Simulating changes in the distribution of the particle marker between particle-phase and fluid-phase dry matter by ±40% resulted in calculated flows of dry matter to the duodenum that differed from the ideal of uniform distribution by 1 to 2%; true digesta flow values were virtually unaffected. These errors are small and can probably be ignored.

Twenty-four lambs (equally representing males and females), born in December 1986, were obtained from each of the Najdi, Awassi and Hejazi sheep breeds kept at the Experimental Station of King Faisal University in Saudi Arabia. The lambs were reared on their dams and fed after weaning on the same diet up to slaughter at 9 months of age. Slaughter and carcass data were analysed for breed and sex differences using the degree of body maturity and growth rate as covariates. After the effects of differences in body maturity and growth rate were removed, significant breed but not sex effects were recorded in skin, feet, carcass and carcass to bone proportions. In Najdi lambs the feet and bone nproportions (g/kg empty body weight) were higher than in Awassi or Hejazi lambs, whereas Awassi lambs possessed lower carcass but higher skin proportions than the other two native breeds.

Breed but not sex affected fat distribution. Awassi lambs had higher tail but lower intermuscular fat content (g/kg total body fat) than Najdi or Hejazi lambs. Most body components were significantly related to the degree of body maturity but not to growth rate.

The effect of maternal undernutrition between the 30th and 96th day of pregnancy on placental growth in single-bearing ewes was determined separately in two experiments in consecutive years (1986 and 1987) at Mount Derrimut Field Station, Deer Park, Australia. In the first experiment, placental growth measured on the 96th day of pregnancy was reduced (473 v. 596 g) by maternal undernutrition, while in the second, placental growth was increased (600 v. 496 g). Foetal weight and its linear dimensions on the 96th day of pregnancy were not significantly affected by maternal u dernutrition in either experiment. The only significant difference in the animals and experimental conditions between the two studies was the liveweight of the ewes at mating, which was c. 10 kg higher in the second experiment compared with the first (P < 0·01). Body condition score and the change in condition score during the respective nutritional treatments were not significantly different between the two experiments. The results suggest that maternal liveweight, possibly body reserves not quantifiable by condition score, protects and even enhances placental growth during a period of maternal undernutrition.

The hatchability of layers' eggs stored and incubated in different positions was examined at the Defence Agricultural Research Laboratory, Almora, India (5500' above sea level) in 1990. Hatchability was found to be highest in the eggs stored and incubated with their narrow end up and lowest in eggs stored and incubated horizontally.