One hundred and ninety hybrids involving 20 broad-based yellow maize populations were evaluated together with their parents for stability in expression of their grain yield potential by means of linear regression on to an environmental index. Both linear and non-linear components were observed to be significant; the linear component, in general, being the more important. Two high yielding parents, namely variety A 3D and composite Jawahar, had general adaptability, while synthetic A 22 was suited to poor environment and variety SO 4D to good environment. Seventeen hybrids had above average yield and the majority of these exhibited general adaptability.

Combining ability analysis revealed that GCA (general combining ability) was more important than SCA (specific combining ability) in the expression of mean yield. Inheritance of linear regression was controlled predominantly by GCA whereas both GCA and SCA were equally important in the expression of non-linear fluctuations. Variety Cuba was the most desirable parent, as it transmitted to its progeny high grain yield potential and low linear response. The other good combiners for grain yield were variety SC 4D and Prolific composite but these transmitted above average linear response.

Lack of association between grain yield and linear regression of both parents and GCA effects indicated their independent mode of inheritance. It suggested, therefore, that high yield can be combined with general adaptability or responsiveness to either good or poor environment.

This paper describes a field study of the variation in leaf water potential (ѱL), leaf conductance (gL) and other aspects of crop water relations in a set of ten spring wheats. The two main soil moisture regimes used were irrigation and drought; the latter being imposed by placing rainwater gutters between the crop rows to intercept a proportion of any rainfall. The development of plant stresses, the changes in leaf conductances during the growing season and the relationship between these variables and soil moisture depletion are described. Mean daytime leaf water potentials declined during much of the season even in well irrigated plots. There was also evidence that stomata tended to be most open during the period just prior to anthesis. Data on variation of ѱL and gL within the crop are also presented and indicate that most evaporation occurs from the flag leaf in the spring wheat canopy.

Although genotypic variation was found for the mean values of ѱL and gL, interactions between variety and water regime were generally non-significant. Although yields were not well correlated with most aspects of crop water relations measured, partly because of the dominance of other factors such as maturity and disease susceptibility, a strong negative correlation was observed between yield and gL for the period 7–14 days before anthesis.

Stomatal frequencies were not related to leaf conductances and there was no evidence that the stomatal behaviour adapted to previous drought stress. The growth responses observed, however, could be regarded as adaptations for reducing evaporation. The results are discussed in relation to the breeding of drought tolerant varieties of wheat.

The mean concentration of plasma albumin in 30 Finnish Landrace x Dorset Horn ewes subjected to intensive breeding decreased as the number of pregnancies increased from three to seven; it also changed significantly within a pregnancy. Gamma globulin concentration was not affected by the number of pregnancies but decreased significantly within a pregnancy. Total plasma protein was affected like albumin by the number and stage of pregnancy.

Plasma volume increased by 23 % in the latter third of pregnancy.

Using data from 140 experiments conducted at sites throughout England and Wales, a relationship between nitrogen supply and the nitrogen yield of cut grass swards was sought. One linear and three non-linear functions were fitted to the data. The non-linear functions fitted the data slightly better than did the linear and, over the range in nitrogen supply normally found, provided consistent predictions of grass nitrogen yield. The recovery of available nitrogen in the herbage was found to decline with level of nitrogen supply from a potential maximum of 79%.

Field experiments, using Vicia faba cvs Herz Freya and/or Maris Bead were made in 1972–5. Population densities were varied and shading treatments were applied. Soil moisture content was monitored throughout. Maximum dry-matter production per plant and per unit area were similar in 1973 and 1974, but lower in 1975. Variations in growth were associated with variations in soil moisture content. When pods began to fill, plants reached maximum total water content and root growth ceased.

Increasing density enhanced, and shading retarded both leaf senescence and seed maturation. Maximum potential seed yield (5–6 t/ha) in 1974 was obtained at 32plants/m2. In 1975, yields of 7–9 t/ha were obtained at 66 plants/m2, probably as a result of retention of many pods by the plants. Since total dry-matter production was lower in 1975 than in 1974 we conclude that photosynthetic potential did not limit yield in the earlier year.

From the patterns of rainfall, soil moisture and plant water content, we suggest that water supply may be a more important factor controlling yield than either solar radiation or plant competition, with the period following pod setting being especially vital. At this time plant water requirement may often be in excess of supply.

N fixation data, estimated by the acetylene reduction technique and by total N content are given for the field experiments reported by Sprent, Bradford & Norton (1977).

Maximum potential acetylene reducing activity per plant varied little from year to year. At low population densities a maximum rate of activity was observed shortly after flowering. As density increased this maximum became less pronounced and environmental factors (such as water supply) exerted increasing effects on activity. Shading prolonged activity and delayed nodule senescence.

Total plant N continued to increase almost to seed maturation. As plants aged, the acetylene reduction technique progressively underestimated N accumulation. Maximum Nfixed/ha/year was over 600 kg. Itis concluded that the potential for N fixation in this crop is sufficient to sustain high yields.

Experiments were made to compare the practices of planting yam at the onset of the dry season (November) or at the beginning of the rains (February). Setts were also planted in February after pre-sprouting either outdoors from November/December, or indoors without water from November. Comparisons were also made between plots that were harvested first in mid-season and again at the end of the season (doubleharvesting), and plots that were harvested only at the end of the season (singleharvesting).

Setts that were pre-sprouted outdoors had low percentage emergence, produced weak plants, and yielded poorly whether double-harvested or single-harvested. Setts prepared and planted in the field in November emerged over a very long time, and attained half-maximum emergence only 10–19 days earlier than setts prepared and planted in February. Whether in double-harvesting or in single-harvesting, tuber yield/sett for the November planting was significantly greater than for pre-sprouted plantings, but not greater than for the direct February planting. The first harvest of the November planting had more mature tubers and a higher percentage of marketable tubers than the others. In all treatments, single-harvesting resulted in slightly greater yield than double-harvesting, but the differences were not significant. Each second-harvest tuber from double-harvesting was more amorphous in shape, more woody, and had more eyes (buds) on it than the single-harvest tuber. It is concluded that for efficiency of land utilization, February planting is preferable to November planting, and that singleharvesting is likely to be more economical than double-harvesting.

The experiment was on permanent grass at Rothamsted from 1974–75. ‘Nitro-Chalk’ (ammonium nitrate-calcium carbonate mixture, 25% N) broadcast in equal amounts for each of three cuts was the standard treatment against which the following were compared: (1) prilled urea (46% N) broadcast like ‘Nitro-Chalk’, (2) aqueous ammonia (26% N) injected in winter in bands 10 cm deep and either 30 or 60 cm apart, and (3) aqueous urea (18% N) injected like the aqueous ammonia. All these fertilizers were applied to give 250 or 375 or 500 kg N/ha in 1974 and all were reapplied in 1975.

In 1974 yields were larger with ‘Nitro-Chalk’ or prilled urea than with the aqueous fertilizers. Aqueous urea gave slightly larger yields than aqueous ammonia. Yields with the aqueous fertilizers were slightly larger when the injector knives were spaced 60 instead of 30 cm apart. Distribution of yield over three cuts was more uniform with ‘Nitro-Chalk’ and prilled urea (divided between cuts) than with the aqueous fertilizers. Injecting the aqueous fertilizers in bands 60 instead of 30 cm apart improved yield distribution only a little. In 1975 yields were slightly larger with the aqueous fertilizers at the first cut, but not in the drought afterwards.

Relative yields over the 2 years (‘Nitro-Chalk’ = 100%) were: prilled urea, 97; aqueous urea in 60 cm bands, 96; aqueous urea in 30 cm bands, 95; aqueous ammonia in 60 cm bands, 92; aqueous ammonia in 30 cm bands, 90.

In 1974 the grass recovered most N from ‘Nitro-Chalk’ and least from aqueous ammonia, but more from aqueous than from prilled urea. Recovery of N from the aqueous fertilizers was larger when injected in bands 60 instead of 30 cm apart, especially when 250 or 375 kg N/ha was given. Little rain fell in summer 1975 and recoveries of N were smaller than in 1974. The grass recovered more of the injected than the broadcast N, but no more with the injector knives 60 instead of 30 cm apart.

A consideration of input-output relationships relating energy intake to its probable utilization for growth, condition and lactation by dairy cows leads to a series of equations describing observable responses. Energy is expressed in terms of units of milk equivalent, common to all equations, and the lactation curve, yn = anò e−cn is shown to be capable of biological interpretation, having regard to the subordinate equations from which it is derived. This expression relates milk production yn during a time interval n through the parameters a, b and c. The validity of the steps by which the function is developed is examined by reference to published work.

Observations were made of the ages at first appearance of each pair of permanent incisors (‘eruption age’), and the time from first appearance to full eruption of each pair (‘eruption period’), for Large East African Zebu cattle (Boran). For females the eruption ages were found to be 108·5±9·9 weeks, 137·2±12·9, 165·7±15·8, and 200·9±18·2 for incisor pairs one to four respectively; for steers the figures were 104·3±7·9, 130·3±10·6, 154·6±13·2, and 180·9±14·0; and for bulls 103·3±8·6, 127·6±11·2, 151·0±12·9, and 181·2±15·7. Females were significantly different from steers (P < 0.01), but steers not significantly different from bulls, for all four incisor pairs.

The distributions of eruption ages for each sex and pair can be considered as Normal for statistical purposes. There is a tendency for eruption to be asymmetrical after the first pair, with the right tooth preceding the left.

Correlations of eruption ages between adjacent pairs are of the order of 0·80 for all pairs and sexes; they decrease progressively as pairs intervene to 0·55 for the first and fourth pairs. Partial correlations approach zero when any intermediate pair is held constant. These results indicate that the whole eruption process is highly interdependent.

Evaluation of age grouping and estimations from the presence of incisors showed that this technique, although limited on its own, is still the best developmental trait for ageing. A steer with one incisor pair present had a probability of 0·108 of being the same age or older than one with two pairs. The ages of steers with one and two incisor pairs present were 115·7±12·05 and 140·7±14·27 weeks respectively.

Heritabilities of eruption age, for the various incisor pairs, varied between 0·91±0·33 and 0·43±0·25 for females, and 0·87±0·37 and 0·11±0·59 for steers.

Sources of environmental variation examined were variation between and within years, both of which were of the same order and a very small proportion of the total variation. The maternal environment had a small effect, probably specifically associated with milk consumption, which had a correlation of —0·22 for females and —0·12 for steers (P < 0.01) with the eruption age of the first incisor pair.

Eruption periods for females were 5·1±2·8 weeks, 5·7±3·8, 6·8±4·5, and 8·8±5·6 for pairs one to four respectively; for steers 4·6±2·6, 4·9±2·9, 5·6±3·8, 7·2±5·3; and for bulls 4·9±2·2, 4·8±2·7, 5·7±3·8, 6·0±3·3. Females were significantly slower than steers (P < 0·05) for the first three incisor pairs only, while steers did not differ significantly from bulls for any pair.

The distribution of eruption periods was positively skewed, and the correlations between pairs ranged between 0·0 and 0·35. Correlations of eruption ages and periods within incisor pairs lay between 0·50 and 0·95.

Variation of eruption periods was not significant within years, but was between years, and arose almost entirely from the first two experimental years. The majority of the heritabilities approached zero.

Growth rate differences probably accounted for the differences in eruption periods between the four incisor pairs and the three sexes. The cause of asymmetry of eruption was not the source of the variation in eruption times within incisor pairs, the first tooth consistently having a greater eruption time.

A comparison was made of the growth curves for early and late eruptors (steers whose eruption age of the first incisor pair was less than the mean, and greater than the mean respectively). From birth to 195 weeks early eruptors were consistently heavier than late eruptors (P < 0·01) by approximately 4% of the overall mean body weight. Growth was linear from birth up to 126 weeks of age, and the variability increased markedly from about 60 weeks of age.

The average daily gain from birth to 195 weeks was 341 g. Linear growth-rates for consecutive stages within this period were generally faster for early eruptors, with the differences ranging between 4 and 6% of the mean for periods exceeding 60 weeks. Comparison of these differences showed that linear growth-rates were only significantly different for growth periods of approximately 120 weeks and longer. When the specific growth-rates were compared no differences were significant.

The differences between the growth rates of fast and slow eruptors (steers whose eruption period was less than the mean, and greater than the mean respectively) were not significant, both for linear and specific growth rates.

Early eruptors had larger heads (head length x head width) relative to body weight (P < 0·05), indicating eruption at an earlier stage of body development. Also early eruptors had longer narrower heads, suggesting slower maturation rates.

Partial correlations between eruption age and head length varied from 0·37 to 0·74 (P < 0·01) showing a close relation with stage of head development. Partial correlations with other measures of skeletal development showed that they were of negligible importance relative to head development.

Relations between eruption age of the first incisor pair and six measures of carcass composition were negligible, as none of the partial regression coefficients was significant.

Birthooat fibre types were investigated in Barki, Merino and their crosses. The halo hair grade was high in the Barki breed, in the Merino a wide range of grades occurred but the majority was low. A trend of a decrease in halo-hair grade and an increase in non-hairy birthcoats occurred with the increase of Merino proportion in the crosses. An anterior reduction in halo-hair density was encountered in all groups under study.

Fibre type arrays were all coarse in Barki and ¼ Merino, the ¾ Merino had 50% fine arrays and 75% of the Merino arrays were fine. A trend towards a maternal influence on the birthcoat was observed in the ⅜ Merino and ⅝ Merino; more fine arrays were encountered in lambs born to dams with more Merino proportion.

Within saddle and ravine arrays, CT/Pre-CT ratio was highly significantly correlated with the pre-natal check as indicated by Merino proportion.

It was suggested, from the birthcoat studies, that ⅝ Merino might be the best combination in the Merino crosses as far as the fibre type arrays were concerned.

Less coarse arrays were encountered in the birthcoat due to selection against kemp in rams used for breeding.

Barley plants normally produce some tillers which die at an early stage, without bearing an ear. To investigate the proposition that these non-ear-bearing tillers may be wasteful of plant resources, two experiments were made in which the effect of tiller growth on the growth and final size of the main shoot was assessed. In one experiment, tillers were removed at a very early stage when they were a few mm long, or later when they were just emerging from the subtending leaf sheath. In the other experiment the main shoot was removed from the embryo and the size of the coleoptile tiller which grew in its absence was measured.

Tiller removal affected the growth and final size of the main shoot. Leaves emerged more quickly on the main shoot of the detillered plants and were bigger and sometimes more in number. The main shoot of the detillered plants was heavier and it bore a greater weight of grain because the ear had more and heavier grains. In the experiments where the main shoot was removed the coleoptile tiller produced more leaves, which emerged more rapidly and it bore more grains than the coleoptile tiller of the intact plants.

It is concluded that tillers, during their initiation and early growth, compete with the main shoot for a limited supply of resources, thus reducing the size of the main shoot. As some of the resources of the plant are used to produce tillers which die at an early stage and make no contribution to the final grain yield, it appears that they should be regarded as wasteful and that their production may reduce the final grain yield. The physiology of the initiation, growth and early death of these non-ear-bearing tillers requires further investigation.

The effects of several detillering treatments on dry-matter production and grain yield in barley were investigated in a series of pot experiments using two water regimes. When ample water was provided, even quite severe reductions in the number of tillers only slightly reduced grain yield in spite of large effects on total shoot dry weight. When all the plants were grown with the same amount of water, however, the plants with few tillers tended to have greater grain yield, higher water use efficiency (in terms of grain yield) and higher harvest index than the plants permitted to tiller freely. This effect was probably related to the greater transpiration rates from the freely tillering plants which led to their suffering a greater degree of water stress than the plants with few tillers. This led to the freely tillering plants having a greater proportion of sterile ears and a lower harvest index. Water stress apparently had no effect on the grain yield of the main shoot or first tiller. It is concluded that genotypes which produce few large tillers having a high rate of survival should be able to achieve relatively high yields in drought conditions without sacrificing yield potential under optimal conditions.

Nine individually penned Finnish Landrace x Dorset Horn ewes with a mean litter size of 2·33 were offered a diet containing 63% digestible organic matter (DOM) and 13% crude protein in the dry matter at a daily intake of 0·82 kg DOM (1·3 x maternal maintenance) from 95 to 110 days of gestation. On day 111 DOMI was abruptly reduced to either 0·67 kg (T1, 0·54 kg (T2) or 0·36 kg (T3)/day and kept at these levels until a few days pre-partum.

Daily N balance before food restriction was 4·9 ± 0·51 g/day. During the periods 3·9 (S1), 11·17 (S2) and 19·25 (S3) days after food restriction daily N balance was 2·8, 2·8 and 3·6 g for θwes on T1, 1·0,1·0 and 0·8 g for those on T2 and –4·1, -4·0and -4·0 g for those on T3. Total lamb birth weight was 8·0, 7·2 and 6·5 kg for treatments T1, T2 and T3 respectively. Using regression analysis it was calculated that plasma glucose concentration in late pregnancy for ewes with a total lamb birth weight of 8 kg fell below the pre-restriction value of 52 mg/100 ml when daily DOMI was reduced to 747 g. At this intake the plasma FFA concentration was 585/i-equiv./I compared with 288 before food restriction. Corresponding values for daily N balance were 5·1 and 4·9 g. A reduction in daily energy intake below 0·75 kg DOM resulted in a rapid decrease in plasma glucose and N balance, the latter being proportional to the increase in the concentration of plasma FFA. The mean daily loss of N from the maternal body was estimated to be 0·4, 1·6 and 6·1 g for treatments T1 to T3 respectively during the period of food restriction.

Two varieties of Lolium perenne, the diploid Hora and the tetraploid Terhoy were sown either as a pure stand or as a binary mixture on to the surface of multipots filled with a standard John Innes compost. Density of sowing was varied over the range of 16, 24, 36, 50 and 100 seeds/pot. There were four replicates. The pattern of germination was followed over a period of 14 days when it was found that (i) the varieties did not differ in their germination when grown alone, but in mixtures the diploid was slower to germinate than the tetraploid, (ii) as the density of sowing per pot was increased, the mean germination time (MGT) was increased, and (iii) the final germination of both verities decreased with increasing density.

In a second experiment the same procedures were followed as before but seed of each variety was sown either as a pure stand or in a mixture of varying proportion as follows: 100:0, 75:25, 50:50, 25:75, 0:100.

The results showed that (i) the diploid had the fastest MGT whilst the mixture values showed no significant variation, and (ii) the final germination percentage of the diploid decreased relative to its pure stand value as its proportion in mixtures decreased, whilst the tetraploid under the same circumstances increased relative to its pure stand value.

It is suggested that differences such as those found could be explained by the presence of germination inhibitors in the seed coats of the two ryegrass varieties.

Seed extracts prepared by soaking ryegrass seed in water were tested for their ability to suppress germination. The tests were carried out by sowing seed on to sand-filled basins moistened with seed extract.

Extracts prepared from the two diploid varieties, S. 24 and Hora and the tetraploid variety Terhoy were able to reduce both the rate of germination and the final percentage germination when applied to the sown seed. The details were as follows, (i) When S. 24 perennial ryegrass seed was used to obtain the extract inhibition was found to be related to the concentration of the extract, (ii) The final germination of diploid seed was reduced by 16% in the presence of its own seed extract and by 27% when tetraploid seed extract was applied, (iii) The final germination percentage of the tetraploid seed was reduced by 14% in the presence of either its own extract or that prepared from the diploid seed, (iv) Simple chemical tests carried out on the seed extract, although not conclusive, gave some indication that the inhibitory substance may have been a member of the alkaloid group.

Three soya-bean (Glycine max L.) genotypes (Bragg, Type I and Hark) were grown in Mollisol supplemented with 0, 2·5, 5·0 mg Zn/kg in pot-culture experiments. The genotypes showed significant differences in their capacity to absorb Zn. Maximum Zn accumulation was found in the genotype Bragg and minimum in Hark. The pattern of Zn distribution in plant parts was also different in the three genotypes and was differently affected by Zn application. The uptake and percentage distribution of 66Zn followed more or less the same trend as that of total Zn. The genotypes differed significantly in R(recovery), A(availability of native Zn) and L(labile soil Zn) value indicating that these three genotypes differed in their capacity for recovering applied and native Zn. The genotype Bragg had maximum R, A and L values. These results correspond well with the reported tolerance of these genotypes to Zn deficiency (Bragg > Type I > Hark).

Growth and tuber yield of local sweet potato cultivars were compared during the 1974 and 1975 growing seasons. Three cultivars significantly outyielded the others. The cultivar effect was associated with differences in individual tuber weight, rate of bulking and percentage of total dry matter diverted into the vine or stem. Mean crop growth rate (C) and percentage of total dry matter diverted into the tubers were greater in the higher yielding cultivars and there was positive and significant correlation between Cand final total dry weight. Leaf area duration (D) was greater in 1975 than in 1974 but the differences between cultivars in D was not consistent. Higher yielding cultivars had significantly greater tuber/leaf ratio than the other cultivars.

Bulking rate and tuber weight were positively correlated with tuber yield, while the percentage of total dry matter diverted into the vine was negatively correlated with tuber yield.

Soil responses to deep (30–35 cm) and normal (15–20 cm) mouldboard ploughing, chisel ploughing and zero-tillage have been compared for 7 years in a field experiment growing continuous spring barley near Edinburgh. The soil was of variable texture, from moderately well-drained sandy loam overlying loam to imperfectly to poorly drained sandy clay loam overlying clay loam, classified as stagnogleyic brown earth to cambio stagnogley soil. Soils of this type derived from Carboniferous till are widely used for cereal production in south-east Scotland. Measurements of soil physical properties were made at crop emergence, midseason and at harvest to characterize seasonal and long-term responses to tillage and traffic. After the first 3 years bulk density responses varied little within or between seasons, showing a compacted horizon from 0–15 cm under zero-tillage and a looser horizon from 21–33 cm under deep ploughing compared with normal ploughing. Immediately below the depth of normal ploughing there was no difference in bulk density between this treatment and zero-tillage while in some years the chisel-ploughing treatment was denser. Moisture content responses on a weight basis, together with air-filled porosity responses, showed large differences between treatments particularly at the time of crop emergency, indicating substantial alterations in the soil profile hydrology. Expressed on a volume basis the increased moisture content near the surface under zero-tillage became more pronounced and the other effects disappeared. Cone resistance responses were proportionately larger than those for bulk density and showed one major difference in that below the depth of ploughing cone resistance was greater for zero-tillage than normal ploughing in the sixth and seventh seasons, but not previously. For bulk density, but probably not for cone resistance, there were no increases after the third season of zero-tillage, the soil reaching an equilibrium density for the current management practices and machinery usage.