Field experiments at Sutton Bonington between 1970 and 1974 tested how crop yields were affected by hand weeding at different stages in the life of early- and latesown crops. Losses where weeds were never controlled ranged from 95% where tallgrowing Chenopodium album L. predominated to 50% when Stellaria media (L.) Vill. and Tripleurospermum maritimum L.) Koch ssp. inodorum Hyl ex. Vaarama (T. inodorum) were most involved.

In five of the seven crops examined the latest date (X) at which weeding had to commence to prevent irreversible effects on growth and yield and the earliest date at which weeding could cease without yield loss (Y) coincided. For late March/early April sowings this occurred 6 weeks after crop emergence, while for late April/early May sowings in which events were more rapid the same stage was reached 4 weeks after emergence. For an early-sown crop in 1973, when rainfall was frequent and heavy and C. album prolific, X preceded Y with an interval of 4 weeks between the two dates (4–8 weeks after crop emergence, mid-May to mid-June). In complete contrast for a late-sown crop in 1974, when the weather was exceptionally dry and C. album virtually absent, Y preceded X and a single weeding at any time between 2 and 8 weeks after emergence would have prevented yield loss.

Sugar beet had generally reached the late singling stage (4–6 true leaves) by the time weeding must have commenced. During the next 6 weeks, final yield was depressed by 120–150kg/ha (1·;5%) with each day that weeds were allowed to remain. However, leaf production continued throughout the season and the crop was capable of recovering from early checks caused by weed competition. It proved possible for crops whose weights were depressed by 25–30% when first weeded to recover completely by harvest.

The effects of submerging sodic and alkaline soils on the kinetics of Zn2+ transformations were investigated. The soils were treated with 0-640 mg Zn/kg soil as ZnSO4. H2O and kept submerged under water in pots at 30–38 °C. The soil solution was analysed periodically up to 72 days for pH, electrical conductivity and Zn2+ ion. Soil pH decreased with increasing amounts of added Zn and with periods of submergence. The rate of decrease was rapid during the first 21 days of submergence but slow thereafter. Zinc concentration in the soil solution increased with the amounts added and decreased with the period of submergence; this decrease was more in the calcareous sodic soils than in other soils. The values of the expression pZn + 2pOH (Zn. hydroxide potential) showed that in submerged calcareous sodic soils, Zn concentration in the soil solution was regulated both by the Zn (OH)2—Zn2+(aq.) and ZnCO3 — Zn2+(aq.) systems up to 21 days (pZn + 2pOH = 16–17–5), and thereafter predominantly by ZnCO3–Zn2+(aq.) (pZn + 2pOH = 17–6–18–8) as a result of the buffering effect of soil carbonate equilibria. In slightly calcareous sodic and slightly calcareous alkaline soils, the soil solution Zn was controlled transitorily by the system: Zn(0H)2 — Zn2+(aq.) before 2–7 days (pZn + 2pOH = 16–0–17–5), ZnCO3–Zn2+(aq.) from 2–7 to 14–21 days (pZn + 2pOH = 17–5–18–8). Thereafter Zn–soil (unknown solid phases) – Zn=+(aq.) system controlled the Zn solubility (pZn+2pOH = 18–8–20–4).

Experiments in 1976 and 1977, in south-east Scotland, with sunflower (cv. Fransol) examined the effects of bitumen mulch applied after sowing, date and depth of sowing on emergence, flowering and yield. Bitumen mulch increased soil temperatures in April and May by 1–4·5 °C resulting in earlier emergence (6–7 days), more complete emergence under adverse conditions of early and deep sowing, and earlier flowering (2–5 days). Delaying sowing from 7 April to 5 May reduced emergence time and time from sowing to first anthesis. Larger seedlings, having an increased leaf area, resulted from bitumen mulching and early sowing.

In the laboratory, increasing temperatures from 5 to 20 °C reduced the average germination time by 0·75 days for each increase of 5 °C. Germination percentage was not affected by temperature over this range.

Average seed yields and oil content were markedly different in 1976 and 1977; 2·22 t/ha and 44·7% for 1976 and 0·95 t/ha and 36·9% for 1977. Bitumen mulch and sowing depth had no effect on seed yield or oil content but delaying sowing until 5 May reduced both. Lower seed yields in 1977 resulted from fewer and smaller seeds. Infection of the seed heads with grey mould (Botrytis cinerea) after flowering was high in both years.

The effect of substituting different amounts of heated and unheated beans for barley in diets to cows, on the flow of total nitrogen (N), total amino acid nitrogen (TAA-N) and individual amino acids into the proximal duodenum was studied. Neither heating of the beans nor increasing their proportion in the diet significantly increased the flow of total N at the duodenum; however, increasing the proportion of beans did increase the flow of TAA-N. The substitution of both forms of cracked beans for barley, and at both levels significantly increased the flows of leucine and aspartic acid; flows of histidine, isoleucine, phenylalanine and serine were increased by substitution of both forms of beans but only at the higher level. In the bean supplemented diets significant proportions of all of the ingested amino acids except methionine were apparently destroyed in the forestomachs. The substitution of beans for barley resulted in a net increase of 0·2 g TAA-N flow into the proximal small intestine for each gram of additional dietary N.

Eight varieties of spring barley differing in their morphology and resistance to lodging were grown in a trial as main plots which were split for seven treatments: a natural control (C), a control with plots which were mechanically supported (S) and four artificially induced lodging treatments: permanent early lodging (PEL); temporary early lodging (TEL); permanent late lodging (PLL) and temporary late lodging (TLL). The seventh treatment (GR) was an application of the growth regulator BAS 09800W. In comparison with S, treatments PEL, TEL, PLL and TLL reduced grain yield by 38–1, 24–8, 22–0 and 13–9 % respectively. Natural lodging in C plots reduced the yield of the two weakest strawed varieties, Guilden and Jupiter, by 8 and 10% respectively in comparison with treatment S. Yields (C) of these two varieties were increased by GR which had no effect on the yield of other varieties, but reduced grain size in some cases. Treatment GR significantly reduced but did not eliminate natural lodging in weaker strawed varieties and reduced the length of the top four internodes. Lodging reduced grain size in terms of 1000–grain weight and sieving fractions and increased the content of husk and protein. Lodging susceptibility was positively correlated with plant height but showed no clear relationship with the number of vascular bundles, stem diameter, wall thickness, or with the content of lignin, cellulose and hemicellulose in the basal internodes. Lodging resistance appeared to be closely associated with short basal internodes.

Nineteen NP experiments were carried out with wheat and barley mostly in the Mesaoria plain of Cyprus over the period 1968–78. The fields were fallowed over the season preceding the experiments. Rainfall ranged from 68 to 405 mm. Kyperounda, a tall durum wheat, Pitic 62, a semi-dwarf aestivum wheat, and Athenais barley were the test varieties. No yield was obtained when rainfall was below 100 mm. Athenais barley consistently outyielded the wheat varieties, particularly Kyperounda, by up to 200% presumably because of earlier heading, which helpedthe crop to escape drought to a certain extent.

Kyperounda wheat and Athenais barley mostly responded to 35 kg N/ha but Pitic 62 benefited from up to 70 kg N/ha. Fertilizer N not taken up in a year of extremely low rainfall remained in the soil and was available to the following crop.

Response to P was more marked when rainfall was below 250 mm being linear over the rates tested (highest rate 26 kg P/ha). Athenais barley responded to P more than the other varieties. Bicarbonate-soluble soil P was between 1 and 10 mg/kg.

Since rainfall is unpredictable it is recommended that 20–40 kg N/ha be applied atseeding together with 13–26 kg P/ha. A similar amount of N should be top dressed in late January. The higher amount refers to the semi-dwarf Pitic 62 wheat and could be increased further if the December-January rainfall, which normally constitutes 40% of the total, is high. These rates refer to crops grown after fallow. For continuous growing the rates would probably have to be increased.

The effect of tiller removal on the growth and development of the main shoot of spring wheat was investigated in plants grown in a glasshouse or growth cabinets. The removal of tillers at different stages from just prior to flag leaf appearance to 10 days after anthesis greatly increased the grain and straw yield of the main shoot. The earlier the tillers were removed the greater was the increase in yield. The increase in grain production was due to an increase in the number of grains per spikelet particularly in the mid and lower regions of the ear. The nitrogen content of the grain was also increased following tiller removal. Additional mineral nutrients supplied either early or late were accumulated by the grain but did not influence the response to tiller removal and it was concluded that neither the number of grains set nor grain growth were limited by the supply of major nutrients. Additional nutrients however greatly increased the yield of tillers and this was associated with a large increase in the grain N, P and K percentages.

In a separate experiment tillers were removed just before ear emergence and the plants were transferred to growth cabinets with either a low or high light regime. Although grain yield was greatly reduced in the lower light regime tiller removal significantly increased the number of grains per ear but to a lesser degree than in the higher light regime. It was concluded that the supply of carbon assimilate was more important than the supply of mineral nutrients in influencing grain set.

The overall response to tiller removal suggests that tillers compete with the main shoot for assimilate and as a result the potential growth and yield of the latter is greatly restricted.

Experiments made over a period of 2 years (1975–6) covering three crop seasons at Pantnagar, India, on the comparative utility of intercropping the principal maize crop with legumes in economizing fertilizer N requirements of the former, indicated that among soya bean, cowpea, pigeonpea and groundnut, soya bean was the most suitable. At 40 kg N/ha intercropping maize with soya bean gave 19·5% more yield than taking it as a pure crop. When the option to use adequate fertilizer N does not exist, as is invariably the case with the average Indian farmer, intercropping maize with legumes, such as soya bean, is the logical way out. All the intercropping treatments left sufficient residual fertility to significantly increase yield of a wheat crop given no fertilizer which followed maize.

Root growth of rice (Oryza saliva L.) is frequentlyinhibited by an adverse physical environment resulting from high moisture stress and strength of soilunder upland conditions, and the effects are often reflected in poor performance of the crop. This necessitates a critical understanding of rice root growth under varying soil physical conditions.

The growth responses of the rice root system to the interaction between moisture regime and bulk density of soil as well as to the induced soil physical characteristics were assessed under controlled glasshouse conditions. Four moisture regimes: 0 (M1), 0–20 (M2), 0–350(M3), and 350–10000 (M4) mb, were superimposed on low, medium and high bulk density treatments in clay, loam and sandy loam soils. The soil physical environment was characterized by measurements of moisture distribution, penetrationenergy and oxygen diffusion rate in soils as functions of depth.

A low moisture stress of 20 mb in low density soils favoured rice root growth. In low density soils, even though the number of roots at the base (proximal end) was maximum under M1, the depth of penetration, volume and dry weight of root were significantly more underM2 than under M1; M3 and M4. Irrespective of bulk density, even though oxygen diffusion rates in soils under M3 and M4 were greater than those under M1 and M2, the number of roots at the base, volume and dry weight of the root system decreased under M3 and M4 owing to low moisture content and high penetration energy in the surface layer (0–5 cm) of all the soil types. Lower moisture content and higher penetration energy at higher bulk densities of the soil types significantly reduced the root growth and especially the depth of penetration.

In a study of two coarse-wool breeds (Awassi and Hamdani) the birthcoat and adult fleece were sampled from six body positions. Mean fibre diameter, mean fibre length, mean staple length and the percentages of fibre types were studied in relation to the birthcoat fibre type arrays.

The birthcoat of the two coarse wool breeds showed only plateau and saddle fibre type arrays. In Awassi lambs, plateau arrays were all P3 type whereas in Hamdani 28·6% of the plateau arrays were Po and the rest were P3 indicating a stronger base in the latter. S/P ratios, calculated from fibre types, were 2·22 and 2·27, at birth, and 3·56 and 2·93 at 4–8 weeks of age, in Awassi and Hamdani respectively. Awassi birthcoats showed more precipice within the CT group than those of Hamdani and plateau arrays were more endowed with the precipice than were saddle arrays.

A composite sample from the back and mid-side, in Awassi, and from the back and britch, in Hamdani, was found to be most representative of the birthcoat fibre types.

In the adult fleece of the Awassi breed, the mean fibre length following plateau arrays exceeded those following saddle arrays.

In Hamdani, the saddle arrays developed into coarser fibres in average diameter than those of plateau arrays whereas in Awassi no difference occurred. Awassi plateau arrays were followed by higher within-staple variability in distribution of fibre length than were saddle arrays, whereas in the distribution of fibre diameter there was no difference. In Hamdani, however, saddle arrays were followed by slightly higher within-stable variability in both length and diameter than were plateau arrays.

Birthcoat samples that had a transition in the CT group or had saddle array developed into adult fleeces with greater frequency of normal distribution in both fibre length and diameter, within staple. Adult fleeces that showed frequent bimodal distribution of both diameter and length, within staple, were those with birthcoats that had a precipice in length, or in coarseness and length, within their CT group or those with birthcoats that had plateau arrays.

Plots were sown with six varieties of perennial ryegrass, one each of Italian, Westerwolds and hybrid ryegrass, and one each of cocksfoot and timothy, in April 1974. D.M. yield was assessed at four cuts each year, on plots receiving 300 kg N/ha annually, for 4 years. Invertebrate populations and plant survival were monitored at intervals. Half the plots were treated regularly from sowing onwards with the systemic insecticide, phorate. Insecticide treatment increased output generally, but the extent varied from year to year and between grass varieties. The persistence of Italian and hybrid ryegrass varieties was dramatically improved by insecticide treatment. The three diploid varieties of perennial ryegrass studied appeared to be less susceptible to pest damage than the three tetraploid varieties. Shoot-fly larvae (Diptera: Chloropidae) were the major obvious cause of damage.

The feasibility of measuring lysine and protein nitrogen in barley using an infra-red reflectance analyser was examined. This is a very rapid technique, requiring no manipulative skills, and measuring several components simultaneously using milled grains. The results show that this instrument is sensitive to changes in lysine and protein nitrogen and can be calibrated to measure these components to a high degree of accuracy. It is shown that the gross morphological and biochemical abnormalities of high lysine mutants do not affect these measurements, indicating that this method is suitable for the rapid screening of material from breeding programmes designed to improve the lysine content of barley proteins.

Two wheat (Triticum aestivum L.) cultivars, Shera and Kalyansona, which differ in grain protein percentage and in its enhancement by fertilizer application were selected for the present study. The analysis was confined to the leaf blades of the main shoot of plants grown at three rates of application of urea giving 0 (N0), 90 (N90) and 180 (N180) kgN/ha. Cv. Shera produced ten leaf blades on its main shoot while cv. Kalyansona had 11. The total dry weight duration of the leaf blades of cv. Kalyansona was higher than that of cv. Shera, particularly at N90 and N180. This was due to a great increase in dry weight of the leaf blades in response to fertilizer nitrogen and to an additional leaf blade. In both the cultivars the in vivo nitrate reductase (NR) activity was highest in the first formed leaf blades and showed a gradual decline in the successively formed ones, at all three nitrogen levels. Cv. Shera showed higher NR activity than cv. Kalyansona in most of the weekly samplings (weighted mean values) through the season. Seasonal mean NR activity was higher in cv. Shera at all three rates of nitrogen application. The difference was, however, significant only at N90. The total amount of NO3- reduced by the leaf blades, which is a function of their NR activity and dry weight duration, was higher in cv. Shera than in cv. Kalyansona at N0. However, at N90 and N180 the differences decreased because of the higher dry weight duration of the leaf blades of cv. Kalyansona.

The estimated amount of NO3- assimilated was less than the actual reduced N at harvest at N0 but at N90 and N180 there was an overestimation. The grains of cv. Kalyansona showed significantly lower protein percentage than cv. Shera at all three nitrogen levels. While low nitrogen per spike was the main cause of lower protein percentage in cv. Kalyansona at N0 as compared with cv. Shera, distribution of almost the same amount of nitrogen to a larger quantity of grains was largely responsible for the lower protein percentage in this cultivar at N90 and N180. The results are discussed in relation to selection criteria used in breeding programmes for the improvement of grain protein content of wheat cultivars

The spring wheat varieties Kolibri, a typical north temperate variety, Pitic 62, a Mexican variety known to respond to vernalization and two selections from the Institute's breeding programme TW 161 and TJB 155 were sown early (2–5 March), during the normal sowing period (27 March) and late (17 April). Primordium initiation was observed until the time of terminal spikelet initiation and the number of leaves and the number of spikelets were analysed in terms of rate and duration of leaf and spikelet primordium initiation. The rate of leaf initiation was affected by time of sowing but not in a systematic way and there were differences between varieties in the way in which the number of leaves changed in response to sowing time. The rate of spikelet initiation increased and the duration decreased with later sowing. There were strong variety × time of sowing interactions. For almost all characters measured, Pitic 62 responded least to time of sowing. Varieties differed in the way in which the number of spikelets per ear responded to time of sowing but in all cases the changes were only small. This waa because the change in the rate of spikelet initiation was almost exactly compensated for by a change in the duration of spikelet initiation. In each variety, the period from terminal spikelet initiation to ear emergence was similar in all sowing treatments and was of similar duration in the main shoot and in the ear-bearing tillers.

The number of leaves per shoot on the tillers was less than the number of leaves on the main shoot and the rate of spikelet primordium initiation of the tillers was faster than in the main shoot. These changes tended to synchronize the time of terminal spikelet initiation. Because of the changes in the number of leaves per shoot and the rate of spikelet initiation the number of spikelets borne on the main shoot and the tillers were similar although the growth period of the tillers was shorter than that of the main shoot.

In field trials made in 1977, the synthetic pyrethroids Deois and Permethrin offered better protection to cowpea flowers and pods but the crop did not outyield that treated with Nuvacron in grain production. Further evaluation of Decis and Permethrin in 1978 showed that the relationships between rate and insect damage, and yield were curvilinear. On the early crop, Decis at 15 g a.i./ha and lOga.i./ha reduced insect damage to flowers and pods, respectively, below the control but yield differences were not significant from 5 to 50 g. Four or five applications of Decis were most effective in reducing insect damage, but yields obtained from them were not better than that from one application. Permethrin at 12·5 g a.i./ha reduced insect damage below the control but produced grain yield which was significantly lower than 25 g and above.

On the late crop, Permethrin was effective from 5 to 25 g in reducing insect damage and providing increased grain yield. One application of Decis was sufficient to reduce pod damage and increase grain yield over the control, but appreciable yields were obtained from the three and four application regimes.

A cost/benefit analysis of insecticide application shows that the synthetic pyrethroids compared favourably with Nuvacron. In 1978, two and three applications of Decis gave the highest net returns on the early and late season crops, respectively. Decis appeared most economical at 10 g on the early crop while Permethrin was most rewarding at 62·5 g in the early crop and 10 g in the late crop. The seasonal differences in weather are discussed in relation to the performance of the crop.

Maris Huntsman winter wheat was sown on 30 October 1974 and grown under typical farming conditions. Between sowing and harvest (5 August 1975), the crop was sampled on 23 occasions and dried samples of individual plant components were analysed for Na, K, Ca, Mg, P, S and N composition.

The concentration of nutrients within the whole plant generally decreased throughout growth but different parts of the plant varied in their behaviour. Uptake of all nutrients ceased at, or shortly after, anthesis in mid-June while dry-matter accumulation continued slowly for a further 2–3 weeks and almost stopped 4 weeks before harvest. The major period of nutrient uptake occurred between mid-April and mid June coincident with the period of rapid shoot growth. Large amounts of potassium and sulphur (almost 50% of the plant's anthesis content) and lesser amounts of calcium (15%) were lost from the plant after anthesis and efflux from the roots into the soil appeared to be the most likely pathway of removal.

Accumulation of nutrients in the ear occurred throughout grain-filling by translocation from other parts of the plant, particularly the leaves and stems: the effects of this redistribution on the production of dry matter after anthesis are discussed.

A rapid method for measuring gas production during incubation of feedingstuffs with rumen liquor in vitro is described. Gas production in 24 h from 200 mg feed dry matter was well correlated with digestibility of organic matter, determined in vivo with sheep. Multiple regression analysis, when it included data from proximate analysis, resulted in an equation (R = 0·98) for prediction of metabolizable energy content, based on 30 experiments with rations varying in protein and crude fibre content, and 59 other experiments with concentrates. Energy content was in the range of 7·7–13·2 MJ ME/kg D.M. (± S.D. = 11·17 ± 1·08). The residual standard deviation of the equation was 0·25 MJ. Gas production was measured in calibrated syringes. The only chemical determinations needed are dry matter, protein and fat. Differences in activity between batches of rumen liquor are corrected by reference to gas production with standard feedingstuffs (hay meal and maize starch).

Great Britain relies heavily on imported food and Cantell (1977) has estimated that within urban areas there are over 100000 ha of dormant land (i.e. derelict and awaiting development) for which the most fundamentally valuable temporary use is growing food, since such land, Cantell claims, could yield 25 million tonnes of potatoes or 4 million tonnes of carrots annually. The national waiting list for allotments exceeds 100000 and, according to Thorpe (1969), vegetables are grown on nearly all (98·3%) urban allotments. Underlying the case for encouraging the agricultural or horticultural use of dormant land is the supposition that, once cleared of junk, urban soils differ little in potential quality from farmland. But this is not necessarily so: Purves & Mackenzie (1970) have reported that vegetables grown in Scottish urban soils were contaminated by trace metals as have Warren, Delavault & Fletcher (1971) in Canada, Beavington (1973) in Australia and Davies (1978) in England. Lead, is one of the commonest urban pollutants and many countries set limits on the concentration permitted in food. In Great Britain the present limit is 2 mg/kg (fresh weight) but it is planned to reduce this to 1 mg/kg.

The authors regret the following errors: Page 102, Appendix Table 1, lines 13, 15, 17, 20 and 22 of the Table should be amended as follows:

Copper, lead and zinc ores have been mined in past years in many western counties of Great Britain leaving a legacy of extensive soil contamination. A survey of north-east Clwyd (Davies & Roberts, 1978) revealed that in the Halkyn Mountain area some 171 km2 of land are contaminated by lead and 69 km2 by cadmium (including 13 km2 containing from 10 to 540 mg Cd/kg soil). The Mendip Hills of Somerset are an ancient leadzinc mining area similar in many ways to Halkyn Mountain and, after some reconnaissance sampling in 1972 and 1974, a trace element survey was initiated in 1977. Topsoil samples (174) were collected on an approximately regular 2×2 km grid from a 600 km8 area of north Somerset including the Mendips (B. E. Davies and R. C. Ginnever, unpublished results). This survey revealed that the Mendips were generally contaminated by cadmium, lead and zinc. Highest soil lead values were found near Wells (11 g/kg) and Charterhouse (73 and 80 g/kg) but in the case of cadmium the survey revealed that some 2 km2 of land around the village of Shipham contained values exceeding 10 mg Cd/kg. Preparatory to detailed investigations planned for 1979 a reconnaissance survey of soils and vegetables from the village was made. Meanwhile, the Department of the Environment announced the results of another (independent) survey which also demonstrated that Shipham possessed a considerable cadmium problem (e.g. McGinty, 1979). A full account of our survey of north Somerset will be published and this paper presents the results from the reconnaissance of Shipham.