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.

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.

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.

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.

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.

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.

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.

In an earlier paper (Little, McLean & Winter, 1977) we reported a technique for the measurement of the phosphorus content of the diet consumed bygrazing cattle, which recently has been used successfully to measure the dietary intake of phosphorus by sheep grazing Mitchell grass (Astrebla spp.) pastures in western Queensland (Beale & McMeniman, 1978). In this technique, phosphorus of salivary origin is distinguished from that of plant origin in samples extruded by oesophageally nstulated animals by prior labelling of salivary phosphorus with the isotope 32P following the intravenous infusion of Na2H32PO4. The difference in specific activity between saliva and extruded bolus is used as the basis of the calculation of the phosphorus content of consumed herbage. Oesophageally nstulated animals may graze experimental pastures for an hour or more while samples are collected from them. It is important to have an accurate measure of saliva speoific activity, representative of that secreted during the grazing period; therefore, application of the technique is facilitated if the rate of change in saliva specific activity during collection periods is slow and linear.

Quantitative information concerning preejaculation sexual preparation of bulls was published some years ago by Collins, Bratton & Henderson (1951), who concluded that about 40% more motile sperm could be obtained by imposing one false mount before ejaculation. It had been suggested that one false mount in bulls is essentially as efficient as two such attempts in terms of sperm output (Branton, D'Arensbourg & Johnston, 1952). More recently Hafs, Knisely & Desjardins (1962) have shown that bulls given a planned 5 min sexual preparation yielded 30% more sperm than those given no preparation. Similarly 10 min preparation resulted in a 12% increase in sperm output when compared with a 5 min preparation. These authors also showed that zero, one, two or three false mounts significantly affected motile sperm output.

Until recent years large incidental additions of sulphate in fertilizers, especially superphosphate and ammonium sulphate, ensured that the major sulphur requirements of crops were adequately met. Increasing purity and concentration of commercial fertilizers, however, have largely eliminated such additions, with corresponding increase in the importance of available soil sulphate and atmospheric sulphur. The latter can readily be measured but its contribution to crops is more difficult to assess. To examine one aspect of this question, the effect of sulphur in rain on the yield and sulphur content of oats has been measured by comparing pot cultures grown in two environments, one with access to both gaseous atmospheric sulphur and rain sulphur and the other to gaseous sulphur only.