Abstract. When sewage sludge is surface‐applied to grassland, herbage may become contaminated with heavy metals from adhering solids, posing a risk to the health of grazing livestock and possibly increasing the entry of heavy metals into food products. A field trial examined factors influencing sludge adhesion to leaf surfaces and changes in the concentration of heavy metals in herbage over time. Metals differed in their persistence on leaves. The time required for metal concentrations in herbage to reach background levels depended on herbage growth, the dry solid content of sludges, their rate of application and the height of the grass when the sludge was applied. The implications of the results for the length of a safe no‐grazing period following sludge application are discussed in the context of UK and EC legislation governing sludge use on agricultural land.

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The manurial value of liquid anaerobically digested sewage sludge (LAS), surface applied once at four different times during winter to contrasting swards, was assessed over each of three growing seasons by comparison with fertilizer N. Four nominal rates of N (0, 18, 36 and 54 kg ha"') were used hased on Ihe inorganic N content of LAS. Herhage dry matfer (DM) and N upiake responses were measured hy cutting three times per year.Application of LAS in late winter compared with early winter led generally to greater N uptake and DM production. Herhage production rcspon.se from LAS ranged from 54 to 30-1 kg DM kg"' N; within this range, larger responses were obtained froni a sown sward than from permanent pasture. The apparentefficiency of LAS compared with fertilizer N ranged from 0-41 to 0-88 (permanent pasture) and 0-20 to 0-77 (sown sward) but occasionally mean apparent efficiencies of over 1 0 occurred because fertilizer N was poorly recovered. There was no residual effect on annual N uptake from applying sludge. It is concluded LAS is a useful nitrogenous manure when applied to grassland in late winter/early spring but more research is needed to elucidate the importance of pathways of N losses following the surface application of LAS, and to quantify these losses.

The effects of rate and pattern of fertilizer S application on herbage production from Perennial ryegrass‐dominant swards at six potentially S‐deficient sites in south‐west Scotland were measured under a silage cutting regime (3 cuts year‐1) with high fertilizer N application (300 kg ha−1 year‐1). Fertilizer S (as gypsum) was applied at annual rates from 0 to 48 kg ha−1 as single spring applications before the first cut or split before each of the three cuts. The residual effect of S in the year following its application was assessed at one site. Applied S increased total DM production at four of the six sites. These increases were restricted to the second and/or third cuts and were generally in the range 10‐30% greater than where no S was applied. Timing of S application was not important in influencing annual DM yield. The residual effect of gypsum in the year following application was small. The supply of available soil S is limiting herbage production in certain areas and soil types of south‐west Scotland. Areas of S deficiency are likely to increase in the future and need to be identified more precisely than they are at present.

A B S T R A C TWinter barley (Hordeum vulgare L cv lgri) plants were grown for 5 weeks in a controlled environment room using a recirculating nutrient solution culture system at a root and shoot temperature of 10°C.When solution NO,-N concentration was varied between 0 and 6 4 m g litre-', shoot endogenous and induced nitrate reductase activity ( N R A , and N R A i respectively) increased asymptotically f o m zero in plants grown with 0 mg NO,-N litre-' to a maximum activity in solutions containing 3 16 mg N 0 3 -N litre-'. Shoot Nitrogen Response Index ( N R I = N R A J N R A , )showed an opposite trend decreasing fiom a maximum of 2.6 at 2 mg NO,-N litre-' to a minimum approaching unity when 3 3 2 mg N litre-' was supplied.In a separate experiment, nitrogen form (NO,-N, NH,-N or a 1:l mixture) had a marked influence on shoot N R A . Enzyme activity was negligible in tissue fiom plants absorbing NH,-N, highest in NO,-fed plants and intermediate in those supplied with both N forms. N R l , however, approached unity in all treatments. The results provide evidence to suggest that N R l may be used as an indicator of the N status of barley plants grown with varied N nutrition.