The effects of varying the sowing date (early September-late October) and plant density (14–70 seeds/m2) on the establishment, overwinter survival, structure and yield of an autumn-sown, florallydeterminate line (CH304/70) of the white lupin (Lupinus albus) were examined in three contrasting growing seasons between 1991 and 1994. Crops established well when sown in early September and were sufficiently cold-hardy to survive prolonged and extremely severe early winter frosts, but crops sown in late October either lost many plants or were destroyed completely. There was a strong interaction between sowing date and autumn weather on crop structure and yield. Late sowing and cold autumn weather restricted the number of mainstem leaves and first-order lateral branches on the plant, and decreased plant height and yield potential.

Despite considerable differences between years in the weather during the summer and autumn, all crops were harvested in early September. Grain yields ranged from 0·3 to 4·5 t/ha depending on season, sowing date and plant density. Yields were strongly correlated with the number of podbearing axes and pods per m2 and, although actual yields differed depending on growing conditions, the same number of pod-bearing axes (100/m2) was required in each year to achieve maximum yield. The effects of sowing date and autumn weather on plant structure were well predicted by a simple developmental model that related vernalization and leaf development to post-sowing temperature.

The effects of recommended application rates of the herbicide methabenzthiazuron (MBT) (2·5 and 4 kg ha-1) on vegetative growth, nodulation and N2 fixation in faba bean plants were studied in the field at Barcelona during 1990 and 1991. Nodulation, specific nitrogenase activity (SNA) of excised nodules, dry weight of plants and seed nitrogen content at harvest were compared in MBT-treated, hand-weeded (HW) and control plants. In 1990 the higher MBT application (4 kg ha-1) caused a decrease in nodulation and acetylene reduction activity (ARA) per plant during the mid-period of pod-fill, and also in vegetative growth, seed production and N content of seeds, whereas the lower rate (2·5 kg ha-1) did not have a significant effect on any of these factors. However, in 1991, growth and herbicide effects were different from those in the previous year. No inhibitory effect of MBT on nodulation, SNA or ARA per plant was observed and vegetative growth, seed production and N content of seeds were not significantly different from those of plants from HW plots. In 1991, both 4 kg ha-1 of MBT and the HW treatment caused a stimulatory effect on seed N recovery and yield compared to control plants. Rates of ARA per plant at late pod-fill were positively related to N recovery by seeds. These differences could have been due to the low rainfall in 1990, which may have permitted MBT to remain in the soil for a longer period and to inhibit N fixation and plant growth in the Vicia faba crop.

Effects of temperature, hydrogen ion and substrate concentrations on conjugation of l-chloro-2,4-dinitrochlorobenzene by glutathione S-transferase from susceptible and dichlorvos-resistant strains of cotton aphid (Aphis gossypii Glover (Homoptera: Aphididae)) were evaluated. Enzymes from both strains had common optimum temperature and substrate concentration values of 30 °C and 10 mM respectively. Also, while enzyme activity of the susceptible strain peaked at pH 7·2, that of the resistant strain showed complete linear dependency up to pH 8·0. Of four subcellular fractions, the 100 000 g supernatant (soluble fraction) gave the highest enzyme activity in both phosphate and Tris/HCl buffers. There was no linear relationship between insecticide application frequency and production of enzyme activity in the susceptible strain but there was a very high positive correlation between these two parameters in the resistant strain.

Four grass species, three hybrids and three mixtures were grown in field swards near Aberystwyth. All swards were amply supplied with nutrients and were cut at 5-week intervals during the year of sowing (1989) and during the following 4 years. The order of the grasses in rate of establishment was: Westerwolds ryegrass > Italian ryegrass (Lolium multiflorum) > Italian ryegrass × perennial ryegrass, Italian ryegrass × meadow fescue, perennial ryegrass (Lolium perenne) > perennial ryegrass × meadow fescue, meadow fescue (Festuca pratensis) > tall fescue (Festuca arundinacea). During the sowing year as a whole, Italian ryegrass was the highest yielding grass, followed by Westerwolds ryegrass. During the remaining period (1990–93), as a whole, the highest yields were obtained from perennial ryegrass sown alone or in a mixture with tall fescue. Tall fescue sown alone was one of the lowest yielding grasses in the year of sowing, but developed to be the highest yielding in 1992 and 1993. Westerwolds ryegrass persisted least well, although some plants did survive until 1992. Italian ryegrass persisted better than Westerwolds and Italian ryegrass × meadow fescue persisted better than Italian ryegrass. Hybrid ryegrass and perennial ryegrass × meadow fescue persisted satisfactorily but with fewer tillers/m2 than perennial ryegrass or tall fescue. The yield of tall fescue in March was as high as that of Italian ryegrass in 1990 and 1991 and higher than that of any of the other grasses in 1992 and 1993; the tiller density of tall fescue was particularly high in March. The yield of mixtures (Italian ryegrass with perennial ryegrass, Italian ryegrass with tall fescue and perennial ryegrass with tall fescue) was, on average, 2·5% more than the mean of the component species when sown alone. When grown with ryegrass, tall fescue was not prominent initially but its proportion in the sward gradually increased.

The transmission of solar radiation within the crop canopies of oilseed rape is decreased both by the plant's yellow petals during flowering, and by the horizontal posture of the pods once they are formed. The significance of each of these morphologies was assessed, in the 1991/92 and 1992/93 growing seasons, by comparing the performances of an apetalous breeding line (N-o-112) and one with erectophile pods (N-5-130) with two conventional commercial genotypes (Falcon and Tapidor).

The apetalous floral layer of line N-o-112 reflected and absorbed significantly less radiation than those of the conventional, petalled genotypes. This resulted in a greater transmission of photosynthetically active radiation (PAR) to the leaf and bract canopy situated below. At peak flowering, 70% more PAR was transmitted through the apetalous floral layer.

The erectophile pods of line N-5-130 were angled 20–25° further from the horizontal than the conventional genotypes. The extinction coefficient (K) of its pod layer during late pod growth ranged from 0·35 to 0·44 as compared to 0·45 to 0·55 in the commercial varieties. Line N-5-130 carried a greater proportion of its total fertile pod number in the lower regions of the pod canopy compared to the two conventional genotypes. It also had a greater overall mean number of seeds per pod, and the number decreased proportionately less with depth in the canopy. The line was thus better able to maintain a higher photosynthetic area and to sustain pod and seed growth at the lower levels of the crop canopy than the conventional, commercial varieties. The potential physiological effects of apetalous flowers and erectophile pods are considered to be sufficiently beneficial for their introgression into near-isogenic lines to be pursued.

The effects of different rates of N fertilizer (0–180 kg N/ha) were tested on the growth, yield and processing quality of sugarbeet in 34 field experiments in England between 1986 and 1988. The experiments were performed using soil types, locations and management systems that were representative of the commercial beet crop in the UK. The responses obtained showed that current recommendations for N fertilizer use are broadly correct, but large differences occurred on some soil types, in some years, between the recommended amounts and the experimentally determined optima for yield. The divergence was largest when organic manures had been applied in the autumn before the beet crop. Calculations using a simple nitrate-leaching model showed that much of the N in the manures was likely to be leached, the extent of leaching being much less if the manure application was delayed until spring. In these circumstances, spring measurement of inorganic mineral N in the soil could improve fertilizer recommendations. In situations where higher than optimum rates of fertilizer N were used, the extra N had little effect on yield. Increasing the rate from 0 to 180 kg N/ha increased the amount of nitrate left in the soil at harvest by only 8 kg N/ha. The amount of inorganic N released into the soil from crop residues at harvest increased by 50 kg N/ha with N application rate, and the fate of this N has not been established.

Potato production in the lowland tropics is constrained by lack of affordable supplies of planting material. Therefore, the potential to produce in situ tuber seed from true potato seed (TPS) seedlings and rooted stem cuttings under nursery conditions in the warm tropics was studied, and their yields were compared with those of the same materials obtained under cool conditions. Subsequently, their field performance in the warm tropics was evaluated.

Tuber yield from TPS seedlings and rooted cuttings transplanted in nursery beds under warm conditions ranged from 50% to < 20% of that obtained in cool conditions, but reductions in tuber numbers were less marked under warm conditions. Survival of seedlings was less than that of stem cuttings, but tuber numbers of seedlings exceeded those of rooted cuttings by a factor of two or more (e.g. 700 m−2 for seedlings v. 224 m−2 for rooted cuttings). Low tuber number is physiologically inherent in cuttings, as is high tuber number in seedlings. Total tuber yields varied significantly amongst clones grown in the warm climate from rooted cuttings, not always in proportion to the number of tubers produced. Differences in tuber yield and tuber number were less marked between the two TPS progenies studied.

The field comparisons highlighted the 30–40% lower yield potential for warm-climate-produced nursery seed materials. Slower emergence and fewer stems apparently were in part responsible for this effect; however, neither tuber number harvested nor the proportion of marketable tubers was affected by site of production of seed materials. Cutting medium-sized warm-produced tubers (mean 23 g), the use of larger sized whole tubers (10–20 g v. 5–10 g) or increasing the planting density of 5 g tubers from 8·8 to 15·5 plants m-2 significantly increased yields by 4·9, 2·25 and 3·5 t ha-1, respectively, but yields were not increased further by 20–40 g tubers nor by 22·2 plants m-2. Small seedling tubers (≤ 5 g) can potentially lead to high stem numbers per unit weight of tubers, but their success in plant establishment was hampered in warm climates, especially in the presence of soil pathogens. Cool-climate-produced seedling tubers and tubers from cuttings can compete physiologically with field-produced seed tubers when used as planting materials in the warm tropics. However, with few exceptions, no crop from tubers produced under warm conditions could match the performance of crops from similar cool-produced tubers when planted out in the warm tropics.

During a 3-year experimental period (between 1992 and 1995), residual effects on yields of subsequent crops of phosphorus applied either to soyabean or wheat, and on recoveries of the added P and changes in the available P, were studied in a soyabean–wheat cropping system on a typic haplustert very low in available P at Bhopal, India. Phosphorus was applied at rates of 0–52 kg P ha-1 (five treatments) to soyabean and 0–39 kg P ha-1 (three treatments) to wheat during the first year, and in the subsequent years the residual effects were studied in relation to fresh applications of 39 kg P ha-1 to each crop. The yields of soyabean and wheat were increased significantly by the application of P to each crop. Phosphorus applied to soyabean showed residual effects in two succeeding crops, whereas P applied to wheat showed a residual effect in only one succeeding crop. Phosphorus applied to soyabean was more efficiently utilized by the succeeding crops compared to that applied to wheat in the rotation. The recoveries of added P were greater with smaller rates of added P and greater in the first two residual crops. Olsen P in soil was adequate only in the first year and it fell below the critical limit in the subsequent two cycles of cropping. Cumulative P uptake by crops determined the levels of available P in the soil and soil test values declined with increase in cumulative P uptake over time.

Pod wall photosynthesis is known to contribute to nearly one-third of rape (Brassica napus) seed weight. The relationship between the number of seeds and the growth of the pod wall, and the effects of single and mixed applications of gibberellic acid (GA), naphthyl acetic acid (NAA) and benzyl adenine (BA) on development of the pod wall were, therefore, examined in potted plants of spring rape under glasshouse conditions.

The size and weight of the pod wall were closely associated with the number of seeds per pod, and a stronger development of tissues was observed in the presence of seeds. Application of BA alone or in combination with GA (GA + BA) to emasculated flowers induced the development of parthenocarpic pods similar in size and shape to the untreated seeded pods. NAA applied singly or in mixtures produced abnormal pods. BA enhanced cell division in all tissues while GA and NAA caused expansion of parenchyma in the mesocarp. Application of BA or GA + BA at 1–5 rather than at 11–15 days after flower opening led to the development of bigger pods. Younger pods responded more than the older ones when they were treated simultaneously. BA or GA + BA application to nonemasculated flowers on the terminal raceme delayed senescence in both basal and apical pods but it increased pod size only in the latter. The balance of cytokinins and gibberellins within a pod seems to play an important role in regulating the growth of the pod wall.

The in vitro resistance of five white and four coloured-flowered lines and cultivars of Vicia faba to seed and root inoculation with spore suspensions of the pathogenic soil-borne fungi, Fusarium culmorum and Pythium debaryanum, was investigated under aseptic conditions in the UK. The presence of foliar diseases was also assessed in the field in 1989/90. White-flowered lines were more susceptible than coloured genotypes to fungal infection during germination but equally resistant during seedling growth. High-tannin containing seed coats had chemical and physical properties which protected seeds against fungal infection during germination. Frequent cracking of the seed coat in a zero-tannin line was associated with a greater fungal contamination of seeds. Resistance to the foliar diseases Uromyces viciae-fabae and Botrytis fabae was not related to flower colour. The results are discussed in relation to emergence in white-flowered types.

The extent of variation in ratoonability was examined in a range of recently bred short-duration pigeonpea [Cajanus cajan (L.) Millsp.] genotypes in 1989/90, 1990/91 and 1991/92 at the ICRISAT Asia Center, Andhra Pradesh, India. Traits with which this variation could be associated were assessed. Differences in the total ratoon yield of two flushes were significant among the genotypes in each season. In a few genotypes, ratoon yield constituted 50% of the total yield, which could be as high as 5·6 t/ha. Total ratoon yield was positively correlated with leaf area index in the last 2 years of experimentation. The relationship of total ratoon yield to main crop yield was significantly positive in 1991/92 only. The results suggest that there is a large variation in ratoonability among short-duration genotypes and that high leaf area retention at main crop maturity appears to contribute substantially to this variation.

Traditionally, only one groundnut (Arachis hypogaea) crop is grown in the uplands during the rainy season (May-October) in Sierra Leone, with sowing starting at the beginning of the rains. However, a recent trend among groundnut farmers is to sow a second crop in September after harvesting the first crop. Thus a system comprising a first (major) and a second (minor) cropping season is being adopted, with the second season crop having to depend largely on moisture stored in the soil. Experiments were conducted in 1993 at the Institute of Agricultural Research Experimental Farm, Njala, to assess the agronomic potential of growing two crops a year. Crop phenology, growth and productivity were strongly influenced by cropping season. Pod yield ranged from 1·63 to 2·58 and from 1·16 to 1·95 t ha-1 in the major season, declining to 0·72–1·29 and 0·57—1·07 t ha-1 in the minor season. Haulm yield, number of mature pods, crop growth rate and partitioning were lower in the minor season by 58, 57, 40 and 13%, respectively. However, kernel quality was higher in the minor season. The results suggest that the growing of two groundnut crops in the uplands is a potentially viable management option in Sierra Leone, and could represent a more efficient utilization of the growing period.

The effect of foliar applications of different formulations of manganese on pea yield and ‘marsh spot’, a seed defect which reduces quality of peas (Pisum sativum) grown for human consumption or seed was evaluated in nine experiments in the East of England from 1992 to 1994. Sprays, at dose rates recommended by the manufacturer, were applied to field peas, cvs Maro or Bunting, on three occasions at the four node pea growth stage, first pod and 14 days later, or on two occasions at first pod stage and 14 days later. Although the sites selected had a previous history of marsh spot in pea crops, there were no visual foliar symptoms of manganese deficiency in peas grown in any year at any site. Applications of manganese did not increase yields compared with untreated peas and there was no effect on maturity. Marsh spot was negligible in untreated peas at sites where soils had the lowest levels of manganese (22 and 44 mg/kg), thus soil analysis for manganese may be inappropriate as a guide to prediction of marsh spot problems. The three spray programmes, which included an early application of manganese at the 4–5 node stage, gave no statistically significant improvements in marsh spot control. There was a good correlation between amounts of manganese applied and reductions in marsh spot, and manganese sulphate, 31% w/w at 3·1 kg/ha applied as a split dose, achieved the best control. An exception was the manganese carbonate 50% w/v formulation which may have been poorly assimilated by the plant. Chelated manganese as MnEDTA 6·4% w/v at the rates recommended by the manufacturer was inadequate for control of marsh spot in all years.

In laboratory tests using stable manure consisting of wheat straw and slurry, ammonia emission was found to have two peaks corresponding to the population dynamics of proteolytic bacteria and amino acid-degrading bacteria respectively. Cumulative ammonia emissions over 14 days were 0·8–23·2% of the initial total nitrogen (Nt) and were both abiotically and biotically induced. Changes in pH had the most significant effect on the abiotically induced ammonia emissions. After 14 days of decomposition, at pH values of 6·0 and 7·5, abiotically induced emissions remained close to the limit of detectability, whereas at pH 9·0 as much as 9·8% of the initial Nt was lost. An increase in storage pressure from 0 to 400 and 800 kp/m2 generally decreased the biotic emissions to 9·6, 2·8 and 2·3%; while increasing the amounts of litter (2·5, 5·0 and 15·0 kg straw/LAU per day) led to a decline not only in the biotic (17·1, 12·8, 3·5%) but also in the abiotic emissions (6·1, 5·5, 1·6%). Varying the temperature (20, 30 and 40 °C) resulted in biotically induced emissions of 7·9, 11·7 and 11·6%, respectively, and abiotically induced emissions of 1·1, 1·4 and 2·2% of the initial Nt. At temperatures of 30 and 40 °C, the amount of microbially digested sources of carbon available was obviously sufficient to permit almost total reincorporation of NH4+ from 4 days onwards.

The effect of dwarfism on leaf number and size was investigated on six pairs of tall and dwarf nearisogenic lines of indeterminate autumn-sown white lupins (Lupinus albus L.). Dwarfism reduced mainstem height by 41% and first-order branch length by 22%. It also slightly decreased the number of leaves on the mainstem and first-order branches without affecting the time of flowering. Leaf size was not reduced. Logistic equations were used to analyse differences in the patterns of light interception by leaf canopies relative to thermal time from sowing during the growth of seven dwarf lines and three tall cultivars sown on different dates. The genotypes studied had long periods of low light interception during their early growth. No differences were found between most of the equation parameters for dwarf and tall genotypes. Only the proportion of light intercepted at flowering differed and this was explained by differences in flowering time. The dwarf character did not limit the ability of the crop canopies to intercept light. It is concluded that the character can be introduced into a wide range of genetic backgrounds without deleterious effects.

An erect, 60-day cultivar of cowpea, IT84S–2246, was grown with adequate soil moisture at two locations in Nigeria in 1990/91, Ibadan (7° N) and Kano (12° N), contrasting in total incident radiation (Q) and at plant population densities of 1·9–7·7 and 5·4–16·3 plants/m2, respectively. Leaf area, radiation interception and dry matter (DM) accumulation and partitioning were measured. Total shoot and seed dry weights were greater at Kano (mean 4·10 and 1·61 t/ha, respectively) than at Ibadan (mean 1·89 and 0·68 t/ha, respectively), and greater athigher plant densities. Relationships between the reciprocal of total shoot (Wt) and seed dry weight (Ws) per plant and plant population density (Np) determined at Kano and Ibadan were linear and parallel; intercepts, however, were significantly different (P < 0·005). The theoretical maximum potential Wt and Ws per unit area (i.e. 1/b) was therefore the same at Kano and at Ibadan, 448 and 170 g/m2, respectively. However, the optimum Np at Kano and Ibadan was markedly different, c. 10 and 40 plants/m2, respectively. These differences in the relations between DM yields and Np at Kano and Ibadan are examined in terms of leaf area, radiation interception and the partitioning coefficient, and the implications for the design of other agronomic investigations in cowpea are discussed.

The Broadbalk Wheat Experiment at Rothamsted (UK) includes plots given the same annual applications of inorganic nitrogen (N) fertilizer each year since 1852 (48, 96 and 144 kg N/ha, termed N1 N2 and N3 respectively). These very long-term N treatments have increased total soil N content, relative to the plot never receiving fertilizer N (N0), due to the greater return of organic N to the soil in roots, root exudates, stubble, etc (the straw is not incorporated). The application of 144 kg N/ha for 135 years has increased total soil N content by 21%, or 570 kg/ha (0–23 cm). Other plots given smaller applications of N for the same time show smaller increases; these differences were established within 30 years. Increases in total soil N content have been detected after 20 years in the plot given 192 kg N/ha since 1968 (N4).

There was a proportionally greater increase in N mineralization. Crop uptake of mineralized N was typically 12–30 kg N/ha greater from the N3 and N4 treatments than the uptake of c. 30 kg N/ha from the N0 treatment. Results from laboratory incubations show the importance of recently added residues (roots, stubble, etc) on N mineralization. In short-term (2–3 week) incubations, with soil sampled at harvest, N mineralization was up to 60% greater from the N3 treatment than from N0. In long-term incubations, or in soil without recently added residues, differences between long-term fertilizer treatments were much less marked. Inputs of organic N to the soil from weeds (principally Equisetum arvense L.) to the N0–N2 plots over the last few years may have partially obscured any underlying differences in mineralization.

The long-term fertilizer treatments appeared to have had no effect on soil microbial biomass N or carbon (C) content, but have increased the specific mineralization rate of the biomass (defined as N mineralized per unit of biomass).

Greater N mineralization will also increase losses of N from the system, via leaching and gaseous emissions. In December 1988 the N3 and N4 plots contained respectively 14 and 23 kg/ha more inorganic N in the profile (0–100 cm) than the N0 plot, due to greater N mineralization. These small differences are important as it only requires 23 kg N/ha to be leached from Broadbalk to increase the nitrate concentration of percolating water above the 1980 EC Drinking Water Quality Directive limit of 11·3mgN/l.

The use of fertilizer N has increased N mineralization due to the build-up of soil organic N. In addition, much of the organic N in Broadbalk topsoil is now derived from fertilizer N. A computer model of N mineralization on Broadbalk estimated that after applying 144 kg N/ha for 140 years, up to half of the N mineralized each year was originally derived from fertilizer N.

In the short-term, the amount of fertilizer N applied usually has little direct effect on losses of N over winter. In most years little fertilizer-derived N remains in Broadbalk soil in inorganic form at harvest from applications of up to 192 kg N/ha. However, in two very dry years (1989 and 1990) large inorganic N residues remained at harvest where 144 and 192 kg N/ha had been applied, even though the crop continued to respond to fertilizer N, up to at least 240 kg N/ha.

The capacity for gas production by three sources of inocula was evaluated at the University of the Azores between 1993 and 1994. The sources were: liquor from the rumen of sheep and slaughtered cattle and a suspension of sheep faeces. The highest gas production was observed in the liquor obtained from sheep rumen. Lower production(p ≤ 0·05) was observed in the rumen liquor obtained from slaughtered cattle, and the lowest results (p ≤ 0·05) were obtained with the suspension of faeces from sheep.

Biogenic amine formation was studied in silages made from perennial ryegrass. In 1991 two batches of grass from the same sward of the ID–DLO permanent pasture were wilted to either 250 or 450 g dry matter (DM)/kg, and ensiled in eight 1-litre laboratory silos for eachtreatment (Expt A). To induce differences in fermentation pattern, the grass was ensiled without additive (CON) or treated with formic acid (5 ml/kg; FA), cell wall degrading enzymes (2·1 ml/kg; ENZ), molasses (50 g/kg; MOL), or inoculated with Lactobacillus plantarum (107 colony forming units (CFU)/g; LP), a combination of Lactobacillus plantarum and Streptococcus faecium (105 CFU/g; LPSF), or Enterobacter sakazakii (6×lO6 CFU/g; EB). One silo for each treatment was opened after 1, 2, 4 and 7 days for pH determination and duplicate silos were opened after 10 and 90 days for pH determination and analysis of fermentation products. Two similar experiments (B and C) were performed using the CON, FA and LP treatments.

Total amine content of the grass was low (0·1–0·2 g/kg DM). The well preserved silages in each experiment contained considerable amounts of amines, ranging from 0·1 g/kg DM in the wilted LP and FA silages to 7·4 g/kg DM in a low DM CONsilage. Tyramine, cadaverine, putrescine and histamine were, in descending order, the principalbiogenic amines formed, representing together 90 (S.E. 9)% of the total biogenic amine contentof the silages. Formation of amines occurred mainly during the first 10 days of fermentation, and was highest in silages with a slow acidification rate. Ensiling at high DM content, with formic acid or inoculation with large numbers of lactic acid bacteria significantly (P < 0·01) reduced the amount of amines in the silage. Total and individual amine contents of the silages were significantly correlated with concentrations of ammonia and acetic acid. It was concluded that the formation of biogenic amines in grass silage is related to protein degradation, and that amine formation can be reduced by restriction of fermentation in the silage, or by achieving rapid acidification during the first phase of ensiling.

Agronomic practices can be modified to decrease autumn soil nitrate and nitrate leaching. This experiment aimed to measure the effectiveness of such practices when integrated into a farming system under UK conditions. The experiment started in autumn 1988 on a sandy soil in Nottinghamshire, UK, and comprised a four-course rotation of potatoes–cereal–sugarbeet–cereal. Three husbandry systems were superimposed, ranging from current commercial practice to most nitrate retentive. Plots were split further to receive either half or full recommended rates of nitrogen (N) fertilizer. Soil mineral N (Nmin) and nitrate leaching (using porous ceramic cups) were measured on selected treatments; this paper presents the findings after five winters.

Autumn Nmin and N leached were strongly influenced by the previous crop, consistently following the order potatoes > cereal > sugarbeet. Pre-harvest management (chiefly N fertilizer input) affected Nmin, and post-harvest management also modified N loss. Cover crops (winter rye or forage rape) after cereals removed 10–40 kg/ha N, depending on previous N management, time and method of establishment. They decreased leaching and were particularly effective if they were able to establish fully before significant drainage occurred. Nmin following sugarbeet, which had received 125 kg/ha N, was less after November lifting than after October lifting (16 and 28 kg/ha N, respectively, as amean of autumns 1989–92). Potatoes left most Nmin (a mean of 60 kg/ha for autumns 1989–92, receiving 220 kg/ha fertilizer N), and their late harvest gave little scope for decreasing leaching losses by establishing green cover before the start of winter. After late harvested root crops (both beet and potatoes), it was often preferable to leave the land fallow over winter, rather than ploughing and drilling a winter cereal.

We show that nitrate leaching can be decreased by simple and inexpensive modifications to an existing crop rotation. Averaged over five winters, adopting such practices decreased the mean N concentration in drainage from 22·3 to 14·5 mg/1.