Nitrogen is an important factor determining grain yield of barley (Hordeum vulgare L.). Optimal rates and application timing can vary according to the environmental conditions under which the crop is grown. For 8 years (1979–86) barley yield, tillering, and leaf-area response to N application rates and timing were studied in southern Spain. The results showed that, under our experimental conditions, the most advantageous N rate for grain yield was 60 kg/ha, either split equally between sowing and tillering, or else with the greater proportion applied at tillering. Nitrogen applied at sowing increased number of tillers per plant, and N applied at tillering favoured tiller survival for later spike formation. In addition, N applied at tillering increased the number of leaves per plant, leaf area per plant, and the leaf area index, the maximum value of which occurred at anthesis.

Results obtained from the plots of a field experiment may be subject to’ representational errors'; that is, they may not exactly reproduce the results that would be expected if the same treatments were applied to whole fields. In particular, the treatment applied to one particular plot often has the potential to affect the adjacent plots; such an effect may be positive or negative according to circumstances, and its magnitude cannot easily be estimated. This paper shows, on theoretical grounds and by simulations, that nearest-neighbour (NN) analysis cannot be relied upon to mitigate the effects of such inter-plot interference, even when the residual variance of the NN analysis is substantially, and by normal criteria significantly, smaller than that of conventional (randomized block) analysis. In certain circumstances, NN analysis of data affected by interference produces greater average bias in estimated treatment differences than conventional analysis.

In order to determine whether cereal crops require fertilizer sulphur (S) in areas estimated as receiving < 20 kg S/ha per year from the atmosphere, the effects of applying agricultural gypsum (10, 20, 30, 40, 60 and 80 kg S/ha), ammonium sulphate (24 and 48 kg S/ha) and foliar-applied elemental S (10 kg S/ha) fertilizers were compared with a nil-S control in replicated field experiments at 12 sites in England and Wales during 1987–90. Averaged across all S treatments, significant (P ≤ 0·01) positive yield responses of 0·4 t/ha were obtained in winter barley at three sites in 1990 on sandy soils in Wales (two sites) and in south-west England (one site). There was no yield advantage in applying > 10 kg/ha of S as gypsum at these sites. Yield responses were best predicted by a nitrogen: S concentration ratio ≥ 17:1 in leaf tissue at anthesis and a S concentration of ≤ 0·1% in the grain dry matter at harvest.

Significant increases in total S and sulphate-S concentrations in leaf tissue at anthesis were obtained from increasing the rates of gypsum applied at ten of the sites, but a significant increase in the concentration of S in the grain at harvest was obtained at only one site. There was no difference in effectiveness between gypsum and foliar-applied elemental sulphur when compared at a single rate of 10 kg S/ha. Comparison of the increases in leaf-S status from maximum application rates of ammonium sulphate and gypsum suggested that ammonium sulphate was the more effective Sfertilizer source. The results confirm that S deficiency is starting to appear in cereal crops in England and Wales.

Nine experiments were carried out on three different soil types in the south-east of Ireland over three years (1989, 1992 and 1993) to test the effect of early, normal and late sowing at three rates of fertilizer nitrogen (100, 125, 150 kg/ha) on the yield and grain quality ex-farm of spring malting barley (cv. Blenheim). Early sowing (January or February) was not possible in 1990 and 1991 due to wet weather. Sowing date had a pronounced effect on grain yield and grain N content in all three years. In 1989 and 1992, the earliest-sown barley (January or February) gave significantly greater yields than latersown crops (March and April) in five of the six experiments. The earliest-sown barley gave the lowest grain N in all six experiments and there was a gradual and significant increase in grain N content as sowing date was delayed. In 1993 the earliest-sown barley (February) gave significantly lower yield and greater grain N than the March-sown crop in all three experiments. The lower yield of the February-sown barley in 1993 was due to the significantly reduced number of grains/ear. The Aprilsown barley gave significantly lower yield and greater grain N than the earlier-sown crops in eight out of the nine experiments. In 1989 and 1992 only one of the six experiments, Ferns 1992, gave a significant yield response to increased rate of N (125 kg/ha). But in 1993, 125 kg N/ha significantly increased grain yield in all three experiments and 150 kg N/ha gave a further significant increase in yield in two of the experiments. Increasing increments of fertilizer N significantly increased grain N in all nine experiments.

The chlorophyll fluorescence parameters ΔF/Fm′ and Fv′/Fm′, related respectively to the quantum yield of photosynthetic electron transport and to the efficiency of excitation capture by the open centres of photosystem II, have been evaluated as possible indicators of drought tolerance in durum wheat. ΔF/Fm′ and Fv′/Fm′ measurements were carried out on excised leaves, both control and dehydrated, of 25 cultivars. ΔF/Fm′ and Fv′/Fm′ values were obtained at two times after the start of fluorescence measurement: at 14 s, i.e. during the induction curve (ΔF/Fm′14s and Fv′/Fm′14s) and at 200s, i.e. at steady state fluorescence (ΔF/Fm′200s and Fv′/Fm′200s).

In dehydrated leaves a mean significant decrease of 20% (P < 0·001) was observed in ΔF/Fm′14s values. In contrast, no great differences were observed between control and dehydrated leaves with regard to ΔF/Fm′200s, Fv′/Fm′14s and Fv′/Fm′200s.

The percentage decrease of ΔF/Fm′14s after dehydration was correlated with the drought susceptibility index (DSI) of the cultivars, evaluated on a yield basis and a significant correlation (r = 0·72, P < 0·001) was found.

At four pairs of sites in the UK, two cultivars of wheat, bred either for autumn (cv. Mercia) or for spring (cv. Tonic) sowing were sown in November 1988 and 1989 and their yield response to springapplied fertilizer N assessed over the range 0–320 kg/ha N. Grain samples were taken at harvest and analysed for those qualities regarded as indicators of suitability for milling. In five experiments, the grain yield of Mercia was up to 1 t/ha greater than that of Tonic, but overall there was no consistent difference between the two cultivars in the optimum economic yield (Yopt)or in the amount of fertilizer N needed to produce it (Nopt). Both cultivars produced c. 17·5 kg of grain per kg of fertilizer N applied up to Nopl. In the five experiments in which Tonic yielded less, it produced grain of greater N concentration than Mercia when given the same amount of fertilizer N. Differences in grain N concentration, while small (< 0·3%), were significant when analysed across sites. In six experiments both cultivars produced grain of 11 % protein at Nopt. There were no consistent or worthwhile increases in specific weight, Hagberg falling number (HFN) or response to the sodium dodecyl sulphate (SDS) sedimentation test of either cultivar from applying more fertilizer N than Nopl. The average specific weight of Mercia grain was 2·5 kg/hi greater than that of Tonic, while Tonic gave larger SDS values of c. 8. There was little difference in HFN. It was concluded that the yield requirement for fertilizer N was similar for these two cultivars of wheat when sown in late autumn, and there was no need to apply differential fertilizer N applications to the cultivars to produce grain of the quality needed for breadmaking. In four experiments the application of plant growth regulator (PGR) increased the yields of both cultivars by c. 0·5 t/ha.

At 14 sites in the UK, spring wheat (Triticum aestivum) cv. Tonic, was sown on three or four dates at each site between October and March in the 1988/89, 1989/90 and 1990/91 seasons. Responses to spring-applied fertilizer N over the range 0–320 kg/ha were determined. Earlier sowing did not increase uptake of soil N by the crop. Fertilizer N increased grain N offtake by between 25 and 140 kg/ha and yield by between 0·3 and 5·5 t/ha, although grain yield was less responsive to fertilizer N at later sowing dates. Apparent recovery of fertilizer N (AFR) also decreased as sowing was delayed but there was no effect of delayed sowing on the amount of grain produced from each kg of fertilizer N recovered. Because fertilizer N recovery decreased with later sowing, the amount of fertilizer N needed to produce the optimum economic grain yield was not reduced. Neither AFR nor optimum fertilizer (Nopt) was related to optimum yield. Regression of Nopt on the difference between optimum yield and yield without fertilizer N (△y) explained 77% of the variance in Nopt. There was an inverse relationship between △y and soil mineral N (SMN) in spring; regression of △y, on SMN in spring accounted for 29% of the variance in △y Current advisory systems which adjust economic fertilizer N recommendations according to anticipated yield are not justified by these results. Moreover the adjustments made, based on yield expectation, appear about three times as large as those needed to minimize residues of fertilizer N left unrecovered by the crop and to reduce the risk of nitrate leaching in the following winter.

The seasonal rate and extent of dry matter (DM) and neutral detergent fibre (NDF) degradation of the African sourveld grasses Alloteropsis semialata, Andropogon appendiculatus, Cynodon dactylon, Elionurus muticus, Eragrostis plana, Harpochloa falx, Heteropogon contortus, Hyparrhenia hirta, Microchloa caffra, Themeda triandra and Tristachya leucothrix in the rumen were measured using the nylon bag technique at the Döhne Agricultural Development Institute, South Africa, in 1993. The size of the soluble fraction (SF) was markedly different (P < 0·05) between species, being largest in A. semialata (22·6%) and smallest in E. plana (13%). Over all species, the mean SF was highest (P < 0·01) in spring (21·6%) and lowest in winter (11·8%). Species differed (P < 0·05) in the size of the potentially digestible fraction (PDF), with H. contortus and T. leucothrix having the largest (71%) and M. caffra the smallest (53%) PDF. Mean PDF declined (P < 0·01) from spring (77·3%) through to winter (55·8 %). The rate of DM degradation (kd) in the rumen also differed (P < 0·01) between species, with C. dactylon and A. semialata having the fastest (0·054) and E. plana and A. appendiculatus the slowest (0·039) degradation rates. Mean kd values were lower (P < 0·05) in winter (0·039) than in the other seasons (0·048).

Neutral detergent soluble (NDS) content was highest in A. semialata (29%) and lowest in E. plana (21·5%). Species similarly varied in the amount of potentially digestible cell wall (PDCW), with E. plana having the highest (57%) and C. dactylon the lowest (45·1%) PDCW content. Mean PDCW content was highest in spring (59·5 %) and lowest in winter (44·6%). Cell wall degradation (kc) rates were fastest (0·04) in C. dactylon and slowest in M. caffra (0·03). Overall, kc declined from spring (0·039) through to winter (0·029). In general, A. semialata, T. triandra and H. hirta appeared to have the most favourable, and E. plana, A. appendiculatusand M. caffra the least favourable, ruminal degradation characteristics. These differences suggest that species composition is likely to have a major impact on potential animal production on these low quality grasslands.

Elemental sulphur (32 kg S/ha) and urea (30 kg N/ha) were applied to the foliage of different winter wheat cultivars, halfat flag leaf emergence and halfat ear emergence, in factorial experiments in 1986, 1987 and 1988. There were no clear visual symptoms of S deficiency, but there was evidence from soil analysis, grain S concentration and grain N:S ratio that the crops were marginally deficient in sulphur. Disease severity was generally negligible. Leaf senescence at the end of grain growth was delayed by sulphur in two of the three years, both with and without urea in 1987, but only with urea in 1988. Sulphur, both alone and mixed with urea, increased grain S concentration from early grain growth in 1986 and 1987, but not until the end of grain growth in 1988. Urea alone reduced yield in 1986 and 1987, but mixing S with the urea compensated for this phytotoxic effect. Yield was not significantly increased by S when compared with plots receiving neither urea nor S.

Maize (Zea mays L.) hybrids with different productivity per unit approximate leaf projected area (ALPA) were compared in China, 1990–92. The results showed that the selection index (SI) values of all the hybrids tested decreased with an increase in population density. Nevertheless, the hybrids with high SI values at low plant densities also had relatively high SI values at high plant densities. Thus, high SI hybrids could be selected at any of these densities. Although no significant yield increase was obtained by using high SI hybrids at plant densities of 52500 plants/ha or lower; significant increases in yield were obtained for high SI hybrids at > 67 500 plants/ha. Leaf area was one of the parameters necessary for determining SI, and this could be predicted with a skewed bell-shaped function simply by measuring the length and breadth of the largest leaf and counting the total number of leaves per plant.

Seed production of annual medics was measured at four sites in Syria and Jordan between 1986/87 and 1988/89. Plots sown to medic in the first year were sown to wheat in the second year, and medic regeneration was measured in the third year. At three of the sites, adjacent plots were established in the second and third years and herbage production, and regeneration where appropriate, were measured in the third year. In this way, genotype × site interactions were used to assess medic adaptation to wheat/pasture rotations, continuous pasture and newly sown pasture.

Seed production was correlated with rainfall, the mean yield of 14 genotypes ranging from zero at 160 mm to 1 tonne/ha at 510 mm. Medicago polymorpha produced the highest yields, though not at the lowest rainfalls. Yields of M. rotata were also above average. There was, however, wide variation between species in seed weight, pod weight and seeds/pod.

Regeneration was better after wheat than after pasture. Herbage production was slightly better after pasture than after wheat, and both were greatly superior to that of newly sown pasture. After 2 years' germination, most genotypes retained more than half (mean 60%) and up to 99% of the seed produced in the first year.

Genotype × environment interactions were tested using analysis of variance (ANOVA), regression (Finlay & Wilkinson 1963) and principal component analysis (PCA). Because adaptation in pasture plants depends on many variables, PCA proved to be the most useful technique and the simplest to apply. ANOVA and regression were limited by their inability to process more than one variable at a time. Regression analysis is further limited by requiring a greater number of sites.

Based on seed production, seed survival, seedling regeneration and herbage production, certain locally collected genotypes of M. rigidula, M. noeana, M. polymorpha and possibly M. rotala, were adapted to conditions in Syria and Jordan. A similar methodology could be used to test pasture legumes throughout west Asia and north Africa

Field experiments were carried out on six sites in eastern Scotland between 1987 and 1989 to determine the effect of nitrogen on the yield, N uptake and grain N concentration of spring barley grown for malting. The effects of fertilizer applications at rates from 0 to 150 kg N ha-1 and the timing of application were studied, using three fertilizer forms: calcium nitrate, ammonium sulphate and ammonium nitrate. Calcium nitrate applications significantly increased grain N concentrations (P < 0·05), and grain yields (P < 0·01 and 0·05) at two sites, above the values obtained with the other fertilizers, but there was no effect at the other sites. Split applications of calcium nitrate increased yields above those from single applications in some treatments at two sites. At low rates, recovery of 15N-labelled fertilizer was greatest when applied as calcium nitrate. Recovery fell at higher rates in calcium nitrate treatments, but rose in ammonium sulphate treatments. Uptake of fertilizer N, during the period of stem elongation in June, was significantly greater (P < 0·05) in the calcium nitrate and ammonium nitrate treatments. Maximum uptake was usually reached by the time of anthesis. Uptake of soil N was not as great during the early sampling periods, but continued up to harvest in most treatments. There was evidence of losses, between anthesis and harvest, of fertilizer N previously taken up by the crop. The uptake of soil N remained constant over the range of fertilizer treatments except with ammonium sulphate, where there was evidence of increased uptake at higher fertilizer rates, possibly due to ‘pool substitution’ of 15N-labelled fertilizer. The variation in soil N uptake between sites was greater than the variation in fertilizer N uptake caused by different forms of fertilizer and different application times.

Bahia grass (Paspalum notatum Flugge) plants were grown in growth chambers at Gif, France, and at Gainesville in Florida, demonstrating that the species is a long-day plant and greatly influenced by light quality during the photosynthetic period. Flowering occurred in all instances when the middle of the dark period was interrupted with red or red + far-red light. With nightly interruptions of farred light, flowering occurred only when a sufficient quantity of far-red was present during the photosynthetic period. Plants grown under short days with nightly interruptions of red, far-red or red + far-red light had less starch accumulation and greater leaf growth and dry weight than plants grown without nightly light interruptions, whatever the light quality during the photosynthetic period. The treatments did not affect the partitioning of assimilates and flowering in the same way.

Four plant species were compared in each of three harvest periods (in August/September) in 1991 and 1992 at Aberystwyth: white clover (Trifolium repens L.), rape (Brassica napus L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). Plant physical structure was considered in relation to rate of intake by sheep, chewing activity and the effectiveness of chewing in breaking the diet into particles.

White clover had a much lower proportion of cell wall than perennial ryegrass, but the rate of intake and the number of chews per min were similar for the two species. White clover petioles broke down into long, thin particles, similar in size and shape to those derived from perennial ryegrass leaf sheaths; many of the clover petioles were not split longitudinally by chewing, in contrast to the ryegrass sheaths. A white clover leaflet was typically broken into about 20 blocky particles, whereas a petiole of similar weight was broken into only about three particles. Veins were close together in ryegrass leaf sheaths and blades, particularly the latter; approximately one in seven strips of weaker tissue between veins was ruptured by chewing leaf sheaths and one in 16 in the case of leaf blades, in each case resulting in particles of c. 2 mm width. Rape had a low proportion of cell wall and a low proportion of vascular tissue in its leaf blades, petioles and stems. Rape leaf blades were eaten quickly, but the stems were eaten slowly. The length and width of particles derived from rape leaf blades were very similar to those of particles derived from white clover leaflets. Spurrey had a high proportion of cell wall and was low in in vitro digestibility, but the rates of intake and chewing were high and relatively few chews were required per g of dry matter ingested. The vascular bundles in the spurrey stems were only half the thickness of the bundles in white clover petioles; pieces of spurrey stem were typically broken at about two places along their length and were not split during eating.

The study illustrates the wide variation in plant anatomy among species which can be available to herbivores and some effects of the abundance, thickness and orientation of vascular bundles on rate of intake, chewing activity and the size and shape of particles produced by chewing.

The leaf-curling plum aphid (Brachycaudus helichrysi Kalt.) is one of the main pests of sunflower (Helianthus annuus L.) in Europe. Yield losses were assessed in open field conditions and natural infestations over a 3-year period in Central West France. Plant variability and the choice of the more vigorous plants by aphids in open field conditions were two factors interfering with the experiments. To improve their sensitivity and to correct for biases without expanding the experimental design, an analysis of covariance was the best compromise. Field and cage experiments were conducted between 1985 and 1989 to assess the influence of aphids on the relationship between stem diameter at harvest and seed yield. As an indicator of plant vigour (size and yield), stem diameter at harvest was the best choice, as neither its relationship with seed yield nor its mean value was affected by aphid infestation. It was then used as a covariate to study yield losses. Aphid populations were quantified weekly from the beginning to the end of the infestations according to the leaf-curling symptom and to the number of aphids per plant. Multivariate analyses followed by cluster analysis identified groups of plants displaying similar infestation dynamics. It was found that when aphid populations reached > 100 per plant at the budding stage, yield losses occurred. When populations were < 100 aphids per plant at the budding stage and then decreased, no yield loss was observed. This gives growers ample time to monitor populations and treat crops.

Safflower (Carthamus tinctorius L.) is an important oilseed crop in India. A severe leaf spot disease caused by Ramularia carthami Zaprom. was observed in 1983 and investigations were carried out in order to analyse the role of environmental factors in disease development. High temperature and normal relative humidity, with dry rainless days, favoured disease development. Studies on the nature of in vivo resistance and susceptibility to R. carthami showed that growth of the fungal germ-tube was slower on resistant than on susceptible safflower cultivars, where the germ-tube extended with or without branching and penetrated infected leaves through the stomata. Of the four safflower cultivars evaluated, none were entirely free from the disease, but on the basis of lesion number and size, cultivar IGFRI-116 was rated as highly resistant.

Nitrate leaching was measured under three pastures – perennial ryegrass and white clover, a herbal ley comprising a mixture of legumes, non-aggressive grasses and deep rooting herbs, and perennial ryegrass fertilized with 400 kg N/ha per year as urea – from 1989 to 1991 at Palmerston North, New Zealand (latitude 40° S). The pastures were regularly mob-grazed by sheep at a stocking rate which varied with the amount of feed available. Drainage was estimated from a daily soil water balance and accumulated over 10 day intervals. Nitrate concentrations in the drainage were measured as the volume-averaged concentrations in the soil solution between 30 and 45 cm depth during these intervals. Although the N applied as fertilizer to the grass was 2·5 times greater than the N estimated to have been fixed by the clover-based pastures, the leaching loss from the former was 6–7 times greater than from the latter. The stocking rate on the grass pasture averaged over each year was only 1·2–1·4 times that on the two clover-based pastures. Leaching from urine patches was estimated to account for 55% of the total N leached from the clover-based pastures, but only 25% of the total leached from the N-fertilized grass.

The amount of NO3-N leached should be related to the cumulative drainage to determine whether the average nitrate concentration exceeds the environmental safety limit of 10 mg NO3-N/1. In 1989, when the total drainage was 215 mm, 21·5 kg N/ha would have had to be leached for the concentration to exceed the limit and none of the pastures did so. In 1990, when the total drainage was 270 mm, the critical amount to be leached was 27 kg N/ha which was exceeded by the Grass + N400, but not by either the Grass-clover (5.8 kg N/ha) or the Herbal ley (7·3 kg N/ha). The utilization of N was more conservative in the clover-based pastures than in the N-fertilized grass.

Potato seed tubers infected or not infected with gangrene (Phoma foveata) were planted at Rothatnsted in 1987 to measure the effect of the disease and of neighbouring plants on yield. The experimental design was constructed so that the effect on growth of six adjacent plants (two nearest neighbours in each direction within rows and one nearest neighbour in each direction across rows) could be estimated for each plant. Total yield, ware (> 150 g) yield and tuber number from individual plants were affected most by the disease but also, in decreasing importance, by the two plants on either side within the same row (first neighbours), the two plants adjacent to the first neighbours (second neighbours) and the two adjacent plants in the rows on either side. Yield and tuber numbers increased as the different combinations of neighbouring plants contained increasing proportions of plants from diseased seed and missing plants; plants compensated for decreasing competition. Tuber size distributions showed that numbers of ware tubers decreased with increasing competition whereas numbers of small tubers were less affected. The fitted model was used to predict yields from crops planted with different proportions of diseased or missing seed tubers.

In 1990–92, field experiments were performed at Broom's Barn Experimental Station to study the effect of 5 years' repeated straw incorporation on sugarbeet. Straw incorporation had no effect on plant population density. Processing quality was reduced by incorporated straw but N had a much larger effect. The effect of incorporated straw on the mineral N content of the soils and N uptake by beet was inconsistent, and this may be related to the amount of soil mineral N present when the straw was incorporated. The efficiency of fertilizer use was unaffected by straw incorporation. On Broom's Barn soils when straw was incorporated, the optimal economic N dressing was c. 120 kg N/ha, and in unincorporated plots it was c. 100 kg N/ha. At the optimal economic N rate, incorporated straw increased beet yields.

Twelve accessions of pigeonpea (Cajanus cajan [L.] Millsp.) were grown on an Alfisol in a humid ecozone in Nigeria in 1989. At 4 and 8 months after planting (MAP), the primary growth was cut to determine the effect of age at first pruning on stump survival and coppice regrowth, and also on total herbage yield in a 12-month pruning cycle. It was clear that a height of 3 m or more is adequate for pigeonpea to receive its first cut with only 10% stool mortalities. Cutting the primary shoot at 8 MAP (in the dry season) ensured greater stump survival and also stimulated rapid coppice shoot regrowth, indicating the advantage of coppicing in the dry season and also at maturity. The total leaf and wood dry matter (DM) production in a 12-month cycle is greatest if the primary shoot was first cut at 8 MAP. This suggests that allowing the trees to become established is beneficial in the pruning management of pigeonpea. Accessions 11563 and 11575 have the ability to produce 7 t/ha of leaf DM from two prunings when first cut at 8 MAP, and significantly outperformed the local variety. The study revealed that pigeonpea does not coppice well and its biomass yields are much lower than that of Leucaena leucocephala.