Soil-applied fungicides for controlling take-all in field experiments with winter wheat

Soil treatment fungicides were tested against take-all (Gaeumannomyces graminis var. tritici) in three field experiments with winter wheat. Fungicides were applied as drenches either before sowing in autumn, and incorporated by rotary harrowing, or to the crop in spring. The most effective treatments were autumn applied benomyl (20 kg/ha) and nuarimol (0·55-4·4 kg/ha). However, the highest nuarimol concentration depressed yield. Benomyl sometimes induced a resurgence of take-all in the second wheat crop after treatment. Nuarimol had no adverse effects in subsequent crops, and neither fungicide hindered the onset of take-all decline in a third crop after treatment. The possible value of soil treatment in future control strategies is discussed.     

Field tests of bacteria and soil-applied fungicides as control agents for take-all in winter wheat

Putative biological and chemical treatments for controlling take-all were used in each of three consecutive years at two locations where winter wheat crops were grown in naturally-infested fields. The chemical treatments more often decreased take-all than the biological treatments, but no treatment consistently and significantly decreased take-all, nor did any cause a significant increase in yield. An isolate of Bacillus cereus var. mycoides and one of B. pumilis, applied as soil drenches in autumn or spring, or in the seed furrows, were usually ineffective. Of the few significant effects on disease, half were associated with increases and half with decreases, and most occurred in April and did not persist to late June. Two strains of Pseudomonas pluorescens applied to the seed were ineffective. The fungicide benomyl, applied as a drench in autumn and spring at 20 kg/ha was ineffective, while nuarimol, applied as a drench in autumn at 2 kg/ha was sometimes effective. Nuarimol incorporated into the seed bed at 2 kg/ha was the most effective treatment. In analyses using a functional relationship model for data from treated and untreated plots 12% of 176 data sets for biological treatments, 38% of 96 data sets for chemical treatments and 81% of 16 data sets for combined treatments showed increasing efficiency of the treatment with increasing disease intensity. These findings also demonstrate an additional advantage of the experimental design, namely that treatments are tested at different disease intensity levels within fields.     

Comparison of natural and artificial epidemics of take-all in sequences of winter wheat crops

Winter wheat was grown for six successive years (Expt 1) and for three successive years (Expt 2) in field experiments on different soil types. Artificial inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici cultured on autoclaved oat grains) was incorporated in the soil of some of the plots just before, or at, sowing of the first winter wheat crop. Expt 1 tested the incorporation of similar amounts of inoculum (212 kg ha^-1) at different depths. Expt 2 tested different amounts of inoculum at the same, shallow depth. Early sowing (September), late sowing (October) and spring inoculation were additional treatments, applied to the first crop only, in Expt 2. Seasonal factors apart, the disease outcome in the first year after inoculation depended on amounts and placement of applied inoculum, as well as date of sowing. Deeper inoculum resulted in less disease (Expt 1). Severe take-all was produced in Expt 2 by incorporating inoculum shallowly in sufficient quantities (400 kg ha^-1 or more). Less inoculum (200 kg ha^-1) generated less disease, especially in earlier-sown plots. Differences in disease amongst inoculum treatments were greatest in the first year and diminished subsequently, particularly where sowing had been early in the first year. In Expt 1, where first crops exposed to artificial inoculum developed moderate-to-severe disease, disease in subsequent second and/or third crops was less. In the fourth crop a second peak of disease occurred, coinciding with a first peak in sequences without added inoculum. Take-all decline (TAD) appeared to be expressed in all sequences thereafter. In Expt 2 in sequences without added inoculum, TAD occurred after a peak of disease in the second crop. Where 400 kg ha^-1 or more of inoculum were added, disease was severe in the first year and decreased progressively in successive years. Disease was less patchy in plots that received artificial inoculum. However, it remains uncertain mat severe disease caused by artificial inoculation achieved an early onset of true TAD. The infectivity of the top 12 cm of soil in the first 3 yr of Expt 1, determined by bioassay, depended on the depth of added inoculum and amount of disease in subsequent crops. However, at the time of the naturally occurring peak of disease severity (in either inoculated or non-inoculated plots) it did not predict either disease or TAD. Differences and similarities amongst epidemics developing naturally and those developing from different amounts and placement of applied inoculum have been revealed. The epidemiological implications of adding inoculum and the potential value of artificially-created epidemics of take-all in field trials are discussed.     

Effects of 20 fungicides on the infectivity of conidia of the aphid entomopathogenic fungus Erynia neoaphidis

The effect of 20 fungicides on theinfectivity of conidia of the entomopathogenicfungus, Erynia neoaphidis, were assessedin the laboratory. After projection on broadbean leaves, conidia were treated withfungicides applied at their recommended fieldrate. Afterwards, the infectivity of theseinocula was assessed using an aphid bioassay.Four fungicides, carbendazim, kresoxym-methyl, nuarimol and thiophanate-methyl reduced the infectivity of the conidia by less than 25% and can be considered harmless for this aphid pathogen. Propiconazole was a little more toxic, with 37% reduction. Other products reducedinfectivity by between 50% and 100%. These are, from the least to the most toxic:flutriafol, prochloraz, epoxyconazole,iprodione, hexaconazole, triadimenol,azoxystrobine, cyproconazole, cyprodynil,flusilazole and tridemorph. Chlorothalonil,fenpropimorph, spiroxamine and tebuconazoletotally inhibited infectivity of the fungi. Analysis of the results according to chemicalclass showed that the benzimidazoles were theleast toxic for E. neoaphidis and themorpholines the most toxic. Effects oftriazoles and strobilurines were variable, withreduction ranging from 37% to 100% fortriazoles and from 17% to 68% forstrobilurines.     

Control of potato cyst-nematode, Globodera pallida, on tomatoes grown under glass, by applying steam or chemical nematicides to the soil

In a sandy loam under glass, potato cyst-nematode, Globodera pallida, was controlled in soil to 20 cm deep, and tomato yields were greatly increased by sheet steaming for 4 h, by 977 kg methyl bromide ha^-1 or by 448 kg Telone (1,3-dichloropropene mixture or Di-Trapex CP (20% methyl isothiocyanate: 15% chloropicrin:65% dichloropropene-dichloropropane mixture) ha^-1 followed by 441 kg dazomet or 11.2 kg oxamyl ha^-1. Sheet steaming, unlike the other treatments, had relatively little effect on the nematode in soil 20 to 40 cm deep. Until the apices of the plants were cut off production of fruit was curvilinear against time in all treated soil but linear against time in untreated soil.     

Fungal populations in podzolic soil experimentally acidified to simulate acid rain

The effect of experimental acidification on the soil microfungal community was studied in the humus layer of a coniferous forest in northern Sweden. The study was made 4 years after the last application of sulfuric acid. Fungal species composition was altered by treatments of 100 and 150 kg sulfuric acid ha^–1 each year for 6 years, yet no differences were found between the control treatment and an application of 50 kg ha^–1. The abundance ofPenicillium spinulosum andOidiodendron cf.echinulatum II increased with increasing rates of acid application, whereas only small changes were found for other isolated fungal taxa. Soil respiration rate and fluorescein diacetate (FDA)-active fungal biomass were significantly different from the control treatment at all 3 levels of acidification.     

Response to inoculation and N fertilization for increased yield and biological nitrogen fixation of common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is able to fix 20–60 kg N ha^–1 under tropical environments in Brazil, but these amounts are inadequate to meet the N requirement for economically attractive seed yields. When the plant is supplemented with N fertilizer, N₂ fixation by Rhizobium can be suppressed even at low rates of N. Using the ¹⁵N enriched method, two field experiments were conducted to compare the effect of foliar and soil applications of N-urea on N₂ fixation traits and seed yield. All treatments received a similar fertilization including 10 kg N ha^–1 at sowing. Increasing rates of N (10, 30 and 50 kg N ha^–1) were applied for both methods. Foliar application significantly enhanced nodulation, N₂ fixation (acetylene reduction activity) and yield at low N level (10 kg N ha^–1). Foliar nitrogen was less suppressive to nodulation, even at higher N levels, than soil N treatments. In the site where established Rhizobium was in low numbers, inoculation contributed substantially to increased N₂ fixation traits and yield. Both foliar and soil methods inhibited nodulation at high N rates and did not significantly increase bean yield, when comparing low (10 kg N ha^–1) and high (50 kg N ha^–1) rates applied after emergence. In both experiments, up to 30 kg N ha^–1 of biologically fixed N₂ were obtained when low rates of N were applied onto the leaves.     

Effect of soil-applied NPK fertilizers on severity of black spot disease (Alternaria brassicae) and yield of oilseed rape

Effect of soil application of eight combinations of NPK fertilizers on the severity of black spot disease (BSD), caused by Alternaria brassicae (Sacc.) Berk., and yield of short duration oilseed rape (Brassica campestris L) were investigated under both pot and field conditions in 1987–88, 1988–89 and 1990–91. The severity of BSD was significantly greater (36–48%) on plants grown in ground treated with NP (N 90 kg ha^–1+P 40 kg ha^–1) applied as urea and single superphosphate respectively than on plants from the unfertilized control (NoPoKo) (o). However, the severity of BSD was significantly smaller (25–33%) when K (40 kg ha^–1) was applied as muriate of potash than in plants from control and NP treatments. The effect of NK (N 90 kg ha^–1+K 40 kg ha^–1) in decreasing the severity of BSD was increasingly more pronounced than the effects of PK (P 40 kg ha^–1+K 40 kg ha^–1), NP and K (40 kg ha^–1) applications. The decrease in the severity of BSD due to K was due to increased production in plants of phenolics which inhibited conidial germination and decreased sporulation of A. brassicae.The decrease in the severity of BSD due to NK application gave consistently increased seed yield 68% more than those of control and other treatments. The K-fertilized plants also showed increased resistance to lodging, increased 1000-seed weight and decreased seed infection. Seeds obtained from K-fertilized plants showed good seed germinability and vigorous seeding growth.     

Chemical aids to drying seeds of beans (Phaseolus vulgaris) before harvest

The effects on seed moisture content of seven different chemical formulations applied to bean (Phaseolus vulgaris) crops in two successive years were observed. Those containing bipyridyl herbicides caused the biggest effects. In 1974, diquat (0–59 kg a.i. ha^-1), applied to a French bean crop cv. Processor 26 days before harvest, decreased seed moisture content by 98 mg g^_1 dry weight below a control value of 438 mg g^_1. In 1975, diquat applied at the same rate to a navy bean crop cv. Seafarer 16 days before harvest, decreased seed moisture content by 123 mg g^_1 below a control value of 364 mg g^_1. Diquat applied at a lower rate (0–3 kg a.i. ha^-J) caused a decrease of 79 mg g^_1 and paraquat decreased seed moisture by 147 mg g^_1. In both years smaller effects were observed for dimexan (15 kg a.i. ha^-1) which decreased seed moisture content by 32 mg g^-1 in 1974 and 72 mg g^_1 in 1975 and for ethephon (1-0 kg a.i. ha^-1) which caused decreases of 78 mg g^_1 in 1974 and 31 mg g^_1 in 1975. In 1975, metham-sodium (70 kg a.i. ha^-1) a soil sterilant, proved almost as effective as the bipyridyls, decreasing moisture content by 105 mg g^_1. Trimming the roots mechanically reduced seed moisture by 67 mg g^_1. Other chemical treatments, tried in 1975 only, were less effective and decreased seed moisture content by 31–60 mg g^_1. These were Wiltz-65 (pentanoic and hexanoic acids, 14-6 kg a.i. ha^-1), N252 (dihydro-dimethyl-dithiin tetroxide, 0–56 kg a.i. ha^-1) and an application of diquat (0–3 kg a.i. ha^-1) to plants treated 10 days before with ethephon (1-0 kg a.i. ha^-1)- In addition to the effects on seed moisture content, all treatments decreased seed yield. The largest decreases were caused by diquat and were attributable mainly to effects on mean seed weight. The paper concludes with an economic analysis which shows that at present prices chemical drying of beans in the field is not worthwhile because the yield loss nullifies any savings in drying costs.     

Effects of take-all (Gaeumannomyces graminis var. tritici) on crop N uptake and residual mineral N in soil at harvest of winter wheat

Background and aims

Take-all, caused by the fungus Gaeumannomyces graminis var. tritici, is the most damaging root disease of wheat. A severe attack often leads to premature ripening and death of the plant resulting in a reduction in grain yield and effects on grain quality (Gutteridge et al. in Pest Manag Sci 59:215–224, 2003). Premature death of the plant could also lead to inefficient use of applied nitrogen (Macdonald et al. in J Agric Sci 129(2):125–154, 1997). The aim of this study was to determine crop N uptake and the amount of residual mineral N in the soil after harvest where different severities of take-all had occurred.

Methods

Plant and soil samples were taken at anthesis and final harvest from areas showing good and poor growth (later confirmed to be caused by take-all disease) in three winter wheat crops grown on the same soil type on Rothamsted Farm in SE England in 1995, 2007 and 2008 (harvest sampling only). All crops received fertiliser N in spring at recomended rates (190–200?kg?N ha^?1). On each ocassion crops were assessed for severity of take-all infection (TAR) and crop N uptakes and soil nitrate plus ammonium (SMN) was determined. Grain yields were also measured.

Results

Grain yields (at 85% dry matter) of crops with moderate infection (good crops) ranged from 4.3 to 13.0?t ha^?1, compared with only 0.9–4.5?t ha^?1 for those with severe infection (poor crops). There were significant (P?<?0.05) negative relationships between crop N uptake and TAR at anthesis and final harvest. At harvest, good crops contained 129–245?kg?N ha^?1 in grain, straw and stubble, of which 85–200?kg?N ha^?1 was in the grain. In contrast, poor crops contained only 46–121?kg?N ha^?1, of which only 22–87?kg?N ha^?1 was in the grain. Positive relationships between SMN and TAR were found at anthesis and final harvest. The SMN in the 0–50?cm layer following harvest of poor crops was significantly (P?<?0.05) greater than that under good crops, and most (73–93%) was present as nitrate.

Conclusions

Localised patches of severe take-all infection decreased the efficiency with which hexaploid wheat plants recovered soil and fertiliser derived N, and increased the subsequent risk of nitrate leaching. The risk of gaseous N losses to the atmosphere from these areas may also have been enhanced.     

Effects of wheat foliar fungicides on the aphid endoparasitoid Aphidius rhopalosiphi DeStefani-Perez (Hym., Aphidiidae) on glass plates and on plants

Abstract: The side-effects of several fungicides used in wheat to control disease at heading growth stage were assessed on the aphid parasitoid Aphidius rhopalosiphi by tests conducted in the laboratory on glass plates and in the greenhouse on young wheat plants. Very few formulations containing only one active ingredient (carbendazim, cyproconazole or epoxyconazole) or combinations of two (carbendazim + cyproconazole, carbendazim + hexaconazole) were harmless to A. rhopalosiphi in the glass-plate tests. There was no apparent synergism between fungicides tested in combinations. The parasitoid mortalities in tests carried out on plants were less and chlorothalonil, epoxyconazole, fenpropidin, fenpropimorph, flusilazole, flutriafol, prochloraz, tebuconazole, tridemorph and a number of combinations (carbendazim + flutriafol, chlorothalonil + cyproconazole, epoxyconazole + tridemorph, chlorothalonil + hexaconazole, chlorothalonil + flutriafol, cyproconazole + prochloraz, epoxyconazole + fenpropimorph, fenpropimorph + propiconazole, propiconazole + tridemorph, triadimenol + tridemorph) were harmless or only slightly harmful to the aphid parasitoid. Several combinations (carbendazim + epoxyconazole, carbendazim + fenpropimorph, carbendazim + flusilazole, carbendazim + tebuconazole, chlorothalonil + fenpropimorph, chlorothalonil + flusilazole, fenpropimorph + fenpropidin, fenpropimorph + prochloraz, fenpropidin + propiconazole, fenpropidin + tebuco nazole, tebuconazole + triadimenol) were toxic for wasps on plants. The parasitoid mortalities were less on plants than on glass plates but the wasps spent less time on treated leaves and in some cases parasitism of aphids was reduced to a large extent. These results suggest that in addition to study of the direct effects of pesticides on beneficial insects (mortalities, reduction of fertility) their effects on the behaviour of the insects should also be studied. Products that induced a repellent effect need further testing in field or semi-field conditions. However, many fungicide combinations that have little or no effect on A. rhopalosiphi can protect wheat against a wide range of diseases and the results obtained in this study indicate that an appropriate and effective protection of wheat at earing growth stage can be achieved with products that have no effects on aphid parasitoids.     

Effect of phosphorus source and rate of application on VAM fungal infection and growth of maize (Zea mays L.)

The effects of two phosphorus (P) sources (triple superphosphate and Ghafsa phosphate rock), applied at rates equivalent to 44kg ha^-1 and 22 kg ha^-1, on vesicular-arbuscular mycorrhizal (VAM) fungal infection in roots, dry matter yield and nutrient content of maize grown in an oxisol and an alfisol, were investigated in a growth cabinet. The application of 44 kg P ha ^-1 resulted in root infection by VAM fungi not was significantly different (P<-0.01) from when no P was applied. Root infection was significantly greater when P was applied as triple superphosphate at the rate of 22 kg ha^-1 the higher rate. Phosphate rock treatments at both rates of application resulted in significantly greater root infection than in controls with no P or when triple superphosphate was applied at 44 kg ha^-1. Plant P uptake increased in all soils with the different P treatments compared with the control. No direct effects of the treatments on the aluminium and zinc contents of maize plants were observed. In the gleyic alfisol, reduced Mn uptake as a result of increased infection of plants with the superphosphate treatments was observed. Higher Mn was also found in plants with the higher rate of superphosphate treatment than with the phosphate rock treatments in the haplustox, although infection rates in plants with the latter treatments were higher. With the exception of plants with the phosphate rock treatment applied at 22kg ha^-1, dry matter yields of plants with all P sources were significantly greater than the controls.     

Nitrogen transfer from arrowleaf clover to ryegrass in field plantings

Arrowleaf clover (Trifolium vesiculosum Savi) and annual ryegrass Lolium multiflorum Lam.) commonly are overseeded in dormant bermudagrass (Cynodon dactylon L. Pers.) sod on coastal plain soils in the southeastern United States. Two field experiments were conducted in consecutive years at different sites to estimate the amount of N transferred from the clover to the annual grass. Nitrogen treatments included 50 kg N ha^-1 as ¹⁵N depleted ammonium nitrate applied in either February or April, and a check (no N applied). Three clippings were made during the cool-season from March to June. In both experiments, less than 5 kg N ha^-1 were transferred from the clover to the grass. Ryegrass yields of dry matter and total N were not increased by growing with clover. Clover growth was typical for the region; average dry matter yield in pure stand was 2,615 kg ha^-1 over the two-year period. Clover in mixed stand fixed between 20 and 60 kg N/ha. Less than 13% of N contained in ryegrass was transferred from arrowleaf clover to ryegrass at any clipping while clover was actively growing. The quantity of N transferred over the entire season was not statistically significant.     

Pre-flowering and post-flowering insecticide applications to control Aphis fabae on field beans: their biological and economic effectiveness

Most spring-sown field beans are treated with insecticides to control Aphis fabae, but there is usually a risk of toxicity to pollinating honeybees if insecticides are applied during flowering. An experiment was repeated at Rothamsted for 6 consecutive years, comparing treatments before and after flowering. It is concluded that (1) pre-flowering treatments (demeton-S-methyl spray at 0–25 kg a.i. ha^-1 or phorate granules at 1–12 kg a.i. ha^-1) were more effective and profitable than post-flowering treatments, (2) application of phorate granules before flowering gave the greatest economic return, and minimised the danger to foraging bees and (3) aphid populations varied considerably from year to year, as did the relationship between aphid infestation and yield, but our evidence supports the suggestion that insecticide spray treatments are profitable if 5% or more of the plant stems are infested at the end of primary aphid migration.     

Control of beet cyst-nematode, Heterodera schachtii, by aldicarb applied to the soil by a vertical band-reciprocating harrow technique or by rotary cultivation

As little as 0.8 kg aldicarb ha^-1 applied to bands of soil 15 cm wide × 15 cm deep, in which sugar beet seeds were sown, increased beet yields as much as did 2.6 or 5.0 kg ha^-1 rotary cultivated into the top 15 cm of soil lightly or moderately infested with beet cyst-nematode, Heterodera schachtii. In a very heavily infested soil, 1.7 kg ha^-1 applied to the bands of soil increased beet yields as much as 2.6 kg ha^-1 rotavated into the top 15 cm of the soil; yields were further increased by 5.0 and 9.9 kg ha^-1 rotavated in but not by 3.5 kg ha^-1 in the bands of soil. Soil populations of the nematode increased little or not at all whether the soil was treated with aldicarb or not. The band treatment was achieved by a vertical band- reciprocating harrow technique, which is described. The advantages of this new technique for the control of beet cyst-nematode and other soil pests of widely spaced row crops are safer application of less pesticide, thereby minimising cost of treatment and any risk to the environment, faster seedbed preparation and adequate control of pest population increase on the susceptible crop, especially if coupled with biological control.     

Are the benefits of yield responses to nitrogen fertilizer application in the bioenergy crop Miscanthus × giganteus offset by increased soil emissions of nitrous oxide?

A field trial was carried out on a 15 year old Miscanthus stand, subject to nitrogen fertilizer treatments of 0, 63 and 125 kg‐N ha^?1, measuring N₂O emissions, as well as annual crop yield over a full year. N₂O emission intensity (N₂O emissions calculated as a function of above‐ground biomass) was significantly affected by fertilizer application, with values of 52.2 and 59.4 g N₂O‐N t^?1 observed at 63 and 125 kg‐N ha^?1, respectively, compared to 31.3 g N₂O‐N t^?1 in the zero fertilizer control. A life cycle analyses approach was applied to calculate the increase in yield required to offset N₂O emissions from Miscanthus through fossil fuel substitution in the fuel chain. For the conditions observed during the field trial yield increases of 0.33 and 0.39 t ha^?1 were found to be required to offset N₂O emissions from the 63 kg‐N ha^?1 treatment, when replacing peat and coal, respectively, while increases of 0.71 and 0.83 t ha^?1 were required for the 125 kg‐N ha^?1 treatment, for each fuel. These values are considerably less than the mean above‐ground biomass yield increases observed here of 1.57 and 2.79 t ha^?1 at fertilization rates 63 and 125 kg‐N ha^?1 respectively. Extending this analysis to include a range of fertilizer application rates and N₂O emission factors found increases in yield necessary to offset soil N₂O emissions ranging from 0.26 to 2.54 t ha^?1. These relatively low yield increase requirements indicate that where nitrogen fertilizer application improves yield, the benefits of such a response will not be offset by soil N₂O emissions.     

<Emphasis Type="Italic">Sesbania exaltata</Emphasis> biocontrol with <Emphasis Type="Italic">Colletotrichum truncatum</Emphasis> microsclerotia formulated in ‘Pesta’ granules

The weed Sesbania exaltata (Raf.) Rydb. ex A.W. Hill (hemp sesbania) was effectively controlled in soybean [Glycine max (L.) Merr.] field test plots over a 2-year testing period (1995–1996) with microsclerotia of the bioherbicidal fungus, Colletotrichum truncatum, formulated in wheat gluten-kaolin granules called ‘Pesta’. Weed control averaged 84% and 88%, respectively, in plots treated pre-plant incorporated (PPI) at ‘Pesta’ rates of 168 or 336 kg ha⁻¹, and 71% and 78%, respectively, in plots treated pre-emergence (PE) at ‘Pesta’ rates of 168 or 336 kg ha⁻¹ over the testing period. Post-emergence (POE) control averaged 30% and 50%, respectively, for the 168 and 336 kg ha⁻¹ treatments, and was significantly less effective than either PE or PPI treatments. Although pathogenesis and mortality occurred in hemp sesbania tissues, satisfactory weed control was not achieved in plots treated at rates of 17 or 84 kg ha⁻¹ with any of the application methods. Soybean yields were significantly greater in test plots treated PPI or PE, as compared to yields from test plots treated either POE, with inert ‘Pesta’ granules, or from untreated controls. Microsclerotia formulated in ‘Pesta’ granules exhibited excellent shelf-life, retaining high viability after storage for 10 years at 4 °C. These results suggest that microsclerotia of C. truncatum formulated in ‘Pesta’ granules offers an effective method for controlling this important weed and preserving the activity of this bioherbicide.     

Growing vetches (Vicia villosa Roth) in irrigated cotton systems: inputs of fixed N, N fertiliser savings and cotton productivity

We compared symbiotic N₂ fixation by winter forage legumes (clovers, medics and vetches) using the ¹⁵N natural abundance technique in three experiments. Vetches (Vicia spp.) were the most productive legumes, and woollypod vetch fixed (shoot+root) up to 265 kg N ha^–1 (mean 227 kg N ha^–1) during a 4–5 months period over winter and early spring. Balansa and Berseem clovers, and Gama medic were highly productive in the first experiment, but fixed significantly less N than woollypod vetch in the second experiment. A 6-year study (1997–2003) compared cotton (Gossypium hirsutum L.) systems with and without vetch, or with faba beans (Vicia faba L.) to assess the effects of these crops on cotton production. Woollypod vetch was grown either between annual cotton crops, or between wheat (Triticum aestivumL.) and cotton crops. Vetch added 230 kg N ha^–1 (174 kg fixed N ha^–1) to the soil when incorporated as a green manure. Faba bean shoot residues and nodulated roots contributed 108 kg fixed N ha^–1 to the soil, following the removal of 80 kg N ha^–1 in the harvested seed (meaned over three crops). Lablab (Lablab purpureus L. – summer-growing and irrigated) added 277 kg N ha^–1 (244 kg fixed N ha^–1) before incorporation as a green manure in the first year of the experiment. The economic optimum N fertiliser rate for each cropping system was determined every second year when all systems were sown to cotton. Cotton following cotton required 105 kg fertiliser N ha^–1, but only 40 kg N ha^–1 when vetch was grown between each cotton crop. Cotton following wheat required 83 kg fertiliser N ha^–1 but no N fertiliser was needed when vetch was grown after wheat (the highest yielding system). Cotton following faba beans also required no N fertiliser. The vetch-based systems became more N fertile over the course of the experiment and produced greater lint yields than the comparative non-legume systems, and required less N fertiliser. While no cash flow was derived from growing vetch, economic benefits accrued from enhanced cotton yields, reduced N fertiliser requirements and improved soil fertility. These findings help explain the rotational benefits of vetches observed in other regions of the world.     

Effects of herbicide chlorsulfuron on growth and nutrient uptake parameters of wheat genotypes differing in Zn-efficiency

Prunings of Calliandra calothyrsus, Grevillea robusta, Leucaena diversifolia and farm yard manure were applied each cropping season at 3 and 6 t dry matter ha⁻¹ to an Oxisol in Burundi. The field plots also received basal applications of nitrogen (N), phosphorus (P) and potassium (K). Application of the tree prunings or farm yard manure decreased the concentration of monomeric inorganic aluminium (Al) in soil solution from 2.92 mg Al dm⁻³ in the control plots to 0.75 mg Al dm⁻³ in the plots receiving 6 t ha⁻¹ Calliandra prunings. The other organic materials also decreased the concentration of monomeric inorganic aluminium in the soil solution. The lowered Al concentration led to a corresponding decrease in the percentage Al saturation of the 0–10 cm soil layer from 80% to 68%. Grain yields of maize and beans were strongly inversely related to the percentage Al saturation of the soil. This confirms that soil acidity was the main constraint to maize and beans production. The yield improvement was mainly attributed to the ameliorating effects of the organic matter application on Al toxicity. The nutrient content had less effect presumably because of fertilizer use. In the best treatments, the yield of maize increased from 0.9 to 2.2 t ha⁻¹ and the corresponding beans yield increased from 0.2 to 1.2 t ha⁻¹. A C Borstlap Section editor     

Association of some plant defense enzyme activities with systemic resistance to early leaf blight and leaf spot induced in tomato plants by azoxystrobin and Pseudomonas fluorescens

Abstract

Azoxystrobin at three different concentrations, namely, 31.25, 62.50 and 125 g a.i. ha^?1 mancozeb (1 kg ha^?1) and Pseudomonas fluorescens (10 kg ha^?1) were evaluated for their efficacy in inducing defense enzymes in tomato against Alternaria solani and Septoria lycopersici. The activity of defense enzymes peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), β-1, 3 glucanase, chitinase, catalase and defense-inducing chemicals (total phenols) was found to be increased in azoxystrobin and P. fluorescens-treated tomato plants. The activity of these defense enzymes and chemicals was higher in azoxystrobin (125 g a.i. ha^?1) and P. fluorescens-treated tomato plants challenge inoculated with the pathogens compared to other treatments. Increased expression of specific isoforms of PO and PPO was also observed due to ISR induction.