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Background and aims: Green manuring can suppress crop diseases and change soil microbial communities, but the functional significances of changes in soil microbial communities are unclear. Methods: Effects of Indian mustard (Brassica juncea), wild rocket (Diplotaxis tenuifolia) and wheat (Triticum aestivum) green manures on cucumber (Cucumis sativus L.) Fusarium wilt disease caused by Fusarium oxysporum f.sp. cucumerinum (FOC) were evaluated. Cucumber rhizosphere microbial communities were analyzed by real-time PCR and high-throughput amplicon sequencing. Furthermore, feedback effects of rhizosphere biota on cucumber resistance to FOC were assessed. Results: All green manures promoted cucumber growth and changed rhizosphere bacterial community composition. Indian mustard and wild rocket green manures decreased Fusarium wilt disease severity and rhizosphere FOC abundance, increased bacterial diversity and abundance of potential plant-beneficial microorganisms. Rhizosphere biota from cucumber cultivated with Indian mustard and wild rocket (but not with wheat) green manures suppressed Fusarium wilt disease and enhanced expression of defense-related genes in cucumber seedling roots. Pseudomonas spp. strains isolated from cucumber rhizosphere cultivated with Indian mustard and wild rocket green manures suppressed cucumber Fusarium wilt disease. Conclusions: Changes in cucumber rhizosphere microbial communities induced by Indian mustard and wild rocket suppressed Fusarium wilt disease by priming for defense in plants. [ABSTRACT FROM AUTHOR]

Aims: The objective was to estimate the fixation of atmospheric nitrogen (Ndfa) by legume (Gliricidia sepium) trees for the benefit of cocoa (Theobroma cacao) trees in agroforestry systems.Methods: Four sites where cocoa and gliricidia were intercropped and one site where gliricidia, cocoa, and orange trees were grown as separate stands were selected in Ghana. Ndfa in gliricidia and cocoa leaves (from all sites) and in shoot axes (in one site only) was assessed by the 15N natural abundance technique. Cocoa trees distant (> 10 m) from the closest gliricidia were used as reference plants.Results: With few exceptions, leaves of gliricidia and cocoa trees growing in proximity had similar δ15N, whereas the foliar δ15N value of gliricidia was lower than that of distant cocoa trees. The Ndfa in gliricidia leaves ranged from 22 to 50% of total leaf N and was 48% in the shoot axis. Root nodules, found only after the wet season, always showed the inner red color indicating effective N2 fixation and the occurrence of Rhizobium tropici and Rhizobium etli. The annually produced shoots of gliricidia, theoretically suitable to become green manure after pruning, contained 31.4 to 38.0 kg N ha−1 derived from the atmosphere.Conclusions: Gliricidia sepium trees are able to take advantage of the association with rhizobial symbionts to fulfill, at least in part, the N needs of their rapidly growing shoots. In mixed-stand agroforestry systems, with intercropped gliricidia and cocoa trees, the amount of N derived from the atmosphere that could enter the soil if the pruned shoots of gliricidia trees are used as green manure could diminish the need for N fertilizers for cocoa trees. [ABSTRACT FROM AUTHOR]

Aims: We investigated the effect of the co-composting of Arachis pintoi (AP) as green manure with different sources of rock phosphate on maize growth and soil properties.Methods: Composts were prepared combining AP and different rock phosphates (simple superphosphate, apatite rock phosphate, reactive rock phosphate and thermophosphate), alone or in combination with AP. The incorporation of AP and natural phosphate was conducted in a greenhouse, and we investigated its effects on plant total dry matter, phosphorus absorption, microbial biomass carbon and phosphorus, total organic carbon, soil basal respiration, enzymatic activities (acid phosphatase, alkaline phosphatase and urease) and the soil microbial structure community.Results: The application of natural thermophosphate phosphates with AP is an efficient management strategy for maize cultivation, with increases of more than 124% in maize dry matter, more than 300% in P uptake and 62% in soil microbial biomass carbon.Conclusions: The use of Arachis pintoi as green manure, combined with natural phosphate sources, represents an alternative fertilisation approach for maize cultivated on Entisols, enhancing the bioavailability of P from natural rock phosphate. It is a sustainable and financially attractive option to ensure the environmental integrity of cultivation, food and soil security. [ABSTRACT FROM AUTHOR]

Aims: To identify the rhizobia nodulating Astragalus sinicus in the acid soils at Xinyang, China and to estimate the effects of fertilization strategies on the rhizobial community.Methods: Soil samples were collected from treatments submitted to different fertilization strategies (chemical fertilizers, A. sinicus green manure, various input levels). Nodules obtained from the A. sinicus trapping plants grown in the soil samples were used for rhizobial isolation. The isolates were grouped into PCR-RFLP genotypes based on analyses of 16S rRNA gene and IGS, and representatives for each genotype were further subjected to phylogenetic analyses of housekeeping genes (16S rRNA gene, atpD, glnII, and rpoB), as well as symbiotic genes (nodC and nifH). Soil physicochemical characteristics were also estimated and redundancy analysis was performed to examine the relations between soil features and distribution of rhizobial genotypes across different fertilization treatments.Results: A total of 257 rhizobial isolates were obtained and discriminated into 12 IGS types in a single 16S rRNA type by RFLP analyses. Further 16S rRNA gene sequence-based phylogeny and multilocus sequence analysis (MLSA) distinguished a minor group (10 strains, 4 IGS types) affiliated to Mesorhizobium huakuii and a main group (247 strains, 8 IGS types) to Mesorhizobium jarvisii, for which a novel symbiovar, sv. astragali, was described. The long-term input of A. sinicus green manure increased rhizobial diversity and modified rhizobial community structures, via the increase of organic matter and decrease of soil pH, available phosphate, available potassium, and total salt.Conclusions: M. jarvisii sv. nov. astragali was the predominant microsymbiont of A. sinicus in the tested acidic soils. The long-term input of green manure modified the soil features, enhancing the genetic diversity of rhizobia associated with A. sinicus and alternating the rhizobial community structure. [ABSTRACT FROM AUTHOR]

Background and aims: Crucifers grown as cover crops are known to reduce sulphate leaching (S catch-crop service) and release large amounts of mineral sulphate for the subsequent cash crop once incorporated into the soil (S green-manure service). Crucifer-legume cover crop mixtures are effective to obtain high nitrogen related services, but few data exist on their performances for S-related services. Our study aimed to assess performances of a wide variety of bispecific crucifer-legume mixtures designed to provide soil S catch-crop and S green-manure services.Methods: A two-year field experiment was conducted at two sites near Toulouse, France (silt clay loam soil) and Orléans, France (sandy loam soil) in which cultivars from eight crucifer species and nine legume species were tested as sole and bispecific cover crops.Results: Crucifer-legume mixtures and crucifer sole cover crops provided the same level of S catch-crop service (12 kg S ha−1), significantly higher than that of legume sole cover crops (4 kg S ha−1). Similarly, crucifer-legume mixtures provided almost the same level of S green-manure service (5.5 kg S ha−1) as crucifer sole cover crops (6.5 kg S ha−1).Conclusion: Our results demonstrate the compatibility and complementarity of certain crucifer and legume species when grown together to provide S and N catch-crop and green-manure services. For a same cover crop species no strong cultivar effect has been highlighted in our growing conditions. [ABSTRACT FROM AUTHOR]

Background and aims: We investigated whether the incorporation of intercropped white clover as a split-dose fertiliser improves N retention of the plant-soil system in leek production.Methods: White clover and leek were grown in pots where clover was stepwise incorporated into soil as fertiliser. Half of the clover was incorporated before leek transplantation (LT), the other half was incorporated 26 (S1) or 41 (S2) days after LT, compared with full incorporation of all clover (F) before LT. 15N injection and leaching studies were performed to investigate interspecific competition and the effects of precipitation on soil N availability.Results: Stepwise incorporations increased or had no effect on leek growth, despite competition for N between white clover and leek. Compared to F, leek grown with stepwise incorporations had similar and lower N accumulation before the second incorporation, but N was higher at the end of the experiment. N2 fixation by white clover increased the total N input into soil and matched N availability with leek N demand and growth rate. Loss of inorganic N by leaching was lowest in S2 and highest in F.Conclusions: Stepwise incorporations of white clover improved N retention in the plant-soil system and could be used to increase leek yield. [ABSTRACT FROM AUTHOR]

Harvesting alfalfa damages crowns and increases the opportunity for entry of pathogens. Incorporation of green manures into soil increases population density of streptomycetes with broad pathogen antagonist activity. This study aimed to measure the impact of wheel traffic on forage yield and plant health and the effect of green manures to reduce disease. Buckwheat and sorghum-sundangrass were incorporated into soil 3 weeks before seeding alfalfa. Total bacteria, streptomycete, and pathogen antagonist densities were measured prior to planting green manures and alfalfa. Wheel traffic was applied 2 days after each forage harvest. Wheel traffic reduced forage yield 12 % to 17 % depending on year and location, significantly reduced plant counts, and increased crown rot compared to the no traffic control. Cultivar had a significant effect on yield, plant counts, and crown rot. Streptomycete density and pathogen antagonists increased when fall-sown green manure crops were incorporated in spring. Forage yields were significantly higher in plots with greater antagonist density when traffic was applied. Green manure treatments did not affect plant counts or crown rot. Mechanical wheel traffic reduces forage yield and increases disease. Green manure crops may provide benefits in alfalfa production systems by increasing pathogen antagonists. [ABSTRACT FROM AUTHOR]

Background and aims: Winter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation. Methods: Two cover crops (Chinese milk vetch, Astragalus sinicus L., hereafter vetch, and rye, Secale cerealis) having different carbon/nitrogen (C/N) ratios were cultivated during the rice fallow season. The fresh above-ground biomasses of vetch [25 Mg fresh weight (FW) ha, moisture content (MC) 86.9 %, C/N ratio 14.8] and rye (29 Mg rye FW ha, MC 78.0 %, C/N ratio 64.3) were incorporated as green manure 1 week before rice transplanting (NPK + vetch, and NPK + rye). The NPK treatment was installed for comparison as the control. During the rice cultivation, methane (CH) and nitrous oxide (NO) gases were collected simultaneously once a week using the closed-chamber method, and carbon dioxide (CO) flux was estimated using the soil C balance analysis. Total GWP impact was calculated as CO equivalents by multiplying the seasonal CH, CO, and NO fluxes by 25, 1, and 298, respectively. Results: Methane mainly covered 79-81 % of the total GWP, followed by CO (14-17 %), but the NO contribution was very small (2-5 %) regardless of the treatment. Seasonal CH fluxes significantly increased to 61 and 122 % by vetch and rye additions, respectively, compared to that of the NPK treatment. Similarly, the estimated seasonal CO fluxes increased at about 197 and 266 % in the vetch and rye treatments, respectively, compared with the NPK control plots. Based on these results, the total GWP increased to 163 and 221 % with vetch and rye applications, respectively, over the control treatment. Rice productivity was significantly increased with the application of green manure due to nutrient supply; however, vetch was more effective. Total GWP per grain yield was similar with the vetch (low C/N ratio) and NPK treatments, but significantly increased with the rye (high C/N ratio) application, mainly due to its higher CH emission characteristic and lower rice productivity increase. Conclusions: A low C/N ratio cover crop, such as vetch, may be a more desirable green manure to reduce total GWP per grain yield and to improve rice productivity. [ABSTRACT FROM AUTHOR]

The integration of multipurpose legumes into low-input tropical agricultural systems is needed because they are a nitrogen (N) input through symbiotic fixation. The drought-tolerant cover legume canavalia ( Canavalia brasiliensis) has been introduced for use either as forage or as a green manure into the crop-livestock system of the Nicaraguan hillsides. To evaluate its impact on the subsequent maize crop, an in-depth study on N dynamics in the soil-plant system was conducted. Microplots were installed in a 6-year old field experiment with maize-canavalia rotation. Direct and indirect N-labelling techniques were used to determine N uptake by maize from canavalia residues and canavalia-fed cows' manure compared to mineral fertilizer. Litter bags were used to determine the N release from canavalia residues. The incorporation of N from the amendment into different soil N pools (total N, mineral N, microbial biomass) was followed during the maize cropping season. Maize took up an average of 13.3 g N m, within which 1.0 g N m was from canavalia residues and 2.6 g N m was from mineral fertilizer, corresponding to an amendment N recovery of 12% and 32%, respectively. Recoveries in maize would probably be higher at a site with lower soil available N content. Most of the amendment N remained in the soil. Mineral N and microbial N were composed mainly of N derived from the soil. Combined total N recovery in maize and soil at harvest was highest for the canavalia residue treatment with 98% recovery, followed by the mineral fertilizer treatment with 83% recovery. Despite similar initial enrichment of soil microbial and mineral N pools, the indirect labelling technique failed to assess the N fertilizer value of mineral and organic amendments due to a high N mineralization from the soil organic matter. [ABSTRACT FROM AUTHOR]

Greater productivity under intercropping has been attributed to the complementary use of environmental resources. However, the rooting pattern of component species under intercropping, which is an important morphological feature considering the complementary uptake of nutrients, has been studied only rarely under field conditions because of inherent technical difficulties. We examined rooting patterns of three green manure species, both sole cropped and intercropped, using a newly developed multi-color staining technique. Species were chosen from different functional groups: sorghum ( Sorghum bicolor (L.) Moench.), a C4 grass; crotalaria ( Crotalaria juncea L.), a legume; and sunflower ( Helianthus annuus L.), a C3 dicot. We also investigated these species’ aboveground biomass and N uptake. Sorghum distributed roots deeper under intercropping than under sole cropping; it was the most important contributor to increased biomass under intercropping. Crotalaria had a deep rooting system under both sole cropping and intercropping. Sunflower, with a shallow rooting system, was suppressed extremely under intercropping, possibly because of water deficiency in late in the season. The rooting patterns of green manure species examined using multi-color staining were related closely to the aboveground performance of these species under intercropping. [ABSTRACT FROM AUTHOR]

Soil-incorporated plant materials have been associated with reduction in soilborne pathogens and diseases. Mechanisms of the biocidal actions are complex and not well understood. A glasshouse experiment, a non replicated field demonstration, and a field experiment were conducted to determine volatile compounds after incorporation of various plant species and their effect on pest control. Cabbage ( Brassica oleracea), canola ( Brassica rapa), kale ( Brassica oleracea var. acephala), lettuce ( Lactuca sativa var. valmaine), two mustard varieties -Caliente ( Brassica juncea) and Green wave ( Brassica juncea), two radish varieties - Oil seed ( Raphanus sativus var. oleiformis) and Cherriette ( Raphanus sativus), common rye ( Secale cereale), and sorghum Sudan grass ( Sorghum bicolor var. sudanese) were used in the glasshouse experiment. Caliente 199 mustard ( Brassica hirta) was planted in the field demonstration and white mustard ( Sinapis alba) was used in the field experiment. Fresh plant materials were chopped manually in the glasshouse experiment and mechanically in the field studies at the flowering stage before incorporation in natural field soils. In the glasshouse experiment, the equivalent biomass dry weight ranged from a minimum of 573 g m−2 for L. sativa var. valmaine to a maximum of 1851 g m−2 for S. bicolor var. sudanese. The average biomass was 792 g m−2 for B. hirta and 804 g m−2 for S. alba in the two field studies, respectively. The glasshouse experiment used a loamy sand field soil inoculated with a natural fine sandy loam soil that was known to contain high populations of Verticillium dahliae. Soils at both field sites belonged to the sandy loam series, and efforts were made to maintain sufficient soil moisture for plant growth. Although the interest was to determine all volatile compounds in general, only methyl sulfide and dimethyl disulfide were identified and subsequently quantified. Depending on plant species and time of sampling (one to seven days after soil incorporation), 2.7 to 346.4 μg g −1 plant dry weight for methyl sulfide and 0 to 283.2 μg g −1 plant dry weight for dimethyl disulfide were found in the glasshouse experiment. In general, high concentrations of dimethyl disulfide and methyl sulfide appeared to have reduced V. dahliae colony counts in bioassay potato stem saps in the glasshouse experiment. However, the correlation was weak ( R 2 = 0.31), but a relatively stronger correlation was obtained ( R 2 = 0.58) when excluding B. oleracea and B. rapa from the regression. Dimethyl disulfide and methyl sulfide were nearly non-detectable in the field demonstration, consequently no disease assessment was made. In the field experiment, a production of 5.2 μg g −1 plant dry weight for methyl sulfide and 1.2 μg g −1 dry weight for dimethyl disulfide was found two days after soil incorporation of S. alba. Compared to the untreated control, total Fusarium oxysporum counts in field soil were significantly lower 39 days after S. alba incorporation. However, no significant impact was found on total Pythium counts. Soil population of citrus nematode ( Tylenchulus semipenetrans) in the S. alba plots was significantly reduced to similar levels found in the untreated control 112 days after S. alba incorporation. Compared to the untreated control, soil density of non plant parasitic freeliving nematodes was higher 39 days after S. alba incorporation. The study demonstrated quantifiable production of methyl sulfide and dimethyl disulfide gases from a variety of plant species in glasshouse and natural field environments. Some beneficial effects against V. dahliae, F. oxysporum, and T. semipenetrans were observed. Additional studies are needed to further elucidate these complex chemical and biological interactions. [ABSTRACT FROM AUTHOR]

In low input (e.g. organic) farming systems where soil phosphorus (P) fertilisers such as superphosphate are not used, maintaining sufficient available soil P for plant growth can be a major challenge. The use of P accumulating cover crops may increase P availability for subsequent crops. We hypothesised that P release from organic residues of legumes (faba bean ( Vicia faba) and field peas ( Pisum sativum)) could supply adequate P to meet the needs of a subsequent crop in a low P soil. A pot experiment was conducted to determine the contribution of P by legume green manure to subsequent corn using 33P labelled legume residues and 32P labelled inorganic fertiliser (KH2PO4). The treatments included two rates of P application, (a) 10 kg P ha−1 as legume root and shoot residues or as inorganic fertiliser with and without a C source, and (b) 38 kg P ha−1as a combination of legume shoot and root residues or a combination of root and inorganic fertiliser and inorganic fertiliser alone. An absolute control (zero P) was also used. Shoot dry matter, P uptake and P source (residues or fertilisers) of total P in corn were measured at harvest. Faba bean and field pea residues alone or in combination with fertilisers contributed up to 10% and 5% of the total P uptake by corn respectively, compared with up to 54% by inorganic fertilisers. Incorporation of field pea and faba bean residues with P concentrations higher than those observed under field conditions, may not always lead to adequate net P release to supply the early growth phase of subsequent crops. [ABSTRACT FROM AUTHOR]

The Brassicaceae species Diplotaxis tenuifolia and Brassica nigra contain high concentrations of glucosinolates, the precursors of isothiocyanates (ITCs) that can have biofumigation effects in amended soils. In a laboratory experiment, incorporation of these plants as green manures into soil was expected to suppress Rhizoctonia solani AG2-1 (ZG5), the causal agent of damping-off in canola ( Brassica napus). The manures were incorporated at 1 (1% w/w) or 5 (5% w/w) g fresh material per 100 g dry soil and incubated for 6 months at 10, 20, or 30°C and at soil water contents of 10%, 40%, or 70% of water holding capacity. R. solani survived for up to 6 months as a saprophyte in un-amended soil at all soil water contents and at 10 and 20°C. A temperature of 30°C suppressed R. solani below the level of detection in all treatments after one week. At 1% concentration, the green manures increased the colonisation of the soil by R. solani, which caused severe damping-off of canola subsequently sown in this soil treatment. Soil amendments at 1% temporarily increased soil microbial activity. The addition of B. nigra or D. tenuifolia green manure at 5% concentration suppressed the saprophytic growth of R. solani incubated at 10 or 20°C over all soil water contents and significantly increased the microbial activity at all soil temperatures and water contents. Canola sown into these pots did not succumb to damping-off. The efficiency of hydrolysis of glucosinolates in the 5% treatment in the first week of incubation ranged from 1.6% for 2-propenyl ITC, extracted from soil containing tissues of B. nigra, to 3.4% for 3-butenyl ITC extracted from soil containing tissues of D. tenuifolia. 2-propenyl ITC could not be detected after 7 d of incubation. In the longer term (weeks to months), the increase of microbial activity, caused by adding green manures at 5%, or volatiles from the green manures, most likely played a dominant role in suppressing R. solani. The impact of ITCs, if any, appears to be short-term (days). [ABSTRACT FROM AUTHOR]

Mesorhizobium huakuii is a free-living bacterium which is capable of establishing a specific symbiotic relationship with Astragalus sinicus, an important winter green manure widely used in Eastern Asia, allowing for nitrogen fixing during this process. Previous studies demonstrate that M.␣huakuii produces quorum-sensing molecules at high cell density and quorum sensing plays a role in biofilm formations. In this study, we isolated and characterized two quorum-sensing deficient mutants in M. huakuii. Analysis of the flanking region of transposon insertions indicated that autoinducer synthase related genes are not homologous to acyl homoserine lactone (AHL) synthase genes that are shared among many Gram-negative bacteria, but related to peptide synthesis, indicating that M. huakuii quorum-sensing signals are distinct from AHLs. Compared with the wild-type strains, these quorum-sensing deficient mutants promoted their growth rate and were defective in nodule formation on host plants, indicative of a critical role of quorum sensing in M.␣huakuii during the host–bacterium symbiotic interaction. [ABSTRACT FROM AUTHOR]

Lack of synchronization between N released from prunings applied to the soil as green manures and crop uptake as well as optimization of protein digestibility for ruminants, remain major research objectives for the selection of multipurpose tree and shrub legumes (MPT) for mixed smallholder systems in the tropics. Prunings of the high tannin, low quality MPT Calliandra houstoniana CIAT 20400 (Calliandra) and the tannin free, high quality MPT Indigofera zollingeriana (Indigofera) were mixed in the proportions 100:0, 75:25, 50:50, 25:75, and 0:100 (w/w) in order to measure the aerobic rate and extent of N release in a leaching tube experiment, and the anaerobic extent of N degradation in an in vitro gas production experiment. Parameters measured in Calliandra:Indigofera mixtures were compared to theoretical values derived from single species plant material (i.e. 100:0 and 0:100). Aerobic N release and apparent anaerobic N degradation increased with increasing proportion of the high quality legume (Indigofera) in the mixture. While N release in the soil was lower than theoretical values in the mixture 50% Calliandra/50% Indigofera, this was not the case with apparent anaerobic N degradation with the same mixture. Aerobic N immobilization was more pronounced for the mixture 75% Calliandra/25% Indigofera than for 100% Calliandra and negative interaction was observed with apparent anaerobic N degradation in the mixture 75% Calliandra/25% Indigofera. Plant quality parameters that best correlated with aerobic N release and apparent anaerobic N degradation in the rumen were lignin + bound condensed tannins ( r=−0.95 and −0.95 respectively, P<0.001). In addition, a positive correlation ( r=0.89, P<0.001) was found between aerobic N release in the leaching tube experiment and apparent N degradation in the in vitro anaerobic gas production experiment. Results show that mixing prunings of MPT materials with contrasting quality is an effective way to modify aerobic N release pattern as well as apparent anaerobic N degradation and could possibly be applied to minimize N losses in the rumen and in the soil. In addition, apparent anaerobic N degradation was identified as good predictor of aerobic N release in the soil, which has resource saving implications when screening MTP to be used as green manures. [ABSTRACT FROM AUTHOR]

We compared symbiotic N2 fixation by winter forage legumes (clovers, medics and vetches) using the15N natural abundance technique in three experiments. Vetches (Viciaspp.) 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 hirsutumL.) systems with and without vetch, or with faba beans (Vicia fabaL.) 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 purpureusL. - 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. [ABSTRACT FROM AUTHOR]

A two-year trial was conducted to determine the effects of green manures and crop sequences on plant disease, streptomycete and bacterial densities, and inhibitory activity of indigenous streptomycetes against four target pathogens. Green manure treatments, buckwheat (Fagopyrum esculentumL.), canola(Brassica napusL.), sorghum-sudangrass (Sorghum bicolor) (L.) Moench ×Sorghumsudanense (Piper) Stapf.), and fallow control were tested in conjunction with three crop sequences in a Phytophthora-infested soil placed in containers. Alfalfa (Medicago sativaL.), potato (Solanum tubersoumL.), or corn (Zea mays L.) was grown in the first year, and alfalfa was grown in all containers in the second year. Compared to fallow controls, alfalfa grown in sorghum-sudangrass- or buckwheat-treated soil had significantly greater stand counts and total biomass, respectively. In addition, alfalfa grown in fallow-treated soils had the greatest Phytophthora root rot as a function of stand count. Crop rotation also had a significant effect on alfalfa root rot and yield. Potato scab disease intensity was greatest on tubers grown in fallow-treated soils, while tubers grown in canola-treated soils had the highest yields (total tuber weight). Green-manure-treated soils tended to have greater streptomycete and bacterial densities than fallow-treated soils. In addition, buckwheat- or sorghum-sudangrass-treated soils had greater proportions of streptomycetes that were antagonistic against the target pathogens than fallow-treated soils. The proportion of antagonists in soil was negatively correlated with alfalfa root rot, and positively correlated with alfalfa stand counts. Inhibitory activity of the streptomycetes was also negatively correlated with potato scab and positively correlated with potato yield. These data suggest that green manures may provide a strategy for increasing pathogen inhibitory activity within the streptomycete community in soil, and, in conjunction with crop rotation, may contribute to the control of a diverse collection of soil-borne plant pathogens on multiple crop species. [ABSTRACT FROM AUTHOR]

On the basis of preliminary experiments, someCrotalariaspecies from Senegal were investigated to determine (1) their susceptibility toMeloidogyne javanicaandM. incognitacompared to a sensitive host (tomato), (2) their mycorrhizal and rhizobial responses, and (3) the effect of their cultivation on the mycorrhizal soil infectivity. The nematode invasion rates onCrotalariaspp. ranked from 0.17 to 7.17% and from 0.58 to 5.25%, respectively, forM. incognitaandM. javanica, vs. 97% and 77% on tomato. Moreover, the inoculated J2 which invaded tomatoes developed into adult females, while those onCrotalariaspp. rarely developed beyond the third stage, confirming that allCrotalariaspp. evaluated are non hosts or poor hosts. In two other experiments,Crotalariaspp. were inoculated with an arbuscular mycorrhizal fungus (Glomus intraradices). Mycorrhization was generally well developed amongCrotalariaspecies, and mycorrhizal colonization enhanced mainly phosphorus content of shoot tissues and always significant plant growth. Inoculation with both rhizobial isolates andGlomus intraradicesenhanced growth and nodule formation on someCrotalariaspecies. The data recorded in both experiments showed, for the first time, thatCrotalariaspp. are highly mycorrhiza dependent, some of them reaching more than 90% mycorrhizal dependency. AmongCrotalariaspecies, twelve were used in two different experiments. A significant correlation was obtained between their mycorrhizal dependencies calculated on the shoot dry mass recorded in each experiment.Crotalariaspp. could be used as pre-crops for providing green manure while at the same time decreasing the level of detrimental nematodes and increasing the level of beneficial mycorrhizal fungi. [ABSTRACT FROM AUTHOR]

Saprophytic soil-borne pathogens can be either actively suppressed by organic amendments or enhanced, depending on soil health conditions. This can be deleterious in the event of selection of a soil-borne population by previous soil management and short crop rotation. Trials were performed in the open field and in pots, using naturally infected soil from intensive crop systems, i.e., soil from fields with 8 years of strawberry cultivation. The aim was to study short-term response of Pythium and soil microbial populations to green manure. The use of green manure in these naturally infested soils, 3–10 weeks after fresh tissue incorporation, caused Pythium populations to increase concurrent with an increase in soil microbial populations, and did not result in the suppression of the pathogen. A more elaborate trial was performed under controlled conditions, amending soil with fresh wheat plant material, air-dried wheat plant material and an organic fertilizer with a high level of humic substances. Although compared to the original soil, all amendments caused a similar increase in organic matter content and small differences in soil respiration, incorporation of fresh, not decomposed, plant material strongly increased Pythium, while the organic fertilizer did not affect the original level of the pathogen population. The increase in total number of fungi and bacteria did not have any suppressive effect on the Pythium population in naturally infested soil used for this study. [ABSTRACT FROM AUTHOR]

Whether grown as pulses for grain, as green manure, as pastures or as the tree components of agro-forestry systems, the value of leguminous crops lies in their ability to fix atmospheric N2, so reducing the use of expensive fertiliser-N and enhancing soil fertility. N2 fixing legumes provide the basis for developing sustainable farming systems that incorporate integrated nutrient management. By exploiting the stable nitrogen isotope 15N, it has been possible to reliably measure rates of N2 fixation in a wide range of agro-ecological field situations involving many leguminous species. The accumulated data demonstrate that there is a wealth of genetic diversity among legumes and their Rhizobium symbionts which can be used to enhance N2 fixation. Practical agronomic and microbiological means to maximise N inputs by legumes have also been identified. [ABSTRACT FROM AUTHOR]

Rice is the most important cereal crop. In the next three decades, the world will need to produce about 60% more rice than today's global production to feed the extra billion people. Nitrogen is the major nutrient limiting rice production. Development of fertilizer-responsive varieties in the Green Revolution, coupled with the realization by farmers of the importance of nitrogen, has led to high rates of N fertilizer use on rice. Increased future demand for rice will entail increased application of fertilizer N. Awareness is growing, however, that such an increase in agricultural production needs to be achieved without endangering the environment. To achieve food security through sustainable agriculture, the requirement for fixed nitrogen must increasingly met by biological nitrogen fixation (BNF) rather than by using nitrogen fixed industrially. It is thus imperative to improve existing BNF systems and develop N2-fixing non-leguminous crops such as rice. Here we review the potentials and constraints of conventional BNF systems in rice agriculture, as well as the prospects of achieving in planta nitrogen fixation in rice. [ABSTRACT FROM AUTHOR]

Corrections to articles including "Intercropping green manure crops: effects on rooting patterns" and "Plant Soil" are presented.Two corrections to articles including "Intercropping green manure crops: effects on rooting patterns" and "Plant Soil" are presented.Two corrections to articles including "Intercropping green manure crops: effects on rooting patterns" and "Plant Soil" are presented.