Mario Tenuta

Ammonia and Nitrous Acid from Nitrogenous Amendments Kill the Microsclerotia of Verticillium dahliae

ABSTRACT This study examined the mechanisms by which nitrogenous amendments such as meat and bone meal kill the soilborne plant pathogen Verticillium dahliae. The effect of nitrogen products from the amendments on the survival of microsclerotia of V. dahliae was examined by solution bioassay and soil microcosm experiments. Ammonia and nitrous acid but not their ionized counterparts, ammonium and nitrite, were toxic to microsclerotia in bioassays. In microcosms, addition of meat and bone meal (2.5%) to an acidic loamy sand resulted in the accumulation of ammonia and death of microsclerotia within 2 weeks. At lower concentrations (0.5 and 1%), microsclerotia were killed after 2 weeks when nitrous acid accumulated (>0.03 mM). In an alkaline loam soil, microsclerotia survived at 3% meat and bone meal and neither ammonia nor nitrous acid accumulated. The toxicity of ammonia to the pathogen was verified by increasing the concentration of meat and bone meal to 4% or addition of urea (1,600 mg of N per kg) to the loam soil resulting in the accumulation of ammonia (>35 mM) and death of microsclerotia. The toxicity of nitrous acid was verified by adding ammonium sulfate fertilizer to an acidic sand soil. Inhibiting nitrification with dicyandiamide revealed that nitrous acid was generated as a result of the accumulation of nitrite and an acidic pH. Thus, levels to which the toxins accumulated and the effective concentration of amendment were dependent upon the soil examined. Of the two mechanisms identified, accumulation of nitrous acid is the more promising strategy to control plant diseases in acidic soil because it is more toxic than ammonia and is formed at lower concentrations of amendments.

Effects of long-term crop management on nematode trophic levels other than plant feeders disappear after 1 year of disruptive soil management

Nematode community analysis may provide a useful tool to quantify soil health. Nematode communities were monitored for 5 years during a 12-year period in the sustainable agriculture farming systems (SAFS) project at UC Davis, where conventional (CONV), low-input (LOW) and organic (ORG) management treatments were compared. After the completion of three 4-year crop rotation cycles, a uniform crop of oats was grown in 2001. The composition of the nematode genera was different from year to year, but there were significant management effects on genus composition in each year, with the CONV treatment being significantly different from the LOW and ORG treatments. Important contributors to the differences in genus composition among treatments were plant parasitic nematodes. Nematode community indices (enrichment (EI), basal (BI) and channel (CI) indices) of the CONV treatment differed from those of the ORG and LOW treatments in 1993, 1994, 1995 and 2000, but not in 2001. The difference in structure index (SI) among management treatments was significant in 1995 and 2000. EI and SI were generally lower, and BI and CI higher in CONV than in LOW and ORG treatments. There were significant crop effects on the community indices throughout the years. Even in 2001, there was a residual effect of the crop grown in 2000 on most nematode community indices. Differences in EI, BI and CI among crops were consistent, while those in SI were not. Meloidogyne javanica(Treub) Chitwood, juveniles added to various soil samples were reduced by 68% in soil where nematode trapping fungi had been added and which had low BI (12) and low CI (20) values. Soil from SAFS plots with a high BI (47) and high CI (70) after 1 year of oats and ploughing, suppressed root knot juveniles much less. There were significant negative correlations between BI and root knot nematode (RKN) suppression ( −0.72) and between CI and RKN suppression (−0.74). Thus, BI and CI appeared to be most valuable as indicators for long-term effects of management on nematode suppression. However, BI and SI may be more suitable as general indicators for the health status of a soil, since CI can be high in highly disturbed agro-ecosystems as well as in undisturbed natural ecosystems. A high BI would indicate poor ecosystem health, while a high SI would indicate a well-regulated, healthy ecosystem. For agricultural soils the presence of large populations of plant parasitic nematodes forms an additional indication of poor ecosystem health, as natural regulation is limited in this case.

Organic amendments as a disease control strategy for soilborne diseases of high-value agricultural crops

Manures and by-products derived from the processing of plants and animals have been used for centuries as sources of fertiliser, but beneficial or detrimental effects on plant diseases were never thoroughly investigated. We found that certain organic amendments controlled a variety of soilborne diseases of potato (including common scab and verticillium wilt), various pests (including plant parasitic nematodes) and weeds at nine field locations in Ontario and Prince Edward Island, Canada. The mechanism of disease control for highnitrogen-containing amendments is the generation of ammonia and / or nitrous acid following degradation of the amendments by microorganisms. The formation of these products to concentrations lethal to pathogens is regulated by the soil pH, organic matter content, nitrification rate, sand content and buffering capacity. Liquid swine manure reduced scab and wilt, but at only three of six locations tested. In acidic soils, swine manure killed Verticillium dahliae within a day after application, but had no effect in neutral or alkaline soils. The toxic components in the manure were identified as volatile fatty acids. Ammonium lignosulfonate reduced scab at all six sites tested. The mechanism of disease control is not yet known. Although many of these amendments reduced pathogen populations, total soil microorganism numbers increased by 10- to 1000-fold after application, indicating that not all organisms were killed. Understanding the mode of action of amendments is essential for the improvement of their effectiveness and assimilation into crop production systems. If costs can be decreased and benefits ensured, organic amendments will have a major role in reducing plant diseases. The discussion on use of these amendments is based on cost/ benefit analysis as well as societal and regulatory considerations.

Volatile Fatty Acids in Liquid Swine Manure Can Kill Microsclerotia of Verticillium dahliae

ABSTRACT Liquid swine manure added to acidic soils killed microsclerotia of the wilt fungus Verticillium dahliae. We investigated whether volatile fatty acids (VFAs) in the manure were responsible for this toxicity. The survival of microsclerotia was determined after exposure to various dilutions of manure or its VFA components. Acetic, propionic, and isobutyric acids constituted the major VFAs in the manure, while n-butyric, n-valeric, iso-valeric, and n-caproic acids were present in lesser amounts. Formic acid was not detected. The individual VFAs were more toxic to microsclerotia as the solution pH was decreased, indicating that the protonated forms of the VFAs were toxic (e.g., acetic acid and not acetate). The effective concentration reducing germination of microsclerotia by 95% (EC(95)) for formic and n-caproic acids was approximately 4 mM, the most toxic of the acids tested; for n-valeric, the EC(95) was 9.2 mM, isovaleric was 16.1 mM acids, and acetic, propionic, n-butyric, and isobutyric acids were approximately 30 mM. The toxicity of acetic acid, and likely all the others, was directly related to the duration of exposure. Inhibition of microsclerotia germination followed identical trends in solutions of the manure or in a mixture of VFAs with equivalent concentrations of the individual acids found in the manure. Similarly, germination declined to the same extent in the atmosphere above the manure or the VFA mixture, confirming the toxicity of VFAs to microsclerotia. Thus, under acid conditions, VFAs in liquid swine manure can kill microsclerotia of V. dahliae.

Liquid Swine Manure Can Kill Verticillium dahliae Microsclerotia in Soil by Volatile Fatty Acid, Nitrous Acid, and Ammonia Toxicity

ABSTRACT In previous studies, liquid swine manure (LSM) was sometimes shown to reduce Verticillium wilt of potato caused by Verticillium dahliae. We also observed that microsclerotia of this fungus died within 1 day, or between 3 and 6 weeks, after addition of LSM to some acid soils and within 1 week in some alkaline soils. In this study, we demonstrated that a volatile fatty acid (VFA) mixture with an identical concentration of VFAs as that found in an effective LSM reduced germination in an acid soil (pH 5.1) to the same extent as the LSM after 1 day of exposure. Germination was reduced by 45, 75, and 90% in the 10, 20, and 40% ([wt/wt] soil moisture) treatments, respectively, with the latter being equivalent to an application of 80 hl/ha. Addition to this acid soil of 19 LSMs (30% [wt/wt] soil moisture) collected from different producers resulted in complete kill of microsclerotia with 12 manures. Effective manures had a total concentration of nonionized forms of VFAs in soil solution of 2.7 mM or higher. In some acid soils (pH 5.8), addition of LSM (40% [wt/wt] soil moisture) did not kill microsclerotia until 3 to 6 weeks later. Here, a reduction in viability of microsclerotia was attributed to the accumulation of 0.06 mM nitrous acid in the soil solution at 4 weeks. When an LSM was added (40% [wt/wt] soil moisture) to an alkaline soil (pH 7.9) where VFAs are not toxic, microsclerotia germination was reduced by 80% after 1 week. Here the pH increased to 8.9 and the concentration of ammonia reached 30 mM in the soil solution. An ammonium chloride solution having an equivalent concentration of ammonium as the manure was shown to have the same spectrum of toxicity as the manure in assays ranging from pH 7 to 9, both in solutions and above the solutions. At pH 9, the concentration of ammonia reached 18 mM and 100% mortality of microsclerotia occurred. Thus, in acid soils, LSM can kill microsclerotia of V. dahliae by VFA and/or nitrous acid toxicity and in alkaline soils by ammonia toxicity. In order to take advantage of these mechanisms for disease reduction, the manure chemical composition, rate of addition, and soil characteristics need to be determined for each instance of use.

Increase in nitrous oxide production in soil induced by ammonium and organic carbon

We observed that soil cores collected in the field containing relatively high NHinf4sup+and C substrate levels produced relatively large quantities of N2O. A series of laboratory experiments confirmed that the addition of NHinf4sup+and glucose to soil increase N2O production under aerobic conditions. Denitrifying enzyme activity was also increased by the addition of NHinf4sup+and glucose. Furthermore, NHinf4sup+and glocose additions increased the production of N2O in the presence of C2H2. Therefore, we concluded that denitrification was the most likely source of N2O production. Denitrification was not, however, directly affected by NHinf4sup+in anaerobic soil slurries, although the use of C substrate increased. In the presence of a high substrate C concentration, N2O production by denitrifiers may be affected by NOinf3sup-supplied from NHinf4sup+through nitrification. Alternatively, N2O may be produced during mixotrophic and heterotrophic growth of nitrifiers. The results indicated that the NHinf4sup+concentration, in addition to NOinf3sup-, C substrate, and O2 concentrations, is important for predicting N2O production and denitrification under field conditions.

Pattern of greenhouse gas emission from a Prairie Pothole agricultural landscape in Manitoba, Canada

To obtain accurate N2O and CH4 emission estimates from the Prairie Pothole Region of North America, knowledge of landscape pattern and soil factors is important. A field study was conducted investigating the temporal and spatial variation in N2O and CH4 emissions from spring to fall 2005 and spring-thaw to post-fertilizer application period 2006 using static-vented chambers located at upper, middle and lower landscape elements planted to spring wheat in 2005 and flax in 2006 and riparian areas in an undulating terrain in southern Manitoba. N2O was emitted during spring-thaw and post-fertilizer application periods for cropped positions and CH4 was emitted about 7 wk after soil thaw for lower and riparian elements. While there was no statististical difference in N2O emission from upper, middle and lower landscape elements, there was greater occurrence of N2O emission hotspots at the lower element, associated with its comparatively higher soil moisture and carbon availability. A location of intense CH4 emiss...

Effect of nitrogen fertilizer rate on nitrous oxide emission from irrigated potato on a clay loam soil in Manitoba, Canada

Gao, X., Tenuta, M., Nelson, A., Sparling, B., Tomasiewicz, D., Mohr, R. M. and Bizimungu, B. 2013. Effect of nitrogen fertilizer rate on nitrous oxide emission from irrigated potato on a clay loam soil in Manitoba, Canada. Can. J. Soil Sci. 93: 1-11. This study examined the effect of N fertilizer application rate on N2O emissions for irrigated potato production on a clay loam soil near Carberry, Manitoba, over two growing seasons. Treatments were an unfertilized control, and urea-N fertilizer application rates of 80, 160 and 240 kg N ha-1, which were applied as split applications. The marketable yield increased at 80 kg N ha-1 relative to the unfertilized control, but did not respond to higher rates of fertilizer. Peak emission of N2O followed fertilizer application and rain or irrigation events. Emission rates following fertilizer application and water addition events were greater from hill than from furrow position in 2009, but not in 2010. In the latter, ponding of water in furrows likely resulted in the greater emissions than from the hill positions. Cumulative N2O emissions and yield based N2O intensity increased linearly with N application rate. The growing season emission factor (EFgs) for percent of added N emitted as N2O was 0.73% and did not increase with N application rate. The adjusted whole-year emission factor (EFwy) assuming 30% of annual emissions are emitted during winter and thaw was 1.04%, being lower than the Canadian IPCC Tier II protocol value of 1.72% for irrigated cropland in Canada. The lower measured EFwy may be because the protocol assumes that under irrigation water input (rain plus irrigation) equals potential evapotranspiration (PET) from May to October, implying no restriction of N2O emissions by water limitation. For the current study, however, the ratio of water input to PET averaged 70%, suggesting water may have restricted N2O emission, therefore resulting in a lower EFwy than predicted by the Tier II protocol. The results of the current study also suggest that a reduction in N2O emissions can be achieved by avoiding fertilizer N applications beyond optimal for marketable yield, limiting irrigation soon after application of N fertilizer, and managing irrigation to prevent ponding of water in furrows.

Identification of specific soil properties that affect the accumulation and toxicity of ammonia to Verticillium dahliae

The accumulation of ammonia in soil amended with meat and bone meal was previously shown to kill microsclerotia of Verticillium dahliae Kleb. This laboratory study examined to what extent cation-exchange capacity, moisture, organic carbon and nitrification, and high levels of sand and bulk density affect the accumulation of ammonia. Two soils were used as models: site B soil a loamy sand of low organic carbon content that when amended with meat and bone meal (2–2.5%) accumulates ammonia in excess of 25 mM, killing microsclerotia, and site L soil, a loam of moderate organic carbon content that does not accumulate ammonia unless amended to at least 4%. Ammonia accumulation was prevented in site B soil by addition of a muck soil that increased the organic carbon content. In site L soil, accumulation of ammonia was achieved by increasing its sand content or by preventing nitrification using the inhibitor dicyandiamide. Other factors such as exchangeable ammonium plus ammonia had similar effects for amended site B and L soils, indicating that cation-exchange reactions involving the absorption of ammonium and ammonia to soil particles are not a primary determinant of ammonia accumulation. Moisture content and density only slightly affected the accumulation of ammonia in site L soil. These findings indicate that concentrations of nitrogenous amendments required to kill V. dahliae microsclerotia can be reduced to practical levels by targeting for amendment soils having low organic carbon and high sand contents while reducing their rate of nitrification.

Mycorrhizal colonization and grain Cd concentration of field-grown durum wheat in response to tillage, preceding crop and phosphorus fertilization.

BACKGROUND A 3-year field trial was conducted to investigate the effect of agricultural management practices including tillage, preceding crop and phosphate fertilization on root colonization by arbuscular mycorrhizal (AM) fungi and grain cadmium (Cd) concentration of durum wheat (Triticum turgidum L.). The relationship between grain Cd and soil and plant variables was explored to determine the primary factors affecting grain Cd concentration. RESULTS Mycorrhizal colonization of the roots was reduced by conventional tillage or when the preceding crop was canola (Brassica napus L.), compared to minimum tillage or when the preceding crop was flax (Linum usitatissimum L.). In contrast, grain Cd was not consistently affected by any treatment. Grain Cd was generally below the maximum permissible concentration (MPC) of 100 microg Cd kg(-1) proposed by WHO. Grain Cd varied substantially from year to year, and could be predicted with 70% of variance accounted for by using the model: grain Cd concentration = - 321.9 + 44.5x ln(grain yield) + 0.26x soil DTPA-Cd + 182.5x soil electrical conductivity (EC)- 0.98x grain Zn concentration. CONCLUSIONS These common agricultural management practices had no effect on grain Cd concentration in durum wheat though they impacted mycorrhizal colonization of roots. Grain yield and to a lesser extent soil conditions of EC and DTPA-Cd and grain Zn influenced grain Cd, whereas mycorrhizal colonization levels did not.