Joji Muramoto

Exploring warm-season cover crops as carbon sources for anaerobic soil disinfestation (ASD)

Background and aimsAnaerobic soil disinfestation (ASD) has been shown to be an effective strategy for controlling soilborne plant pathogens and plant-parasitic nematodes in vegetable and other specialty crop production systems. Anaerobic soil disinfestation is based upon supplying labile carbon (C) to stimulate microbially-driven anaerobic soil conditions in moist soils covered with polyethylene mulch. To test the effectiveness of warm-season cover crops as C sources for ASD, a greenhouse study was conducted using a sandy field soil in which several warm-season legumes and grasses were grown and incorporated and compared to molasses-amended and no C source controls.MethodsGreenhouse pots were irrigated to fill soil porosity and covered with a transparent polyethylene mulch to initiate a 3-week ASD treatment prior to planting tomatoes. Soilborne plant pathogen inoculum packets, yellow nutsedge (Cyperus esculentus L.) tubers, and Southern root-knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood; M.i.) eggs and juveniles were introduced at cover crop incorporation.ResultsIn nearly all cases, ASD treatment utilizing cover crops as a C source resulted in soil anaerobicity values that were equal to the molasses-amended fallow control and greater than the no C source fallow control. In trial 1, Fusarium oxysporum Schlechtend.:Fr. (F.o.) survival was reduced by more than 97% in all C source treatments compared to the no C source control but there was no effect of C source in Trial 2. Carbon source treatments were inconsistent in their effects on survival of Sclerotium rolfsii Sacc. (S.r). In general, the number of M.i. extracted from tomato root tissue and root gall ratings were low in all treatments with cover crop C source, molasses C source, or composted poultry litter. Germination of yellow nutsedge tubers was highest in the no C source control (76%), lowest in the molasses control (31%), and intermediate from cover crop treatments (49% to 61%).ConclusionsWarm-season cover crops have potential to serve as a C source for ASD in vegetable and other crop production systems, but more work is needed to improve consistency and further elucidate mechanisms of control of soilborne plant pathogens and weeds during ASD treatment utilizing cover crops.

Strawberry Cultivars and Mycorrhizal Inoculants Evaluated in California Organic Production Fields

Thirteen commercial strawberry cultivars were evaluated in side-by-side comparisons in five experiments in organic strawberry production fields in central California. Seven cultivars were common to all five experiments; six additional cultivars were included in one to four of the experiments. Of the seven cultivars that were evaluated in all five experiments, the largest market yield was consistently obtained from Aromas, Seascape, or Pacific. Preliminary analyses detected a strong positive correlation between total fruit yield and the nitrogen status of plants, suggesting characteristics in nitrogen uptake and metabolism may be a significant factor in determining yield of commercial strawberry cultivars tested in organic fields. None of the seven commercially prepared mycorrhizal inoculants tested resulted in an increased marketable fruit yield in organic or nonfumigated fields. However, the effects of the treatments on mycorrhizal colonization and total yield varied among experiments. For example, in one of six experiments, a commercial inoculant increased total yield over the nontreated control but did not influence marketable fruit yield.

Anaerobic Soil Disinfestation and Soilborne Pest Management

Anaerobic soil disinfestation is a biologically based, preplant soil treatment that provides an alternative to chemical fumigation for soilborne pest and disease management. The method involves the incorporation of organic amendments that contain a labile carbon source, covering soil with clear or gas-impermeable polyethylene tarp, and irrigating until saturation. Populations of facultative anaerobes utilize the carbon source and deplete the soil of oxygen for a short period of time. The approach has been tested for use in multiple crops, soil types, and regions and inputs can be modified to target specific pathogens. It is a particularly valuable tool for use in organic production, for use in fumigant buffer zones, and for use in regions where soil solarization is not feasible due to environmental constraints. In addition to oxygen depletion, the mechanisms involved in disease suppression include biological control and the production of organic acids. Significant shifts in the composition of the soil microbial community occur during the treatment, and the effects of ASD can be seen beyond the first cropping system and have the potential to contribute to the development of a disease-suppressive soil.

Integrated Biological and Cultural Practices Can Reduce Crop Rotation Period of Organic Strawberries

A team of researchers conducted a replicated on-farm experiment with the break period between strawberry crops (continuous strawberries with broccoli residue incorporation, one-year break, two-year break, three-year break, and seven-year break) as the main plot and cultivar as the split plot in Moss Landing, Central Coastal California. We hypothesized that the use of non-host rotation crops for Verticillium wilt plus bio-fumigation with broccoli, incorporation of mustard cover crop residues, use of relatively resistant strawberry cultivars, and compost application would suppress disease sufficiently to grow strawberries successfully in rotation every two or three years. Although a positive correlation between break period and marketable fruit yield existed, integrated use of biological and cultural practices allowed one to three-year breaks to have a statistically similar yield as seven-year break for this low Verticillium dahliae pressure field over a five-year period.

Soil fertility and crop growth under poultry/crop integration

Innovative sources of soil fertility are of utmost importance to growers in light of rising fertilizer costsand environmental concerns. Integrating livestock and crop production is one channel by which agricultural practitioners can enhance soil fertility. For this research, soil fertility was analyzed in pastured poultry/crop agroecosystems to determine whether freeranging birds and pasture could be used to replace or supplement non-manure-based fertilizers. Soils from adjacent cropped areas were compared to plots with a recent history of pastured poultry use on two farms, and crop plants were grown in each type of soil in a replicated greenhouse experiment. Spatial variation in soil fertility was also assessed relative to locationof poultry coops. Pasturedpoultry plots had elevated soil total C, total N, NH4 –N, NO3 –N, Olsen P, exchangeable K, organic matter, cation exchange capacity and electrical conductivity relative to the control of typically managed organic farm soils without pastured animal inputs. These soil fertility changes conferred greater biomass and height to sunflowers and beans grown in these soils relative to control soils for most treatments. Results suggest that pastured poultry can effectively fertilize soil for certain crops but that a need exists for more research into (1) phosphorus management and (2) ensuring a spatially uniform distribution of manure.

Anaerobic soil disinfestation is an alternative to soil fumigation for control of some soilborne pathogens in strawberry production

Alternatives to soil fumigation are needed for soil-borne disease control. Our goal was to test anaerobic soil disinfestation (ASD) as an alternative to soil fumigation for control of critical soil-borne pathogens in California strawberry production. Controlled environment experiments were conducted at 25°C and 15°C testing different materials as carbon sources for ASD using soil inoculated with Verticillium dahliae. Field trials were conducted in three locations comparing ASD with 20Mg ha−1 rice bran (RB) against fumigated and untreated controls, steam, mustard seed meal and fish emulsion. In ASD treated soils, temperature and anaerobicity were critical for control of V. dahliae, but multiple carbon inputs reduced inoculum by 80-100%. In field trials, ASD with RB provided control of a number of pathogens, and in three of four trials produced marketable fruit yields equivalent to fumigation. Little weed control benefit from ASD was found. ASD with RB also induced changes in the soil microbiome that persisted through the growing season. When equivalent yields were obtained, net returns above harvest and treatment costs with ASD RB were 92–96% of those with bed fumigation based on average prices over the previous 5 years. ASD can be a viable alternative for control of some soil-borne pathogens. Growers are adopting ASD in CA strawberry production, but research to determine optimal soil temperatures, anaerobicity thresholds and carbon sources for effective control of specific pathogens is needed. This article is protected by copyright. All rights reserved.

Anaerobic Soil Disinfestation and Brassica Seed Meal Amendment Alter Soil Microbiology and System Resistance

ABSTRACT Brassica seed meal amendments and anaerobic soil disinfestation (ASD) control a spectrum of soil-borne plant pathogens via a diversity of mechanisms. Transformations in microbial community structure and function in certain instances were determinants of disease control and enhanced plant performance. For instance, in strawberry field soils, increased strawberry yields in response to ASD were attained in a carbon-source input-dependent manner. ASD conducted with rice bran as the carbon input, but not molasses, resulted in significantly greater yields. Effective ASD treatments, but not ineffective treatments, resulted in increased abundance of bacteria in phylum Bacteroidetes in treated soils, specific genera of which are known to provide biological disease control. Brassica seed meal amendment resulted in development of a soil system suppressive towards disease incited by the root pathogen Macrophomina phaseolina. Brassica seed meal treated orchard soil systems exhibit resistance to re-infestation by soil-borne pathogens, including the plant parasitic nematode Pratylenchus penetrans. System resistance is associated with significant and prolonged changes in rhizosphere microbiology and specifically amplification of specific organisms with potential to parasitize P. penetrans.

Effect of Anaerobic Soil Disinfestation and Mustard Seed Meal for Control of Charcoal Rot in California Strawberries

ABSTRACT Anaerobic soil disinfestation (ASD) and mustard seed meal (MSM) appear to be promising non-fumigant alternatives for soilborne pathogens control. However, studies of their effect on charcoal rot caused by Macrophomina phaseolina in California strawberry are limited. A demonstration field trial with ASD with rice bran 20 t ha–1 (ASD-RB), MSM 4.5 t ha–1 (MSM), and ASD with rice bran 6.7 t ha–1 + MSM 4.5 t ha–1 (ASD-RB+MSM) treatments was conducted in a M. phaseolina-infested organic field in Oxnard, CA. A doubling of fruit yields relative to the grower standard, and a reduction in plant mortality by M. phaseolina, was achieved by ASD-RB. MSM failed to control M. phaseolina and resulted in fruit yields that were more than 20% below the ASD-RB yield. Fruit yield in the ASD-RB+MSM plot was intermediate between ASD-RB and MSM. Treatment effects on soil pH, EC, inorganic N dynamics, and soil microbial communities were also examined.