Compost tea is a term used to refer to an aqueous solution produced using composted animal or vegetative matter. Over 10,000 customers have purchased equipment for home production of compost tea in the United States (Carpenter-Boggs, 2005). Interest was fostered mostly by anecdotal evidence shared in newsletters and specialty publications targeting home and smaller market fruit and vegetable producers. Compost tea may or may not be actively aerated during production. Amendments to tea such as molasses, cane syrup, or fruit are intended to facilitate multiplication of microbes beneficial to crops (Ingham, 2000). Most compost teas are filtered to remove the compost but retain the microbes that were grown in the composting and brewing (Ingham, 2000). Compost tea is thought to act more as a microbial inoculant that stimulates soil or foliar microbial population effectiveness than as a nutrient source (Carpenter-Boggs, 2005).
Claims of benefit from compost-steeped microbial tea are broad and include improved crop yield, vigor, quality, and resistance to diseases and pests (Carpenter-Boggs, 2005; Grobe, 1997). However, variable effects from a variety of tea production and application methods have been reported. Several foliar pathogens were reported to be suppressed by aerated and nonaerated microbial teas (Scheuerell and Mahaffee, 2002). Early blight [Alternaria solani (Ell. & Mart) L.R. Jones & Grout] of tomato (Lycopersicon esculentum Mill.) and purple blight [Alternaria porri (Ellis) Cif.] of onion (Allium cepa L.) were suppressed by a nonaerated compost tea (Haggag and Saber, 2007). Compost tea application may not be consistently beneficial. Compost tea applied to potato (Solanum tuberosum L.) increased incidence of silver scurf (Helminthosporium solani Dur. & Mont.) and black scurf (Rhizoctonia solani Kuhn), but did not affect incidence of dry rot (Fusarium sp.), common scab [Streptomyces scabies (Thaxter) Waksman & Henrici], early blight, bacterial soft rot [Erwinia carotovora var. carotovora (Jones) Dye] (Al-Mughrabi, 2006), or late blight [Phytophthora infestans (Mont.) deBary] (Sturz et al., 2006). Some compost tea formulas increased yield of broccoli (Brassica oleracea var. italica Plenck) (Sanwal et al., 2006), onion, and tomato crops (Haggag and Saber, 2007). Compost teas prepared with chicken manure consistently reduced disease and increased yield of onion and tomato crops (Haggag and Saber, 2007). However, not all tea formulas increased yield (Al-Mughrabi, 2006; Haggag and Saber, 2007).
Commercially available microbial sources may replace compost as an inoculant and could simplify compost tea production. These may also decrease variability (Scheuerell and Mahaffee, 2002) between batches and alleviate human health concerns about pathogens (Kannangara et al., 2006) in compost tea. A class of microbial teas was developed by Teruo Higa, Professor of Horticulture at the University of the Ryukyus, Okinawa, Japan, and contains what he called “effective microorganisms.” These commercial products contain selected species of microorganisms, which are predominantly lactic acid bacteria and yeasts, and smaller numbers of photosynthetic bacteria, actinomycetes, and other organisms (Higa and Parr, 1994). Higa hypothesized that by increasing microbial diversity of soils, effective microorganisms improve soil quality, enhance crop production and quality, and create a more sustainable environment.
The benefits of effective microbes have been demonstrated in crop systems in Japan, China, Sri Lanka, India, Bangladesh, and Brazil. Research reported yield increased by soil application of effective microbes in combination with organic and conventional fertilizers in tomato (cv. Momotaro T96) (Wang et al., 1999), sweet orange (Citrus sinensis Osbeck cv. Pera) grafted to lemon rootstock (Citrus limonia Osbeck cv. Cravo) (Paschoal et al., 1998), onion (cv. Taherpur), and string bean (Vigna sesquipedalis L. cv. Topgreen) (Chowdhury et al., 1996). Yield increase was related to increased fruit set (Wang et al., 1999) and increased total chlorophyll content (Chowdhury et al., 1996).
The reported effects of effective microbes on soil include increased nutrient availability (Sangakkar and Weerasekera, 2001); increased aggregation, porosity, and water infiltration (Tokeshi et al., 1996); and increased organic matter, pH, and cation exchange capacity (Paschoal et al., 1998). Effective microbes in a rice bran carrier (EM Bokashi) was reported to increase rice (Oryza sativa L.) grain yield; this was associated with increased soil organic matter content, microbial biomass, and available nutrients as well as improved soil porosity and permeability compared with organic and chemical fertilizer treatments without effective microbes (Shao et al., 2003).
Manure teas are another variant on the concept of compost tea. The product may serve only as a diluted liquid fertilizer (Diver, 2005), but it is hypothesized by some to be a potential stimulant of indigenous soil microbial populations (Jim Barlow, agronomist and commercial producer of microbial products, personal communication). A tea is made from a solution that contains animal manure. Multiplication of microbes from the manure is encouraged by aeration and additives, which may include a sucrose source and yeast to help diversify the microbial population. However, the soil environment is probably not optimal for many of the microbial organisms in the manure tea, which are consumed by indigenous microbes. Manure tea is hypothesized to be beneficial not because of individual ingredients, but like compost tea, because of the microbial population grown in the tea.
Variability in microbial tea effects is probably attributable, in part, to variation in tea production methods. Ingredients, brew conditions (aeration, temperature, and time), application rate, frequency, and mechanism may all vary (Scheuerell and Mahaffee, 2002). It is also hypothesized that microbial tea effects may vary by crop, season, and soil condition (Carpenter-Boggs, 2005). This variability discourages scientific investigation and publication despite positive anecdotal reports. Improved yield is an important consideration for growers waiting to review credible evidence of microbial tea benefit.
This study evaluated the effect of two microbial teas made from: 1) a homemade manure tea recipe; and 2) a commercially available microbial source. The selection was because of interest on the part of Kansas State University research and extension clientele. The commercial product was an effective microbe culture produced in our region by a former student of Teruo Higa with the trade name Efficient Microbes™ (Sustainable Community Development, Kansas City, MO). The manure tea recipe was chosen at the request of Trees for Life, a nonprofit agriculture and educational organization with their home office in Wichita, KS. It was considered to be a potential low-cost agriculture input for impoverished tropical regions (Calovich, 2005). A scientific study was desirable before promoting it within their network. We recognize that manure tea application to leafy green vegetables would not meet U.S. Department of Agriculture National Organic Program guidelines, but it is not out of step with producer practices in many developing countries.
It was hypothesized that microbial tea applications improve the soil microbial environment and this would be reflected in improved plant growth. It was also hypothesized that the microbial tea benefit might be affected by nutrient source (organic or conventional fertilizer). The objective of this study was to evaluate the effect of microbial teas made from manure and from Efficient Microbes™ on crop yield and microbial biomass in a sandy loam soil. The effect of Efficient Microbes™ on crop yield was also evaluated on a loam soil.
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