Organic Fertilizers for Greenhouse Tomatoes: Productivity and Substrate Microbiology

Organic fertilizer regimens consisting of combinations of composts (yard waste, swine manure, or spent mushroom substrate) and liquid fertilizers (fishor plant-based) were evaluated against conventional hydroponic fertilizers in two experiments with greenhouse tomatoes grown in peat-based substrate. Crop yield and fruit quality were evaluated and several assays of substrate microbial activity and community profiles (fluorescein diacetate analysis and EcoLog, values, nematode counts) were conducted. Crops grown in 20% to 40% compost (yard waste or yard waste plus swine manure) plus a continuously applied liquid source of organic potassium (K), calcium (Ca), magnesium (Mg), and sulphate (SO4) could not be sustained more than 1 month before nutrient deficiencies became visible. Supplementation with a nitrogen (N)and phosphorus (P)containing plant-based liquid fertilizer at the point when plant deficiencies became apparent subsequently produced yields’80% that of the hydroponic control. In a second experiment, the proportion of mushroom or yard waste compost was increased to 50% of the mix, and liquid delivery of K, Ca, Mg and SO4 plus either plant-based or fish-based Nand P-containing liquid feeds was started at the date of transplanting. In this case, organic yields equal to that of the hydroponic control (8.5 kg/plant) were observed in some treatments. The most productive organic treatment was the mushroom compost supplemented with a low concentration of the plant-based liquid fertilizer. In general, organic tomatoes had a lower postharvest decay index (better shelf life) than did the hydroponic controls, possibly as an indirect consequence of overall reduced yield in those treatments. High concentrations of both organic liquid feeds resulted in lower yields as a result of treatment-induced fusarium crown and root rot. In contrast to some previous studies, those treatments showing fusarium crown and root rot also had the highest gross microbial activity. Measures of gross microbial activity and numbers of microbivorous nematodes were higher (average of 37% and 6.7 times, respectively) in compost/organic feed treatments than in the hydroponic control. Community physiological profiles of the bacterial populations, on the other hand, did not differ between organic and hydroponic treatments. Nematode populations were significantly correlated with gross microbial activity in the organic treatments. Organic production methods encourage the use of organic waste materials as substitutes for chemical fertilizers. This may be an effective way to use the high volumes of urban yard waste and waste organic materials emanating from dairy, poultry, swine, or greenhouse operations and is therefore of potentially significant environmental value (Cheng et al., 2004; Mazuela et al., 2005). Chong (Chong, 2005; Chong and Purvis, 2004) has developed recommendations for use of a variety of waste and compost products in the nursery industry, some of which could be applied to organic production settings. Amending soil or potting media with some organic wastes can improve soil physical properties with increased porosity and waterholding capacity as well as improved biological characteristics (Celik et al., 2004; Lee et al., 2004; Marinari et al., 2000). Although a good deal of research has been conducted on the use of organic waste in field vegetable production (Ball et al., 2000; Smith et al., 2001), relatively little has been done in greenhouse vegetable production. A full range of organic wastes, from municipal wastes to agricultural residues, could potentially be used as compost feedstock, depending on local availability and country legislation for organic products. For example, composts produced from several different types of agricultural residues may be suitable materials for container media or in field soils (Martı́nez et al., 2005). Rippy et al. (2004) found that several combinations of vermicompost plus organic liquid feeds produced yields similar to those of conventional hydroponic treatments. Liquid fertilizers formulated for organic agriculture are often made from organic wastes and can be applied as a foliar spray or through drip irrigation lines as an alternative to chemical fertilizer. Cheng et al. (2004) used a greenhouse tomato crop to recover part of the nutrients from swine wastewater to reduce the risk of nitrogen (N) and phosphorus (P) losses to the environment. This has proven to be a feasible and promising alternative technology for converting swine wastewater into value-added product. Liedl et al. (2004) found that liquid effluent of digested poultry litter appeared to function as well as a commercial hydroponic fertilizer for tomatoes after balancing the forms of N (NO3/NH4) and supplementing with Ca(NO3)2 and MgSO4. Abbasi et al. (2004) used fish emulsion in a peat mix to grow radish and cucumber seedlings. The result suggested that fish emulsion had both nutritive value for plant growth as well as diseasesuppressive properties and thus might be useful for organic or conventional transplant production. Organic residues act not only as a source of nutrients and organic matter, but also may increase the size, biodiversity, and activity of the microbial populations in soil, thereby influencing structure, nutrient turnover, and many other related physical, chemical, and biological parameters (Albiach et al., 2000). Organic residues can differ substantially in Received for publication 9 Jan. 2009. Accepted for publication 19 Mar. 2009. We acknowledge the financial support of the BC Greenhouse Growers’ Association Research Council and the Matching Investment Initiative of Agriculture and Agri-Food Canada and the generous in-kind support of All Seasons Mushrooms, Great Pacific Bioproducts, Technaflora Plant Products, and the Vancouver composting facility. We also gratefully acknowledge the China Scholarship Council. The technical assistance of Glenn Block is appreciated. Use of trade names does not imply endorsement of the products named nor criticism of similar ones not named. To whom reprint requests should be addressed; e-mail [email protected]. 800 HORTSCIENCE VOL. 44(3) JUNE 2009 terms of their effects on soil or substrate microbial activity and derived benefits like disease suppression (Borrero et al., 2004; Hoitink and Boehm, 1999; Kannangara et al., 2000; Litterick et al., 2004; Noble and Coventry, 2005; Ntougias et al., 2008; Zinati, 2005). For example, Martı́nez et al. (2005) estimated microbial activity by fluorescein diacetate analysis (FDA) and found that microbial biomass was higher in composted cork thin waste mixed with rice hulls than in peat used in soilless strawberry production. Relatively little is known of the relationships among organic waste amendments, microbial activity, and overall production in the context of organic practices, especially with respect to containerized greenhouse production. Furthermore, to our knowledge, there is no information available comparing the substrate microbial activity of organic and hydroponic systems. The objective of this study was to develop methods of producing organic greenhouse tomato plants, which show the long-term health and productivity expected of hydroponic plants. The emphasis was on using fertilizers and byproduct organic materials that are available in enough supply to be used in large commercial greenhouse operations and in keeping with the organic philosophy, locally produced. The effects of composts and fertilizers on substrate biological activity, and the relationships between biological activity and productivity, were also determined. Materials and Methods General crop information. Two experiments were conducted in 2008 at the Pacific Agri-Food Research Center, Agassiz, BC, Canada (lat. 49 15# N, long. 121 46# W). The first experiment involved a beefsteak cultivar and the second used a cluster cultivar. In each, seed was sown into 4-inch (10cm) pots filled with a peat/perlite (4:1 ratio by volume) mixture and transplanted at a density of 2.75 plants/m into a 75-m (64-m growing area) venlo-style greenhouse compartment where the trials were conducted. In all experiments, the peatmoss was Sungrow OMRI white course peat (Allies Wholesale, Abbotsford, BC, Canada) and the perlite (TerraLink Horticulture Inc., Abbotsford, BC, Canada) was medium grade. The greenhouse environment was computer-controlled (Argus Controls, White Rock, BC, Canada). Greenhouse temperature set points were 19 to 21 C during the day and 17 to 19 C at night. Relative humidity was maintained between 40% and 80% day and 35% and 70% night using ventilation and misting throughout the growing season. Plants were irrigated (fertigated) with fertilizer solution multiple times each day based on light sum, which ranged from 250 to 500 Wm (irrigation frequency was low early in the trials to minimize leaching but increased as the plants grew). Each irrigation event delivered 132 mL of nutrient feed to each plant over 1 min through two pressure-compensated drippers (4 L h or 66 mL min). Leaching ranged from 10% to 30%. Nightly irrigations occurred every 4 to 6 h. Plants were pruned and trained according to commercial production practices (Anonymous, 1996) except that stem density was not modified through the growing season. Fruit were harvested three times per week. Expt. 1. Seeds of the beefsteak cultivar Rapsodie (Rogers/Syngenta Seeds, Boise, ID) and the rootstock, Maxifort (deRuiter Seeds, Bergschenhoek, The Netherlands) were sown on 2 Jan. Maxifort is resistant to Verticillum sp., Fusarium oxysporum races 1 and 2, Fusarium oxysporum fsp. Radicislycopersici (crown rot), most common species of plant-parasitic nematodes, and Pyrenochaeta lycopersici (corky root). Grafting took place from 22 to 25 Jan. Plants were transplanted into 15-L pots (h = 23 cm, w = 31 cm at the top) (one plant per pot) on 26 Feb. in the experimental greenhouse compartment. Two composts were compared in this experiment: yard waste (YW) compost and swine (Sw) compost. Yard waste compost was produced by the City of Vancouver Green Waste Recycling Program. It is a Class A compost produced according to British Columbia’s Organic Matter Recycling Regulation (Government of British Columbia, 2007) using feedstocks consisting solely of yard waste and lawn clippings. Certified organic swine compost was obtained from Gelderman Farms, Abbotsford, BC, Canada. Mineral analysis of the composts is detailed in Table 1. Four substrates or combinations of substrate were compared, all with a base of peat/perlite: 1) peat/perlite (control); 2) 20% yard waste compost; 3) 40% yard waste compost; and 4) 20% swine compost plus 20% yard waste compost. All mixes were blended on a volume/volume basis. Three liquid feeds were also tested: 1) a standard hydroponic tomato feed; 2) organic feed A consisting of potassium (K), calcium (Ca), magnesium (Mg), and sulphate (SO4) derived from organic potash, calpril, and dolopril (Terralink Horticulture Inc., Abbotsford, BC, Canada) at concentrations similar to the standard hydroponic feed; and 3) organic feed B, consisting of organic feed A supplemented with a blend of commercially available liquid products certified by OMRI (Organic Materials Review Institute, Eugene, OR) as a source of N (Table 2). The blend consisted of PuraVida Grow (6–4–4), PuraVida Bloom (2–6–6), and Thrive-Alive (1–1–1), all plant-based products from Technaflora Table 1. Chemical characteristics of the composts used in the experiments. Characteristic Units Yard waste Swine Mushroom Electrical conductivity (mS cm) 2.78 13.4 2.92