Indoor Organics: Soil Nutrient Profiles in Organically Fertilized Greenhouse Media.

Most organic fertilizers are designed for outdoor field production.  As organic agriculture becomes increasingly widespread, more growers are producing organically indoors.  It is not well understood how these fertilizers behave in greenhouse settings.  This study took three common winter greenhouse crops and four widely available organic fertilizer options and evaluated soil properties and crop yield.  Arugula (Eruca sativa), mizuna (Brassica rapa var. nipposinica), and red giant mustard (Brassica juncea) were grown separately in 11 by 22 inch flats under 24°C days and 13°C nights with an 18 hr photoperiod.  Treatments were replicated three times, and the experiment was run twice.  The organic fertilizers used were fish emulsion (Drammatic 2-5-0.2 on Sunshine Natural and Organic Potting Mix), poultry litter (Sustane 8-4-4 on Sunshine Natural and Organic Potting Mix), a commercially available “all in one” potting mix (Purple Cow Potting Mix 0.5-0.2-0.4), and a custom blend used by organic winter greenhouse growers (peat, vermiculite, leaf litter compost, greensand, rock phosphate, blood meal, and lime), in addition to a conventional comparison (CalMag 15-5-15 on SunGro LC8 potting mix).  Fertilizer rates were calculated based on field recommendations for nitrogen in low organic matter soils for each crop. The “all in one” potting mix and the organic winter greenhouse blend exceeded nitrogen recommendations.  Media samples were collected at planting and at harvest, and plant samples were collected at harvest.  The plant samples were analyzed for yield and the plant and media samples were analyzed for nutrient content including N, P, K, Fe, Ca, Mg, Na, Mn, Zn, Cu, Mo, and B.  The treatments varied widely in soil nutrient content.  Yield was significantly affected by treatment (p<0.001) and ranged from a low of 37.98 g per container of arugula with fish emulsions to a high of 229.52 g per container of mizuna with “all-in-one” potting mix.