Seaweed extract, fish emulsion, and soybean meal (SBM) are United States Department of Agriculture (USDA) National Organic Program (NOP) allowed substances used by organic vegetable growers as fertilizers. Soil applied SBM and foliar applied seaweed, fish, fish/seaweed, 20-20-20, and a water control were tested on field-grown sweet peppers, broccoli, and lettuce to determine their effects on plant nutrition and crop yield.The SBM was applied at three rates: 0, 2466, and 4932 kg.ha-1 (0, 2200, and 4400 lb.acre-1).To test the duration of the SBM as a soil fertilizer, peppers, broccoli, and lettuce were grown in succession on the same beds after the initial SBM application.The foliar fertilizers were also tested on peppers on a certified organic farm for comparison to the research station study.In 2002, transplanting one day after SBM application caused fertilizer burn to the pepper roots.In 2003, peppers were planted one week after SBM application without harm to plant roots.SBM positively increased the nutrient level and yield of broccoli in 2002 and peppers in 2003.Lettuce yield was not affected by the SBM treatments because the previous pepper and broccoli crops had likely exhausted the SBM fertilizer.The foliar sprays did not affect plant nutrient levels or yields in any crop at either location.Greenhouse studies were conducted to investigate the effect of SBM on germination and growth of eight common vegetables.Treatments included five rates of SBM: 0, 1093, 2186, 3279, and 4372 kg.ha-1 (0, 975, 1950, 2925, and 3900 lb.acre-1) and two application methods: surface applied (SA) and incorporated (IN) into the media.For all vegetables combined, at applications of 1093 and 2186 kg.ha-1 IN SBM, shoot weight increased by 20% and 10%, respectively, compared to the unfertilized control.At the same rate of SA SBM, shoot weight was reduced by 6% and 18% respectively.At all rates of SA SMB, shoot weight was more reduced in small seeded vegetables (spinach, lettuce, carrot, and radish) than in large seeded vegetables (squash, cucumber, bean, and pea).At 3279 and 4372 kg.ha-1 of IN SBM, shoot weight of small seeded vegetables was reduced by 8% and 46%, respectively.The EC and pH of the media increased with increased rates of SBM and were greater with SA SBM than with IN SBM.Levels above pH 6.5 and EC 1.0 dS.m-1 were measured on day 7 for media at all SBM rates.These levels could be inhibitory to germinating seeds.Because SBM reduced growth of small seeded vegetables, it is not recommended that small seeded vegetables be surface fertilized with SBM or that they be sown directly into soil where SBM has been recently incorporated.SBM incorporated at low rates (<2186 kg.ha-1) could prove to be a useful fertilizer for large seeded crops without concerns of inhibition by SBM.Field studies were conducted to investigate the optimal rate and timing of SBM fertilization in plasticulture sweet pepper production.SBM was applied at three rates: 0, 2421, and 4842 kg.ha-1 (0, 2165 and 4330 lb.acre-1).Sweet peppers were then transplanted at four intervals following SBM incorporation and black plastic application: one day, three days, seven days, and fourteen days.Growth was initially inhibited in peppers planted into the high rate of SBM less than one week after incorporation.By the end of the season, these peppers had recovered and had a biomass greater than the unfertilized control.Peppers fertilized with the low rate of SBM did not suffer an initial inhibition and had the highest yield of marketable peppers at all planting times.This study suggests a moderate rate of SBM should be applied at least two weeks before the intended planting date.
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The Use of Marine Derived Products and Soybean Meal as Fertilizers in Organic Vegetable Production
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