Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2002
Publication Date: 11/21/2002
Citation: Chellemi, D. O., Lazarovits, G. 2002. Effect of Organic Fertilizer Applications on Growth Yield and Pests of Vegetable Crops. Proceedings of Florida State Horticultural Society. Interpretive Summary: The supply of quality organic fertilizers has been a limiting factor for Florida organic vegetable growers (Monaghan et al., 1994). This study demonstrated that supplemental use of organic fertilizers can significantly impact marketable yields in a certified organic production farm. Soil pH, NH3, and counts of total fungi were increased at an application rate of 560 kg of N/ha. However, this application rate was phytotoxic to pepper, resulting in stunting and mortality of plants. Furthermore, yield reductions occurred at application rates greater than 310 and 400 kg of N/ha for pepper and tomato, respectively. Phytotoxicity and negative effects on yield could be avoided by delaying the planting date. This study also demonstrated that organic fertilizers can provide benefits to Florida vegetable crop production that extend beyond soil fertility. Control of southern blight, caused by Sclerotium rolfsii, was achieved at application rates below those phytotoxic to the crop and detrimental to yield. In this study, organic fertilizers stimulated microbial activity in the soil by increasing counts of fungi and bacteria. It is possible that the control of southern blight observed in the 2001 tomato and pepper experiments was due to a biological as well as a chemical effect of the organic fertilizer. In the search for alternatives to methyl bromide, studies have indicated that no single chemical or nonchemical tactic is available that will provide the same consistent level of broad-spectrum pest control as methyl bromide and it has been argued that an integrated approach to pest management is needed in the development of alternatives to methyl bromide. By providing multiple horticultural and pest control benefits, organic fertilizers are well suited for use in integrated pest management programs for soilborne pests of fresh market vegetables.
Technical Abstract: Field experiments were conducted to measure the yield response of Cantaloupe (Cucumis melo), pepper (Capsicum annuum), and tomato (Lycopersicon esculentum) to an organic fertilizer derived from hydrolyzed feather, meat, bone, and blood meal, sulfate of potash and langeinite (Nature Safe 10-2-8). The effects on soilborne pests, soil nutrient concentrations, and soil microorganism populations were also determined. The field site had been previously cropped to tomato using conventional production practices and was judged to have low soil fertility. Application of 560 N, 99 P, 448 K (kg/ha) resulted in an increase in soil pH, ammonia concentrations and counts of total soil fungi, but not total soil bacteria. Based on observations of growth, necrosis and mortality an application rate of 448 N, 90 P, 358 K (kg/ha) was phytotoxic to pepper. Phytotoxicity on tomato was observed at an application rate of 1120 N, 198 K, 896 P (kg/ha). A quadratic effect of application rate was observed for yield of pepper (r2=0.83) and tomato (r2=0.98). Optimum yields were projected to occur at 310 N, 27 P, 206 K (kg/ha) for pepper and 400, 36, 266 kg of N, P, and K/ha for tomato. A second location that had been previously cropped to vegetables under certified organic production guidelines and had moderate levels of soil fertility, was used to test the effect on cantaloupe yields. An application rate of 112 N, 10 P, 74 K (kg/ha) of Nature Safe increased early yields as compared to a formulation of dried poultry manure (NOPI 5-4-5) applied at 112 N, 39 P, 93 K (kg//ha) or an unfertilized control. However, final total yields of cantaloupe were similar among the three treatments. The effect of fertilizer rates on emergence of yellow (Cyperus esculuntus) and purple nutsedge (C. rotundus) was erratic with suppression observed at rates phytotoxic to pepper. Reductions in the incidence of southern blight, caused by Sclerotium rolfsii, occurred on tomato and pepper at application rates below the rates required for optimum yields. This study demonstrates that organic fertilizers can provide multiple benefits for Florida vegetable production systems including improving fertility, increasing soil microbial populations, and reducing the incidence of a soilborne disease.