Negrete-Aveiga, Ana M.

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    Organic sweet pepper yield and soil microbial communities as afected by a commercial organic fertilizer and sunn hemp as a cover crop in Puerto Rico
    (2013) Negrete-Aveiga, Ana M.; Brunner, Bryan; College of Agricultural Sciences; Whitmire, Stefanie; Valencia, Elide; Van Bloem, Skip; Department of Crops and Agro-Environmental Sciences; Chansky, Ricia
    Sunn hemp (Crotalaria juncea) is a legume cover crop that produces large amounts of biomass which, combined with its relatively high nitrogen (N) content and N-fixing capacity, can potentially offset N fertilizer needs by providing nitrogen to the subsequent crops in organic production. This can be economically beneficial if fertilizer inputs are reduced without a yield reduction. This is especially true when organic growers have the need to buy commercial organic fertilizers, and it is more critical in an island like Puerto Rico, where all imports must be shipped in, adding to the cost. Furthermore, the numerous benefits to soil health and the environment contribute to the system’s sustainability. This study was conducted at the Agricultural Experimental Station of Lajas, University of Puerto Rico for two growing seasons, the first one starting in December 2011 (2011 Experiment) and the second one in April 2012 (2012 Experiment). The specific objectives of this experiment were to: 1) determine fruit yield of sweet pepper (Capsicum chinense) as affected by a commercial organic fertilizer (BioFlora Dry Crumbles™ 6-6-5) and the use of sunn hemp as a cover crop; 2) determine the status of the soil microbial community size and structure under cover crop and N fertilization treatments; and 3) assess other soil parameters such as pH, organic matter, and enzyme activity. To evaluate cover crop and N interactions a 2x4 factorial arrangement of treatments was used. No cover crop and cover crop were the two levels of one factor, and 0, 56, 112, and 168 were the four levels of the second factor, which indicated the kilograms of N per hectare (ha) supplied by the commercial fertilizer BioFlora (6-6-5). There was no significant effect of cover crop for both experiments, however, the 2011 Experiment indicated a trend toward reduced yields when the cover crop was used, which could be attributed to sunn hemp’s allelopathic properties. N fertilization did have a significant effect on sweet pepper yields, with 112 and 168 kg N ha-1 the fertilization rates that resulted in the highest yields for the 2011 Experiment with no significant difference between them. In the 2012 Experiment, the 168 kg N ha-1 resulted in highest yield. Differences in N fertilizer needs between experiments could be attributed to different factors such as soil properties, weather conditions (temperature and precipitation) and pest incidence. Regarding soil microbial community size and structure, there were no significant differences found among treatments according to individual evaluation of total FAMEs. However, the principal component analysis (PCA) indicated an early shift in the microbial community structure due to cover crop use. Other studies have demonstrated that soil microbial composition is affected by different management practices which indicate that replicating these experiments could confirm the early differences seen in this study over time. The rest of the soil parameters assessed indicate favorable conditions, even though organic matter content was lower than expected.