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ARS Home » Plains Area » Lubbock, Texas » Cropping Systems Research Laboratory » Wind Erosion and Water Conservation Research » Research » Publications at this Location » Publication #333183
Title: Soil microbial communities as affected by organic fertilizer and sunn hemp as a cover crop in organic sweet pepper production in Puerto Rico

Author
item NEGRETE, ANA - University Of Puerto Rico
item VALENCIA-CHIN, ELIDE - University Of Puerto Rico
item Acosta-Martinez, Veronica

Submitted to: Journal of Agriculture of the University of Puerto Rico
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic production in Puerto Rico is at an early stage and research is needed to validate the sustainability of different management practices. The soil microbial component has been used as early indicators of shifts in soil quality/health, however, to our knowledge information is lacking on the soil microbial component under organic production in Puerto Rico. This research initiated evaluation of selected soil properties including the microbial communities in order to evaluate the effects of Tropic sunn (Crotalaria juncea) as a cover crop and a commercial fertilizer on soil quality under an organic sweet pepper production system. The study was conducted at the Agricultural Experimental Station of Lajas, University of Puerto Rico under a Vertisol during one growing season, starting on April 2012. Soil samples were analyzed with two methods available to characterize the microbial community structure of soils [high throughput phospholipid fatty acid (PLFA) and the ester-linked (EL-FAME) extraction] according to the relative abundance of bacterial (i15:0, a15:0, i17:0, a17:0, cy17:0, cy19:0) and actinomycetes (10Me16:0, 10Me17:0, 10Me18:0) vs. AMF (16:1'5c) and saprophytic fungal (18:2'6c) FAMEs. ANOVA revealed no significant effect of cover crop and N fertilization rates on FAME markers for different microbial groups or in the microbial community size (according to total FAMEs). Although, it was not possible to compare thoroughly the two methods (PFLA and EL-FAME) due to lack of significant differences among treatments, this study elucidated three important findings: i) the arbuscular mycorrizal fungal (AMF) indicator (16:1w5c) showed similar abundance with both methods; (ii) the fungal:bacterial (F:B) ratios were also similar with both methods, and (iii) the PCAs from both methods showed a trend of separation in the microbial community structure of the cover crop vs. no cover crop. This trend of early shifts in microbial community structure due to cover crops is of ecological significance due to potential future benefits on biogeochemical cycling in this soil under organic farming. The selected soil properties evaluated in this Vertisol can provide background data to establish a soil quality index under organic farming production.

Technical Abstract: Organic production in Puerto Rico is at an early stage and research is needed to validate the sustainability of different management practices. This research initiated evaluation of selected soil properties including the microbial communities to evaluate the effects of Tropic sunn (Crotalaria juncea) as a cover crop and a commercial fertilizer on soil quality under an organic sweet pepper production system. Our long-term goal is to increase information on the soil microbial component under agroecosystems in Puerto Rico. The study was conducted at the Agricultural Experimental Station of Lajas of the University of Puerto Rico under a Vertisol during one growing season, starting on April 2012. The field experiment was a randomized complete block design with four replications of a 2x4 factorial arrangement of treatments. Treatments were cover crop and no cover crop, and four N fertilization rates [(0, 56, 112 and 168 kg N ha-1; supplied by a commercial fertilizer (6-6-5)]. Soil samples were analyzed using a high throughput phospholipid fatty acid (PLFA) and the ester-linked (EL-FAME) extraction procedures to characterize the microbial community structure according to the relative abundance of bacterial (i15:0, a15:0, i17:0, a17:0, cy17:0, cy19:0) and actinomycetes (10Me16:0, 10Me17:0, 10Me18:0) vs. arbuscular mycorrizal fungal (AMF,16:1'5c) and saprophytic fungal (18:2'6c) FAMEs. ANOVA revealed no significant effect of cover crop and N fertilization rates on FAME markers for different microbial groups or in the microbial community size (according to total FAMEs). Although, it was not possible to compare thoroughly the two methods (PFLA and EL-FAME) due to lack of significant differences among treatments, this study elucidated three important findings: i) the (AMF) indicator (16:1w5c) showed similar abundance with both methods; (ii) the fungal:bacterial (F:B) ratios were also similar with both methods, and (iii) the PCAs from both methods showed a trend of separation in the microbial community structure of the cover crop vs. no cover crop. This trend of early shifts in microbial community structure due to cover crops is of ecological significance due to potential future benefits on biogeochemical cycling in this soil under organic farming. The selected soil properties evaluated in this Vertisol can provide background data to establish a soil quality index under organic farming production.