Date of Award


Degree Name

MS in Agriculture - Crop Science


Horticulture and Crop Science


Dr. John Phillips



Effects of Compost, Legume Cover Cropping and Vermicompost Extract Foliar Applications on Nutrition and Yield of Washington Navel Oranges

William Payton Carling

An experiment was conducted to test the effects of four treatments on Washington navel orange (Citrus sinensis) trees in regards to nutrient content of the leaves and fruit, soil nutrient content and properties, and fruit yield. The four treatments included: compost (C) and vermicompost extract foliar (VEF) applications, legume cover cropping (LCC) and VEF applications, VEF applications, and a control. The treatments were implemented from February 2010 to April 2011 and sampling occurred in May 2011. Fruit Growers Laboratory, Inc. (FGL) conducted the soil, leaf, and fruit analyses. The test site was located in San Isidro, Baja California Sur, Mexico.

The compost used was made onsite with livestock manure, carbon-based farm waste, and water, and applied around the drip-lines of 8 WNO trees once every two months. The vermicompost and vermicompost extract was made onsite by introducing red wiggler worms (Eisenia fetida) into horse manure, allowing 1 month for casting content to build up, and collecting the extract as water was filtered through the material. Vermicompost extract was applied using a backpack foliar sprayer on 8 WNO trees twice a month. The legume cover crop treatment consisted of two plantings at a rate of approximately 72 seeds per square foot around the drip-lines of 8 WNO trees. Black-eyed peas (Vigna unguiclata) were planted in April 2010 and minimally incorporated using a hoe and shovel in August 2010. Fababeans (Vicia faba) and dry peas (Pisum sativum) were planted in January 2011 and minimally incorporated into the soil in March 2011. WNO leaf and soil analyses were compared to FGL optimum ranges.

The C+VEF treatment showed trends of increased soil and leaf nitrogen, phosphorus, potassium, calcium, zinc, and copper levels and improved soil properties by raising soil organic matter percentage, saturation percentage, and moisture percentage. The control treatment had low or deficient values in these nutrients and soil properties. The LCC+VEF treatment increased nitrogen in the soil and leaf content but decreased organic matter percentage. The VEF treatment increased nitrogen and potassium content in the leaf but increased sodium beyond FGL optimum range. The C+VEF treatment had the highest yield and the greatest amount of nutrients removed as a result of yield. The C+VEF treatment had more available nutrients in the soil for WNO tree uptake and future crops.

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