Abstract

Alternative fertilization practices, such the use of vermicompost (VC), have shown great potential to improve both the physical and biological attributes of soils and supplement the nutrient status of soils to improve fertility for vegetable crop production. Modification of soils with coffee vermicompost (CVC) has the potential to improve soil organic content, structure, and microbial activity. Generally, organic fertilizers with slow release nutrient capabilities efficiently use nitrogen and reduce nitrate levels in leafy green vegetables and have been shown to increase ascorbic acid (AA) content. A greenhouse study was conducted over two growing seasons (2011 and 2012) to assess the influence of four CVC rates (0, 25%, 50%, and 75% v/v of soil mix) on Spinacia oleracea growth parameters including fresh leaf weight, leaf area, plant height, leaf number, fresh leaf ascorbic acid (AA) and dry leaf nitrate (DLN). Spinach leaf number and fresh leaf weight increased with CVC rate for both growing seasons and were best described by increasing linear relationships. Surprisingly, spinach AA content remained the same whether DLN content was high or low; and AA and nitrate content were both at highest levels with the 75% v/v CVC treatment in both years. These results indicated that applications of an alternative fertilizer such as CVC can improve spinach yield and that AA content does not always decrease with higher VC application rates, even as nitrate content increases.

Keywords: Ascorbic acid; Coffee vermicompost; Leaf nitrate; Organic agriculture