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CHARACTERIZING PILIGRASS (HETEROPOGON CONTORTUS) AS LIVING MULCH FOR TROPICAL VEGETABLE CROPS

Masters of Science thesis and oral defense seminar of Melinda Moata

ABSTRACT

An experiment was conducted in Hawai’i during spring 2008 to fall 2009 to examine the response of cabbage (Brassica oleracea var. capitata) and zucchini (Cucurbita pepo L.) in a native Heteropogon contortus (piligrass) living mulch (LM) system and compare it to a conventional bare ground (BG) system. B. oleracea var.capitata was planted in two different seasons, fall 2008 and spring 2009. It was rotated with C. pepo L. in winter 2008 and summer 2009. The study consisted of field a experiment and laboratory analyses for plant and soil. Data was collected for weed control, insect population, pest and disease damage, crop yield, and soil properties. The results of this study, piligrass LM had: 1) consistently reduced weed biomass up to five times compared to BG, 2) provided habitat for insects, thus it increased total population and biodiversity of insects, and 3) reduced plant and fruit damages due to pests and diseases. Nevertheless, BG yield was five times higher than LM treatment. For the soil analyses, it can be concluded that piligrass as a LM had higher total N (Nitrogen), total C (carbon), and NH₄⁺ (ammonium) with similar level of NO₃^- (nitrate) compared to the BG plots. Furthermore, P (phosphorous), K (potassium), Ca (calcium), Mg (magnesium), and pH in both LM and BG plots were not significant different. Analysis of the phytotoxicity of soil from three tests (germination bioassay, charcoal mitigation of inhibitor, and soil phenolic) did not clearly detect any inhibitory substances in the soil. The piligass LM improved the physical quality of soil by increasing WAS (water aggregate stability), maintaining SM (soil moisture) and reducing surface ST (soil temperature). Therefore, improved understanding about the use of piligrass as a LM is important to advance our knowledge of using LM in tropical agricultural systems.