Bioactive Compounds in Selected Cover Crops Grass and Their Potential Effect On Weed Control.

Abstract

Synthetic herbicides are widely used for weed control in conventional agricultural systems. Although considered as most effective and time saving approach, the wide spread use of synthetic herbicides has long lasting effects on our food production systems and the general environment due to their residual effects. Public pressure to reduce the use of synthetic pesticides including herbicides has considerably increased in recent years parallel to an increasing number of health sensitive food consumers. Organic farming provides an alternative choice for health sensitive consumers.  The use of cover crops in a form of hay/dry grass mulch provides an alternative to application of herbicides for weed control in organic farming. Cover crops harvested and belled as hay before seed setting are used to cover open spaces purposely to suppress weed growth by depriving them from light supply. In addition to shading effect on weed seeds and seedlings, bioactive compounds in the form of secondary metabolites released from cover crop biomass upon decomposition could have broader effects both positive and negative on weed growth. Such effects may include phytotoxicity, root growth regulation, antimicrobial, moisture retention and nutrient transformation effects in the soil. This study investigated the contents of total flavonols, total phenols, chlorophylls, tannins and lipids in four cover crop grass species namely Black oat, Rye grass, Triticale and Geogia gore. Initial results indicate that contents of these compounds vary between plant species and different parts of the same plant. Black oat had the highest contents of flavonoids in above ground parts (4.5µg/ml), while rye grass recorded the highest contents in whole plant samples 4.38µ/ml followed by Triticale 3.66µg/ml and lastly Geogia gore 2.76µg/ml. Bellow ground plant parts of all plant species had the lowest contents of flavonoids (1.27, 1.19, 0.59 and 1.43µ/ml for Black oat, Rye grass, Triticale and Geogia gore respectively. Phenols in all plant species followed similar trends as flavonoids, while chlorophyll a was highest in Black oat sample (13.04µg/ml), followed by Triticale (7.99), Geogia gore (7.70) and lastly, Rye grass (7.17) µg/ml) respectively. Contents of chlorophyll b were highest in Black oat followed by Geogia gore, Triticale and lastly Rye grass. Observed variations in contents of these compounds could have significant effects on their suitability for use in weed management and soil amendment hence a need for understanding their fate in the soil.