Does Salinity Enhance Allelopathic Effects of Tribulus terrestris L. in Citrullus Vulgaris Schrad. Agroecosystems at Nobaria, Egypt? Experimental Investigation

Field observations in summer season at year 2013 showed that growth and yield of Citrullus vulgaris at Nobaria district, Egypt was highly affected by some unidentified stressful conditions. Presumably, the problem was confined considerably to the two combined factors; soil salinity and suppressive effects of Tribulus terrestris (a common weed dominant in C. vulgaris fields in the study area). Weeds are considered as an integral part of the natural and agroecosystems and its allelopathic activity has been suggested to be part of their success. Field and laboratory experiments were carried out to confirm the preceding hypothesis. The interaction between the two factors was found to be harmful to C. vulgaris plant. Field experiment revealed that phytomass and leaf area index (LAI) of the study plant were significantly reduced in the vicinity of T. terrestris (poor weed management) than in good weed management. Likewise, in laboratory test the interaction between both salinity and allelochemicals watery extracted from T. terrestris plant severely affected germination efficiency, hypocotyl-radicle length and germination index of C. vulgaris compared to the effect of just one factor. In conclusion, T. terrestris had a considerably suppressive effect on the growth and yield of C. vulgaris, which was increased under slight or moderate salinity. Importantly, weed management in desert agro- ecosystems is an essential strategy to avoid a wide array of interactions between crop-weed from one side and weed- external climatic and edaphic factors from the other side.