Wheat straw placement effects on total phenolic compounds in soil and corn seedling growth

The effects of placement of wheat (Triticum aestivum L.) straw on the release of phenolic compounds potentially phytotoxic to corn (Zea mays L.) seedling growth were examined in plastic pots under controlled conditions in growth cabinets. The treatments were soil only (control), soil with straw only in the top 2.5 cm, and soil with mixed straw. Each of these treatments was either sown or not sown with corn. Corn radicle length and seedling biomass were significantly reduced, relative to other treatments, when wheat straw was present only in the top layer of soil. Water extracts from soil with surface straw had higher amounts of total phenolic compounds than the other treatments at each of the sampling times. The concentration of phenolic compounds increased with time, with average amounts at 14 and 28 d being 53 and 77%, respectively, of the concentration at 42 d. The presence of corn reduced the amount of phenolic compounds at 14 and 42 d compared with when corn was absent (P = 0.01). Water extracts prepared from soil after 42 d from all the treatments were used to investigate germination of com seeds. Germination of corn seeds and radicle extension were inhibited by water extracts from all the above soils at 42 d compared with the control (deionized water). Coleoptile length was inhibited when concentration of phenolic compounds exceeded 10 ppm. Soil NO3-N differences among the treatments were insignificant at the various sampling times. This indicated that the observed corn growth differences were mainly due to the presence of phenolic compounds.