Allelopathic Effects Of Wheat Straw Mulch On Maize (Zea Mays L.) Seedling And Weeds In No-till Systems

Trials were conducted in laboratory, green house and field in Beijing region to identify and quantify the allelochemicals and to study the change of their concentrations in wheat straw leachate (WSL) and soil under wheat straw mulch (WSM). The joint action of wheat allelochemicals was also studied. Efficacy of cultural measures to eliminate the negative effect of allelopathy of wheat straw on early growth of summer maize (Zea mays L.) and to enhance weeds control was discussed.The WSL inhibited significantly the growth of seedlings of maize and several predominant weeds in summer maize in Beijing region, namely, crabgrass (Digitaria sanguinalis (L.) Scop), barnyardgrass (Echinochloa crus-galli (L.) Beauv), redroot pigweed (Amaranthus retroflexus L.) and velvetleaf (Abutilon theophrasti Medic). Organic acids in WSL with phytotoxicity to maize seedling growth was identified by HPLC as phenolic acids including p-hydroxybenzoic acid (p-HBA), vanillic acid (VA), cinnamonic acid (CA) and ferulic acid (FA). The concentrations of phenolic acids varied with extraction temperature and time. The same phenolic acids were identified and quantified in the no-till soil in rotations of wheat-maize.The phenolic acids affected root growth of maize and crabgrass (D. sanguinalis). The inhibition of maize was less than of crabgrass at the same concentration. Joint actions of binary mixtures of four phenolic acids were mostly antagonistic response on perennial ryegrass (Lolium perenne L.) and additive or synergistic response on field forgetmenot (Myosotis arvensis (L.) Hill).The responses of various maize cultivars were significant difference on interaction of length and amount of WSM. Either mulching or soil-incorporated of wheat straw influenced early growth of maize at 5mm or 10mm precipitation.Results of field trails indicted that germination of maize seeds was reduced observably with WSM in no-till system of wheat-maize rotations. 9000kg·hm^-2 WSM reduced maize plant height, root number and leaf area, even though added nitrogen into the soil. To add 195kg N·hm^-2 in 4500kg·hm^-2 WSM plot improved maize seedlings growth, increased root number, leaf area and dry weight of plant shoot.Weeds were suppressed significantly by WSM. Adding 195kg N·hm^-2 with 4500kg·hm^-2 WSM increased inhibition on weeds. Contents of phenolic acids in soil with WSM were under the critical concentration for maize damage. Allelopathic efficacies of wheat straw were affected by maize cultivars, wheat straw length, precipitation and placement of wheat straw.