Study Of Dormancy Mechanism And Emergence Model About D.Sanguinalis And A.Retroflexus Seeds

Weed germination is influenced by many factors, especially by soil temperature, water content, pH, texture and the depth where seeds are located. At present, reliable models about predicting weed germination are few. A series of experiments were conducted in a green-house of the China Agriculture University from 2002 to 2004 to build emergence models of Digitaria sanguinalis and Amaranthus retroflexus and understand their dormancy mechanics. The result indicated that, for the emergence of these two weed species, the most suitable temperature range was 30-40℃. The lowest soil water content for the emergence of both weed species was 20%. The suitable soil water content was 80% for D. sanguinalis and 60% for A. retroflexus. The models of the emergence rate (E) of Digitaria sanguinalis and Amaranthus retroflexus regarding to temperature (T), water content (W), and day (D) were E = 40.50847(1 - 8.83exp((- 40.9513 + 0.5863w +7.9515T - 0.0031W2- 0.3448T2- 0.0772WT + 0.0045T3+ 0.0004W2*T + 0.0003W*T2)*day)) and E = 6.25887(1 - 3.48exp((-38.8623 + 0.5826W + 8.2626T - 0.0029W2 - 0.2988T2 - 0.0882WT + 0.0089T3 + 0.0006W2*T - 0.0006W*T2)*D)), respectively.The emergence rates of D. sanguinalis and A. retroflexus decreased as seed depth increased in all soil types. Maximum depth of D. sanguinalis and A. retroflexus emergence was 5 cm in loam soil, 6 cm in sandy soil, and 6 cm in clay soil. Emergence rate of both weed species in sandy soil was higher than in loam soil and clay soil.The model of A. retroflexus emergence rate and seed depth (L) in loam, sand, clay soils were E = 9.8889L - 10.2587L2+ 1.0581L3+ 74.3581, E = 9.1706L - 7.1764L2+ 0.6313L3 + 70.1212, and E = 76.9091 - 23.7222L + 0.9924L2 + 0.1237L3, respectively. The models of D. sanguinalis emergence rate and seed depth in loam, sand, clay soils were E = 8.6689L - 9.8988L2 + 2.0586L3 + 76.2585, E = 10.8958L-8.1865L2+ 1.0813L3 + 72.1846, and E= 10.8958L-8.1865L2+ 1.0813L3 + 72.1846, respectively.A. retroflexus preferred to weak acid circumstance, while D. sanguinalis to neutral circumstance for germination. Both weed species had higher germination rate in low light intensity than in high light intensity.When non-dormant seeds of D. sanguinalis and A. retroflexus were placed in soil where conditions were not suitable for their germination, they became the second dormancy. The content of growth promoting hormones 1AA GA3, ZR, and Z decreased and growth inhibitory hormone ABA increased as the seed depth increased in soil. Germination rate of maturity seeds collected both weed species increased as storage period increased because the content of the growth promoting hormones increased and the growth inhibitory hormone decreased with time. Electric conductivity of dormant seed is higher than that of non-dormant seed.