Seedling emergence under no-till conditions from increasing seed burial depth.

The adoption of conservation agriculture can produce several economic and environmental benefits but implies modifications in terms of crop management. Weed control is a crucial aspect and, as mechanical control is limited or absent, dependence on herbicides increases especially during the transition from conventional to conservation tillage systems, because seeds of arable weed species remain viable in the soil while species adapted to no-till regimes simultaneously start to spread. The different arable weeds could present diverse adaptive ability to emerge under the conditions of no-till systems according to their specific biological and ecological characteristics. Information on the emergence dynamics of arable weeds during the transition period from inversion tillage to no-till conditions could contribute to the development of effective IWM strategies. Two field experiments were conducted at Legnaro (Padova, Italy) to evaluate the ability of five troublesome arable weeds to emerge from increasing depths (1, 2, 5 and 10 cm) over a two year period of burial in simulated no-till conditions. The studied species were Setaria viridis (L.) Beauv. Sorghum halepense (L.) Pers., Digitaria sanguinalis (L.) Scop., Amaranthus retroflexus L. and Abutilon theophrasti Medik. Two hundreds seeds per replicate were sown on November 2006 and 2007 and there was no further soil disturbance throughout the duration of the experiments. Emerged seedlings were weekly counted and removed from March to the end of August for the two years following each sowing. Since no significant effect of the factor “experiment” was detected, data of the two experiments were pooled. Seedlings mainly emerged during the first year after sowing and from depth of 1 and 2 cm. The inhibiting effect of increasing burial depth on seedling emergence varied among the different species with stronger effect on small-seeded species. The only exception was A. theophrasti, the largest-seeded species, which presented a notable depth-mediated emergence inhibition with total emergence of 10.9 % ± 1.20 SE from depth of 5 cm and no emergence from 10 cm. Sorghum halepense was the least affected species by burial depth, even emerging from a depth of 10 cm and having the highest total seedling emergence (42.8 % ± 4.86 SE). Amaranthus retroflexus was instead highly affected by burial depth, with no emergence from depths of 5 and 10 cm and the lowest total seedling emergence (10.0 % ± 2.71 SE). Differences in emergence percentage as affected by burial depth and no-till conditions were obtained among species, showing their diverse adaptive ability to these specific environmental conditions. The lack of stimuli (light, oxygen, temperature fluctuation) required by buried seed for dormancy break and germination has been reported as a possible cause of depth-mediated inhibition of seedling emergence under no-till conditions. Analyzing how no-till conditions influence affect dormancy cycle of buried weed seeds could facilitate the creation of effective IWM strategies for the transition period from conventional to conservation tillage systems.