Influence of soil tillage on red rice emergence

Fourteen field experiments were conducted in rice growing area, five in 1995 and nine in 1996 to investigate the influence of tillage types for the seed preparation on red rice (Oryza sativa L. var. sylvatica) seedling densities. In each experiment three tillage treatments were compared: mouldboard ploughing 20 cm deep, harrowing 8-10 cm deep and no tillage. For each type of tillage red rice emergences were put in relation to seed reserves determined in the 0-10, 10-20 and 0-20 deep layers. Seed bank in the 0-10 cm layer resulted the most appropriate to determine seedling emergences both for ploughing and minimum tillage. For both tillage systems seed reserves and emergences showed a linear relationship. In average the emergence percentages were 2.5% in ploughed soils and 7.2% in harrowed soils. Emergences of seedlings counted in no-tillage soils did not fit a unique regression equation as they had a percentage of emergences ranging from 3% to 66% of the seed bank.