Cultivation effects on the dynamics of a Johnson grass seed population in the soil profile

Abstract

The effect of maize and wheat cultivation on a Johnson grass ( Sorghum halepense (L.) Pers.) seed population, and its vertical distribution in a 20-cm soil profile was evaluated from autumn to early spring. The experiment was carried out in plots with 2 different types of seed-banks: 1. (A) with 1 generation of seeds distributed on the surface of the soil; 2. (B) with 2 generations of seeds, 1 buried and the other distributed on the surface of the soil. The wheat system had one tilling operation in April with a mouldboard plough and rotary cultivator and another one in August, before sowing, with the rotary cultivator only. The maize system had 2 tilling-operations with a mouldboard plough and rotary cultivator; the first one in April and the second one in October, before sowing. Treatments were a combination of cultivation systems and seed-bank types. A significant seed loss was detected only in those plots under the maize cultivation system with 2 generations of Johnson grass seeds. Tilling with the mouldboard plough and rotary cultivator significantly changed the vertical pattern of seed distribution. No appreciable modification was observed after cultivation with the rotary cultivator alone. The mouldboard plough appeared to be more efficient at burying seeds (ca. 80%) than at bringing them to the surface (ca. 38%). In the maize crop system, after sowing, there was a significantly greater number of full florets (25%) in the 0–4-cm layer, in relation to the total in the soil profile, than in the wheat crop system (7%). Ecological implications of these cultivation methods on Johnson grass seed dynamics are discussed.