Blade specifications for strip-tillage on excessively moist clay soils in Southern Bangladesh
Intesifiying cropping on fallow lands during southern Bangladesh’s dry winter season is challenged by predominantly clay soils that retain excess post-monsoon season soil moisture. Use of convetional machinery to repetitively till and manually establish crops can delay dry season sowing by days or weeks, precluding timely crop esblishment and exposing crops to late-season soil salinity, terminal heat, flash floods, and other risks. Two-wheeled tractors with attachable rotavators are used for strip-tillage by removing some of the tillage blades which allows rapid single-pass strip-till furrow formation and crop establishment. Current practice of using commercially available bent or straight C blades operated at the depth of 50-60 mm however results in either excessive soil throwing (with bent blades) or an incomplete furrow (with straight bladeds) in the excessively moist clay soil condition. Both result in poor seed coverage, increased seed predation, reduced germination and suboptimal plant stands. This study aimed to improve seedbed furrow quality in the most clay soils (moisture content of 28.2%, bulk density 1.44 gcm-1). We tested (4 blades/row providing a cutting width of 50 mm and rotor diameter of 342 mm) were operated at 470 rpm and forward speed of 0.4 ms-1. Both blade desing and operating depth significantly affected seedbed furrow depth, width, bacfill (loose soil remaining in the furrow after strip-tillage), and production of optimum clods (1-20 mm) and unwanted fines (<1 mm.) While none of the blades could produce enough backfill at the cutting depth of 50 mm, use of grater depths produced sufficient backfill only in case of the straight blades. Irrespective of the cutting depth, the all the blades produced a high percentage of optimum clods, but a low percentage of lines. We consequently recommended use of straight blades (slightly longer to provide a rotor diameter of 420-450 mm) and an operating depth of 75-100 mm so that the rotor or blade holders do not touch the ground or hinder residue flows.