SOIL COMPACTION BY MANURE SPREADERS EQUIPPED WITH STANDARD AND OVERSIZED TIRES AND MULTIPLE AXLES

A study was conducted on a heavy clay soil to evaluate soil compaction induced by different traffic treatments associated with liquid manure spreader systems. Five spreader weights (from 96 to 218 kN), two runn ing gears (tandem and tridem, i.e., three axles) and two types of tire (conventional low section tire and oversized tire) were combined to o btain six traffic treatments, representative of liquid manure spreadin g operations in Quebec. Soil dry bulk density (rho(b)) and cone index (CI) were measured to evaluate compaction. Tire rut depths and the lat eral influence zone were also investigated in the study. For a single pass of a spreader soil compaction was confined to the tilled layer (a bout 0-250 mm depth) regardless of traffic treatments, and this did no t affect emergence rates and yields of soybean under the particular so il and climate conditions that prevailed at the time of the study. Nei ther tandem nor tridem running gears were found to adequately contain soil compaction within the tilled layer for total spreader weights exc eeding 154 kN. The acceptable limitation for a tandem spreader with co nventional 21.5L-16.1 tires would be a total load of about 96 kN, resu lting in average ground pressures of 150 kPa or less. If medium capaci ty spreaders are required, oversized tires are recommended for manure spreading on prairies or post-seeding applications on small grain crop s. Finally, the recourse to multiple-axle running gears for larger spr eaders to maintain or reduce unit load per axle or ground pressure doe s not result in less soil compaction than lower capacity tandem spread ers with comparable axle loads and ground pressure.