Weed control efficiency of reduced atrazine doses and its effect on soil organisms in maize (Zea mays L.) fields of south western Nigeria

Two field experiments were conducted to assess the weed control efficiency of four graded doses of atrazine (100, 75, 50, and 25% of the recommended dose of 2.5 kg-a.i. ha-1) and hoeing (control) as well as its effects on soil biota. Although the highest weed control efficiency was achieved with full dose of atrazine, there was no significant (p = 0.05) difference between this and the lower rates. The lower doses, however, were superior to hoe weeding. Differences in maize yields were also not statistically significant, implying the economic advantages of using 25% recommended dose. Response of soil organisms to atrazine doses varied with organisms. Significantly (p = 0.05) higher earthworm population was observed in the 0, 25, and 50% doses compared to 75 and 100%. The highest number of worm cast (9.90) was obtained in the control while the least (3.47) was for the 100% recommended rate. Similarly, bacterial population was inversely related to atrazine rates with the highest values for the control (290 x 106 cfu-g-1) and the least in the 100% recommended rate (29 x 106 cfu-g-1). Fungi and ascomycetes, however, showed a reverse trend.