Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Abstract

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan ( Carya illinoinensis ) orchards in the US southwestern region. Given the paucity of data regarding indaziflam's impact on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effect of different application rates of indaziflam on soil microbial activity, diversity and biochemical processes related to nitrogen cycling. During 2 consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown, and that were treated with indaziflam applied at 2 different rates (25 and 50 g ai ha -1 ). Soil samples were collected one week before and one week after herbicide application, and used for determination of soil microbial biomass, microbial diversity, nitrogen (N) mineralization and β-glucosaminidase enzyme activity. Soil samples collected from control mesocosms were treated in the laboratory with 2 rates of indaziflam (75 and 150 g ai ha -1 ) to determine immediate impact on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. Results showed a slight to moderate decrease in microbial diversity (7 % in 2015, 44 % in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed with soils from the mesocosms (33% decline) and soils treated with indaziflam in the laboratory (45 % decline). The mineral N pool was generally dominated by NH 4 + after indaziflam application, an observation consistent with the drastic decrease (75 %) in nitrification activity measured in the laboratory experiment. This study results indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on total soil microbial activity but could affect N cycling processes.