Effect of Clay, Soil Organic Matter, and Soil pH on Initial and Residual Weed Control with Flumioxazin

Calvin F Glaspie,Wesley J Everman,Donald Penner,Eric A L Jones,John A Pawlak

doi:10.3390/agronomy11071326

Abstract

Greenhouse studies were conducted to evaluate the effects of soil organic matter content and soil pH on initial and residual weed control with flumioxazin by planting selected weed species in various lab-made and field soils. Initial control was determined by planting weed seeds into various lab-made and field soils treated with flumioxazin (71 g ha−1). Seeds of Echinochloa crus-galli (barnyard grass), Setaria faberi (giant foxtail), Amaranthus retroflexus (redroot pigweed), and Abutilon theophrasti (velvetleaf) were incorporated into the top 1.3 cm of each soil at a density of 100 seeds per pot, respectively. Emerged plants were counted and removed in both treated and non-treated pots two weeks after planting and each following week for six weeks. Flumioxazin control was evaluated by calculating percent emergence of weeds in treated soils compared to the emergence of weeds in non-treated soils. Clay content was not found to affect initial flumioxazin control of any tested weed species. Control of A. theophrasti, E. crus-galli, and S. faberi was reduced as soil organic matter content increased. The control of A. retroflexus was not affected by organic matter. Soil pH below 6 reduced flumioxazin control of A. theophrasti, and S. faberi but did not affect the control of A. retroflexus and E. crus-galli. Flumioxazin residual control was determined by planting selected weed species in various lab-made and field soils 0, 2, 4, 6, and 8 weeks after treatment. Eight weeks after treatment, flumioxazin gave 0% control of A. theophrasti and S. faberi in all soils tested. Control of A. retroflexus and Chenopodium album (common lambsquarters) was 100% for the duration of the experiment, except when soil organic matter content was greater than 3% or the soil pH 7. Eight weeks after treatment, 0% control was only observed for common A. retroflexus and C. album in organic soil (soil organic matter > 80%) or when soil pH was above 7. Control of A. theophrasti and S. faberi decreased as soil organic matter content and soil pH increased. Similar results were observed when comparing lab-made soils to field soils; however, differences in control were observed between lab-made organic matter soils and field organic matter soils. Results indicate that flumioxazin can provide control ranging from 75–100% for two to six weeks on common weed species.

Highlights

Interactions between a soil-applied herbicide and soil medium are complex
Herbicide adsorption in soil is often evaluated by deriving a Kd value, a measure of the amount of herbicide in solution to herbicide adsorbed to soil particles [2]
Flumioxazin control varied by soil characteristics and weed species (Table 2)

Summary

Introduction

Interactions between a soil-applied herbicide and soil medium are complex. A relative equilibrium is reached soon after the application of a herbicide to soil [1,2]. The portion of herbicide that is not sorbed to the soil particle surface is generally considered available for weed control [3,4]. The amounts and types of particles in the soil and the soil’s pH can greatly affect herbicide adsorption. A Kd value is often adjusted for soil organic matter (SOM) due to the magnitude of its role in herbicide binding [2,5,6]. Soil organic matter can differ greatly in functional group type and abundance, depending on the origin of the SOM, soil pH, climate, and the microbial community [7,8]. Soil organic matter is not the sole sorbent for many herbicides. Due to their net negative charge, can interact with herbicides in many ways. Clay is reported as the major adsorption surface for certain herbicides [5]

Methods

Results

Conclusion