Smart Harrowing—Adjusting the Treatment Intensity Based on Machine Vision to Achieve a Uniform Weed Control Selectivity under Heterogeneous Field Conditions

Roland Gerhards,Marcus Saile,Gerassimos G. Peteinatos,Michael Spaeth,Jannis Machleb

doi:10.3390/agronomy10121925

Abstract

Harrowing is mostly applied with a constant intensity across the whole field. Heterogeneous field conditions such as variable soil texture, different crop growth stages, variations of the weed infestation level, and weed species composition are usually not considered during the treatment. This study offers a new approach to sensor-based harrowing which addresses these field variations. Smart harrowing requires the continuous adaptation of the treatment intensity to maintain the same level of crop selectivity while ensuring a high weed control efficacy. Therefore, a harrow was equipped with a sensor-system to automatically adjust the angle of the harrow tines based on a newly developed decision algorithm. In 2020, three field experiments were conducted in winter wheat and spring oats to investigate the response of the weed control efficacy and the crop to different harrowing intensities, in Southwest Germany. In all experiments, six levels of crop soil cover (CSC) were tested. The CSC determines the balance between crop damage and weed removal. Each experiment contained an untreated control and an herbicide treatment as a comparison to the harrowing treatments. The results showed an increase in the weed control efficacy (WCE) with an increasing CSC threshold. Difficult-to-control weed species such as Cirsium arvense L. and Galium aparine L. were best controlled with a CSC threshold of 70%. However, 70% CSC caused up to 50% crop biomass loss and up to 2 t·ha−1 of grain yield reduction. With a CSC threshold of 20% it was possible to control up to 98% of Thlaspi arvense L. The highest crop biomass, grain yield, and selectivity were achieved with an CSC threshold of 20–25% at all locations. With this harrowing intensity, grain yields were higher than in the herbicide plots and a WCE of 68–98% was achieved. Due to the rapid adjustment of tine angle, the new sensor-based harrow allows users to apply the most selective harrowing intensity in every location of the field. Therefore, it can achieve equal weed control efficacies as using herbicide applications.

Highlights

Concerns about negative side-effects of herbicides on ground and surface water, biodiversity, human health and residues in the food chain, and the increasing problem of herbicide resistant weed species, are major factors for an increasing interest in non-chemical weed control methods [1,2].Mechanical weed control methods such as harrowing and hoeing, are highly promising alternatives to chemical weed control
The highest crop biomass, grain yield, and selectivity were achieved with an crop soil cover (CSC) threshold of 20–25% at all locations
This study presents a new approach to mechanical weeding with a sensor-based harrow for post-emergence weed control in cereals

Summary

Introduction

Mechanical weed control methods such as harrowing and hoeing, are highly promising alternatives to chemical weed control. The success of mechanical weeding highly depends on the crop, the Agronomy 2020, 10, 1925; doi:10.3390/agronomy10121925 www.mdpi.com/journal/agronomy. Agronomy 2020, 10, 1925 present weed species composition, the growth stages of the weeds, and soil and weather conditions. Harrowing can achieve 80–90% weed control efficacy (WCE) against mostly annual broad-leaved weeds in spring cereals (spring barley, oat, and triticale) [3,4,5]. Mechanical weeding can achieve almost the same weed control efficacy as herbicides. Light and friable soils combined with dry and sunny weather are ideal conditions for harrowing [7]. Wet soil is less favorable for harrowing and weeds have better chances to recover [8]

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