Mapping of wheat lodging susceptibility with synthetic aperture radar data

Sugandh Chauhan,Roshanak Darvishzadeh,Sander H Van Delden,Mirco Boschetti,Andrew Nelson

doi:10.1016/j.rse.2021.112427

Abstract

Crop lodging reduces yield quantity and grain quality of cereal crops. Understanding seasonal variation in crop lodging susceptibility enables lodging risk assessments and predictions of associated crop yield losses. We demonstrate a novel remote sensing-based approach, using sparse field observations and widely available synthetic aperture radar (SAR) satellite imagery, to map a safety factor against root lodging (SFA) in wheat. SFA quantifies the ability of the rooting system to support the self-weight moment of the whole plant and can be used as an indicator of in-season root lodging susceptibility. SAR satellite images, from Sentinel-1 and RADARSAT-2, were acquired synchronously with field measurements in Jolanda di Savoia, Ferrara, Italy during the 2018 winter wheat growing season. The field data included measurements from non-lodged (healthy) wheat such as plant height, height at the centre of gravity, self-weight moment of the whole plant, soil anchorage strength, SFA and those from lodged wheat such as crop angle of inclination, lodged area and the point of plant failure (stem or root). Field measurements confirmed that SFA decreased progressively through the season and was consistent with the observed lodging. Strong and significant correlations through the season were observed between SFA and SAR satellite image metrics. The validated regression models showed a strong relationship between field-measured SFA and the metrics from RADARSAT-2 (R2CV = 0.84, RMSECV = 0.54) and Sentinel-1 data (R2CV = 0.73, RMSECV = 0.59). However, it is possible that the relationship between SFA and SAR parameters is confounded by the variations in crop biomass, which is highly correlated with SFA (r = −0.71, p < 0.0001). Our study, for the first time, demonstrates the use of remote sensing SAR data for lodging susceptibility assessment. Current and planned satellite platforms have the potential for large scale, operational assessment of lodging susceptibility in cereal crops.

Highlights

Crop lodging, which is the permanent displacement of the crop’s stem from its vertical position (Pinthus, 1974), can cause severe yield reductions by up to 75% in cereals (Berry and Spink, 2012)
An extensive study (Berry et al, 2003a) examining 15 winter wheat cultivars at three UK sites between 2000 and 2002 showed that root lodging varied between 2 and 47%, while stem lodging was observed in only 0–19% of the wheat cultivars
We found evidence of a certain degree of surface scattering from the wheat fields, which is depicted by a moderate correlation between safety factor against root lodging (SFA) and the Cloude_surf metric (r = 0.69) (Fig. 8b)

Summary

Introduction

Crop lodging, which is the permanent displacement of the crop’s stem from its vertical position (Pinthus, 1974), can cause severe yield reductions by up to 75% in cereals (Berry and Spink, 2012). Lodging is caused by either stem failure (stem lodging) or anchorage failure (root lodging) and the most probable form of lodging is governed by genetic, management and environmental factors (Berry et al, 2003a). High plant population density increases the susceptibility of root lodging over stem lodging, while the early application of nitrogen fertilizer may favour stem lodging (Berry et al, 2000). An extensive study (Berry et al, 2003a) examining 15 winter wheat cultivars at three UK sites between 2000 and 2002 showed that root lodging varied between 2 and 47%, while stem lodging was observed in only 0–19% of the wheat cultivars

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