Effects of agricultural management practices on earthworm populations and crop yield: validation and application of a mechanistic modelling approach

Abstract

1. There is little consensus on how agriculture will meet future food demands sustainably. Soils and their biota play a crucial role by mediating ecosystem services that support agricultural productivity. However, a multitude of site-specific environmental factors and management practices interact to affect the ability of soil biota to perform vital functions, confounding the interpretation of results from experimental approaches. Insights can be gained through models, which integrate the physiological, biological and ecological mechanisms underpinning soil functions. 2. We present a powerful modelling approach for predicting how agricultural management practices (pesticide applications and tillage) affect soil functioning through earthworm populations. By combining energy budgets and individual-based simulation models, and integrating key behavioural and ecological drivers, we accurately predict population responses to pesticide applications in different climatic conditions. 3. We use the model to analyse the ecological consequences of different weed management practices. Our results demonstrate that an important link between agricultural management (herbicide applications and zero, reduced and conventional tillage) and earthworms is the maintenance of soil organic matter (SOM). 4. We show how zero and reduced tillage practices can increase crop yields while preserving natural ecosystem functions. This demonstrates how management practices which aim to sustain agricultural productivity should account for their effects on earthworm populations, as their proliferation stimulates agricultural productivity. 5. Synthesis and applications. Our results indicate that conventional tillage practices have longer term effects on soil biota than pesticide control, if the pesticide has a short dissipation time. The risk of earthworm populations becoming exposed to toxic pesticides will be reduced under dry soil conditions. Similarly, an increase in soil organic matter could increase the recovery rate of earthworm populations. However, effects are not necessarily additive and the impact of different management practices on earthworms depends on their timing and the prevailing environmental conditions. Our model can be used to determine which combinations of crop management practices and climatic conditions pose least overall risk to earthworm populations. Linking our model mechanistically to crop yield models would aid the optimization of crop management systems by exploring the trade-off between different ecosystem services.

Forecasting tillage and soil warming effects on earthworm populations

“…EEEworm builds on the same principles as previously published models of the epigeic earthworm Eisenia fetida and the endogeic earthworm Aporrectodea caliginosa , namely the combination of energy budgets and movement in response to trade‐offs in environmental conditions (Johnston, Hodson, Thorbek, Alvarez, & Sibly, ; Johnston, Holmstrup, et al., ; Johnston et al., ). Previous models proceeded in daily time steps and represented 2D cross sections of the soil surface for epigeic or the soil profile for endogeic earthworms, set up with 10 × 10 cm patches and species‐specific energy budget parameters and behavioural rules.…”

“…Daily and seasonal fluctuations in soil conditions (e.g. soil temperature, SOM, plant litter) are modelled according to observed seasonal and vertical relationships (for further details, see Johnston, Holmstrup, et al., ; Johnston et al., and Appendix ).…”

“…As in Johnston et al. (), our model parameter values are not estimated from the data, and hence, conventional statistical methods of assessing R 2 values (using p values) are not applicable. R 2 > .5 indicates a good prediction of the independent data.…”

“…In this paper, we present the EEEworm (Energy–Environment–Earthworm) model, a mechanistic individual‐based model (IBM) of the anecic earthworm Lumbricus terrestris in the soil system. The model is developed from a previously published mechanistic model, which has demonstrated excellent predictive power for endogeic earthworms (Johnston, Sibly, Hodson, Alvarez, & Thorbek, ). During model simulations, individual physiology and behaviour respond to trade‐offs in prevailing environmental conditions and population dynamics emerge.…”

Earthworm Positively Influences Large Macropores Under Extreme Drought Conditions and Conservation Tillage in a Chinese Mollisol

“…Earthworm population is largely influenced by tillage managements in different agricultural systems (van Schaik et al, 2016). Conservation tillage generally resulted in higher earthworm populations than conventional tillage (Johnston et al, 2015). Hence, in order to more accurately obtain the rangeability in soil macroporosity caused by earthworm activity, it is necessary to study the soil macroporosity changes caused by the same number of earthworms under different tillage practices.…”