Modeling Hairy Vetch and Cereal Rye Cover Crop Decomposition and Nitrogen Release

Madhav Dhakal,Gurbir Singh,Rachel L Cook,Taylor Sievers

doi:10.3390/agronomy10050701

Abstract

Empirical models could help us to understand the process of plant residue decomposition and nutrient release into the soil. The objective of this study was to determine an appropriate model to describe the decomposition of hairy vetch (Vicia villosa Roth) and cereal rye (Secale cereale L.) cover crop (CC) residue and nitrogen (N) release. Data pertaining to above and belowground CC residue mass loss and N release for up to 2633 cumulative decomposition degree days (112 d) after litterbag installation were obtained from two cropping system experiments, a 1-yr study conducted in 2015 and a 2-yr study during 2017 to 2018 in the humid subtropical environment of southern IL, USA. Six exponential and two hyperbolic models were fit to percent mass and N remaining data to find the one with minimum Akaike information criterion (AIC) and residual sum of squares. Modified three-parameter single exponential and two- or three-parameter hyperbolic models best met the assumed criteria of selection for above and belowground CC residue, respectively. Fitting a double exponential model to combined data for percent mass and N remaining identified two mass and N pools, a fast and a slow pool with different rate constants. A five-parameter double exponential with an asymptote met the preset criteria and passed all tests for normally distributed population, constant variance, and independence of residuals at α = 0.05 when fit to combined data of hairy vetch shoot mass and N remaining. However, a two-parameter hyperbolic and three-parameter asymptotic hyperbolic model provided the best fit to a combined data of cereal rye shoot mass and N remaining, respectively. Both hyperbolic decay models showed a good fit for belowground mass decomposition and N release for both CCs. Cereal rye had a poorer fit than hairy vetch for mass and N remaining of both above and belowground mass. The best-selected decay models can be used to estimate the decomposition and N release rates of hairy vetch and cereal rye above and belowground residue in a similar environment.

Highlights

Cover crop (CC) residue is a source of soil organic matter, and its degradation is critical to subsequent crop productivity
The current study provides an overview of performances of the commonly used empirical models in CC decomposition and N mineralization studies
Five-parameter double exponential and hyperbolic decay models had standard error of estimate (SEE) comparable to the modified single exponential model, these models failed the tests for normality and independence of residuals (Durbin-Watson), whereas the modified single exponential model passed those tests, including the constant variance of errors

Summary

Introduction

Cover crop (CC) residue is a source of soil organic matter, and its degradation is critical to subsequent crop productivity. Inherent properties of the residue such as carbon-nitrogen (CN) ratio, fiber fractions, and lignin concentration can greatly affect the litter decomposition and nutrient cycling [3,4,5]. These properties differ between C3- and C4-derived soil organic matter [6] and between grass and legume residue [7], which may impact decomposition and nutrient release kinetics, indicating the possibility of the usefulness of the different approaches for modeling those kinetics. There is a lack of uniformity in using decay models for decomposition and mineralization studies for similar substrates, which vary from simple one parametric single exponential first-order models to the complex multiparametric consecutive exponential models

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Conclusion