Soil Organic Carbon Dynamics in Semi-Arid Irrigated Cropping Systems

Andrew M. Bierer,April B. Leytem,Robert S. Dungan,Amber D. Moore,David L. Bjorneberg

doi:10.3390/agronomy11030484

Abstract

Insufficient characterization of soil organic carbon (SOC) dynamics in semi-arid climates contributes uncertainty to SOC sequestration estimates. This study estimated changes in SOC (0–30 cm depth) due to variations in manure management, tillage regime, winter cover crop, and crop rotation in southern Idaho (USA). Empirical data were used to drive the Denitrification Decomposition (DNDC) model in a “default” and calibrated capacity and forecast SOC levels until 2050. Empirical data indicates: (i) no effect (p = 0.51) of winter triticale on SOC after 3 years; (ii) SOC accumulation (0.6 ± 0.5 Mg ha–1 year–1) under a rotation of corn-barley-alfalfax3 and no change (p = 0.905) in a rotation of wheat-potato-barley-sugarbeet; (iii) manure applied annually at rate 1X is not significantly different (p = 0.75) from biennial application at rate 2X; and (iv) no significant effect of manure application timing (p = 0.41, fall vs. spring). The DNDC model simulated empirical SOC and biomass C measurements adequately in a default capacity, yet specific issues were encountered. By 2050, model forecasting suggested: (i) triticale cover resulted in SOC accrual (0.05–0.27 Mg ha–1 year–1); (ii) when manure is applied, conventional tillage regimes are favored; and (iii) manure applied treatments accrue SOC suggesting a quadratic relationship (all R2 > 0.85 and all p < 0.0001), yet saturation behavior was not realized when extending the simulation to 2100. It is possible that under very large C inputs that C sequestration is favored by DNDC which may influence “NetZero” C initiatives.

Highlights

Soil organic carbon (SOC) accumulation is of interest in agroecosystems as a gauge of relative soil quality through benefitting physical soil properties and influencing soil biogeochemistry
To assist interpretation, using assumed bulk densities of 1.28 g cm3 and 1.37 g cm3 for 0–15 cm and 15–30 cm depths, respectively, 20 Mg ha–1 is slightly less than 0.5% soil organic carbon (SOC)
Empirical measurements indicated a commercial dairy forage rotation of corn-barleyalfalfax3 accumulated SOC (0.6 ± 0.5 Mg ha–1 year–1) while a commercial rotation of wheat–potato–barley–sugarbeet had not significantly changed in 8 years excluding the effects of manure

Summary

Introduction

Soil organic carbon (SOC) accumulation is of interest in agroecosystems as a gauge of relative soil quality through benefitting physical soil properties and influencing soil biogeochemistry. Interest in SOC as a pool for global C sequestration continues as the Intergovernmental Panel on Climate Change (IPCC) promotes increasing SOC as part of integrated response options to mitigate global C emissions [1]. The magnitude of mitigation that SOC storage can provide is dependent on climate, soil, and agroecological conditions [2]. Some climates are predisposed for SOC sequestration while others are less inclined to sequester C [6]. Various management practices such as varied tillage regimes, winter cover during annual cropping rotations, and manure, biosolids, or nitrogen applications have been shown to affect SOC accumulation [7,8,9]. The importance of discussing SOC accumulation contextually among various climates and management strategies cannot be understated

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Results

Conclusion