Temporal Change of Soil Carbon on a Long-Term Experimental Site with Variable Crop Rotations and Tillage Systems

Ahmed Laamrani,Aaron A Berg,Michael March,Paul R Voroney,Bill Deen,Ralph C Martin,Adam W Gillespie

doi:10.3390/agronomy10060840

Abstract

The impacts of tillage practices and crop rotations are fundamental factors influencing changes in the soil carbon, and thus the sustainability of agricultural systems. The objective of this study was to compare soil carbon status and temporal changes in topsoil from different 4 year rotations and tillage treatments (i.e., no-till and conventional tillage). Rotation systems were primarily corn and soy-based and included cereal and alfalfa phases along with red clover cover crops. In 2018, soil samples were collected from a silty-loam topsoil (0–15 cm) from the 36 year long-term experiment site in southern Ontario, Canada. Total carbon (TC) contents of each sample were determined in the laboratory using combustion methods and comparisons were made between treatments using current and archived samples (i.e., 20 year and 9 year change, respectively) for selected crop rotations. Overall, TC concentrations were significantly higher for no-till compared with conventional tillage practices, regardless of the crop rotations employed. With regard to crop rotation, the highest TC concentrations were recorded in corn–corn–oats–barley (CCOB) rotations with red clover cover crop in both cereal phases. TC contents were, in descending order, found in corn–corn–alfalfa–alfalfa (CCAA), corn–corn–soybean–winter wheat (CCSW) with 1 year of seeded red clover, and corn–corn–corn–corn (CCCC). The lowest TC concentrations were observed in the corn–corn–soybean–soybean (CCSS) and corn–corn–oats–barley (CCOB) rotations without use of cover crops, and corn–corn–soybean–winter wheat (CCSW). We found that (i) crop rotation varieties that include two consecutive years of soybean had consistently lower TC concentrations compared with the remaining rotations; (ii) TC for all the investigated plots (no-till and/or tilled) increased over the 9 year and 20 year period; (iii) the no-tilled CCOB rotation with 2 years of cover crop showed the highest increase of TC content over the 20 year change period time; and (iv) interestingly, the no-till continuous corn (CCCC) rotation had higher TC than the soybean–soybean–corn–corn (SSCC) and corn–corn–soybean–winter wheat (CCSW). We concluded that conservation tillage (i.e., no-till) and incorporation of a cover crop into crop rotations had a positive effect in the accumulation of TC topsoil concentrations and could be suitable management practices to promote soil fertility and sustainability in our agricultural soils.

Highlights

Soil holds the largest pool of terrestrial carbon (C), exceeding the combined C found in the atmosphere and in vegetation [1,2,3]
analysis of variance (ANOVA) results found that both tillage practice and cropping rotation system and selected interactions significantly influenced the Total Carbon (TC) concentrations (p < 0.001; Figure 3)
Regardless of tillage system, the highest TC concentrations were recorded in the CCOB** rotation planted with a red clover cover crop in both cereal phases, followed by CCAA, corn–corn–soybean–winter wheat (CCSW)* with red clover in the cereal phase, and CCCC rotations with mean concentrations of 3.01%, 2.94%, 2.76%, and 2.75%, respectively (Table 2)

Summary

Introduction

Soil holds the largest pool of terrestrial carbon (C), exceeding the combined C found in the atmosphere and in vegetation [1,2,3]. Agricultural soils occupy 35% of the global land surface area [4,5]. Encompass 12% of the global soil carbon stocks [6]. Changes in cropland soil carbon stocks are regulated by complex interactions between the local soil environmental conditions and climate, as well as by agricultural management practices [7]. It is widely recognized that current and past agricultural management practices have influenced soil carbon levels and dynamics, which in turn affect soil quality and health, crop yield potentials, and atmospheric CO2 concentrations [8,9,10]. Numerous researchers have demonstrated that management practices such as manure application, conservation tillage, cover cropping, and residue retention can increase soil carbon stocks on agricultural lands [11].

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Discussion

Conclusion