Influence of manure and tillage on soil carbon and soil organic matter in silt loam soils of corn–soybean–forage systems

Introduction

An increasing number of farms in Northeast Ohio are being managed under reduced or conservation tillage practices, while those under conventional or intensive tillage are decreasing. Additionally, the use of on-site farm manure among the growers is commonplace. Therefore, it is important to understand how the various management practices of these farms are impacting soil health, soil carbon stocks and crop yields.

Materials and Methods

This on-farm study takes place in the temperate climate of the midwestern United States on a silt loam soil. It focuses on the impact of tillage (mouldboard plough [MP], vertical/chisel tillage [VT] and no-tillage [NT]) and fertilizer (manure included or not) management practices on soil properties. Twelve agriculture fields and two woodland sites, for reference, on Canfield silt loam soils were selected for assessment in this project. Corn (Zea mays L.)–soybean (Glycine max L.) rotations and mixed forage Hayfields were the crops considered. Crop yields at each farm along with soil organic matter (SOM), total carbon (TC), total nitrogen (TN), bulk density, pH, soil test phosphorus (P), potassium (K) and sulphur (S) were assessed at two depths, 0–15 and 15–30 cm. Results of the first 2 years of the study (2020 and 2021) are presented here.

Results

At the surface soil depth (0–15 cm), TC content was not different among cultivated fields (36 Mg  ha⁻¹), but was significantly less than Hayfields, which had the same amount of TC as the wood sites (58 Mg ha⁻¹). There was no significant difference in soil test P, K or S due to tillage. Analysis of variance revealed no statistical difference due to fertilizer. At the soil surface depth, principal component analysis, supported by analysis of similarities (ANOSIM), determined that measurements of TC, TN and SOM distinguished a difference in Hayfields compared to cultivated fields (R-statistic = 0.33; p = 0.001), but little difference when the 15–30 cm soil depth was considered (R-statistic = 0.17; p = 0.001). ANOSIM also determined a slightly significant (R-statistic = 0.065; p = 0.031) difference in fertilizer at the deeper soil depth. Correlation analysis revealed a strong positive relationship between SOM and corn grain yield (r = 0.59) and TN and corn grain yield (r = 0.39).

Conclusions

There was no significant loss of TC among increasing tillage intensities possibly due to the inclusion of manure fertilizer in tilled fields even though there were only slight statistical differences between fields that utilized manure and those that did not. The use of manure was not detrimental in terms of soil test P for most farms, but should be used judiciously. Inclusion of perennial crops such as hay in rotation with crop production can improve TC and TN content. Finally, increasing SOM could potentially increase corn grain yield, but no causal relationship has been determined yet.