Influence of continuous application of feedlot manure and legacy treatments on soil organic carbon, soil hydrophobicity, and soil water repellency
Miller, J.J., Owen, M.L., Hao, X., Yang, X.M., Drury, C.F., Chanasyk, D.S. (2021). Influence of continuous application of feedlot manure and legacy treatments on soil organic carbon, soil hydrophobicity, and soil water repellency. Canadian Journal of Soil Science, [online] 101(3), 439-451. http://dx.doi.org/10.1139/cjss-2020-0074
Plain language summary
Although the water drop penetration time findings suggested no issues with restricted infiltration of free water into the soil surface (i.e, air-soil interface), sub-critical soil water repellency (SWR) as indicated by the repellency index method suggested a reduced rate of wetting (under negative potential) deeper into the soil caused by hydrophobic coatings. Hydrophobic coatings on soil aggregates as indicated by soil hydrophobicity and repellency index methods may have positive and negative effects on soil. The soil organic carbon had a significant positive response to application rate under both dryland and irrigation, and followed an exponential trend with soil organic carbon concentration sharply increasing and then levelling off at 70 Mg ha-1 under dryland and at 110 Mg ha-1 under irrigation. This exponential trend for soil organic carbon concentration suggests a maximum capacity from feedlot manure, and was likely related to greater decomposition at higher application rates over time.
The soil hydrophobicity had similar positive responses to manure rate (i.e., soil organic carbon) under dryland and irrigation, but repellency index had a negative response to soil organic carbon under dryland and a positive response under irrigation. We speculate that this might be due to complex correlations between water repellency parameters and specific organic compounds that might be contributing to soil water repellency, as well as greater decomposition of soil organic carbon under irrigation than dryland. Overall, positive responses of soil organic carbon and soil hydrophobicity to application rate supported our hypothesis, but it was not supported for repellency index. The hypothesis of greater soil organic carbon, soil hydrophobicity, and repellency index for continuous versus legacy treatments was also supported for soil organic carbon and soil hydrophobicity, but not for repellency index.
Continuous or discontinued manure applications to agricultural soils may impact soil organic carbon (SOC) and water balances because of manure carbon inputs and the potential for manure-induced soil hydrophobicity (SH) and soil water repellency (SWR). A laboratory study was conducted using a long-term (44 yr) field experiment on a clay loam soil to determine the effect of application rate of feedlot manure under dryland (0, 30, 60, and 120 Mg·ha−1 wet weight) and irrigation (0, 60, 120, and 180 Mg·ha−1 ) on SOC, SH, and SWR. In addition, we compared the effect of 44 yr of continuous annual manure applications (C44) to legacy treatments which had discontinued applications for 14 (D14) or 30 yr (D30). Laboratory measurements were conducted on air-dried and sieved (<2 mm) soil to determine SOC, SH using Fourier transform infrared spectroscopy, and SWR using the repellency index (RI) method. Mean RI values for all treatments ranged from 2.20 to 13.0, indicating subcritical (RI > 1.95) SWR. Manure application rate had a significant (P ≤ 0.05) and positive effect on SOC and SH, and both followed an exponential model. In contrast, RI had a negative response to the application rate under dryland and had no response under irrigation. Overall, positive responses of SOC and SH to application rate supported our hypothesis, but it was not supported for RI. The hypothesis of greater SOC, SH, and RI for continuous versus discontinued treatments was also supported for SOC and SH but not for RI.