Agricultural Soil Properties Following Amendment with Cedar Wood Chips and Livestock Manure

Abstract

Encroachment of eastern redcedar (Juniperus virginiana L.) and underutilization of livestock manure are two areas of concern for the Great Plains. Developing a new market for woody biomass generated from forest and rangeland management activities is critical to incentivizing management of these trees by landowners. Thus, a collaborative research project was initiated in 2015 at two field sites in the Nebraska Sandhills to promote the utilization of two perceived “waste” products, livestock manure and cedar wood chips, as amendments to improve the health of agricultural soils. The objective of this research was to assess the impact of three years of woody biomass applications with and without cattle manure, swine manure, and liquid nitrogen fertilizer on soil chemical, physical, and biological properties, as well as crop productivity. Research was conducted on two commercial crop production fields in north central Nebraska from fall 2015 until fall 2018. Twenty-four plots measuring 10 m x 12 m (33 ft x 39 ft) and separated by 10 m buffers were established at each site in the fall of 2015 and annual organic amendments applied via surface broadcast in the fall of each year of the study included woody biomass applied at 17.3 Mg ha^-1 (WB1), woody biomass applied at 30.9 Mg ha^-1 (WB2), WB1 + 28 kg UAN ha^-1 (WBLN), WB1 + cattle manure (WBCM), WB1 + swine manure (WBSM), and a no amendment control (CONT). WBCM, WB1, and WB2 significantly increased soil organic matter compared to CON. The surface application of all organic amendments except WBLN decreased bulk density in the top 10 cm of soil while WBCM and WB2 increased sorptivity. Woody biomass amendments did not significantly affect soil biological properties, and soil nitrate concentrations in the top 20 cm of soil were not reduced. Thus, there was no evidence of N immobilization as has been reported with incorporated woody biomass. In general, crop yields were not impacted by these amendments. In one crop year, WBLN increased rye yield while WB2 reduced it. This was likely due to increased early season NO₃-N prior to fertigation in WBLN and reduced stands due to the heavy application of biomass in WB2. Since both sites were under long term no-till management and irrigation, soil moisture was not impacted by the amendments, but soil temperature was more stable with amendments. Applied alone or co-mingled with cattle manure, woody biomass increased SOM after three annual applications. These amendments also significantly decreased bulk density and increased soil sorptivity compared to non-amended soil. Specifically, the surface application of all organic amendments except WBLN decreased bulk density in the top 10 cm of soil while WBCM and WB2 increased sorptivity. Woody biomass amendments did not significantly affect soil biological properties, and soil nitrate concentrations in the top 20 cm of soil were not reduced. Encroachment of eastern redcedar (Juniperus virginiana L.) and underutilization of livestock manure are two areas of concern for the Great Plains. Developing a new market for woody biomass generated from forest clearing activities is critical to incentivizing management of these trees. Ultimately, woody biomass amendments have the potential to improve soil health through increases in organic matter and improved soil physical properties. The addition of inorganic N to woodchips at the time of biomass application is likely unnecessary as there was no evidence of N immobilization due to increased surface C. Further, an application of 17.3 Mg ha^-1 of woodchips (WB1) was sufficient to reap the benefits of soil health improvements without increasing the risk of yield loss due to poor stand, indicating that application of woodchips at a higher rate likely will not provide greater returns.