Soil physiochemical properties and enzyme activities are often considered as important indicators of the soil health dynamics in various land-use systems (Bunemann et al. 2018). Soil physiochemical properties and enzyme activity also significantly impact the presence and activity of the soil microorganisms. Therefore, activities of soil enzymes are important in assessing ecosystem functioning. Land-use is a key driver of soil physiochemical properties and enzyme activities and is one of the major factors influencing biodiversity and ecosystem functioning (Lange et al. 2015; Sala et al. 2000). Silvopasture, an agroforestry practice that combines trees with forage and livestock production, has recently gained prominence as an ecologically sustainable and environmentally desirable land-use system (Haile et al. 2008). This form of a sustainable land-use system is gaining popularity in the southeastern United States. The southeastern United States holds considerable potential for developing the silvopasture system as it has mild and moist climatic conditions suitable for commercial timber and grazing livestock production (Rietveld & Francis 2000). As forest-use land constitutes 61.9% of the total land area in the southeast, the rapidly emerging concept of silvopasture is believed to have an economic impact on producers in this region. However, its impacts on soil properties remain unexplored. Limited studies have reported the impact of change in existing woodland to a silvopasture land-use system on soil physiochemical properties (Staley et al. 2008). Recently, research focused on enzyme activities in forest ecosystems (Saiya-Cork et al. 2002; Xu et al. 2015; Yin et al. 2014) have emerged, however, only countable studies on enzyme activities in silvopastoral management are documented. Therefore, this study aimed at comparing the selected soil enzyme activities and soil physiochemical properties of southern-pine silvopasture and southern-pine/hardwood mixed woodland systems.
The study site consisted of six fenced woodland plots (WS; 690 trees ha-1) and six fenced silvopasture plots (SPS; 305 trees ha-1) one acre each, located at Atkins Agroforestry Research and Demonstration Site, Tuskegee University, Tuskegee, Alabama, USA (Figure 1). The WS was established in 2005 and is mainly dominated by 13- year-old mixed pine: longleaf (Pinus palustris Mill.) and loblolly (Pinus taeda L.) with some oaks (Quercus nigra L.; Quercus falcate Michx.), and sweetgum (Liquidambar L.) as the over-story trees. The SPS established in 2014 by thinning out the existing woodland consists of 13-year-old longleaf and loblolly pine. Different warm-season and cool-season grasses and legumes were planted in the SPS plots with no-till- drill method after site establishment. Sheep and goats were rotationally stocked in the SPS plots based on forage availability. Soil samples were collected by a random composite soil sampling approach using a stainless-steel auger at 0–10 cm depth. Samples were analyzed for soil physiochemical properties [total phosphorus (TP), extractable phosphorus (Mehlich P), total nitrogen (TN), nitrate (NO3-N), organic matter-soil organic carbon (SOC), and pH] and enzyme assay using a microplate fluorimetric method as described by Deng et al. (2011).
Land-use change has a significant impact on soil physiochemical properties. TN, SOC, Mehlich P, pH, and NO3-N were significantly higher in SPS soil compared to WS soil which might have been impacted due to differences in land management practices in SPS and WS. The TP was higher in SPS but not significantly (Figure 2). Similarly, enzyme activities were significantly affected by land-use types and were highest in SPS as compared to WS. Acidic phosphatase, alkaline phosphatase, phosphodiesterase, and β-glucosidase activities were higher in SPS compared to WS (Figure 2). The mixed impact of leguminous crops, organic manure, and chemical fertilizer application in SPS might have assisted in increased enzyme activities in SPS compared to WS.
The study showed a significant increase in selected soil enzyme activities and physiochemical properties in the silvopasture system compared to the woodland system. Our study demands further study on the long-term impact of silvopasture and woodland land-use systems on soil properties. These findings benefit farmers by increasing our understanding of the impact of change in land-use systems from woodland to silvopasture on soil quality and dynamics for agriculture sustainability.
Figure 1 Southern-pine silvopasture (left) and southern-pine/hardwood mixed woodland (right) systems at the Atkins Agroforestry Research and Demonstration Site, Tuskegee University, Tuskegee, Alabama, USA
Figure 2 Soil physiochemical properties and enzyme activities in woodland and silvopasture land-use systems. abc Means with different superscripts in a row differ (*p<0.05, **p<0.01, ***p<0.001). TP- Total Phosphorus; TN- Total Nitrogen; SOC- Soil Organic Carbon; OM- Organic Matter AP- acidic phosphatase, AKP- alkaline phosphatase, DIST- phosphodiesterase, and GLU- β-glucosidase
*Note- This article is a part of a manuscript that has been submitted for publication in the Agroforestry Systems journal and is currently under review.
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