Long-Term Biosolids Applications to Overgrazed Rangelands Improve Soil Health

Cassidy M Buchanan,James A Ippolito

doi:10.3390/agronomy11071339

Abstract

Overgrazed rangelands can lead to soil degradation, yet long-term land application of organic amendments (i.e., biosolids) may play a pivotal role in improving degraded rangelands in terms of soil health. However, the long-term effects on soil health properties in response to single or repeated, low to excessive biosolids applications, on semi-arid, overgrazed grasslands have not been quantified. Using the Soil Management Assessment Framework (SMAF), soil physical, biological, chemical, nutrient, and overall soil health indices between biosolids applications (0, 2.5, 5, 10, 21, or 30 Mg ha−1) and application time (single: 1991, repeated: 2002) were determined. Results showed no significant changes in soil physical and nutrient health indices. However, the chemical soil health index was greater when biosolids were applied at rates <30 Mg ha−1 and within the single compared to repeated applications. The biological soil health index was positively affected by increasing biosolids application rates, was overall greater in the repeated as compared to the single application, and was maximized at 30 Mg ha−1. The overall soil health index was maximized at rates <30 Mg ha−1. When all indices were combined, and considering past plant community findings at this site, overall soil health appeared optimized at a biosolids application rate of ~10 Mg ha−1. The use of soil health tools can help determine a targeted organic amendment application rate to overgrazed rangelands so the material provides maximum benefits to soils, plants, animals, and the environment.

Highlights

Soil is an essential, non-renewable resource with potentially rapid degradation rates and extremely slow formation and regeneration processes [1]; soil degradation and regeneration are functions of soil utilization
Bulk density and water-stable aggregates (WSAs) were nearly maximized in this system, with indicator scores near 1.00 (Table 3)
Within the Soil Management Assessment Framework (SMAF), both bulk density (Bd) and WSAs are key components used to quantify physical soil health. Since both indicator scores were near 1.00, their combined contribution to the soil physical health index (SHI) led to a 1.00 in this soil health score (Table 4). This outcome suggests that this soil has the ability to meet rangeland plant and ecosystem requirements for water, aeration, and soil strength over time

Summary

Introduction

Non-renewable resource with potentially rapid degradation rates and extremely slow formation and regeneration processes [1]; soil degradation and regeneration are functions of soil utilization. Utilizing soils erroneously leads to lost land productivity, impacting food availability and cost, climate change, biodiversity, and ecosystem services [1]. Rangeland degradation occurs as a result of vegetation removal or limited/lack of grazing management, causing shifts in species composition, loss of biodiversity, biomass, animal productivity, and soil erosion [2,4]. Improving the fundamental understanding of how rangeland soils may function at their greatest level is paramount for sustaining all facets of life. This concept essentially references soil health, or “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans” [5]

Methods

Results

Conclusion