Can Biosolids Land Application Improve Soil Health?

Improving soil health is based on the premise that soils have the ability to optimally function within natural or managed (agro)ecosystems to sustain plant productivity and to create an environment conducive to system resiliency. Global evidence suggests that biosolids land application can positively alter some function(s) within the context of soil health, yet to date no one has effectively tackled this concept within the context of biosolids land application. We utilized a 22-year biosolids dryland wheat-fallow research location jointly operated between South Platte Renew (Englewood, Colorado) and the Department of Soil and Crop Sciences at Colorado State University (Fort Collins, CO) to answer the question 'Can biosolids really improve soil quality/soil health aspects?' Soil samples (20 cm depth — plow layer) were obtained from plots (four replicates, randomized complete block design) receiving either biosolids (0, 2.2, 4.5, 6.7, 9.0, 11.2 Mg/ha) or N fertilizer (0, 22, 45, 67, 90, 112 kg/ha) every other year over 22 years. We utilized the Soil Management Assessment Framework (SMAF) to identify changes in soil texture, organic C content, clay percentage, wet aggregate stability, microbial biomass C, potentially mineralizable N, pH, EC, extractable P and K, bulk density, and beta-glucosidase activity. Within SMAF, data are scored as unitless values, from 0 to 1, based on pre-determined functions associated with either 1) more is better, 2) less is better, or 3) somewhere in the middle is better. The above indicators were then pooled into categories associated with changes in soil physical, chemical, nutrient, biological, or overall soil health indices. Results showed that soil organic C, potentially mineralizable N, and extractable P were greater in biosolids treated plots as compared to N fertilizer plots. Increasing biosolids application rate increased soil organic C, and other trends existed favoring biosolids over N fertilizer applications. However, when indicators were pooled into respectively soil health indices, increasing biosolids application positively influenced soil chemical, biological, and overall soil health. Biosolids applications improved biological soil health as compared to N fertilizer applications, suggesting that the combination of increasing soil organic matter, microbial biomass C, potentially mineralizable N, and the ability of microorganisms to degrade readily available cellulosic material, was enhanced with biosolids land application. Within this dryland wheat-fallow agroecosystem, biosolids can indeed be utilized to improve soil health, potentially leading to improved resiliency and sustainability.