Abstract

The study of interrelationships among soil health indicators is important for (i) achieving better understanding of nutrient cycling, (ii) making soil health assessment cost-effective by eliminating redundant indicators, and (iii) improving nitrogen (N) fertilizer recommendation models. The objectives of this study were to (i) decipher complex interrelationships of selected chemical, physical, and biological soil health indicators in pastures with history of inorganic or broiler litter fertilization, and (ii) establish associations among inorganic N, potentially mineralizable N (PMN), and soil microbial biomass (SMBC), and other soil health indicators. In situ soil respiration was measured and soil samples were collected from six beef farms in 2017 and 2018 to measure selected soil health indicators. We were able to establish associations between easy-to-measure active carbon (POXC) vs. PMN (R2 = 0.52), and N (R2 = 0.43). POXC had a noteworthy quadratic relationship with N and nitrate, where we found dramatic increase of N and nitrate beyond an inflection point of 500 mg kg−1 POXC. This point may serve as threshold for soil health assessment. The relationships of loss-on-ignition (LOI) carbon with other soil health indicators were discernable between inorganic- and broiler litter-fertilized pastures. We were able to establish association of SMBC with other soil variables (R2 = 0.76) and there was detectable difference in SMBC between inorganic-fertilized and broiler litter-fertilized pastures. These results could be useful for cost-effective soil health assessment and optimization of N fertilizer recommendation models to improve N use efficiency and grazing system sustainability.

Highlights

  • Soil is a complex and dynamic ecosystem; a deep understanding of complex interrelationships between soil health indicators is required for sustainable utilization of this non-renewable resource

  • We documented significant relationships of active carbon (POXC) with potentially mineralizable N (PMN), N, LOI, Bulk Density (BD), and SMBC, which substantiates the importance of POXC as an measured soil health indicator within the Southern Piedmont, USA

  • Of particular importance is our finding of the strong positive relationship of POXC with N and PMN, which showed the ability of active carbon-fraction to influence dynamics of nitrogen cycling in pastures

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Summary

Introduction

Soil is a complex and dynamic ecosystem; a deep understanding of complex interrelationships between soil health indicators is required for sustainable utilization of this non-renewable resource. Many indicators provide redundant information; the study of their interrelationship is very important for cost-effective assessment of soil health. Soil health is highly affected by climate and management [4,5,6,7], and a deeper understanding of interrelationship between soil health indicators and management factors [8], such as fertilizer source and grazing system, is highly important [9]. Nitrogen fertilizer remains one of the most important inputs in agricultural production [11]; Sustainability 2021, 13, 4844.

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