Anaerobically mineralized nitrogen within macroaggregates as a soil health indicator

Abstract

Anaerobically mineralized nitrogen (AN) in bulk soil (ANBS) has been described as a soil health indicator. Considering that large macroaggregates (2000–8000 μm, MA) are more sensitive to management practices than the bulk soil (i.e. whole soil), AN within MA (ANMA) would be a better soil health indicator than ANBS. The aim of this study was to evaluate if ANMA is a better indicator of: i) soil organic carbon (SOC) and particulate organic carbon (POC) in bulk soil (SOCBS and POCBS, respectively) and ii) aggregate stability (AS) than ANBS. Soil samples were taken at 0–5 and 5–20 cm from 46 continuously cultivated plots (CC) and a reference plot for each CC (pseudo-pristine, PRIS). These soils, located in the Argentinean Pampas, were classified as Mollisols with contrasting surface textural classes. The AS, SOCBS, POCBS, ANBS, SOC (SOCMA), and POC (POCMA) within MA and ANMA were determined separately at 0–5 and 5–20 cm soil depths and estimated at the 0–20 cm layer. The ANMA was a good indicator of SOCBS (R2 0.75, 0.48, and 0.61 at 0–5, 5–20 and 0–20 cm depths, respectively), POCBS (R2 0.66, 0.31, and 0.49, respectively), and AS (R2 0.80, 0.68, and 0.76, respectively). The ANMA performed similarly to predict SOCBS, POCBS, and AS as compared to ANBS, because ANMA was closely correlated to ANBS (r 0.90 at 0–20 cm). Since ANMA determination is more time-consuming than ANBS determination, its use as a soil health indicator would not be convenient. Therefore, the use of ANBS would be recommended over ANMA as a variable to monitor soil health.