Soil survey reveals a positive relationship between aggregate stability and anaerobically mineralizable nitrogen

GARCÍA, GISELA V.; WYNGAARD, NICOLÁS; REUSSI CALVO, NAHUEL I.; SAN MARTINO, SILVINA; COVACEVICH, FERNANDA; STUDDERT, GUILLERMO A.

ECOLOGICAL INDICATORS

ELSEVIER SCIENCE BV

Año: 2020 vol. 117

1470-160X

Soil health status should be monitored to allow planning sustainable management, but indicators available donot encourage frequent soil health evaluation because of the complexity, time-consumption, and expensivenessof the methodologies. Aggregate stability (AS) is a good soil physical health indicator associated with soil (SOC)and particulate (POC) organic carbon but is difficult to monitor. Anaerobically mineralizable nitrogen (AN) hasbeen proposed as soil health indicator because is cheap, simple, and safe to measure, is sensitive to soil-usechanges, is also related to soil (SOC) and particulate (POC) organic carbon, and is frequently determined byfarmers in Mollisols of the Southeastern Argentinean Pampas to support soil fertility diagnosis. We hypothesizethat AN is positively related to and can be used as indicator of AS. Soil samples were taken at 0?5 and 5?20 cmdepths from 46 sites throughout the southeastern Buenos Aires province, Argentinean Pampas. In each site, wesampled Mollisols under continuous cropping (CC) and others that had not been disturbed for many years(pseudo-pristine, PRIS). We determined texture, SOC, mineral-associated organic C, POC, AS and AN. We alsocalculated variable values for 0?20 cm. Soil organic carbon, POC, AN and AS were reduced by continuouscropping. Anaerobically mineralizable N was positively related to SOC (R2 = 0.74, 0.46, and 0.62 at 0?5, 5?20,and 0?20 cm) and POC (R2=0.73, 0.33, and 0.60, respectively). An important proportion of the total variabilityin AS was explained by SOC (R2 = 0.77, 0.65, and 0.73 at 0?5, 5?20, and 0?20 cm, respectively), POC(R2 = 0.75, 0.63, and 0.73, respectively), and AN (R2 = 0.78, 0.69, and 0.81, respectively). The AS increasedwith the increase of SOC, POC, and AN at all three depths, with slopes that did not differ between CC and PRIS,but with intercepts that differed. Neither sand nor clay contents significantly contributed to explain the variationsin AS as a function of SOC, POC, and AN. An independent validation of the regression model relating ASand AN at 0?20 cm was done and the output was very good (RPIQ (ratio of performance to interquartile distance)= 2.20). Results support our hypothesis because AN was positively related to AS. Consequently, ANwould be a good indicator of AS, SOC, and POC. Based on our results, we consider that a simple and cheap soilanalysis as AN can not only be used to diagnose soil fertility, but to monitor soil physical and biochemical healthstatus.