Abstract
Soil organic matter (SOM) and especially its labile fractions such as particulate organic matter (POM) are very sensitive to soil use and strongly influence soil ecosystem services. Particulate organic matter has been proposed as a soil quality/health indicator but its determination is tedious and time consuming (i.e. manhours). Anaerobic mineralizable nitrogen (AN) is closely related to the soil organic fraction and is very easily determined. Therefore, we proposed to evaluate AN as a soil quality/health indicator through the assessment of its relationship with SOM, POM, soil aggregate stability (AS), and maize (<em>Zea mays</em> L.) relative yield (RY) under different long term soil uses for cropping at Balcarce, Argentina (37º 45’ 14’’ S, 58º 17’ 52’’ W). Soil samples had been taken at two depths (0-5 and 5-20 cm) in the fall of 1998, 2000, 2003, 2006, 2009, and 2012 from a long term tillage system (TS, conventional (CT) and no-tillage (NT)) and nitrogen fertilization (NF, with and without nitrogen as fertilizer) experiment on a complex of Typic and Petrocalcic Argiudolls. Carbon contents in SOM (SOC), POM (POC) and AN were determined in all soil samples, whereas AS was determined in other soil samples taken in 2006, 2009 and 2012 from the arable layer (0-20 cm). Regardless of TS and NF, SOC, POC and AN decreased with time under cropping at both 5-20 and 0-20 cm. In the uppermost layer (0-5 cm) decreases of all three variables were observed only under CT. Anaerobically mineralized nitrogen variation related to SOC (R<sup>2</sup> 0.59 - 0.78, <em>P </em>&lt; 0.05) and especially POC (R<sup>2</sup> = 0.80-0.85, <em>P </em>&lt; 0.05) variations. Likewise, changes in maize RY related better (R<sup>2</sup> 0.92 and 0.95 (<em>P </em>&lt; 0.05) for CT and NT, respectively) to variation in AN, than to SOC and POC variations. Besides, changes in the aggregate mean weight diameter (DMWD) related acceptably to AN at 0-20 cm (R<sup>2 </sup>= 0.67, <em>P </em>&lt; 0.05) and much better at 0-5 cm (R<sup>2 </sup>= 0.86, <em>P </em>&lt; 0.05). Both coefficients of determination were higher than those obtained relating DMWD to SOC or POC. Given the easiness of its determination, its sensitivity, and that it relates to the variation of different key soil parameters and crop behavior, AN could be proposed as an effective soil quality/health indicator. However, studies should be carried out taking into account a broader range of soil and management situations in order to validate the trends observed in this work.
Highlights
Organic matter (SOM) content strongly influences soil functioning in the agroecosystem and on its ecosystem services
This increases the need of N fertilization (NF) and, of a precise and trustable diagnose of N availability that should take into account soil N mineralization capacity (Domínguez et al 2006; Sainz-Rozas et al 2008) and how it is managed
Due to the minor differences observed in bulk density (BD), analyses of variance result patterns for SOC, and POC expressed in concentration and in stock (Table 2) were quite similar
Summary
Organic matter (SOM) content strongly influences soil functioning in the agroecosystem and on its ecosystem services. The properties and maintenance of the soil pore system which regulate water and air dynamics depend on SOM content and characteristics They determine the nutrient supply, activity and diversity of soil biota, and the capacity of a soil to resist disturbances and subsequently re-organize itself, all of which are characteristics that define soil quality/health (Weil and Magdoff 2004; Lal 2010). The reduction in tillage intensity (e.g. under no-tillage, NT) may lead to an increase in PMN, but lower soil disturbance and the consequent less mineralization rate would produce N deficiency for crops (Domínguez et al 2001, 2006). The determination of PMN requires very long aerobic incubations and cannot be performed to follow mid-term changes due to management (Echeverría et al 2000)
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