Carbono extraíble en agua caliente como indicador de salud de molisoles del sudeste bonaerense

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Abstract

Una agricultura sustentable requiere indicadores tempranos del estado de salud edáfica (ISE). Se necesitan variables fácilmente medibles como el carbono extraíble en agua caliente (CAC) para favorecer su uso. El objetivo fue evaluar el CAC como ISE analizando: i) la magnitud de los cambios en CAC producidos por el uso agrícola, en comparación con los producidos en el COT y en el COP, y ii) la relación entre CAC, COP, COT, nitrógeno de amonio producido durante incubaciones anaeróbicas cortas (NAN) con estabilidad de los agregados. Se analizaron muestras de suelo (0-5 y 5-20 cm) de 32 lotes de producción (LP) y situaciones seudoprístinas (SP) localizados en el sudeste bonaerense. Se determinó: densidad aparente (DA), cambio en el diámetro medio ponderado de los agregados (CDMP), COT, COP, NAN y CAC. En 0-20 cm, el CAC varió entre 0,69 y 1,41 g kg-1 para los LP y entre 0,75 y 2,36 g kg-1 para las SP, representando, en promedio, 3,23% y 3,57% del COT, respectivamente. Se relacionó negativamente con la DA y el CDMP, y positivamente con COT y COP expresados como stock referidos a una masa equivalente (COT ME y COP ME, respectivamente) y con NAN. Además, el CAC en los LP cayó 35%, respecto a las SP, y COP ME y COT ME cayeron 62% y 25%, respectivamente. El CAC podría utilizarse como ISE, ya que fue sensible a los cambios por el uso agrícola del suelo y se relacionó con otras propiedades edáficas utilizadas como ISE. Su determinación es sencilla, rápida y económica, favoreciendo su adopción por los laboratorios de análisis.

Translated abstract

Sustainable agriculture requires early soil health indicators (ISE). Some easily measurable variables, as hot-water extractable carbon (CAC), are needed to monitor soil health status frequently. The aim of this study was to evaluate CAC as an ISE. We explored: i) the magnitude of the changes in CAC, total organic carbon (TOC), and particulate organic carbon (POC) due to cropping, and ii) the relationship between CAC, POC, TOC, and ammonium nitrogen mineralized in anaerobiosis (NAN) with aggregate stability. Soil samples (0-5 and 5-20 cm) from 32 production fields (LP) and pseudo-pristine situations (SP) from Southeastern Buenos Aires province were analyzed for: bulk density (DA), change of mean weight aggregate diameter (CDMP), TOC, POC, NAN, and CAC. At 0-20 cm depth, CAC ranged between 0.69 and 1.41 g kg-1 for LP and between 0.75 and 2.36 g kg-1 for SP. Hot-water extractable carbon represented 3.23% and 3.57% of TOC for LP and SP, respectively. Hot-water extractable carbon was negatively related to DA and CDMP, and positively related to TOC or POC expressed as stock related to an equivalent mass (TOC ME and POC ME), and to NAN. Under LP CAC dropped 35% respect to SP, whereas POC ME and TOC ME decreased 62% and 25%, respectively. The CAC could be used as an ISE, given it was sensitive to the changes produced by cropping and it related to some other soil properties that indicate soil health status. Its determination is simple, fast, and cheap, which favors its adoption by commercial soil testing laboratories.

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The Microbial Efficiency-Matrix Stabilization (MEMS) framework integrates plant litter decomposition with soil organic matter stabilization: do labile plant inputs form stable soil organic matter?

M. Cotrufo, Matthew Wallenstein, Claudia Boot … (2013)

The decomposition and transformation of above- and below-ground plant detritus (litter) is the main process by which soil organic matter (SOM) is formed. Yet, research on litter decay and SOM formation has been largely uncoupled, failing to provide an effective nexus between these two fundamental processes for carbon (C) and nitrogen (N) cycling and storage. We present the current understanding of the importance of microbial substrate use efficiency and C and N allocation in controlling the proportion of plant-derived C and N that is incorporated into SOM, and of soil matrix interactions in controlling SOM stabilization. We synthesize this understanding into the Microbial Efficiency-Matrix Stabilization (MEMS) framework. This framework leads to the hypothesis that labile plant constituents are the dominant source of microbial products, relative to input rates, because they are utilized more efficiently by microbes. These microbial products of decomposition would thus become the main precursors of stable SOM by promoting aggregation and through strong chemical bonding to the mineral soil matrix. © 2012 Blackwell Publishing Ltd.