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2016-12-23T18:37:48

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SSSA 75th Anniversary PaperT he Big Bang, the point in space and time from which all matter and energy in the universe supposedly emanated, is thought to have occurred sometime around 13.7 billion yr ago (Bloom, 2010). During the past 4.5 billion yr since the Earth coalesced and cooled, the planet has undergone alterations and transformations via (for example) plate tectonics, volcanism, and orogenies, which spawned severe changes in the composition and structure of the atmosphere, the oceans, and the land surface-including the biosphere and pedosphere. Other major natural forcing factors have included solar processes and orbital and galactic variations, which changed the amount of solar energy the Earth received (Intergovernmental Panel on Climate Change, 2007). Solar insolation and the structure and composition of the Earth's surface drive many ecosystem processes that have formed the soils we observe on the landscapes of today. VALUE OF SOILS IN THE ANTHROPOCENEDuring the last three centuries, human actions have produced profound shift s in the Earth system, becoming the main driver of global environmental change.

Soil degradation is a critical and growing global problem. As the world population increases, pressure on soil also increases and the natural capital of soil faces continuing decline. International policy makers have recognized this and a range of initiatives to address it have emerged over recent years. However, a gap remains between what the science tells us about soil and its role in underpinning ecological and human sustainable development, and existing policy instruments for sustainable development. Functioning soil is necessary for ecosystem service delivery, climate change abatement, food and fiber production and fresh water storage. Yet key policy instruments and initiatives for sustainable development have under‐recognized the role of soil in addressing major challenges including food and water security, biodiversity loss, climate change and energy sustainability. Soil science has not been sufficiently translated to policy for sustainable development. Two underlying reasons for this are explored and the new concept of soil security is proposed to bridge the science–policy divide. Soil security is explored as a conceptual framework that could be used as the basis for a soil policy framework with soil carbon as an exemplar indicator.

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There is a pressing need for rapid and cost‐effective tools to estimate soil C across larger landscapes. Visible–near‐infrared diffuse reflectance spectroscopy (VNIRS) offers comparable levels of accuracy to conventional laboratory methods for estimating various soil properties. We used VNIRS to estimate soil total organic C (TC) and four organic C fractions in 141 samples collected in the Santa Fe River watershed of Florida. The C fractions measured were (in order of decreasing potential residence time in soils): recalcitrant C (RC), hydrolyzable C (HC), hot‐water‐soluble C (SC), and mineralizable C (MC). Soil samples were scanned in the visible–near‐infrared spectral range. Six preprocessing transformations were applied to the soil reflectance, and five multivariate techniques were tested to model soil TC and the organic C fractions: stepwise multiple linear regression (SMLR), principal components regression, partial least squares regression (PLSR), regression tree, and committee trees. Total organic C was estimated with the highest accuracy, obtaining a coefficient of determination using a validation set (Rv2) of 0.86, followed by RC (Rv2 = 0.82), both using PLSR. The SC fraction was modeled best by SMLR (Rv2 = 0.70), while PLSR produced the best models of MC (Rv2 = 0.65) and HC (Rv2 = 0.40). The addition of TC as a predictor improved the VNIRS models of the soil organic C fractions. Our study indicates the suitability of VNIRS to quantify soil organic C pools with widely varying turnover times in soils, which are important in the context of C sequestration and climate change.