Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass‐loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large‐scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass‐loss rates and stabilization factors of plant‐derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy‐to‐degrade components accumulate during early‐stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass‐loss rates and stabilization, notably in colder locations. Using TBI improved mass‐loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early‐stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Roots contribute more to refractory soil organic matter than above-ground crop residues, as revealed by a long-term field experiment

We revisited the well documented and ongoing long-term 'Ultuna continuous soil organic matter field experiment' which started in 1956 at the Swedish University of Agricultural Sciences. The objective of the experiment is to quantify effects of six organic amendments and mineral N fertilizers on the crop and soil. We used the ‘equivalent soil mass’ concept for estimating changes in the topsoil C stocks in all 15 treatments. C inputs from amendments were measured and those from crops were calculated using allometric functions and crop yields. Clustering C inputs into seven categories by quality allowed us to calculate a ‘humification’ coefficient for each category. Here, these coefficients simply were based on the fraction of total C input that still remains in the topsoil after about 50 years. As indicated by previous studies, this coefficient was highest for peat, followed by sewage sludge, manure, sawdust and aboveground crop residues. The most interesting result from the current investigation is that the optimized coefficient for root-derived C was about 2.3 times higher than that for aboveground plant residues. The calculated results were found to be robust in a sensitivity analysis. Our findings strongly support the hypothesis that root-derived C contributes more to relatively stable soil C pools than the same amount of aboveground crop residue-derived C

Soil properties and landscape factors affecting maize yield under wet spring conditions in eastern Canada.

Spatial variation in soil properties is attributable in part to redistribution of moisture and topsoil and to soil compaction associated with water-logging. Digital Elevation Models (DEMs) can define topography at a fine scale where these processes may occur as related to field landscape positions such as footslope, depression, crest, and plateau. Our objective was to relate micro-relief (slope, elevation) to soil physical properties and to maize (Zea mays L.) yield under wet spring conditions and delineate soil management units in the field. The experimental 9-ha field was located in the St-Lawrence Lowlands, Quebec, Canada. A topographical survey was conducted using an all-terrain vehicle (ATV) equipped with high-precision Global Positioning System (GPS) receivers sampling 3-D coordinates to generate a grid as fine as 3 m. The GPS sampling method was compared to a total station (TS) for land survey on a 20-m grid. Soil samples and grain yield were collected and geo-referenced on a 30-m grid. Kriging, mapping, and correlation analyses were conducted. Topographic data sampled using a GPS receiver embedded on an ATV were accurate (<10 cm) compared to TS. Soil compaction indexes (bulk density, clay and clay/OM ratio) were the most closely related to yield (r2=-0.57 to -0.60). An independent dataset across the St-Lawrence Lowlands indicated that maize yield exceeding 10 t ha-1 in 1999 and 2000 was obtained with clay/OM ratios less than 12. The DEM and clay/OM ratio distribution maps were useful to locate five landscape positions of clay accumulation, water-logging, and soil compaction, forming two soil management units. In the footslope and depression management units, specific allocation of organic amendments may increase maize yield

Reading tea leaves worldwide : decoupled drivers of initial litter decomposition mass-loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models