Soil Science

Phillips, Jonathan D.

doi: 10.1097/SS.0000000000000246pmid: N/A

ABSTRACT Understanding evolution of soils and landforms (and other Earth surface systems) has itself evolved from concepts of single-path, single-outcome development to those that recognize multiple possible developmental trajectories and different maturely developed states. Soil geomorphology and pedology should now move beyond showing that multiple trajectories are possible to investigating why some evolutionary pathways (EPs) are common and persistent, whereas others are rare and transient. A typology of EPs is developed and applied to soil formation in the North Carolina coastal plain. Some EPs are impossible because of violation of generally applicable laws or absence of necessary conditions; others are currently impossible, having occurred in the past but requiring conditions that no longer exist. Improbable paths are possible but rare, because necessary circumstances involve rare events or boundary conditions. Inhibited EPs are also possible but rare because of resistance factors or feedbacks that prevent or inhibit them. Transient paths may be common but are not long-lived or well preserved and are thus rarely observed. Recurring but nonrepeating EPs occur in different locations but are irreversible in any given location and cannot recur except in the case of system-resetting disturbance or new inputs. Recurring EPs are not inhibited or self-limited, occur in different locations, and may be repeated because of ongoing or recurrent processes or conditions. Selected path types occur in multiple situations, but with increased probability due to feedbacks or responses that encourage or enhance recurrence and/or persistence. The case study shows examples of all possible EP types.

Maier, Martin; Lang, Verena

doi: 10.1097/SS.0000000000000245pmid: N/A

ABSTRACT While several diffusivity models have been developed for mineral soils, there are few data for the forest humus layers that overlie, and are distinct from, the mineral soil. We measured soil gas diffusivity of the organic layer of spruce and beech stands. Total pore space and relative soil gas diffusivity were much higher in the humus layer than in mineral soil. An exponential diffusivity function was used to describe relative soil gas diffusivity in the humus layer of all spruce sites using one parameter set. The best-fit parameters exceeded the range recommended for mineral soil, indicating the distinctness in pore structure of mineral soil and the organic layer. Different model parameter sets were required to describe the different types of humus at the beech sites. As a consequence, traditional predictive models developed for mineral soil should not be used to derive diffusivity values to interpret the aeration status of the forest humus layer. Specific parameter sets should be used for calculating soil gas fluxes through these layers using the gradient flux approach.

Khademalrasoul, Ataallah; Kuhn, Nikolaus J.; Elsgaard, Lars; Hu, Yaxian; Iversen, Bo V.; Heckrath, Goswin

doi: 10.1097/SS.0000000000000247pmid: N/A

ABSTRACT Application of biochar to soil has been suggested as a nonstructural best management practice to mitigate runoff potential and soil loss. However, empirical data substantiating these effects are still scarce. Rainfall was presently simulated under controlled conditions to study the effects of biochar on erosion and runoff potential with sandy loam soil sampled from a field experiment 2 years after biochar amendment (2 kg m−2). The field experiment comprised four untreated and four biochar-treated plots that were amended with biochar produced from birchwood. In the laboratory, aggregate stability and organic carbon (OC) in topsoil (0–0.2 m) were analyzed. Soil loss and runoff were measured during a 3.5-h rainfall simulation using a round flume setup. Organic C was also determined in the eroded sediment, soil crust, and bulk soil of each flume after simulations. While runoff was not affected by treatment, biochar-treated soils showed significantly lower soil loss rates compared with untreated soils, reducing the cumulative soil loss by 41%. This was attributed to the aggregating effects of OC from the biochar application and delayed crust formation. The reduced erosion of OC from biochar-treated soils also resulted in lower OC enrichment ratios in the sediment and thus less OC export than from untreated soils. The results illustrated that biochar application already in the short term (2 years) can lead to an improvement of soil aggregation, thereby enhancing aggregate stability and leading to a reduction in soil loss. However, extrapolation of these positive results must be done with caution because the scale of the flume limited the erosive forces acting on the soil. Before an extrapolation of the results, an upscaling of erosion tests to field scale is therefore required.

Rekik, Fatma; van Es, Harold; Hernandez-Aguilera, J. Nicolas; Gómez, Miguel I.

doi: 10.1097/SS.0000000000000248pmid: N/A

ABSTRACT Understanding the effects of soil health (SH) on the quality of high-value crops such as coffee may enable farmers to receive financial benefits prompted by product differentiation and price premiums. This study assessed the existence and nature of the relationship between coffee cup quality and SH. Soil and coffee seed samples were collected from 68 member-farms of a cooperative participating in a high-quality coffee value chain and 67 non–member-farms located across six municipalities in Cauca, Colombia, and 117 farms across two municipalities in Antioquia, Colombia. Elevation was recorded on each farm. Soil samples were tested for 13 SH indicators including wet aggregate stability, available water capacity, active carbon, organic matter (OM), protein, respiration, pH, P, K, Mg, Mn, Fe, and Zn. Coffee samples were tested by professional cuppers for physical, granulometric, and sensorial traits including fragrance/aroma, flavor, aftertaste, acidity, body, uniformity, sweetness, clean cup, and balance. Pearson correlation tests, principal component analysis, and canonical correlation analysis were conducted on all measured variables for Cauca and Antioquia separately and combined. Results show that coffee quality and sensorial traits tended toward a negative relationship with physical and biological SH, primarily with the indicators available water capacity and OM and the labile OM-related soil properties active carbon and respiration, whereas chemical indicators variably correlated with coffee quality. This suggests that coffee may be similar to wine grapes in that high-quality products not necessarily derived from soils with high values of SH indicators. The results of this study can guide further work to identify suitable management strategies that maximize coffee quality without significantly jeopardizing production or the environment.