Soil Formation Rate Research Articles

Impact of climate change on soil erosion and the efficiency of soil conservation practices in Austria

SUMMARYThe goal of the present study was to assess the impact of selected soil protection measures on soil erosion and retention of rainwater in a 1·14 km2 watershed used for agriculture in the north-east of Austria. Watershed conditions under conventional tillage (CT), no-till (NT) and under grassland use were simulated using the Water Erosion Prediction Project (WEPP) soil erosion model. The period 1961–90 was used as a reference and results were compared to future Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2 (2040–60).The simulations for the NT and grassland options suggested runoff would decrease by 38 and 75%, respectively, under the current climatic conditions. The simulation results suggest that, under future climate scenarios, the effectiveness of the selected soil conservation measures with respect to runoff will be similar, or decreased by 16–53%.The actual average net soil losses in the watershed varied from 2·57 t/ha/yr for conventional soil management systems to 0.01 t/ha/yr for grassland. This corresponds to a maximum average annual loss of about 0·2 mm, which is considered to be the average annual soil formation rate and therefore an acceptable soil loss. The current soil/land use does not exceed this limit, with most of the erosion occurring during spring time. Under future climate scenarios, the simulations suggested that CT would either decrease soil erosion by up to 55% or increase it by up to 56%. Under these conditions, the acceptable limits will partly be exceeded. The simulations of NT suggested this would reduce annual soil loss rates (compared to CT) to 0·2 and 1·4 t/ha, i.e. about the same or slightly higher than for NT under actual conditions. The simulation of conversion to grassland suggested soil erosion was almost completely prevented.The selected soil conservation methods maintain their protective effect on soil resources, independent of the climate scenario. Therefore, with small adaptations, they can also be recommended as sustainable soil/land management systems under future climatic conditions.However, based on the available climate scenarios, climate-induced changes in the frequency and intensity of heavy rainstorms were only considered in a limited way in the present work. As the general future trend indicates a strong increase of rainstorms with high intensity during summer months, the results of the present study may be too optimistic.

Tillage pedogenesis of purple soils in southwestern China

Land cultivation and tillage process, and their consequent impacts on soil erosion, have been criticized as the main cause of degradation of land or soil quality. However, purple soils, classified as Regosols in FAO Taxonomy or Entisols in USDA Taxonomy, are formed from purple rocks of the Trias-Cretaceous system, have been developed or at least accelerated the development due to continual tillage operation, especially digging and ridging. The present study took micromorphological investigation on the sedimentary rocks and the soils under different operations of tillage. Results show that the purple rock of Feixiangguan Formation of the Trias system (T1f) is the easiest to physical weathering and the most fertile soil material enriched in nutrients, and it has been, therefore, mostly cultivated and intensively tilled around the year. It has the fastest soil formation rate. Soil formation rate in the cropland with conventional tillage is higher than that in the forestland and the grassland. It implies that the artificial brokenness and tillage disturbance play a great role in physical weathering and initiating soil formation processes.

Determination of Soil Loss Tolerance of an Entisol in Southwest China

Soil loss tolerance (T value) serves as an ultimate criterion for determining if erosion control measures are necessary to preserve long‐term soil productivity; therefore, it must be determined scientifically and rationally. In this study, soil formation rates (SR) of the purple soils (Entisols in the U.S. Soil Taxonomy and Regosols in the FAO soil classification) in the hilly area of Sichuan, China, were determined in field plots (measured SR) for three treatments: (i) soil type (J2s, J3s, and J3p soils) and parent materials or bedrock, (ii) vegetation (wheat [Triticum aestivum L.]–maize [Zea mays L.], loquat tree [Eriobotrya japonica (Thunb.) Lindl.], and perennial ryegrass [Lolium perenne L.]), and (iii) soil depth (10, 20, 40, and 60 cm). The measured values were further used to test the applicability of the Barth equation (estimated SR) for the test soils. The measured SR varied among the treatments as a result of different characteristics of soil parent materials (PM) and different temperature and soil moisture at the interface between the soil and the parent materials. The trends (the order of increase or decrease) of measured and estimated soil formation rates were the same, however, for the soil type and vegetation treatments, but not for the soil depth treatments. The measured SR values were 800 Mg km−2 yr−1 for J3s purple soils and 1200 Mg km−2 yr−1 for J2s and J3p purple soils in the study region. The estimated SR values were closely related to runoff volumes but were substantially lower than the measured values. It was concluded that the Barth equation is not a reliable prediction model for estimating the soil formation rate for short‐term and plot‐scale observations. Therefore, T values should be determined by the measured SR values in the experimental region.

Nutrient Release from Weathering of Purplish Rocks in the Sichuan Basin, China

Purplish soils having high fertility with mineral nutrients inherited from the parent rock are widely distributed in the hills along the Yangtze River, especially in the Sichuan Basin. Pot and field weathering experiments were conducted to mimic rock weathering and nutrient release processes in order to better understand soil fertility and nutrient compensation. Three types of purplish rock formations formed in the Jurassic period, Shaximiao (J 2s), Suining (J 3s), and Penglaizhen (J 3p), as well as one type formed in the Cretaceous period, the Chengqiangyan group (K 1c), were used in this study. Results showed that the soil formation rate was in the range from 11.2 to 19.6 mm every year, and rock weathering was in the order of J 3s > J 3p > J 2s > K 1c. Because more rock surface was exposed to sunlight and rainfall in field conditions, pot weathering was slower than field weathering. Nutrient release rates increased with rock weathering and was in the order similar to that of rock weathering: J 3p > J 3s > J 2s > K 1c. Potassium release was the most important in all rocks; after 2 years of weathering, 19.4% to 46.9% of K was released from the initial parent rocks, which suggested that K release from weathering could meet most of the crop K requirement in purplish soils. Thus, rapid release of nutrients from weathering of purplish rocks was key to nutrient replenishment and fertility of purplish soils.

Soil slips on weathering-limited slopes underlain by coarse-grained granite or fine-grained gneiss near Seoul, Republic of Korea

The chemical, mineral, physical, and mechanical properties of two soil layers on soil-slip scars in slopes underlain by coarse-grained granite and fine-grained granitic gneiss near Seoul, Republic of Korea, were examined. Our aim is to study the effect of the mineral grain size of the bedrock on the soil layer structure and the return period of shallow soil slips. Because of the coarser slope materials in granite resulting from weathering, the permeability is larger and the weathering front has a copious water supply; also, because of the smaller specific surface area of the minerals, restricted leaching produces grus from the bedrock, so that the rate of formation of soil (and in particular the slip plane) due to chemical weathering is faster. Since, on granite slopes, the leaching proceeds toward the surface, the sliding plane is deeper with coarser soft grus, resulting in the existence of a minimum c value in the soil layer. On gneiss slopes, by contrast, leaching cannot proceed with decreasing soil depth, and the sliding plane is deeper with finer soft grus just above hard grus and has similar c and ϕ values as the upper soft grus because the grain size of both soils is the same. In the granite soil layers, the sliding plane corresponds to the minimum shearing resistance, whereas in the gneiss soil layers, the shearing resistance increases gradually with soil depth, and the sliding plane is formed when the weathering front is located deeper. Because of the faster soil formation rate and the shallower slip depth in granite slopes, the return period of occurrence of soil slips should be shorter in granite slopes than in gneiss slopes.

The life-time concept as a tool for erosion tolerance definition

By definition, erosion tolerance should consider the conservation of the soil as a natural resource essential for crop production. Erosion rates greater than soil renewal will cause soil depth loss. A minimum soil depth was defined as the depth in which the inputs (fertilizers, crop residues) and management technology (irrigation, improved genetic crop quality) were insufficient to prevent economic productivity loss. Thus, erosion rates greater than soil formation are acceptable only during the time in which the soil does not reach the minimum depth. We have defined this time period as life-time. The life-time concept was applied to the Ceveiro watershed (1,945 ha) located in a sugarcane growing region in the Southeast of Brazil Erosion rates were estimated with the Universal Soil Loss Equation and soil depths were measured by field surveys. Depth change and life-time calculations, considering a soil formation rate of 0.2 mm y-1, and assuming the present scenario of land use and a minimum soil depth of 1.0 m were made using the Geographic Information System. Land use represented 1,319 ha (68%) of sugarcane, 346 ha (18%) of forests and 278 ha (14%) of pasture. The area in which soil erosion was less than soil formation (not associated to long term impacts) represented 475 ha (24%), which included the total forest areas and 48% of pastures. The total sugarcane area had erosion rates greater than soil formation. The area with erosion rates greater than soil formation rates and soil depth less than 1.0 m, which resulted in a life-time equal to zero (soil erosion impacts are presently irreversible) was 832 ha (42%). This area was composed of 702 ha of sugarcane and 130 ha of pastures. The remaining area (erosion greater than formation and soil depth > 1.0 m) represented 638 ha (32%), which was composed of 620 ha of sugarcane and 18 ha of pasture. The half-lifetime for the watershed was estimated as 350 yr. The life-time concept was effective to evaluate the extreme soil degradation risk of the Ceveiro watershed in an integral and reliable form.