Soil quality assessment in different dammed-valley farmlands in the hilly-gully mountain areas of the northern Loess Plateau,China

There are numerous valley farmlands on the Chinese Loess Plateau(CLP),where suffers from low soil quality and high risk of soil salinization due to the shallow groundwater table and poor drainage system.Currently,research on the evolution processes and mechanisms of soil quality and salinization in these dammed-valley farmlands on the CLP is still inadequately understood.In this study,three kinds of dammed-valley farmlands in the hilly-gully areas of the northern CLP were selected,and the status of soil quality and the impact factors of soil salinization were examined.The dammed-valley farmlands include the new farmland created by the project of Gully Land Consolidation,the 60-a farmland created by sedimentation from check dam,and the 400-a farmland created by sedimentation from an ancient landslide-dammed lake.Results showed that(1)the newly created farmland had the lowest soil quality in terms of soil bulk density,porosity,soil organic carbon and total nitrogen among the three kinds of dammed-valley farmlands;(2)soil salinization occurred in the middle and upper reaches of the new and 60-a valley farmlands,whereas no soil salinization was found in the 400-a valley farmland;and(3)soil salinization and low soil nutrient were determined to be the two important factors that impacted the soil quality of the valley farmlands in the hilly-gully mountain areas of the CLP.We conclude that the dammed-valley farmlands on the CLP have a high risk of soil salinization due to the shallow groundwater table,alkalinity of the loessial soil and local landform feature,thus resulting in the low soil quality of the valley farmlands.Therefore,strengthening drainage and decreasing groundwater table are extremely important to improve the soil quality of the valley farmlands and guarantee the sustainable development of the valley agriculture on the CLP.

Genesis and soil environmental implications of intact in-situ rhizoliths in dunes of the Badain Jaran Desert,northwestern China

Desert rhizoliths are generally found as weathered,broken and scattered samples on dune field surface,but rarely insitu in their initial states buried under the soil of desert in the Badain Jaran Desert,northwest China.This study off ers an assessment of the morphological,mineralogical,and chemical properties of intact and in-situ rhizoliths found in soils of swales and depressions among dune chains.The characteristics of these rare and precious objects were assessed using optical polarizing microscopy,cathodoluminescence,scanning electronic microscopy,radiocarbon dating,and stable isotopic analyses,providing the opportunity for discussion of the rhizolith formation mechanisms and associated environmental conditions.Field and laboratory investigations showed that the in-situ intact rhizoliths were formed only in the places where Artemisia shrubs are living,and the remaining root relicts within rhizoliths belong to this species.The spatial distribution of rhizoliths also suggested that low topographic positions on a landscape provided soil moisture,and redox environments favored rhizolith formation.A semi-closed redox environment in the subsoil at swales and depressions,where water is always present,along with the sandy soil texture,facilitated fast water percolation to deeper depths and condensation.Such a soil environment not only provides water for Artemisia growth,but also for the weathering of minerals such as felspars and calcite from primary carbonates,and for the decomposition of root relicts.Furthermore,harsh climatic conditions,such as strong winds and solar radiation,led to water evaporation through dead root channels and triggered the calcification along the root relicts.The entrapped lithogenic carbonates and to a lesser extent the decomposition of Artemisia roots provided the carbon sources for the rhizoliths formation,while the weathering of soil minerals,particularly feldspars and carbonates,was the main source of Ca.Rhizoliths in the Badain Jaran desert formed relatively quickly,probably over a few soil drying episodes.This led to the entrapment of a large quantity of lithogenic carbonates(more than 90%of carbon)within rhizolith cement.The re-dissolution of the entrapped lithogenic carbonates in rhizolith tubes should be taken into account in the paleoenvironmental interpretation ofC ages,the latter suggesting that rhizoliths formed during the Holocene(~2053 years cal BP,based on root organic relicts).

Soil erosion differences in paired grassland and forestland catchments on the Chinese Loess Plateau

In this study,two adjacent gauged catchments on the Chinese Loess Plateau were selected,in which one catchment was afforested and one was restored with natural vegetation in 1954.The distributions of soil erosion rates were estimated between 2010 and 2020 with a high spatial resolution of 2 m in the paired catchments based on the Revised Universal Soil Loss Equation model(RUSLE)and Geographic Information Systems(GIS).The results showed that the simulated soil erosion rates in 2010-2020 averaged 12.58 and 8.56 t ha^(-1)a^(-1)for the grassland and forestland catchment,respectively.Moreover,areas with high soil erosion rates(>80t ha^(-1)a^(-1))were mainly distributed in the topography with steep slope gradients(>45°).Comparisons between simulated soil erosion rates and observed annual sediment loads indicated that the simulation results of the grassland catchment were lower than the observed values,while it was reversed in the forestland catchment.We conclude that the RUSLE model cannot simulate the gravity erosion induced by extreme rainfall events.For the forestland catchment,insufficient streamflow and dense vegetation coverage are crucial factors resulting in hindering the movement of sediments.

Effects of land use and cultivation time on soil organic and inorganic carbon storage in deep soils

The vertical distribution and exchange mechanisms of soil organic and inorganic carbon(SOC,SIC)play an important role in assessing carbon(C)cycling and budgets.However,the impact of land use through time for deep soil C(below 100 cm)is not well known.To investigate deep C storage under different land uses and evaluate how it changes with time,we collected soil samples to a depth of 500 cm in a soil profile in the Gutun watershed on the Chinese Loess Plateau(CLP);and determined SOC,SIC,and bulk density.The magnitude of SOC stocks in the 0-500 cm depth range fell into the following ranking:shrubland(17.2 kg m-2)>grassland(16.3 kg m-2)>forestland(15.2 kg m-2)>cropland(14.1 kg m 2)>gully land(6.4 kg m 2).The ranking for SIC stocks were:grassland(104.1 kg m^2)>forestland(96.2 kg m^2)>shrubland(90.6 kg m-2)>cropland(82.4 kg m 2)>gully land(50.3 kg m-2).Respective SOC and SIC stocks were at least 1.6-and 2.1-fold higher within the 100-500 cm depth range,as compared to the 0-100 cm depth range.Overall SOC and SIC stocks decreased significantly from the 5th to the 15th year of cultivation in croplands,and generally increased up to the 70th year.Both SOC and SIC stocks showed a turning point at 15 years cultivation,which should be considered when evaluating soil C sequestration.Estimates of C stocks greatly depends on soil sampling depth,and understanding the influences of land use and time will improve soil productivity and conservation in regions with deep soils.