Southern Loess Plateau Of China Research Articles

Effects of the combined application of livestock manure and plant residues on soil organic carbon sequestration in the southern Loess Plateau of China

Increasing soil organic carbon (SOC) sequestration enhances the stability and productivity of agricultural ecosystems. Organic material application is a direct and effective way to maintain and improve SOC sequestration. However, currently, there is little knowledge on efficient practices for combined organic material application to improve SOC sequestration. In this study, we evaluated the effect of three organic materials alone or in combination on SOC sequestration in a 4-year field experiment. Eight treatments were included: control (CK, conventional chemical fertilizer), green manure (G), straw (S), decomposed sheep manure (M), green manure plus straw (GS), green manure plus sheep manure (GM), straw plus sheep manure (SM), green manure, and straw plus sheep manure (GSM). In 2020, decomposed sheep manure application (M, SM, GM and GSM) resulted in the greatest cumulative SOC sequestration (9.5–10.8 Mg C ha−1), followed by those in treatments S (6.1 Mg C ha−1) and GS (6.9 Mg C ha−1). The SOC sequestration efficiency in the M treatment (44.8 %) was greater than that in the others (15.2–34.8 %). A random forest model revealed that organic material quantity and quality, enzyme activity, and microbial community composition were the primary factors determining SOC sequestration. Sheep manure application increased SOC sequestration by increasing lignin quantity and proportion. Incorporating green manure and straw return enhanced SOC sequestration by promoting microbial growth and increasing soil C-acquiring enzyme activity. However, interactions between sheep manure and plant residues resulted in decreases in SOC sequestration efficiency compared with sheep manure application alone. This is because combined fertilization stimulated microbial growth and enzyme activity, causing changes in microbial community structure and accelerating organic material and SOC decomposition. Thus, we do not recommend combining livestock manure with straw or green manure to improve SOC sequestration and soil quality in the southern Loess Plateau.

Plastic film-mulched ridges and straw-mulched furrows increase soil carbon sequestration and net ecosystem economic benefit in a wheat-maize rotation

The application of soil mulching has been widely used to increase crop production in arid, semi-arid, and sub-humid areas, with plastic film-mulched ridges and straw-mulched furrows (RFPS) proving to be more effective as compared with other soil mulching practices. However, few research studies have comprehensively assessed the impacts of RFPS on greenhouse gas (GHG) emissions, grain yield, net ecosystem carbon budget (NECB), and net ecosystem economic budget (NEEB) compared against the single practices of either plastic film mulching or straw mulching. A three-year field experiment was conducted on a wheat (Triticum aestivum L.)-maize (Zea mays L.) rotation field in the southern Loess Plateau, China. Four treatments were evaluated: (1) conventional flat planting without mulching (CK), (2) flat planting with plastic film mulching (PM), (3) flat planting with straw mulching (SM), and (4) RFPS. All mulching practices significantly increased wheat and maize yields as well as the seasonal cumulative carbon dioxide (CO2) emissions from soil respiration (Rs) and ecosystem respiration (Re) compared with CK. RFPS had the greatest annual grain yield and the greatest Rs for wheat seasons. The average annual NECB values for CK and PM were − 1.47 and − 1.05 Mg CO2-eq ha−1 yr−1, respectively, where the negative values indicated that the soil in CK and PM acted as a carbon (C) source. SM and RFPS acted as C sinks because of the straw C input, having average annual NECB values of 1.46 and 1.74 Mg CO2-eq ha−1 yr−1, respectively. PM, SM, and RFPS significantly increased the average annual NEEB by 31.4%, 70.5%, and 60.3%, respectively, compared with CK. Although RFPS had greater C input and grain yield income, it also had greater Rs, harvest removal C loss, and agricultural input costs, resulting in similar NECB and NEEB to what was observed with SM. Considering that the greatest grain yields were obtained with RFPS, this production practice should be a promising method for maintaining greater, more stable crop production, while increasing soil C sequestration and NEEB for the wheat-maize cropping system in dry semi-humid regions such as the southern Loess Plateau of China.

Increasing soil organic carbon sequestration and yield stability by no‐tillage and straw‐returning in wheat–maize rotation

AbstractKnowledge about the changes in soil organic carbon (SOC) stocks and grain yields under different field management practices is necessary for achieving agricultural sustainability. An 8‐yr experiment for testing different tillage and straw management practices was conducted in a wheat (Triticum aestivum L.)–maize (Zea mays L.) rotation system in the southern Loess Plateau of China. Three tillage methods (control with no‐tillage and straw removal [CK], no‐tillage with straw stubbles 30–40 cm in height [NT], and rotary tillage with straw incorporation [RT]) were applied before maize planting, and two straw treatments (straw return [SR] and no straw return [SR0]) were applied after maize harvest. Over the 8 yr, SOC stocks exhibited similar dynamic changing trends in all treatments but were higher under NT, RT, and SR than under CK‐SR0. Compared with the initial soil, SOC stock increased the most (34.1%) in NT‐SR. Compared with the CK‐SR0, the NT‐SR, RT‐SR, CK‐SR, NT‐SR0, and RT‐SR0 increased wheat grain yields by 47.2, 36.8, 24.9, 25.1, and 20.0%, respectively. Similar trends were found for maize grain yields. The NT, RT, and SR increased crop yield stability with the highest sustainable yield index in NT‐SR for both wheat (.67) and maize (.70). Overall, the combination of no‐tillage with wheat straw stubbles 30–40 cm in height and maize straw return was the best strategy for improving SOC stocks, grain yields, and agricultural sustainability for grain production in dry, sub‐humid areas of northwestern China.

Changes in soil physical and chemical properties after short drought stress in semi-humid forests

The Loess Plateau region of China is under increasing water shortage due to declining soil water content after reforestation. Thus, assessing the changes in soils properties in reforested lands is critical for sustainable restoration of vegetation. We conducted a continuous rainfall manipulation experiment from June 2015 to November 2016 using mature black locust (Robinia pseudoacacia) on southern Loess Plateau of China. The soil hydrological properties, aggregate distribution and aggregate organic carbon (OC) and total nitrogen (N) concentrations were measured. Two years of drought stress caused a significant decline in saturated hydraulic conductivity and total porosity, but an increase bulk density in the 0–10 cm soil layer. The short drought stress significantly decreased soil aggregate stability due to a decline in macro-aggregate mass. Drought stress significantly decreased total soil OC concentration and macro- and micro-OC or N concentrations, but had no significant effect on total N concentration after two years of drought. Furthermore, the influence of short drought on soil hydrological properties, aggregate distribution and aggregate OC and total N concentrations was mainly evident at the depth of 10 cm. Our results indicated that short drought has the potential to damage soil properties. The results of this study could provide more insight into the sustainability of afforestation in semi-humid areas of China's Loess Plateau.

Sap flow of black locust in response to short-term drought in southern Loess Plateau of China

Soil water shortage is a major factor influencing the ecology and hydrology of vegetation in China’s semihumid Loess Plateau. However, few studies have experimentally assessed how expected changes in precipitation will affect sap flow in semihumid forest ecosystems. In this study, we measured the sap flow of black locust (Robinia pseudoacacia Linn.) under ambient and drought (induced by throughfall exclusion) conditions in 2015 and 2016, and investigated the relationship between stand transpiration and environmental factors in the semihumid China’s Loess Plateau. Throughfall exclusion significantly decreased sap flux density and stand transpiration by 39% and 28%, respectively, in 2016, which may have been due to the cumulative droughts effect from both 2015 and 2016. Throughfall exclusion caused a significant reduction in soil moisture, leaf area index (LAI), and stem diameter. Stand transpiration was positively correlated with LAI (P < 0.01), but precipitation and soil moisture did not correlate with stand transpiration at a daily timescale, suggesting that LAI can be used as a proxy for stand transpiration. Our results highlight that precipitation must be considered when planting black locust in semihumid regions. These findings provide basic information about the management of water resources and vegetation restoration in the semihumid China’s Loess Plateau and possibly other water-limited regions around the world.

Effects of tillage, mulching and N management on yield, water productivity, N uptake and residual soil nitrate in a long-term wheat-summer maize cropping system

A thorough understanding of coupled effects of soil management (tillage), mulch and N rate on the wheat-maize system is crucial for achieving sustainable agriculture in the southern Loess Plateau of China. This study was based on a 12-year (2003–2015) field experiment and aimed to evaluate the impact of three wheat-maize systems (S) which varied in terms of tillage, mulch, wheat row spacing and irrigation management (CT, conventional tillage with no mulch; RFM, ridge-furrow with plastic film-mulched ridges and straw-mulched furrows; CTM, conventional tillage with straw mulch) combined with N fertilizer rates (0, 120 and 240kgNha−1) on crop yield, water productivity (WP, kg grain per kg of water input), N uptake, residual soil nitrate (RSN) and soil physicochemical properties. Results demonstrated that RFM significantly increased maize yield in comparison with CT in all 12 years, while CTM increased yield in comparison with CT from year 3 onwards. By contrast, wheat yield was not strongly influenced by RFM and CTM from 2004 to 2012 (except for 2008). Maize yields of RFM were significantly higher than those of CTM from the third year onwards. Compared with CT, the other two practices, and more so RFM, showed beneficial effects on crop yield, the amount of stored water, WP, N uptake and RSN. N fertilization significantly increased crop yield, WP and N uptake, while no significant difference was observed between the N120 and N240 treatments. Notably, considerable buildup of RSN to∼490kgNha−1 at maize harvest and ∼340kgNha−1 at wheat harvest were observed in 0–200cm soil depth when 240kgNha−1 was applied. These results suggest that the conventional N rate of 240kgNha−1 is excessive, and risks serious contamination of the groundwater as a result of NO3−-N leaching. The N120 treatment was characterized with considerably lower RSN accumulation after harvest, while maintaining crop yield. Thus, we concluded that the RFM practice with 120kgNha−1 application could reduce irrigation water and fertilizer inputs and increase crop land and water productivity, and is a promising strategy for developing sustainable agriculture in the southern Loess Plateau and other areas with similar climate and cropping systems.

Pollution characteristics and ecological risk assessment of heavy metals in three land-use types on the southern Loess Plateau, China.

The accumulation of heavy metals in agricultural soils has been the subject of great concern because these metals have the potential to be transferred to soil solutions and subsequently accumulate in the food chain. To study the persistence of trace metals in crop and orchard soils, representative surface soil samples were collected from terrace farmland that had been cultivated for various numbers of years (3, 8, 12, 15, and >20years), terrace orchard land that had been cultivated for various numbers of years (4, 7, 10, 12, 15, 18, 25, and >30years), and slope farmland with various gradients (3°, 5°, 8°, 12°, 15°, and 25°) and analyzed for heavy metals (As, Cr, Cu, Hg, Ni, and Zn). These samples were collected from Nihegou catchment of Chunhua county in the southern Loess Plateau of China. The six heavy metals demonstrated different trends with time or gradient in the three land-use types. The Cu and Zn contents of the soil were higher than the referee background values of the loessal soil, and the contents of Cr and Ni, and especially those of As and Hg, were lower. Cu was the only heavy metal that just met the Grade III Environmental Quality Standard for Soils of China, while the others reached grade I. Cu and Hg were considered contaminant factors and Hg was a moderate potential ecological risk factor in the catchment. Of the sites investigated, 89.5% fell into the category with a low degree of contamination (C d ) and rest were moderate, while all three land-use types had low potential ecological risk (RI). Changes of C d and RI were consistent with the cultivated time in the terrace farmland and terrace orchard land. Values of RI increased while C d decreased with the increasing of slope gradient in the slope farmland. Evaluating the ecological risk posed by heavy metals using more soil samples in a larger study area is necessary on the Loess Plateau of China.

A fluidized landslide occurred in the Loess Plateau: A study on loess landslide in South Jingyang tableland

The South Jingyang tableland is located on the southern Loess Plateau of China. Ever since the introduction of the water division project in the 1970s, more than 40 loess landslides have occurred in this tableland-terrace slope topography here. On the morning of March 8, 2016, a loess landslide induced by irrigation occurred in Jiangliu Village on the South Jingyang tableland, and around 20,000m3 of loess rapidly slid along a 65-m high slope for 260m. The moisture content of the slip mass displayed a dramatic change along the slip direction: the water saturation degree in the landslide depression was relatively high, and the leading edge was in a flow state; there were some local natural sub-areas, but the overall area showed a characteristic fluidized. A field investigation indicated that while macropores developed in the loess and deep joints provided a preferential passage for the infiltration of irrigation water, which became a major water source for the slip mass, the softening of the toe part of the slope caused by irrigation became the major factor resulting in the instability of the slip mass. Undrained triaxial shear tests on loess in natural water content and fully saturated state show that the enhanced saturation degree not only lowered the soil mass strength but also increased pore water pressure, resulting in the zoning status of the Jiangliu landslide. The angle of reach formed during this landslide was approximately 14°, which demonstrated motion characteristics of long-runout. Further, considering the standing water at the slope foot and unique properties of slip soils after the landslide occurred, it is speculated that the motion mechanism of this high-speed and long-runout landslide was associated with loess liquefaction that led to sharp decrease in shear strength of the displaced landslide materials during the shear process.

Nitrous oxide emissions from solar greenhouses during summer fallow in the Loess Plateau of China

AbstractIn Northern China, vegetables are usually grown in solar greenhouses using intensive fertilization and cultivation, which produces significant greenhouse gas (GHG) emissions to the atmosphere. In this study, the nitrous oxide (N2O) emissions from 12 solar greenhouses with different fertilization practices (without manure application (SG); with chicken (SG‐CM) or swine (SG‐SM) manure application) were measured in the southern Loess Plateau of China during the summer fallow (35–61 days) in 2013 and 2014. The daily N2O fluxes varied over the ranges of 0.002–0.041, 0.014–12.58, and 0.005–8.41 mg N m−2 h−1 with averages of 0.037, 0.81, and 1.70 mg N m−2 h−1 in the SG, SG‐CM, and SG‐SM greenhouses, respectively, and the total N2O emissions were 1.17, 12.0, and 16.0 kg N ha−1, respectively. Significantly high peak N2O emissions were observed at the beginning of the summer fallow and after manure application, accounting for more than 80% of the total N2O emissions. The management practices of polythene removal, greenhouse enclosure for a week, and tillage also significantly increased the N2O daily fluxes and total emissions. Linear regression analyses showed that soil moisture and manure application were the main factors controlling the N2O emissions during summer fallow, followed by the residual mineral N in the soil. The results indicated that solar greenhouses cause high N2O emissions during summer fallow and farmers should use appropriate measures to mitigate these emissions. © 2015 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

The reconstruction of palaeoenvironment during development of the fourth palaeosol in the southern Loess Plateau of China

The fourth palaeosol (S4) of the Brunhes Epoch (780,000–0years B.P.) at Shuangzhu, Tianjiapo, and Hejiacun in the Guanzhong Plain developed over about 40ka and varies in thickness from 3.6 to 4.0m. It consists of four horizons: the first (uppermost) is a well developed red–brown clay horizon (Bts), the second is a dark yellowish-brown weathering-cracked loess horizon (Cs) with red ferruginous argillans, the third is a yellowish-brown weathering-cracked loess horizon (Cl) without red ferruginous argillans, and the fourth consists of CaCO3 nodules (Ck). The two weathering-cracked loess horizons, which are a major feature differentiating a pedocomplex from a palaeosol, have not been found previously in Chinese palaeosol. The ferruginous clay argillans are composed of montmorillonite–illite with some kaolinite minerals. The pedocomplex suggests that a moist subtropical climate prevailed between 420,000 and 360,000years in the southern parts of the Chinese Loess Plateau. Its profile is Bts–Cs–Cl–Ck–Co. When the pedocomplex was developed, the mean annual temperature and precipitation were about 16°C and 1000mm respectively, about 3°C higher and 400mm more than at present in the Guanzhong Plain. The removal depth of CaCO3 and the weathering-cracked loess layer indicate that the gravitational water reached a depth of at least 3.2m, and the moisture content in S4 would have been sufficient to sustain forest development at that time. In the typical interglacial in which S4 was developed, the Qinling Mountains lost their function as the boundary between the subtropical and temperate zones of China, and water-bearing air masses resulting in rich rainfall could frequently reach the southern Loess Plateau.

Corrigendum: Water Science and Technology 68(4), 821–828: Evaluation of the AquaCrop model for simulating yield response of winter wheat to water on the southern Loess Plateau of China, W. Zhang, W. Liu, Q. Xue and X. Han

Corrigendum: Water Science and Technology 68(4), 821–828: Evaluation of the AquaCrop model for simulating yield response of winter wheat to water on the southern Loess Plateau of China, W. Zhang, W. Liu, Q. Xue and X. Han

Evaluation of the AquaCrop model for simulating yield response of winter wheat to water on the southern Loess Plateau of China

The objective of this study was to evaluate the performance of the FAO-AquaCrop model in winter wheat in the southern Loess Plateau of China. Multi-year field experimental data from 2004 and 2011 were used to calibrate and validate the model for simulating biomass, canopy cover (CC), soil water content, and grain yield under rainfed conditions. The model performance was evaluated using root mean square error (RMSE) and Willmott index of agreement (d) as criteria. The RMSE ranged from 0.16 to 0.38 t/ha for simulating aboveground biomass, 1.87 to 4.15% for CC, 0.50 to 1.44 t/ha for grain yield, and 5.70 to 22.56 mm for soil water content. The d ranged from 0.22 to 0.89, 0.25 to 0.43, 0.36 to 0.62 and 0.95 to 0.98 for aboveground biomass, CC, soil water content and grain yield, respectively. Generally, the model performed better for simulating CC and yield than biomass and soil water content. The results further indicated that AquaCrop is capable of simulating winter wheat yield under rainfed conditions. Further improvement may be needed to capture the variation of different management practices such as fertility and irrigation levels in this region.

OSL dating of a Holocene loess-paleosol sequence in the southern Loess Plateau, China

Optically stimulated luminescence (OSL) dating of polymineral fine-grained loess samples collected from the southern Loess Plateau of China was conducted using the single-aliquot regenerative-dose (SAR) protocol. A ‘Double-SAR’ procedure in which aliquots are subjected to both infrared (IR) and blue stimulations was used, and two sets of equivalent dose (D e ) determinations were produced. These doses are assumed to be predominantly related to the feldspathic and quartz fine grain populations, respectively. The results revealed that the OSL ages estimated by infrared stimulated luminescence (IRSL) signals and those estimated by [post-IR] stimulated luminescence ([post-IR] OSL) signals disagreed. Specifically, the ages estimated using the IRSL signals were smaller than those estimated using [post-IR] OSL signals. The results of an anomalous fading test of the two types of OSL signals revealed that the [post-IR] OSL signals from the etched sub-sample (by H2SiF6 and HF) and the un-etched sub-sample did not fade significantly. However, the IRSL signals from the un-etched sub-sample showed obvious signs of fading. These findings indicate that the lower age estimated by IRSL is due to the anomalous fading of feldspar IR signals in the polymineral fine grains. For samples collected from greater than 100 cm, the estimates of their OSL ages using two types of luminescence signals generally agreed with their pre-estimated ages, especially those of the [post-IR] OSL signals. However, for the three samples that were collected from a depth of less than 100 cm, their OSL ages were remarkably underestimated, possibly due to the enhanced human activity (such as soil cultivation) that has occurred in the region since 3000 a B.P.

Soil water dynamics and deep soil recharge in a record wet year in the southern Loess Plateau of China

Terrestrial water cycles are influenced by hydrologic and textural properties of the deep loess layer in the Loess Plateau . Analyses of soil water profile distributions are needed to understand the regional water cycle processes and to guide agricultural production and sustainability . The objective of this study was to quantify the extent of deep soil water recharge and soil water profile dynamics during 1987–2003, especially in a record wet year of 2003, in common cropping systems in a semiarid-subhumid region of the southern Loess Plateau. The Chinese Ecological Research Network (CERN) site and a long-term rotation experiment site in a flat tableland were selected for this study. Soil moisture profiles were measured by a neutron probe to a depth of 6 m in 2003. The precipitation of 954 mm at the Changwu County Meteorological Station in 2003 was 63.4% higher than the long-term average (584 mm), and was a record high since 1957. Although cropping systems affected deep soil water recharge, the persistent dry soil layer formed between 2- and 3-m depths in croplands, resulting from many years of intensive cropping, was fully replenished in all cropping systems in 2003. Further frequency analysis indicated that the desiccated layer between 2- and 3-m depths would be fully recharged at least once in about 10 years for all existing cropping systems excluding continuous alfalfa. This finding should alleviate concerns about the formation of a permanent deep-soil desiccation layer as well as its potential impact on the long-term sustainability of the existing intensive cropping systems in the region.

Simulating site-specific impacts of climate change on soil erosion and surface hydrology in southern Loess Plateau of China

Abstract Proper spatial and temporal treatments of climate change scenarios projected by General Circulation Models (GCMs) are critical to accurate assessment of climatic impacts on natural resources and ecosystems. The objective of this study was to evaluate the site-specific impacts of climate change on soil erosion and surface hydrology at the Changwu station of Shaanxi, China using a new spatiotemporal downscaling method. The Water Erosion Prediction Project (WEPP) model and climate change scenarios projected by the U.K. Hadley Centre's GCM (HadCM3) under the A2, B2, and GGa emissions scenarios were used in this study. The monthly precipitation and temperature projections were downloaded for the periods of 1900–1999 and 2010–2039 for the grid box containing the Changwu station. Univariate transfer functions were derived by matching probability distributions between station-measured and GCM-projected monthly precipitation and temperature for the 1950–1999 period. The derived functions were used to spatially downscale the GCM monthly projections of 2010–2039 in the grid box to the Changwu station. The downscaled monthly data were further disaggregated to daily weather series using a stochastic weather generator (CLIGEN). The HadCM3 projected that average annual precipitation during 2010–2039 would increase by 4 to 18% at Changwu and that frequency and intensity of large storms would also increase. Under the conventional tillage, simulated percent increases during 2010–2039, compared with the present climate, would be 49–112% for runoff and 31–167% for soil loss. However, simulated soil losses under the conservation tillage during 2010–2039 would be reduced by 39–51% compared with those under the conventional tillage in the present climate. The considerable reduction in soil loss in the conservation tillage indicates the importance of adopting conservation tillage in the region to control soil erosion under climate change.

A comparison of explicit and implicit spatial downscaling of GCM output for soil erosion and crop production assessments

Spatial downscaling of climate change scenarios can be a significant source of uncertainty in simulating climatic impacts on soil erosion, hydrology, and crop production. The objective of this study is to compare responses of simulated soil erosion, surface hydrology, and wheat and maize yields to two (implicit and explicit) spatial downscaling methods used to downscale the A2a, B2a, and GGa1 climate change scenarios projected by the Hadley Centre’s global climate model (HadCM3). The explicit method, in contrast to the implicit method, explicitly considers spatial differences of climate scenarios and variability during downscaling. Monthly projections of precipitation and temperature during 1950–2039 were used in the implicit and explicit spatial downscaling. A stochastic weather generator (CLIGEN) was then used to disaggregate monthly values to daily weather series following the spatial downscaling. The Water Erosion Prediction Project (WEPP) model was run for a wheat–wheat–maize rotation under conventional tillage at the 8.7 and 17.6% slopes in southern Loess Plateau of China. Both explicit and implicit methods projected general increases in annual precipitation and temperature during 2010–2039 at the Changwu station. However, relative climate changes downscaled by the explicit method, as compared to the implicit method, appeared more dynamic or variable. Consequently, the responses to climate change, simulated with the explicit method, seemed more dynamic and sensitive. For a 1% increase in precipitation, percent increases in average annual runoff (soil loss) were 3–6 (4–10) times greater with the explicit method than those with the implicit method. Differences in grain yield were also found between the two methods. These contrasting results between the two methods indicate that spatial downscaling of climate change scenarios can be a significant source of uncertainty, and further underscore the importance of proper spatial treatments of climate change scenarios, and especially climate variability, prior to impact simulation. The implicit method, which applies aggregated climate changes at the GCM grid scale directly to a target station, is more appropriate for simulating a first-order regional response of nature resources to climate change. But for the site-specific impact assessments, especially for entities that are heavily influenced by local conditions such as soil loss and crop yield, the explicit method must be used.

Charcoal records of fire history in the Holocene loess–soil sequences over the southern Loess Plateau of China

Charcoal preserved in accretionary loess–soil profiles within the southern part of the Loess Plateau has recorded fire history and landscape evolution connected with climatic variations and human activities. Local wildfires occurred frequently during the late last glacial period and the early Holocene before 8500 years BP when steppe vegetation expanded from the Inner Mongolian Plateau southerly over the Loess Plateau. During the Holocene climatic optimum between 8500 years BP and 3100 years BP, natural wildfires were largely reduced. Pedogenesis of the Luvisols and Isohumisols was intensified because of the increased monsoonal precipitation and soil moisture. Localized fires in connection with human activities occurred in different patterns at the study sites. Fire seems to have been applied to vegetation clearance for land reclamation for millet cultivation at many places during the Neolithic and early Bronze Age. Levels of biomass burning were very high during the late Holocene, when the climate became drier and historical land-use became more intensive. At some sites, the intensity of human disturbance by fire and cultivation increased continuously during the last 3100 years. At the other sites, local fires occurred most frequently between 3100 years BP and 1500 years BP during the major period of land reclamation for cereal cultivation. Human burning of the landscape has been reduced since then.

Simulating potential response of hydrology, soil erosion, and crop productivity to climate change in Changwu tableland region on the Loess Plateau of China

Knowledge of the impacts of climate change on agro-ecosystems is needed for developing optimal conservation and production practices. The objective of this study was to evaluate the potential impacts of projected climate changes during 2070–2099 under three emissions scenarios (A2a, and B2a, and GGa1) on hydrology, soil loss, and crop production in Changwu tableland region on southern Loess Plateau of China. Monthly projections for the periods of 1950–1999 and 2070–2099 were used from the Hadley Centre's general circulation model (HadCM3). A stochastic weather generator (CLIGEN) was used to downscale monthly HadCM3 projections to daily values at three spatial scales. The Water Erosion Prediction Project (WEPP) model was run for a wheat–wheat–maize rotation under conventional and conservation tillage at the 8.7% and 17.6% slopes. HadCM3 predicted a 23–37% increase in annual precipitation, 2.3–4.3 °C rise in maximum temperature, and 3.6–5.3 °C rise in minimum temperature for the region over the century. Compared with the present climate, predicted percent increases under climate changes, as averaged over the three spatial scales for each emissions scenario and slope, ranged from 29 to 79% for runoff, 2 to 81% for soil loss, 15 to 44% for wheat grain yield, 40 to 58% for maize yield, 25 to 28% for crop transpiration, 21 to 34% for soil evaporation, and 4 to 12% for long-term soil water reserve under the conventional tillage. However, adoption of the conservation (delayed) tillage could reduce runoff by 18–38%, and decrease soil loss by 56–68% as compared to the conventional tillage under the present climate. These results suggest that the use of the conservation tillage would be sufficient to maintain low runoff and erosion levels and thus protect agro-ecosystems under projected climate changes.

Climatic Aridity and the Relocations of the Zhou Culture in the Southern Loess Plateau of China

Several Holocene loess-soil profiles at the archaeological sites of the political center, and later, the capital cities of the predynastic Zhou and Western Zhou Dynasty (ca. 1400–771 B.C.) inthe southern Loess Plateau were studied multi-disciplinarily. It provides insights into monsoonal climatic change and the relocations of the Zhou culture in this climatically sensitive semiarid zone. Both the analytical data and written records indicate that increased climatic aridity at 1150 B.C. induced a considerable environmental deterioration and degradation of natural resources, especially water shortages, decreases in precipitation and deficits in soil moisture. These resulted in poor harvest and great famines, plagues, domestic upheavals, population migrations, and even conflicts between Zhou people who subsisted on dry farming and nomadic tribes on the northern steppe during the development of the Zhou culture. It seems that persistent droughts forced Zhou people to move from the upland plateau to the lowland riverbanks step by step through relocations, following a direction of increasing climatic humidity, soil moisture, water availability and biodiversity. The southward migration of the nomads on the steppe of the northern Loess Plateau and the Mongolia Plateau in response to the climatic aridity was another dynamic force that caused the relocations of the Zhou culture.

Abruptly increased climatic aridity and its social impact on the Loess Plateau of China at 3100 a B.P.

A multi-disciplinary research with integration of the theory and methods of climatic change and history was carried out in the southern Loess Plateau of China. High-resolution soil-sedimentary data define an abruptly increased climatic aridity at 3100 a B.P. on the southern Loess Plateau. It was caused by a shift from the dominance of the maritime monsoon to the continental monsoon in the East Asia. The marked aridity induced a considerable deterioration of environment and degradation of land resources. Consequently, both the livestock failure of the nomadic tribes in the north and the crop failure of the Han Chinese in the south resulted in large-scale nomadic southward migration, and dislocations of the political capital and capital cities of the predynastic Zhou culture. Land use of arable farming was replaced largely by pastoral farming on the plateau. The combination of severe drought and resultant great famine was the fundamental cause of social instability and eventual collapse of the Shang Dynasty at 3000 a B.P. This suggests that the impact of abrupt climatic change was profound at 3100 a B.P. in the present semi-arid zone.