Total Soil Water Content Research Articles

Can we identify tipping points of resilience loss in Mediterranean rangelands under increased summer drought?

Mediterranean ecosystems are predicted to undergo longer and more intense summer droughts. The mechanisms underlying the response of herbaceous communities to such drier environments should be investigated to identify the resilience thresholds of Mediterranean rangelands. A 5-year experiment was conducted in deep and shallow soil rangelands of southern France. A rainout shelter for 75 days in summer imposed drier and warmer conditions. Total soil water content was measured monthly to model available daily soil water. Aboveground net primary production (ANPP), forage quality, and the proportion of graminoids in ANPP were measured in spring and autumn. Plant senescence and plant cover were assessed in summer and spring, respectively. The experimental years were among the driest ever recorded at the site. Therefore, manipulated summer droughts were drier than long-term ambient conditions. Interactions between treatment, community type, and experimental year were found for most variables. In shallow soil communities, spring plant cover decreased markedly with time. This legacy effect, driven by summer plant mortality and the loss of perennial graminoids, led to an abrupt loss of resilience when the extreme water stress index exceeded 37 mm 10 day-1, characterized by a reduction of spring plant cover below 50% and a decreased ANPP in rainy years. Conversely, the ANPP of deep soil communities remained unaffected by increased summer drought, although the presence of graminoids increased and forage nutritive value decreased. This study highlights the role of the soil water reserve of Mediterranean plant communities in modulating ecosystem responses to chronically intensified summer drought. Communities on deep soils were resilient, but communities on shallow soils showed a progressive, rapid, and intense degradation associated with a loss of resilience capacity. Notably, indexes of extreme stress were a better indicator of tipping points than indexes of integrated annual stress. Considering the role of soil water availability in other herbaceous ecosystems should improve the ability to predict the resilience of plant communities under climate change.

Investigating soil quality in cold highland agricultural fields with different soil types

ABSTRACT To evaluate the soil quality of alpine farmland and elucidate the key factors influencing productivity levels under the current agricultural paradigm, we conducted an extensive collection of soil samples. In total, 234 soil samples (0–20 cm) were collected from Menyuan County, the heartland of the southern slope of the Qilian Mountains. These samples represented four predominant soil types, including cold calcic soil, luvic chernozem, calcareous meadow soil, and calcareous gray cinnamon soil. Moreover, by employing principal component analysis, we established a minimum data set (MDS) that encapsulated the essential parameters for the comprehensive evaluation of the soil quality of farmland in the study area. Upon evaluating the soil quality index, the rankings were as follows: luvic chernozem (0.63) > calcareous gray cinnamon soil (0.58) > calcareous meadow soil (0.58) > cold calcic soil (0.55). Overall, the results highlighted that the significant impact of soil total nitrogen (TN), available potassium (AK), and soil water content (SWC) on soil quality within the study area. Therefore, in the context of land management practices, careful attention should be paid to the management of soil TN, AK content, and SWC to avoid the degradation of cultivated land into abandoned fields.

Evaluation of AquaCrop’s Ability to Simulate Water Stress Based on 2-Year Case Study of Maize Crop

To apply AquaCrop to the study of agricultural soil moisture in the North China Plain, a water-treatment experiment on summer maize was carried out at the Fengqiu experimental station of the Chinese Academy of Sciences from 2017 to 2018. A water treatment was used to achieve field water capacities of 20 (W1), 40 (W2), and 60 (W3) cm soil layers under irrigation, and a rain-fed treatment (W0) was added. The model parameters were calibrated using the measured data in 2017. Then, they were applied to 2018 to verify the ability of the model to simulate water stress. The results showed that the variation trends for crop yield, canopy coverage, total soil water content, and the curve in the growth cycle simulated via AquaCrop were consistent with the actual observations; the results of a discrete analysis showed that the values of b (regression coefficient), R2 (determination coefficient), and EF (efficiency) were close to 1, and the values of the RMSE (root mean square error) were close to 0, which proved that the model could simulate dynamic changes in summer maize yield, canopy coverage, and total soil water content well. AquaCrop had good applicability in the North China Plain and could be applied to the study of agricultural water consumption and water-use efficiency in this area. The simulated values obtained can serve as an easily obtainable source of long-term experimental data in areas with frequent non-extreme weather events.

Effects of Different Tillage Depths on Soil Physical Properties and the Growth and Yield of Tobacco in the Mountainous Chongqing Region of China

Tobacco (Nicotiana tabacum L.) is the most important cash crop in the mountainous Chongqing region, where mini rotary tillers are widely used for land preparation. The decline in tobacco yields has been partially attributed to deteriorating soil physical properties and the formation of plough pans as a result of the repeated use of the mini rotary tiller. The objective of this study was to evaluate the effects of different tillage depths on soil physical properties and the growth and yield of tobacco. Three tillage depths were evaluated: mini rotary tillage to 15 cm (T15) as a control, medium-deep tillage to 25 cm (T25), and deep tillage to 35 cm (T35). Total porosity, capillary porosity, and soil water content were measured for each treatment, and the root distribution, agronomical traits, and dry matter accumulation were monitored at different growing stages. Tobacco yield and output value were determined following the harvest. Compared to T15, T35 significantly increased total porosity and capillary porosity in the 10–40 cm soil layer and soil water content in the 0–40 cm soil layer, while T25 improved soil physical properties but not significantly. T35 significantly promoted dry matter accumulation and root, stem, and leaf growth compared to T15, while differences in some agronomic traits between T25 and T15 were not significant. Compared to T15, T35 and T25 increased the tobacco yield by 17.2–18.9% and 8.0–10.1%, respectively, and increased the output value by 44.4–46.4% and 29.2–32.6%, respectively. The results indicate that deep tillage improves soil physical properties, breaks plough pans, stimulates root growth, and increases tobacco yield and output value.

Beneath the Surface: Investigating soil microbial and metazoa communities at various depths in a natural desert ecosystem inhabited by Karelinia caspia

Soil organisms play a pivotal role in terrestrial ecosystems, sparking growing curiosity about the comprehensive diversity of subterranean biota across large ecological levels. Soil inhabitants’ exhibit varied responses to soil physicochemical properties (SPPs) across desert ecosystem. Yet, the knowledge of their population dynamics across different soil depths (SDs) in the indigenous natural dominant zone of Karelinia caspia, a primary desert shrub in China, remains limited. This study employed advanced illumina sequencing to assess soil bacteria, fungi, archaea, protist, and metazoa populations across six distinct SDs (0 to 100 cm) within the K. caspia desert landscape. Our findings indicate a descending alpha diversity pattern in bacteria, archaea, and protists as soil depth increases, contrary to fungi and metazoa, which exhibit the opposite trend. SDs significantly shape soil biota beta diversity, notably impacting bacteria, protists, and fungi, as revealed by Non-Metric Dimensional Scaling. Prominent classes include Actinobacteria, Sordariomycetes, Nitrososphaeria, Spirotrichea, and Nematoda for soil bacteria, fungi, archaea, protists, and metazoa, respectively. Correlation analysis between predominant biotic communities' vertical distribution and SPPs variations revealed total potassium (TK) and pH's pronounced influence on bacteria, while fungi were affected by total nitrogen (TN) and soil water content (SWC). Archaea exhibit sensitivity to SWC, available potassium (AK), and available phosphorus (AP); protists respond to C/N-Ratio, nitrate (NO3), and total phosphorus (TP); metazoa correlate with SWC, pH, and NO3. Overall, these findings offer valuable insights regarding population fluctuations of soil biota within naturally established K. caspia across vertical soil strata within China's desert ecosystem.

Effects of thinning on accumulation of soil microbial residue carbon of Picea asperata plantations in sub-alpine region of western Sichuan, China

Microbial residues are an important component of soil organic carbon (SOC). It is unclear how long-term thinning affects the accumulation characteristics of microbial residue carbon (C). We analyzed the differences in soil physicochemical properties, microbial communities, extracellular enzyme activities, and microbial residue C in topsoil (0-10 cm) and subsoil (20-30 cm) in Picea asperata plantation of non-thinned (control, 4950 trees·hm-2) and thinned for 14 years (1160 trees·hm-2) stands, aiming to reveal the regulatory mechanism of thinning on microbial residue C accumulation. The results showed that thinning significantly increased SOC content, total nitrogen content, available phosphorus content, the proportion of particulate organic C, soil water content, C-cycle hydrolase, and acid phosphatase activities, but significantly reduced the proportion of mineral-associated organic C. Thinning significantly affected the content of fungal and microbial residue C, and the contribution of microbial residue C to SOC, and these effects were independent of soil layer. The content of fungal and microbial residue C was 25.0% and 24.5% higher under thinning treatments. However, thinning significantly decreased the contribution of microbial residue C to SOC by 12.3%, indicating an increase in the proportion of plant-derived C in SOC. Stepwise regression analysis showed that total nitrogen and soil water content were key factors influencing fungal and micro-bial residue C accumulation. In summary, thinning promoted microbial residue C sequestration by altering soil pro-perties and changed the composition of SOC sources.

Quantification of Water Released by Thawing Permafrost in the Source Region of the Yangtze River on the Tibetan Plateau by InSAR Monitoring

AbstractThe source region of the Yangtze River (SRYR, 1.4 × 105 km2 above Zhimenda station) on the Tibetan Plateau (TP) has 78% permafrost coverage. The streamflow depth increased at a rate of 2.5 mm/a since 2000. Quantification of the water contribution brought by permafrost thawing is a difficult task. In this study, we used Sentinel‐1 data and the SBAS‐InSAR technique to monitor terrain deformation from September 2016 to December 2021, and then utilized the long‐term deformation rate to assess ground ice meltwater release and the seasonal deformation to evaluate water storage in the active layer. Results reveal that 55.3% of the terrain in the SRYR has subsidence >2.5 mm/a, indicating widespread ground ice melting. The release rate of ground ice meltwater is 4.3 mm/a in the entire SRYR, above 6 mm/a at the Dangqu and Tuotuo River subbasins. The water release rate is relatively small (∼3%) in comparison to the streamflow depth of 151 mm per year during the investigation period of 2017–2021. We did not detect a strong increasing or decreasing trend among the 5‐year seasonal deformation, which reflects that the total soil water content in the active layer did not change significantly during the short investigation period. The results provide a data basis for ground ice richness and loss information in the SRYR and help to understand the impact of permafrost thawing on the regional water cycle in the permafrost environment.

Atributos físicos do solo submetido a ensilagem com diferentes conjuntos mecanizados

ABSTRACT The evaluation of the physical attributes of the soil in cultivated areas is essential for understanding the impacts of agricultural operations, especially those with intense machine traffic. Therefore, the present study aimed to evaluate the physical attributes of the soil submitted to silage with different mechanized sets. A randomized block design was adopted with three treatments: forage harvester with a one-row cutting platform (T1), forage harvester with a three-row cutting platform (T2), and T2 with a forage harvester with a conveyor wagon. Before ensiling and 24 hours after the operation, intact samples of soil classified as Latossolo Vermelhoamarelo álico, intact, were collected to determine the micro, macro, and total porosity, soil density, and volumetric soil water content according to the methodology proposed by the Brazilian Agricultural Research Corporation (Embrapa). After ensiling, the resistance to soil penetration was measured with an electronic manual penetrometer, before and after ensiling, at the A horizon of the soil in the layers of 0.0-0.2 m and 0.2-0.4 m. We analyzed the data by establishing the confidence interval using the t-test at 10% probability. The sets reduce the macroporosity and total porosity of the soil in the 0.0-0.2 m and 0.2-0.4 m soil layers. T2 promoted greater total density in the 0.0–0.2 m layer. The silage increased the resistance to soil penetration to a depth of 0.15 m.

Long-term reduced tillage and winter cover crops can improve soil quality without depleting moisture

California farmers who use reduced-disturbance tillage and winter cover cropping can boost production and improve soil health. However, some farmers are hesitant to try these conservation practices due to uncertainty about whether planting winter cover crops will deplete soil moisture in already drought-stricken regions. Our study addresses these concerns by looking at how long-term reduced-disturbance tillage and winter cover cropping, compared to fallowed soils with standard tillage, affected soil moisture. Although we found a statistical difference in total soil water content, the difference was only about 0.3 inches of water per foot of soil. On average, the soil water content of the top 0–96 inches was highest for the reduced-disturbance fields with winter cover crops. This was especially evident during our driest field season, from November 1, 2017, to March 15, 2018, when cumulative rainfall was only 1.9 inches. Our findings show that winter cover cropping and reduced-disturbance tillage can improve soil without depleting soil water levels in row crops.

Functionality of methane cycling microbiome during methane flux hot moments from riparian buffer systems

Riparian buffer systems (RBS) are a common agroforestry practice that involves maintaining a forested boundary adjacent to water bodies to protect the aquatic ecosystems in agricultural landscapes. While RBS have potential for carbon sequestration, they also can be sources of methane emissions. Our study site at Washington Creek in Southern Ontario, includes a rehabilitated tree buffer (RH), a grassed buffer (GRB), an undisturbed deciduous forest (UNF), an undisturbed coniferous forest (CF), and an adjacent agricultural field (AGR). The objective of this study was to assess the diversity and activity of CH4 cycling microbial communities in soils sampled during hot moments of methane fluxes (July 04 and August 15). We used qPCR and high-throughput amplicon sequencing from both DNA and cDNA to target methanogen and methanotroph communities. Methanogens, including the archaeal genera Methanosaeta, Methanosarcina, Methanomassiliicoccus, and Methanoreggula, were abundant in all RBSs, but they were significantly more active in UNF soils, where CH4 emissions were highest. Methylocystis was the most prevalent taxon among methanotrophs in all the riparian sites, except for AGR soils where the methanotrophs community was composed primarily of members of rice paddy clusters (RPCs and RPC-1) and upland soil clusters (TUSC and USCα). The main factors influencing the composition and assembly of methane-cycling microbiomes were soil carbon and moisture content. We concluded that the differences in CH4 fluxes observed between RBSs were primarily caused by differences in the presence and activity of methanogens, which were influenced by total soil carbon and water content. Overall, this study emphasizes the importance of understanding the microbial drivers of CH4 fluxes in RBSs in order to maximize RBS environmental benefits.

A three-dimensional experimental study on bank retreat: The coupled role of seepage and surface flow

The coupled role of seepage and surface flow on bank retreat has long been neglected, partly due to the concealment and complexity of seepage erosion. To fill this gap, we set up a three-dimensional laboratory experiment to explore bank retreat process in response to seepage and surface flow. During each experiment, we measured the changes of total soil stress, matric suction, and water content within the bank, as well as flow velocity and suspended sediment concentration near the bank. Results show that a rapid decrease in matric suction, the bank toe undercutting consequent to seepage erosion, the formation of tension crack on the bank top, and the occurrence of toppling or shear failure is the typical sequence of the observed bank retreat process under seepage flow. The inclusion of surface flow erodes slump blocks and so promotes cantilever formation, leading to additional bank failure. Compared with the case where only seepage is considered, the frequency of toppling failure under the coupled effect of seepage and surface flow decreases, but the contribution to the bank retreat increases by 37 %. The time taken to collapse in three-dimensional experiments is at least 1.5 h earlier than that of two-dimensional experiments, indicating the importance of preferential flow pathways of seepage. Overall, this research illustrates how surface flow interacts with seepage flow to control bank retreat process and is indeed a first step toward a fully understanding of multifactor-driven bank retreat.

Parameterizing the AquaCrop model for potato growth modeling in a semi-arid region

The AquaCrop model was used to model potato growth in a hot semi-arid environment under diverse irrigation managements including water saving irrigation treatments in two growing seasons of 2012 and 2013. The potato cultivars were Agria and Ramos in 2012, and Agria and Sante in 2013. The irrigation treatments were full irrigation and different static and dynamic deficit irrigation managements. The model was calibrated with the data of the cultivar Agria under full irrigation and static deficit irrigation in 2013. Validation was performed using the data from the other potato cultivars and growing seasons, by keeping the conservative crop parameters adjusted in calibration and changing those non-conservative parameters referring to the crop development. Analysis showed that biomass simulation was highly affected by the normalized water productivity (WP*). Unlike the previous studies on modeling with AquaCrop that assumed only one WP* for the whole growing period, we found that it is required to calibrate one WP* for the first half of the growing season until flowering, and then recalibrated WP* for the late growing season. One single WP* assumed for the whole growing season could not simulate the declining potato growth at the late growing season satisfactory, when potatoes were subject to water stress and high air temperature (heat stress). The simulations of the calibrated model showed that the model could simulate total soil water content, volumetric soil water content, and tuber dry yield satisfactory. In addition, the model showed excellent performance in simulation of the total actual evapotranspiration and end-season water productivity. The AquaCrop model was good in simulating the in-season biomass, though it showed fair simulation of biomass in the late growing season. Overall, the performance of the AquaCrop model was reasonable and satisfactory, and the model is a reliable analytical tool for irrigation water management and proper decision making in potato production under variable water resources in the hot semi-arid areas. • AquaCrop has been used for modeling potato growth in a hot and semi-arid region. • AquaCrop had satisfactory performance in simulating soil water content and tuber dry yield. • AquaCrop had excellent performance in simulating end-season actual evapotranspiration and water productivity. • Two WP* values were assumed to differentiate the effects of water and heat stresses on different growing periods. • The calibrated WP* was assigned 13 and 10 g m −2 during the early and late growing season, respectively.

Response of soil water and carbon storage to short-term grazing prohibition in arid and semi-arid grasslands of China

Appropriate management practices play an important role in the sustainable use of grassland. Prohibition of grazing is beneficial to restore degraded grasslands and increase carbon stocks. To determine the effects of short-term grazing prohibition upon carbon and water stocks in grassland ecosystems an ecohydrological experimental station was established in Erlitu Ranch, Xilinguole League, Inner Mongolia. The station was used to conduct research on vegetation, moisture and other characteristics diagnostic of grassland health. Changes in green above-ground plant parts, below-ground biomass, soil carbon content, soil water content, pH, and total nitrogen between grassland with and without grazing were assessed by ANOVA, and structural equation modelling was used to investigate the interactions among these various factors. The results revealed that after grazing prohibition, the above-ground and below-ground biomass, soil total nitrogen, pH, and soil water content increased. Soil carbon storage increased by 1.27% in the soil layers above 30 cm and decreased by 13.74% in the deeper layers. Correlation analysis indicated that soil water content was positively correlated with carbon content, and closely related to other factors. Grazing prohibition improves soil physical properties and soil water reserves, which indicates an effective management practice in promoting the recovery of grasslands in arid areas.

Evaluation of AquaCrop model performance under mulched drip irrigation for maize in Northeast China

Establishing scientific management and grain production strategies through crop models is an important means to ensure stable and increased food production. To explore the performance of the AquaCrop model for simulating maize growth under mulched drip irrigation in Northeast China, the model was calibrated and verified locally based on three years of measured field data. The simulation effects of canopy cover (CC), total soil-water (TSW), aboveground biomass, crop evapotranspiration (ETC) and grain yield under mulched or nonmulched drip irrigation treatments with different water stress conditions were evaluated and compared. The study found the model had a good simulation effect on CC excluding the rainfed treatment, the root mean square error (RMSE) was <15.2%. The simulated values of TSW and ETc were quite different from those observed in the field. The TSW content was generally underestimated in the middle and late stages of maize growth, with RMSE values ranging from 12.8 to 60.7 mm. The simulated ETC values were generally high, and the prediction error of some treatments exceeded 20%. The model simulated the aboveground biomass and yield well in the calibration year (2016) and the RMSE values were 0.9–2 t/ha and 0.8 t/ha, respectively, but the simulation performance of predicting yield declined in the verification year, and the prediction error exceeded 20%. Compared with the mulched treatments, the model had a better simulation effect on the nonmulched treatments. In general, the simulation of soil moisture under drip irrigation needs to be improved, and the larger overestimation of transpiration and the lower underestimation of evaporation caused to overestimate the maize ETc. It is recommended to improve the simulation of mulched drip irrigation to ensure model applicability in the region of interest.

Effect of winter cover crops on water soil storage, total forage production, and quality of silage corn

Cover crops provide a wide range of benefits to farms and the environment, but this is not reflected in current adoption rates of cover cropping. If cover crops are grown for forage they may raise more interest among farmers whether as feed or as income. The objective of this study was to evaluate if introducing annual winter cover crops will contribute to the yield and quality of annual forage production and will affect soil water content. The experiment included common vetch (Vicia sativa L.), triticale (x Triticosecale Wittm. ex A. Camus) and their mixture as winter forage cover crops, fallow with nitrogen fertilization, and control plot (fallow without fertilization). The main crop was silage corn. A 2-year study was performed at three locations in northern Serbia. The following indices were calculated: forage productivity index (FP) as a ratio between cover crop and silage corn dry matter yield, forage cover crop yield advantage index (FCCYa) as a ratio between total forage yield on cover crop or fertilization treatment and control plot, and forage cover crop protein advantage index (FCCPa) as a ratio between total protein yield on cover crop or fertilization treatment and control plot. The total forage yield in 2012/2013 was higher due to more favorable weather conditions. FP was the highest on treatment with triticale in the first year and on the mixture in the second year. FCCYa was above 1, and higher on cover crop treatments in two locations. Introducing forage cover crops in crop rotation with silage corn showed an advantage in protein yield with all cover crop species, resulting in FCCPa above 1. Forage production at a location with lower FCCYa should be more focused on yield-quality balance. In contrast, in a temperate region in some years annual winter cover crops have a potential negative impact on available soil water storage for cash crop production compared to fallow-corn systems. Results indicate that cover crops impact the annual total forage yield and soil water content, but this alternation is not a species-specific effect. In the region with recurrent drought, forage yield uncertainty may be lessened by winter cover crops which enable reduced dependence on the main forage crop production.

Hydro-physical properties of agriculturally used peatlands in Liang Anggang Protected Forest, South Kalimantan, Indonesia

The utilization of peatlands as agricultural areas that do not pay attention to proper water management will result in peatland degradation. To restore the degraded peatlands, it is necessary to explore the peat’s hydrological and physical characteristics. Therefore this study investigates the hydro-physical peat characteristics in the peatlands that have been converted into agricultural use. The research was carried out in the Liang Anggang Protected Forest area, specifically in the area converted to agricultural land. Undisturbed peat samples were collected in both intensive and un-intensive agricultural sites. Peat characteristics were analysed in the laboratory include bulk density, particle density, porosity, total soil water content, and hydraulic conductivity variables. The result shows that peat characteristics in the intensive agricultural land significantly indicate higher bulk density and particle density with the values 0.30 g/cm3 and 0.91 g/cm3, respectively. Still, significantly lower values are found in porosity (66.87%), total soil water content (226.95%), and hydraulic conductivity (0.0025 cm/s). Degraded peatland restoration that functions as a protected forest must be carried out through rewetting activities and maintaining the water table depth. On the other side, the peatland whose function is designated as an agricultural area, wetland farming systems should be applied using adaptive crop species.

Fractal and multifractal analysis of soil particle-size distribution and correlation with soil hydrological properties in active layer of Qinghai–Tibet Plateau, China

The soil hydrological properties (HPs) in active layers regulate soil water migration and affect the evolution of permafrost and biogeochemical cycles. There is relatively little understanding of the changes in soil HPs as a result of soil particle-size distribution (PSD) in the permafrost regions of the Qinghai–Tibet Plateau. In this study, different land-cover types, namely alpine wet meadow (AWM), extremely degraded wet meadow (EDWM), alpine meadow (AM), degraded alpine meadow (DAM), alpine steppe (AS), and alpine desert (AD), were used to determine the relationships between soil PSD and HPs. Soil HPs were determined using borehole nuclear magnetic resonance, and soil PSD (0–2 mm) was analyzed using fractal and multifractal theory. The results showed that vegetation degradation caused coarse soil particle accumulation in the root zone, reflected by the soil single-fractal dimension (Dv: 2.12–2.50). The Dv values showed significant positive correlations with soil clay and silt content as well as a negative correlation with sand content. Results from the generalized fractal and singularity spectra suggested an even distribution of soil particles in the root zone of the AWM, AM, and AD sites. Vegetation degradation increased the soil PSD capacity dimension (D0), information dimension (D1), correlation dimension, D1/D0 ratio, and Hölder exponent of order zero. This was indicative of a narrow soil PSD range and non-uniform soil texture in the root zone. Although capillary water dominated the total soil water content in the alpine soils, soil water composition was also dependent on the vegetation type and soil stratigraphic distribution. Soil particle composition and multifractal dimensions were found to be effective parameters for forecasting soil HPs in the non-root zone of alpine soils. However, the presence of vegetation weakens the relationship between soil PSD and HPs. This study contributes to the accurate evaluation of hydrological and biogeochemical cycles in permafrost regions.

The effects of hummock-hollow microtopography on soil organic carbon stocks and soil labile organic carbon fractions in a sedge peatland in Changbai Mountain, China

Hummock-hollow microtopography is common in the northern peatlands of the world, but its effects on soil organic carbon (SOC) components are still poorly understood. In this study, we investigated effects of microtopography on SOC stocks and soil labile organic carbon (LOC) fractions in a sedge peatland in Changbai Mountain in northeast China. We found that SOC and soil LOC fractions had much heterogeneity in microtopography. SOC concentration in hummocks was significantly higher than under hummocks and in hollows. On average, the total SOC stock to a depth of 0.3 m below the ground surface was 19.00 kg C/m2. Fifty six percent of the total SOC stock was stored in soils in and under hummocks, despite the hummock only covering 30% of the total area. Light fraction organic carbon (LFOC), easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in hummocks were significantly higher than under hummocks and in hollows. Redundancy analysis (RDA) identified that SOC explained most variations in soil LOC fractions (59.6%), followed by soil total phosphorus (7.4%) and soil water content (6.6%). Our findings indicate that the hummock is an important carbon pool in the sedge peatland. Hummock-hollow microtopography creates heterogeneity in hydrological conditions and soil physicochemical properties, and thus influences SOC stocks and soil LOC fractions at a small scale. This study highlights the importance of microtopography in carbon storage and cycling and has direct implications for the assessment of the carbon sequestration function in northern peatlands.

The effects of degradation on alpine grassland resilience: A study based on meta-analysis data

Alpine grasslands on the Qinghai-Tibet Plateau (QTP) provide irreplaceable ecosystem services to local and global communities. However, intensive human activities have caused severe grassland degradation during recent decades. Due to the harsh environment, these degraded grasslands recover slowly or may be irrecoverable after they degenerate to a certain stage. To understand the changes in the resilience of alpine grassland on the QTP after degradation, we evaluated the resilience indexes of the plant, soil and plant-soil systems of grasslands at different degradation stages based on an integrated assessment system and data extracted from 53 published studies in this region. The results showed that,with grassland degradation, most plant indicators including plant height, aboveground biomass, belowground biomass, Cyperaceae, Gramineae, and soil indicators including silt, clay, soil organic carbon, soil total nitrogen, available nitrogen, available phosphorus, available potassium, and soil water content gradually decreased; soil variables including sand, bulk density, and soil temperature showed an increasing trend; and Margalef richness index, Shannon-Wiener index, Pielou evenness index, and forbs first increased and then decreased. The resilience indexes of the plant, soil and plant-soil systems all displayed an obvious downward trend with the increase of degradation degree, which indicates that reduction of grassland resilience is the coordinated degeneration of vegetation and soil. To restore degraded grassland, we should focus on improving both soil and vegetation status to enhance the resilience of grassland ecosystems.

Parameterization of the AquaCrop model for simulating table grapes growth and water productivity in an arid region of Mexico

Currently, the AquaCrop model has been widely tested for many fruit/grain crops; root and tuber crops; leafy vegetables, or forage crops, but is restricted to annual herbaceous species, while deciduous crops have received less if no attention. In this context, this study aims to test for the first time the ability of the AquaCrop model to simulate canopy cover (CC), actual evapotranspiration (ETa), total soil water content (TWC), biomass (B) and fruit yield (FY) of table grapes vineyards (Vitis vinifera L., cvs. Perlette and Superior) at the Costa de Hermosillo, Sonora in Northwest Mexico. Observed weather and soil physical parameters, with measured crop parameters from an experiment conducted during 2005 were used to develop climate, soil and crop input files for AquaCrop and for calibrating the model. While collected data during the 2006 growing season were used to validate the model. The model adequately simulated CC, ETa and TWC during 2005 and 2006. The Root Mean Square Error (RMSE) between observed and measured CC, ETa and TWC were 5.18%, 0.46 mm/day and 10.11 mm during 2005, and 8.82%, 0.84 mm/day and 9.1 mm during 2006, respectively. The good accuracy of simulations of CC, ETa and TWC by the model have been confirmed by additional statistical parameters like the coefficient of determination (R2), The Mean Bias Error (MBE), the Willmott’s index of agreement (d) and the Nash–Sutcliffe Efficiency (NSE).For the B and FY simulations, the results showed that the model correctly reproduced the B and FY with NRMSE value of 8.8%. The estimated average value of FY (14.56 t/ha) for both seasons are in the range of the potential yield (14–18 t/ha) of table grapes in the irrigated Costa de Hermosillo in northwest Mexico.After the validation of the AquaCrop model, it was used to evaluate the irrigation scheduling by the farmer as well as to assess the water productivity computed as the ratio of crop production to crop water use. The results showed that, the recommended irrigation by the model was about 547 mm and 509 mm, which it is about half of that applied by the farmer (1006 mm and 929 mm) during 2005 and 2006, respectively. This large difference, which represents approximately 54% and 57% of the irrigation supply, is lost through deep percolation and could be saved without vegetation suffering from water stress while maintaining the same yield. The high loss of water by percolation affects significantly the water productivity (WP), which decreases from 3.22 to 1.74 kg/m3 if we consider the transpiration (WPTr), and the sum of ETa and Percolation (WPETa+Pr) for WP computations, respectively. Consequently, the AquaCrop model can be used as an operational tool by decision makers and growers to improve irrigation management. This is of crucial importance in arid and semi-arid regions where water is becoming increasingly scarce.