Mean Soil Water Content Research Articles

Impact of Historical Agrarian Landforms on Soil Water Content Variability at Local Scale in West Carpathian Region, Slovakia

The historical agrarian landforms (AL) represent man-made features that alter the hydrological process on cultivated hillslopes. Soil water content (SWC) and its spatial and temporal variability represent an important state indicator for understanding of these processes. In order to assess the differences between individual AL in terms of SWC stability, continuous soil moisture measurements at five different monitoring localities characterized by a specific combination of AL and environmental factors were performed. Temporal SWC stability was evaluated using mean relative difference (MRD) and its standard deviation (SDRD). Differences in mean SWC and MRD values demonstrated the difference between saturated inner part of the AL and external parts such as terraced slopes and mounds, soil depths, and slope positions. In order to analyze the relationship between SWC and environmental variables, the methods of constrained ordination were applied. The most influential factors that regulate SWC variability during the periods of rain were identified as: stone content, sand fraction content, slope orientation, type of agrarian landform, and its orientation against the contour lines. Results also pointed to the fact that different factors predominate among individual localities and, therefore, SWC variability reflects the effect of combination of various environmental factors rather than effect of single parameter. Besides the improved understanding of SWC variability, our results also highlight the importance of AL in regulating the hydrological processes at historical agricultural landscape of the West Carpathian region.

A global synthesis of transpiration rate and evapotranspiration partitioning in the shrub ecosystems

Transpiration (T) is a fundamental process in understanding the ecophysiology of plants, and it is the dominant component of evapotranspiration (ET) in the terrestrial water cycle. Although previous studies have examined T characteristics of shrub ecosystems in some regions, global-scale synthesis that integrates the spatial variations of T, ET and ratio of T to ET (T/ET) and the associated influences of bio-/abiotic factors in the shrub ecosystems is currently lacking. In this study, we synthesized and analyzed T rate, ET rate and T/ET of the shrub ecosystems from the peer-reviewed articles using field observations around the world. These studies were mainly distributed in drylands with aridity index (ratio of precipitation to potential ET) < 0.65, which accounted for 86.4% of the study locations. Globally, the mean daily T and ET rates of shrubs were 1.5 ± 1.0 mm d−1 and 2.4 ± 0.8 mm d−1, with coefficient of variation of 63.2% and 36.2% among the study locations, respectively. Mean T/ET of the shrubs over the growing season was 0.54 ± 0.14, which was generally lower compared with forest, grassland and cropland ecosystems. The T rate of shrubs was positively related to shrub age, shrub height, leaf area index, and vegetation coverage (p < 0.05), and the effects of biotic factors on T rate were stronger compared with abiotic factors. The ET rate of shrubs was positively related to aridity index, long-term annual mean precipitation, mean soil water content, as well as shrub height and vegetation coverage (p < 0.05). By contrast, the effects of biotic factors on variations of shrub T/ET were weaker than those of abiotic factors, and the T/ET of shrubs was negatively related to aridity index, long-term annual mean precipitation and mean soil water content, but positively related to latitude (p < 0.05). This study is an important supplement of our knowledge gap in terrestrial water cycle, and the findings suggest that T accounted for about half of the water into atmosphere from shrub ecosystems, and the variations of T rate of shrubs were mainly controlled by biotic factors, whereas ET rate and T/ET was mainly affected by abiotic factors.

Artificial forest conversion into grassland alleviates deep-soil desiccation in typical grass zone on China’s Loess Plateau: Regional modeling

Afforestation has significantly increased vegetation cover and has slowed soil erosion on China’s Loess Plateau (CLP). However, intensive afforestation activities in semi-arid regions that are in excess of local water availability can cause imbalances in the soil water budget. This can cause soil desiccation, which in turn builds up dry soil layers (DSL) in the soil profile. The occurrence of DSL can threaten the sustainable development of restored ecosystems in water-scarce regions. Knowledge of the spatial characteristics of DSL in artificial forests and their response to land-use change is critical for optimal soil water management and ecological sustainability in the CLP. Therefore, the spatial characteristics of DSL under artificial forest in a typical grassland area on the CLP were investigated. The temporal (2015–2040) dynamics of soil water content (SWC) in the 0–5 m soil profile after the land-use change were simulated and analysed using the Hydrus-1D software. Based on the investigation, DSL existed at some 81% of the sampling sites in the typical grassland area on the CLP. The occurrence of DSL was graded as severe, with a mean thickness of 297 cm and mean SWC of only 9%. The model simulation showed that two phases of SWC dynamics developed after land-use change. One of the phases is the gradual recovery of SWC after the conversion of artificial forests into grassland. The other is that of SWC fluctuations with rainfall under grassland conditions. It requires some 2–13 years (mean of ~7 years) for the soil water to recover in the 0–5 m soil profile after artificial forest is converted to grassland across the semi-arid grass zone of the CLP. Structural equation modelling showed that the duration of DSL recovery was driven directly or indirectly by the degree of dryness of the DSL, soil hydraulic properties, and slope. It is therefore concluded that DSL in the 5-m soil profile can fully recover if there is a vegetation shift in the semi-arid grassland area of the CLP. This is critical for prediction studies of DSL dynamics and sustainable soil water management in water-scarce plateau regions.

GEA Group, Germany

Afforestation has significantly increased vegetation cover and has slowed soil erosion on China’s Loess Plateau (CLP). However, intensive afforestation activities in semi-arid regions that are in excess of local water availability can cause imbalances in the soil water budget. This can cause soil desiccation, which in turn builds up dry soil layers (DSL) in the soil profile. The occurrence of DSL can threaten the sustainable development of restored ecosystems in water-scarce regions. Knowledge of the spatial characteristics of DSL in artificial forests and their response to land-use change is critical for optimal soil water management and ecological sustainability in the CLP. Therefore, the spatial characteristics of DSL under artificial forest in a typical grassland area on the CLP were investigated. The temporal (2015–2040) dynamics of soil water content (SWC) in the 0–5 m soil profile after the land-use change were simulated and analysed using the Hydrus-1D software. Based on the investigation, DSL existed at some 81% of the sampling sites in the typical grassland area on the CLP. The occurrence of DSL was graded as severe, with a mean thickness of 297 cm and mean SWC of only 9%. The model simulation showed that two phases of SWC dynamics developed after land-use change. One of the phases is the gradual recovery of SWC after the conversion of artificial forests into grassland. The other is that of SWC fluctuations with rainfall under grassland conditions. It requires some 2–13 years (mean of ~7 years) for the soil water to recover in the 0–5 m soil profile after artificial forest is converted to grassland across the semi-arid grass zone of the CLP. Structural equation modelling showed that the duration of DSL recovery was driven directly or indirectly by the degree of dryness of the DSL, soil hydraulic properties, and slope. It is therefore concluded that DSL in the 5-m soil profile can fully recover if there is a vegetation shift in the semi-arid grassland area of the CLP. This is critical for prediction studies of DSL dynamics and sustainable soil water management in water-scarce plateau regions.

Efficient prediction of profile mean soil water content for hillslope-scale Caragana korshinskii plantation using temporal stability analysis

Spatio-temporal variability in soil water content (SWC) increases the difficulty in soil water resource management and vegetation construction in arid and semi-arid regions. Our objectives were to investigate the spatial variability and temporal stability of SWC and identify representative locations for reliably predicting the profile mean SWC (MSWC) of a 33-year-old Caragana korshinskii plantation on typical sunny and shady hillslopes on the Loess Plateau, China. The profile SWC (0–180 cm) in three sampling belts and five hillslope positions (upper position, UP; upper-middle position, UMP; middle position, MP; lower-middle position, LMP; lower position, LP) were measured 27 times for both the hillslopes in 2018 and 2019. The mean relative difference (MRD), the standard deviation of the MRD (SDRD), and an index of temporal stability (ITS) were used to identify representative locations of the MSWC. The results indicated that the SWC presented different horizontal but similar vertical change trends in the five hillslope positions. The profile MSWC on the sunny hillslope (8.89%) was lower than that on the shady hillslope (9.44%). The mean Spearman correlation coefficients of the temporal patterns ranged from 0.6 to 0.8 for the five soil layers on both hillslopes. The characteristics of temporal stability differed in both temporal persistence and the representative locations for the five soil layers on the sunny and shady hillslopes. The mean ITS values generally decreased with increasing soil depth. Ultimately, the representative locations for estimating the profile MSWC were determined to be the MP-2 location on the sunny hillslope and the MP-3 location on the shady hillslope based on the MRD, SDRD, and ITS values. The representative locations have the lowest ITS values and represent the MSWC accurately, with root mean square error (RMSE) and mean error (ME) values of less than 1%. In addition, the soil organic carbon, clay, silt, and sand contents greatly affect the spatial and temporal distributions of the soil water at the hillslope scale. Our study provides a rapid and accurate method for determining profile MSWC in C. korshinskii plantations on typical sunny and shady hillslopes and could also support valuable guidance for the rational management of hillslope-scale SWC resources for similar dry regions.

Analysis of the spatio-temporal variability of soil water dynamics in an arid catchment in South Africa

The accurate quantification of soil water dynamics is critical as it is a key parameter in the soil-plant-atmosphere continuum. This study was conducted to analyse the spatio-temporal variability of soil water dynamics in dry areas. The Soil and Water Assessment Tool (SWAT) was used to estimate the dynamics of soil water balance. The model was calibrated and validated by the regionalization with physical similarity approach. Unlike the revap water (water drawn upwards from shallow groundwater tables), the soil water, percolation and lateral flow increased with precipitation. The Mann Kendall trend test also shows that there was no trend in both the annual and monthly soil water content (SWC) and percolation; however, there was a decreasing trend (1.091 mm per annum) in the revap water. The contribution of the revap water to evapotranspiration (ET) varied from 9% during summer to 32% during spring. The SWC also exhibited a higher spatial variation. Larger part of the catchment recorded a long-term annual mean soil water content varying between 0.1 and 0.2 mm mm−1. The soil water anomaly (SWA) consistently follows the trends of dry and wet seasons in the study area. Although the use of model-derived drought monitoring indices are relevant for farmers and decision makers in arid areas, it requires intensive verification over much larger scales to increase the reliability of model results.

Parameterization of the AquaCrop model for cowpea and assessing the impact of sowing dates normally used on yield

The AquaCrop model was evaluated considering a data set from a cowpea (BR3-Tracuateua cultivar) cultivation in Castanhal/Brazil under different irrigations during the reproductive phase, which is sensitive to water deficit. Data on leaf area index (LAI), soil water content (SWC), biomass, and final yield of two harvests were used for model calibration (2013) and validation (2014). LAI data were used for parameterization of canopy cover (CC), and some crop parameters obtained in the field. The model was also used to evaluate the impacts of sowing dates, as well as the strategy of using an economical irrigation threshold (60% of Readily Available Water) on the water use and crop yield. Regarding the results after parameterization of the canopy cover curve, the model efficiency index (EF) presented a satisfactory performance (0.98), which is due to the high correlation coefficient (R2 = 0.99) between the simulated and observed values and the low values of normalized root mean square error (NRMSE < 6.33%). For model performance in simulating SWC, there was high efficiency (EF > 0.70) for all treatments, with low estimated errors and NRMSE representing 8.12% of mean SWC observations during validation, indicating high precision for simulation of biomass and cowpea yield. The model performance index ranged from 0.92 to 0.94 for biomass and from 0.92 to 0.99 for final yield. These results showed that AquaCrop is suitable for simulating biomass production and yield of cowpea. Additionally, sowing in early April is appropriate for better water use and productivity and the tested irrigation threshold can be indicated to significantly improve final crop yields.

The Root-Soil Water Relationship Is Spatially Anisotropic in Shrub-Encroached Grassland in North China: Evidence from GPR Investigation

To analyze the root-soil water relationship at the stand level, we integrated ground-penetrating radar (GPR), which characterized the distribution of lateral coarse roots (&gt;2 mm in diameter) of shrubs (Caragana microphylla Lam.), with soil core sampling, which mapped soil water content (SWC) distribution. GPR surveys and soil sampling were carried out in two plots (Plot 1 in 2017 and Plot 2 in 2018) with the same size (30 × 30 m2) in the sandy soil of the semi-arid shrubland in northern China. First, the survey area was divided into five depth intervals, i.e., 0–20, 20–40, 40–60, 60–80, and 80–100 cm. Each depth interval was then divided into three zones in the horizontal direction, including root-rich canopy-covered area, root-rich canopy-free area, and root-poor area, to indicate different surface distances to the canopy. The generalized additive models (GAMs) were used to analyze the correlation between root distribution density and SWC after the spatial autocorrelation of each variable was eliminated. Results showed that the root-soil water relationship varies between the vertical and horizontal directions. Vertically, more roots are distributed in soil with high SWC and fewer roots in soil with low SWC. Namely, root distribution density is positively correlated with SWC in the vertical direction. Horizontally, the root-soil water relationship is, however, more complex. In the canopy-free area of Plot 1, the root-soil water relationship was significant (p &lt; 0.05) and negatively correlated in the middle two depth intervals (20–40 cm and 40–60 cm). In the same two depth intervals in the canopy-free area of Plot 2, the root-soil water relationship was also significant (p &lt; 0.01) but non-monotonic correlated, that is, with the root distribution density increasing, the mean SWC decreased first and then increased. Moreover, we discussed possible mechanisms, e.g., root water uptake, 3D root distribution, preferential flow along roots, and different growing stages, which might lead to the spatially anisotropic relationship between root distribution and SWC at the stand level. This study demonstrates the advantages of GPR in ecohydrology studies at the field scale that is challenging for traditional methods. Results reported here complement existing knowledge about the root-soil water relationship in semi-arid environments and shed new insights on modeling the complex ecohydrological processes in the root zone.

Soil Moisture Estimation and Its Influencing Factors Based on Temporal Stability on a Semiarid Sloped Forestland

Soil water content (SWC) plays a crucial role in the hydrological cycle and ecological restoration in arid and semi-arid areas. Studying the temporal stability of SWC spatial distribution is a requirement for the dynamic monitoring of SWC and the optimization of water resource management. The SWC in a Pinus tabulaeformis Carr. forest on the slope of the Loess Plateau of China were analyzed in five soil layers (0–100 cm with an interval of 20 cm) in the rainy and dry seasons from July 2014 to November 2017. The mean SWC was estimated and the main factors affecting the temporal stability of the SWC were further analyzed. Results showed that the SWC had strong temporal stability during the two seasons for several consecutive years. The temporal stability of SWC and the number of representative locations varied with season and depth. The elevation, soil total phosphorus (STP), clay, silt, or sand content of the representative locations approached the corresponding mean value of the study area. A single representative location accurately represented the mean SWC for the five depths in the rainy and dry seasons (RMSE &amp;lt;2%; rainy season: 0.81 &amp;lt; R2 &amp;lt; 0.94; dry season: 0.63 &amp;lt; R2 &amp;lt; 0.83; p &amp;lt; 0.01). The mean relative difference (MRD) and the relative difference standard deviation (SDRD) changed with the seasons and were significantly correlated with elevation, root density, and sand and silt content in two seasons (p &amp;lt; 0.05). Elevation, root density, and sand content were the main factors influencing the change of SWC temporal stability in different seasons. The results provide scientific guidance to monitor SWC by using a small number of locations and enrich our understanding of the factors affecting the temporal stability of SWC in the rainy and dry seasons of the Loess Plateau of China.

Spatial heterogeneity of throughfall and its contributions to the variability in near-surface soil water-content in semiarid mountains of China

Throughfall (TF) is one of the most important factors affecting forest surface soil moisture. However, TF heterogeneity and its contributions to the variability in near-surface soil water-content (SWC) in a spruce forest in semiarid mountain ecosystems are poorly understood, and may determine plant survival. Here, we systematically investigated variability of TF in a Picea crassifolia stand within a protected semi-arid mountain ecosystem, and evaluated the contributions of TF to near-surface SWC variability obtained from TF gauges and SWC measurements at the plot level. Results showed that TF variability tended to decline with an increase in rainfall amount, intensity, and duration, and then tended to be stable after a value of 24.1 mm, 3.1 mm h−1 and 789.8 min, respectively. Both TF and surface SWC were highly spatially variable, but the spatial patterns appeared to be stable over time based on time-stability analysis. The mean SWC increment exhibited a strong positive power relationship with plot mean TF, and the percent of locations with SWC increments increased similarly to TF amount for individual rainfall events. TF, soil bulk density, and litter fall biomass can significantly (P < 0.05) affect the stability of SWC increments. Therefore, our research indicated that further research should consider the relative importance of, and interactions among precipitation characteristics, soil heterogeneity, and vegetation characteristics. Our results may be useful for land managers involved in enhancing the water conservation capacity of semi-arid mountain forest ecosystems, where climatic conditions, soil quality and vegetation characteristics will determine the supply of multiple forest ecosystem functions.

Influence of no-tillage and precipitation pulse on continuous soil respiration of summer maize affected by soil water in the North China Plain

Soil respiration (RS) from cropland in response to tillage practices contribute to global climate change. We quantified the effect of no-tillage (NT) and conventional tillage (CT) on RS and precipitation in the North China Plain (NCP). An in-situ automatic sampling and measurement method was applied during the maize (Zea mays L.) growth stages in 2018 and 2019. The continuous daily RS, soil water content and temperature were monitored during all the maize growth stages, whereas maize grain yield, aboveground biomass, and soil microbial biomass were measured after harvest. The mean RS across tillage practices on bright days was higher in 2018 (16.69 g CO2 m−2 d−1) than that in 2019 (12.99 g CO2 m−2 d−1). Compared with CT, NT increased RS on bright days by 31.44% in 2018 and 15.60% in 2019. However, mean RS on rain-affected days across tillage practices was lower in 2018 than that in 2019. NT increased mean RS after precipitation in 2018 (p < 0.05). The contribution of RS after precipitation to cumulative RS (across tillage practices) was higher in 2019 (51.90%) than that in 2018 (41.18%). Mean soil water content and temperature were higher in 2018 than that in 2019 (p < 0.05). NT increased soil water content on bright days in 2019. Furthermore, soil water content was more important in regulating RS in 2018, while soil temperature was more critical after precipitation in 2019. Crop productivity was lower in 2019 than in 2018 (p < 0.05). However, neither crop productivity nor soil microbial biomass varied with tillage practices (p > 0.05). Overall, influence of tillage practices and precipitation on RS were different according to soil water content. Therefore, it is necessary to decrease excessive irrigation to reduce RS in dry years and to conduct continuous observations on RS after precipitation in the NCP.

Spatio‐temporal variability of multi‐layer soil water at a hillslope scale in the critical zone of the Chinese Loess Plateau

AbstractUnderstanding the spatio‐temporal variability of soil water content (SWC) in the Critical Zone (CZ) is essential to balance plant‐water benefits and to enhance the ability to monitor and predict drought. In current study, the spatial variability and temporal stability of multi‐layer SWC to a depth of 500 cm (35 soil layers) at 27 sampling sites were evaluated at a hillslope scale. A total of 64 SWC measurements were obtained from 28 March, 2017 to 23 December, 2018. We hypothesized the existence of a “special point” that is temporally stable both in horizontal direction (which means different layers) and in vertical direction (which means different profiles). We found a clear seasonal dynamic pattern of mean SWC for all sites in the 0–500 cm profile, with SWC varying from 4.0 to 24.8%. In the horizontal layer, both the 130‐cm and 140‐cm layers contained a maximum number of temporal stability sites (N = 4) which all located at H11, H13, H14 and H26. In the vertical profile, H19 was the most stable site, followed by H10 and H26, with 15, 10 and 6 stable layers, respectively. The decreasing order of SWC temporal stability was 200–500 cm, 0–500 cm and 0–200 cm, which means the temporal stability of SWC in 0–500 cm profile was more dependent on the 0–200 cm sub‐profile. At a three‐dimension scale, the most temporal stability layer and site was 180‐cm of H1 and H21 of 220‐cm, which confirmed our hypothesis. This study provides an accurate description of SWC spatio‐temporal variation at the hillslope scale, which is helpful for addressing eco‐hydrological models and water management issues in the Earth's CZs.

Determinants of the Asymmetric Parameter in the Generalized Complementary Principle of Evaporation

AbstractThe complementary principle, which was first proposed by Bouchet (1963), illustrates a complementary relationship among the actual evaporation, the potential evaporation, and the apparent potential evaporation. It has generated increasing attention for estimating evaporation by using only routinely observed meteorological variables (radiation, wind speed, air temperature, and humidity) without complex surface property parameters. However, this principle still poses great challenges because of the underlying uncertainties in estimating its critical parameter, namely, asymmetric parameter b. In this study, we adopted a sigmoid generalized complementary function and utilized the eddy covariance (EC) data from 217 sites around the world to determine b values in different ecosystems and their correlation with environmental factors. We found b has a mean value of 6.01 ± 0.08. The asymmetric parameter b is small in dry regions (i.e., the desert ecosystem, 0.42 ± 0.02) and increases as the land surface wetness improves. The ecosystem mean air temperature and vapor pressure deficit have negative correlations with b (Pearson correlation coefficients are −0.57 and −0.52, respectively), and the mean soil water content has a positive correlation with b (0.69). Besides, the sigmoid function has a favorable capability in estimating evaporation no matter based on the site‐specific b values or the ecosystem mean b values. The ecosystem mean b values given in the current study also perform acceptably in the independent verifications, indicating these values can be applied extendedly for regional and global studies.

Evaluation of crop water stress index and leaf water potential for differentially irrigated quinoa with surface and subsurface drip systems

A 2-year field experiment was conducted with the objectives to evaluate the physiological and yield response of quinoa cv Titicaca to various deficit irrigation strategies applied with surface drip (SD) and subsurface drip systems (SSD) under the Mediterranean climatic conditions in 2016 and 2017. The treatments consisted of regulated deficit irrigation (RDI), partial root-zone drying (PRD50), conventional deficit irrigations (DI50, DI75) and full irrigation (FI) under SD and SSD. A rainfed treatment was also included. The experimental design was split plots with four replications. DI75 and DI50 received 75 and 50% of FI, respectively. PRD50 plots received 50% of FI, but from alternative laterals in each application. RDI received 50% of FI during vegetative stage until flowering, then received 100% of water requirement. The results indicated that RDI resulted in water saving of 23 and 21% for surface drip (SD) and SSD systems, respectively, and RDI produced statistically similar yield to FI treatment in both experimental years. DI75 treatment resulted in water savings of 16% for both drip methods in the first year and 10 and 25% for SD and SSD systems, respectively, in the second year. Thus, RDI and DI75 treatments appear to be good alternative to FI for sustainable quinoa production in the Mediterranean environmental conditions. Greater leaf water potential (LWP) and smaller crop water stress index (CWSI) values were measured in FI plots under both drip systems than deficit irrigation treatment plots. Significant second-order polynomial relations were determined between CWSI and LWP for the drip systems. Leaf area index (LAI), LWP decreased and CWSI increased as the drought increased. CWSI correlated significantly (P < 0.01) and negatively with grain yield, dry matter yield, LAI, and mean soil water content indicating that grain yield of quinoa declined with increasing CWSI values. All these relations are best described by significant second-order polynomial equations. The results revealed that quinoa should be irrigated at LWP values between − 1.35 and − 1.60 MPa, and average CWSI value of approximately 0.35 for high yields.

Spatiotemporal variability of soil–water content at different depths in fields mulched with gravel for different planting years

Information about the spatiotemporal variability of soil–water content (SWC) is important for the management of soil resources. We present a case study of the temporal stability and variability of SWC at various depths in 32 × 32 m2 fields mulched with gravel for different planting years, a form of mulching that has been widely used by farmers in the loessial area of China for over 300 years, also, same analysis has been done on a bare land as CHECK. SWC was measured weekly from May to August 2013, May to August 2014, July to October 2015 and June to September 2016 in the 0–10, 10–30 and 30–50 cm layers. The higher SWCs of the gravel-mulched fields than the bare land decreased with depth and length of mulching, indicating the degradation of the fields. SWC was more variable in the surface soil, and the variability gradually decreased with depth. Locations representative of the field-mean SWCs were identified based on the stability of the SWC spatial patterns over time and along the soil profile in 2013. The mean SWCs at different soil layers for 2014, 2015 and 2016 were estimated by the measured SWCs of representative locations which were determined using the data of 2013, with high coefficients of determination ranging between 0.926 and 0.997. The monitoring of field-mean SWC over a long period of time from representative locations is thus feasible. Our results will provide a theoretical reference for monitoring SWC in a large scale from few observations and aid the management of gravel mulched field.

The Effects of Temperature and Humidity on a Field Population of Bradysia odoriphaga (Diptera: Sciaridae).

The production of Chinese chives is reduced throughout China due to a root-feeding dipteran pest Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae), therefore deciphering the conditions influencing its growth and development are important in developing ecological control strategies. A study was conducted from 2014 to 2017 to determine the relationship between the abundance of B. odoriphaga and temperature (atmospheric and soil), soil water content, and atmospheric humidity in a Chinese chive field in Beijing City, China. Numbers of adults peaked in March and October to November and were lowest in July to August and December to next February; numbers of larvae were highest in December to next February and lowest in July to August. From 2014 to 2017, the numbers of adults and larvae were significantly correlated with monthly mean atmospheric temperatures and soil temperatures, but were not significantly correlated with monthly mean atmospheric relative humidity and soil water content. However, for both adults and larvae, numbers were significantly greater with high soil water contents compared with drought treatment. The results of this study suggest that the very low soil water contents, high atmospheric temperatures, and high soil temperatures were critical for regulating field populations of B. odoriphaga.

Eight years of variations in ecosystem respiration over a residue-incorporated rotation cropland and its controlling factors

The carbon dioxide emissions from cropland play important roles in the regional carbon budget. In this study, continuous measurements of the ecosystem respiration (RE) were obtained using the eddy covariance technique in a winter wheat–summer maize double cropping agroecosystem mainly between 2004 and 2012 in order to identify the among-year variations in RE and the related factors responsible. The annual RE, estimated by Lloyd and Taylor model, which was the most accurate, was 1866.4 ± 105.75 g C m−2 year−1 and it ranged from 1650.68 g C m−2 year−1 to 1945.57 g C m−2 year−1 during the eight years. The seasonal RE values were 867.98 ± 125.24 g C m−2 year−1 and 890.55 ± 131.34 g C m−2 year−1 for wheat and maize, respectively. Additionally, crop residue carbon ranged from 322.73 g C m−2 year−1 in 2012 and 453.49 g C m−2 year−1 in 2007. Correlation analysis indicated that the interannual variations in wheat and maize RE were correlated with the seasonal mean soil water content (W-Ws) and maximum leaf area index (W-LAImax) of wheat, and seasonal mean air temperature of maize (S-Ta), respectively. A rest method was attempted to investigate whether these relationships were occasional or inevitable. The rests of RE, i.e. the difference between simulated and observed RE values, were significantly influenced by LAI of wheat and hourly Ta of maize season but not by hourly Ws of maize season, indicating that the influence of W-LAImax and S-Ta on RE were inevitable outcomes and that of W-Ws on wheat RE was occasional. So we suggested that one should not confirm the controlling factors of interannual variations in carbon fluxes just from simple relationships, which may be statistical coincidences and do not correlated with biotical processes.

Combined effects of moss crusts and pine needles on evaporation of carbonate-derived laterite from karst mountainous lands

The development of biocrusts and litter cover has been promoted by the vegetation restoration of karst mountainous lands in recent decades. However, the contribution of biocrust and litter to the karst terrestrial water cycle is still unclear. The interactive effects of moss crusts and pine needles on evaporation processes were explored by inserting microlysimeters (20 cm radius and 35 cm height) into the karst mountainous lands to collect undisturbed soils. Four moss crust biomass levels (0, 0.32, 0.64 and 0.96 kg m−2) and three pine needle biomass levels (0, 0.32 and 0.64 kg m−2) were used to estimate the influences of moss crusts and pine needles on evaporation losses and surface temperatures. In addition, the performances of two simplified evaporation concepts considering the interaction effects of moss crusts and pine needles were also assessed. The effect of pine needle cover on reducing evaporation rates was stronger than that of moss crusts. Moreover, the influences of moss crusts on the evaporation rate were obviously restricted by the higher biomass of pine needles, while the effects of pine needles on the evaporation rate were not highly affected by the moss crusts. Furthermore, thermal signatures showed that the pine needles had a much larger positive effect on the surface temperature (pr = 0.50) compared to the effect of the moss crusts (pr = 0.17). There was a significant relationship between the value of Ebare-soil/E0 and the mean soil water content SWCmean for bare soils. The predictive ability of the one-parameter concept (weighted average vegetation coefficient kc) was slightly better than that of the double-parameter concept (moss crust factor kMC and pine needle factor knp). The key ecohydrological role of ground cover in controlling evaporation cannot be neglected for karst mountainous land management and preventing rocky desertification.

Reducing yield-scaled global warming potential and water use by rice plastic film mulching in a winter flooded paddy field

Winter flooded paddy fields emit considerable amounts of CH4 and N2O that add to global warming potential (GWP). However, mitigating the GWP and water use without compromising crop yield in the fields is poorly documented. A 3 year-round field experiment was conducted with the use of PM (plastic film mulching cultivation with water-saving irrigation in rice season while drainage in winter season) in comparison of two traditional paddies that were flooded in the winter season but either rain-fed (TC1) or continuously flooded (TC2) in the rice season. Shifting TC1 into PM significantly promoted rice tiller and increased grain yields by 23 %, showing a significant increase in effective number of panicles per m2 (40 %), total filled grains per m2 (55 %) and filled grains percentage (4.2 %). Changing TC2 into PM, however, had little effect on these variables. Compared with TC1 and TC2, the PM reduced annual water use by 20–69 %. Meanwhile, it decreased annual cumulative CH4 emissions by 23–64 % and increased N2O emissions by 56–4.2 %. This change was probably related to the significant decreases in both dissolved organic carbon content (DOC) and CH4 production potential (MPP) for CH4, and much higher NH4+-N concentration at the beginning of the rice season and a more favorable soil water content (SWC) for N2O. Because mean CH4 emission was positively correlated with mean DOC and MPP, and mean N2O emission was negatively related to mean SWC, respectively. Overall, the PM reduced annual GWP by 18–60 % and yield-scaled GWP by 34–60 % relative to TC1 and TC2. The findings suggest that the application of PM in the winter flooded paddy fields substantially mitigates GWP and has a great potential to reduce water use while maintaining high yields.

The spatial variability of soil water content in a potato field before and after spray irrigation in arid northwestern China

Abstract Assessing the spatial variability of soil water content is important for precision agriculture. To measure the spatial variability of the soil water content and to determine the optimal number of sampling sites for predicting the mean soil water content at different stages of the irrigation cycle, field experiments were carried out in a potato field in northwestern China. The soil water content was measured in 2016 and 2017 at depths of 0–20 and 20–40 cm at 116 georeferenced locations. The average coefficient of variation of the soil water content was 20.79% before irrigation and was 16.44% after irrigation at a depth of 0–20 cm. The spatial structure of the soil water content at a depth of 20–40 cm was similar throughout the irrigation cycle, but at a depth of 0–20 cm a relatively greater portion of the variation in the soil water content was spatially structured before irrigation than after irrigation. The autocorrelation of soil water contents was influenced by irrigation only in the surface soil layer. To accurately predict mean soil moisture content, 40 and 20 random sampling sites should be chosen with errors of 5% and 10%, respectively.