Soil Water Content Response Research Articles

黄土丘陵区坡耕地与撂荒地土壤水分对降雨的响应特征

为了揭示黄土丘陵区不同土地覆被方式下土壤含水量对不同强度降雨的响应过程，选取山西省冯家沟小流域农耕地和撂荒地为研究对象，基于2019年4-10月降雨和土壤含水量以小时为单位的观测数据，分析了土壤含水量对不同强度降雨的响应规律。结果表明：（1）小雨、中雨、大雨和暴雨对土层的影响深度分别为20、20、60 cm和60 cm，研究区降雨最主要的形式-小雨对土壤水分的补给作用较小。（2）各强度降雨过程中，除0-10 cm土层外，农耕地土壤含水量均大于撂荒地，且大雨条件下农耕地各土层土壤含水量变化较显著，而撂荒地仅0-10 cm和10-20 cm土层土壤含水量有所增加。（3）不同土层土壤含水量对降雨的响应不同，表层响应相对明显而深层相对减弱；农耕地土壤平均含水量最大值出现在50-60 cm土层，而撂荒地出现在30-40 cm土层。（4）本地区农耕地土壤含水量高于撂荒地，表明在该地区适当的作物种植有较好的储存土壤水分的作用。本研究的结果对地区水资源的高效利用和水土流失防控提供了一定的科学依据。;In order to reveal the response process of soil water content to different rainfall intensities under different land cover modes in Loess hilly region. This study selected the cultivated land and abandoned land in Fengjiagou small watershed of Shanxi Province as the research objects. Based on the observation data of rainfall and soil water content in hours from April to October 2019, the response of soil water content to different rainfall intensities was analyzed. The results showed that:(1) The influence depths of light rainfall, moderate rainfall, heavy rainfall and torrential rainfall on soil layer were 20, 20, 60 cm and 60 cm, respectively. The main form of rainfall-light rainfall had little effect on soil moisture in the study area. (2) During each rainfall intensity, except 0-10 cm soil layer, the soil water content of the cultivated land was higher than that of abandoned land, and the soil water content of each soil layer in the cultivated land changed significantly under heavy rainfall conditions, while the soil water content of abandoned land was only increased in 0-10 cm and 10-20 cm soil layers. (3) The content of soil water among soil layers had different response to rainfall, and the response of surface soil moisture was more responsive than that of the deep soil water content. The maximum average soil water content appeared in 50-60 cm soil layer in the cultivated land, while the abandoned land appeared in the 30-40 cm soil layer. (4) The soil water content of the cultivated land was higher than that of the abandoned land, indicating that appropriate crop planting in this region had a better role in storing soil moisture. The results of this study provide a scientific basis for the efficient utilization of regional water resources and the prevention and control of soil erosion.

Evaluating foliar characteristics as early indicators of plant response to biochar amendments

Biochar amendments are widely promoted for increasing soil nutrient availability and plant yield, and although many plant species show positive growth responses, neutral to negative effects can also occur. Although biochar effects on plant yield may not yet be evident in the first growing season after amendment, foliar characteristics such as nitrogen (N) and chlorophyll concentrations are known to respond to changes in soil fertility and therefore may provide an early indication of plant performance. In this study, we investigated the effects of contrasting biochar treatments on soil nitrogen (N) forms and plant chlorophyll, and the relationships between soil and plant nitrogen status, for two economically important conifer species, Abies balsamea (L.) Mill and Picea pungens Englem., as well as forb and grass weeds. We applied two types of pyrolysis biochars (hereafter, USB and BGR) that differed in feedstock type (pine wood versus mixed forest harvesting residue) at contrasting application rates (low, high, and untreated control) to a fine sandy loam soil. We measured soil water content (SWC), pH, and inorganic nitrogen (NH4+, NO3−, and total inorganic N (TIN)), as well as plant foliar N, and chlorophyll content (Chl-a, -b, -ab), and fluorescence (Fv/Fm). SWC response was variable whereas all treatments except USB low increased pH. All treatments decreased inorganic N concentrations relative to the control, although differences diminished over the study period. USB high decreased Picea foliar N concentration whereas all treatments decreased grass foliar N. BGR decreased Abies Fv/Fm (low) and Picea Chl-a, Chl-ab (both levels), and Chl-b (low), whereas USB increased Abies Chl-ab (high). There was a weak positive relationship between foliar N and soil NH4+ (r2 = 0.14) and NO3− (r2 = 0.11) in Abies seedlings, and between foliar N and TIN (r2 = 0.16, 0.11) in both conifers. Abies foliar N showed a weak positive effect on Chl-a (r2 = 0.22), Chl-b (r2 = 0.10), and Chl-ab (r2 = 0.22). Soil NO3− (r2 = 0.14) and TIN (r2 = 0.14) showed a weak negative correlation with Picea foliar Fv/Fm. This study shows that biochar type and amendment level influence soil and plant nitrogen responses, as well as their relationships, and responses may differ between plant species. Evaluating foliar characteristics shows promise as an early indicator of plant response to biochar, and may provide additional important information for evaluating contrasting biochars as potential sustainable soil amendments.

Response of soil water content and temperature to rangeland desertification in an alpine region with seasonally frozen soil and plateau pika (Ochotona curzoniae) burrows

Variations in soil temperature and water content are important indicators of land desertification, and play a significant role in ecological environments in desert regions, thus could help in establishing effective measures to combat desertification. In this study, the changing characteristics of plateau pika (Ochotona curzoniae) burrows, soil water content, and temperature under three levels of desertification (slight, medium, and severe) were assessed. The number of pika burrows was investigated in quadrats with areas of 400 m2. The areas of pika burrow mounds were obtained by taking pictures vertically and measured by AutoCAD, 2007. Soil temperature and water content were monitored by soil temperature and moisture smart sensors installed at depths of 5, 10, 20, and 50 cm. Data were recorded at 10-min intervals by Hobo Data Loggers. The greatest number of pika burrows and the greatest area of pika burrow mounds were found in the medium desertified site, followed by the slightly desertified site, and no pika burrows were found in the severely desertified site. With increasing desertification degree, vegetation coverage and soil water content decreased. The onset dates of soil freeze and thaw in the severely desertified site were both earlier, and the duration of freezing days was shorter, than those in the slightly desertified site at each soil depth. The medium desertified site showed the earliest onset of soil freeze, latest onset of soil thaw, and longest duration of soil freezing days. The annual mean soil temperature was highest in the severely desertified site within 50-cm soil depth of the ground surface due to the loss of vegetation coverage and soil water content, and lowest in the medium desertified site within 20-cm soil depth due to the cooling effects of pika burrows. Desertification resulted in the loss of vegetation cover and reduced soil water content, leading to higher soil temperatures. However, the cooling effects of pika burrows could reduce soil temperatures. These findings provide insights into the impacts of rangeland desertification on soil environments, thereby helping in establishing effective measures to combat desertification.

The effects of topography on aboveground biomass and soil moisture at local scale in dryland grassland ecosystem, China

Water is the primary limiting factor for grassland vegetation in dryland regions. Topography is considered to play an important role in the distribution of soil moisture, which will significantly affect grassland ecosystems. To examine the response of soil water content (SWC) and aboveground biomass (AGB) of grassland vegetation to precipitation patterns and topography, a 6-year investigation was conducted during the period from 2012 to 2017 in a semiarid steppe of Inner Mongolia, China. The study area was divided into three parts based on the landscape position, i.e., top area (TA), slope area (SA) and bottom area (BA). The results suggested that SWC and AGB would be significantly affected by topography and precipitation patterns. A significant negative relationship was found between the SWC and the altitude of the sampling sites. In the dryer years (2013–2017), the AGB of the BA was significantly higher than that of the SA and TA. However, a non-significant difference was found for the AGB values between the three landscape positions in the wetter year (2012). During the growing season, variation of AGB and SWC was similar in 2014 but differed in 2015. AGB exhibited a significant positive relationship with SWC above a minimum value. Precipitation significantly affected the AGB of grassland, and moderate rainfall events were more effective than light rainfall events for grassland vegetation. Moreover, the distribution of species varied in different areas, which may result in the differences in the responses of AGB to soil moisture and precipitation. This study clarifies the effects of micro-topography on soil moisture and grassland ecosystems at a local scale in dryland regions, which provides useful information for grassland ecosystem management.

The effects of introducing Flemingia macrophylla to rubber plantations on soil water content and exchangeable cations

Rubber-based (Hevea brasiliensis) agroforestry systems are the best way to resolve the environmental problems caused by rubber monoculture. Rubber–Flemingia macrophylla (nitrogen-fixing plants) systems have become popular in Xishuangbanna, Southwest China. Soil water content and exchangeable cations (Ca2+, Mg2+, K+, and Na+) are important for sustainably managing forest ecosystems. In this study, we investigated the responses of soil water content and exchangeable cations in rubber and rubber–Flemingia macrophylla systems. Soil water content increased in the 0–90 cm soil layer as the rubber plantations aged, and the mature rubber plantations had similar soil water storage to rainforests. The rubber plantations use soil water in the 30–90 cm soil layer to avoid drought stress during the long, dry season. The introduction of Flemingia macrophylla to the young rubber plantations significantly increased soil water depletion in the 30–90 cm soil layer. The introduction of Flemingia macrophylla to the mature rubber plantations had no significant effects on soil water in the 0–90 cm soil layer. The introduction of Flemingia macrophylla to the differently aged rubber plantations mitigated soil acidification by decreasing nitrogen inputs. The total exchangeable cations in the 0–90 cm soil layer sharply decreased as the rubber plantations aged due to the acceleration of soil acidification. When soil pH was below 5.5, 7.85 cmol kg−1 of soil exchangeable cations were released when the pH decreased by one unit. However, the introduction of Flemingia macrophylla to the differently aged rubber plantations effectively reduced the release of soil exchangeable cations by mitigating soil acidification. In conclusion, rubber–Flemingia macrophylla systems can mitigate soil acidification and reduce the release of soil exchangeable cations relative to rubber monoculture.

Stratification response of soil water content during rainfall events under different rainfall patterns

AbstractMany researchers have studied the influence of rainfall patterns on soil water movement processes using rainfall simulation experiments. However, less attention has been paid to the influence under natural condition. In this paper, rainfall, soil water content (SWC), and soil temperature at 10‐, 20‐, 30‐, 40‐, and 50‐cm depths were simultaneously monitored at 1‐min intervals to measure the variation in SWC (SWCv) in response to rainfall under different rainfall patterns. First, we classified rainfall events into four patterns. During the study period, the main pattern was the advanced rainfall pattern (38% of all rainfall events), whereas the delayed, central, and uniform rainfall patterns had similar frequencies of about 20%. During natural rainfall, rainwater rapidly passed through the top soil layers (10–40 cm) and was accumulated in the bottom layer (50 cm). When a high rainfall pulse occurred, the water storage balance was disturbed, resulting in the drainage of initial soil water from the top layers into the deeper layers. Therefore, the critical function of the top layers and the bottom layers was infiltration and storage, respectively. The source of water stored in the bottom layer was not only rainfall but also the initial soil water in the upper soil layers. Changes in soil temperature at each soil depth were comonitored with SWCv to determine the movement characteristics of soil water under different rainfall patterns. Under the delayed rainfall pattern, preferential flows preferred to occur. Under the other rainfall patterns, matrix flow was the main form of soil water movement. Rainfall amount was a better indicator than rainfall intensity for SWCv in the bottom layer under the delayed rainfall pattern. These results provide insights into the responses of SWCv under different rainfall patterns in northern China.

An End-Member-Based Two-Source Approach for Estimating Land Surface Evapotranspiration From Remote Sensing Data

Evapotranspiration (ET) is one of the key variables in the water and energy exchange between land surface and atmosphere. This paper develops an end-member-based two-source approach for estimating land surface ET (i.e., the ESVEP model) from remote sensing data, considering the differing responses of soil water content at the upper surface layer to soil evaporation and at the deeper root zone layer to vegetation transpiration. The ESVEP model first diverges the soil-vegetation system net radiation into soil and vegetation components by considering the transmission of direct and diffuse shortwave radiation separately from the transmission of longwave radiation through the canopy, then calculates the four dry/wet soil/vegetation end-members with the diverged soil and vegetation net radiations, and last separates soil evaporation from vegetation transpiration based on the two-phase ET dynamics and the four end-member temperatures. The model can overall produce reasonably good surface energy fluxes and is no more sensitive to meteorology, vegetation, and remote sensing inputs than other two-source energy balance models and surface temperature versus vegetation index ( $T_{R}$ –VI) trapezoid models. A reasonable agreement could be found with a small bias of ±8 W/ $\text{m}^{2}$ and a root-mean-square error within 60 W/ $\text{m}^{2}$ (comparable to accuracies published in other studies) when both model-estimated sensible heat flux and latent heat flux from MODIS remote sensing data are validated with ground-based large aperture scintillometer measurements.

Responses of soil moisture to precipitation pattern change in semiarid grasslands in Nei Mongol, China

Aims Under global climate change, precipitation patterns were predicted to change with larger seasonal and annual variations and more extreme events in the semiarid regions of northern China. Water availability is one of the key limited factors in semiarid grasslands. Changes in precipitation patterns will inevitably affect ecosystem structure and function through soil water condition. Our objective was to investigate the response of soil water content to changes of precipitation pattern, especially its pulse response to precipitation events. Methods Two semiarid steppe sites (Duolun and Xilinhot) in Nei Mongol were chosen and meteorological stations were installed to monitor precipitation and soil volumetric water content (VWC) at five soil depths (0–10 cm, 10 cm, 20 cm, 30 cm, 50 cm) from 2006 to 2013. The pulse response of VWC at 0–10 cm to an individual precipitation event was simulated by an exponential equation. Important findings Significant seasonal and inter-annual variations of VWC were observed at the Duolun and Xilinhot sites. VWC at 50 cm soil layer in Xilinhot showed an obvious increase during the early spring due to the influences of snow melting. Mean surface (0–10 cm soil layer) VWC was significantly correlated with annual precipitation across eight years, but VWC in the deeper soil layers (10–50 cm) were not impacted by precipitation. We also found that the precipitation event larger than 2 mm could induce a significant increase in surface (0–10 cm soil layer) VWC, and could be regarded as an effective precipitation in this region. The maximum increment of ©植物生态学报 Chinese Journal of Plant Ecology 陈敏玲等: 内蒙古半干旱草原土壤水分对降水格局变化的响应 659 doi: 10.17521/cjpe.2015.0155 surface VWC after the events and lasting time (Tlasting) were determined by the event size, while showed negatively linear correlations with the initial soil water content before the events. Vegetation development (leaf area index) did not show significant impacts on the responses of surface soil moisture to precipitation pulses. The infiltration depth of rain water was also determined by rain size and pre-event soil moisture. In average, soil water can infiltrate 1.06 cm and 0.79 cm deeper in Duolun and Xilinhot with 1 mm more precipitation, respectively. Therefore, our results suggest that the event size and pre-event soil moisture were the most important factors affecting response patterns of soil moisture to rain events in semiarid ecosystems.

Responses of soil water content to change in plant functional traits in evergreen broadleaved forests in eastern Zhejiang Province

Responses of soil water content to change in plant functional traits in evergreen broadleaved forests in eastern Zhejiang Province

Characteristics of deep drainage and soil water in the mobile sandy lands of Inner Mongolia, northern China

Quantification of deep drainage and the response of soil water content to rainfall patterns are critical for an effective management strategy of soil water conservation and groundwater utilization. However, there has been little information on how rainfall characteristics influence soil water dynamics and deep drainage in mobile sandy lands. We used an underground chamber to examine the responses of deep drainage and soil water content in mobile sandy lands to rainfall characteristics in Inner Mongolia during the growing seasons of 2010, 2011 and 2012. Results showed that rainfall in this area was dominated by small events (≤5 mm), which increased soil water content in the surface soil layers (0–40 cm), but did not increase soil water content in the deeper soil layers (greater than 40 cm). Soil water content at the 0–100 cm depth increased significantly when the total amount of rain was >20 mm. Rainfall amount, intensity and the duration of dry intervals were significantly related to the soil water content in different soil layers. Deep drainage was significantly correlated with rainfall amount and intensity, but not with the duration of dry intervals. The coefficients of deep drainage in the mobile sandy lands ranged from 61.30% to 67.94% during the growing seasons. Our results suggested that rainfall infiltration in the mobile sandy lands had considerable potential to increase soil water storage while recharging the groundwater in this region.

Responses of soil microorganisms and water content in forest floor horizons to environmental factors

The study focused on the temporal dynamics of soil water content (SWC) and soil microbial activity characterized by basal respiration and catalase activity in the litter (OL), fragmented (OF), and humus (OH) subhorizons of the forest floor and the mineral A-horizon, in relation to air temperature and rainfall. The study was conducted at three plots (old-growth Norway spruce (Picea abies Karst.) forest, even-aged mature commercial spruce stand, grassland dominated by Calamagrostis sp.) located in the Biosphere Reserve Polana (Slovakia, 19°28′E, 48°38′N) during four years. SWC as well as microbial activity differed among horizons as well as among plots. Generally, organic horizons in the old-growth forest exhibited higher microbial activity than in the managed forest, but no significant differences were observed for the A-horizon. On the other hand, the A-horizon showed higher catalase activity in the grassland than in both forest stands. The responses of SWC and microbial activity to air temperature and rainfall differed among horizons. SWC responded most sensitively to short-term temperature fluctuations in the OL horizon. In the underlying horizons, cumulative positive effects of high temperature (lasting 5–15 days) were reflected in the basal respiration. SWC responded rapidly to precipitations, but the effect lasted generally not more than 2 days. In contrast, catalase activity was negatively correlated with the precipitation amount; however, with increasing depth this relationship became less distinct.

Yield and water use efficiency of barley in a semiarid Mediterranean agroecosystem: Long-term effects of tillage and N fertilization

Conservation tillage systems (no-tillage, NT; and minimum tillage, MT) are being adopted in rainfed agroecosystems of the Mediterranean basin where water availability is the main limiting factor for crop productivity. We hypothesized that long-term adoption of conservation tillage systems would increase water use efficiency (WUE) and its response to N fertilizer additions due to improved soil water content. A field experiment was established in 1996 on a loamy Xerofluvent Typic in the Ebro river valley (NE Spain). The experiment compared three nitrogen (N) fertilization levels (zero, 0 kg N ha −1, medium, 60 kg N ha −1, and high, 120 kg N ha −1), under three tillage systems (CT, conventional tillage; MT and NT), annually cropped to barley ( Hordeum vulgare, L.) as is usual in the region. Ten years after the experiment establishment, during four consecutive growing seasons, 2005–2006 to 2008–2009, we evaluated the response of soil water content, soil nitrate, above-ground dry matter, grain yield and yield components to long-term (>10 years) tillage and N fertilization treatments. The long-term sustainability of NT and MT was confirmed. Mean yield and WUE under long-term conservation tillage systems were 66% and 57% higher than under CT, respectively. This improvement was mainly attributed to improved soil water usage under conservation tillage, mainly due to reduced water use during the pre-anthesis period. However, in a wet year yield did not significantly differ among tillage systems. The improvement of WUE with N fertilization was confirmed under NT, which medium and high N fertilizer level increased 98% mean grain yield and 77% mean WUE compared to CT. The increased response of crop and yield to N fertilization under NT was due to improved soil water content. Soil N accumulation together with the lower water accumulation explained the lack of response to N fertilization under CT, even on a wet growing season (i.e., 2008–2009). Long-term NT adoption was a sustainable practice for barley monoculture in the region, allowing for reduced costs and yield increase with N fertilizer additions. N fertilizer rates on rainfed Mediterranean croplands should be adjusted depending on the reduction of tillage intensity and rainfall of the year. In our system and as an example for this agroecosystems, N fertilizer rates should be kept at or below 60 kg N ha −1, and should be further reduced on intensively cultivated soils.

Experimental nitrogen, phosphorus, and potassium deposition decreases summer soil temperatures, water contents, and soil CO<sub>2</sub> concentrations in a northern bog

Abstract. Ombrotrophic peatlands depend on airborne nitrogen (N), whose deposition has increased in the past and lead to disappearance of mosses and increased shrub biomass in fertilization experiments. The response of soil water content, temperature, and carbon gas concentrations to increased nutrient loading is poorly known and we thus determined these data at the long-term N fertilization site Mer Bleue bog, Ontario, during a two month period in summer. Soil temperatures decreased with NPK addition in shallow peat soil primarily during the daytime (t-test, p < 0.05) owing to increased shading, whereas they increased in deeper peat soil (t-test, p < 0.05), probably by enhanced thermal conductivity. These effects were confirmed by RMANOVA, which also suggested an influence of volumetric water contents as co-variable on soil temperature and vice versa (p < 0.05). Averaged over all fertilized treatments, the mean soil temperatures at 5 cm depth decreased by 1.3 °C and by 4.7 °C (standard deviation 0.9 °C) at noon. Water content was most strongly affected by within-plot spatial heterogeneity but also responded to both N and PK load according to RMANOVA (p < 0.05). Overall, water content and CO2 concentrations in the near-surface peat (t-test, p < 0.05) were lower with increasing N load, suggesting more rapid soil gas exchange. The results thus suggest that changes in bog ecosystem structure with N deposition have significant ramifications for physical parameters that in turn control biogeochemical processes.

Preferential water flow in a glacial till soil

Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in glacial till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a till slope (7–10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in glacial till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.

Nonuniform sprinkler irrigation and crop yield

The influence of nonuniform water application by sprinkler on the variability of soil water content and corn yield was studied on two experimental plots differing in their texture and hydraulic characteristics (Table 2). Variograms, autocorrelations and cross-correlations of soil water contents (θ), crop yield of sweet corn (Y), and net water application (Q) were calculated (Fig. 2). The correlograms show trends which are similar for all these three variables, θ , Y and Q. The trend of soil water content and crop yield appears to be casued by the trend in water application. Filtering out the trends by scaled variograms shows that soil properties of both experimental plots may be considered as homogeneous so that the responses of soil water content and in turn of crop yield resulted mainly from the nonuniformity of water application (Fig. 3). Redistribution of soil water after irrigation caused crop yield to be more uniform in plot B, in which the soil hydraulic properties led to more significant water flow, than in plot A. The coefficient of variation of dry matter yields in the two plots were 24 and 34%, respectively (Table 5). Dry matter yield response to net water application, as measured in collection cans, was fitted to the Mitscherlich's model — the “law of diminishing returns” (Fig. 4). Using normal distribution to characterize the probability density function of water application (Fig. 5) and the Christiansen coefficient to characterize the uniformity criteria in the fitted Mitscherlich's model enabled relative crop yield to be expressed as a function of Christiansen coefficient and the total amount of irrigation water (Fig. 6).