•Responses of soil water and salt dynamics to varied rainfall events and hydrological years were evaluated.•Salt leaching and deep drainage occurred mainly due to summer-concentrated rainfall during ...wet year.•Salt decrease percentage in the CL was greater than that in the GL in all hydrological years.•One brackish water irrigation application is avail salt leaching both in cropland and grassland.
Soil salination challenges sustainable agricultural production and management in the lowland area of the North China Plain (NCP). This study investigated the effect of varied rainfall events and hydrological years on deep drainage and salt leaching in Nanpi County in the NCP. Field experiments were conducted to measure soil matric potential (SMP) and soil water electrical conductivity (ECw) in 300 cm profiles of an irrigated cropland (CL) and unirrigated grassland (GL). The HYDRUS-1D model was calibrated and validated to optimize soil water and salt transport parameters using the SMP and ECw data obtained in 2015 and 2016, respectively. The results showed that the HYDRUS-1D model was reliable to simulate soil water and salt migration in 300 cm profiles at both sites. The salt leaching depths and degrees were positively correlated with precipitation amount. The heavy rain (45 mm) and rainstorm (68 mm) favored salt leaching within 100 cm, and severe and extreme rainstorms resulted in salt leaching within 150–200 cm both in the CL and GL. The SDP in the CL was greater than that in the GL in all hydrological years owing to agricultural cultivation and irrigation. Salt leaching in the 300 cm profiles mainly occurred in the rainy seasons of wet year, with the salt decrease percentage (SDP) being 61% in the CL and 42% in the GL. Salt leaching due to precipitation was sufficient in the irrigated CL in all hydrological years, and precipitation in normal rainfall years could remove 70–80% of soil salts within 50–63 cm soil depth. Grass growth without irrigation led to water deficits and salt accumulation when the annual precipitation amount was less than that in wet years. The results demonstrated that precipitation, combined with irrigation using of brackish and freshwater, could be usefully for soil salt leaching. A recommended irrigation scheme for water saving and salt control in CL and GL is one brackish water irrigation application and three freshwater irrigation applications each year in the NCP.
•A 28 season field experiment being used to analyze the responses of winter wheat yield and WUE to ET.•Yield and WUE being continuously increased from 1987 to 2015 under irrigated condition.•Yield ...was reduced under rainfed condition recently due to the reduction in rainfall.•The sensitivity of grain yield to the fluctuation in seasonal ET was increased.
Improving grain yield and water use efficiency (WUE) under limited irrigation is very important for food security in water shortage regions. This paper summarized a long-term field experiment (from 1987 to 2015, 28 growing seasons of winter wheat) on the responses of winter wheat to different levels of water stress under the changing background of cultivars, soil fertility and weather conditions at a site in the North China Plain (NCP). The results showed that during the past 28 seasons soil organic matter and N contents were significantly increased at the experimental site and the atmospheric evaporation demand (ET0) was increased and seasonal rainfall was reduced. Although yield was continuously increased from 1987 to 2015 under irrigated condition, the yield of winter wheat under rain-fed condition decreased recently as compared with that during 2000s due to the higher ET0 and less seasonal rainfall. WUE was increased continuously from past to present, especially under water stress condition, indicating that the winter wheat used water more efficiently under the current growing conditions. This could be attributed to the increase in harvest index, improved N status in soil and the reduced soil evaporation. Overall, the sensitivity of grain yield to the fluctuation in seasonal ET was increased from 1980s to present. Yield reduction rate under water stress was greater under current growing conditions than that back in 1980s and 1990s. However, even with the changes in the responses to water stress, irrigation scheduling of one irrigation application from recovery to jointing for winter wheat could achieve relative stable yield and higher WUE through the 28 seasons and should be taken as optimized irrigation scheduling under limited water supply condition.
► ET partitioning was investigated by a combined isotopic and micro-meteorologic method. Evaporation can reach up to 30% of water consumption for winter wheat. Evaporation depth was detected deep to ...the 20
cm depth under soil surface. And, root water uptake occurred mainly above 40
cm for well-watered treatment. These results could amount to a significant water savings for the North China Plain.
Groundwater overdraft threatens the future of irrigated agriculture in the North China Plain. Because irrigated winter wheat is the dominant user of extracted groundwater, improved understanding of water cycling through the soil–plant–atmosphere continuum during wheat cultivation in the North China Plain is necessary for improving the sustainable utilization of limited water resources and promoting food security. In this paper, a combination of micrometeorological and stable isotope techniques was used to investigate evapotranspiration and soil water dynamics in a typical winter wheat agro-ecosystem (Luancheng Agro-ecosystem Experiment Station, Hebei Province). Stable isotope mixing models were used with eddy covariance evapotranspiration estimates and micro-lysimeter evaporation measurements to partition evapotranspiration and determine temporal variability of root water uptake depths. Results suggest that evaporation during the winter wheat irrigation season can reach up to 30% of the total water consumption (almost two typical irrigations). The main depths of root water uptake were 0–40
cm. Therefore, it is suggested that the planned irrigation wetting depth can be reduced at least to 40
cm, rather than the traditional 100
cm, as a means of water conservation. Widespread implementation of these practices could amount to a significant water savings for the North China Plain.
•Soil salt dynamics were dominated by seasonal precipitation and hydrological year.•Soil salt accumulated during the growth period, and leaching out under abundant rainfall during growth period of ...maize.•Soil salt accumulated in dry and normal years and leached in wet years, especially in the extremely wet year.•The effect of irrigation times of brackish water was greater than that of soil texture on soil salt accumulation.•It is feasible that using brackish water for long-term irrigation in the lowland area of the North China Plain.
In the North China Plain (NCP), increased water shortages and food yield increase present serious threats to the sustainability of cultivated lands. Irrigation by brackish or saline water is a possible solution to alleviate freshwater shortages. It is critical to understand the soil salt variations and the characteristics of salt accumulation and leaching under long-term brackish water irrigation in cultivated croplands. In this study, the HYDRUS-1D model was calibrated and validated, and then applied to evaluate that how 20 years of irrigating with brackish water affects soil salinity and soil salt transport in wheat-maize cultivated lands with different texture layers in the lowland of NCP. The results showed that the simulations of soil matric potential and soil salt concentrations fitted well with the measured values. Soil salt dynamics were dominated by seasonal precipitation and hydrological years. Seasonal rainfall distribution determined seasonal characteristics of salt changes in shallow layers (0–100 cm). Soil salt accumulated during the growth period of winter wheat corresponding to the dry season, and was greatest at the harvest. Soil salt leached down to deeper soil layers under abundant rainfall during growth period of maize. The annual soil salt in 300 cm profiles were driven by hydrological years, and soil salt could be accumulated in dry and normal years and leached in wet years, especially in the extremely wet year. Soil salt accumulation was higher under two brackish water irrigations compared to one irrigation for winter wheat, and soil salinity in homogeneous soils was less than in the heterogeneous soil with clay loam interlining. The results showed the effect of irrigation times of brackish water was greater than that of soil texture on soil salt accumulation. Our results demonstrated that wheat and maize could be grown well under one irrigation with brackish water a year. Salt accumulation increased with the number of irrigation events that used brackish water for winter wheat. The brackish water irrigation was evaluated and the results demonstrated that partial substitution of fresh water by brackish water for irrigation is feasible in the lowland area of the NCP. It is more suitable for long-term brackish water irrigation in relatively homogeneous soil than in heterogeneous soil. These simulated results are helpful to provide appropriate management measures for long-term brackish water irrigation and fresh water saving, and provide a basis for assessing the environmental effect under long-term brackish water irrigation.
Biochar is a beneficial soil amendment; however, biochar-based properties are mainly determined by the feedstocks and the pyrolysis temperature. Nevertheless, considering the vast biomass of ...halophyte, little is known about how the halophyte-derived biochar improves saline soils. In this study, we firstly produced biochars by using three different halophytes, including
Tamarix chinensis
(recretohalophyte),
Suaeda salsa
(euhalophyte), and
Phragmites australis
(pseudo-halophyte) at 300, 500, and 700 °C, and compared their chemical and physical properties. We applied halophyte (
Tamarix chinensis
and
Phragmites australis
) biochars (pyrolysis at 500 °C) into 0–20 cm saline soil at 2% and 4% (w/w) rates to investigate the saline soil water, salt, and pH dynamics in a 12-month column experiment. The results showed that as the pyrolytic temperature increase, biochar yield and pore diameter decreased by 37.5–44.0% and 34.6–89.7%, respectively; in contrast, biochar pH, specific surface area, and total volume increased by 24.8–47.8%, 3–37 times and 1–9 times, respectively. The halophyte types significantly controlled biochar carbon and dissolved salt content and electrical conductivity. Halophyte biochar application can increase soil water and salt content, and application of 4% of
Tamarix chinensis-
derived biochar can increase more soil moisture than the soil salinity, and it can maintain soil pH at a stable level, which would be a potential way to improve saline soil properties. The results are valuable for choosing halophyte types and optimizing pyrolytic temperatures for halophyte biochar production through specific environmental usage.
Timely monitoring and precise estimation of the leaf chlorophyll contents of maize are crucial for agricultural practices. The scale effects are very important as the calculated vegetation index (VI) ...were crucial for the quantitative remote sensing. In this study, the scale effects were investigated by analyzing the linear relationships between VI calculated from red-green-blue (RGB) images from unmanned aerial vehicles (UAV) and ground leaf chlorophyll contents of maize measured using SPAD-502. The scale impacts were assessed by applying different flight altitudes and the highest coefficient of determination (R
) can reach 0.85. We found that the VI from images acquired from flight altitude of 50 m was better to estimate the leaf chlorophyll contents using the DJI UAV platform with this specific camera (5472 × 3648 pixels). Moreover, three machine-learning (ML) methods including backpropagation neural network (BP), support vector machine (SVM), and random forest (RF) were applied for the grid-based chlorophyll content estimation based on the common VI. The average values of the root mean square error (RMSE) of chlorophyll content estimations using ML methods were 3.85, 3.11, and 2.90 for BP, SVM, and RF, respectively. Similarly, the mean absolute error (MAE) were 2.947, 2.460, and 2.389, for BP, SVM, and RF, respectively. Thus, the ML methods had relative high precision in chlorophyll content estimations using VI; in particular, the RF performed better than BP and SVM. Our findings suggest that the integrated ML methods with RGB images of this camera acquired at a flight altitude of 50 m (spatial resolution 0.018 m) can be perfectly applied for estimations of leaf chlorophyll content in agriculture.
Soil salinization is one of the major land degradation processes that decreases soil fertility and crop production worldwide. In this study, a long-term coastal saline soil remediation experiment was ...conducted with three salt-tolerant plant species:
Mill. (LCM),
Lour. (TCL), and
Linn. (GHL). The three plant species successfully remediated the saline soil but showed different efficacies. The archaeal, bacterial, and fungal communities in barren soil and in four rhizocompartments (distal-rhizosphere soil, proximal-rhizosphere soil, rhizoplane, and endosphere) of the three plant species were assessed. All three plant species significantly decreased the richness of the archaeal communities but increased that of the bacterial and fungal communities in both the rhizosphere and rhizoplane compared with those in the barren soil. The archaeal and bacterial community structures were strongly influenced by the rhizocompartment, while specific fungal communities were recruited by different plant species. The microbial taxa whose abundance either increased or decreased significantly during remediation were identified. Soil electrical conductivity (EC) was identified as the main factor driving the variation in microbial community composition between the remediated and barren soil, and total nitrogen (TN), total carbon (TC), and available potassium (AK) were the main factors driving the differences among plant species. This report provides new insights into the responses of the root zone microbial communities of different salt-tolerant plant species during phytoremediation.
Despite knowing that phytoremediation by salt-tolerant plants is an effective technology for ameliorating saline soils and that microorganisms contribute significantly to plant stress tolerance and soil fertility, we still lack a comprehensive understanding of how microbes respond to the growth of salt-tolerant plants and the subsequent decline in soil salinity. The results of this study revealed different response patterns among bacterial, archaeal, and fungal communities and indicated that the decline in archaeal abundance might be a sign of successful remediation of coastal saline soils. The recruitment of specific fungal communities by different plant species indicated the importance of fungi in plant species-specific remediation functions. We also identified the taxa that may play key roles during remediation, and these taxa could potentially be used as indicators of phytoremediation. Overall, these findings highlight the importance of microbes in the phytoremediation of saline soil and suggest that the mechanisms involved are plant species specific.
The vegetation index (VI) has been successfully used to monitor the growth and to predict the yield of agricultural crops. In this paper, a long-term observation was conducted for the yield ...prediction of maize using an unmanned aerial vehicle (UAV) and estimations of chlorophyll contents using SPAD-502. A new vegetation index termed as modified red blue VI (MRBVI) was developed to monitor the growth and to predict the yields of maize by establishing relationships between MRBVI- and SPAD-502-based chlorophyll contents. The coefficients of determination (R2s) were 0.462 and 0.570 in chlorophyll contents’ estimations and yield predictions using MRBVI, and the results were relatively better than the results from the seven other commonly used VI approaches. All VIs during the different growth stages of maize were calculated and compared with the measured values of chlorophyll contents directly, and the relative error (RE) of MRBVI is the lowest at 0.355. Further, machine learning (ML) methods such as the backpropagation neural network model (BP), support vector machine (SVM), random forest (RF), and extreme learning machine (ELM) were adopted for predicting the yields of maize. All VIs calculated for each image captured during important phenological stages of maize were set as independent variables and the corresponding yields of each plot were defined as dependent variables. The ML models used the leave one out method (LOO), where the root mean square errors (RMSEs) were 2.157, 1.099, 1.146, and 1.698 (g/hundred grain weight) for BP, SVM, RF, and ELM. The mean absolute errors (MAEs) were 1.739, 0.886, 0.925, and 1.356 (g/hundred grain weight) for BP, SVM, RF, and ELM, respectively. Thus, the SVM method performed better in predicting the yields of maize than the other ML methods. Therefore, it is strongly suggested that the MRBVI calculated from images acquired at different growth stages integrated with advanced ML methods should be used for agricultural- and ecological-related chlorophyll estimation and yield predictions.
•Winter wheat yield of 33 seasons was used for seasonal variation analysis.•Calibrated CERES-Wheat model was used to simulate the yield under seven scenarios.•Weather-driven simulated yield was in a ...declining trend.•Yield improvement by cultivars was 25% during 1990s and 52% recently.•Yield improvement by the increase in chemical fertilizer input was 7.4% and 6.8%.
Long-term field measured yield data provides good opportunity to assess the impacts of climate and management on crop production. This study used the yield results from a long-term field experiment (1979–2012) at Luancheng Experimental Station in the central part of the North China Plain (NCP) to analyze the seasonal yield variation of winter wheat (Triticum aestivum L.) under the condition of sufficient water supply. The yield change of winter wheat over the last 33 growing seasons was divided into three time periods: the 1980s, the 1990s, and the years of 2001–2012. The grain yield of winter wheat during the 1980s was relative stable. During the 1990s, the annual yield of this crop was continuously increased by 193kg/ha/year (P<0.01). While for the past 12 years, yield of winter wheat was maintained at relative higher level, but with larger seasonal yield variation than that back in 1980s. CERES-Wheat model was calibrated and was used to verify the effects of management practices on grain yield. Seven scenarios were simulated with and without improvements in management. The simulated results show that the yield of winter wheat was decreased by 5.3% during 1990s and by 9.2% during the recent 12 seasons, compared with that during 1980s, under the scenario that the yield of winter wheat was solely affected by weather. Seasonal yield variation caused by weather factors was around −39% to 20%, indicating the great effects of weather on yearly yield variation. Yield improvement by cultivars was around 24.7% during 1990s and 52.0% during the recent 12 seasons compared with that during 1980s. The yield improvement by the increase in soil fertility and chemical fertilizer input was 7.4% and 6.8% during the two periods, respectively. The initial higher soil fertility and chemical fertilizer input might be the reasons that the responses of crop production to the further increase in chemical fertilizer were small during the simulation period. Correlation analysis of the grain yield from the field measured data with weather factors showed that sunshine hours and diurnal temperature difference (DTR) were positively, and relative humidity was negatively related to grain yield of winter wheat. The climatic change trends in this area showed that the DTR and sunshine hours were declining. This type of climatic change trend might further negatively affect winter wheat production in the future.
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