YANG Jinkang, YANG Qiuyun, ZHU Linan, REN Shuaishuai, ZHANG Jingjing, HUA Dangling
Effects of different amendments on the absorption and transport of Cd in soil-wheat system in calcareous chao soil
[Background] A certain area of high-yield farmland in North China has been seriously polluted due to the cadmium containing sewage irrigation for many years. Soil pollution degradation threatens grain production, and soil degradation caused by heavy metal pollution urgently needs to be rehabilitated. To find a material or compound formula that can be both low cost and remediation efficiency is very necessary for the remediation of heavy metal pollution in slightly alkaline soil in northern China. Compared with the total amount of heavy metals in soil, the bioavailability and form of heavy metals in soil have more influence on biotoxicity. Among the existing remediation technologies of heavy metal pollution in soil, the in-situ chemical fixation remediation technology can better satisfy the remediation and treatment of moderate and mild heavy metal pollution in terms of methods and time, and is especially suitable for the large-scale moderate and mild contaminated farmland in China. At present, there are no efficient, cheap and environmentally friendly remediation materials suitable for calcareous chao soils in the north of China.[Methods] In order to screen the stabilizing materials suitable for ecological restoration of degraded soil polluted by heavy metal Cd in calcareous chao soil, field and potted wheat experiments were carried out in a farmland polluted by heavy metal Cd in calcareous chao soil. The effects of single application of silicon-calcium-magnesium fertilizer (abbreviated to Si-Ca-Mg fertilizer), hydroxyapatite and chicken manure on soil pH, soil Cd bioavailability and Cd absorption, transport and enrichment in various organs of wheat plant during wheat maturity were studied.[Results] The contents of DTPA-Cd in soil and Cd in wheat organs decreased by different stabilizing agents. The contents of DTPA-Cd in soil and Cd in wheat grains decreased by 0.60%-73.66% and 8.03%-90.88%, respectively, compared with the control. Each stabilizing treatment changed the chemical form of Cd and reduced the activity of Cd in soil. Si-Ca-Mg fertilizer and hydroxyapatite significantly increased soil pH and reduced the activity and migration of Cd in the soil. Chicken manure reduced soil pH value, which was not conducive to soil Cd stabilization. Soil DTPA-Cd content was negatively correlated with soil pH value among all treatments, but positively correlated with Cd content in various organs of wheat plants, which all reached extremely significant levels.[Conclusions] Field and pot experiments showed that the Si-Ca-Mg fertilizer had better effect for Cd pollution remediation. However, considering the cost, remediation effect and the influence on farmland ecology, accurate application dosage and further quantitative research about Si-Ca-Mg fertilizer in slightly alkaline soil should be determined.
WANG Yue, CHEN Lixin, FAN Haiyan, YANG Shengli, ZHANG Zhiqiang
Effects of water saving and nitrogen reduction on the water and nitrogen use efficiency of summer maize in Beijing
[Background] North China is the main production area of summer maize, but there are problems with insufficient water resources and excessive application of nitrogen fertilizer in this area, which not only reduces water and nitrogen use efficiency, but also leads to the accumulation of soil nitrate nitrogen and increases the risk of environmental pollution. There are relatively few researches on determining the optimization goals of water and nitrogen management based on maize yield, resource utilization efficiency and environmental effects. This paper explored the irrigation and nitrogen levels that can meet the multiple goals of maize under precipitation conditions.[Methods] A two-factor completely random combination was used for field experiments at the irrigation experimental station in Tongzhou district, Beijing from June to October 2019. The experiment set 4 irrigation levels (W0:0, W1:60 mm, W2:120 mm, and W3:180 mm) and 4 nitrogen application levels (N0:0, N1:150 kg/hm2, N2:275 kg/hm2, and N3:400 kg/hm2). The field water consumption was calculated based on the water balance, and the soil nitrate nitrogen content was determined through soil sampling and laboratory tests, the effects of irrigation and nitrogen application on maize water consumption, yield, water and nitrogen use efficiency, and nitrate nitrogen accumulation were analyzed, and multiple regression and spatial analysis methods were used to determine the irrigation and nitrogen application for meeting the multiple goals of maize.[Results] 1) With the increase of irrigation water, the proportion of soil water storage in water consumption decreased. Under W1 irrigation treatment, the soil water storage ratio of N1 treatment increased by 16.99% compared with N0 treatment. Nitrogen application was beneficial to improve the utilization of soil water. 2) The yield increased first and then decreased with the increase of irrigation and nitrogen application. The yield of W1 treatment increased by 18.89% compared with W0 treatment, the yield of N1 treatment increased by 29.54% compared with N0 treatment. W1N1 treatment improved water use efficiency and nitrogen partial factor productivity while obtaining high yield. 3) The accumulation of 0-100 cm soil nitrate nitrogen increased significantly with the increase of nitrogen application rate. Increasing irrigation promoted the downward migration of nitrate nitrogen. W1 treatment significantly reduced the risk of nitrate nitrogen leaching. 4) Yield, water and nitrogen use efficiency reached more than 95% of their optimal values simultaneously when the irrigation amount was 81-102 mm and the nitrogen application was 143-161 kg/hm2, and nitrate nitrogen accumulation was low.[Conclusions] Therefore, irrigation of 81-102 mm and nitrogen application of 143-161 kg/hm2 in North China under the conditions of precipitation in dry years may meet the growth of maize, achieve the optimization goal of ensuring yield, improving water and nitrogen use efficiency and reducing environmental pollution risks. The research may provide theoretical reference and technical support for the reasonable and effective development of agricultural water and soil resources and sustainable agricultural development in North China.
Developing the Benggang economics to transform the Benggang-erosion control to the Benggang utilization as resources
[Background] Benggang is a fragmented landform formed by the overall collapse of slope soil. Benggang erosion, the most serious erosion type in South China, has caused extremely intensive land degradation. Current control patterns of the Benggang erosion, neglecting the resource endowment of the Benggang lands themselves, either focus on ecological restoration with less attention on economic benefits, or use mechanized equipment to totally change the Benggang's landscape and morphology.[Methods] By analyzing the resource endowment of the Benggang lands, we put forward the concept of the Benggang economics. Furthermore, we analyzed the major patterns to develop the Benggang economics and its relevance to the Benggang-erosion management, and gave some specific measures to promote the Benggang economics.[Results] 1) The authors argued that the Benggang lands had a number of distinctive resource endowments. First of all, the Benggang lands may serve as earth-science popularization education bases; secondly, the spectacular landscape associated with intensive soil collapse can be used to develop tourism; thirdly, the alluvial sandy soil layer has potential to substitute river sand as constructional materials; and finally, the distinctive surface conditions related to the sandy soil in combination with the high daily temperature variation can foster characteristic agricultural products. 2) Based on these resource endowments, we proposed the notion of the Benggang economics and suggested that we should fully develop the primary industry together with the secondary and the tertiary industries on Benggang lands, thereby maximizing the land use efficiencies. The primary industry should mainly rely on the characteristic agriculture associated with the distinctive surface conditions on Benggang lands, rather than the traditional planting industry. The secondary industry mainly refers to the exploitation of the alluvial sands as a new mineral resource. The tertiary industry refers to the tourism and the associated services. The tourism has potentials to promote the whole Benggang economics and should receive more attention. The government should select some Benggang lands as science popularization education base for students, whereby attracting people and developing the Benggang economics. The Benggang economics implies 1) the original Benggang landscape should maintained as well as possible so as to utilize its own resource endowments as much as possible; 2) the gully measures such as check dams should receive priority in controlling the Benggang erosion risk. Accordingly, the government should allow the peasants to exploit and sell the alluvial sands so that they are willing to remove the alluvial deposition behind the dam regularly.[Conclusions] As an initiative idea, the Benggang economics is closely relevant to rural revitalization. Governments should promote the establishment of demo bases of the Benggang economics as soon as possible.
WANG Yuepu, QIN Wei, YANG Wentao, WANG Yujie, WANG Yunqi, JIANG Tao
Investigating optimal time window for UAV terrain measuring by considering weather and land cover conditions: Taking the Northeast Black Soil Region as an example
[Background] The Structure from Motion (SfM) technology based on the Unmanned Aerial Vehicle (UAV) platform is an important optical remote sensing technology to measure high-precision digital terrain. The SfM technology is often influenced by clouds and vegetation cover, whereas the UAV platform could be impacted by winds. This work aims to explore the optimal time window to measure terrain by the UAV-SfM survey in the Black Soil Region of Northeast China by considering dynamic changes of local climate and vegetation.[Methods] The study area covers three climatic zones:The cold temperate zone, the middle temperate zone and the warm temperate zone. For different climatic zones in the Black Soil Region of Northeast China, the climate data of a typical site from 1988 to 2017 and the dynamics of vegetation coverage and snow cover in 2020 were analyzed. Typical DJI UAV operating parameters were used as the initial screening conditions for annual average climate data (temperature, wind speed and precipitation), and the medium vegetation coverage condition (FVC<0.6) was then used as the screening basis for vegetation coverage to determine the appropriate period for the UAV terrain survey.[Results] 1) The temperature and wind speed of the three meteorological stations were analyzed comprehensively. It was found that the temperature curve changed as a quadratic function, and the average wind speed curve and the maximum continuous wind speed curve had the same trend. Temperature and wind speed were satisfied in the cold temperate zone from mid-April to early October, in the middle temperate zone from early April to mid-October, and in the warm temperate zone from mid-March to mid-November. 2) The probability of daily precipitation curves in the three meteorological stations fluctuated greatly and were not significantly representative, thus it could not be used as the standard for estimating investigating optimal time window. 3) By analyzing the land cover conditions of the three sites, it was found that the ground was covered with snow from October to March of the following year, and the vegetation coverage exceeded 0.6 from May to October, which made it impossible to carry out UAV topographic survey. The cover conditions that met terrain acquisition range from March to the end of April and from the end of September to November. Comprehensive analysis of meteorological and cover conditions, we found that the most suitable periods for the cold, middle and warm temperate zones were from mid-April to early May, from mid-April to mid-May, and from mid-March to the end of April or from the end of September to the beginning of November.[Conclusions] By applying the results of this paper, the UAV-SfM survey may effectively avoid adverse periods and ensure obtaining the best results. The findings of this work could guide terrain measuring works in the field of soil and water conservation.
LIU Kai, LI Wenbin, ZHAO Yue, HAN Qiaoling, ZHANG Pengchong, ZOU Songyan, TAN Jianbiao
Rapid extraction technology of the root morphological characteristics via minirhizotron image
[Background] The morphology of roots and the distribution of soil layers reflect the growth state and utilization strategy of soil water-trophic resources,it has a great significance to improve the quality of plantation cultivation and soil and water conservation. However, the traditional root research methods, such as soil drill method, soil column method, have complex test processes and cause certain damages to the root system. Therefore, it is very important to propose a new experiment and research method that may achieve nondestructive, automatic and digital monitoring of root growth state.[Methods] Selecting 3 healthy trees(Populus tomentosa), designing the experiment based on the minirhizotron technology, and taking 14 days as the data collection period, the root distribution in different soil layers was obtained. Root image was clipped and the true value was obtained via manual annotation. After image filtering processing, the Otsu, K-means, and FCM(fuzzy C-means clustering algorithm) methods were used to segment images. The correct rate was selected as the quantitative analysis index, and the experiment results were obtained.[Results] Through the qualitative analysis, there was over-segmentation when Otsu method was used to have image segmentation for the two types of root, and over-segmentation and under segmentation for the K-means method. The segmentation results via FCM method for the two types of roots were similar to the one via manual annotation. Through quantitative analysis, correct rate by K-means and FCM method were similar, all better than that by Otsu method. The accuracy of FCM method reached 90%.[Conclusions] The experiment was designed and was in steady operation, and the changes of root systems were obtained under different soil layers, i.e., the nondestructive monitoring was achieved. Through image segmentation, the segmentation algorithm was obtained by which its average error rate was <10%, i.e., the automatic monitoring was achieved. The characteristic parameters such as total root length was taken as example, the root growth turnover under different drip irrigation strategies was analyzed, and showed good applicability, which offered an efficient and nondestructive approach for the root ecology research.
Response of soil erosion to typical topographic factors in the rocky mountain area of North China: Taking Fangshan district as an example
[Background] The current soil erosion researches in Fangshan district did not cover the response of soil erosion to typical topographic factors, thus supplementary research is in demand. The 3 main objectives of this study are for quantitative assessment of the distribution pattern and dynamic characteristics of soil erosion, analysis of the response of soil erosion to topographical factors in Fangshan district, and to provide reference for soil erosion prevention and control.[Methods] We used USLE model combined remote sensing inversion and GIS spatial overlay analysis technology to calculate the soil erosion modulus and erosion amount in Fangshan district from 2013 to 2018. Then we calculated the six factors (R, K, L, S, P, and C) of the USLE based on the meteorological data, vegetation index data, land use data and soil attribute data. Thus we obtained the erosion amount and modulus, and divided erosion levels to analyze the soil erosion status of Fangshan district, and the erosion status under different typical topographic conditions.[Results] 1) The soil erosion amount in Fangshan district has gradually decreased in each year, from a maximum of 70.694×104 t in 2013 to 29.082×104 t in 2018. 2) Soil erosion was divided into 6 grades by intensity, showing that the average annual rate of slight erosion was 64.13%, followed by light erosion accounted for 29.99%, the other higher grade areas accounted for <6%. 3) The ratio of slight erosion area gradually increased in each year. The soil erosion modulus at the elevation of[400, 800 m) was the highest, followed by the elevation range lower than 400 m. More than 40% of the erosion amount occurred in the area where elevation was higher than 400 m. In the[0°,25°) slope grade, the soil erosion modulus increased with the increase of the slope; but at slope grade higher than 25°, the soil erosion modulus decreased with the increase of the slope. The soil erosion of this grade for areas with slope of[0°, 5°)accounted for more than 70% of the total erosion.[Conclusions] The overall annual soil erosion in Fangshan district has gradually decreased over time. From 2013 to 2018, the total amount of soil erosion has decreased by 58.86%. The ratio of slight erosion intensity area rose from 55.74% in 2013 to 71.70% in 2018. The overall soil erosion degree in Fangshan district is light or slight. The analysis of the response of soil erosion to topographical factors shows that there is the highest soil erosion modulus at[400, 800) m elevation interval and the slope grade of[15°, 25°), indicating it is the focus area of soil erosion prevention and control in the future.
GONG Guoli, LIU Xin, YAO Ling, REN Lixia, WANG Min
Improvement and application of wind factor in RWEQ model
[Background] Wind is the most important driver of soil wind erosion and the most important input parameter in the RWEQ (revised wind erosion equation) model for quantitatively estimating wind erosion. The actual wind speed changes all the time. Substituting the average wind speed into the model will make the calculated wind erosion less. Therefore, the model requires no less than 500 wind speed values to estimate the wind factor. However, wind speed data with high temporary resolution is difficult to acquire. For all this, how to select downscaling techniques for wind speed data is worth studying.[Methods] Two-parameter Weibull distribution model, as well as the fitting method of daily average and maximum wind speed were used to fit wind speed respectively. The fitting results of the two methods were compared with the measured results respectively. The measured data were the observed values of national meteorological stations, including daily four periodic wind speed values, daily mean and daily maximum wind speed values. According to the comparison results, the wind speed downscaling method was modified, and the revised wind speed values were substituted into the RWEQ model to obtain the spatial distribution of wind factors in North China.[Results] 1) There was an error in the wind erosion force between by the two-parameter Weibull distribution model and by the measured wind speed, the relative error value was in 0.19 to 0.95, the mean relative one reached 0.52. Regression analysis results showed that the correlation coefficient between two of them reached 0.97, and the significance level P<0.01. 2) For the wind speed value >5 m/s, the relative error value between the fitting results and the measured results were 0.01-0.18, and the mean one was 0.09, correlation coefficient reached 0.82, and the significance level P<0.01. The fitting result in the high wind speed area (>5 m/s) was small with a slope of 0.74. 3) The fitting method of daily average and daily maximum wind speed also couldn't be directly applied to estimate wind erosion in North China. However, the wind erosion force fitted by this method had a strong correlation with the results calculated by the measured wind speed (R2=0.96). According to the spatial distribution of wind erosion force in March from 2000 to 2010 calculated by this correlations, areas of high wind factor value were distributed mostly around the Inner Mongolia Plateau, also in the Northeast China and the Qinghai-Tibet Plateau.[Conclusions] Two-parameter Weibull distribution model underestimated the value of wind speed (especially for wind speeds >5 m/s). The wind erosion force calculated by the fitting method of daily average and daily maximum wind speed is correlated with the one from the measured wind speed, thus this correlation can be used to estimate the wind erosion force. Based on comparing the common methods, this paper improved RWEQ model in the calculation of wind factor, revealed climate driver in wind erosion area, and provided a theoretical instruction for control the wind erosion in North China.
Research progress in impact of vegetation pattern on soil erosion in the slope-gully system of the Loess Plateau
[Background] The Loess Plateau of China is one of the most eroded areas in the world. The slope-gully system as a basic erosion unit in this area is not only a sediment source for the whole watershed, but also the key part in implementing soil and water conservation measures. Understanding the underlying erosion processes on the slope-gully system will provide more efficient strategies to implement effective soil and water countermeasures for protecting rare land resources and ecological environment. Since 1980, some soil and water conservation measures have been implemented in this area. Land use and vegetation cover have changed greatly, and which have deeply affected the process of rainfall, runoff, sediment production and sediment transport.[Methods] With the aid of Web of Science and CNKI, we collected over 60 classical papers based on the keywords of "slope-gully system" or "relationship between slope and gully" and conducted a literature review. For the papers published before 1999(large-scale "Grain for Green project" implemented), the erosion patterns, sediment sources and impacts of upland incoming flow on erosion of slope-gully system were summarized; and the for the papers after 1999, the effects of revegetation on erosion of slope-gully system were emphatically analyzed. The future research highlight was also pointed out based on the above analysis.[Results] 1) Great progresses have been achieved in understanding the impacts of vegetation recovery on slope-gully erosion system on the Loess Plateau in recent years. The vertical erosion distribution zone of slope-gully system has been widely recognized and the identification of sediment source indicated that inner-gully area produced more sediment for most circumstances. 2) Various vegetation patterns on the slope changed runoff hydraulic parameters and the incoming runoff amount and sediment concentration for the gully slope, which altered the erosion patterns of downslope and sediment yield of the whole system. 3) Due to the complexity of vegetation patterns and insufficient data, it is difficult to quantify upslope runoff and sediment impacts on downslope erosion process under different vegetation patterns conditions.[Conclusions] Focusing on the mutual influence and constrains of vegetation patterns and soil erosion process, more simulation and outdoor experiments should be carried out to obtain suitable parameter to illustrate the impacts of vegetation pattern on soil erosion and establish a prediction model combined vegetation patterns and soil erosion process at slope-gully system. This will deepen the relationship between vegetation pattern and soil erosion on the slope-gully system and be the future hotspot.
