中国生态农业学报(中英文)

A review of microplastics in the soil environment

ZHANG Jiajia, CHEN Yanhua, WANG Xuexia, NI Xiaohui, LIU Dongsheng, LI Lixia, ZOU Guoyuan

2021, 29(6): 937-952. doi: 10.13930/j.cnki.cjea.200915

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Abstract:
Microplastics are plastic particles widely distributed in the environment. In recent years, environmental pollution caused by microplastics has attracted widespread attention. Many studies have reported the negative effects of microplastics on the aquatic environment, but the impact of microplastics on the terrestrial environment, especially on soils, has not been extensively investigated. This study systematically reviewed the recent researches on the sources, distribution, pollution characteristics, analysis methods, ecological effects, environmental effects, and control measures of soil microplastics, and proposed relevant countermeasures for research and governance. This review showed that 1) the sources of soil microplastics included residues of agricultural plastic film, land use of sludge, organic fertilizer application, surface runoff, sewage irrigation, and atmospheric deposition. 2) The methods of separation, extraction, identification, and their advantages and disadvantages for determining soil microplastics were summarized, but standardized detection and quantitative technologies were lacking. 3) Microplastics could affect the soil structure and physical and chemical properties, threatened the growth of plants and animals, and changed the diversity of microbial communities. 4) Microplastics could adhere to pollutants on the surface, causing physical and chemical environmental pollution, endogenous toxic substances releasing, and inducing compound pollution. 5) The prevention and control measures of microplastic pollution were mainly focused on three factors:research and development of biodegradable plastic products, input control of microplastics from the source, and strengthening international cooperation. This study also proposed three areas in need of further development:a standard unified quantitative analysis method, more accurate traceability analysis technology, and better scientific research on microplastic pollution in the soil. The results presented here provided a better understanding of the environmental behavior of microplastics in the soil and proposed ideas for further exploration. This review also provided a theoretical basis and reference for the ecological risk assessment of soil microplastics and prevention of pollution caused by them.

Analytical techniques for studying soil microplastics

LIU Dongsheng, ZOU Guoyuan, CHEN Yanhua, LIANG Lina, LI Lixia

2021, 29(6): 953-960. doi: 10.13930/j.cnki.cjea.200921

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Microplastic pollution has garnered recent attention in the field of environmental science. However, owing to the limitations of samplings, pretreatments, and analytical techniques, the sizes of the detected microplastics are generally large. Quantitative analysis methods are not yet well-developed; thus, the existing publications are incomparable. The analysis of soil microplastics is challenging because of their complex components and surface attachments. To better understand the current status of research and the development trends, the analytical techniques used in soil microplastics research were examined, compared, and summarized for thermal, spectral, and microscopic techniques in this paper. Microplastics have been qualitatively and quantitatively analyzed via spectral analysis, and the dominant techniques are Fourier-transform infrared spectroscopy and Raman spectroscopy. The components and masses have been analyzed via thermal analysis, including pyrolysis gas chromatography-mass spectrometry and thermogravimetric-spectrometry. Shape and size have been characterized via microscopic analysis. Optical and electron microscopies are the most commonly used techniques. The analytical techniques of microplastics are increasing in abundance, but the identification and quantification of soil microplastics remain a complex task. The standardization of analytical technologies is key to evaluating microplastic pollution. Each technique has its advantages and disadvantages, and the combination of analytical techniques is expected to efficiently and accurately analyze soil microplastics qualitatively and quantitatively. Analytical techniques should be selected based on the scientific objective. Meanwhile, some techniques require further exploration and verification for microplastics in real soil.

Research progress on the adsorption and desorption of typical pollutants on microplastics

XU Li, LI Haixia, HAN Lihua, ZOU Guoyuan, CHEN Yanhua, LIU Dongsheng, XUE Yinghao, LU Anxiang

2021, 29(6): 961-969. doi: 10.13930/j.cnki.cjea.200925

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Abstract:
In recent years, microplastic pollution in the environment has attracted attention worldwide. The large specific surface area and strong adsorption capacity of microplastics lead to interactions with typical environmental contaminants (such as organic pollutants and heavy metals), thereby changing the environmental behavior of these pollutants. It is important to identify the adsorption and desorption processes and mechanisms of organic pollutants and heavy metals on microplastics to better understand the corresponding changes in the environmental behavior and toxic effects of these substances. This paper reviews the adsorption and desorption of organic pollutants and heavy metals by microplastics. The processes and mechanisms of adsorption and desorption of typical pollutants on microplastics are discussed from three aspects:microplastic properties (types, morphology, surface functional groups, polarity, adsorption sites, crystallinity, and aging degree), pollutants properties (surface functional groups, hydrophobicity, polarity, and concentration), and environmental factors (temperature, pH value, salinity, ionic strength, surfactant, and biofilm). The adsorption and desorption of organic pollutants and heavy metals by microplastics are mainly affected by surface adsorption, pore filling, complexation, and hydrophobicity. The adsorption kinetics of microplastics for pollutants mostly conformed to the kinetic (quasi) second-order model, but some conformed to the first-order model. The adsorption isotherms largely conformed to the Freundlich, Langmuir, and Henry models, and some conformed to the linear and composite models. In the future, research on the adsorption and desorption of new pollutants by microplastics should be expanded and the processes and mechanisms of interaction between microplastics and typical pollutants should be further clarified to establish relevant databases and models. This review provides a reference for follow-up research on the adsorption and desorption of typical pollutants by microplastics and a scientific basis for understanding the environmental behavior of microplastics.

Effects of polyethylene microplastics on the microbial community structure of maize rhizosphere soil

DING Feng, LAI Jinlong, JI Xiaohui, LUO Xuegang

2021, 29(6): 970-978. doi: 10.13930/j.cnki.cjea.200677

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The use of agricultural polyethylene films results in polyethylene microplastic accumulation in the soil, causing microplastic pollution, which has attracted the attention of scholars worldwide. To study the effects of polyethylene microplastics on the microbial community structure of crop rhizosphere soil, corn was grown with different polyethylene powders (average molecular weights:2000, 5000, and ≥ 100 000) to simulate microplastic pollution in agricultural soil. There were five treatments in this experiment:planting maize without polyethylene (CK), planting maize with 2000 (T1), 5000 (T2), and ≥ 100 000 (T3) molecular weight polyethylene powder, and non-planting maize without polyethylene (CK0). Differences in mineral element metabolism in different parts of maize plant at the heading stage and variation in the rhizosphere soil microbial community structure were analyzed. The results showed that the mineral element content differed in different parts of maize. Iron and copper were mainly concentrated in the roots; calcium, manganese, and magnesium were most abundant in the leaves; and potassium was mainly concentrated in the stems. After adding the polyethylene microplastics of different molecular weights, the mineral elements in different parts of the plant increased compared with CK; the increase was greatest under the 2000 molecular weight polyethylene treatment. Microbial diversity analysis showed that the polyethylene microplastics had different effects on the microbial community composition in the maize rhizosphere. Except for Proteobacteria and Burkholderiaceae, the abundance of bacteria decreased under the 2000 molecular weight polyethylene treatment compared to CK. The abundance of bacteria and fungi increased under the ≥ 100 000 molecular weight polyethylene treatment compared to CK. In general, the mineral elements contents in different parts of the maize plant increased compared with CK after the addition of polyethylene. Two-thousand molecular weight polyethylene reduced the abundance of bacteria and fungi in the soil, whereas ≥ 100 000 molecular weight polyethylene increased the abundance of bacteria and fungi in the soil; the number of microorganisms related to the degradation of environmental pollutants in each treatment increased, which helped the soil cope with microplastics stress.

Effects of plastic film residues on the photosynthetic characteristics and biomass accumulation of soybean (Glycine max)

HUANG Shan, FAN Tinglu, LIU Mengjuan, CHEN Ronghuan, LIANG Chutao, CHENG Wanli, CHEN Yanhua, XUE Sha, YANG Xiaomei

2021, 29(6): 979-990. doi: 10.13930/j.cnki.cjea.200923

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Agricultural plastic film mulching technology has greatly promoted the development of agricultural production and social economics, especially in the arid and semi-arid areas of China. However, due to high fragmentation, low recovery, and long-term degradation, the accumulation of plastic residues in the soil has increased annually, which threatens crop growth, soil health, and the sustainable development of agriculture. Although many studies have focused on the effects of agricultural film residues on soil quality, the effects of plastic type (degradable or non-degradable) and the cumulative abundance of plastic on crop photosynthetic characteristics have rarely been reported. In this study, soybean (Glycine max) was investigated for its light and carbon dioxide (CO₂) response characteristics under different plastic residue addition (polyethylene[PE] and biodegradable plastic[BP] mulch film; plastic size:0.5-2 cm; addition levels:0, 0.1%, 0.5%, and 1.0%) at the flowering and early pod stages. Plant biomass and soil samples were collected at the flowering and harvesting stages to examine the effects of the different plastic residues on plant growth and soil quality. The results showed that the light compensation point (LCP) of soybean leaves decreased by 23.96% at the flowering stage and increased by 51.38% at the beginning of the pod stage in the PE treatment groups, suggesting that the weak light utilization ability of soybean leaves increased at the flowering stage and decreased at the beginning pod stage. LCP decreased by 54.82%, and the light saturation point increased by 58.12% in the BP treatment groups at the beginning of the pod stage, which improved the ability of strong light adaptation and increased the range of light energy utilization. The PE and BP residues increased the dark respiration rate (R_d) by 30.56% and 22.28%, respectively, increasing dry substance consumption. With increasing amounts of plastics, the maximum photosynthetic capacity decreased by 36.49% and 23.56% in the PE and BP treatments, respectively, indicating that the CO₂ utilization capacity of soybean was inhibited. Furthermore, the CO₂ compensation point (CCP) decreased by 67.96% and 38.91% in the PE and BP treatments, respectively, which indicated the improved CO₂ utilization capacity of the leaves at low CO₂ levels. The photorespiration rate (R_p) also decreased, reducing dry substance consumption. At the flowering stage in the BP treatment with 0.1% and 0.5% plastic addition, the underground biomass decreased significantly with increased plastic residue (P < 0.05), but there were no significant differences in the aboveground and underground biomass among the other treatments. Pearson correlation analysis was used to analyze the fitting parameters of the light response and CO₂ response curves with biomass. At the harvesting stage in the PE treatments, the aboveground biomass was negatively correlated with LCP, whereas R_p, CCP, and the initial carboxylation efficiency were strongly correlated with biomass accumulation (aboveground + underground). Further research is required to identify the mechanisms by which plastic residues affect crop growth, especially for the photosynthetic properties. Such work will enable a better understanding of the ecological risk of microplastics.

Temporal characteristics and influencing factors of evapotranspiration and water use efficiency on sloping farmlands with purple soil

CHEN Lu, ZHANG Xifeng, WANG Yanqiang, GAO Meirong, TANG Jialiang

2021, 29(6): 991-1007. doi: 10.13930/j.cnki.cjea.200757

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Evapotranspiration (ET) and water use efficiency (WUE) are important indices of the carbon and water cycles in farmland ecosystems. There are few systematic studies on the water cycle process in the soil-plant-atmosphere continuum in purple soil areas, and analyses of long-term changes in ET and WUE and its influencing factors in agroecosystems are lacking. In this study, the eddy covariance system was used to obtain carbon-water flux data from 2014 to 2018. The dynamic characteristics of ET and WUE in agroecosystems under rain-fed winter wheat-summer corn rotations on sloping farmlands with purple soil and the impact of major environmental factors were analyzed to provide a scientific basis for seasonal drought and rational water responses. The results showed that the diurnal dynamics of ET had a single peak, and the maximum value of each month occurred around 14:00. ET was highest in August and lowest in January. Seasonally, the magnitude of ET diurnal variation was the largest in summer, followed by spring, and there was relatively little variation in winter and autumn. Leaf area index and air temperature were the most important environmental factors affecting ET of the purple soil in sloping farmlands, followed by the vapor pressure deficit. ET had a linear relationship with net radiation and vapor pressure deficit (P < 0.05). ET also had an exponential growth relationship with air and soil temperature (P < 0.05) but tended to decrease with increasing air relative humidity (P < 0.05). The diurnal dynamics of WUE from 9:00 to 17:00 was first decreasing and then increasing. Seasonally, WUE in winter was the largest, and in winter and autumn was higher than in spring and summer. The leaf area index and carbon dioxide (CO₂) flux were the dominant factors affecting WUE of the purple soils in sloping farmland, and air temperature, relative humidity, and vapor pressure deficit were the secondary factors influencing WUE. WUE decreased exponentially with net radiation and soil temperature (P < 0.05) and decreased linearly with the increasing air temperature (P < 0.05). WUE first decreased and then increased with the soil water content. WUE was significantly negatively correlated with the vapor pressure deficit (P < 0.05) and significantly positively correlated with the air relative humidity (P < 0.05). The differences between two hydrological years showed that WUE in the maize planting period in summer may be more sensitive to precipitation, and the soil moisture in winter had a significant effect on ET and WUE in the sloping farmlands. Due to the lack of data series during this study, further study of the detailed dynamics of ET and WUE in the purple soil sloping farmland ecosystem is needed to explore the systematic adaptation strategies of seasonal drought in the local crops during spring and summer.

Differences in and driving forces of cultivated land expansion in the Manas River Basin oasis, Xinjiang

LIAO Na, WANG Yuejian, XU Hailiang, FAN Zili, ZHANG Zhengyong, YAO Junqiang, ZHANG Qingqing, HUANG Yan

2021, 29(6): 1008-1017. doi: 10.13930/j.cnki.cjea.200646

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The Xinjiang modern oasis is an example of a long-term expansion of the oasis arable land in regiments of the Xinjiang Production and Construction Corps and local townships under different operating modes (corps farm and local household contracting). This paper used image data from six periods (1958 to 2018) to assess the change degrees of land use of the 144 Regiment of Shihezi Reclamation Area and Lanzhouwan Town of Manas County in the Manas River Basin. This study examined the process of oases expansion in regiments and local town, and analyzed the driving forces of expansion using multiple stepwise regression. Finally, to assess oasis expansion in the whole basin, the oasis expansion model was used to calculate the appropriate scale of oasis cultivated land. The oasis change process in the 144 Regiment and Lanzhouwan Town had obviously increased the arable land area, and the increased arable land was mainly transformed from grassland and forest land. The driving factors of the regiment arable land expansion were water-saving irrigation area, water resources runoff, and average income of farming and herding industries. The local driving factors were income per capita, average income of farming and herding industries, and gross agricultural product. Moreover, the arable land in the basin had greatly exceeded the appropriate size, and the potential ecological security had been highlighted. All levels of government in the basin should follow the concept and construction requirements of "mountains-rivers-forests-farmlands-lakes-grasslands life community" to promote the comprehensive development of the basin, accelerate the construction of a modern land resource management system, scientifically delineate the ecological red line, strictly limit the scale of oasis expansion, and promote optimal land use by the corps and localities. Adherence to the strictest water resources management system, "water to determine the land" could aid efficient water resource use, prevent and control oasis desertification, promote soil degradation management and land remediation, and improve the efficiency of land use to protect the quantity, quality, and ecology of the oasis arable land.

Spatio-temporal evolution of carbon stocks in the Yellow River Basin based on InVEST and CA-Markov models

YANG Jie, XIE Baopeng, ZHANG Degang

2021, 29(6): 1018-1029. doi: 10.13930/j.cnki.cjea.200746

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The Yellow River Basin is an important carbon sink and carbon stock area of terrestrial ecosystems in China, and land use/cover change is the primary reason for variation in the carbon stocks. Therefore, accurately predicting future land use/cover changes and their impacts on regional carbon stocks is important for a better understanding of regional terrestrial ecosystems. This study aimed to explore the law of spatio-temporal changes in land use in the Yellow River Basin from 2005 to 2018 and to predict the characteristics of carbon stock changes under two scenarios of ecological protection and natural change in 2030. The CA-Markov model was used to predict the land use/cover spatial pattern in two scenarios:the ecological conservation scenario and the natural change scenario, based on its law in the Yellow River Basin from 2005 to 2018. The InVEST model was used to estimate the carbon stock in six phases of the Yellow River Basin from 2005 to 2030 based on the revised carbon density. The results highlighted land use change and transition among land use types. From 2005 to 2018, the areas of forest, water, and built-up land in the Yellow River Basin continued to increase, but the areas of cropland, grassland, and unused land decreased. The main transfer characteristics of land use types were from cropland to built-up land and grassland, and from cropland and grassland to forest. During the 13 years, the carbon stock of the whole basin decreased by 28.734×10⁶t. The simulation results of land use changes under two scenarios with the CA-Markov model showed that compared with the natural change scenario, the ecological protection scenario led to reductions in grassland and cropland in 2030, which was less than that in 2018. The expansion of built-up land was restricted under the ecological scenario, and the scale of expansion was substantially reduced, both of which facilitated the generation of ecological effects in the Yellow River Basin. Furthermore, in 2030, the carbon stocks under the natural change scenario and the ecological protection scenario were reduced by 258.863×10⁶t and 30.813×10⁶t, respectively, compared with 2018. This study provides a scientific basis for adjusting the land use structure and land use management decision-making, improving the regional carbon stock capacity, and promoting ecological civilization construction in the Yellow River Basin.

Spatial-temporal changes in green water and its driving factors in the Bashang area of Hebei Province

SHI Jiali, ZHANG Xiaolong, LI Hongjun, SHEN Yanjun

2021, 29(6): 1030-1041. doi: 10.13930/j.cnki.cjea.200806

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The Bashang area is a semi-arid farming-pastoral zone in Hebei Province and represents an important ecological barrier northwest of the capital. Green water plays an important role in maintaining the stability of the semi-arid ecosystem in Bashang and ensuring the safety of the ecological environment in the Beijing-Tianjin-Hebei region. However, a quantitative understanding of the temporal and spatial distribution of green water in this area and underlying driving factors is lacking. This study used Global Land Surface Satellite (GLASS) evapotranspiration products to quantitatively analyze the spatio-temporal changes in green water and evaluated the effect on changes in green water of temperature, precipitation, net radiation (R_n), gross primary productivity (GPP), and land use at the county level (Kangbao, Guyuan, Shangyi, and Zhangbei Counties) from 2001 to 2015. These results provide a scientific basis for the construction of the "Capital Water Conservation Functional Zone and Ecological Environment Support Zone" and more efficient use of the water resources in the Bashang area. This study used the linear trend method to assess the changing trends of green water, and based on the pixel and correlation coefficient methods to analyze the driving factors of green water variation. Multiple regression analysis was used to calculate the contribution rate of each driving factor. The results showed that: 1) the amount of green water in the four counties showed an overall insignificant downward trend from 2001 to 2015. The maximum value was in 2003 (415.34 mm), and the minimum value was in 2009 (322.35 mm). The annual average green water amount was 371.11 mm. The seasonal variation of green water amount was obvious. Summer had the highest amount of green water, followed by spring, autumn, and winter. 2) The amount of green water increased from northwest to southeast regions, most of which showed a decreasing trend. Guyuan County had the highest amount of green water, and Kangbao County had the least amount. Across the regions, 21.2% showed an increasing trend in the volume changes of green water, and 78.8% of the regions showed a decreasing trend from 2001 to 2015. 3) From 2001 to 2015, the precipitation, temperature, and GPP showed an overall increasing trend, whereas R_n showed an insignificant downward trend. Green water was positively correlated with precipitation and GPP and negatively correlated with temperature and R_n. The contribution rate of each influencing factor was in the following order: GPP > temperature > precipitation > R_n. The GPP contribution rate was as high as 51%. The above-mentioned factors primarily affected temporal changes in green water. 4) The highest amount of green water was in the forest land, followed by grassland, cultivated land, construction land, and unused land. There were no significant differences in the amount of green water among land-use types, but the trend of green water changes was significantly affected by land-use changes. Land use directly affected the spatial distribution of green water.

Comparison of machine learning for predicting and mapping soil organic carbon in cultivated land in a subtropical complex geomorphic region

REN Biwu, CHEN Hanyue, ZHANG Liming, NIE Xiangqin, XING Shihe, FAN Xieyu

2021, 29(6): 1042-1050. doi: 10.13930/j.cnki.cjea.200939

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Soil organic carbon (SOC) is a key indicator of soil quality and ecosystem health. At present, machine learning (ML) models for predicting soil properties based on environmental variables are increasingly popular; however, the performance of different ML algorithms in predicting and mapping SOC, especially at high spatial resolutions, have not been compared. This study aimed to develop, evaluate, and compare the performance of Support Vector Machine (SVM), Random Forest (RF), and Ordinary Kriging (OK) models for predicting and mapping the SOC contents in the northeast of Fujian Province. Remote sensing vegetation indices were derived from Sentinel-2 image data with a spatial resolution of 10 m. These vegetation indices, along with selected terrain and climate factors, were adopted as environmental variables to map SOC using the SVM and RF models. The results showed that the performance of the RF model (RMSE[root-mean-square error]=2.004, r=0.897) was better than that of the OK model (RMSE=4.571, r=0.623) and explained most of the SOC spatial heterogeneity. The SVM model had the poorest prediction accuracy (RMSE=5.190, r=0.431). SOC mapped from the three models had similar spatial patterns, with an increasing SOC gradient from east to west and from south to north of the study area. SOC in the farmlands predicted with the RF model varied in the range of 15.33±4.07 g·kg^-1. Elevation and rainfall were the most important variables for the RF and SVM models, respectively, whereas the remote sensing vegetation indices were less important than elevation.

Effects of organic fertilizer maturity degree on nitrogen utilization efficiency of chemical fertilizer

ZHANG Yong, XU Zhi, WANG Yuyun, DENG Yaqin, LIU Meiju, YIN Yuanping, ZHENG Kui, LOU Yisheng, ZHAO Bing

2021, 29(6): 1051-1060. doi: 10.13930/j.cnki.cjea.200945

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The application of organic fertilizers promotes efficient chemical fertilizer use, but the effects and mechanisms of organic fertilizers with different maturation degrees are unresolved. To explore the effects of applying organic fertilizer with different maturity degrees on chemical nitrogen utilization efficiency for a practice of combined organic-inorganic fertilizers application, a pot experiment of lettuce (Lactuca sativa var. ramosa Hort.) was conducted using nitrogen-15 (¹⁵N) tracer technology. The organic fertilizers with different maturity degrees, which indicated by the germination index of cress (Lepidium sativum L.) (GI), were applied with ¹⁵N-labelled chemical fertilizer. A treatment without organic fertilizer application (CK) was set up as the control and following the principle of equal nutrient and carbon input, three treatments with different maturity degrees of organic fertilizer: ¹⁵NPK (nitrogen-15, phosphorus, potassium) + 50% GI organic fertilizer (GI50), ¹⁵NPK + 80% GI organic fertilizer (GI80), and ¹⁵NPK + 100% GI organic fertilizer (GI100) were tested. The results showed that, compared to CK, the GI50, GI80, and GI100 treatments significantly (P < 0.05) increased lettuce biomass, ¹⁵N uptake and ¹⁵N use efficiency by 30.5%-56.1%, 40.0%-91.0%, and 15.5%-41.8%, respectively. The biomass, ¹⁵N uptake, and ¹⁵N use efficiency of GI80 significantly (P < 0.05) increased by 17.1%, 31.8%, and 35.4%, respectively; those of GI100 significantly (P < 0.05) increased by 19.6%, 15.8%, and 22.8%, respectively, compared to GI50. Compared to CK, ammonium-nitrogen (¹⁵NH₄⁺-N) in GI50, GI80, and GI100 treatments significantly increased by 44.9%-74.2% (P < 0.05), nitrate-nitrogen(¹⁵NO₃^--N) significantly decreased by 8.4%-38.1% (P < 0.05), and net nitrification rate significantly decreased by 10.8%-24.6% (P < 0.05). Compared to GI50, GI80 increased ¹⁵NH₄⁺-N by 7.9%-11.5%, significantly decreased ¹⁵NO₃^--N and net nitrification rate by 18.5%-50.4% (P < 0.05) and 15.0%-28.2% (P < 0.05), respectively; GI100 significantly increased ¹⁵NH₄⁺-N by 11.5%-26.9% (P < 0.05), significantly decreased ¹⁵NO₃^--N and net nitrification rate by 15.8%-22.7% (P < 0.05) and 12.5%-23.9% (P < 0.05), respectively. The microbial biomass nitrogen (MBN) and MB¹⁵N in soil slowly increased. Compared to CK, GI80 and GI100 treatments significantly increased MB¹⁵N by 67.3%-94.1% (P < 0.05). Compared to GI50, GI80 and GI100 treatments increased MB¹⁵N by 6.0%-23.8% and 6.9%-25.5% (P < 0.05), respectively. The MB¹⁵N in each treatment accounted for 54.9%-71.6% (P < 0.05) of the MBN. Correlation analysis showed that MB¹⁵N and ¹⁵NH₄⁺-N had significant positive correlations with the ¹⁵N absorptive amount and ¹⁵N utilization rate; and the redundancy analysis showed that MB¹⁵N was the key driving factor of the absorption and utilization of ¹⁵N in chemical fertilizers. Therefore, an appropriate increase in the maturity of organic fertilizer (GI ≥ 80%) when applying organic and inorganic fertilizers can enhance the nitrogen fixation ability of soil microorganisms, improve soil nitrogen levels, slow the conversion rate of soil ¹⁵NH₄⁺-N to ¹⁵NO₃^--N, reduce the net nitrification rate, and inhibit soil nitrification, thereby improving the nitrogen utilization efficiency of chemical fertilizer. The results of this study provide an important basis for understanding the mechanisms of appropriately improving the maturity degree of organic matter to enhance chemical nitrogen use efficiency.

Soil fertility improvement increases maize yield and reduces loss during mechanized grain harvest

YU Xiaofang, LEI Juanwei, GAO Julin, MA Daling, WANG Zhigang, HU Shuping, SUN Jiying, Qing geer, QU Jiawei, WANG Fugui

2021, 29(6): 1061-1075. doi: 10.13930/j.cnki.cjea.200695

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The rates of maize grain yield loss, grain crushing, and impurity during mechanized grain harvest in China are high. To reduce grain yield loss, the effects of soil fertility improvement on mechanized grain harvest quality were investigated to provide a theoretical basis for optimizing tillage and straw returning measures. Maize cultivars 'XY696' and 'XM6' were planted at high and low densities under different soil fertilities: low fertility (with tillage and straw returning measures of strip cultivation and no-tillage), medium fertility (with subsoiling and deep tillage), and high fertility (with straw incorporation, subsoiling, and straw incorporation with deep tillage). The farm rotary tillage (with much lower fertility) served as the control treatment. The following mechanized grain harvest quality indicators were measured: ear height uniformity, lodging rate, dehydration rate, and grain moisture content, as well as the yield and yield components. The results showed that soil fertility, maize cultivar, and planting density significantly (P < 0.05) affected the quality indexes of mechanized grain harvest, maize morphology characteristics, grain dehydration, and maize yield. Soil fertility improvement reduced grain yield loss during maize mechanized grain harvest, whereas the grain crushing and impurity rates did not change with soil fertility improvement. Under high planting density, yield loss decreased by 12.55-15.70 percentage for each fertility unit. Yield loss increased with increasing planting density, and the loss rate of 'XY696' was more than that of 'XM6'. Soil fertility improvement led to an increase in ear height uniformity (5.35-9.69), reduced maize lodging (5.44-9.75 percentage), and increased the grain dehydration rate (0.048-0.090%·d^-1). Optimization of these indexes may explain the reduction in yield loss at high fertility. Increased planting density reduced ear height uniformity and increased the maize lodging and grain dehydration rates. Soil fertility improvement effectively alleviated the negative impacts of densification. 'XY696' had lower ear height uniformity, higher lodging, and slower dehydration compared to 'XM6', which led to higher grain loss for 'XY696'. Soil fertility improvement increased the ear numbers per unit area, grain numbers per ear, and 1000-grain weight, ultimately increasing yield by 1878.5-2544.4 kg·hm^-2 for each fertility unit increase. The increase in maize grain yield was due to a reduction in grain yield loss during mechanized maize grain harvest. The number of ears per unit area increased, whereas the grain number per ear and the 1000-grain weight decreased when the planting density increased. Maize grain yield increased when the planting density increased at high fertility levels. Therefore, soil fertility improvement via tillage and straw returning can increase maize yield and reduce yield loss during mechanized grain harvest in Inner Mongolia. Under high soil fertility, a reasonable planting density increase can improve the yield and harvest quality and decrease the grain moisture content. Reduced mechanized grain loss can be achieved by selecting maize cultivars with high lodging resistance, high ear height uniformity, and a fast dehydration rate.

Water saving potential and mechanisms of subsurface drip irrigation: A review

YAO Jiawei, QI Yongqing, LI Huaihui, SHEN Yanjun

2021, 29(6): 1076-1084. doi: 10.13930/j.cnki.cjea.200980

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Subsurface drip irrigation is a water-saving irrigation technology with high water efficiency due to small irrigation volume and increased crop yield. Subsurface drip irrigation can effectively reduce evaporation and drainage and improve irrigation water productivity, whereas its' high degree of automation can reduce labor, operation, and management costs. This technique is an important irrigation technology in water-deficient areas in China. Here, we reviewed the development of subsurface drip irrigation technology, systematically compared the effects of various irrigation methods on crop yield, irrigation volume, and evapotranspiration, discussed the soil water movement process influenced by multiple factors under subsurface drip irrigation (from indoor control experiments and established mathematical models), revealed the water-saving and yield-increasing mechanisms of subsurface drip irrigation, and highlighted the key technical parameters of subsurface drip irrigation systems and their effects on crop yield and water use efficiency. Finally, we presented the difficulties of this system and called attention to the problems that required further research. This study examined the water conservation potential of subsurface drip irrigation and its underlying mechanisms, providing a scientific basis for promoting the widespread application of subsurface drip irrigation technology.

Water and salt transport simulation in the wheat growing area of the North China Plain based on HYDRUS model

LI Qi, LI Fadong, ZHANG Qiuying, QIAO Yunfeng, DU Kun, ZHU Nong, YANG Guang, LI Junfeng, HE Xinlin

2021, 29(6): 1085-1094. doi: 10.13930/j.cnki.cjea.200828

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Abstract:
Soil moisture and salinity are key factors that affect crop growth. Thus, it is important to investigate the mechanisms of water and salt transport to further clarify the process of soil water utilization in crops. The HYDRUS-1D model was applied to examine the spatial distribution and vertical variation in soil water and salinity and to explore the factors influencing water and salt transport. The model incorporated long-term soil moisture observation data and the results of indoor soil column experiments at the Yucheng Comprehensive Experimental Station, Chinese Academy of Sciences, a typical farmland in the North China Plain. Moreover, the applicability of the HYDRUS-1D model to the study area was evaluated. The results showed that the simulation of water transport in shallow soil had greater errors than that in deep soil, owing to the influence of external factors. The root mean square errors (RMSEs) of the water transport simulation results were 0.0348 cm³·cm^-3, 0.0179 cm³·cm^-3, 0.0179 cm³·cm^-3, 0.0122 cm³·cm^-3, and 0.0053 cm³·cm^-3 at 10 cm, 20 cm, 30 cm, 40 cm, and 60 cm, respectively. The mean value of the Nash-Sutcliffe efficiency (NSE) coefficient was 0.826, and the coefficient of variation was 0.0560, indicating that the simulations of water transport were stable and consistent with the measured values. The soil column experiment results showed that after irrigation with 8 L water, salt salinity in the vertical direction first increased and then decreased; the RMSEs of the simulation results of salt transport were 0.181 g·kg^-1, 0.131 g·kg^-1, 0.120 g·kg^-1, 0.034 g·kg^-1, and 0.027 g·kg^-1 after 12 h, 24 h, 40 h, 45 h, and 48 h, respectively. The mean error was 0.174 g·kg^-1, which was in good agreement with the measured values, indicating that the model was suitable for the simulation of water and salt transport in the study area. However, owing to the influence of evaporation, tillage, and crop root system, large variations in physical and chemical properties resulted in large deviations between the simulated and measured values of salt transport in shallow soil, and the NSE coefficient reached 9.71. After 48 h of infiltration, the soil salinity peaked at 23 cm, 26 cm, and 29 cm depth with 8 L, 16 L, and 24 L irrigation quotas, respectively. These results showed that increased irrigation quotas can enhance salt leaching. This study confirmed that the HYDRUS-1D model could be used for theoretical studies of water and salt transport in the study area. This study also provides a theoretical basis for further exploration of water and salt transport in winter wheat, optimizing farmland water resource management, and improving the water resource utilization efficiency in the North China Plain.

Distribution of rice straw phosphorus resources in China and its utilization potential under straw return

CHAI Rushan, HUANG Jing, LUO Laichao, TIAN Da, ZHANG Liangliang, YE Xinxin, ZHANG Ligan, GAO Hongjian

2021, 29(6): 1095-1104. doi: 10.13930/j.cnki.cjea.200722

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Abstract:
Large amounts of rice straws are produced in the main rice-cultivating areas of China. Rice straw returning is a major contributor of phosphorus input in the field. Clarification of the contribution of rice straw returning to soil phosphorus input could provide scientific references and guidance for the optimization of phosphorus management and the regulation of soil phosphorus balance. Based on the rice production statistics from China Rural Statistical Yearbook and related data from a literature survey, the temporal and spatial distribution characteristics of rice straw phosphorus resources from 2013 to 2018 and the amount of straw phosphorus returning to soil per unit sown area were estimated for different rice-cultivating provinces and regions of China. In 2018, the amounts of straw from early rice, double cropping late rice, and medium and late rice in the main rice-cultivating areas of China were 23.27, 27.83, and 135.27 million tons, respectively. Rice straw was mainly produced in the Middle Reaches and the Lower Reaches of Yangtze River, accounting for 33.6% and 21.8% of the total national rice straw yields, respectively. The rice straw phosphorus resources was tended to increase from 2013 to 2018, increasing from 0.597 million tons phosphorus pentoxide (P₂O₅) in 2013 to 0.628 million tons P₂O₅ in 2018. The rice straw phosphorus resources were mainly distributed in Heilongjiang (15.0%), Hunan (12.5%), Jiangsu (10.0%), Hubei (9.9%), and Jiangxi (9.6%) in 2018. During 2013-2018, the annual average phosphorus inputs by straw incorporation in the main rice-cultivating provinces of China were 13.9-15.1 and 16.0-20.9 kg(P₂O₅)·hm^-2 for early rice and double cropping late rice, respectively. For medium and late rice, the annual average phosphorus inputs by straw incorporation reached as high as 19.3-29.3 kg(P₂O₅)·hm^-2. Nationally, the soil phosphorus inputs from straw incorporation were 14.4, 18.2, and 24.4 kg(P₂O₅)·hm^-2 for early rice, double cropping late rice, and medium and late rice, respectively. Based on the results of this study, the application rate of phosphate fertilizer in different rice-cultivating provinces should be adjusted according to the contribution of rice straw returning to the soil phosphorus input. This will help to maintain the soil phosphorus balance and reduce surplus phosphorus accumulation and phosphorus loss to surface water.

Extraction method of irrigated arable land in the Chahannur Basin based on the ESTARFM NDVI

CHEN Xiaolu, WANG Yanfang, Zhang Hongmei, LIU Fenggui, SHEN Yanjun

2021, 29(6): 1105-1116. doi: 10.13930/j.cnki.cjea.200880

Abstract(195) HTML (176) PDF(30)

Abstract:
Remote sensing extraction technology for crops is a promising research method for remote sensing applications. However, it is limited by the spatial and temporal resolution of the remote sensing data; it is difficult to identify crops with similar spectral characteristics. In this study, the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) was used to fuse MODIS and Landsat data to obtain normalized difference vegetation index (NDVI) time series data of the Chahannur Basin with a temporal resolution of 8 days and a spatial resolution of 30 m. The correlation coefficient between the ESTARFM NDVI and the Landsat NDVI during the same period was 0.94. Harmonic analysis of the NDVI time series filter was used to smooth the ESTARFM NDVI data. Finally, the irrigated arable land was extracted using a support vector machine (SVM) with irrigated cultivated land samples. The results showed that the total area of irrigated arable land in the watershed is 1958.24 km². The total area of Shangdu, Xinghe, Shangyi, Kangbao, and Huade Counties accounts for 94% of the watershed, and the irrigated arable land is 616.67 km², 337.36 km², 409.85 km², 290.93 km², and 239.38 km², respectively. The region primarily grows sunflowers, beets, potatoes, and other long-growing crops from the beginning of April to the end of September and vegetables (including celery, Chinese cabbage, cabbage) from the beginning of May to the beginning of August. Cultivated land in Zhangbei, Chahar Youyiqianqi, Houqi, and Xianghuangqi Counties accounts for 6% of the total cultivated land in the basin, and the total irrigated land in the four counties is 64.05 km². Real sample verification indicates that the total classification accuracy is 93.18%, and the Kappa coefficient is 0.91. The results show that the NDVI time series obtained from the data fusion model reflects real changes in crops, and the use of SVMs to extract irrigation arable land in the Chahannur Basin is suitable.

Spatial and temporal variability in soil pH of Shaanxi Province over the last 40 years

WANG Hong, CAO Jing, WU Junhua, CHEN Yiping

2021, 29(6): 1117-1126. doi: 10.13930/j.cnki.cjea.200778

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Abstract:
Rapid development of the economy has increased the occurrence of declining cultivated land quality, such as acidification and salinization in China. To provide a scientific basis for adjustment of topsoil pH and to realize the rational use of land resources in Shaanxi Province, this study examined pH of 705 topsoil samples from Shaanxi Province using a soil/water ratio of 2.5/1 in 2017 and incorporated soil pH data from the second national soil survey in 1980s. The spatio-temporal changes and classification characteristics were analyzed via ArcGIS, and the influencing factors were investigated by correlation analysis and analysis of variance methods. General statistical analysis and normality tests were performed in Excel 2016 and SPSS 22.0; and the GS+9.0 software was adopted to obtain the best fitting model. The ordinary Kriging method was used for spatial interpolation analysis and mapping. The study is important for sustainable agriculture development and ecological environment protection in Shaanxi Province. The results showed that pH values of farmland soil in northern Shaanxi, Guanzhong, and southern Shaanxi were 8.25, 7.91, and 6.25, respectively, and the corresponding levels were 5 (alkalescence), 5 (alkalescence), and 3 (weak acidity), respectively. The order of soil pH in the administrative regions was Yan'an > Yulin > Tongchua > Xianyang > Weinan > Xi'an > Baoji > Shangluo > Ankang > Hanzhong. The topsoil pH in Hanzhong City showed moderate variation, whereas the other cities in Shaanxi Province showed weak variation. Compared with the 1980s, the farmland soil in northern Shaanxi and Guanzhong showed an alkalization trend, whereas the surface soil in southern Shaanxi showed an acidification trend. In the administrative regions, the topsoil in Yulin, Ankang, Hanzhong, and Shangluo showed an acidification trend, and the soil in other cities showed an alkalization trend. The optimal fitting semi-variance function model of farmland soil pH in northern and southern Shaanxi was a linear model, and the optimal fitting semi-variance function model of farmland soil pH in Guanzhong was a Gaussian model; both showed strong spatial correlation. Furthermore, the topsoil pH in northern Shaanxi was primarily influenced by structural factors, whereas the topsoil pH in Guanzhong and southern Shaanxi was influenced by structural and random factors. The spatial distribution characteristics of topsoil pH were sporadic in northern Shaanxi, and that in Guanzhong and southern Shaanxi was higher in the east than in the west. Changes in soil pH were affected by natural and human factors, such as topography, soil type, climate, and fertilization. Slope and elevation were significantly (P < 0.05) correlated with topsoil pH in Shaanxi Province; lower slopes and higher altitudes had higher soil pH. To promote sustainable agriculture development and regional food security, soil salinization should be prevented in northern Shaanxi and Guanzhong and acidification should be prevented in southern Shaanxi.

2021 Vol. 29, No. 6