中国生态农业学报(中英文)

Impact of climate change on grain yield and its trend across Guanzhong region

ZHAO Ruxin, WANG Huixiao, DONG Yuxuan

2020, 28(4): 467-479. doi: 10.13930/j.cnki.cjea.190752

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Abstract:
Climate change dominated by warming has a significant impact on grain yield. From an examination of grain yield, climatic yield and climate potential productivity (CPP), this paper systematically analyzed the response of grain yield to climate change in Guanzhong, Shaanxi, one of China's main food-producing areas. Datasets were climate variables at 8 meteorological stations, grain yield statistics from Guanzhong region during 1983-2016, and the precipitation and temperature simulation results from 4 global climate models of the Intersectoral Impact Model Intercomparison Project for 2021-2050. Mutation analysis, trend analysis, and sensitivity analysis were all used in the study. The results showed that the annual average temperature of Guanzhong region was increasing significantly at the rate of 0.05 ℃·a^-1, and a significant increase in the maximum temperature was contributing most to this trend. Meanwhile, annual average precipitation showed a decreasing trend at the rate of -1 mm·a^-1 but was not significant. During 1983-2016, the average annual grain yield of Guanzhong region was 3 599 kg·hm^-2. Although showing fluctuations, it increased at the rate of 57.17 kg·hm^-2·a^-1 (P < 0.001). There was a positive correlation between the climatic yield and temperature in many parts of Guanzhong. The increase in temperature had promoted an increase in climatic yield in Guanzhong to a certain extent, but not significantly (the increase was 0.85 kg·hm^-2·a^-1 and P>0.05). The CPP of Guanzhong region ranged between 7 000-12 000 kg·hm^-2 over 34 years. Due to the fluctuations in temperature, the average CPP after 1995 was higher than that before 1995, which meant that the change in CPP after 1995 was the main driving source of the increasing trend of CPP during the whole study period. During 2021-2050, the average CPP of Guanzhong region under RCP 2.6 scenario will be higher than that of RCP 6.0. However, the CPP decreases under the RCP 2.6 scenario but increases under the RCP 6.0 scenario. There is a plenty room for promotion of climate resources used by crops in Guanzhong region, and climate change has had a positive effect on the grain yield in Guanzhong, but this effect will not persist.

Effects of sowing dates on grain yield of spring maize in the Three-Province of the Northeast China under climate change

BAI Fan, YANG Xiaoguang, LIU Zhijuan, SUN Shuang, ZHANG Zhentao, WANG Xiaoyu, GAO Jiqing, LIU Tao

2020, 28(4): 480-491. doi: 10.13930/j.cnki.cjea.190585

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Abstract:
Northeast China is the most sensitive area to climate change, where is also the important region of maiza production in China. It has both theoretical and practical significance to explore suitable sowing date of spring maize in three provinces of Northeast China (Heilongjiang Province, Jilin Province and Liaoning Province) under climate change. Meteorological data from 1981 to 2015 and agro-meteorological observations, including maize phenology data, yield data, and soil data from 1981 to 2012, were used to construct an APSIM-Maize model. The data were collected from the potential cultivation zones of spring maize in the three provinces of the Northeast China. The model was calibrated and validated in different climatic zones across the study area and related parameters were established accordingly. The potential yields and climatic potential yields of spring maize during different decades were then determined by setting different sowing dates based on the validated APSIM model. Combined with the indices of yield level and yield stability, the suitable range of sowing dates was determined under different conditions during different decades in each climatic zone. The results showed that the simulated values, including the days from sowing date to flowering date and maturity date, and the yield, were in agreement with the observed values for the seven spring maize varieties in the study area. This indicated that the APSIM model accurately simulated the phenological development and yield information of spring maize in the study area. Under the condition of sufficient irrigation, the suitable sowing date in the study area ranged from April 16 to May 19. A latitudinal distribution was exhibited for the suitable sowing date with the date moving earlier from south to north. The suitable sowing date of maize in the 1990s and 2000s was earlier than that in the 1980s, and this advanced trend was more significant in the 1990s than in the 2000s. However, under rainfed conditions, the suitable sowing period in the first, third, fifth, seventh, and ninth climatic zones displayed a delayed trend, with the delay ranging from 3 days to 6 days. Compared with the yield simulated using the sowing date applied in current production, the yield simulated using the theoretical suitable sowing date increased by 2.84%-9.96% in different climatic zones during different decades under rainfed conditions. This research supports the use of the APSIM model in Northeast China for applications such as the selection of suitable sowing dates under future climate scenarios.

Dry-wet evolution and its influencing factors in single cropping rice growing season in Southwest China

CHEN Chao, PANG Yanmei, XU Fuxian, GUO Xiaoyi

2020, 28(4): 492-502. doi: 10.13930/j.cnki.cjea.190727

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Abstract:
Research on regional dry-wet evolution and its influencing factors during the crop growing season is critical for sustainable agricultural development and food security. In this study, which is based on the daily meteorological data from 316 meteorological stations in the rice-growing area of Southwest China from 1961 to 2015, and on calculation of the ratio of precipitation to reference crop evapotranspiration (ET₀) in a single cropping rice growing season in Southwest China, the characteristics of dry-wet evolution from 1961 to 2015 were analyzed. The sensitivity of ET₀ to the main climatic factors and attribution rates to ET₀ of the main climatic factors were studied, and the factors influencing dry-wet evolution were also discussed. The results showed that the semi-humid climatic regions with a single cropping rice growing season in Southwest China were mainly distributed in the south of Panxi area of Sichuan and the center and northeast of Yunnan, but that the rest of Southwest China comprised humid climatic regions. Compared with 1961-1990, the area of the semi-humid climatic region in Southwest China increased during 1991-2015, while the area of the humid climatic region decreased. During the single cropping rice growing season, 40.8% of the sites in Southwest China became wet from 1961 to 2015, and the rest of the region became dry. The climate became wet in the northeast of Sichuan basin and the northeast of Yunnan because of increasing precipitation and decreasing ET₀. The positive effect caused by the increasing precipitation on the humidity index exceeded the negative effect caused by the increasing ET₀, which resulted in the climate becoming wet in the Panxi area of Sichuan. The positive effect caused by the decreasing ET₀ on the humidity index exceeded the negative effect caused by the decreasing precipitation, which resulted in the climate becoming wet in the south of Chongqing, and in the north and west of Guizhou Province. In contrast, most of Yunnan showed a dry trend with decreasing precipitation and increasing ET₀. The climate became drier in other areas of Southwest China because the negative effect caused by the decreasing precipitation on the humidity index exceeded the positive effect of the decreasing ET₀. During the single cropping rice growing season, the ET₀ decreased with increasing average temperature and relative humidity in Southwest China, but the ET₀ increased with increasing sunshine hours and wind speed. The significant decline in sunshine hours and wind speed in Southwest China was the main reason for the decrease in ET₀. The study provided a scientific basis for reduction of the possible climate risks of the single cropping rice growing season in Southwest China under global climate change.

Current problems and proposed solutions of emergy evaluation in agricultural systems

WANG Xiaolong, LIU Xingxing, SUI Peng, CHEN Yuanquan

2020, 28(4): 503-512. doi: 10.13930/j.cnki.cjea.190776

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Abstract:
Emergy evaluation (EME) is an extensively used method for the assessment of ecological economic systems which has been applied in a diverse array of fields, with more recent application in agricultural systems. However, despite an increasing number of studies using the EME approach to assess agricultural systems, some of the evaluation principles of EME have been misunderstood by researchers applying the method resulting in unreliable assessments. Therefore, this study aimed to investigate issues identified from prior research using EME in the assessment of agricultural systems. Five common problems were identified: 1) disordered selection of unit emergy values (UEV) caused by updated global emergy baselines, 2) incomplete definition of system boundary, 3) arbitrary calculation of emergy contribution derived from environmental resources, 4) inoperable classification of system inputs, and 5) non-conservation between input and output emergy in agricultural systems. Concurrently, we proposed related solutions for resolving the identified problems which included: standardizing the selection principle of UEV in the EME; defining system boundary based on a standard of 'four-dimensional space-time scale'; constructing formulas to reasonably reflect energy contributions from soil and water for agricultural production in the EME; setting four standards to order the classification of input resources of agricultural systems; and applying the emergy accounting algebras to ensure the emergy conservation in research. We hope that our research will initiate further discussions on approaches to EME assessment in agricultural practices thus promoting a more standardized application of the emergy method in future studies.

Effect of straw returning on ammonia emissions from soil in a wheat-maize multiple cropping system in the Guanzhong region, China

LYU Hongfei, MA Xingxia, YANG Gaihe, FENG Yongzhong, REN Guangxin, LI Na, XIE Chenghui, XU Hongwei

2020, 28(4): 513-522. doi: 10.13930/j.cnki.cjea.190627

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Abstract:
Reducing agricultural ammonia emissions is considered the most economical and effective method to mitigate haze pollution. Notably, ammonia emissions caused by fertilizer application in agricultural practices are a significant contributor to atmospheric ammonia. In this context, this study aimed to explore the effect of straw returning on ammonia emissions from soil using a winter wheat-summer maize multiple cropping system to provide a theoretical basis for reducing agricultural ammonia emissions to control haze pollution. The study was conducted from June 2018 to June 2019, in the Shaanxi Guanzhong region, China. The experiment used a random block design encompassing different straw returning treatments—no straw returning (S0), half straw returning (S0.5), and full straw returning (S1), as main treatments; and different fertilizer applications—no fertilization (F0), 20% fertilizer reduction (F0.8), and conventional fertilization (F1), as sub-treatments. Soil ammonia emissions, inorganic N (in 0-40 cm of soil), and crop yield, were measured for all treatments. The results showed that straw returning and fertilization, and the interaction between the two, had a significant effect on cumulative ammonia emissions (C) in the summer maize season. Conversely, straw returning had no significant effect on C in the winter wheat season. The C of the entire wheat-maize multiple cropping system was 1.31-19.26 kg·hm^-2, accounting for 2.17%-4.69% of the fertilizer application. Performance among the treatments was as follows: S0F1 > S0.5F1 > S1F1 > S0F0.8 > S0.5F0.8 > S1F0.8 > S1F0 > S0.5F0 > S0F0. Notably, straw returning showed an increase in C without fertilization. However, when compared with no straw returning, straw returning combined with fertilization significantly reduced the C and the amount of ammonia loss that occurred. There was no significant difference in ammonia emissions between full and half straw return treatments. Notably, the ammonia emission reduction effect of S1F0.8 and S0.5F0.8 treatments were the most significant for the study, reducing 38.64% and 37.35% from S0F0.8 treatment, respectively. Straw returning combined with N fertilizer also demonstrated a significant reduction in NO₃^--N and NH₄₊-N in soil, while increasing the yield of summer maize by 6.23%-20.20%, and winter wheat by 16.60%-28.17%. Further to this, PCA analysis indicated that S0.5F0.8 and S1F0.8 treatments were the optimal treatment combinations of those tested for the study, providing a balance between ammonia emission reduction and increased crop production. Therefore, our findings indicate that long-term straw returning combined with fertilizer reduction could improve crop yield as well as reduce soil ammonia emissions, suggesting an agricultural practice that can assist in the reduction of agricultural ammonia emissions, and thus help mitigate haze pollution in the Guanzhong region.

Effects of low nitrogen stress on foxtail millet seedling characteristics and screening of low nitrogen tolerant varieties

LIAN Ying, LU Juan, HU Chengmei, NIU Yinquan, SHI Yugang, YANG Jinwen, WANG Shuguang, ZHANG Wenjun, SUN Daizhen

2020, 28(4): 523-534. doi: 10.13930/j.cnki.cjea.190847

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Abstract:
Screening and cultivating low-nitrogen-tolerant crop varieties can be used as an effective measure for increasing the nitrogen-use efficiency of plants, reducing nitrogen fertilizer use, as well as limiting environmental pollution during cultivation. In the present study, 45 foxtail millet varieties were grown in different nitrogen conditions, low nitrogen (0.1 mmol·L^-1) and normal nitrogen (5 mmol·L^-1), using hydroponic methods. Nitrogen efficiency of plants was subsequently measured based on 22 indicators about growth, biomass, nitrogen content, nitrogen accumulation and physiology efficiency. The low nitrogen tolerance of the tested foxtail millet varieties was evaluated by using the comprehensive low nitrogen tolerance coefficient method and the membership function method based on principal component analysis. The results showed that foxtail millet seedlings exposed to low nitrogen stress demonstrated varying degrees of improvement compared to seedlings grown in normal nitrogen condition for root length, root-shoot ratio, number of root; and root, shoot, and plant nitrogen physiology efficiency. The remaining 17 indicators demonstrated different levels of reduction under low nitrogen stress. Forty-five foxtail millet varieties were subsequently divided into five categories (strong resistant, resistant, medium resistant, sensitive, and highly sensitive) for screening; five varieties with relatively strong low nitrogen tolerance were screened (varieties 11, 14, 17, 35, and 39). A GGE double plot was used to analyze the variety-low nitrogen tolerance related indexes. The predominant low nitrogen tolerance traits of low nitrogen tolerant varieties 39 and 14 were dry weight of root, fresh weight of root, and root length; while varieties 11, 35, and 17 were identified as having traits fresh weight of shoot, leaf number, leaf width, leaf length, nitrogen accumulation of plant, nitrogen accumulation of shoot, dry weight of plant, dry weight of shoot, nitrogen accumulation of root, root number, seedling height, and SPAD. Our results suggest that there are some differences in the low nitrogen tolerance mechanisms of different millet varieties. These findings provide a material basis for the breeding of foxtail millet varieties with low nitrogen resistance.

Effect of applying nitrogen fertilizer on nitrogen metabolism and distribution in grapevine under magnetic treatment of water

ZHU Hong, KONG Linggang, ZHANG Zhihao, BI Sisheng, LING Chunhui, WEI Ye, YAN Pan, WANG Huatian, MA Fengyun, LIU Xiumei, TANG Jin, CHEN Shuying, CONG Guizhi

2020, 28(4): 535-544. doi: 10.13930/j.cnki.cjea.190648

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Abstract:
The aim of this study was to investigate nitrogen (N) absorption and distribution, as well as nitrogen-use efficiency, of grape seedlings grown in magnetic and non-magnetic water treatments. One-year-old grape (Vitis vinifera×V. labrusca L. hybrid) seedlings were planted in pots and fertilized with exogenous ¹⁵N, and then grown under different magnetic water treatments or a control (untreated irrigated water). The proportional content of different forms of N, the activities of key enzymes relative to N metabolism, and the fate of N in leaves, stems, and roots of treated grape seedlings were analyzed. Under N application, we found that compared with the non-magnetic treatment (NMT), the magnetic treatment of water (MTW) appeared to promote N uptake and N-use efficiency in treated grape seedlings, while also optimizing the N allocation pattern and improving N assimilation ability of N fertilizer. We also identified that the total content of N in the leaves and roots (and in the plant generally) of treated seedlings were significantly increased when grown in the MTW. Conversely, the degree of contribution by N fertilizer (Ndff) to total N was not significantly different. Notably, the N utilization efficiencies of leaves and roots was significantly increased under MTW compared to that of the NMT treatment. The N allocation rate in leaves showed a marked increase under MTW, while that in stems showed a significant decrease. Additionally, it was found that the activities of glutamine syntheses and glutamic synthase increased significantly in the leaves, but decreased in the roots of treated seedlings. Finally, we identified that MTW increased the N-use efficiency and fixing capacity of plants and, additionally, alleviated the loss of N fertilizer in grape seedlings. Compared with treatments applying N fertilizer, the content of inorganic N and total N were promoted by 3.03%-3.45% in soil when exposed to MTW with N application. The utilization rate, residual rate, and recovery rate of seedlings increased by 36.39%-76.50% under MTW after the addition of ¹⁵N, and the loss rate of ¹⁵N decreased significantly (35.33% reduction). Based on our findings, it appears that the magnetic treatment of water can be effective in promoting N absorption and allocation in grape seedlings while also improving the plant fertilizer use efficiency from soil.

Analysis of kernel dry down process after physiological maturity of spring maize based on diffusion theory in the North China

WANG Jintao, DONG Xinliang, XIAO Yu, LIU Qingsong, ZHANG Dongmei, HAN Jinling, LIU Yi, GAO Guangrui, LIU Zhanmao, SUN Hongyong

2020, 28(4): 545-557. doi: 10.13930/j.cnki.cjea.190906

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The moisture content of grains after physiological maturity (MCAM) is the key determinant of the quality of mechanical grain harvesting (MGH), which can significantly improve the production efficiency of maize. Therefore, the aim of this study was to accurately estimate MCAM, analyze the main influencing factors, and determine the harvest time of maize, and select appropriate varieties for MGH. In 2017 and 2018, spring maize field experiments were carried out in Botou, Nandagang, and Yutian of Hebei Province; and Yuci of Shanxi Province. Seven common maize varieties and three densities of each variety were set up each year to monitor MCAM. Variety characteristics, management, meteorological data, and grain moisture content after physiological maturity were determined. A model based on the diffusion theory was used to simulate MCAM considering the atmospheric temperature and humidity. The area under the dry down curve (AUDDC) was used to select the varieties that performed well in the grain dry down. The results showed that the model based on diffusion theory could simulate MCAM well. The year, site, and variety had significant influence on the grain moisture content at physiological maturity (M₀) and the moisture diffusion rate (k), which were parameters of the model. However, the planting density had no significant effect on these two parameters. Stepwise linear regression analysis showed that ET₀, the maximum temperature, and irrigation amount at grain-filling stage had significant positive effects on M₀. The ET₀ during the 30 days after physiological maturity and the rainfall in the middle-late grain-filling stage had significant positive effects on k. In contrast, rainfall during the entire growth period had a significant negative effect on k. The number of husk layers had the greatest influence on M₀ (positive effect), and the number of leaves had the greatest influence on k (negative effect). Ten days after physiological maturity, the MCAM of spring maize in North China could be reduced to 28% in almost all circumstances and to 25% in half of the circumstances. The AUDDC during the 10 days after physiological maturity of each variety, was calculated using the model. Compared with the average AUDDC, it was found that 'Jingnongke 728' 'Zhang1453' 'Huanong 887' 'Guangde 5' and 'Jinkeyu 3306' displayed excellent dry down performance.

Comparing the cold resistance of roots of different wine grape varieties

YANG Yu, ZHANG Xiaoyu, CHEN Renwei, LIU Zhaoyu, LI Fanghong, FENG Rui, WANG Jing, LI Hongying

2020, 28(4): 558-565. doi: 10.13930/j.cnki.cjea.190787

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Winter freezing injury of wine grape refers to the phenomenon in which grape tissue cells are injured or even killed when they are exposed to temperatures lower than 0 ℃. Northern China in winter is colder and drier than areas of similar latitude elsewhere in the world. Winter freezing injury is one of the most significant limiting factors restricting the development of wine grape cultivation in northern China. Different parts of the grapevine vary in their resistance to cold. The root has the least resistance as it does not have the process of dormancy in winter. However, the cold tolerance level of the root depends on the genetic character of the wine grape varieties. An investigation into the cold resistance of roots of different wine grape varieties should provide scientific guidance on the monitoring, early warning, and prevention of winter-freezing injury of wine grape in northern China. In this paper, roots from eight common varieties of wine grape, such as 'Cabernet Sauvignon', 'Merlot', 'Marselan', 'Vidal', 'Syrah', 'Beimei', 'Beihong' and 'Longyan', in the eastern foothills of Helan Mountain were selected and tested. The freezing experiment on these roots was carried out by an artificial freezing system simulating the natural cooling and freezing processes. The temperatures of the supercooling point and the frozen point, the concentrations of the soluble sugar and the soluble protein, the relative electronic conductivity, and the semi-lethal temperature of the roots were measured in the laboratory. The critical temperatures for roots of different varieties were further identified using correlation analysis and cluster analysis. After that, the cold resistance abilities of roots of eight tested wine grapes were comprehensively analyzed for the indicators mentioned above. The following conclusions were drawn: 1) The content of soluble protein in the root significantly affected the cold resistance ability of wine grapes. 2) The cold resistance ability of roots from the eight varieties could be grouped into three categories: the light cold resistance type ('Cabernet Sauvignon', 'Merlot', 'Syrah'), for which the supercooling point was -3.8 ℃ to -3.2 ℃, the frozen point was -2.8 ℃, to -2.3 ℃, and the semi-lethal temperature was -4.34 ℃ to -3.19 ℃; the moderate cold resistance type ('Beimei', 'Marselan', 'Vidal'), for which the supercooling point was -5.4 ℃ to -4.4 ℃, the frozen point was -4.1 ℃ to -3.7 ℃, and the semi-lethal temperature was -5.90 ℃ to -4.43 ℃; the strong cold resistance type ('Beihong', 'Longyan'), for which the supercooling point was -6.4 ℃ to -6.3 ℃, the frozen point was -5.2 ℃ to -4.8 ℃, and the semi-lethal temperature was -6.55 ℃ to -6.11 ℃. 3) The cold resistance abilities of roots of the eight varieties varied from strong to light in this order: 'Beihong' > 'Longyan' > 'Beimei' > 'Vidal' > 'Marselan' > 'Cabernet Sauvignon' > 'Merlot' > 'Syrah'. The results showed that both temperatures of the supercooling point and the frozen point for the grape roots could be used as indicators to evaluate the cold resistance ability of grapes.

Effects of mixed saline-alkali stress on germination of rice

JIN Mengye, LI Xiaohua, LI Fangze, HUANG Zhanbin

2020, 28(4): 566-574. doi: 10.13930/j.cnki.cjea.190750

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Soil salinization has an important effect on seed germination of plants. In recent years, the effects of soil salinization on plant growth and crop yield have become more severe, and the area covered by salinized soil has increased. In order to study the effects of combined salt and alkali stress on the germination of rice seeds, two neutral salts (NaCl and Na₂SO₄) and two alkaline salts (NaHCO₃, Na₂CO₃) were mixed in five proportions: A (1:1:0:0), B (1:2:1:0), C (1:9:1:0), D (1:1:1:1), and E (9:1:1:9); and each proportion had four concentrations (50 mmol·L^-1, 100 mmol·L^-1, 150 mmol·L^-1 and 200 mmol·L^-1) to simulate 20 kinds of saline-alkali stress environments. Deionized water was used as the control (CK). The germination rate, germination potential, final germination rate, germination index, and average germination time of rice seeds were determined during the experiment, and the influences of the various salt solutions on the germination of rice seeds were explored. The results showed that, compared with the control, the germination rate, germination potential, and germination index of rice seeds were reduced by 9.2%-74.4%, 10.0%-48.9%, 5.6%-55.6%, and average germination time was prolonged by 3.2%-96.4% after culture under two neutral salt mixed stress solutions. When the proportion of alkaline salts in the stress solution increased, respectively, compared to the control, the germination rate in the B-E groups decreased by 8.9%-96.5%, 15.0%-98.0%, 7.5%-98.7%, and 18.9%-95.7%; the germination potential decreased by 20.0%-94.4%, 13.2%-97.8%, 3.3%-100%, and 36.7%-94.4%; the germination index decreased by 16.7%-94.4%, 22.2%-100%, 16.7%-100%, and 27.8%-94.4%; and the average germination time was extended by 0.8-4.5 times. These results showed that a stress solution containing two neutral salts and two alkaline salts had a stronger inhibitory effect on the germination of rice seeds than that only containing two neutral salts. After the non-germinated rice seeds in saline-alkaline stress solution were transferred to distilled water and cultured for 7 d, the final germination rates of rice seeds were above 73.33%, indicating that the stress solution did not destroy the activity of rice seeds, but only temporarily inhibited the germination. The experimental results showed that, compared with the single application of neutral salt, the mixed stress of neutral salt and alkaline salt inhibited the germination of rice seeds to a greater extent, and when the concentration of the mixed neutral salt and alkaline salt solution reached 200 mmol·L^-1, the seed germination rate was close to zero.

Impact of the 'Grain for Green' project on the spatial and temporal pattern of habitat quality in Yan'an City, China

XIE Yifan, YAO Shunbo, DENG Yuanjie, JIA Lei, LI Yuanyuan, GAO Qing

2020, 28(4): 575-586. doi: 10.13930/j.cnki.cjea.190762

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In an attempt to alleviate increasing pressure caused by human activities on the environment, numerous ecological restoration projects have been implemented around the world. The 'Grain for Green' project in China is currently the largest and most extensive ecological restoration project globally. Research indicates the substantial investment given to this project has achieved significant ecological benefits. Habitat quality is an important indicator of the ability of an ecosystem to provide sustainable conditions for persistence of individuals and populations. Accordingly, this study aimed to investigate the temporal and spatial patterns of habitat quality in Yan'an City, the piloted research area of the 'Grain for Green' project, to identify the impact of the restoration project on the city. Research into the impacts of this project are of great significance for successful implementation of ecological restoration projects moving forward, as well as expanding knowledge on regional ecosystems, and on socio-economic sustainable development. Land use/land cover data of Yan'an City in 2000, 2008, and 2015 were evaluated for the study. The habitat quality index of Yan'an City in 2000, 2008, and 2015 was estimated based on the ArcGIS platform and the InVEST model. The temporal and spatial evolution pattern of habitat quality and its driving factor and spatial clustering characteristics were discussed by using the exploratory spatial data analysis. Our results showed that the main feature of land use change in Yan'an City from 2000 to 2015, driven by the 'Grain for Green' project was the conversion of cultivated land to woodland and grassland; the area of woodland and grassland increased significantly in the city during the study period. The habitat quality of Yan'an City in 2015 was relatively good, demonstrating a pattern of high habitat quality in the south, low habitat quality in the north. The habitat quality index showed an upward trend during the study period; the regional average habitat quality index increased from 0.69 in 2000 to 0.71 in 2015. Additionally, habitat quality of the study area as a whole showed significant positive global spatial autocorrelation, and habitat quality, as well as its spatial variation, indicated obvious spatial clustering differentiation characteristics. Forest-rich areas, such as Huangling County and Huanglong County in the south, exhibited predominately high-high agglomeration characteristics highlighting the need for these areas to remain the focus of ecological protection measures. Conversely, low-low and high-low agglomeration areas were found interspersed, and concentrated in the north (i.e., Baota County, Zichang County, Ansai County, Wuqi County, and in other counties as well as agricultural areas of this region); accordingly, ecological restoration in northern areas should be strengthened and consolidated. Our results indicate that the 'Grain for Green' project will likely affect the processes and functions of the Yan'an City ecosystem by changing land use patterns and structure. In particular, the increase of forestland and grassland in this area will significantly promote the improvement of regional habitat quality. Therefore, by optimizing land use pattern and structure (in particular forest and grassland habitats) will assist in the development of a more coordinated and balanced policy for ecological protection and economic development in response to regional ecological problems, while systematically improving regional habitat quality and ecosystem stability.

Spatial pattern of cultivated land change in Fujian Province from 1990 to 2015

QU Shengqiu, LIU Yanfang, YIN Chaohui, ZHANG Ziyi

2020, 28(4): 587-598. doi: 10.13930/j.cnki.cjea.190653

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In order to provide references and arguments for changes in cultivated land quality and yield, and to provide suggestions for the government to further strengthen cultivated land protection, this study examined the spatial patterns of cultivated land change in Fujian Province from 1990 to 2015, at the patch level. In addition to exploring the spatial characteristics of change in cultivated land quantity, this study further explored spatial attribute and environmental characteristics of cultivated land change map spots, aiming to comprehensively describe the changes of cultivated land. This research considered three aspects: the change characteristics of cultivated land quantity, the spatial attribute characteristics of cultivated land change map spots, and the environmental characteristics of cultivated land change map spots. Based on the DEM data and land use data of Fujian Province from 1990 to 2015, mathematical statistical analysis and spatial methods were employed to draw the following conclusions: 1) the area of cultivated land in Fujian Province decreased by 7.12% from 1990 to 2015. In terms of the spatial distribution of net change rate, the number of districts in which cultivated land was at a net loss state in Fujian Province increased during the period of 1990-2015, while the intensity of loss decreased significantly. In addition, from 1990 to 2015, the dynamic degree of cultivated land transfer had been a significant decline, which was reflected in the improvement of the stability of cultivated land resources in Fujian Province. Furthermore, high spots of dynamic degree of cultivated land transfer were distributed in the east, and low spots were distributed in the west. 2) The distribution direction of the occupied and supplemented cultivated land change patches in Fujian Province remained the same during the period of 1990-2015. The occupied cultivated land patches were mainly concentrated in the eastern coastal areas, while the position of the supplementary cultivated land patches changed significantly, gradually shifting to the northeast and southeast regions of Fujian Province. During the period of 1990-2015, the number of occupied and supplemented cultivated land patches in Fujian Province became more balanced. The area of supplementary cultivated land patches was smaller than that of occupied cultivated land patches, while the shape of supplementary cultivated land patches was more regular than that of occupied cultivated land patches. 3) The cultivated land resources in Fujian Province showed trends of "elevation rising" "slope rising" "shifting to shady slope" "away from water" and "relatively concentrated", during the period of 1990-2015. In summary, the protection of cultivated land in Fujian Province still needs to be strengthened. First of all, the government should further restrict the loss of cultivated land in the eastern part of Fujian Province. Secondly, if conditions permit, the area of each supplementary cultivated land should be increased as much as possible. Finally, the government should take effective measures to protect high-quality cultivated land with lower elevation, lower slope, and better light and irrigation conditions.

Hyperspectral estimation of saline soil electrical conductivity based on fractional derivative

TIAN Anhong, ZHAO Junsan, ZHANG Shunji, FU Chengbiao, XIONG Heigang

2020, 28(4): 599-607. doi: 10.13930/j.cnki.cjea.190865

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Abstract:
The integer-order differential (first-order or second-order) preprocessing method is often used in traditional electrical conductivity inversion models, but it ignores the hyperspectral reflectance information at the fractional-order differential. In this paper, a hyperspectral method based on fractional differential to estimate the electrical conductivity of saline soil was proposed. The salinized soil in Changji, Xinjiang was used as the research subject. The surface soil samples of 0-20 cm were collected in May 2017, the field hyperspectral of the saline soil was measured by a FieldSpec^®3 Hi-Res spectrometer, and physical and chemical parameters of soil electrical conductivity were tested in the laboratory. Next, the Grünwald-Letnikov fractional derivative calculation between 0.0-order and 2.0-order was programmed in MATLAB 2019a software (order interval is 0.1). Then, the variation law of the correlation coefficient curves between soil hyperspectral and electrical conductivity under 21 kinds of differentials was analyzed. When the maximum correlation coefficient of each fractional derivative was greater than 0.5, the corresponding wavelength was selected as the sensitive wavelength. Finally, the stepwise multiple linear regression model was used to predict the electrical conductivity. The results showed that the fractional derivative preprocessing method could display the variation details of the correlation coefficient curve under different fractional orders, and more peaks and troughs appeared in the whole band. The eight sensitive wavelengths of electrical conductivity were 400 nm, 418 nm, 567 nm, 1 667 nm, 2 132 nm, 2 193 nm, 2 257 nm, and 2 258 nm. The best model for estimating electrical conductivity was located at the 0.5^th-order. The relative percent difference (RPD) value of the verification set was 1.99, the determination coefficient (R²) was 0.81, and the root mean square error (RMSE) was 1.08. This model had the ability to estimate the electrical conductivity because the RPD value was greater than 1.8. This study explored the difference in electrical conductivity estimates under different fractional derivatives and provided a new method for electrical conductivity estimation, which could be of considerable value for research into improvement of saline soils in the arid regions of Xinjiang.

Nitrogen losses and Cu, Pb changes of paddy field affected by adding duckweed under biogas slurry application

SONG Die, HE Zhonghu, DONG Yonghua, DAI Wei, YANG Xiaolei, CAO Linkui, SHA Zhimin

2020, 28(4): 608-618. doi: 10.13930/j.cnki.cjea.190825

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Abstract:
Nutrient loss and heavy metal accumulation are major problems in the utilization of biogas slurry as a resource. Duckweed, which can absorb nitrogen and phosphorus and take up heavy metals, can be used to control environmental pollution in biogas slurry irrigation. To study the effects of duckweed on nitrogen loss and reduction in Cu and Pb heavy metals in a paddy field fertilized with biogas slurry, a field experiment was conducted in Jinshan District, Shanghai, China. The experiment comprised four treatments: (1) chemical fertilization (CF); (2) chemical fertilization + duckweed (CF + D); (3) biogas slurry (BS); (4) biogas slurry + duckweed (BS + D). The changes in nitrogen concentration in paddy field surface water, nitrogen-loss load in runoff water, and the levels of Cu and Pb in soil, rice grain and straw under different treatments were measured and compared. The results showed that the trends in the variation of total nitrogen (TN) and ammonia nitrogen (NH₄⁺-N) concentrations in the surface water of different treatments were the same. The concentrations reached peak values on the first day after each fertilization, and then decreased day by day. On the fifth day after fertilization, they dropped below 30% of the peak. The peak value of nitrate nitrogen (NO₃^--N) concentration lagged by 3-7 days. The addition of duckweed when biogas slurry application significantly reduced TN content in surface water, and the total TN loss load of BS+D treatment was 3.67 kg·hm^-2. Compared with the CF treatment, the TN loss load with BS+D treatment was lower by 37.2%. The Cu and Pb contents of the soil treated with BS+D was 22.65 mg·kg^-1 and 49.05 mg·kg^-1, which was not significantly different to levels in the other treatments, but the available Cu and Pb levels in the soil treated with BS+D treatment were significantly higher than those treated with CF, by 18.6% and 17.5%, respectively. There was no significant difference in the contents of Cu and Pb in rice straw and grain, but the grain content of Cu in BS+D treatment decreased by 41.1% compared with BS treatment. In summary, adding duckweed to field applied with biogas slurry can reduce nitrogen loss in paddy fields, and can control the increase of Cu and Pb in soil and rice grain and straw to a certain extent. It can be an effective means to control water and soil pollution under biogas slurry irrigation mode.

2020 Vol. 28, No. 4