中国生态农业学报(中英文)

Regionalization of the matching degree of water, soil, and heat resources in Central Asia based on ecosystem services using PSO-SOFM neural network

YAN Xue, HUANG Farong, LI Qian, ZHOU Hongfei, LI Lanhai

2021, 29(2): 241-255. doi: 10.13930/j.cnki.cjea.200412

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Abstract:
Regionalization of the matching degree of water, soil, and heat resources is of great significance for regional agricultural planning. The long-term unreasonable management of water, soil, and heat resources has caused regional resource shortages and environmental problems in Central Asia, which seriously threatens agricultural production in this region. However, few studies have investigated the regionalization patterns of the matching degree of water, soil, and heat resources in Central Asia. In this study, the spatio-temporal patterns of four ecosystem services, including vegetation carbon sequestration, soil conservation, water supply and conservation, and biodiversity conservation, were quantified by using remote sensing data. Combined with the Particle Swarm Optimization (PSO) and Self-Organizing Feature Map (SOFM) neural network, the regionalization of the matching degree of water, soil, and heat resources was examined. The relationships among various eco-environmental factors of different matching degree zones were assessed using Spearman's rank correlation analysis. The effects of temperature and precipitation on ecosystem services in Central Asia were analyzed by using partial correlation analysis. The results showed that the ecosystem services were generally high in the southeast while low in the northwest, decreasing from the mountains to the oases and the deserts. The four ecosystem services showed different degrees of change from 2000 to 2015 in Central Asia. Areas with significantly reduced vegetation carbon sequestration and soil conservation accounted for 84.81% and 84.82% of Central Asia, respectively, and areas with significantly reduced water supply and conservation and biodiversity conservation accounted for 69.48% and 19.8% of Central Asia, respectively. However, the ecosystem services from water supply and conservation and biodiversity conservation increased in some areas. The PSO-SOFM neural network model performed well in the regionalization of the matching degree of water, soil, and heat resources in Central Asia. The matching degree of water, soil, and heat resources in Central Asia can be divided into five categories with 21 sub-categories according to the patterns of ecosystem services. At the spatial scale, there were significant differences in the ecosystem services among different matching degree zones. Precipitation was the most important limiting factor affecting the ecosystem service values and matching degree, whereas the effects of temperature and soil properties were less important. At the temporal scale, the areas with a significant positive correlation between precipitation and ecosystem services were larger. The significant effect of temperature on ecosystem service values was mainly concentrated in ecological sensitive zone of northern Kazakh steppe and semi-desert, ecological fragile zone of desert in Central Asia, ecological sensitive zone of central semi-desert in Central Asia and ecological sensitive zone of semi-desert in Badghyz and Karabil. In other regions, temperature and precipitation were not the main factors affecting ecosystem services. Changes in the ecosystem service values may be related to land use types. Combined with the ecological and geographical conditions of different matching degree zones, this study provides useful information for the development and utilization of water and land resources, agriculture and animal husbandry development, and environmental protection in Central Asia.

Analysis of agricultural water resource vulnerability and its variable characteristics in Central Asia

YU Shui, HUANG Farong, LI Lanhai

2021, 29(2): 256-268. doi: 10.13930/j.cnki.cjea.200433

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Abstract:
Agricultural water utilization is a key link between natural environment and socio-economic system. It is important to investigate the vulnerability of agricultural water resources to secure water resource sustainability and mitigate flood and drought risks. To investigate the variable characteristics of agricultural water resource vulnerability in Central Asia, an index system was established with 18 indicators from three components—exposure, sensitivity, and adaptation—according to the scheme of vulnerability assessment. Based on the data on socio-economic factors, topography, land cover, and soil from 1992 to 2017, agricultural water resource vulnerability in Central Asia was calculated via the Equal-Weights and Principal Component Analysis (PCA) method. The results showed that the vulnerability of agricultural water resources in Central Asia was high in the south and low in the north. Among the five countries in Central Asia, the highest agricultural water resource vulnerability occurred in Turkmenistan, followed by Uzbekistan, Tajikistan, and Kyrgyzstan; the lowest agricultural water resource vulnerability occurred in Kazakhstan. These spatial patterns varied little over the past 26 years. Agricultural water resource vulnerability in Central Asia showed an increasing-decreasing-stabilizing pattern during the study period. Regional changes in the agricultural water resource vulnerability were dominated by a steady state during the entire study period. The variations in agricultural water resource vulnerability differed spatially over time, increasing in the west of Kyrgyzstan and Turkmenistan, declining in Uzbekistan, Tajikistan, and the Aral Sea region of Kazakhstan, and with little variation in the rest of the study area. Sensitivity analysis indicated that the agricultural water resource vulnerability varied in different areas of Central Asia. Temporal variations in the agricultural water resource vulnerability in the north were negatively related to the farmland irrigation quota and irrigation index but positively related to other indices. The sensitivities of indices were more complex in the south. Correlation analysis demonstrated that the forest coverage rate, proportion of agricultural water, farmland irrigation quota, water stress index, irrigation index, and agricultural water productivity ratio more strongly affected the spatial differences in agricultural water resource vulnerability than the other factors. Therefore, intensive agriculture practices, cropping structure adjustments, application of drought-tolerant crop varieties, and water-saving irrigation technology and measures should be implemented to reduce the vulnerability of agricultural water resources in Central Asia. This study analyzed the spatial and temporal variations in agricultural water resource vulnerability in Central Asia, explored the impact factors of these variations, and proposed recommendations to reduce the vulnerability of agricultural water resources. This work can inform agricultural water resources planning and management, adjustments of the agricultural production structure, and help to secure sustainable agricultural development in Central Asia.

Characteristics of crop water footprint changes in five Central Asian countries from 1992 to 2017

MA Chi, YANG Zhongwen, SONG Jinxi, HAO Cailian, XIA Rui, JIA Ruining, CHEN Yan, ZHANG Xiaojiao

2021, 29(2): 269-279. doi: 10.13930/j.cnki.cjea.200404

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Abstract:
This study analyzed the spatio-temporal characteristic of crop water footprint in five Central Asian countries from 1992 to 2017 using the crop water footprint as the assessment method, in order to reveal the structure of crop water footprint, and clarify the contribution of main crops that caused the change of water footprint in the five Central Asian countries. The results showed variation in the crop water footprints of these five Central Asian countries. From 1992 to 2017, changes in green water footprints were similar to those in their respective planting areas, and the overall trend was decreasing (-9.7×10⁹ m³). The overall blue water footprint also tended to decrease (-5.6×10⁹ m³). There were significant differences in the spatial distribution of crop water footprints in the five Central Asian countries. Kazakhstan had the highest green water footprint (average 49.6×10⁹ m³), much higher than the other four countries (average 3.6×10⁹ m³). Uzbekistan had the highest blue water footprint (average 15.3×10⁹ m³). From 1992 to 2017, the countries with the largest growth rates in the green and blue water footprints of crops were Turkmenistan (87.6%) and Kyrgyzstan (32.3%). The countries with the largest reduction rates in the green and blue water footprints were Kazakhstan (-20.7%) and Uzbekistan (-24.2%). The green water footprint of crops in Central Asia was mainly from cereals, and the blue water footprint was mainly from cereals and oil crops. The water footprint structure of cereals was mainly composed of wheat, rice, and corn, and the water footprint structure of oil crops was mainly composed of cotton. Kazakhstan had the largest reduction in green water footprint and accounted for most of crops with reduced green water footprint, barley (51.6%) and wheat (28.2%). Uzbekistan had the largest reduction in blue water footprint, with cotton (61.9%) contributing the most. The aim of this study was to examine the impact of crop yield on the virtual water content of crops and expand the virtual water content of dozens of crops in these five Central Asian countries. This avoids the shortcomings of inaccurate calculations of the long-term water footprint series in previous studies where the virtual water content remains unchanged. Research on the water footprint of crops in Central Asia revealed that the water footprint was declining, and the main crops causing the water footprint declines had been identified. These results can be used to optimize crop planting and water conservation in Central Asia.

Variations in and predictions of irrigation water requirements of cotton and winter wheat in Central Asia

TIAN Jing, SU Chenfang

2021, 29(2): 280-289. doi: 10.13930/j.cnki.cjea.200407

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Abstract:
Agricultural irrigation consumes most of the fresh water in Central Asia (CA). Therefore, changes in irrigation water use have direct effects on water resources, water management, and water resource allocation. The crop water requirement (CWR) is a direct indicator of agricultural irrigation; the CWR of cotton and winter wheat (the two main crops of CA) was investigated in this study. Based on the CWR method proposed by the Food and Agriculture Organization (FAO), the CWR and total irrigation water of cotton and winter wheat in irrigated croplands in CA were calculated from 2006 to 2015. Changes in the irrigation cropland area and cotton and winter wheat CWR from 2006 to 2015 were also analyzed. To assess the near-future status of agricultural water resources in CA, the irrigated cropland area in 2030 was predicted via the CA_Markov method, and the CWR of the two crops in 2030 was explored. Land cover data from the European Space Agency Climate Change Initiative (ESA CCI) was used to identify the irrigation cropland. Digital Elevation Model (DEM) data from the Shuttle Radar Topography Mission (SRTM), population density data from the Socioeconomic Data and Applications Center, and river vector data from Natural Earth were used to predict the irrigated cropland area in 2030. The results showed that irrigated cropland in CA increased by 492 km² from 2006 to 2015, with increases in Kazakhstan, Kyrgyzstan, and Turkmenistan, and decreases in Tajikistan and Uzbekistan. The CWR of cotton and winter wheat tended to increase in most areas. The CWR of cotton increased rapidly from 2006 to 2015 (2.5-4.3 mm·a^-1) in Turkmenistan and eastern Kazakhstan but decreased in Kyrgyzstan. For winter wheat, the largest CWR increase (10 mm·a^-1) was in Turkmenistan, and no changes were observed in the other four CA countries. In 2030, the irrigated cropland in Turkmenistan was predicted to increase by 30.5% compared with 2015, and Turkmenistan is the only country to increase irrigated croplands in the near future. This will lead to a notable increase in the CWR of cotton and winter wheat. The results showed that there will be an increase of 28 km³ for the total irrigation water of cotton and 17 km³ for winter wheat in Turkmenistan in 2030. The other four countries were predicted to have decreased irrigation cropland compared with 2015, with decreases of 7.4%, 5.8%, 3.4%, and 0.9% for Uzbekistan, Tajikistan, Kazakhstan, and Kyrgyzstan, respectively. Although Uzbekistan is predicted to decrease irrigation cropland in 2030, the increase in winter wheat CWR will increase the total irrigation water by 10-14 km³. Therefore, Uzbekistan and Turkmenistan will face severe shortages in irrigation water resources in the near future.

Changes in water requirements for production and virtual water trade of cotton in Central Asia

XIN Ping, HAN Shumin, YANG Yonghui, ZHOU Xinyao, ZHOU Hongfei

2021, 29(2): 290-298. doi: 10.13930/j.cnki.cjea.200492

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Abstract:
Cotton is an important agricultural export item in Central Asia. Given the increasing shortage of water resources, it is necessary to evaluate the water requirements for cotton production and the virtual water trade of cotton for sustainable water resource management. In this study, the water requirements and specific water demands of cotton in the five countries of Central Asia were estimated from the long-term meteorological data from 175 stations using the ArcGIS spatial interpolation and crop coefficient method along with the distribution of cotton cultivation. Parameters for the specific water demands and the production and trade data from the Food and Agriculture Organization (FAO) as well as the amounts, change trends, and water requirements for production and virtual water trade of cotton in 1992-2017 were analyzed. Finally, the impact of virtual water trade on the water resources in Central Asia was evaluated. The results showed that: 1) the cotton water requirement was 761.0-1033.9 mm, the specific water demand was 2834.4-5732.1 m³·t^-1, and the value of Uzbekistan cotton was 4263.8 m³·t^-1, which was dominant in the calculations of water requirement for cotton production and the amount of exported virtual water of cotton. The parameters for the specific water demand were reliable for the spatial-weighted calculation processes. 2) From 1992 to 2017, the water requirement for cotton production and the net exported virtual water amount of cotton trended downward due to decreases in the total production and export amounts of cotton. The decrease in total cotton production resulted from a decline in harvested area, and low yields in some Central Asian areas directly led to decreased water demand for production (from > 30 billion m³ to > 20 billion m³). An increase in cotton consumption was the main reason for declining virtual water exports in Central Asia; the net exported virtual water volume dropped from 20 billion m³ to 5 billion m³. From 1992 to 2017, the annual water requirement for production, net exported virtual water, and the ratio of net exported amount to production amount of cotton were 23.72 billion m³, 14.74 billion m³, and 62.1%, respectively. At present, approximately one-third of the water requirement for cotton production is exported via virtual water trade despite falling cotton exports. 3) In Central Asia, 6.5% of the renewable water resources (not including water loss in farmlands and conveyance loss in irrigation events) was exported in the form of cotton exports in 1992-2017. In Uzbekistan and Turkmenistan, 18.4% and 12.7% of the renewable water resources were exported, respectively, which negatively impacted the regional water resources and induced water shortages.

Spatial variation in major water quality types and its relationships with land cover in the middle and lower reaches of Aral Sea Basin

ZHANG Yongyong, TAN Xiang, LI Fadong, RUAN Hongwei, YU Jingjie, GAO Yang, ZHAI Xiaoyan

2021, 29(2): 299-311. doi: 10.13930/j.cnki.cjea.200429

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Water resources and environmental issues in the Aral Sea Basin of Central Asia are global concerns. In this study, the water quality variables (i.e., basic physical and chemical attributes, different forms of nutrients, other elements, cations, and anions) from 21 sampling sites in the middle and lower reaches of Aral Sea Basin were measured in 2019 to explore water environmental variations and their causes. Spatial variation in 20 water quality variables was investigated, and the representative water quality types, spatial differences, and their causes were identified via multivariate analysis methods (i.e., principal component analysis and cluster analysis). Furthermore, the effects of land cover on the spatial variation in water quality types were explored. The results showed that: 1) the values of electronic conductivity (EC) and total dissolved solids (TDS) increased from the middle to the lower reaches, and the highest values were in the Aral Sea. This indicates that the concentrations of anions and cations increased from the middle to the lower reaches. For the nutrient variables, high phosphorous concentrations were in the middle reaches of Amu Darya, and high nitrate-nitrogen concentrations were in the Syr Darya. For the different forms of carbon, the highest concentrations were in the Amu Darya, particularly in the delta area of lower reaches. 2) The water quality at all sampling sites can be divided into three water quality types according to the similarity classification of water quality variables. The first type had low concentrations for most water quality variables, which were distributed in the middle reaches of Syr Darya and the Aral Sea. The second type had high concentrations of different forms of nitrogen and phosphorus, which were distributed in the middle and lower reaches of Amu Darya. The third type had high concentrations of carbon, anions, and cations, which were distributed in the Aral Sea. The water quality concentrations of the first and second types were mainly due to rock weathering processes on bare land, and the anions and cations were mainly derived from the weathering of silicates and evaporites. The concentrations of the third type were mainly due to the evaporation and crystallization processes of a dry climate, and the anions and cations were mainly derived from the weathering of silicates and evaporites, which may also be affected by carbonate weathering. 3) With an increase in the buffer zone radius for each sampling point (0.5 km to 10 km), the significant land cover changed from bare land to water, shrubland, grassland, mixed farmland, and vegetation for the first water quality type; the most significant land cover was water. There were no significant relationships between the second water quality type and land cover. For the third water quality type, the significant land cover changed from water to water, mixed farmland, and vegetation—the most significant land cover was water. Therefore, spatial variation in the water quality variables was mainly affected by the local climate conditions (i.e., climatic drought and intensive evapotranspiration) and the mainland cover types (i.e., bare land, water, farmland, grassland, and urban). To improve the water environmental conditions in the middle and lower reaches of Aral Sea Basin, stream flow should be increased to recharge the Aral Sea and weaken the evaporation and crystallization processes in the lower reaches of Aral Sea. Vegetation restoration and a return of farmland to forest and grassland should also be strengthened in the riparian zone, particularly in the middle and lower reaches of Amu Darya and Syr Darya and the Aral Sea.

Spatial-temporal variations in drought conditions and their climatic oscillations in Central Asia from 1990 to 2019

PENG Yu, LI Fadong, XU Ning, KULMATOV Rashid, GAO Kechang, WANG Guoqin, ZHANG Yongyong, QIAO Yunfeng, LI Yanhong, YANG Han, HAO Shuai, LI Qi, KHASANOV Sayidjakhon

2021, 29(2): 312-324. doi: 10.13930/j.cnki.cjea.200927

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The rapid shrinking of the Aral Sea has prompted the scientific community to focus on Central Asian drought. To clarify the moisture conditions of Central Asia over the past 30 years and to investigate the climate drivers of change, in this study, we used the Palmer Drought Index (PDSI) to assess the spatial and temporal characteristics of drought in the five Central Asian countries (Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan and Kyrgyzstan) from 1990 to 2019. PDSI was combined with the cross-wavelet transformation to reveal the driving influence of climate oscillations on drought conditions. The results showed that the drought indicators displayed a cyclical alternation with an increasing variability, a weakening of the dry summer/autumn and wet winter/spring seasonal drought characteristics, and the possibility of a new dry period after 2018. The general drought intensity gradually decreased from the southwest to the northeast and progressively increased from the southeast mountainous area to the central and western plains. The drought center shifted from the southwestern hinterland to the northwestern regions of Kazakhstan. The Pamir and West Tianshan Mountains showed a fluctuating and increasing drought trend. The Tibetan Plateau Index (TPI) showed an apparent driving effect on PDSI changes, with high cyclical intensity throughout the 1990-2019 period (1-3 years [1995-2000], 4-5 years [2010-2015], 8-10 years [2010-2015], and 8-10 years [2016-2019]) with three distinct interannual-scale oscillatory cycles. Overall, drought conditions tended to improve, with increased drought variability and significant spatial variability; the TPI is the atmospheric oscillator driving PDSI variability.

The land-use and land-cover change characteristics and driving forces of cultivated land in Central Asian countries from 1992 to 2015

HAN Haiqing, WANG Xuhong, NIU Linzhi, LIANG Xiujuan, JIANG Xiaohui, TAN Zhuting

2021, 29(2): 325-339. doi: 10.13930/j.cnki.cjea.200406

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Five countries located in the center of Eurasian continent (i.e., Central Asian countries) are important nodes along the Belt and Road Initiative, a global development strategy launched by China. The Central Asian countries' land-use and land-cover change (LUCC) characteristics from 1992 to 2015 were analyzed. The European Space Agency Climate Change Initiative global land cover data were used to determine the land-use degree, dynamic attitude, and transfer matrix by geographic information system (GIS) spatial analysis, and the driving force of cultivated land was explored using geographical detectors. The results showed that in the Central Asian countries, the area of cultivated and urban lands continuously increased, and that of forests, grasslands, and water areas decreased. Forests (7.88×10⁴ km²) and grasslands (5.27×10⁴ km²) were converted into cultivated land, and cultivated land (0.50×10⁴ km²) was converted into urban areas. The transfer between land-use types was country-specific (e.g., cultivated land was created from forests and grasslands in Kazakhstan, Kyrgyzstan, and Tajikistan and from unused land in Turkmenistan; cultivated land became urban areas in Uzbekistan) and closely associated with human activities. Urban land had the highest growth rate in all countries, followed by cultivated land (except in Uzbekistan), and cultivated land was the most variable land-use type. The land-use degree slowly increased (comprehensive index of land use degree was 193.34 in 1992, 197.41 in 2015), indicating that land-use was in the development stage. Land-use types ranked as follows (by land-use degree): cultivated lands > forests > grasslands > unused lands > water areas > urban lands. The driving forces for cultivated land changes were analyzed using geographical detectors and showed that the annual average precipitation had a significant effect. Social and agricultural factors also played a decisive role in the short term. The total population and rural population had the greatest influence on cultivated land expansion, followed by the per unit area grain yield. Interactive detection showed that interactions between factors were mutually reinforcing. In particular, super-positioning rural population and crop production index explained cultivated land expansion. The primary factors affecting cultivated land expansion were population growth and agricultural production improvement. These results are useful for planning sustainable land use in Central Asian countries.

Influence of cybernetic theory, information theory, and system's theory on the development of agroecology in China

LUO Shiming

2021, 29(2): 340-344. doi: 10.13930/j.cnki.cjea.200693

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Cybernetic theory, information theory and system's theory play an unique role on the formation of the disciplinary structure of agroecology during the early stage of agroecology development in China. In the discipline of agroecology in China, attentions were not only paid on energy and material flows, such as the structure of species, population, community, ecosystem and landscape, but also on information flow including natural information flow and artificial information flow, and on capital flow, including the value chain and its monetary representation, that is capital flow. Agroecology in China paid attention not only on the energy and material transformation structure of agroecosystem such as producer, consumer and decomposer, but also on the control and regulation of agroecosystem structure including natural control and regulation structure, and artificial control and regulation structure. In artificial control and regulation structure, direct control and indirect control approaches could be identified. Crop cultivation and animal raising actions exerted by the farmers on farm belong to direct control approach, and the market situation, government policy, national legislation, social tradition, education and information transmission which could affect the action of the farmers on farm, belong to indirect control mechanism. This disciplinary structure of agroecology based on cybernetic theory, information theory and system's theory is essential to further exploration of the excellent traditional Chinese agricultural practices, to stimulate the thought on basic and applied agroecology research, and to open up new approach for the ecological transformation of agriculture in this information era.

Advances in plant nitrous oxide (N₂O) emissions

HU Huixian, YUAN Dan, ZENG Jiarui, YAO Jinzhi, HE Xiaodong, QIN Shuping, HU Chunsheng, ZHOU Shungui

2021, 29(2): 345-354. doi: 10.13930/j.cnki.cjea.200444

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Nitrous oxide (N₂O) significantly affects atmospheric environment quality and global climate change. N₂O emissions intensify greenhouse effects and lead to terrestrial reactive nitrogen loss and stratospheric ozone consumption. Soil is considered the primary source of N₂O emissions from terrestrial ecosystems. However, recent studies indicate that plants also contribute to terrestrial ecosystem N₂O emissions. Plant N₂O emissions have been increasingly studied over the last decade, but a review of the N₂O plant emission pathway and regulatory mechanisms is lacking. This paper summarized the traditionally recognized N₂O sources and sinks, and proposed that terrestrial plants may be another unrecognized N₂O source. Two potential plant N₂O emission pathways were analyzed: 1) soil microorganisms produce N₂O which is then emitted by plants or 2) plants produce N₂O via metabolism or the action of endophytes. Subsequently, key factors were analyzed (e.g., nutrients, light, temperature, plant organs, and growth stage) to determine the effects on and mechanisms of N₂O plant emissions. This study suggests that specific plant N₂O production pathways and their contributions to global N₂O emissions should be explored, with a focus on the physiological and biochemical processes of plants and the role of the symbiotic microorganisms in N₂O production.

Effects of climate change on phenophases and annual climate resources distribution and utilization of major food crops under a double-cropping system in Anhui Province

RUAN Xinmin, CHEN Xi, YUE Wei, ZHAN Xinchun, CONG Xihan, DU Hongyang, SHI Fuzhi, LUO Zhixiang

2021, 29(2): 355-365. doi: 10.13930/j.cnki.cjea.200459

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To examine the effects of climate change on the phenophases and annual climate resources distribution and utilization of major food crops under a double-cropping system in Anhui Province, this study analyzed variations in the phenophases of different cropping systems in different regions and the effects of climate change on distribution and utilization of accumulated temperature, radiation, and precipitation. The analyses included linear fitting, correlation analysis, and regression analysis and incorporated data of the daily average temperature, daily sunshine hours, and daily precipitation from 1992 to 2013 of twelve meteorological stations in the Jianghuai area. The results showed that the sowing date of winter wheat was significantly advanced (P < 0.05) by 3.03 days (d) per decade, on average, under the double-cropping system of winter wheat-soybean in the area along Huaihe River from 1992 to 2013. Changes in the maturity stage of winter wheat were not significant, but the average increase in the whole growth period was 3.54 d per decade. The soybean sowing date and flowering date were significantly delayed (P < 0.05) by 3.06 and 0.86 d per decade, respectively, and the average decrease in the whole growth period was 3.65 d per decade. For the double-cropping system of winter wheat-single rice in the Jianghuai region, the sowing date, heading date, and maturation date of rice were significantly advanced (P < 0.05) by 5.12, 3.87, and 2.92 d per decade, respectively; and the whole growth period increased by 2.20 d per decade Wheat showed the same trends as rice, though non-significant, and the whole growth period was shortened by 0.8 d per decade. For the double cropping rice, the change in phenophases for early rice was non-significant, and the whole growth period was shortened by 0.6 d per decade, on average. The sowing date of late rice was delayed by 1.14 d per decade, on average, whereas the heading date and maturation date were advanced by 0.71 and 6.85 d per decade, respectively. The advance of the maturation date was extremely significant (P < 0.01). The whole growth period of late rice was shortened by 5.17 d per decade. The accumulative temperature increased for winter wheat in Huaibei, single rice in Jianghuai, and double rice along the Yangtze River but decreased for soybean and winter wheat in Jianghuai. The radiation of winter wheat, early rice, and late rice increased, whereas that of soybean and single rice decreased. The precipitation of the first-season crops decreased, but that of the second-season crops increased. The climatic productivity of winter wheat-single rice planting patterns was the highest of all cropping systems. Linear regression analysis showed that the accumulative temperature and radiation were significantly positively correlated with the yield of double-cropping rice and winter wheat in Huaibei (P < 0.05), and radiation and temperature were the main limiting factors for further improvements to its production. Excessive temperature and precipitation of single-season rice in the Jianghuai region also limited yield improvements. Climate change has affected the phenophases of crops in double-cropping systems and influenced the allocation and utilization efficiency of climate resources. The adverse effects of climate change on crops can be offset by improving the varieties, changing the sowing dates, and enhancing stress tolerance.

Spatial distribution characteristics and influencing factors of star-level rural tourism areas in Jiangsu Province

SONG Juyu, JIANG Weibing, HE Lan

2021, 29(2): 366-378. doi: 10.13930/j.cnki.cjea.200269

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By studying the spatial distribution patterns and influencing factors of star-rated rural tourism areas in Jiangsu Province, China, we aimed to provide a reference for the development of rural tourism. Seven hundred and twenty-six three-star and above rural tourist areas in Jiangsu Province were selected the adjacent index, geographic concentration index, density of nuclear analysis, buffer analysis, and unbalanced indices (e.g., ArcGIS spatial analysis and SPSS correlation analysis) were used to analyzed the specific types, spatial distribution patterns of and influencing factors of Jiangsu star-level rural tourist areas with the star-level of tourism resources as classficaiton standard. The results showed that 1) the star-rated rural tourism areas in Jiangsu Province are divided into three categories: agricultural garden, village, and a combined agricultural garden and village. 2) Five-star rural tourism areas were uniformly distributed, but other star-rated rural tourism areas were concentrated, had a high degree of centralization, and were primarily distributed in southern and middle Jiangsu. 3) The spatial distribution of star-rated rural tourism areas in Jiangsu Province is slightly unbalanced, forming high-density and sub-high-density clustering areas in southern and middle Jiangsu, but northern Jiangsu has primarily low-density clustering areas. 4) The star-rated rural tourism areas are mainly distributed within 20-40 km of the suburban area. The conclusion is that the economic level, tourism resources, tourism policy orientation, and traffic conditions are the important factors affecting the spatial distribution of each star-rated rural tourism area in Jiangsu Province. In this regard, the development of rural tourism areas in Jiangsu Province is discussed: 1) promoting regional coordinated development, especially in the middle and north of Jiangsu, 2) strengthening the integration of cluster development and building a rural tourism cluster, and 3) focus on upgrading, developing, and promoting low-star rural tourism areas to high-star areas.

Effect of rice-fish-chicken ridge cultivation on stem lodging resistance, panicle traits, and yield of rice

LIANG Yugang, CHEN Yisha, CHEN Lu, MA Weiwei, MENG Xiangjie, HUANG Huang, YU Zhengjun

2021, 29(2): 379-388. doi: 10.13930/j.cnki.cjea.200438

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Based on previous studies of ridge cultivation, rice-fish co-culture, and rice-chicken co-culture, we proposed an integrated technology of ridge cultivation of rice combined with fish and chicken co-culture (RFC), and observed its' obvious yield and economic benefits. The objective of this study was to determine the effects of RFC on stem lodging resistance, panicle traits, and grain yield in rice. Field experiments were conducted in 2018 and 2019 to compare the stem lodging resistance characteristics, panicle traits, and rice yield when grown under conventional ridge cultivation (CK), ridge cultivation of rice-fish co-culture (RF), ridge cultivation of rice-chicken co-culture (RC), and RFC. The results showed that the height, fresh weight, gravity center height, and internode length of rice plants differed among the treatments in both years, but the differences were not significant. RFC and RC had higher internode outer diameters and wall thicknesses, panicle lengths, and panicle fresh weights than CK, but the differences were not significant. RFC and RC produced similar rice yields as CK. RF had a lower internode outer diameter and wall thickness, panicle length, and panicle fresh weight than CK, but the differences were not significant except for the panicle fresh weight in 2019 (P < 0.05). RF produced a significantly higher grain yield than CK in both years (P < 0.05), with an average increase of 29.98%. RFC and RC had higher average stem-breaking resistances than CK by 19.69% and 8.10% in 2018 and 2019, respectively. In particular, the difference in stem-breaking resistance between RFC and CK was significant for the fourth and fifth internodes (P < 0.05). RF had a smaller stem cross-section modulus and lower stem-breaking resistance than CK, but the differences were not significant. RFC and RC had lower average maximum bending stress by 17.85% and 15.08%, respectively, and a lower average lodging index by 4.35% and 4.26%, respectively, than CK in 2018 and 2019, respectively, but the differences were not significant. RF had a higher average internode lodging index than CK by 11.47%, and the differences were significant for the third internode in 2018 and the second to the fifth internodes in 2019. In conclusion, RFC and RC increased the panicle length and panicle fresh weight of rice plants, stabilized the rice yield, increased the stem internode diameter and wall thickness, enhanced the stem-breaking resistance and cross-section modulus, and reduced the stem maximum bending stress and lodging index. Our study suggests that RFC and RC are preferable for developing strong stems and improving rice lodging resistance.

Effects of reducing water and nitrogen supplies in rotated wheat with previous plastic mulched maize

GUO Yao, CHEN Guiping, YIN Wen, ZHAO Cai, YU Aizhong, FAN Zhilong, HU Falong, FAN Hong, CHAI Qiang

2021, 29(2): 389-399. doi: 10.13930/j.cnki.cjea.200451

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Abstract:
To combat low crop productivity in long-term continuous cropping systems, it is necessary to study the effects of no-tillage and continued mulched plastic to optimize cultivation and establish cost-saving and benefits-increasing technology in Hexi irrigated areas in Gansu Province. A field experiment was conducted in northwestern irrigated areas in 2016-2017 to evaluate the yield, light energy, irrigation water utilization, and economic benefits of all combinations of two tillage practices, two irrigation levels, and three nitrogen application levels on wheat. The two tillage practices included no-tillage and continued mulched plastic in previous maize (NT) and conventional tillage in previous maize after removing the mulched plastic from soil (CT). The two levels of irrigation included the local conventional irrigation amount, 2400 m³·hm^-2 (high: I2), and the local conventional irrigation amount reduced by 20%, 1920 m³·hm^-2 (low: I1). The three levels of nitrogen application included the local conventional nitrogen amount, 225 kg·hm^-2 (high: N3), the local conventional nitrogen amount reduced by 20%, 180 kg·hm^-2 (medium: N2), and the local conventional nitrogen amount reduced by 40%, 135 kg·hm^-2 (low: N1). The results showed that NT increased the leaf area duration (LAD) of wheat across all growth stages by 21.6% to 26.1%, and the LAD remained high from the wheat filling to the maturity stage, increasing by 41.3% to 45.2% (P < 0.05), compared with CT, and delaying senescence. A 20% reduction in irrigation and N application combined with NT (NTI1N2) resulted in a greater LAD (by 34.8% to 50.7%) from the wheat filling to the maturity stage than CT with conventional high levels of irrigation and nitrogen (CTI2N3). NT increased wheat grain yield, light use efficiency, and irrigation water use efficiency by 10.1% to 10.4%, 5.6% to 12.3%, and 10.1% to 10.3% (P < 0.05) compared with CT, respectively. The grain yield, light use efficiency, and irrigation water use efficiency were significantly increased by 15.2% to 22.0%, 8.1% to 18.5%, and 44.0% to 52.5% with NTI1N2 compared with CTI2N3, respectively. NT integrated with reduced irrigation and nitrogen application reduced the production cost and improved the net return and input-output ratio. The NTI1N2 treatment increased the net return and input-output ratio by 22.9% to 23.9% and 34.8% to 35.1%, respectively. In addition, the benefit per cubic meter of water increased by 53.6% to 68.9% with NTI1N2 compared with CTI2N3 treatment. These results suggest that no-tillage and continued mulched plastic in previous maize with low irrigation (1920 m³·hm^-2) and medium nitrogen (180 kg·hm^-2) can reduce costs and increase the benefits of wheat production in Hexi irrigated areas in Gansu Province.

Lycium barbarum root water uptake characteristics in the Qaidam Basin irrigation

ZHOU Yanqing, GAO Xiaodong, WANG Jiaxin, ZHAO Xining

2021, 29(2): 400-409. doi: 10.13930/j.cnki.cjea.200435

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Abstract:
Lycium barbarum (Chinese wolfberry) helps ecosystems by providing storm protection and sand immobilization, and it is also a cash crop for Qaidam Basin farmers. L. barbarum is a common crop in arid regions, such as the Qaidam Basin, China, but drought and water scarcity have constrained industry development. Identifying crop water-use strategies is important for designing efficient irrigation systems. Seasonal L. barbarum water-use was investigated in 2018 in the Qaidam Basin Huaiten Tula Irrigation Area. Natural oxygen stable isotope tracers were used to measure the oxygen stable isotope composition (δ¹⁸O) of water in the xylem and soil of L. barbarum orchards with three field management practices (conventional flat planting, CK; flat-planting full-film mulching, MF; and ridge-furrow full-film mulching, MR). The soil water contribution to root water uptake was analyzed using the MixSIAR Bayesian mixing practices. The soil water and soil water δ¹⁸O profile distribution showed that all soil layers (shallow: 0-20 cm; middle: 20-60 cm; and deep: 60-100 cm) were potential water sources for L. barbarum. During the sprouting period (starting May 25, 2018), CK and MF plants used primarily shallow soil water, accounting for 45.9% and 37.7% of the total water use, respectively, due to the larger amounts of shallow-layer soil water. MR plants used the same amount of water from each layer. During the blossom and fruiting period (starting July 9, 2018), the soil water content increased in all soil layers. Compared with that in CK plants, the shallow-layer soil water use increased by 13.5% in MF plants and decreased by 11.1% in MR plants. During the fruit ripening period (starting July 30, 2018), water consumption increased. Compared with that in CK plants, shallow-layer soil water use increased in MF (by 11.7%) and MR (by 24.0%) plants. During the defoliation period (starting September 22, 2018), the water content in the shallow-layer soil was lower than that in the other soil layers, and all of the treatment groups used primarily deep-layer soil water. These results showed that shallow-layer soil contributions were positively correlated with water content, indicating that L. barbarum is sensitive to changes in the shallow-layer soil water. There were significant differences in the root water uptake among the three field management practices. Mulching and ridge-furrow treatments increased the soil water content and, compared with that in CK plants, the MF and MR treatments increased the shallow-layer soil water use. The soil water content was higher and the water source was more flexible during the growth period with the MR treatment than with the CK and MF treatments. These results suggest that MR is a better field water management practice for promoting the sustainable and healthy development of L. barbarum orchards.

Sugarcane planting area and growth monitoring based on remote sensing in Guangxi

XIE Xinchang, YANG Yunchuan, TIAN Yi, LIAO Liping, MO Chongxun, WEI Junpei, ZHOU Jinyu

2021, 29(2): 410-422. doi: 10.13930/j.cnki.cjea.200419

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Abstract:
Sugarcane planting in Guangxi has been affected by natural disasters, resulting in decreased yields. The information on spatio-temporal dynamics of the sugarcane planting area and growth can provide a reference for planting structure optimization and facilitate disaster control. This study incorporated 652 optimized band combinations of the LANDSAT 8 Operational Land Imager (OLI), normalized difference vegetation index (NDVI), digital elevation model (DEM), and other auxiliary identification characteristic variables into the random forest classification method to interpret continuously in multi-temporal aspects. Google Earth and high-resolution remote sensing image comparison and correction were used to obtain a high-precision sugarcane planting area distribution in Guangxi from 2014 to 2018. The MODIS-NDVI data was used to build a monitoring model of the growth potential difference for dynamic monitoring of sugarcane stem elongation in Guangxi in the last five years. The results showed that: 1) the interpretation method was effective, the overall classification accuracy of sugarcane planting area in Guangxi was >92%, the Kappa coefficient was >0.8, and the five-year mean area relative error was -10.7%. 2) In 2014-2018, the planting area of sugarcane in Guangxi had rapidly decreased in the early stage and slowly increased in the late stage. The main planting areas were in Chongzuo, Nanning, and Laibin. The whole planting area showed a distribution pattern of local agglomeration and overall fragmentation and dispersion, which was closely related to the underlying environmental elements, such as topography, soil type, and river system distribution. 3) The NDVI difference model reflected the interannual and intra-annual spatio-temporal changes in the elongation trend of sugarcane stems in Guangxi, and the yearly growth trend of sugarcane changes frequently between good, normal, and poor. These results revealed the response mechanism of sugarcane in Guangxi to regional climate change, alternation of drought and flood, and the dynamics of soil and water conservation on the underlying surface. Furthermore, this study provides a scientific foundation for optimizing the regional sugarcane planting structure and evaluating water resource utilization efficiency.

2021 Vol. 29, No. 2