中国生态农业学报(中英文)

A commentary and development perspective on the consecutive monoculture problems of medicinal plants

WU Hongmiao, LIN Wenxiong

2020, 28(6): 775-793. doi: 10.13930/j.cnki.cjea.190760

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Abstract:
The consecutive monoculture problem, also known as replant disease, is a common disorder from modern agricultural practices. It has been reported that more than 70% of medicinal plants, especially those tuberous roots, have been affected. This disease has become a key factor restricting the quality and development of medicinal plants. This study analyzed three common problems with the formation of continuous cropping obstacles in medicinal plants, which includes the acidification of rhizosphere soil induced by root exudates, microbial community structure imbalance in the rhizosphere, and the severity of plant virus disease. The primary factors include:differentiation and evolution of microorganisms mediated by root exudates in rhizosphere soil, allelopathic interactions of soil-borne pathogens, soil acidification induced by rhizosphere bacterial community imbalance, increased rhizosphere soil-borne pathogens, decrease of beneficial microorganisms aggravating soil fungal diseases, and concomitant development of viral diseases. We analyzed the potential advantages of new rhizosphere management strategies on abating continuous cropping obstacles such as soil sterilization, microbial fertilizer application, diverse crop cultivation, and biochar management. This study recommended researchers to focus on rhizosphere ecological processes in continuous cropping obstacles by selecting the soil food web as the starting point, utilizing modern system biology and chemical ecology technology to analyze the interaction and mechanisms among plant-soil-microorganisms mediated by root exudates under continuous monoculture regimes. Therefore, we need to focus on the niche relationship between soil nematodes and viruses during the occurrence and development of continuous cropping obstacles, and elucidate the ecological mechanisms of soil acidification mediated by continuous cropping, as well as the co-evolution mechanism of pathogens responding to root exudates. Furthermore, several strategies can be combined to alleviate the continuous cropping obstacles. Overall, we should consider the economic, social, and ecological benefits to achieve "prevention-oriented" and "comprehensive management".

Effects of potato and maize compound planting on soil allelochemicals and soil bacterial community structure

LIU Xianwen, GUO Huachun

2020, 28(6): 794-802. doi: 10.13930/j.cnki.cjea.190780

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Abstract:
To investigate the effects of potato and maize compound planting on allelochemicals accumulation and bacterial community structure, soil samples from continuous potato cropping, continuous maize cropping, potato and maize intercropping, and potato-maize rotation were collected in the eighth year of the experiment. Allelochemicals extracted from the soil were determined by GC-MS. Then, Illumina Miseq high-throughput sequencing technology was used to sequence the 16Sr DNA V4-V5 regions of soil bacteria to analyze changes in soil bacterial diversity and community structure. The results showed that:1) continuous cropping of maize and potatoes led to the accumulation of allelochemicals, 2) continuous maize cropping caused soil to accumulate more fatty acids such as oleic acid, linoleic acid, eicosanoic acid, and lignoceric acid, and 3) potato continuous cropping produced soil with more accumulated fatty alcohols such as 1-octadecanol and 1-eicosanol. Rotation reduced the accumulation of most allelochemicals, and the number of allelochemicals that were reduced by intercropping was smaller than that by rotation. The soil bacteria community structure changed significantly among different planting patterns. Compared with continuous cropping, intercropping and rotation had higher Ace and Chao indices. At the phylum level, the abundance of Actinobacteria was significantly higher under rotation than under continuous cropping of potato, the abundance of Bacteroides was significantly lower under intercropping than under continuous cropping of maize, and the abundance of Acidobacteria was significantly higher under both potato and maize continuous cropping than under rotation cropping. At the genus level, some beneficial bacteria such as Arthrobacter and Lysobacteria were relatively more abundant in compound planting soils. Through correlation analysis, it was found that the abundances of Pedomicrobium and Pirellula genera were significantly positively correlated with fatty alcohols, and that of Flavobacterium, Lysobacteria, and Microbacteria genera were significantly negatively correlated with fatty acids. Compound planting of potato and maize reduced the accumulation of allelochemicals in the soil, thus inhibiting reduction in soil bacterial abundance, increasing the abundance of beneficial bacteria, and ameliorating the issues associated with continuous cropping.

Effects of interface barrier materials on rice yield, nitrogen use efficiency, and NH₃ volatilization

WANG Mengfan, YU Yingliang, YANG Bei, HOU Pengfu, YANG Linzhang, XUE Lihong, SUN Qingye

2020, 28(6): 803-812. doi: 10.13930/j.cnki.cjea.200049

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Abstract:
NH₃ volatilization emissions cause significant nitrogen losses in rice fields. Effective control of NH₃ volatilization emissions in rice fields is critical to increase rice yield and nitrogen use efficiency. Interface barrier materials are environmental-friendly and low cost, making them suitable as a completely different method of reducing NH₃ volatilization. This study therefore explored the impacts of interface barrier materials on rice yield and nitrogen use efficiency, which may help to achieve rice yields with low costs and reduced environmental pollution. In this study, three interface barrier materials including two surface molecular film materials:polylactic acid (PLA) and lecithin (LEC) materials were formulated as surface molecular film materials and were sprayed evenly on the field after fertilization at the basal, tillering, and earing rice stages. Rice bran was also evenly spread over the field after fertilization on the same day. The rice yield and yield composition, pH and nitrogen concentration in paddy surface water, soil nitrogen content, nitrogen use efficiency and NH₃ volatilization were investigated. The experiment involved five treatments:CK (no N fertilizer), CKU (only urea), RB (rice bran + urea), PLA (polylactic acid + urea), and LEC (lecithin + urea). Fertilizer additions and field management practices remained the same across all treatments. The results showed that the RB, PLA and LEC treatments significantly increased rice yield compared to CKU treatment by 13.0%, 21.0%, and 24.1%, respectively. The nitrogen fertilizer utilization rate of LEC treatment significantly increased by 19.0% compared to the CKU. The RB treatment significantly increased yield by 13.0% compared to CKU, but did not significantly affect the nitrogen utilization rate. The addition of RB and PLA significantly increased the effective spike number in rice, but the LEC treatment produced no significant difference in this variable. The number of grains and the seed setting rate did not differ significantly under the CKU from their interface barrier materials added. The addition of interface barrier materials reduced NH₃ volatilization by 12.3%-19.9% in comparison with CKU, and the PLA treatment significantly reduced NH₃ volatilization by 19.9%, and performed best. It was followed by the LEC treatment with a reduction of 14.3%. The reductions in NH₃ volatilization may be related to the changes in surface water pH, NH₄⁺-N concentration, and soil NH₄⁺-N content caused by the addition of interface barrier materials. Compared to the CKU treatment, all treatments increased the NH₄⁺-N concentration but lowered the pH in surface water, especially during the tillering stage. The soil NH₄⁺-N content was also improved in the PLA treatment. This study shows that the application of interface barrier materials in rice fields is a feasible technical approach to reduce NH₃ volatilization and increase rice yield and nitrogen use efficiency.

Effects of different organic matters on crop yields, soil quality and heavy metal content in irrigated desert soil

YAO Jiaxuan, E Shengzhe, YUAN Jinhua, SHI Xiaojuan, CHE Zongxian

2020, 28(6): 813-825. doi: 10.13930/j.cnki.cjea.190850

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Abstract:
The Hexi Corridor is a famous irrigated agricultural area in Northwest China. However, ecological weakness and heavy long-term chemical fertilizer application has caused problems such as low organic matter content, soil structure degeneration, and low crop yield. Returning organic materials into the field is the main solution to improve soil fertility; however, it also risks causing heavy metal pollution in the soil. This study aimed to explore the effect of soil quality and crop yield response to different types of applied organic materials in the field. The long-term positioning experiment consisted of 8 treatments:no fertilizer (CK) as control, conventional fertilizer (NP), 70% conventional fertilizer respectively, with cow dung (0.7NP+NF), with biogas residue (0.7NP+ZZ), with sewage sludge (0.7NP+WN), with chicken manure (0.7NP+JF), with mushroom substrate residue (0.7NP+JZ), and with pig manure (0.7NP+ZF). We studied how partially replacing chemical fertilizers with different organic materials affected the physical and chemical soil properties, soil organic carbon sequestration efficiency, total nitrogen; the activation coefficients of nitrogen, potassium, and phosphorus, as well as crop yield, and heavy metal content. The results showed that the effect of annual applications of organic materials with 70% chemical fertilizer on yield was equivalent to that of NP of wheat and corn. Compared with NP the soil organic matter, total nitrogen, and available nitrogen content significantly increased under six organic materials treatments; the total phosphorus and available phosphorus content of sludge, chicken manure, and pig manure treatments significantly improved; and the available potassium content, soil phosphorus activity, and soil potassium activity of cow manure, biogas residue, and chicken and pig manure treatments also significantly improved. The organic carbon soil sequestration rate of cow dung, biogas residue, sewage sludge, mushroom substrate residue, and chicken and pig manure treatments were 36.42%-71.61% significantly higher than that of NP. While, the nitrogen soil sequestration rate was 6.47%-49.44% significantly higher than NP, except the mushroom residue treatment. Long-term applications of chicken manure and mushroom substrate residue significantly increased the total copper content by 4.17 mg·kg^-1 and 14.2 mg·kg^-1, respectively; sludge, chicken manure, and mushroom substrate significantly increased total content of zinc by 13.53 mg·kg^-1, 22.60 mg·kg^-1, and 49.73 mg·kg^-1, respectively. In conclusion, applications of 4 500 kg·hm^-2organic materials could replace 30% nitrogen and phosphorus fertilizer without reducing the crop yield. The degree that different organic materials affected soil fertilization was varied; sewage sludge, chicken manure, and pig manure were better than cow manure and biogas residue, while mushroom substrate residue was slight worse. When planting wheat, the annual carrying capacity for copper and zinc from organic materials should be less than 53.01 g·hm^-2 and 221.30 g·hm^-2, respectively. When planting corn, the annual carrying capacity of copper and zinc from organic matter should be lower than 153.40 g·hm^-2 and 347.04 g·hm^-2, respectively, to allow soil environmental quality to be stable without deteriorating.

Effects of straw mulching and sowing methods on water consumption characteristics and yield of potato in arid region of Northwest China

QIAN Yuping, TIAN Huihui, CHENG Hongbo, MA Jiantao, CHAI Yuwei, LI Yawei, CHAI Shouxi

2020, 28(6): 826-834. doi: 10.13930/j.cnki.cjea.190722

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Abstract:
In order to clarify the evapotranspiration, water use efficiency, and yield of potatoes under different straw mulching planting patterns in rainfed agricultural areas of Northwest China, four straw strip mulching patterns (D40:40 cm wide of planting and coverage strips, single row planting; S40:40 cm wide of planting and coverage strips, double-row planting; D50:50 cm wide of planting and coverage strips, single row planting; S50:50 cm wide of planting and coverage strips, double-row planting), plastic film mulching (DM), and traditional flat planting (CK) were set to study the potato evapotranspiration, water-use efficiency, and yield of each treatment. The results showed that under four straw mulching treatments, the average potato yield increased by 34.0% and water-use efficiency increased by 21.5% compared with CK; while they significantly reduced averagely by 31.3% and 25.0%, respectively compared with DM treatment. The yield and water-use efficiency of 40 cm planting structures increased by 4.5% and 6.8%, respectively compared with 50 cm planting structures. The yield of double-row planting was 4.4% higher than that of single row planting, however, water-use efficiency had no significant differences. The amount, intensity, and model coefficient of water consumption during the sowing-budding period decreased under straw strip mulching conditions by 14.5%, 15.2%, and 15.4%, respectively compared with CK, but they increased by 20.9%, 19.0%, and 31.5%, respectively compared with DM. During the budding to tuber bulking period, there were no significant differences in water consumption, water intensity, and water modulus coefficient between the straw mulching treatments and CK; however, compared with DM a significant reduction in water consumption (20.7%), water intensity (22.2%), and water modulus coefficient (13.9%) in the four straw mulching patters. The averages under straw mulching treatments increased during tuber bulking to mature peirod by 51.7% (water consumption), 52.4% (water intensity), and 50.0% (water modulus coefficient), respectively, compared with CK. Under the four straw mulching treatments, the weight per tube and the commodity rate of potato significantly increased by 17.3% and 31.8%, respectively, while the tubers number per plant and the small tuber rate decreased by 7.5% and 17.6%, respectively, compared with CK. It can be seen that cultivation using straw strip mulching can alleviate the water shortage of potato plants in the later stages, by reducing the water consumption before bud growth stage and increasing the water consumption after tuber enlargement stage, extending the duration of plant photosynthesis after tuber enlargement, improving the accumulation of organic matter, and thus improving yield. In the four straw strip mulching patterns, the yield of double row planting treatment was 4.4% higher than that of single row planting, while the water use efficiency had no significant difference between them. In this study, single row planting with the planting band︰mulching band=40 cm︰40 cm, and double row planting with the planting band︰mulching band=50 cm︰50 cm were more suitable straw strip mulching planting mode of potato in the rainfed agricultural areas of Northwest China.

Variety screening of mechanical grain harvest and analysis of influencing factors of summer maize in Sichuan Province

KONG Fanlei, ZHAO Bo, ZHAN Xiaoxu, LI Xiaolong, CHEN Xiang, LIU Qinlin, YUAN Jichao

2020, 28(6): 835-842. doi: 10.13930/j.cnki.cjea.200036

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Abstract:
The variety screening experiment for mechanical grain harvest was carried out in Zhongjing, Sichuan Province from 2017 to 2019 to screen suitable Sichuan summer maize varieties for mechanical grain harvesting and identify the factors influencing the quality of mechanically harvested grain. Factors such as mechanical grain quality, grain moisture content, and yield were analyzed based on 98 tests of 28 maize varieties. Results showed that high broken grain and ear loss rates were the main issues with the mechanical grain harvest of Sichuan summer maize. The average broken grain rate, impurity rate, ear loss rate, and total grain loss were 5.63%, 2.39%, 4.12%, and 4.76%, respectively; with ear loss accounting for 86.55% of total grain loss. Grain moisture content was positively correlated with broken grain, impurity, and grain loss rates, while there was no significant correlation between grain moisture content and ear and total grain loss rates. High grain moisture content was the main cause of grain breakage rates during harvest; delaying the harvest period could effectively reduce the grain moisture content and thus, reduce grain breakage rates. At the same time, the mismatch between the spacing of planting and harvesting rows was the main cause behind high ear loss rate (86.55% of total grain loss). Ensuring that the harvest was performed in opposite rows could significantly reduce the ear loss rate and greatly reduce total grain loss. Four maize varieties ('zhongyu 3, ' 'yudan 30, ' 'zhenghong 6, ' and 'yanke 288') were screened out, which were suitable for the mechanical grain harvest of Sichuan using the average yield and grain moisture content during the harvest period as indicators.

Differences in mechanical threshing broken rate between superior and inferior maize grains

ZHAO Bo, WU Yawei, LI Xiaolong, CHEN Xiang, DENG Changchun, ZHU Xiaoyong, YUAN Jichao, KONG Fanlei

2020, 28(6): 843-851. doi: 10.13930/j.cnki.cjea.200111

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Abstract:
High grain broken rate is the main limiting factor encountered when mechanically harvesting maize grains. Owing to different filling degrees, the structures of superior and inferior maize grains are different. Therefore, the objectives of this study were:1) to explore the difference in mechanical threshing broken rate between superior and inferior grains and factors that influence this; 2) to select a mechanical strength evaluation index with a high correlation with grain broken rate. Two maize varieties ('Zhongyu 3' and 'Xianyu 1171') were selected, and superior and inferior grains were mechanically threshed separately. Moisture content, 100-grain weight, mechanical strength, starch grain shape, and grain broken rate were compared and analyzed for the superior and inferior grains over three mechanical threshing dates (August 9, August 16, August 23). The results showed that the broken rate of inferior grians of 'Zhongyu 3' was higher than that of superior grains threshed on August 9, August 16, and August 23; and that the broken rate of 'Xianyu 1171' inferior grains was higher than that of superior grains on threshing dates August 16 and August 23. The moisture content and 100-grain weight of superior grains were significantly higher than those of inferior grains across different mechanical threshing dates. At the same time, the superior grains had an obvious mechanical strength advantage over the inferior grains. The results also showed that there were significant negative correlations between broken rate and facade crushing strength (r=-0.46^**), broken rate and germ crushing strength (r=-0.34^*), which could be used to better reflect the breaking resistance of grains. The horny endosperm starch granules of superior grains were larger than those of inferior grains, and the floury endosperm starch granules were mainly polyhedral in the superior grains but were mainly spheroid in inferior grains. The difference in moisture content between superior and inferior grains could not reliably reflect breaking resistance. Differences in grain weight and mechanical strength were the main factors behind differences in broken rate between superior and inferior grains. The present study highlighted the importance of the differences between superior and inferior grains in maize mechanical harvesting as well as the relationship between grain mechanical strength and breaking resistance.

Improved methods for separating apoplastic washing fluid from roots and leaves in cotton seedlings

WANG Guo, FENG Kang, LI Qian, XUE Huiyun, LI Lijie, ZHANG Zhiyong

2020, 28(6): 852-859. doi: 10.13930/j.cnki.cjea.200092

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Abstract:
Apoplast washing fluid (AWF) contains minerals, metabolites, and proteins that plays an important role in plant growth and development, as well as provides biotic and abiotic stress resistance. AWF extraction is the basis of exploring the function of AWF constituents. It is generally performed via vacuum infiltration-centrifugation technique; which varies in processes and detailed parameters depending on the plan species, organs, and culture conditions. Hydro-cultured cotton seedlings were used to investigate AWF separation processes and parameters suitable for cotton root and leaf development, and further improve methods for cotton root or leaf AWF separation. Compared with traditionally split sampling (i.e., splitting samples into segments or pieces), sampling a complete unit was simple and significantly decreased the ratio of malate dehydrogenase (MDH) activity in AWF to symplast washing fluid (SWF), which usually is used to affirm the degree of AWF substances polluted by SWF; indicating that AWF components would better to examine. Furthermore, the fresh weight increments and the AWF diluting factor after vacuum infiltration of the roots had no significant change, but significantly increased in the leaves. This indicates that vacuum infiltration is only essential for leaves, with a vacuum strength/time at -60 kPa/1 min, and about 110 s recovery from vacuum to normal atmospheric pressure. Leaf areas with dark color increased with vacuum intensity or time, which could be used as a simple indicator for determining the suitability for AWF separation. Finally, comprehensive analyses of the AWF volume, soluble protein content ratio and MDH activity ratio of AWF to SWF indicated that the suitable centrifuge forge/time was 800×g/10-20 min for the root, and 400×g/5 min for the leaf. This refined and optimized method will lay down the foundation for efficient study of AWF components such as the accuracy and reliability of proteomics and metabolomics. The approach towards establishing this method should allow it to be generally applicable to other plants.

Safe utilization of heavy metal-contaminated farmland: Goals, technical options, and extendable technology

LI Xiaofang

2020, 28(6): 860-866. doi: 10.13930/j.cnki.cjea.200103

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A major task for current soil environmental study is to form problem-solving schemes for the safe utilization of contaminated farmland. Is the scientific community able to provide such schemes as quickly as possible to meet the need by the national "Action Plan for Soil Pollution Prevention and Control"? Here we analyzed the fundamental concepts and decision tree for soil pollution control, based on which the goals, technical options and extendable technology for the safe utilization of contaminated farmland were explored. It is proposed that safe utilization of the contaminated farmland could be referred both in the broad sense and in the narrow sense, with the narrow safe utilization being the priority. The safe utilization of contaminated farmland aims to the production of foods meeting the national food standards, but not the immobilization or cleanup of soil contaminants. Selection and cultivation of low-Cd crops is a promising technology, while the coupled use of metal immobilizers may increase the upper threshold of farmland metal contamination suitable for the safe utilization. We suggest that cost, effect and secondary eco-toxicity are important criteria for evaluating the safe utilization technology, and the form of the extendable technology may consider the traditional agronomic elements like seeds, fertilizers and tillage regime. This work is supposed to promote the translation of soil pollution control knowledge to the safe farming technology, which may ultimately serve the goals of the "Action Plant for Soil Pollution Prevention and Control".

Lead accumulation and low-molecular-weight organic acids secreted by roots in Sonchus asper L.-Zea mays L. intercropping system

QIN Li, HE Yongmei, WANG Jixiu, LI Bo, JIANG Ming, LI Yuan

2020, 28(6): 867-875. doi: 10.13930/j.cnki.cjea.190841

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Abstract:
There is a close relationship between low-molecular-weight organic acids (LMWOAs) secreted by plant roots and plant accumulation of heavy metals when intercropping accumulators and crops in heavy metal-contaminated soils. However, the specific mechanism behind this remains unclear. Sonchus asper L. Hill is a native hyper accumulator that can be found in Yunnan. Plant growth, amounts of LMWOAs secreted by plant roots, rhizosphere soil extractable lead (Pb) contents, and plant Pb accumulation characteristics were studied under S. asper-Zea mays L. intercropping in soil that was collected from a farmland surrounding a mining area, in order to investigate the effects of the LMWOAs produced by intercropping roots on heavy metal bioavailability in soils. The results showed that the aboveground and root biomass, root length, root inner diameter, and root volume of S. asper were significantly increased (P < 0.05), and that the root biomass, root length, root diameter, and root volume of Z. mays were significantly increased (P < 0.05) under the intercropping systems compared to under the monoculture systems. The major LMWOAs secreted by the roots of both S. asper and Z. mays were citric acid and oxalic acid. Intercropping resulted in an increase and decrease in the LMWOA contents secreted by S. asper and Z. mays roots, respectively. The bio-available Pb content in the rhizosphere soil of S. asper increased by 85.2% (P < 0.05), and that of Z. mays decreased by 26.1% (P < 0.05) under intercropping. The Pb content, enrichment factor, and transfer coefficient increased by 18.0%-43.2%, increased by 26.0%, and reduced by 42.0% in S. asper under intercropping, respectively. Compared to the monoculture system, the shoot Pb content and Pb transfer coefficient decreased by 24.3% and 43.1% (P < 0.05) in Z. mays under the intercropping system, respectively. The amounts of citric acid and oxalic acid secreted by S. asper roots were significantly positively correlated with the soil bio-available Pb content, and the bio-available Pb content in soil was significantly positively correlated with S. asper shoot and root Pb contents. The results indicate that intercropping increases the uptake and accumulation of Pb in S. asper. These are both closely correlated with increases in soil bio-available Pb, which is mediated by plant roots that secrete LMWOAs.

Effects of multi-factor on water use efficiency as identified by the SEM method in irrigated wheat farmlands in the North China Plain

ZHANG Chuanwei, QI Yongqing, DAI Maohua, ZHANG Yucui, SHEN Yanjun

2020, 28(6): 876-886. doi: 10.13930/j.cnki.cjea.190924

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Abstract:
Water use efficiency (WUE) is usually embedded in a variety of ecosystem models to assess the ecosystem response to climate change. However, under natural conditions, multiple environmental factors affect WUE directly and indirectly by influencing the canopy structure. Currently, the mechanisms that influence WUE are not clear. In order to clarify the synergistic effect of various factors on the WUE of winter wheat, experiments were conducted in the Luancheng Agro-Ecosystem Experimental Station, Chinese Academy of Sciences. Variables were observed using an eddy covariance system during key growth stages (greening, jointing, heading, filling) of winter wheat in 2015 (warm and wet year) and 2016 (warm and dry year). The variation in winter wheat WUE and the controlling mechanisms of various factors (net radiation, R_n; air temperature, T_a; vapor pressure deficit, VPD; wind speed, WS; soil water content, SWC) were analyzed by means of a structural equation model (SEM). The structural equation model can systematically analyze the impacts of different factors on WUE on the basis of interactions among different factors. Compared to traditional univariate or multiple linear regression, SEM had intermediate variables, which can decompose the effects of micrometeorological factors into direct and indirect effects. In this study, leaf area index (LAI) was the intermediate variable. The results showed that average WUE in 2015 was 1.52 g(C)·kg^-1(H₂O), while it was 1.22 g(C)·kg^-1(H₂O) in 2016. T_a, LAI, and VPD were the main factors that influenced WUE, regardless of whether the year was warm and wet (WW) or warm and dry (WD). Leaf area index and T_a had positive effects on WUE, while VPD inhibited WUE, which means that under similar temperatures, increased water vapor content in the air can enhance WUE. T_a, LAI, and VPD were of different importance in WW and WD years. LAI was the most significant influencing factor in WW years, while T_a played a more important role in WD years. In WW years, VPD not only affected WUE directly but also indirectly through altering LAI, while it only had a direct effect in WD years. R_n also was different between WW and WD years, having a significant effect on WUE in WW year but no significant effect in WD year. This phenomenon was caused by the heavier and more frequent rainfall in WW year. Obviously, taking the climate conditions in different years into consideration will increase accuracy when simulating WUE. WS had no significant effect on WUE, probably because WS only affects the leaves receive sufficient radiation in the upper part of the canopy, and these effects can be ignored for leaves inside the canopy. Farmland ecosystems have different tolerances and responses to radiation and temperature at different growth stages. LAI can be set as an intermediate variable to reveal this stepwise change in SEM. Therefore, for ecosystems with large seasonal changes in canopy structure, SEM is a powerful tool to investigate mechanisms of environmental control. This research can provide a scientific basis for accurately simulating WUE and predicting the response of WUE to climate change.

Spatial distribution pattern and change characteristics analysis of cultivated land in the Manas River Basin from 1975 to 2015

ZHU Lei, YANG Aimin, XIA Xinxin, WU Hongqi

2020, 28(6): 887-899. doi: 10.13930/j.cnki.cjea.190624

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Abstract:
The objective of this study was to reveal the spatial distribution characteristics and change trend of cultivated land, taking the Manas River as the study area, by extracting the cultivated land information based on 1975, 1990, 1995, 2000, 2005, 2010, and 2015 series of land use data, via spatial autocorrelation, gravity center mode, standard deviational ellipse, and geography informatic spectrum analysis. The results revealed that there was significant global positive correlation and strong local spatial heterogeneity in the spatial distribution of cultivated land. The cultivated land showed an aggregated time series trend, which first weakened, then strengthened, and then weakened again across the study period. The land formed a high-high agglomerate distribution situation with a left core in Shanghudi Township of Shawan County, and a right core in Beiquan Town of Shihezi City. The overall spatial change in the cultivated land showed a clear, significant shift to the northwest, and the moving speed of the cultivated land's center of gravity experienced a process of "slowed (1975-1995)-accelerated (1995-2005)-decelerated (2005-2015)". The spatial distribution pattern of the standard deviation ellipse appeared more obvious in the northwest direction after 1995, and the area of ellipse increased substantially. The growth range of the cultivated land was constantly strengthened and had a trend of expansion to the northern desert area of the basin. Through LISA frequency geo-spectrum analysis, we found that the total proportions of stable invariant and low frequency types accounted for 84.58%, and the spatial pattern of cultivated land was relatively stable. The overall spatial aggregation of the cultivated land generally shifted from a state of "Low-Low" aggregation "Low-High" aggregation to a state of "High-High" aggregation, which showed high-density expansion of cultivated land in the Manas River Basin from 1975 to 2015. By constructing the geo-spectrum of LISA frequency and combining the gravity center model and standard deviation ellipse, spatial evolution trends in the regional cultivated land were comprehensively and dynamically outlined, and the theoretical basis and decision-making foundations for scientific management and effective protection of cultivated land resources were provided.

Changes in agricultural resource input and productivity in Kenya and China

Dorris Chebeth, BAI Zhaohai, MA Lin

2020, 28(6): 900-909. doi: 10.13930/j.cnki.cjea.200019

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Both Kenya and China are facing great challenges in feeding their populations; this is particularly problematic in Kenya, where the population will be projected to increase by 1.4 times from 2018 to 2100. Food production has been greatly improved in China, but it still lags behind in Kenya. In this study, we systematically compared the changes in agricultural resources and crop/livestock productivity, as well as their relationships with the resource input levels and agricultural production structure, to try to provide insights into reducing food insecurity and poverty in Kenya. Our results revealed that Kenya had 2-3 times more natural resources, such as cropland, grassland, and annual precipitation, per capita than did China in the 1960s, which was similar to the daily food energy and protein supply. Currently, Kenya still has higher natural resources per capita, but has lower food security and quality when compared to China. This is due to the continued rapid increase in crop and livestock productivity regarding energy and protein production in China. From 1961 to 2017, crop protein productivity increased by 44% in Kenya, while in China it increased by 282%. Our results showed that crop and livestock productivity positively correlated with the input of fertilizers, concentrate feeds, machinery, and pesticides, as seen in China. Meanwhile, the structure of crop and livestock production also showed a large impact on the changes in productivity, such as the harvest area of vegetables/fruits to the total harvest area and the ratio of monogastric animals for livestock production. Overall, both agrochemicals and structure have strong impacts on the increase in productivity, and these could be potential options in Kenya to improve productivity due to the low input of resources into crop and livestock production.

Economic benefits and carbon footprint of a spring mung bean-summer maize cropping system in the North China Plain

WANG Shang, LI Kangli, NIE Jiangwen, YANG Yadong, ZANG Huadong, ZENG Zhaohai

2020, 28(6): 910-919. doi: 10.13930/j.cnki.cjea.190916

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The North China Plain is an area of major grain production in China. The intensive winter wheat-summer maize cropping system has led to increasingly excessive nitrogen fertilization, over-exploitation of groundwater, and increased carbon emissions. Therefore, adjusting the existed planting structure and constructing a resource-saving planting system is critical to alleviate the ecological problems of the region. Here, the yield, economic benefits, carbon emissions, and carbon footprint were evaluated between spring mung bean-summer maize (MM) and winter wheat-summer maize (WM) cropping systems based on a field experiment and life cycle assessment (LCA). The yields of mung bean and maize were 1 760.1 kg·hm^-2 and 8 775.8 kg·hm^-2 under the MM treatment, respectively. The annual economic equivalent yield and annual net income of the MM treatment were 18 833.4 kg·hm^-2 and 27 085 ￥·hm^-2, respectively, which were 20.4% lower (P < 0.05) and 20.2% higher than those under the WM treatment, respectively. The annual carbon emission from the MM treatment was 4 642.1 kg(CO₂-eq)·hm^-2, which was 36.1% lower than that from the WM. Additionally, the carbon footprint per unit of economic benefit of the MM treatment was 0.17 kg(CO₂-eq)·￥^-1, 48.5% lower (P < 0.01) than that of WM. Therefore, the introduction of MM systems to replace some WM systems could potentially increase the net income of farmers, as well as reduce carbon emissions and carbon footprint.

Ecological value estimation method of the straw pyrolysis engineering

WANG Ying, WANG Yajing, WANG Hongyan, WANG Huan, BI Yuyun

2020, 28(6): 920-930. doi: 10.13930/j.cnki.cjea.190563

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Abstract:
The straw pyrolysis project is an ecological production project designed to convert high quality agricultural straw waste into gas, carbon, oil, and liquid. It has an important practical significance for conserving national energy and reducing emissions in the China's agricultural fields. It has been an important scientific basis to accurately estimate the ecological value of the straw pyrolysis project and provides a systematic and comprehensive quantitative evaluation index system and calculation method to effectively promote green development in agriculture. This paper analyzed the ecological value composition of straw pyrolysis engineering based on the dichotomy theory of ecological value theory. It was concluded that the main ecological beneficial assets generated by the project of straw pyrolysis project were emission reduction and waste resource commercialization. The general formula for estimating the ecological value of straw pyrolysis project established was the ecological value of straw pyrolysis and the gasification project (V_PE)=the monetary value of straw pyrolysis project emission reduction (V_EB) + the economic value of straw resource products (V_RC). In the calculation process, the life cycle analysis (LCA) method was selected to measure the net emission reduction of the straw pyrolysis project, and then the net emission reduction was valued with the help of carbon dioxide shadow prices to obtain the project's emission reduction (V_EB). Furthermore, the economic value of straw resource products achieved by the ecological production project (V_RC) was calculated. Finally, V_EB and V_RC were included to obtain the ecological value of straw pyrolysis and gasification engineering (V_PE). The method was designed using the literature research method to analyze the parameter selection required by each calculation link, and the parameter system required for the calculation process was provided. This study attempted to achieve substantial breakthroughs and innovations during the integration of both method and parameter research in the following three aspects:firstly, the ecological value estimation model of straw pyrolysis project was constructed; not limited to analysis and research from the emission reduction benefits perspective, with a more systematic and comprehensive ecological value estimation method and its required parameter system was established. Secondly, the potential value of the project should be reasonably converted into the "real market value"; in this study, the ecological benefits of the straw pyrolysis project were monetarily priced and measured. Thirdly, this study considered the impact of different technological levels and product energy conversion rates on greenhouse gas emissions during the process of estimating the displacement reduction of end-use energy products. Throughout the study, the general idea of "scientific modelling, reasonable pricing, and accurate estimation" was followed to provide a reliable foundation and support the decision to formulate the national energy saving and emission reduction plans.

Design and implementation of the land ecological security warning system

ZHANG Cheng, HUANG Fangfang, SHANG Guobei

2020, 28(6): 931-944. doi: 10.13930/j.cnki.cjea.190782

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Abstract:
Land ecological security is one of the core issues in regional ecological security. Quantitative, visual, and automatic evaluation and prediction of land ecological security status and real-time warning are of great significance for the sustainable use of land resources. Taking Hebei Province as an example, an index system of land ecological security was constructed based on the pressure-state-response (PSR) model. In addition, a projection tracking model was used to evaluate the land ecological status, a principal component correlation analysis model was used to identify the main influencing factors of land ecological security, and the spatial difference coefficient model was used to analyze the spatial and temporal pattern of land ecological security. The Markov prediction model was adopted to predict the land ecological security level, an early warning mechanism was established by dividing the early warning levels of land ecological security, and the land ecological security warning system was developed by using the graphical user interface (GUI) of MATLAB. The results showed that:1) From 2010 to 2018, the land ecological security index of Hebei showed an overall increasing trend, shifting from 0.300 to 0.611, with an average annual growth rate of 12.92%. The status of the land ecological security had changed from "deteriorating grade" to "sensitive grade". The warning level had changed from "super-severe warning" to "moderate warning". However, the overall level of land ecological security was still low. 2) The main limiting factors of land ecological security were population density, industrialization rate, pesticide input per unit area of cultivated land, load of industrial wastes per unit area of land, proportion of urban construction land, proportion of industrial land, and energy consumption per 10 000 ￥ GDP. 3) The regional differences in land ecological security in different prefecture-level cities of Hebei Province had been decreasing continuously and became stable in recent years. By 2018, the coefficient of spatial difference was 32.54%, and the differences between cities still cannot be ignored. The state of land ecological security in most prefecture-level cities was at "sensitive level", and the warning level was "moderate warning". The level of land ecological security needs to be further improved. 4) From 2019 to 2025, the land ecological security index of Hebei Province is predicted to show a steady upward trend, and by 2025, it predicted to be 0.834, reaching the "less security level, " with a warning level of "slight warning." There is now greater potential for land ecology to develop in a benign direction.

2020 Vol. 28, No. 6