中国生态农业学报(中英文)

Application of ecological network analysis in nitrogen cycling in agroecosystems: Progress and prospects

LI Xiaobo, KAZANCI Caner, ZHANG Jing, FAN Ruqin, MA Qianqian, DU Jianjun

2022, 30(3): 325-332. doi: 10.12357/cjea.20210767

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Abstract:
Nitrogen cycling in agroecosystems is directly related to food security and environmental protection and has received worldwide attention. Ecosystem nitrogen cycling involves the migration and transformation of nitrogen among various ecosystem components, characterized as integrity and complexity. However, existing studies have mostly focused on partial cycling processes and provide limited information about the changes in nitrogen cycling at the system level. By constructing an ecological network that simulates the flow of material or energy in a complex system, ecological network analysis (ENA) analyzes within-system interactions and system-wide properties from a holistic perspective. Therefore, applying ENA to examine agroecosystem nitrogen cycling as a whole has great application and development prospects. In this paper, we first introduce the principle and recent development of ENA, including the development of network particle tracking (NPT), which extends the application of ENA from steady-state to dynamic ecosystem models, and the application of NPT in developing new system-wide indicators, including the indirect effect index (IEI) and storage-based cycling index (SCI). Then, we introduce the main advantages of ENA and the primary procedures in the application of ENA and further demonstrate a case study of applying ENA to study nitrogen cycling in a rice field. Finally, we point out that the main problems hindering the application of ENA in agroecosystems are the difficulty and high cost of gathering empirical data required to build the network models and the scarcity of scientists who are knowledgeable in both ENA and the nitrogen cycling of agroecosystems. Regarding these problems, we provide possible coping strategies (e.g., building long-term experiments for data collection, making the best of historical data, developing more effective methods to facilitate network construction, and encouraging interdisciplinary cooperation) and further discuss the prospects of applying ENA in nitrogen cycling in agroecosystems.

Effect of biochar on soil microbial metabolic activities

TAN Chunling, LIU Yang, HUANG Xuegang, ZHANG Junyuan, LUO Wenhao

2022, 30(3): 333-342. doi: 10.12357/cjea.20210542

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Abstract:
The application of biochar in agriculture and the environment has attracted widespread concern. Biochar can enhance soil fertility and reduce toxic effects on soil ecosystems through the fixation and degradation of soil pollutants. The metabolic activity of soil microorganisms is the main driving force in soil element cycles and organic pollutant degradation and is an important index reflecting soil health. However, the understanding of the differences in microbial metabolic activities under the influence of different types of biochar is still incomplete, impeding its sustainable development and application; therefore, it is necessary to investigate the application of biochar to soil microorganisms. This review summarized the mechanisms by which biochar (derived from different raw material sources and pyrolysis temperatures) on soil microbial abundance, diversity, community structure, and activity changes to deeply explore the positive or negative effects of biochar on soil microorganisms. We also focused on the electron transfer process of microbes mediated by biochar, soil fertility improvement induced by biochar-microbe interaction, pollution remediation, and pathogenic microorganism control. The porous structure of biochar provides habitats for microorganisms, while its mineral content can provide nutrients, and high-temperature biochar can increase the pH of acidic soil, providing a suitable environment for the growth of microorganisms. The functional groups with redox activity in biochar can mediate the electron transfer process and promote microbial metabolism. However, the polycyclic aromatic hydrocarbons, volatile organic compounds, environmentally persistent free radicals, and heavy metals contained in biochar have inhibitory effects on the growth and metabolism of microorganisms. Nevertheless, aging and pickling treatments can effectively reduce their toxicity. The effects of biochar and microorganisms on soil fertility improvement, pollution remediation, control of pathogenic microorganisms, and the related mechanisms were also discussed. In practical applications in agriculture, it was found that biochar can promote the abundance and metabolic activity of functional microorganisms such as nitrogen-fixing, phosphorus-dissolving, potassium-dissolving, and pollutant-degrading bacteria. Therefore, under the joint action of biochar and microorganisms, soil fertility can be improved, polluted soil can be repaired, and the detrimental effects of pathogenic microorganisms on crops can be controlled. Suggestions on the efficient utilization of biochar were put forward, and directions for future research biochar and microorganisms were proposed.

Crop allelopathy types: Current research status and prospects in China

LIN Zhimin, MUHAMMAD Umar Khan, FANG Changxun, LIN Wenxiong

2022, 30(3): 343-355. doi: 10.12357/cjea.20210418

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Abstract:
In this review, we present details of recent advances in research on different types and action modes of crop allelopathy in China. In particular, we focus not only on direct and indirect allelopathy but also on intra- and interspecific interactions, with the aim of informing international peers of the ongoing developments in this field. The term crop allelopathy was first defined in 1984, and since that time, substantial progress has been made in this area, during which the concept of crop allelopathy has been broadened to encompass plant-soil-microbial interactions, including amensalism, autotoxicity, and facilitation in cropping systems. Recent studies have revealed that donor plants are able to trigger the expression of defense-related genes, resulting in the release of specific metabolites (allelochemicals) into the environment. In particular, allelopathic crops have been found to secrete these chemicals into the soil environment via root exudation in response to stresses induced by target plants (such as weeds), which in turn results in allelopathic amensalism and allelopathic commensalisms in cropping systems. The amensalistic and commensalistic components of crop allelopathy can be further divided into intra- and interspecific interactions based on mode of action. Interspecific interactions involve the inhibitory or facilitative effects of donors on recipient plants, depending on the types, concentrations, and bio-activity of allelochemicals; whereas intraspecific interactions include auto-promotive and auto-toxic effects, which can be either positive or negative. The current consensus indicates that both positive and negative allelopathic interactions are mediated via changes in rhizosphere soil microbial composition and structure in response to root allelopathic secretions. In this regard, however, there is often an imbalance in the composition of soil microbial communities, which is largely attributable to an increase in pathogen populations and reduction in those of beneficial bacteria as a consequence of consecutive monoculture cropping. Such imbalances inevitably lead to three undesirable outcomes in continuous cropping systems, namely, soil nutrient sequestration, soil acidification, and the outbreak of soil-borne diseases, thereby resulting in reduced crop yields and quality. Conversely, in the case of positive allelopathic interactions, continuous cropping can contribute to promoting increases in microbial diversity mainly as a consequence of increments in the populations of beneficial bacteria and corresponding reductions in pathogenic microorganisms, thereby enhancing soil micro-habitats, and thus increasing crop yield and quality. Given these responses, a key priority for future research is more in-depth studies of the structure and function of rhizosphere microbial communities, and appropriate modification of rhizosphere habitats, with the aim of producing high-yielding good quality crops for sustainable agricultural development.

Evapotranspiration of typical agroecosystems in the North China Plain based on single crop coefficient method

YANG Tianyi, WANG Jun, ZHANG Hongmei, LI Rongji, ZHANG Yucui, SHEN Yanjun

2022, 30(3): 356-366. doi: 10.12357/cjea.20210336

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Abstract:
The crop coefficient method recommended by FAO56 is a method to calculate the actual evapotranspiration of crops, which can simply and accurately reflect the evapotranspiration patterns and characteristics of different agroecosystems during different growth stages. Although the crop coefficient method is widely used, there are still some problems in applying this method in the North China Plain. Research on a single agroecosystem of winter wheat-summer maize has been conducted for a long time. However, there is a lack of systematic and comprehensive research on the evapotranspiration patterns of various typical agroecosystems in the North China Plain through the single crop coefficient method. Therefore, it is difficult to provide quantitative theoretical support for water consumption management and planting structure adjustment. Furthermore, the variation in crop coefficients for the typical pear orchard agroecosystem, the main fruit and the most important economic crop in the North China Plain, is urgently needed. In this study, the crop coefficients and evapotranspiration patterns of different growth stages of irrigated crops in the typical agroecosystems of winter wheat-summer maize farmland, cotton field, and pear orchard in the North China Plain were examined and verified from 2016 to 2017. The entire growth stage was divided into initial, developing, mid, and end stages based on the crop growth stages and physiological characteristics. According to the single crop coefficient method recorded in FAO56 manual, the average crop coefficients of the initial, developing, mid, and end stages of different crops were 0.60, 0.88, 1.07, and 0.72 for winter wheat; 0.46, 0.76, 1.01, and 0.80 for summer maize; 0.34, 0.71, 1.07, and 0.78 for cotton; 0.81, 0.91, 1.02, and 0.96 for pear trees, respectively; while the calculated actual evapotranspiration was 694.3 mm, 472.2 mm, and 825.7 mm for the above three ecosystems, respectively. Evapotranspiration measured by the eddy covariance systems was 701.4 mm, 496.5 mm, and 763.5 mm for winter wheat-summer maize, cotton field, and pear orchard agroecosystems, respectively. Both the calculated and measured actual evapotranspiration values of the four crops showed a single-peak change from the initial to the end stages, with the same trend. The correlation coefficients between the calculated and measured evapotranspiration for all three agroecosystems were greater than 0.8. The calculated actual evapotranspiration values compared to the measured values during the growth stage of winter wheat-summer maize, cotton, and pear orchard agroecosystems were 1.0% lower, 4.9% lower, and 8.1% higher, respectively. This study not only provided the crop coefficients of wheat, maize, and cotton but also filled the gap in the research on crop coefficient of pear trees in this region. It is particularly important that this study used the observed evapotranspiration by the eddy correlation system to verify the calculated evapotranspiration using the single crop coefficient method at the same spatial and temporal scale, which shows the applicability of the calculated crop coefficients in the region. The applicability of the single-crop coefficient method in different agroecosystems in the North China Plain was clarified. This research provides a scientific basis for making reasonable irrigation plans and achieving precise management of crop water consumption.

Characteristics of ecosystem energy closure and CO₂ flux in a rice-wheat rotation area along the coast of East China

XU Min, XU Jingzheng, LIU Wenjing, XU Meng, XU Jingwei, GAO Ping, LUO Xiaochun

2022, 30(3): 367-379. doi: 10.12357/cjea.20210731

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Abstract:
To scientifically evaluate the variation characteristics of energy flux and the carbon sequestration capacity of a winter wheat and one-season rice rotation farmland ecosystem on the coast of East China, we collected flux observations in winter wheat and one-season rice rotation farmland from a vorticity field observation experiment throughout the growth period from 2019 to 2020. We used the flux data processing software of American LI-COR Company to control the data quality and obtained a set of 30 min data sequences. After quality control, carbon sequestration of rice and wheat and its environmental impact factors and multi-time scale variation characteristics of solar net radiation (R_n), latent heat flux (LE), sensible heat flux (H), soil heat flux (G), and CO₂ flux (F_C) were studied and analyzed using energy balance and statistical methods. The results showed that the energy balance ratio of the effective energy and turbulent flux was 0.80, which indicated a high energy closure and reliable flux observations. The variations in monthly LE and R_n over the year showed an “inverted U” distribution, and these two variations were synchronous. The peak value mainly occurred from May to August, and the valley value mainly appeared from January to February and November to December. The fluctuation magnitudes of H and G were significantly lower than those of LE and R_n. Hourly F_C during the day presented a “U-shaped” single peak quadratic curve, thereby indicating that CO₂ was generally absorbed during the day and discharged at night. The daily absorption peak of CO₂ mainly occurred during 10:00–12:30. Daily and monthly F_C generally showed “W-type” variation characteristics throughout the year. The annual carbon emission periods were mainly concentrated in January, June, November, and December, whereas the rest of the year was classified as a carbon absorption period. The absorption peaks were at the jointing and booting stages of winter wheat (March to April) and rice (August). The carbon sequestration during the growth period of winter wheat from February to May was 387.4 g(C)∙m⁻² and 382.2 g(C)∙m⁻² in 2019 and 2020, respectively. Carbon sequestration during the growth period of rice from July to October was 678.2 g(C)∙m⁻² and 599.7 g(C)∙m⁻² in 2019 and 2020, respectively. During the day, when the air temperature increased, the CO₂ absorption capacity of winter wheat and rice increased; however, this absorption trend decreased when the difference in saturated water vapor pressure was greater than 1.7 kPa. The absorption capacity of CO₂ at night was mainly affected by temperature. The capacity of carbon absorption revealed clear diurnal and seasonal variations in coastal winter wheat and rice rotation farmland ecosystems. Considering the annual carbon balance, this ecosystem is a carbon sink. Moreover, it is a robust carbon sequestration area.

Integrated management improves spring maize yield and resources use efficiency, and reduces the carbon footprint in Northeast China

LIU Zhiming, SI Yu, YAO Fanyun, ZHENG Peifeng, LAN Tianjiao, LYU Yanjie, WANG Yongjun

2022, 30(3): 380-388. doi: 10.12357/cjea.20210405

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Abstract:
Northeast China is the largest maize production region in the country, but the long-term management approach of production aiming at high yield has led to the cropping system becoming a major source of greenhouse gas emissions. Effective measures to improve resource efficiency and reduce environmental costs based on guaranteed yields have become an urgent need for industrial agricultural development. In this study, an integrated management mode (IM), including wide- and narrow-row alternative planting (90 cm for wide rows and 40 cm for narrow rows), high planting density (90 000 plants∙hm⁻²), application of chemical regulation agents at the 15-leaf spread of maize, and reduction of nitrogen fertilizer (28.0% and 9.1% in semi-humid and semi-arid areas, respectively) was selected in the semi-arid and semi-humid areas of the central Northeast Plain, while sub-membrane drip irrigation was applied in the semi-arid area, in 2019 and 2020. The differences between IM and farmers’ mode (FM: 65 cm equal row spacing and planting density 60 000 plants∙hm⁻² without chemical regulation) in different ecological areas in Northeast China were comparatively analyzed in terms of maize grain yield, and use efficiencies of accumulated temperature and light energy, economic benefits, and carbon footprints. The results showed that, compared with FM, maize yield of IM in the semi-humid and semi-arid areas averagely increased by 24.2% and 25.6%, respectively, mainly because of a 50% increase in planting density resulting in 48.5% and 57.0% increases in the number of harvested ears; whereas the number of ears and thousand-kernel weight only decreased by 8.5% and 11.0% averagely in two areas for two years, respectively. The cumulated temperature production efficiency in the semi-humid area increased by 21.1%, the light energy use efficiency increased by 21.0%; in the semi-arid area, the cumulated temperature production efficiency and light energy use efficiency improved by 20.7% and 22.0%, respectively. Therefore, the annual net returns of IM in the semi-humid and semi-arid areas increased averagely by 32.9% and 24.4%, respectively, compared with FM. Meanwhile, the total carbon emission of IM in the semi-humid area was 2860.1 kg (CO₂-eq)·hm⁻², which was 18.7% lower than that of FM; while the total carbon emission of IM in the semi-arid area was 8.9% higher than that of FM, at 2729.6 kg (CO₂-eq)·hm⁻². The carbon footprint per unit grain yield of IM in the semi-humid and semi-arid areas was 0.20 kg (CO₂-eq)·kg⁻¹ and 0.22 kg(CO₂-eq)·kg⁻¹, respectively, which was 39.4% and 15.4% lower than that of FM. In summary, the IM in Northeast China was able to achieve synergistic improvements in grain yield, accumulated temperature production efficiency, light energy utilization efficiency, and economic benefits, and significantly reduce the carbon footprint, especially in the semi-humid area; the semi-arid area showed increased carbon emissions but had a higher yield increase than the semi-humid area, which ultimately also significantly reduced the carbon footprint. Therefore, an integrated management mode is recommended for maize production in Northeast China.

Regulating effect of deep tillage and delamination fertilization on the yield formation of summer maize

XU Ping, YANG Xianjie, DENG Xuebin, YANG Zhen, SUN Yanling, ZHANG Zhengbin

2022, 30(3): 389-398. doi: 10.12357/cjea.20210128

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Abstract:
In the Huang-Huai-Hai Plain, the hard stubble seeding of summer maize has caused a shallowed top soil layer, which induced decreasing of use efficiencies of sources, such as light, heat, water, and fertilizers of summer maize. Therefore, this experiment applied a new tillage-fertilization technology, deep tillage and delamination fertilization (DTDF), to solve the above problem. In the experiment, two treatments were set: DTDF+seeding (DTDF) and hard stubble seeding and fertilization (HSSF); the soil bulk density, soil moisture content, and soil nutrients contents were investigated at the big trumpet, tasseling, silking, late filling stages of summer maize. In addition, the growth and development traits, dry matter accumulation traits, and yield components of summer maize were investigated too. Finally, the water use efficiency and partial nitrogen productivity of summer maize were analyzed. The results showed that the soil bulk density was significantly reduced, soil water content was increased. Soil contents of nitrogen, phosphorus, and potassium at 20–40 cm were higher than those at 0–20 cm under DTDF treatment, indicating a mitigating effect on surface accumulation of nutrients. The plant height and leaf area per plant of summer maize during the big horn to silking stages, the dry leaf weight during the big horn to tasseling stages, and the dry ear weight during the silking to late filling stages under DTDF treatment were significantly higher than those under HSSF treatment. Ear diameter, grain number per row, 100-grain weight, cob weight, grain weight per plant, straw weight per plant, and yield under DTDF treatment were also higher than those under HSSF treatment. The DTDF treatment significantly increased water use efficiency, partial nitrogen productivity, and maize yield compared with the HSSF treatment. Therefore, the DTDF optimized the soil bulk density, water and nutrient distribution, regulated maize growth and development, and increased yield, water use efficiency, and partial nitrogen productivity of summer maize. This study provides a theoretical basis and technical support for the high-quality development of farmland and sustainable green improvement of maize production in the Huang-Huai-Hai Plain.

Photosystem damage mechanism in flag leaves of winter wheat under high temperature

YANG Cheng, LI Xiangdong, DU Simeng, ZHANG Deqi, SHI Yanhua, WANG Hanfang, SHAO Yunhui, FANG Baoting, CHENG Hongjian, WEI Fang

2022, 30(3): 399-408. doi: 10.12357/cjea.20210469

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Abstract:
High temperatures are one of the main environmental stresses at the filling stage of winter wheat. The reduction in wheat photosynthesis caused by heat stress affects the filling of wheat and reduces grain yield. China is rich in wheat cultivars, and their photosynthetic sensitivity to high temperatures varies. Investigating the mechanism of high-temperature damage to the photosynthetic apparatus of wheat flag leaves can help to rationalize wheat high-temperature resistance resources. In this study, 35 wheat cultivars planted widely in Henan Province during different historical periods were selected. The parameters related to photosynthetic electron transfer of all wheat cultivars were measured and analyzed using fast chlorophyll fluorescence, 820 nm light reflection, and delayed fluorescence synchronization determination. First, according to the maximum photochemical efficiency (F_V/F_M) under high temperature, 35 wheat cultivars were divided into two groups: high-temperature insensitivity and high-temperature sensitivity, and the parameters measured for the two types of wheat cultivars were averaged. The results showed that J and I points of chlorophyll fluorescence induction curves were raised and the maximum quantum yield for primary photochemistry (φP_O), quantum yield for electron transport (φE_o), quantum yield for reduction of end electron acceptors at the PSⅠ acceptor side (φR_o), and performance index (PI_ABS) were significantly reduced in the two types of wheat cultivars under high-temperature stress. Moreover, the rise and decrease extents of high-temperature sensitive type were greater than those of high-temperature insensitive type, indicating that the PSⅡ light energy capture efficiency, the efficiency of the absorbed light energy to drive electrons downstream of the primary electron quinone acceptor Q_A, its efficiency to the PSⅠ end, and the re-reduction ability of the PQ pool decreased more in the leaves of the sensitive wheat cultivars under high temperatures. There was no significant decrease in the maximum decrease slope of the 820 nm light reflection curve (V_PSⅠ) in either types of wheat cultivars, and the maximum increase slope of the 820 nm light reflection curve (V_PSⅡ-PSⅠ) in both types of wheat cultivars significantly decreased. Furthermore, the decline of V_PSⅡ-PSⅠ in the high-temperature sensitive wheat cultivars was greater than in the insensitive ones, indicating that the PSⅠ activity was not affected and the donor side of PSⅠ had a greater extent of damage in the high-temperature sensitive wheat cultivars. Values of both characteristic points of the delayed fluorescence induction curves (I₁ and I₂) decreased. At the same time, I₂/I₁ increased significantly at high temperatures and increased even more in high-temperature sensitive wheat cultivars, indicating that PSⅡ activity decreased and the efficiency of PSⅠ donor-side electron transfer to the end of PSⅠ increased. Based on the complementarity and confirmation of the three research methods, it is concluded that the difference in PSⅡ reaction center activity, PSⅡ light energy capture, and electron transfer from the acceptor side of Q_A to PSⅠ downstream is the main reason for the difference in photosynthetic ability between two types of wheat cultivars under high temperature. The PSⅡ donor side and PSⅠ activity have no direct impact on the high-temperature resistance of wheat. The results of this study help understand the current status of high-temperature resistance of wheat cultivars in the Huanghuai wheat-planting area and provide references for the breeding selection of high-temperature-resistant cultivars and innovation in cultivation techniques.

Effect of shading on the accumulation of Cd, Pb and Zn of Sedum plumbizincicola

CHEN Si, YAN Kai, HE Yongmei, ZHAN Fangdong, ZU Yanqun, LI Yuan, CHEN Jianjun, LI Bo

2022, 30(3): 409-418. doi: 10.12357/cjea.20210579

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Abstract:
This study aimed to investigate the effect of shading on the accumulation characteristics of Cd, Pb, and Zn in Sedum plumbizincicola. S. plumbizincicola has strong tolerance and uptake ability for Zn and Cd, and is a promising remediation plant for Zn- and Cd-contaminated soil. To promote the application of S. plumbizincicola in remediation practices of heavy metal polluted soil of Pb-Zn mining area in Yunnan Province, S. plumbizincicola was planted in the slag field of the Lanping Pb-Zn mining area in Nujiang, Yunnan Province. In the experiment, a shade net was laid to reduce the light intensity by 25%, and the effects of shading on plant biomass and chlorophyll; contents and accumulation of Cd, Pb, and Zn in different organs; as well as subcellular distrubition of Cd, Pb and Zn in leaves and stems were investigated. The results indicated that the shading treatment significantly reduced the Cd, Pb, and Zn contents in the stems and leaves of S. plumbizincicola (P<0.01); and significantly decreased the accumulation of Cd, Pb, and Zn in the stems and leaves by 17.6%−67.4% (P<0.05 or P<0.01). Moreover, compared with the no-shading condition, the Cd and Zn enrichment and transfer coefficients of S. plumbizincicola were significantly reduced when grown under shading conditions (P<0.05). The shading treatment significantly decreased the transport coefficient and biological transfer factor of Pb (P<0.05). Under the shading treatment, the Cd content in the leaf cell wall of S. plumbizincicola was significantly reduced (P<0.05), while the Pb content significantly increased (P<0.05). At the same time, the content of Zn in the organelles and soluble parts of S. plumbizincicola was significantly reduced by 11.8%−57.3% (P<0.05). In the stems and leaves of S. plumbizincicola, the HAc-extractable and HCl-extractable forms of Zn, and NaCl-extractable forms of Cd and Pb were dominant. In addition, the shading treatment increased the content of HAc-extractable Cd in the leaves of S. plumbizincicola by three times (P<0.01) and produced a significant reduction in the content of the water-extractable Cd (P<0.05, P<0.01). In addition, the ethanol-, HAc-, and HCl-extractable Zn forms were reduced by 30.2%−58.6% in the leaves of S. plumbizincicola (P<0.01). Thus, shading reduced vacuolar compartmentalization and cell wall retention in S. plumbizincicola as well as the content of insoluble phosphate-like inert heavy metals, and ultimately reduced the ability of S. plumbizincicola to enrich and transport Cd and Zn.

Determination of volatile oil and non-volatile organic compounds contents and ultrastructure changes in the petals of Dendrobium huoshanense upon Zn application

ZHU Wangsheng, DAI Jun, CHEN Naidong, WANG Jiahong

2022, 30(3): 419-430. doi: 10.12357/cjea.20210486

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Abstract:
The petals of Dendrobium huoshanense have great potential as functional food because of their pleasant fragrance and health values. To obtain high-quality raw materials for functional food production, more attention is being directed toward improving the food quality traits of D. huoshanense petals under field cultivation conditions. In this study, we investigated the effects of Zn application on the volatile oil and non-volatile organic compounds contents in the petals of D. huoshanense. Furthermore, the mechanism was also studied from the perspective of petal ultrastructural changes. Volatile oil constituents were investigated using gas chromatography-mass spectrometry. The contents of non-volatile organic compounds, including soluble sugar, free amino acids, and phenolic compounds, were investigated using chemical analysis methods. Ultrastructural changes were observed via transmission electron microscopy. The results showed that Zn application increased the yield of volatile oils (primarily terpenes and their derivatives) and non-volatile organic compounds from the petals of D. huoshanense. Different levels of Zn treatments changed the production of the above-mentioned volatiles and non-volatile compounds to varying degrees. The maximum rate of increase in the content of volatile oil, soluble sugars, free amino acids, and phenolic compounds was 28.57%, 33.53%, 28.89%, and 58.41%, respectively. Ultrastructural changes at the cellular level showed that Zn application promoted vacuole fusion and increased the production of mitochondria, starch grains, and lipid droplets. In conclusion, Zn application improves the production of volatile oils and non-volatile organic compounds. Ultrastructural analysis has provided new anatomical insights into the production of volatile oils and non-volatile organic compounds.

Impact of substitution of synthetic nitrogen fertilizer with organic fertilizers on nitrogen loss from sloping cropland of purple soil

HU Dongni, DONG Zhixin, ZHU Bo

2022, 30(3): 431-440. doi: 10.12357/cjea.20210592

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Excessive N fertilizer application not only increases crop productivity, but also induces substantial environmental N losses that cause large environmental pollution risks. This study aimed to examine the effects of substituting synthetic N fertilizers with organic fertilizers on the reduction in environmental N losses from croplands in purple soil areas. Therefore, we conducted a one year field investigation to measure N-loss pathways and fluxes, crop productivity, and soil environmental variables in a wheat-maize rotation system under long-term different fertilization regimes with the same N rate, including the control (no fertilizer; NF); synthetic N fertilizer only (N); pig manure substituting 100% synthetic N fertilizer (pig manure; OM); regular synthetic N, P, and K fertilizer (NPK); combination of pig manure with synthetic N, P, and K fertilizer (OMNPK; pig manure substituting 30% synthetic N fertilizer); and combination of straw residue returned with synthetic N, P, and K fertilizer (CRNPK; straw residue substituting 15% synthetic N fertilizer). The results showed that N losses via surface runoff and sediment were in the range of 1.12–3.52 kg(N)∙hm⁻² and 1.48–7.26 kg(N)∙hm⁻², respectively. The N leaching losses via interflow ranged from 12.53 to 76.72 kg(N)∙hm⁻², which were over 10 times greater than those for surface runoff; nevertheless, N leaching losses accounted for 90.6% of the total hydrological N losses. These results indicate that N leaching via interflow is the predominant pathway of hydrological N losses, thereby highlighting that sloping cropland of purple soil is one of the hotspots of N leaching losses from agricultural soils in China. Compared with that of the NPK treatment, the substitution of synthetic N fertilizer with organic fertilizers (OM, OMNPK, and CRNPK treatments) decreased the total hydrological N losses by 32.1%, 27.5%, and 21.2%, respectively. This was mainly because practices with substitution of synthetic N fertilizer with organic fertilizers significantly decreased N leaching losses via interflow compared with the application of synthetic N fertilizer only. Furthermore, considering the crop yields, the substitution of synthetic N fertilizer with organic fertilizer treatments (OM, OMNPK, and CRNPK treatments) significantly increased the total annual crop yields by 23.0%, 17.8%, and 4.1%, respectively, and decreased the yield-scaled total hydrological N losses by 24.3% to 44.8%. Therefore, the long-term substitution of synthetic N fertilizer with organic fertilizer can not only increase the crop productivity of both wheat and maize, but also decrease environmental N losses, thereby decreasing the risk of agricultural non-point source pollution in the purple soil region. Overall, the substitution of synthetic N fertilizer with organic fertilizers can be recommended as an optimized agricultural N management strategy to reduce synthetic N fertilizer rates and improve N use efficiency in agricultural systems of the purple soil region.

Identification of high natural-value farmland and its spatial distribution pattern: Taking Yunnan Province as an example

FANG Yishu, AI Dong, YANG Yuting, SUN Weijian, DAI Yao

2022, 30(3): 441-450. doi: 10.12357/cjea.20210501

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Abstract:
Farmland protection in China faces huge challenges, and the quantity and quality control of cultivated land is a fundamental prerequisite for protection. At the same time, to promote the sustainable development of agriculture in China, it is necessary to enhance the resilience of agricultural ecosystems. Therefore, from the perspective of natural value, it is important to explore the identification and spatial distribution of high natural-value farmland. This article drew on researches into farmland protection by many scholars, introduced the concept of high natural-value farmland, and explored the role of high natural-value farmland in the construction of China’s farmland ecosystem. Taking Yunnan Province as an example, ArcGIS and InVEST models were used for quantitative analysis as an identification method for exploring high natural-value farmland in Southwest China. It used four sets of land use data in 2009, 2012, 2015, and 2018 to calculate the quality of farmland habitat in each year, and the spatial distribution patterns of high natural-value farmland in each year were studied. The main conclusions were as follows. 1) According to existing literature, it was concluded that high natural-value farmland was mainly divided into the following three types: ① farmland with a high proportion of semi-natural vegetation; ② farmland with low-intensity agriculture or small-scale semi-natural farmland mosaic; and ③ farmland for maintaining the survival of rare species. At the same time, high natural-value farmland is ecologically fragile and usually presents a small-scale mosaic form. 2) According to the evaluation results, from the perspective of the time pattern, the proportion of high natural-value farmland changed little from year to year, with an average of 10.86%, mainly small patches adjacent to forest land and water. Farmland with a low natural-value accounted for the largest proportion (82.43%). It was widely distributed in Yunnan Province and had a high production value. This showed that the “ecological-production” value of farmland in Yunnan Province varied considerably. The production value of concentrated contiguous areas was high, but the natural value was low, while the production value of small plots adjacent to forest land and relatively fragmented waters was low, but the natural value was high. 3) From the perspective of spatial pattern, the natural value of farmland in Yunnan Province is generally low; moreover, the proportion of farmland with high natural value is relatively low. It is distributed in parts of northwestern and northeastern Yunnan. The patches are fragmented and scattered around the contiguous farmland. Otherwise, there are two groups of factors that affect the distribution of high natural-value farmland. One group includes human factors: economic growth, urban development, and environmental pollution. The second group includes natural factors: topography, changes in precipitation, temperature distribution, and vegetation cover. Finally, the study analyzed farmland ecosystem biodiversity and agricultural cultural heritage protections from the perspective of natural resources. We proposed policies for farmland protection at different levels or returning farmland to forests, thus realizing the protection concept of “co-governance and joint construction, and the same management and protection.”

A spatial random forest interpolation method with semi-variogram

WANG Mingxin, FAN Chao, GAO Bingbo, REN Zhoupeng, LI Fadong

2022, 30(3): 451-457. doi: 10.12357/cjea.20210628

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Abstract:
The strong spatial heterogeneity of soil environmental variables causes difficulties in improving spatial interpolation accuracy. It is difficult to obtain a high interpolation accuracy by leveraging spatial correlation and spatial heterogeneity. Machine learning methods can fuse the information of multi-dimensional auxiliary variables to improve the interpolation accuracy of soil attributes, but they cannot effectively utilize the spatial position relationship information to further improve the interpolation accuracy. Based on the random forest spatial prediction framework, this study combined the spatial semi-variogram with the random forest algorithm and proposed a spatial random forest interpolation method with a semi-variogram. Taking soil heavy metal data from the Xiangtan County of Hunan Province as an example, the proposed method was used to implement spatial interpolation of soil Cr. The interpolation accuracy was compared with the random forest method, distance-based random forest spatial prediction method, ordinary Kriging method, and regression Kriging method. The results showed that the accuracy was improved by more than 10% compared with the traditional Kriging method. Compared with the new machine learning spatial interpolation method, the accuracy was improved by more than 5%. Furthermore, the mapping of the proposed results had a more reasonable spatial distribution and detailed information. Thus, we concluded that the proposed method could effectively combine auxiliary variable information and spatial location information and improve the interpolation accuracy of soil environmental variables.

Impact of water-saving irrigation on the planting of food crops based on the regulation effect of agricultural labor resources

XI Yunxiao, LIU Jing, CHANG Ming

2022, 30(3): 458-469. doi: 10.12357/cjea.20210693

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Abstract:
In recent years, the rapid development of agricultural water-saving irrigation in China has effectively saved water resources and increased the comprehensive production capacity of land, thereby providing a strong guarantee for the country’s food security. However, relevant research has not yet reached a consensus on the impact of water-saving irrigation measures on the sown area of grain crops. Therefore, based on provincial panel data from 2006 to 2019, this study used the two-way fixed effect model and the moderating effect model to empirically analyze the impact and mechanism of water-saving irrigation measures on the sown area of grain crops with agricultural labor resources as the moderating variable. The study found that 1) in the study year, water-saving irrigation measures could significantly promote the increase in the sown area of grain crops. The promoting effect was more significant effect under less agricultural labor resources, indicating a negative regulatory role of agricultural labor resources. 2) The promoting effect of water-saving irrigation measures on the sown area of grain crops and the negative regulatory effect of agricultural labor resources were found to be mainly reflected in wheat and corn, and their effects on rice were not significant. 3) By re-differentiating the water-saving irrigation measures into modern (spray irrigation, micro-irrigation, low-pressure pipe irrigation) and traditional (canal seepage control) types, it was found that modern water-saving irrigation measures with labor-saving effects could increase the sown area of wheat and corn, and agricultural labor resources still had a negative regulatory effect; traditional water-saving irrigation measures did not have clear labor-saving effects and could only promote an increase in the wheat planting area. Based on the above conclusions, we believed that in the context of the large non-agricultural transfer of agricultural labor resources at this stage, different types of water-saving irrigation measures could be built according to local conditions to promote the sown area of grain crops, thereby ensuring national food security for the realization of rural revitalization and socialist modernization.

Successful experience and policy inspirations of organic agriculture in the Unite States from the perspective of green development of agriculture

MA Jian, YU Hao, LUO Xiaojuan

2022, 30(3): 470-483. doi: 10.12357/cjea.20210509

Abstract(400) HTML (181) PDF(83)

Abstract:
The development of organic agriculture is conducive to restoring the ecological balance; it is also important in improving the quality and safety of agricultural products, realizing the green development of agriculture, and comprehensively promoting rural revitalization in China. To achieve the overall sustainable development of agriculture, the United States began organic agriculture development in the 1940s. After more than 80 years, some progress has been made, notably in six areas: production, market sales, trade interaction, standard certification management, financial subsidies, and scientific research. The main experience of United States organic agriculture includes improving agricultural legislation to build the legal basis of sustainable agricultural development, implementing organic agriculture assistance projects through financial subsidies to reduce production costs during organic conversion, and encouraging farmers to choose organic agriculture. In addition, innovations in organic technology and improvements in organic scientific research are critical to the industry. At the same time, the international certification and recognition of organic standards have been actively promoted, the world’s first market scale has been created, and the internationalization level of organic agriculture has been improved. However, organic agriculture in the United States is still a small industry under the national agricultural layout, especially regarding the area of organic agricultural land. Moreover, the number of organic farms accounts for a low proportion in the whole country, and their distribution in various states is uneven. For instance, the scale of organic farmland and the number of organic farms in the West, Midwest, and Northeast are clearly better than those in the South. Meanwhile, there is also an imbalance in the import and export trade structures of organic agricultural products. Therefore, under the data analysis and literature review, this paper believes that there are three main reasons for the above problems in the United States: the high operating cost of organic agriculture, the weak competitive advantage of organic agricultural products, and the limited technical support and financial investment. Based on these outcomes, the following suggestions are put forward for the high-quality development of organic agriculture in China: first, cultivating new organic agriculture business organizations and broadening the marketing channels of organic products; second, establishing the top-level design concept and building an accurate policy support system; third, promoting organic agriculture legislation, strengthening scientific research investment and technological innovation, and improving the organic certification system and promoting international certification and accreditation actively.

Evaluation of farmers’ subjective willingness to protect important agricultural heritage systems: A case study of the Dike-Pond Agricultural System, Foshan, Guangdong

SU Yanfang, WANG Siyuan, LI Erna, LIAO Sentai

2022, 30(3): 484-494. doi: 10.12357/cjea.20210472

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Abstract:
Farmers play an essential role in multi-stakeholder collaborative mechanisms for the protection of important agricultural heritage systems. Investigating and evaluating the subjective willingness of farmers to protect agricultural heritage systems is of great significance for guiding the protection and sustainable development of important agricultural heritage systems. However, insufficient farmer participation has caused heritage protection to face various practical challenges, and it is necessary to study the subjective willingness of farmers. Using the analytical framework of farmers’ participation in heritage protection under situational interaction, this study employed the Dike-Pond Agricultural System in Foshan, Guangdong (one of China’s Nationally Important Agricultural Heritage Systems) as an example and adopted the Q methodology for research design. Farmers were invited to rank the Q statements of heritage protection voluntarily after in-depth interviews. The Q-Sorts data were analyzed using the PQ Method 2.35 software, and the cognition, emotion, attitude, and behavior of farmers with different protection intentions were further discussed and compared. The results showed the following: 1) The software extracted four representative factors. Their eigenvalues were 10.334, 4.028, 2.741, and 1.891, and four factors were accepted and interpreted after factor rotation. According to the scores of each statement, farmers’ protection willingness was divided into four types: potential protection willingness oriented, avoidance protection willingness oriented, native protection willingness oriented, and development protection willingness oriented. 2) The willingness of farmers to protect the heritage was closely related to their age, educational background, and work in agriculture. Among them, elderly small-scaled farmers mainly have low protection willingness, while large-scaled farmers were groups with potential protection willingness. 3) There were obvious differences in the three aspects of cognition, attitude, and behavior among farmers with different degrees of willingness to protect. Native protection willingness-oriented and development protection willingness-oriented farmers had a higher awareness of heritage protection than the other farmers, but the difference was that they focused on different protection methods. Avoidance protection willingness-oriented farmers did not pay attention to heritage protection and emphasized the role of the government. Among them, weak cognition and livelihood difficulties were the main reasons for farmers’ low willingness to protect. The innovative aspect of this study was to comprehensively use qualitative and quantitative methods of Q methodology to design research to explore farmers’ willingness to protect from their subjective vocabulary and summarize and analyze different protection willingness types. To increase the willingness of farmers to protect heritage sites and fulfill their role in protecting the Dike-Pond Agricultural System, it is necessary to improve farmers’ understanding of important agricultural heritage systems, strengthen the livelihood guarantees for farmers in heritage areas, stimulate the protection potential of farmers with potential protection willingness, and enhance their ability to participate in heritage protection.

2022 Vol. 30, No. 3