中国生态农业学报(中英文)

Microplastics in agroecosystem: Research status and future challenges

LYU Yihan, ZHOU Jie, YANG Yadong, ZANG Huadong, HU Yuegao, ZENG Zhaohai

2022, 30(1): 1-14. doi: 10.12357/cjea.20210442

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Abstract:
Microplastics (MPs) pollution has attracted global attention in recent years. Despite the remarkable benefits arising from the production of plastic for film mulching, irrigation, and organic fertilizer application, there are increasing concerns associated with the vast amount of plastic entering the agroecosystems and its subsequent potential environmental problems. More specifically, MPs (particles<5 mm in size), typically formed from the disintegration of larger plastic debris by tillage and UV radiation, accumulate in agroecosystems and eventually enter the food chain, threatening human and animal health. On the basis of the current evidence, we summarized the source, abundance, mitigation, and detection methods of MPs in agroecosystems. We evaluated the potential ecological risks of MPs to crop growth, microbial activity, soil nutrient cycling, and greenhouse gas emissions. It is found that MPs could either directly or indirectly impact the plant-soil-microbe interactions once incorporated into soil, through the following mechanisms: First, owing to their chemical inertia and structural characteristics, MPs have been recognized as carriers of hazardous substances (e.g., organic pollutants, heavy metals, and pathogens), in addition to their toxic additives (i.e., plasticizers). After making contact with the soil, the migration of plastic particles likely facilitates the transport of sorbed contaminants and contributes to a great ecological risk for crop growth, enzyme activity, and microbial activity. MPs could also alter soil physicochemical properties, that is, they may change the soil aggregation stability, bulk density, and water holding capacity, resulting in diverse effects on microbial functions and plant growth. MPs could also serve as a novel ecological habitat for microorganisms living at the soil-plastic interface (i.e., microplastic spheres), allowing the formation of unique microbial communities. The second mechanism involves the fact that MPs are particles that contain a high carbon content, typically around 90%, making them relatively unique in relation to other pollutants as they can drive diverse consequences for other element cycles (e.g., nitrogen and phosphorus). Direct effects are likely to be minimal because MPs contain mostly negligible amounts of nitrogen and phosphorus. However, alterations in soil structure and physicochemical properties would be expected to change microbial processes, including the nitrogen and phosphorus related enzymes, since soil properties indirectly control soil oxygen availability, which in turn influences CO₂, N₂O, and CH₄ formation. Due to the high degree of variability in polymer type, size, shape, and concentration, the impacts of MPs on soil biogeochemical processes and their underlying mechanisms remain unclear, and further detailed research is therefore needed. Thus, we propose some research priorities regarding the future challenges of MPs in agroecosystems.

Effects of combined application of microbial organic fertilizer and chemical fertilizer on ammonia volatilization in a paddy field with double rice cropping

ZHANG Jing, ZHU Xiao, SHEN Jianlin, LI Yong, WANG Juan, WU Jinshui

2022, 30(1): 15-25. doi: 10.12357/cjea.20210355

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Abstract:
Ammonia (NH₃) volatilization is one of the significant causes of nitrogen (N) loss in farmland. When NH₃ is released into the atmosphere, it reacts with acid gases to form secondary aerosols, which has a critical impact on air quality. This study aimed to simultaneously evaluate the effects and identify key mechanisms of combined applications of microbial organic fertilizer and chemical fertilizer on reducing ammonia volatilization in paddy fields. A two-year field experiment was conducted in a typical double-cropping rice field in Changsha County, Hunan Province. There were four fertilization treatments: no nitrogen fertilizer (CK), surface application of chemical nitrogen fertilizer (CON), a substitution of 40% chemical fertilizers with microbial organic fertilizers and surface application of chemical fertilizer (CB), and 30% reduction of chemical fertilizer with a substitution of 40% chemical fertilizers with microbial organic fertilizers and deep application of chemical fertilizer (RBD). NH₃ volatilization was measured using the intermittent closed chamber ventilation method in a two-year rice growing period (2019−2020), and the ammonium-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) concentrations in the surface water were also measured. The results showed that under the same nitrogen application rate, NH₃ volatilization was significantly (P<0.05) reduced in CB treatment compared to CON treatment, and the rice grain yield for CB treatment was not significantly different from that for CON treatment in all the four rice seasons. NH₃ volatilization was lowest in RBD treatment compared to CON and CB treatments. The differences in rice grain yield between CON and RBD treatments was significant (P<0.05) for the late-rice season in 2019, while the differences were not significant for the remaining three seasons. In the early-rice season, the average cumulative NH₃ volatilization losses of CON, CB, and RBD were 33.1 kg(N)∙hm⁻², 24.8 kg(N)∙hm⁻² and 12.2 kg(N)∙hm⁻², respectively. The NH₃volatilization losses of CB and RBD decreased by 25.2% and 63.2%, respectively, compared to CON. In the late-rice season, the average cumulative NH₃ volatilization losses of CON, CB, and RBD treatments were 50.4 kg(N)∙hm⁻², 32.4 kg(N)∙hm⁻² and 14.7 kg(N)∙hm⁻², respectively. The NH₃ volatilization losses of CB and RBD decreased by 35.6% and 70.9%, respectively, compared to CON. The magnitude of NH₄⁺-N concentrations in the surface water showed the same trend with the NH₃ volatilization across the treatments in the rice seasons. Furthermore, there were significantly (P<0.01) positive correlations between these two parameters, which indicated that application of microbial organic fertilizer as well as deep application of chemical nitrogen fertilizer played a role in reducing NH₄⁺-N concentrations in the surface water, and thus, reduced NH₃ volatilization. Based on the two-year field experiment conducted here, this study revealed that microbial organic fertilizer combined with deep application of nitrogen-reduced fertilizer can reduce ammonia volatilization by 60%, while maintaining rice yields. Thus, in conclusion, microbial organic fertilizers combined with deep applications of reduced nitrogen fertilizer can effectively reduce the application rate of nitrogen fertilizer and mitigate ammonia volatilization in double-cropping paddy fields.

Effects of interspecific maize and soybean interactions on the community structure and diversity of rhizospheric bacteria

LIN Weiwei, LI Na, CHEN Lishan, WU Zeyan, LIN Wenxiong, SHEN Lihua

2022, 30(1): 26-37. doi: 10.12357/cjea.20210222

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Abstract:
Studies on the effects of the interspecific interactions of maize||soybean intercropping on the rhizosphere microbial community structure and their relationship with crop yield are of theoretical and practical significance for elucidating the yield effects of interspecific crops in intercropping systems. The aim of this study was to explore the changes in microbial community structure in the rhizospheres of soybean and maize planted under an intercropping system (soybean||maize) with a 2∶3 line ratio and a randomized design pattern with three types of partitions between two crop roots. The intercropping partitions were a mesh barrier (MB, with exchange of root extudates without roots interaction) or a polythene film barrier (PB, without exchange of root extudates and roots interaction) to separate the maize roots from soybean roots or no barriers (NB) between the roots. An independent monoculture (M) was set up as a control. BIOLOG and terminal restriction fragment length polymorphism (T-RFLP) assays were used to investigate the microbial community diversity in the maize||soybean rhizospheres. The results showed that the land equivalent ratios (LERs) under NB, MB, and PB conditions were 1.39, 1.13, and 0.98, respectively, at a plant row ratio of maize||soybean of 2∶3. These findings suggest that the LER increases with increased interspecific root interactions from PB to NB under the same intercropping pattern. Further analysis revealed that the microbial diversity and evenness indexes in the rhizosphere of both intercropped maize and soybean similarly increased with the increase in interspecific root interactions from PB to NB. Average well color development (AWCD) analysis showed that the rhizospheric microbial communities under NB and MB conditions had the strongest overall ability to utilize carbon sources as substrates, whereas those under PB and M conditions had a lower ability in this regard. The enhancement of interspecific root interactions increased the ability of rhizospheric microbes of intercropped soybean to utilize amines, polymers, amino acids, and carbohydrates (four types of carbon-source substrates) by 181.01%, 32.6%, 37.84%, and 78.28%, respectively. However, the capability of microbes in the intercropped soybean rhizosphere for utilizing two other carbon sources (phenols and carboxylic acids) decreased. Moreover, the ability of the microorganisms in the intercropped maize rhizosphere to utilize carboxylic acids, carbohydrates, and amines increased by 46.26%, 6.54%, and 15.84%, respectively, whereas their ability to utilize phenols, polymers, and amino acids decreased. T-RFLP analysis revealed a significant increase in the abundance of dominant bacteria, such as Rhodococcus (Actinomycetes) and Halobacillus (Firmicutes), in the rhizosphere of intercropped soybean under NB compared with that under PB; whereas the abundance of beneficial dominant bacteria, such as Rhodococcus (Actinomycetes) and Bacillus (Spirochetes), markedly increased in the rhizosphere of intercropped maize under NB conditions compared with that under PB conditions. As a result, the crop yield and LER increased under intercropping conditions.

Research progress on the formation mechanism of subsurface flow and its eco-hydrological effects

ZHAO Yuhan, CAO Jiansheng, ZHU Chunyu, YANG Hui

2022, 30(1): 38-46. doi: 10.12357/cjea.20210277

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Abstract:
Water is an important basic resource for human survival and economic and social development. However, the water cycle has undergone profound changes under the dual influence of climate change and human activities. Subsurface flow, a key part of the runoff process and a major replenishment source for rivers and lakes, has a critical impact on runoff formation, water conservation, and nutrient transport. The understanding of subsurface flow processes is an important and popular topic in the fields of hydrology, soil science, and ecohydrology, however, it is a complex scientific problem that is difficult to disentangle. In this article, it was found that from 1990 to 2020, the number citation frequency of published articles related to subsurface flow in China have gradually increased. The researches mainly focused on the environment, engineering, water resources, and agriculture, focusing on topics such as purplish soil, wetlands, and nitrogen. In addition, we analyzed the main factors affecting subsurface flow formation, including soil, topography, vegetation, rainfall, etc. Furthermore, we summarized several ecological and hydrological effects of interflow, including the soil nutrient transport effect, soil and water conservation, runoff regulation, and hydrological forecasting effect. Finally, we highlighted some limitations in current research on interflow and discussed future research priorities, ultimately providing an important scientific basis for crucial ecosystem restoration and water conservation improvements.

Variation characteristics of soybean yield since 1952 and its influencing factors in China

QIN Tingting, CAO Xinyue, ZHOU Zequn, CHU Chaoqun, FANG Yutong, QU Le’an, ZHI Junjun, WANG Zhen, GENG Tao

2022, 30(1): 47-56. doi: 10.12357/cjea.20210227

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Abstract:
Over the past several decades, the consumers’ demand for soybeans has grown rapidly in China, resulting in a significant increase in the gap between production and demand. Therefore, increasing the total soybean output is of critical importance to ensure food security. Given that it is difficult to increase the total area of cultivated land in China, improving soybean yield per unit area land has become the primary measure for increasing the total soybean output. However, the determinants that directly affect soybean yield, the regional spatial heterogeneity of yield remain unclear. In this study, data from agricultural statistical yearbooks at both the provincial and prefecture levels in China as well as meteorological data (e.g., temperature, precipitation, and sunshine duration) from 1952 to 2017 (comprising 1952, 1965, 1978, 1990, 2000, 2010, and 2017) were collected, whereupon 13 factors closely related to soybean production were selected from the perspective of planting management measures, natural factors, scientific and technogical levels, social factors, and economic factors. Several boosted regression tree models were built to quantify the relative importance of each factor and to determine the mechanism through which it influenced soybean yield; to analyze the variation characteristics of soybean yield; and to reveal the spatiotemporal characteristics of key driving forces across the national scale and among the four major soybean-producing areas (i.e., the northern spring soybean area, the summer soybean area in the Huang-Huai-Hai Basin, the spring and summer soybean area in the Yangtze River Basin, and the southern soybean area) over a long period since 1952. The following results were obtained. 1) The coefficient of variation of soybean yields in different years ranged from 34.1% to 73.2%, indicating that there were substantial differences in yield across the regions in China. The boosted regression tree model could effectively explain 43.3% of the soybean yield variability and quantitatively revealed the nonlinear relationship between each factor and soybean yield in the national scale. 2) The most important factor affecting soybean yield in China since 1952 was the soybean sown area as a percentage of the total crop sown area (relative importance of 20.9%), followed by the illiteracy rate (18.9%) and fertilizer consumption (pure amount) per hectare (10.7%). 3) Spatial differences existed in the dominant driving factors of soybean yield among different main production areas. The main driving factors of the northern spring soybean area were the total power of agricultural machinery per hectare (13.1%) and the illiteracy rate (11.8%); those for the summer soybean area in the Huang-Huai-Hai Basin were the fertilizer consumption (pure amount) per hectare (25.6%) and pesticide consumption (pure amount) per hectare (18.4%); those for the spring and summer soybean area in the Yangtze River Basin were the R&D expenditure as a percentage of regional GDP (21.5%) and the effective irrigation area as a percentage of the crop sown area (14.3%); and those for the southern soybean area were the fertilizer consumption (pure amount) per hectare and the primary industry as a percentage of regional GDP (13.3%). 4) The soybean sown area as a percentage of the total crop sown area was the most important factor that affected soybean yield during 1952–2017, both before and after the reformation and opening up of China. Additionally, the illiteracy rate and fertilizer consumption (pure amount) per hectare were two other important factors for the period before the reformation and opening up of the country, whereas the total power of agricultural machinery per hectare and annual average temperature were important factors afterwards. This study revealed the determinants of soybean yield and its spatiotemporal heterogeneity in China since 1952 and determined the effective measures for improving the yield of this important crop. These findings should be useful for soybean production-related departments at both the provincial and prefecture levels in China for improving the rational usage of fertilizers and pesticides, increasing the level of mechanization, and enhancing the knowledge level of agricultural producers.

Responses of photosynthetic fluorescence characteristics, pollination, and yield components of maize cultivars to high temperature during flowering

MU Xinyuan, MA Zhiyan, ZHANG Lanxun, FU Jing, LIU Tianxue, DING Yong, XIA Laikun, ZHANG Fengqi, ZHANG Jun, QI Jianshuang, ZHAO Xia, TANG Baojun

2022, 30(1): 57-71. doi: 10.12357/cjea.20210313

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Abstract:
High temperatures during the flowering stage are likely to have a significant negative impact on maize growth and development, which is one of the most important factors affecting maize high and stable yield. This study aimed to evaluate the response of photosynthetic fluorescence characteristics, pollination, and yield components of different maize cultivars to high temperatures during the flowering stage to provide a theoretical basis for the stable and high yield of summer maize production under climate warming in the future. This study used heat-resistant maize cultivars, ‘XD20’ and ‘ZD958’, and heat-sensitive maize cultivars, ‘XY335’ and ‘NH101’, as research materials in a greenhouse. Then the influence of high temperature during the flowering stage (from 7 d before silking to 7 d after silking) on grain yield, leaf photosynthetic fluorescence characteristics, pollination, dry matter mass were investigated. High temperature during flowering significantly reduced the kernel number per ear and significantly increased the blank stem rate of different summer maize cultivars, leading to a significant decrease in grain yield. The grain yield decline of heat-resistant cultivars was less than that of heat-sensitive cultivars. Compared with the control, the kernel number per ear of the heat-resistant and heat-sensitive cultivars under high temperature significantly decreased by 22.25% and 67.18%, respectively, the 100-grain weight decreased by 2.03% and 5.00%, the blank stem rate significantly increased by 206.37% and 283.00%, and the grain yield significantly decreased by 31.84% and 67.33%, respectively. High temperature during flowering reduced effective green leaf area and chlorophyll content, impaired photosystem II, and significantly decreased the photosynthetic performance of the four maize cultivars. Under high-temperature stress, the leaf area of the heat-resistant and heat-sensitive cultivars decreased by 0.79% and 7.46%, the chlorophyll content decreased by 4.53% and 5.16%, the net photosynthetic rate (P_n) decreased by 19.9% and 31.6%, and the maximum photochemical efficiency (F_v/F_m) of PS Ⅱ decreased by 0.79% and 1.47%, respectively. After the high-temperature stress, some parameters of photosystem Ⅱ recovered, and chlorophyll content and P_n returned to the control level. High temperatures during flowering had little effect on the tassel branch number, tassel floret number, and ear filament number; but shortened the pollen shedding duration, lengthened the anthesis-silking interval, and significantly reduced the setting rate. Under high-temperature stress at the flowering stage, the tassel branch number of heat-resistant and heat-sensitive cultivars decreased by 4.76% and 13.66%, the tassel floret number decreased by 8.53% and 8.32%, the tear filament number decreased by 6.10% and 7.17%, the pollen shedding duration decreased by 10.81% and 26.94%, the anthesis-silking interval increased by 58.93% and 85.00%, the pollination duration decreased by 17.91% and 58.95%, and the kernel setting rate decreased by 14.77% and 63.10%, respectively. Shortening pollination duration was the main reason for the lower kernel setting rate. High temperature during flowering significantly reduced dry matter mass and the distribution ratio of dry matter to the ear or grain of four maize cultivars. After high-temperature stress, the dry matter mass per plant of heat-resistant and heat-sensitive cultivars decreased by 13.7% and 17.6%, and the distribution ratio of dry matter in the ear decreased by 49.16% and 56.51%, respectively; at maturity, the dry matter mass per plant decreased by 16.40% and 25.73%, and the distribution ratio of dry matter in the grain decreased by 7.08% and 46.80%, respectively. High temperature during flowering decreased the photosynthetic performance, inhibited the coordinated development of male and female panicles, and significantly reduced kernel setting rate, kernel number per ear, and grain yield. Compared with heat-sensitive cultivars, heat-resistant cultivars had higher photosynthetic capacity and pollination fruiting ability under high-temperature stress; their yield was less affected by high temperature.

Effect of shading on saponin content and biochemical indexes of Paris polyphylla Smith var. chinensis (Franch.) Hara in northern Zhejiang

CHEN Wen, LIU Shouzan, GENG Dongjie, GU Yiwen, LI Zhe, PAN Jieyu, BAI Yan

2022, 30(1): 72-81. doi: 10.12357/cjea.20210323

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Abstract:
Paris polyphylla Smith var. chinensis (Franch.) Hara is a rare traditional herb, the rhizome of which (named Paridis Rhizoma) is commonly used for its antitumor and anti-inflammatory effects. P. polyphylla mainly comprises saponins, the production of which is affected by the intensity of light. Therefore, the determination of the most suitable shading degree for this herb plant in northern Zhejiang can lay the foundation for the promotion of its’ artificial cultivation. In this study, the effects of different degrees of shading on the accumulation of saponins in P. polyphylla and on changes in their biochemical indices were explored. The plants were maintained at the arboretum test site of Zhejiang Agriculture and Foresty University, China (30°15ʹN, 119°43ʹE) from June to September 2019. Black shading nets were used to create different shading conditions (70%, 80%, and 90%). Six-year-old P. polyphylla plants were used as the test materials, and their contents of saponins, photosynthetic pigments, malondialdehyde (MDA), and osmotic adjustment substances as well as antioxidative enzymes activities were measured to determine their response to shading conditions.The results showed that the saponin content was negatively correlated with the superoxide dismutase (SOD) activity, peroxidase (POD) activity, and MDA content (P<0.01), but positively correlated with the chlorophyll a/b ratio, catalase (CAT) activity, and soluble protein content (P<0.05). The 80% shading condition was most beneficial to saponin accumulation, as evidenced by the highest total saponin content (7.19 mg·g⁻¹) in the plant compared with that yielded by the 70% (3.79 mg·g⁻¹) and 90% (1.85 mg·g⁻¹) shading conditions. The contents of all types of saponins were the highest under the 80% shading condition (polyphyllin Ⅰ: 1.45 mg·g⁻¹; polyphyllin Ⅵ: 2.52 mg·g⁻¹; and polyphyllin Ⅶ: 3.22 mg·g⁻¹). Additionally, the contents of photosynthetic pigments (total chlorophyll: 4.72 mg·g⁻¹) and soluble proteins (11.28 mg·g⁻¹) were higher in plants under 80% shading than in those under 70% (total chlorophyll: 2.94 mg·g⁻¹; soluble protein: 9.23 mg·g⁻¹) and 90% shading (total chlorophyll: 3.81 mg·g⁻¹; soluble protein: 7.72 mg·g⁻¹). However, the activities of POD (2.89 U·g⁻¹·min⁻¹) and SOD (105.01 U·g⁻¹·min⁻¹), contents of MDA (11.90 μmol·g⁻¹) and proline (8.88 mg·g⁻¹) in plants under 80% shading were lower than those in plants under 70% (POD: 3.20 U·g⁻¹·min⁻¹; SOD: 123.38 U·g⁻¹·min⁻¹; and MDA: 13.89 μmol∙g⁻¹; proline: 11.48 mg·g⁻¹) and 90% shading (POD: 4.90 U·g⁻¹·min⁻¹; SOD: 165.09 U·g⁻¹·min⁻¹; and MDA: 15.46 μmol∙g⁻¹; proline: 12.68 mg·g⁻¹). Moreover, compared with the plants treated with 80% shading, those treated with 70% and 90% shading showed significantly lower contents of total saponins. In summary, different degrees of shading significantly influenced the P. polyphylla saponin content and primary metabolism. The data from this study provide a theoretical reference for the artificial cultivation and quality improvement of P. polyphylla in northern Zhejiang.

Effects of nano-Se foliar spraying and photoperiod on lettuce growth and quality

LIANG Yi, HAO Wenqin, SHI Yu, WANG Xunjun, HAN Ruifeng, CHENG Yongsan, ZHANG Yi

2022, 30(1): 82-91. doi: 10.12357/cjea.20210366

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Abstract:
Nano-Se (nano-selenium) and illumination length are two important factors those are used for improving vegetable nutritional quality and yield. Although the effects of exogenous Se and photoperiod on the growth and quality of lettuce are well-studied separately, there are few studies reporting on the combination effect of these two factors. As such, in this study, we assessed the interaction of nano-Se and photoperiod on the growth and quality of lettuce; in addition, we derived the optimal combination of photoperiod and nano-Se concentration for the growth of lettuce, with the aim of providing a theoretical basis and technical starting point for plant factories to apply nano-Se under lighting systems. To accomplish this, we used ‘Italian Bolting-resistant’ lettuce (Lactuca sativa L.) in a hydroponics system with three photoperiods (light/dark: 12 h/12 h, P1; 16 h/8 h, P2; or 20 h/4 h, P3). In addition, the lettuce leaf surfaces were treated with a spray containing 0 μmol∙L⁻¹ (N1), 24 μmol∙L⁻¹ (N2), or 48 μmol∙L⁻¹(N3) of nano-Se. The two factors were randomly combined, resulting in a total of nine photoperiod and nano-Se treatment combinations. The results revealed that first, the P2N3 treatment had a positive effect on plant height, aboveground fresh weight, underground fresh weight, and root activity. The P2N2 treatment resulted in plant height to increase significantly (P<0.05) by 13.16% and 21.74% when compared to the P1N2 and P3N2 treatments, respectively; and the P2N3 treatment resulted in the lettuce fresh weight to increase by 56.13% and 15.14% when compared to the P1N3 and P3N3 treatments, respectively, but the difference was not significant. Second, prolonging the light period increased the chlorophyll content of the lettuce, with the highest chlorophyll a and chlorophyll b contents being found in the P3N3 treatment, whereas the highest carotenoid content was found in the P3N2 treatment. Third, the soluble sugar, K, Na, and Fe contents in the lettuce increased significantly under P2 treatment, whereas the nitrate content decreased significantly (P<0.05). The P3 treatment increased the soluble protein content and reduced the sugar content. But the longer illumination period was not conducive to an accumulation of amino acids, Ca, Mg, Zn, Fe, nor Mn in the lettuce, instead, inhibitory effects were displayed. The P2N3 treatment resulted in an increased content of various amino acids in the lettuce. Interestingly, the P3 treatment in combination with nano-Se foliar spraying resulted in an increase in the amino acid content of the lettuce, however, the amino acid content decreased with an increasing nano-Se concentration. Compared with P1, the P2 and P3 treatments improved the lettuce quality, which was further improved by nano-Se leaf spraying. Finally, the principal component analysis on the growth and quality indices of the lettuce showed that 48 µmol∙L⁻¹ of nano-Se foliar spraying (i.e., the N3 treatment) under a 16 h/8 h (i.e., the P2 treatment) photoperiod resulted in the greatest improvement to lettuce growth and quality.

Effects of exogenous melatonin on the morphology and antioxidant enzyme activities of cotton seedlings under salt stress

DUAN Wenjing, MENG Yanjun, JIANG Dan, LIU Liantao, ZHANG Ke, ZHANG Yongjiang, SUN Hongchun, BAI Zhiying, LI Cundong

2022, 30(1): 92-104. doi: 10.12357/cjea.20210411

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Abstract:
Melatonin is an effective antioxidant that can promote the growth and development of plants under stress and alleviate stress-induced damage. The growth and development of cotton, an important cash crop in China, is severely impacted by salt stress. As such, here, we explored the regulatory effect of melatonin on the growth and development of cotton under salt stress by soaking ‘Guoxin Cotton No. 9’ seeds in different concentrations of melatonin (0, 0.1, 1, 10, 50, 100, 150 mmol∙L⁻¹) under 150 mmol∙L⁻¹ NaCl. We determined the root morphology (total root length, total surface area, total volume, number of lateral roots, root length, surface area and diameter), seedling height, and dry matter weight; thereafter, the most suitable melatonin concentration, 10 μmol∙L⁻¹, was selected. Then, we measured and analyzed the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), as well as the contents of malondialdehyde (MDA) and soluble sugar in leaves and roots of cotton seedlings and the height, biomass, as well as root morphology indexes under 150 mmol∙L⁻¹ NaCl, 10 μmol∙L⁻¹ melatonin, and 150 mmol∙L⁻¹ NaCl plus 10 μmol∙L⁻¹ melatonin. The results revealed that under salt stress, the height of seedlings decreased, root systems were underdeveloped, dry matter weights decreased, the activities of antioxidant enzymes (SOD, POD, CAT, and APX) decreased, and soluble protein content decreased; however, the MDA content was found to increase when compared to normal, salt stress-free condition. After soaking the seeds in 10 μmol∙L⁻¹ melatonin and 150 mmol∙L⁻¹ NaCl, seedling heights and biomass, total root lengths, number of lateral roots, diameter of taproots, activities of SOD, POD, CAT, APX, and content of soluble sugar all increased, but MDA content decreased in roots and leaves. In the absence of salt stress, soaking the seeds in 10 μmol∙L⁻¹ melatonin did not significantly increase the plant heights, but significantly increased taproot diameters, SOD, POD, CAT, and APX activities, as well as soluble sugar content in the cotton plant roots (P<0.05); however, significantly decreased MDA content (P<0.05). Spearman correlation analysis of 19 indices revealed that the total dry weight of seedlings was significantly and positively correlated with plant height, total root length, main root length, root mean diameter, total lateral root number, SOD, POD, CAT, and APX activities in roots and leaves, and soluble sugar content; however, there was a significant and negative correlation between total dry weight and MDA content in roots and leaves. With these comprehensive analyses, we show that exogenous melatonin could alleviate the damage caused by salt stress in cotton seedlings, promote an increase in plant height and dry matter accumulation, improve the resistance of cotton seedlings to salt stress by promoting lateral root development and thickening of main root, and increase the antioxidant enzyme activity and soluble sugar content. In addition, we reveal that exogenous melatonin can promote the development of cotton seedlings under salt stress-free condition; this provides a theoretical basis for the development and utilization of melatonin as well as the regulation of cotton cultivation.

Response mechanism of soil fungal community in farmland during a period of chromium stress

BAI Xue, ZHAO Xinyu, JING Xiuqing, ZHAO Xiaodong, YAN Pingmei, ZHAO Pengyu

2022, 30(1): 105-115. doi: 10.12357/cjea.20210503

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Abstract:
Heavy metal chromium (Cr) is one of China’s main soil pollutants and poses a great threat to its agricultural soils, especially in the Shanxi Province, where the soil Cr content is higher than the national average. A new millet (Setaria italica) variety, ‘Jingu 21’, has many advantages such as high quality, high yield and disease resistance. To investigate the changes and response mechanisms of fungal communities in agricultural soils during a period of Cr stress, we used soil (alkaline brown soil) planted with ‘Jingu 21’ as this study’s experimental material. Soil samples were taken before the introduction of Cr (CK), as well as 6 h (Cr_6 h) and 6 d (Cr_6 d) after 1 mmol L⁻¹ of Cr⁶⁺was introduced to the soil. High-throughput sequencing and statistical analysis of the data were used to investigate the response mechanism, the soil fungal community establishment, and the functional prediction of fungal communities in ‘Jingu 21’ soils during the period of Cr stress. The spatial and temporal distribution patterns of soil fungal communities were investigated using the non-metric multidimensional scale analysis, the soil fungal community establishment driving mechanism was investigated by constructing an interspecific symbiotic network diagram and a neutral community model (NCM), and the changes in soil fungal community function were investigated using FUNGuild. The results revealed that the composition and structure of soil fungal communities differed significantly at the phylum and genus levels during the period of Cr stress, and the Shannon diversity index of the community decreased significantly (P<0.05) at the Cr_6 d stage (4.17 for CK, 3.81 for Cr_6 h, and 3.23 for Cr_6 d). The spatial and temporal distribution patterns of fungal communities were similar within the same Cr stress period and differed significantly across these periods. The fungal community establishment was dominated by stochastic process (beta NTI: −0.16 for CK, −0.71 for Cr_6 h, and −0.23 for Cr_6 d). The interspecific symbiotic network analysis revealed that the fungal species were mostly positively correlated with each other; the interspecific symbiotic network of the Cr_6 d stage had a higher number of edges, average degree, and average path length than those of the CK and Cr_6 h stages, indicating that the community was more stable in the Cr_6 d stage than in the CK and Cr_6 h stage. Gibberella, Fusarium, and Chrysosporium were the key genera in the network diagram. The NCM quantified the stochastic processes further indicated that the soil fungal community was widely distributed (migration rate m: 0.066 for CK, 0.132 for Cr_6 h, and 0.163 for Cr_6 d). The FUNGuild function prediction showed that the soil fungal community was dominated by pathogenic and saprophytic trophic types. In addition, the abundance of sensitive bacteria, such as Mortierella and Gibberella, decreased, and the abundance of resistant bacteria, such as Fusarium, increased, indicating that Cr stress may affected the abundance of sensitive and resistant fungi in the soil, with the highest abundance of Fusarium indicating possible soil contamination with pathogenic bacteria. Ultimately, the results of this study revealed that the fungal community in soil planted with ‘Jingu 21’ changed significantly during a period of Cr stress; the soil fungal community establishment was dominated by stochastic processes; the diffusion restrictions of the community gradually decreased; and the interspecific relationships were complex and primarily symbiotic. In conclusion, herein, we simulated the stress response of soil microbial communities to Cr stress by treating agricultural soils with Cr⁶⁺. In addition, we demonstrated the response mechanism of soil fungal communities during a period of Cr stress, which is an important consideration for the treatment and remediation of heavy metal-contaminated soils and the promotion of sustainable agricultural development.

Impact of nitrogen application on nitrate nitrogen leaching in winter wheat and summer maize rotation system based on a literature analysis

XIAO Guangmin, RU Shuhua, SUN Shiyou, ZHAO Ouya, HOU Limin, WANG Ce, WANG Ling, LIU Lei, ZHANG Guoyin

2022, 30(1): 116-125. doi: 10.12357/cjea.20210426

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Abstract:
Nitrogen (N) leaching is one of the main routes of N loss in farmlands. The entry of nitrate N into water can cause human poisoning and water eutrophication, resulting in serious damage to human health and ecological environments. This study was carried out to explore the effects of different N fertilization rates, crop types, and monitoring methods on nitrate N leaching in the winter wheat and summer maize rotation system, which is the main cropping system used in China. To this end, the China National Knowledge Infrastructure (CNKI) database and Web of Science (WoS) Core Collection database were used to collect publications on nitrate N leaching in winter wheat and summer maize rotation systems from 1980 to 2020. Data from these papers on the effects of N application rates, crop types, and monitoring methods on nitrate N leaching from winter wheat and summer maize rotation systems were then analyzed using regression and T tests. It was found that an increase in the N fertilization rate exponentially increased the nitrate N leaching amount in this cropping system. The fitted equations for the relationship between nitrate N leaching amount and N fertilization rate in the winter wheat and summer maize seasons were y = 0.4633e^0.0109^x and y = 1.1011e^0.0103x, respectively. Although there was no significant difference between the N fertilization rates in the winter wheat (218 kg∙hm⁻²) and summer maize seasons (190 kg∙hm⁻²), the nitrate N leaching amount (8.8 kg∙hm⁻²) and rate (3.5%) in the winter wheat season was lower than those (amount: 13.9 kg∙hm⁻²; rate: 6.4%) in the summer maize season. In both the winter wheat and summer maize seasons, there was a significant exponential correlation between the N fertilization rate and nitrate N leaching amount, as measured using two different methods — lysimeter and solution collection, resulted in fitted equations of y = 0.2448e^0.0143^x and y = 0.6108e^0.0098^x in the winter wheat season, respectively, and y = 1.0284e^0.0102^x and y = 0.972e^0.011^x in the summer maize season, respectively. Thus, both methods can be used to measure nitrate N leaching reliably. The fitting accuracy of the regression equation for the N application rate and nitrate N leaching amount was better when the N application rate was less than 300 kg∙hm⁻², but the accuracy decreased with a further increase in the N application rate. In conclusion, because more nitrate N leaching occurs in the summer maize season than in the winter wheat season, the leaching problem in the summer maize season necessitates greater attention.

Trinity protection and evaluation of farmland ecosystem in the Central Plain of Liaoning, Northeast China

QIAN Fengkui, ZHANG Xiaoxia, ZHANG Jingye, SUN Fujun

2022, 30(1): 126-137. doi: 10.12357/cjea.20210402

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Abstract:
Farmland is an essential natural resource, and in recent times, farmland protection has become an issue of increasing global concern. Trinity protection of farmland quantity, quality, and ecological conditions (FQQEC) is a systematic hierarchical concept that encompasses the innovative application of theory and technology toward the transformation from traditional to modern farmland protection. In this empirical study, which focuses on the Central Plain of Liaoning, China, we sought to assess the spatial agglomeration of FQQEC by utilizing spatial autocorrelation analysis and dividing the farmland trinity protection zone based on spatial overlay analysis. The results revealed that the distribution of the spatial agglomeration of FQQEC showed distinct correlations of high-high (36.2%, 24.2%, and 9.7% of the total area for farmland quantity, quality, and ecological conditions, respectively), low-low (19.5%, 12.6%, and 11.6% coverage), high-low (0.6%, 1.2%, and 0.7% coverage), low-high (0.4%, 0.4%, and 1.3% coverage), and non-significant (43.3%, 61.4%, and 76.7% coverage) types, and the rank order of the degree of spatial agglomeration was farmland quantity > farmland quality > ecological conditions, which also represented the diverse distribution and utilization characteristics of FQQEC. On the basis of these findings, trinity protection zoning of farmland was established through different permutations and combinations of H-, L-, and non-significant types, and finally grouped into four primary and ten secondary categories. Collectively, our results indicate that wherever possible, it is essential to enhance the desirable impacts of the H type and eliminate the detrimental impacts of the L type in the FQQEC, based farmland consolidation, including the establishment of high-standard and permanent farmland, and adopting sustainable agricultural practices.

Development of a decision support system for irrigation management to control groundwater withdrawal

WANG Hongxi, LI Hongjun, QI Yongqing, DONG Zengbo, LI Fei, YAN Chao, SHAO Liwei, ZHANG Xiying

2022, 30(1): 138-152. doi: 10.12357/cjea.20210676

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Abstract:
Hebei Province is an important grain production area in China. The high grain production of the main crops, winter wheat and summer maize, depends on irrigation, which primarily comes from underground water sources. However, the over-extraction of groundwater for many years has caused the groundwater level in this region to decline continuously, threatening the sustainable development of irrigation agriculture. Under the national policy of limited groundwater extraction, achieving the goal of controlling groundwater extraction, and simultaneously using available water to maintain regional food productivity, is of great importance to achieve regional food security and sustainable water usage. In this study, we proposed and tested an irrigation decision system designed to set a limit on the groundwater withdrawal amount and to optimize irrigation scheduling, with the aim of using the limited irrigation water efficiently. We proposed that the water drawn from underground was to be controlled by real-time recordings of irrigation electricity consumption, based on the electricity meter readings collected by the State Grid Hebei Electric Power Company, which has implemented a project to update the electric recording of pumping-wells in the Hebei Plain, and the electricity consumption of each pumping well to allow remote recording in real time. By converting “electricity consumption to irrigation water use”, the electricity meters was used to regulate and control groundwater withdrawal to achieve the groundwater withdrawal target. The pumping limit setup for each well was to be decided based on the available groundwater, which was adjusted annually based on the groundwater recharge amounts from rainfall, surface water, and lateral flow. Based on the available groundwater, water rights could be endowed to each piece of land, which could be regulated by converting the total electricity used in pumping water based on the conversion coefficient of “electricity consumption to irrigation water use” for each well. Under limited groundwater pumping, we established an optimized irrigation schedule using calibrated crop models based on field experiments, with the soil water low limit for guiding the irrigation schedules being set up for winter wheat and summer maize. We used the calibrated crop model, Agricultural Production Systems sIMulator (APSIM), to simulate the crop production under a total annual irrigation amount of 210 mm with irrigation application numbers of three to ten and irrigation amounts of 70 to 21 mm per irrigation, based on meteorological data from the Luancheng Station for the period 2009–2019. Based on the simulation results, we determined the irrigation scheduling and the soil water content lower limit to guide the irrigation regulation. Furthermore, we developed and tested methods to forecast soil water changes, with the aim of determining the timing and amount of irrigation required based on the soil water threshold levels simulated by the crop model. Ultimately, we suggested the integration of groundwater withdrawal control by electric meters, and the calculation of irrigation timing and quantity under the limited water supply, based on soil water forecasting, to form a precisely controlled irrigation decision support system that achieved the goal of groundwater withdrawal control and improves the water use efficiency of crops under a limited water supply. This system, which ultimately has practical benefits for irrigation management applications, provides an efficient management tool for the government to control underground water withdrawal, as well as individual farmers who have different cultivating land areas, allowing them to use their limited water resources more efficiently.

Influencing factors and spatial effects of organic agriculture adoption: Based on survey data of farmers in Xinjiang

LU Yu, XIANG Ping’an, YU Liang

2022, 30(1): 153-165. doi: 10.12357/cjea.20210587

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Abstract:
In recent years, as an important implementation measure to realize agricultural green development and rural revitalization, organic agriculture faces both opportunities and challenges and needs public policy support. Farmers are the direct production decision-maker, clarifying the influencing mechanism of farmers’ organic agriculture adoption is reasonable in allowing the design of effective extension policies to promote the development of organic agriculture for the public sector. On the basis of questionnaire survey and on-the-spot interview data of 516 farmers in seven cities in Xinjiang Uygur Autonomous Region, this study constructed a spatial Durbin Probit model to explore the influencing factors and their spatial effects of farmers’ adoption of organic agriculture. Direct effects and spatial spillover effects of characteristic variables on farmers’ organic agriculture adoption were determined using the partial differential method. The main findings revealed that first, 59.3% of the farmers adopted organic agriculture, with income expectation being the key influencing factor. In addition, more organic farmers were located in southern Xinjiang and less in northern Xinjiang, indicating that poor ecological suitability does not constitute an obstacle to the development of organic agriculture. Compared with conventional farmers, organic farmers had a positive understanding of organic agriculture, were more willing to obtain relevant information about organic agriculture through social networks, realized interactive learning and mutually beneficial support, joining cooperative organizations more actively, and had a higher degree of social trust among similar farmers. Second, the demonstration area, cooperative organizations, social networks, social norms, contract guarantees, social trust, risk preference, guiding policy, incentive policy, number of laborers, farmers’ cognition degree of organic agriculture, and age had significant, positive, and independent effects on the adoption of organic agriculture. The total effects of these factors decreased following the above order. It is worth noting that there were differences in the role of social networks in different dimensions, more specifically, the positive effect of the industrial organization network on farmers’ adoption of organic agriculture was greater than that of the neighborhood network. From the perspective of government policies, there were differences in the impact of guidance policies and incentive policies on organic and conventional farmers, but there was no significant difference in restraint policies. Third, the adoption of organic agriculture by neighboring farmers had a positive spatial correlation. Farmers’ organic agriculture adoption was mainly influenced by the direct effects of the influencing factors. However, the neighbors’ spatial spillover effects cannot be ignored, especially regarding their participation in industrial organizations and the organic product certification demonstration area. The public sector can shift organic agriculture support policy toward the demonstration operators and promote farmers’ adoption of organic agriculture by increasing publicity, financial and technical support, cultivating and developing cooperation organizations such as agricultural leading enterprises and farmers’ cooperative organizations, establishing a national organic product certification demonstration (creation) area, and improving farmers’ awareness of organic agriculture. This study made the following contributions: first, it has investigated the influencing factors and spatial effects of farmers’ organic agriculture adoption based on survey data, helping to understand the spatial mechanism of farmers’ organic agriculture adoption and accounting for the lack of empirical evidence at the farmer level; second, it has empirically examined the role of social networks in different dimensions, which is crucial to understanding the role of neighborhood versus industrial organization forces in the diffusion of organic agriculture, which ultimately, can help policymakers to effectively induce behavioral changes by prioritizing programs that target either individual households or neighborhood networks and communities.

Agricultural water price policy reform and water saving technology adoption tendencies from the perspective of farmers’ differentiation: Based on a survey in Hebei Province

LIU Weizhe, WANG Xiqin

2022, 30(1): 166-174. doi: 10.12357/cjea.20210330

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Abstract:
Agricultural water price policy reform is an important innovation in agricultural water resource management that aims to guide farmers in adjusting their irrigation behavior in response to demand-side management. In this study, we considered the agricultural water price reform in Hebei Province as the research topic and use empirical tests to assess the influence of water price policy reform on farmer adoption of water-saving technology. Herein, we discussed the differences in farmer perspectives regarding the adoption of water-saving technology based on technical attributes and variation in farmers endowment. The results indicated that: 1) the “raising price for exceeding amount” water price policy reform mode altered the relative economy of water-saving technology usage and promoted the use of water-saving technologies. 2) Farmer differentiation led to differences in water-saving technology selection; more specifically, low part-time farmers (proportion of non-agricultural income < 50%) preferred to use drought-resistant varieties and traditional water-saving technologies, whereas high part-time farmers (proportion of non-agricultural income > 50%) preferred to use drought-resistant varieties only. Additionally, the water price policy reform did not effectively promote the use of sprinkler and drip irrigation of farmers. 3) Improving farmer awareness of the effectiveness of water-saving technology and the reality of water scarcity forecasts, as well as reducing the risk perception of farmers to the use of water-saving technology, effectively benefited the adoption of water-saving technology. Finally, the degree of non-agricultural employment was found to have a significant negative impact on the local use of water-saving technology. Based on these results, we suggested the following implications for policy: 1) the continuation of vigorous agricultural water price policy reform promotion and the improvement of the reform system and mechanism design; 2) the strengthening of water-saving technology advocation and ensuring the appropriate promotion of technical attribute characteristics;. 3) focusing on differences in the endowments of farmers and striving to alleviate endowment constraints; 4) increasing publicity efforts aiming to enhance farmer awareness of water-saving technologies and water regimes, as well as helping farmers establish the appropriate water-saving awareness and water use concepts. This study provides empirical support for the practical effects of water price policy reform. Additionally, it is subdivided according to the attribute differences of various water-saving technology elements and describes farmers irrigation adaptation behavior in detail.

2022 Vol. 30, No. 1