中国生态农业学报(中英文)

Interspecific below-ground interactions driven by root exudates in agroecosystems with diverse crops

YIN Xiaotong, YANG Hao, YU Ruipeng, LI Long

2022, 30(8): 1215-1227. doi: 10.12357/cjea.20220150

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Abstract:
Interspecific interactions mediated by root exudates play an important role in biodiversity-ecosystem functioning (BEF) relationships. We reviewed and explained the advances in interspecific root-root interactions mediated by root exudates in agroecosystems with crop diversification, and highlighted the following: root exudates mobilize insoluble nutrients in the soil, facilitating the uptake of nutrients by the crop and neighboring plants; the increased accumulation of heavy metals by hyperaccumulating plants can reduce the accumulation of heavy metals in associated food crops; alteration of soil microbial community mediated by root exudates from one species can reduce the pathogens in the other crop species; root exudates, as signal substances, also play important roles in mediating the root-root recognition and plasticity response between species; for example, field weeds can be suppressed by root exudates from intercropped allelopathy plants with field crops. In addition, we highlighted some perspectives on practical applications and new methods of research on root exudates in crop diversification systems. These advances provide a theoretical basis for building sustainable agricultural ecosystems by matching the root secretions and signaling substances of different crop species, improving resource utilization, reducing pests and diseases through enhanced interspecific facilitation, and reducing fertilizer and pesticide inputs owing to suppression of weeds through allelopathic effects.

The definition, methods and key issues of grassland ecosystem carrying capacity

YAN Lingyan, KONG Lingqiao, ZHANG Lu, OUYANG Zhiyun, HU Jinming

2022, 30(8): 1228-1237. doi: 10.12357/cjea.20210905

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Abstract:
Grassland is the largest terrestrial ecosystem in China, and its important function is the material basis for the survival and development of herders. Simultaneously, the grassland ecosystem is fragile and sensitive, with serious degradation problems, posing a threat to ecological security and economic development. The study of the carrying capacity of grassland ecosystems is of great value to achieve the balance of grass-livestock, the sustainable use of grassland, and maintenance of ecological security in ecologically fragile areas in China. This paper combs through concepts related to the carrying capacity of grassland ecosystems, and proposes a conceptual framework for assessing the carrying capacity of grassland ecosystems. Based on the summary of the existing assessment methods of grassland ecosystem carrying capacity, this paper focuses on the research methods and quantitative models involved in the current carrying capacity of grassland ecosystems and finally analyzes the fields and directions that need to be strengthened in the future for the carrying capacity of grassland ecosystems. At present, methods for assessing grassland ecosystem carrying capacity mainly involve quantification using the livestock carrying capacity. Most of the existing methods incorporate estimations based on forage productivity, agricultural and sideline product prices, pasture yield, and net primary productivity, or normalized difference vegetation index. The existing problems are mainly: 1) grass yield is affected by multiple factors, in different study areas it varies greatly, and data is difficult to obtain or estimate accurately; 2) the amount of forage loss caused by wildlife, pests, and diseases is ignored; 3) stocking rate is converted without considering the weight and age of the livestock; and 4) there exists a lack of a multifactorial integration model and predictive and early warning model. Future research should be lucubrated as follows: 1) build a perfect basic theoretical system for grassland ecosystem carrying capacity research; 2) improve the evaluation index system of grassland ecosystem carrying capacity and optimize the evaluation model; 3) strengthen dynamic monitoring and standardization of parameters; and 4) establish prediction and early warning mechanisms, and scientifically determine the carrying threshold of grassland ecosystems.

Effects of grassing on orchard ecosystem services: a global meta-analysis

HU Pan, GAO Xiaodong, ZHAO Xining, YU Liuyang, HE Nana

2022, 30(8): 1238-1248. doi: 10.12357/cjea.20210752

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Abstract:
Smallholder-run orchards are often managed using clear cultivation, that is, removing grass cover to remove competition for water and nutrient with fruit trees. This business-as-usual intensification has caused severe ecological and environmental issues related to soil desiccation, soil erosion, low soil organic C (SOC) sequestration, and the excessive use of chemical fertilizers. Sod culture in orchards is an advanced soil management system because of its ecological benefits, such as regulating the ecosystem services of orchards and ameliorating the soil micro-environment; as well as its economic benefits, such as improving the productivity of orchards, thus providing income for farmers. To date, there is a lack of comprehensive and quantitative research evaluating the ecosystem service function of sod culture in orchards. The objective of this study was to quantify the effects of sod culture on orchard ecosystem services to provide a scientific basis for orchard soil management and sod culture technology promotion and application. A total of 1387 pairs of data were collected from 118 peer-reviewed research papers published between 1996 and 2020. The meta-analysis method was used to quantitatively study the impact of sod culture on ecosystem service functions in orchards in terms of provisioning service (fruit yield and quality), regulating services (soil moisture, soil temperature, and SOC), and supporting services (soil total N). The heterogeneity of the influence of sod culture in orchards on ecosystem service functions was elaborated from four aspects: altitude, climate, grass species, and orchard types. The results showed that compared with clear tillage orchards, the grassing system significantly increased the provisioning service (fruit yield and soluble solid matter), regulating services (SOC and soil moisture), and supporting services (soil total N). The average increasing rate for these five indicators was 20.7% (95% confidence interval [CI]: 17.4%−24.2%), 5.1% (95% CI: 2.3%−8.6%), 24.7% (95% CI: 20.9%−27.8%), 8.1% (95% CI: 6.9%−9.3%), and 15.6% (95% CI: 6.80%−9.49%) respectively. Grassing had a negative effect on titratable acid content of fruits and soil temperature, which was 10.8% (95% CI: −14.5% to −6.9%) and 10.6% (95% CI: −12% to −9.2%) lower than that in clear-cultivated orchards, respectively. However, this negative effect actually helps improve the quality of fresh fruit and avoid the damage of high temperature to fruit trees, and thus is conducive to improving the provisioning and regulating services of orchard ecosystems. Furthermore, sod culture had a positive effect on fruit yield, but its influence and extent of its effect on fruit quality varied among orchard types, climate, and altitude. Different orchard types, grass species, and climate had positive effects on regulating services (soil moisture and SOC) and supporting services (soil total N). Overall, the study showed that the sod culture in orchards greatly increased fruits yield and soil carbon, and improved the climate in orchards, thereby improving the provisioning, regulating, and supporting services of orchards. Our findings provide insights into the development of science-based orchard management practices and have great significance for ensuring the quality, efficiency, and sustainable development of orchards globally.

Nitrogen migration along the soil-forage-livestock interface for Sorghum bicolor×S. sudanense

LI Yuan, ZHAO Haiming, YOU Yongliang, WU Ruixin, LIU Guibo, YANG Zhimin, ZU Xiaowei

2022, 30(8): 1249-1257. doi: 10.12357/cjea.20210898

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Abstract:
In this paper, we discussed the nitrogen migration rule of the soil-forage-livestock interfaces for Sorghum bicolor×S. sudanense to provide a theoretical basis for rational fertilization of the grass. A field experiment in which the plot contained micro area was conducted and different ¹⁵N application rates, including 0 kg∙hm⁻² (CK), 90 kg∙hm⁻² (N90), 180 kg∙hm⁻² (N180), 270 kg∙hm⁻² (N270), and 360 kg∙hm⁻² (N360), were set up. The indexes of nitrogen migration rule were analyzed using the ¹⁵N isotope labeling method under different ¹⁵N treatments. The indexes included plant utilization rate, soil residual rate, loss rate, and distribution rate to stem or leaf of ¹⁵N at the interface of forage-livestock; and the digestibility, utilization rate, and residual rate of ¹⁵N of sheep and cows at the interface of forage-livestock for S. bicolor×S. sudanense. The results showed that the total hay yield in the N180 treatment was significantly higher than that in the CK and N90 treatments (P<0.05), but there was no significant difference from those in the N270 and N360 treatments. At the interface of soil-forage, the plant utilization rate and soil residual rate of ¹⁵N were the highest, while the loss rate was lowest under the N180 treatment, and there were significant differences between N180 and N360, but there were no significant differences among the N180, CK, and N90 treatments. At the interface of forage-livestock, the ¹⁵N digestibility of sheep under the N180 treatment was significantly higher than that under the N360 treatment, but there was no significant difference with those under other treatments; and the ¹⁵N utilization rate of dairy cows under the N180 treatment was the highest, but the difference was not significant. On average, the ¹⁵N migration rule of the soil-forage interface was as follows: the soil residual rate was 25.22%, the utilization rate was 23.95%, and the loss rate was 50.83%; the distribution rate of leaf (54.35%) was higher than that of stem (45.65%) for S. bicolor×S. sudanense. After the S. bicolor×S. sudanense was ¹⁵N-labeled and further digested by ruminants, the ¹⁵N migration rule of soil-forage-livestock (sheep) interface was as follows: the soil residual rate was 25.22%, the residual rate of forage was 4.49%, the utilization rate of sheep was 19.46%, and the loss rate of ¹⁵N was 50.83%, while at the interface of soil-forage-livestock (dairy cows) was 25.22%, 5.78%, 18.17%, and 50.83%, respectively. These results provide a theoretical basis for rational fertilization and transformation of soil-forage-livestock for S. bicolor×S. sudanense.

Effect of intensive farming practice on soil organic carbon stock in Huantai County

HU Zhengjiang, KANG Xiaohan, XUE Xujie, LIAO Yan, WU Wenliang, MENG Fanqiao

2022, 30(8): 1258-1268. doi: 10.12357/cjea.20220268

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Abstract:
Agriculture is an important source of greenhouse gas (GHG) emissions and an important approach for carbon stock enhancement in terrestrial ecosystems. Optimization of farming practices can not only improve the utilization efficiencies of chemical fertilizer, but also increase the soil organic carbon (SOC) and hence improve soil fertility with the prerequisite of high and stable grain yield, and mitigate the greenhouse effect via increased SOC. The study chose the intensive farmland of Huantai County in Shandong Province, the first county to achieve 1000 kg of grain per mu (15 tons per hectare) in North China, to analyze the impacts of farming practices including fertilization, organic manure application, and crop straw incorporation, on SOC stock in the whole county. A biogeochemical model, DeNitrification-DeComposition (DNDC), was validated at the plot and regional scales for its applicability to SOC simulation. Five scenarios of farming practices were set, with full consideration of the natural and social conditions of Huantai County. With 2011 as the baseline year, the SOC changes in farmland soil within 30 years after 2011 were simulated. The simulation using the DNDC model showed that, under the scenario of maintaining the farming practices of 2011 (annual average chemical fertilizer of 500 kg(N)∙hm⁻² and 90% crop straw incorporation), the SOC content increased by 28.1%, 39.2%, and 44.9%, respectively, at 10, 20, and 30 years after 2011. This indicates that there is still room for soil organic matter to increase under current climate conditions, mainly due to crop straw incorporation in Huantai County. However, the increase in SOC is not linear, the increasing rate declines over time, and SOC saturation will occur for the farmland soil in Huantai County. Among the five farming practice scenarios, an annual average chemical fertilizer application rate of 400 kg(N)∙hm⁻², straw incorporation ratio of 90%, and animal manure application rate of 40 kg(N)∙hm⁻² can maximize farmland SOC content, reaching 16.2 g∙kg⁻¹ at 30 years after 2011. These results can provide a scientific basis for evaluating the farmland SOC pool in the North China Plain and provide technical support for the optimization of farming practices and policy improvement.

Assessment of the N₂O emission reduction potential in greenhouse vegetable fields based on the DNDC model

KE Huadong, KONG Chenchen, LEI Haojie, DING Wuhan, LI Hu

2022, 30(8): 1269-1282. doi: 10.12357/cjea.20210735

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The large amount of N₂O emission associated with high water and fertilizer inputs in greenhouse vegetable fields has become a salient issue. As N₂O is one of the major greenhouse gases, the research on reducing N₂O emissions can provide not only a reference for the formulation of carbon reduction plans for greenhouse vegetable fields but also a scientific basis to realize China’s “dual carbon” target. In this study, the N₂O emission of a typical greenhouse cucumber-tomato system in the Beijing suburbs was studied by using field monitoring and the DNDC model. The model was calibrated using field observations, and farmers’ conventional practices were set as the baseline scenario. The scenarios with changes in field management practices (e.g., irrigation method, N application rate, and replacement of chemical fertilizer by organic fertilizer) and regulation of soil physicochemical properties (soil organic carbon, pH, etc.) were set. N₂O emissions were obtained from 1250 simulations of the DNDC model for single scenario and multiple combinations of scenarios, and their emission reduction potentials were evaluated. The results showed that the DNDC model can simulate the soil temperature, soil water-filled pore space, vegetable yield, and N₂O emissions in greenhouse vegetable fields. The total N₂O emissions in the baseline scenario were 12.18 kg(N)∙hm⁻². The variation in the N₂O reduction potential of greenhouse vegetable fields ranged from 12.23% to 17.58% under the single-factor scenario. The sensitivity index showed that N₂O emissions were more sensitive to soil pH regulation and fertilizer reduction than to the other scenarios, with N₂O emissions (10.28 kg(N)∙hm⁻²) reduced by 15.60% and 14.86% for the 1.2-unit-change-in-soil-pH scenario and the 30% fertilizer reduction scenario (10.38 kg(N)∙hm⁻²), respectively, compared to the baseline. The multiple combination scenarios showed that a reduction of 31.69% in N₂O emissions from the baseline could be achieved with a combination of drip irrigation, 30% reduction in chemical N application, and 30% reduction in organic fertilizer. The N₂O reduction potential further improved to 55.58% (6.77 kg(N)∙hm⁻²) for the same combination in the low soil organic carbon and high pH soil scenarios. Overall, the DNDC model can simulate the field environment and overcome the drawbacks of limited treatment settings and high monitoring costs in field experiments, providing a useful method to quantitatively assess and reduce N₂O emissions in greenhouse vegetable fields. The combination of regulating soil physicochemical properties and optimizing water and fertilizer management can effectively reduce N₂O emission in greenhouse vegetable fields.

Reducing ammonia emission via reactor composting technology

LIU Juan, CAO Yubo, JIAO Yangmei, WANG Xuan, MA Lin

2022, 30(8): 1283-1292. doi: 10.12357/cjea.20220100

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Composting is an important way to recycle manure into soil as an organic fertilizer or conditioner. However, approximately 50% of the total nitrogen in manure is lost in the form of ammonia during composting, and this loss has an environmental impact on human health. Therefore, to reduce ammonia emission during the composting process to improve the quality of organic fertilizer and reduce its impact on the environment, this study intends to explore a composting method with low ammonia emissions, economy, and high efficiency. In this study, we used quantitative data from full-scale composting systems (windrow composting and reactor composting) in an industrial sheep farm to compare the ammonia emissions from traditional windrow composting and reactor composting, and quantitatively analyzed the ammonia recovery efficiency and influencing factors of gaseous scrubbers, as well as the economic benefits of windrow composting, reactor composting, and reactor composting combined with scrubbers. The results showed that windrow composting and reactor composting emitted 193 g NH₃ and 75 g NH₃ for 1 ton dry compost materials, respectively. Compared with traditional windrow composting, reactor composting reduced ammonia emissions by 61.1% (P<0.01), which was further increased to 82.3% (P<0.01) when the reactor was composted with a gaseous scrubber. The ammonia recovery rate decreased with an increase in the absorption time. The result showed that ammonia recovery rate of the scrubber was 82.0% (P<0.05) when the solution was fresh and gradually decreased to 39.8% (P<0.05) after 5 h. In addition, the ammonia recovery rate was significantly influenced by the temperature and NH₄⁺-N concentration of the absorption solution. For instance, the ammonia recovery rate decreased from approximately 80% to 20% when the temperature of the solution increased from 30 ℃ to 40 ℃ to 50 ℃. In terms of the cost of composting, reactor composting needed 116.9 Yuan per ton of manure, which was higher than that of traditional windrow composting (87.4 Yuan per ton of manure). The ammonia reduction costs of reactor composting and the scrubber were 22.0 Yuan per kg NH₃ and 16.5 Yuan per kg NH₃, respectively, when compared with windrow composting, which was lower than the value of the European Union. In addition, reactor composting had a higher efficiency than windrow composting, with composting cycles of 8 and 45 days for reactor composting and windrow composting, respectively. In conclusion, reactor composting can significantly reduce ammonia emissions, and most of the ammonia can be recovered when combined with a gaseous scrubber. The pH, NH₄⁺-N concentration, and temperature of the scrubber solution significantly affected the ammonia recovery rate. Improving the ammonia recovery rate and operational stability of the gas washing tower is a direction for future research to develop ammonia emission reduction technology. Consequently, reactor composting combined with a gaseous scrubber is recommended, which is an efficient and feasible composting technology with great potential for reducing ammonia emission.

Effects of rice-crayfish coculture on rice yield and food security

NI Mingli, DENG Kai, ZHANG Wenyu, SHANG Yongqing, WEI Feng, YUAN Pengli, LI Zhun, FAN Dan, CAO Cougui, WANG Jinping

2022, 30(8): 1293-1300. doi: 10.12357/cjea.20210891

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Rice-crayfish coculture (RC) refers to an integrated agriculture mode that combines crayfish breeding and rice planting. This mode has developed rapidly in China in recent years owing to its high economic benefits. The effect of large-scale promotion of RC on grain yield has attracted attention. Thus, to explore whether the large-scale popularization of RC has an adverse simultaneous impact on local rice yield and total grain yield, the influence of the proportion of cultivation ditches on rice yield was analyzed, the development status of RC in different regions was compared, and whether RC is suitable for further promotion was investigated. This study analyzed the impact of the RC mode on rice yield through long-term positioning experiments, household surveys in different ecological areas, and statistical yearbook data from Hubei Province over the past 10 years. The results showed the following: 1) RC expanded the area, increased the total yield, and improved farmer enthusiasm for planting rice. There was a significant positive correlation between the RC mode planting area and the rice planting area. The rice-planting area in Qianjiang City, Jingzhou City, and Hubei Province increased by 77.77%, 16.23%, and 12.20%, respectively, and the total rice yield increased by 68.12%, 16.61%, and 20.49%, respectively, in recent 10 years. Simultaneously, the summer grain (wheat) yield in Hubei Province had remained stable over the last 10 years. 2) The average proportion of cultivation ditches of crayfish (G) in the Hubei RC-producing area was 13.42%, and G affects rice yield to a certain extent. Without considering G, the rice yield, when using the RC mode, increased by 17.63% compared to that of traditional rice monoculture. When G≤10%, the RC rice yield was slightly lower than that of traditional rice monoculture, but the difference was not significant. However, under the conditions of 10%<G<20% and G≥20%, rice yield significantly decreased by 18.19% and 34.81%, respectively. 3) There are advantages and disadvantages in RC development areas. The yields of rice and crayfish in Jianghan Plain and the plain along the river in eastern Hubei were better than those on the hills of central and northern Hubei. Previous research results showed that RC can stabilize the yield of rice under appropriate G conditions. Simultaneously, owing to the high economic effect of RC, an increasing number of farmers have joined the industry in recent years, which has promoted an increase in the total yield of rice in the regions. However, there are obvious regional adaptability differences in RC. Only in advantageous regions can give full play to their role in stabilizing grain yield and increasing efficiency. Therefore, the field engineering construction associated with the RC mode should be standardized according to G≤10%, and adhering to the development of RC mode according to local conditions can maintain rice and crayfish income and food security, which is an important guarantee for the sustainable and healthy development of the rice-crayfish industry in China.

Cotton mega-environment investigation and test environment evaluation for the national cotton variety trials in the northwest inland cotton production region

QIAO Yintao, SUN Shixian, ZHAO Suqin, YANG Xiaoni, XU Naiyin

2022, 30(8): 1301-1308. doi: 10.12357/cjea.20220012

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Plant breeding has played a key role in increasing agricultural productivity and meeting the increasing needs of the world, while the prevalence of genotype-by-environment interaction (GE) in multi-year, multi-location variety trials impedes variety selection and application efficiency. The Northwest Inland Cotton Production Region (NICPR) is currently the most important cotton-growing region, occupying more than 80% of the total cotton acreage in China. Therefore, mega-environment (ME) investigation and test environment evaluation are beneficial for the rational utilization of experimental resources and the improvement of the efficiency of cotton variety trials conducted in the NICPR. The objective of the present study was to demonstrate the application efficiency of the existing genotype main effect plus GE (GGE) biplot and a newly proposed location grouping (LG) biplot in exploring ME and comprehensively evaluating test environments using identification ability, representativeness, and desirability index based on the lint cotton yield of national cotton variety trials in the NICPR from 2011 to 2020. (1) The LG biplot revealed that the majority of test environments, including Shawan, Wujiaqu, Kuytun, Shihezi, Dunhuang, Bole and Jinghe, belonged to the same ME and suitably represented the targeting early-maturing cotton production region, while the test environment Usu was delineated out as an outlier of the early-maturing cotton ME. The test environment Makit in the medium-early maturing ME was also identified as an outlier in the southern Xinjiang cotton growing region, while the other test environments covering Bazhou, Alaer, Shache, Kuqa, Baicheng, Korla, and Tumxuk were all positively correlated and suitably represented the medium-early maturing ME. (2) The differences in identification ability among all test environments were not significant at P>5% level. The representativeness and desirability of Usu and Markit displayed significant differences from other test locations in the same ME, while the differences among other test locations were not significant. (3) According to the desirability index, the comprehensive ordination of the test environments in the early maturing cotton region was ranked as Shawan > Jinghe > Wujiaqu > Dunhuang > Bole > Shihezi > Kuytun > Usu. Similarly, on the basis of the desirability index, the ordination of test locations in the medium-early maturing cotton region was listed as Bazhou > Tumxuk > Alaer > Korla > Shache > Baicheng > Kuqa > Makit. It was clear that Usu and Makit should be removed from cotton variety trial scheme optimization for test efficiency improvement. The results of the study not only presented the highly efficient function of LG and GGE biplots in test environment evaluation in cotton variety trials in the NICPR and provided a theoretical basis for the optimization of the cotton regional trial schemes in Northwest Inland, but they also set a good example for future application in similar studies on other crops for other target crop growing regions.

Comparison of matter production and the light and temperature resources utilization efficiencies of the main cropping systems for paddy fields in the Dongting Lake region

ZHAO Yang, GAO Dujuan, LI Chao, CHEN Youde, CUI Ting, TONG Zhongquan, LUO Xianfu

2022, 30(8): 1309-1317. doi: 10.12357/cjea.20210698

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Abstract:
Reasonable cropping systems can match crop growth demand and natural resource supply. This comparison of the main cropping systems for paddy fields aims to identify the dominant cropping system in the Dongting Lake area and to provide a theoretical basis for optimizing resource allocation and the establishment of high-yield and high-efficiency planting patterns. From 2016 to 2018, four main cropping systems for paddy fields in the lake area were selected as research objects. The efficiency and energy of dry matter production, light and temperature resource utilization efficiencies, and the economic benefits of different patterns were analyzed. Among the four modes, the winter fallow-middle rice one-cropping system had the lowest year-round average efficiency and energy of dry matter production, and distribution rates of effective accumulated temperature and light energy distribution, which were 18.330 kg·hm⁻²and 27.00 MJ·m⁻², 70.0% and 49.2%, respectively, indicating that the winter fallow-middle rice system did not fully utilize the light and temperature resources and that the efficiency and energy of dry matter production were low. The oilseed rape-early rice-late rice triple-cropping system had the highest year-round average efficiency and energy of dry matter production, which were 31.525 kg·hm⁻² and 48.22 MJ·m⁻², respectively, but the year-round average growth period was 364.5 days. The distribution rates of year-round effective accumulated temperature and light energy from 2016 to 2017 reached 102.5% and 102.6%, respectively, indicating that the oilseed rape-early rice-late rice system lacked light and temperature resources and that it was difficult to meet the demands of the three crops. The triple-cropping system had the lowest net income, with an average of 8738 ¥∙hm^–2 over two years. The growth season of the winter fallow-early rice-late rice system was concentrated from early April to mid-to-late October. In winter, temperature and light resources were wasted. The year-round average net income of the winter fallow-early rice-late rice system was 9009 ¥·hm⁻², which was only 75.3% of the winter fallow-middle rice system and 62.3% of the oilseed rape-middle rice system. The time for oilseed rape-middle rice double-cropping system was available throughout the whole year, with an average utilization rate of 88.9%, and the year-round average distribution rates of effective accumulated temperature and light energy were 86.6% and 87.7%, respectively. The highest net income for oilseed rape-middle rice was 14 468 ¥·hm⁻², which was obviously higher than that of the other three models. Compared to the other three models, the oilseed rape-middle rice two-cropping system could make full use of the light and temperature resources, and the efficiency and energy of dry matter production were higher. It was also the highest net income model and suitable for development in the Dongting Lake area.

Climatic resources and drought characteristics of maize sown in different dates in the hilly area of central Sichuan: A case study of Zhongjiang, Sichuan

LAN Tianqiong, LI Sijin, LAN Hanjun, DENG Changchun, DU Xia, CHEN Mouhao, CUI Shilei, YUAN Jichao, KONG Fanlei

2022, 30(8): 1318-1327. doi: 10.12357/cjea.20210906

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Abstract:
The hilly area of central Sichuan is one of the main maize-producing areas in Southwest China, where seasonal drought is the main agro-meteorological disaster. It is of great significance to study the climatic resources and drought characteristics of maize at different growing periods with different sowing dates for maize drought avoidance and disaster reduction in this area. Using Zhongjiang County in the hilly area of central Sichuan as an example, based on the surface meteorological observation data of Zhongjiang Meteorological Station from 1981 to 2020, eight sowing dates with 20 days intervals were set from late March to early June to analyze the change laws of main agro-climate resources during maize growth periods under different sowing dates. At the same time, based on the crop water deficit index (CWDI), the drought characteristics of maize at different growth periods under different sowing dates were studied to provide a scientific basis for the selection of suitable sowing dates and the prevention of staged drought during the growth periods of maize in the hilly region of central Sichuan. The results showed that first, over the past 40 years, the changes in climatic resources during the maize growth season of each sowing date showed a trend of decreasing sunshine hours, increasing temperature, and decreasing rainfall. With the delay in sowing date, the daily average temperature, growing degree days, and heat degree days first increased and then decreased, while the sunshine hours gradually decreased and the rainfall gradually increased. Therefore, appropriately delaying the sowing date of maize is beneficial for improving the utilization of sunshine, heat, and rainfall resources. Second, with the delay in sowing date, the CWDI during the maize sowing–jointing and jointing–tasseling periods noticeably decreased, and the CWDI during the tasseling–filling of maize sown on the late-March was significantly higher than that on other sowing dates. Delaying the sowing date can reduce the risk of water deficits during the maize growth periods. Third, there were differences in most susceptible growing period to drought among different sowing dates. Maize sown in late March, late May, and early June had the highest drought frequencies during the sowing–jointing stage, and maize sown from early April to mid-May had the highest drought frequency during the jointing–tasseling stage. Fourth, the drought intensity at each growing period of maize sown in different dates was dominated by light and moderate drought, followed by severe drought, with extreme drought occurring the lowest. When the sowing date was delayed, the maize drought intensity decreased from moderate to mild. Appropriately delaying the sowing date of maize can reduce the frequency of drought, especially the frequency of severe and extreme drought. The proper sowing date of maize in the study area is before mid-May. When maize is sown in late March and early April, attention should be paid to drought resistance management prior to the grain-filling period. When sowing from mid-April to mid-May, attention should be paid to drought resistance management before tasseling to prevent high temperature risks during the filling-maturity stage.

Suitability of the cosmic-ray fast neutron soil moisture monitoring method in a low-latitude plateau

WANG Zhongjin, WU Su, WU Dongli, ZHANG Zhenqiang, ZHAO Jie, LI Peng, CHEN Haibo

2022, 30(8): 1328-1335. doi: 10.12357/cjea.20210895

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Abstract:
The cosmic-ray fast neutron soil moisture monitoring method has a large monitoring range, is unaffected by soil salinity, allows real-time and non-destructive in situ measurement, and is of significance for drought and flood warning, water-saving irrigation, ecological environment protection, and soil productivity improvement. To clarify the suitability of the cosmic-ray fast neutron soil moisture monitoring method in the low-latitude plateau, this study conducted a large-scale soil moisture investigation using oven-drying method in the southern Chinese city of Dali (25°42ʹ14″N, 100°10ʹ34″E) from May to September 2020 to verify the accuracy of the cosmic-ray fast neutron method. At the experimental site, a cosmic-ray fast neutron soil moisture station, frequency domain reflectometer (FDR) soil moisture station, and rainfall monitoring station were installed. FDR was used for continuous monitoring and comparison, and the correlation of soil moisture in the 0–50 cm soil layer was analyzed. Combined with the observation data of rainfall stations, the response ability of cosmic-ray fast neutrons and FDR to continuous changes in soil moisture was studied. The experimental results showed that the determination coefficient of the linear equation (R²), root-mean-square error (RMSE), and absolute error between the soil moisture content measured by the cosmic-ray fast neutron method and by the multi-point mean value of the oven-drying method were 0.898, 0.013 cm³∙cm^–3, and 0.027 cm³∙cm^–3, respectively. This shows that the cosmic-ray fast neutron method can accurately measure the regional soil water content in low-latitude plateaus. In the long time series, the cosmic-ray fast neutron method and FDR have a consistent trend of soil moisture changes in the 10 cm soil layer, and the determination coefficient of the linear equation (R²) was 0.839. This shows that the cosmic-ray fast neutron method can respond to soil moisture changes over time, similar to FDR. In terms of sensitivity to precipitation, if the precipitation amount was more than 2 mm for the precipitation process, and both methods had obvious responses. For the precipitation process with precipitation below 2 mm, the cosmic-ray fast neutron method was slightly better than FDR. However, more obvious sensitivity was not observed in this experiment, especially for the precipitation process with precipitation below 1 mm, which may be related to the loose texture of the surface soil in the experimental area and the rapid shift of sunny and rainy weather. In this experiment, the cosmic-ray fast neutron soil moisture monitoring method was suitable in the low-latitude plateau region, was not sensitive to the spatial variability of soil moisture, and was accurate and reliable for measuring the average soil moisture content in the range of 100 m. It meets the current soil moisture observation requirements, can provide real-time soil moisture information, effectively improving the efficiency and accuracy of mesoscale soil moisture monitoring, and provides a reference for related soil moisture monitoring research and applications.

Characteristic wavelength selection and hyperspectral inversion of soil iron oxide

ZHAO Hailong, GAN Shu, WANG Junjie, HU Lin

2022, 30(8): 1336-1345. doi: 10.12357/cjea.20220177

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Abstract:
Understanding the soil content of iron oxide is of great significance in revealing the soil environment and guiding crop production. Hyperspectral is widely used for inversion of soil physical and chemical properties owing to its high spectral resolution and strong wavelength continuity. However, hyperspectral data have the disadvantage of wavelength redundancy; therefore, the selection of characteristic wavelengths is a necessary step for soil hyperspectral modeling and analysis. The traditional method for selecting the characteristic wavelength of soil iron oxide is single, and only correlation coefficient (CC) method is used to select characteristic wavelengths. Hence, there are too many input variables in the model, which reduces its prediction accuracy. The purpose of this study was to explore the predictive ability of different models constructed by using correlation analysis combined with various characteristic wavelength selection algorithms for soil iron oxide content and compare the accuracy of the models constructed by using the correlation coefficient method. A total of 135 soil samples were collected from the surface of the study area in the southern margin of Lufeng Dinosaur Valley in Yunnan Province. The spectral reflectance and iron oxide content of the samples were measured in the laboratory. The Kennard-Stone algorithm was used to divide the soil samples into a calibration set of 95 samples and validation set of 45 samples. The soil spectral curve was smoothed by Savizky-Golay as the original spectral reflectance (OR), and the original spectrum was transformed using first-order differential reflectance (FD) and reciprocal logarithm reflectance (RL). Based on the correlation analysis of iron oxide content with original spectrum and its transformed spectrum, the iteratively retaining informative variables (IRIV), competitive adaptive reweighted sampling (CARS), and successive projection algorithm (SPA) were used to extract the characteristic wavelength. With the extracted characteristic wavelength as the independent variable and the iron oxide content as the dependent variable, inversion models were constructed by using random forest regression (RF) and partial least squares regression (PLSR). The prediction accuracy of these models was evaluated by comparing the determination coefficient (R²), root mean square error (RMSE), and the ratio of performance to interquartile distance (RPIQ). The results showed that the further use of IRIV, CARS, and SPA algorithms to extract the characteristic wavelength after correlation analysis could effectively reduce the number of modeling variables. For the four characteristic wavelength selection methods, it is necessary to fit with different spectral transformation and modeling methods for improving the prediction accuracy. Comprehensive comparison of all the characteristic wavelength selection methods showed that the PLSR model built using the RL-CC-CARS method achieved the best performance. The R², RMSE, and RPIQ the validation set were 0.826, 5.600 g∙kg⁻¹, and 3.618, respectively. Based on the 1∶1 scatter plot, the measured soil iron oxide contents and the predicted ones of RL-CC-CARS-PLSR were close to the 1∶1 line and had good prediction results. Appropriate variable selection can improve the performance of the model, simplify the regression model, and improve the accuracy of iron oxide estimation. This study provides a reference for the inversion of soil iron oxide content using hyperspectral data.

The potential and the impact factors for phosphorus recovery from wastewater via struvite precipitation

Erick K. MUTAI, WANG Xuan, MA Lin

2022, 30(8): 1346-1354. doi: 10.12357/cjea.20210764

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Abstract:
Phosphorous (P) is an essential nutrient for living organisms, and there is a concern regarding the challenges of both supply uncertainty and the linked aquatic eutrophication. Phosphorus recovery through struvite precipitation technology has attracted much attention in research as it prevents eutrophication and forms a slow-release fertilizer that serves as an alternative source of P in both synthetic wastewater (SW) and real waste (RW). However, only inorganic soluble P is involved in the reaction. Therefore, the ratio of organic P, which is up to 30%–40% of total P in real wastewater systems, leads to a variation of P recovery rates in practice. There is a lack of knowledge on the underlying differences and the factors causing the disparity in the P recovery, and few studies have attempted to quantify the gap in the P recovery rates of SW and RW. Data mining was conducted using 103 studies with 1186 observations to quantify the P recovery rate in SW and RW, establish the underlying factors affecting the P recovery, and derive solutions. Results showed that P recovery rate in SW (83.6%) was higher than that in RW (76.9%). A large variation in the P recovery rate (20.4% to 99.9%) in RW was detected since it was more sensitive to pH and foreign ions, such as calcium. Magnesium and calcium were found to impact struvite crystallization; magnesium had a positive impact at a specific Mg∶P ratio between 1 and 2, with SW being more sensitive, while calcium inhibited struvite formation. P precipitation is an abiotic process, and organic P concentration plays a crucial role in the total P recovery rate. Aeration played an important role in the mineralization of organic P. Therefore, supplying aeration at a flow rate of 6 L∙min⁻¹ was beneficial for both total and inorganic P recovery. Increasing the Mg∶P ratio was not a crucial factor for P recovery in practice, but it significantly impacts the components of the precipitate.

Difference in activation and absorption of different insoluble Cd between two tomato varieties with different Cd accumulation

ZHANG Yukun, GAO Xitong, WANG Xiaomin, DUAN Yajun, LYU Shi, WANG Xue, LU Qianying, FENG Shengdong, YANG Zhixin

2022, 30(8): 1355-1361. doi: 10.12357/cjea.20210809

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Abstract:
Soil Cd pollution is becoming increasingly hazardous, and the effective state of Cd largely affects its biological effectiveness. The difference in the activation of insoluble Cd directly affects the uptake and accumulation of Cd in vegetables, and there are obvious differences in the uptake and accumulation capacity of different tomato varieties for Cd. However, the difference in the activation of Cd insoluble forms of CdS and CdCO₃ by different Cd-accumulation tomato varieties remains unclear. Therefore, in this study, the seedlings of two tomato varieties with different Cd-accumulation capacity (high-Cd-accumulation type ‘Cooperative 8’ and low-Cd-accumulation type ‘Provence’) were used as research objects. The activation effects and absorption differences of two types of insoluble Cd (CdS and CdCO₃) were studied through hydroponic experiments, and the effects of two types of insoluble Cd on plant growth were analyzed. The purpose of this study was to provide a theoretical basis for reducing the risk of tomato Cd pollution, ensuring the safety of tomato production and reasonable selection of tomato varieties. The results showed that the activation effect of CdCO₃ and CdS of high-Cd-accumulation type ‘Cooperative 8’ significantly increased the available Cd concentration in solution by 62.1% and 51.0% compared to the Cd concentration in non-planting tomato solution (P<0.05), while the low-Cd-accumulation type ‘Provence’ significantly promoted the dissolution of insoluble CdCO₃ by 39.4% (P<0.05). However, the activation of insoluble CdS was not significant, and the activation of insoluble Cd by ‘Cooperative 8’ was significantly higher than that of ‘Provence’. In terms of plant Cd uptake, the shoot and root Cd contents of ‘Cooperative 8’ were significantly higher than those of ‘Provence’ under insoluble CdS treatment, which increased by 80.2% and 111.7% (P<0.05), respectively. Under insoluble CdCO₃ treatment, the shoot and root Cd contents of ‘Cooperative 8’ were 105.2% and 153.8% higher than those of ‘Provence,’ respectively (P<0.05). Compared with the treatment without insoluble Cd, the treatment with insoluble CdS increased the plant height, root length, and biomass of ‘Provence’ by 15.0%, 10.1%, and 15.5% (P<0.05), respectively, while decreased the plant height, root length, and biomass of ‘Cooperative 8’ by 5.0%, 9.8% and 11.3% (P<0.05), respectively. Plant height, root length, and biomass of ‘Cooperative 8’ were significantly lower than those of ‘Provence’ under the two insoluble Cd treatments (P<0.05). In conclusion, the high-Cd-accumulation variety of tomato promoted the activation of the two insoluble Cd forms significantly more than the low-Cd-accumulation variety of tomato, and the bioeffectiveness of Cd was significantly improved. The absorption and accumulation of available Cd by high-Cd-accumulation tomato variety were significantly higher than those of low-Cd-accumulation tomato variety, which significantly inhibited the growth of tomato plants with high accumulation. However, CdS treatment had a significant stimulating effect on the growth of the low-Cd-accumulation variety ‘Provence’.

Effects of Pseudomonas TCd-1 inoculation on Cd uptake, rhizosphere soils enzyme activities and Cd bioavailability in rice (Oryza sativa) varieties with different Cd tolerance

LIU Linglin, WANG Dunfei, HUANG Mingtian, XIAO Qingtie, YOU Wu, QIAN Xin, ZHENG Xinyu, LIN Ruiyu

2022, 30(8): 1362-1371. doi: 10.12357/cjea.20210854

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Abstract:
Heavy metal contamination in rice (Oryza sativa) is a serious problem. Microbial remediation is a promising technique to reduce Cd accumulation in rice. To explore the rhizosphere-associated ecological mechanism of Pseudomonas TCd-1-induced reduction of Cd uptake in rice, two rice varieties, high Cd-tolerant variety ‘Teyou 671’ and low Cd-tolerant variety ‘Baixiang 139’, were used. A set of soil culture pots treated with 10 mg∙kg⁻¹ Cd were employed to evaluate the effects of Pseudomonas TCd-1 inoculation on rice Cd uptake and enzymes activities in rhizosphere soils. The results showed that the Cd content in different parts of both the high and low Cd-tolerant rice varieties significantly decreased (P<0.05) after inoculation of Pseudomonas TCd-1, and the bioconcentration factor (BCF) of Cd decreased by 35.14% and 47.79% (P<0.05), respectively. However, no significant changes were found in the translocation factor (TF). Meanwhile, in rhizosphere soils of the high and low Cd-tolerant rice varieties, the content of exchangeable Cd decreased by 15.89% and 23.81% (P<0.05), Fe-Mn oxide bound Cd increased by 39.58% and 28.81% (P<0.05), and organic matter Cd increased by 36.11% and 25.00% (P<0.05), respectively. In addition, the activities of acid phosphatase, urease, saccharase, cellulase, and catalase significantly increased by 26.74%, 12.07%, 62.50%, 81.17%, and 5.13%, respectively; while the polyphenol oxidase activity decreased by 12.40% in the rhizosphere soils of low Cd-tolerant rice variety. In rhizosphere soils of high Cd-tolerant rice variety, the activities of acid phosphatase, urease, sucrase, cellulase, and polyphenol oxidase decreased by 7.19%, 9.39%, 25.53%, 16.20%, and 11.44%, respectively; while catalase activity increased by 5.13%. There were significant differences in enrichment characteristics, rhizosphere soil enzymes activities, and the proportions of different chemical forms of Cd in rhizosphere soils of different Cd-tolerant rice varieties after inoculation with the TCd-1 strain. The results indicated that inoculation with the strain may partly remediate the changes in soil enzymes activities caused by Cd pollution. In conclusion, Pseudomonas TCd-1 can improve Cd tolerance and inhibit Cd uptake and accumulation in rice, mainly by reducing the bioavailability of soil Cd and restoring the changes in soil enzymes activities caused by Cd pollution.

Effects of direct saline irrigation and nitrogen and phosphorus application on a coastal saline-alkali soil planted Tamarix chinensis

YANG Lilin, YANG Youshan, LI Lingman, QIU Fagen, ZHU Xiangmei

2022, 30(8): 1372-1380. doi: 10.12357/cjea.20210669

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Abstract:
In order to cope with the outstanding problems of spring drought, salt return, and lack of both N and P in coastal severe saline-alkali region, we utilized the rich underground saline water resources and the Tamarix’s characteristics of both fixation carbon (C) and discharge salt to achieve the goals of elimination of salt and drought stress, deficiency of both soil N and P, and improvement green ecological landscape in coastal severe saline soils as well. Tamarix chinensis Lour., a shrub species, is a species with strong salt-tolerant and water conservation ability that is widely planted in saline-alkali soils. This species plays an important role in improving the regional ecological landscape reformation and maintaining the stability of the coastal ecosystem, like the coastal wetlands in northern China. A two-factor experiment was conducted about saline water and fertilization in the Tamarix chinensis soil over a four-year period in coastal saline-alkali soil in the low plain of North China. Six treatments included no fertilizer as control (CK, WCK), only applying N (N, WN), applying both N and P (NP, WNP), each corresponding to no irrigation (the first) and irrigation with local phreatic saline water containing 8.02−9.34 g·L⁻¹ salt (the second), respectively. The results showed that the salt content in the 0−30 cm soil layer of Tamarix chinensis land decreased by 32.7% on average after the first saline irrigation, which had a significant desalination effect on the severe saline-alkali coastal soil, but after three consecutive-year saline irrigation, the salt content in 0−30 cm soil layer averagely increased by 11.2%−18.3%; yet the available P (Olsen-P) content in 0−90 cm soil layer decreased by 19.4%−32.1%, the contents of microbial carbon (Cmic) and microbial nitrogen (Nmic) in 0−30 cm soil decreased by 15.5% and 19.7% respectively. However, compared with the control WCK, the WNP treatment, i.e. saline irrigation and applying NP, decreased the salt content of 0−30 cm soil by 36.1%, in the meanwhile significantly decreased the total N, water content and contents of 0−30 cm soil layer, Olsen-P of 30−60 cm layer as well. WNP was conducive to increase of 0−30 cm Cmic, soil organic matter (SOM) and ammonium acetate extractable K (Kex) content. Our experiment provides evidence that P was a strongly limited nutrient, saline irrigation-associated fertilization of N and P can effectively alleviated the risk of soil secondary salinization caused by continuous saline irrigation, relieve the limitation of key nutrients deficiency like P and N, and promote the soil microbial activity, with the strongest evidence for saline irrigation and soil nutrient management for artificial Tamarix chinensis in severe saline-alkali coastal soil.

2022 Vol. 30, No. 8