中国生态农业学报(中英文)

Mechanisms and influencing factors of soil organic carbon sequestration by minerals

CHEN Mengdie, CUI Xiaoyang

2022, 30(2): 175-183. doi: 10.12357/cjea.20210320

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Abstract:
Soils, which play an active role in the global carbon cycle, are the largest store of carbon in terrestrial ecosystems. Considering the increasing seriousness of the greenhouse effect, it is of utmost importance to enhance the stability of organic carbon in soil. Previous studies have verified that mineral sorption is one of the most significant organic carbon stabilization mechanisms. The capacity and stability of the organic carbon adsorbed by minerals are affected by multiple factors. Soil mineral type, crystallinity, and mineral particles sizes affect the mineral adsorption capacity and mechanism. Amorphous phase minerals such as allophane and imogolite have a strong adsorption capacity for organic carbon. It is widely accepted that plant-derived carbon is preferentially adsorbed by coarse minerals and microbial-derived carbon is strongly adsorbed by fine minerals. This is because microbial-derived mineral-associated organic carbon formed by microbial pathways is enriched in areas of microbial “hot spots”, namely mineral surface pores. Microorganism degradation of soil organic carbon has a dual effect on the formation of mineral-bound organic carbon. On one hand, microorganisms and minerals compete for reactive organic carbon; thereafter, one part of the carbon is mineralized into CO₂, and the other part is converted into microbial biomass carbon, which is recycled by microorganisms or adsorbed by minerals. On the other hand, microorganisms degrade resistant organic carbon, and as a result, partially processed organic carbon is more easily adsorbed by minerals. The assimilation of plant-derived carbon into microbial biomass carbon is an important precursor for soil organic carbon stabilization. Microbial degradation of soil organic carbon reduces the molecular size of biomolecules and adds oxygen-containing functional groups to soil organic carbon, both of which are essential for mineral adsorption of organic carbon in the soil. Besides the aforementioned factors, soil physical and chemical properties and land use affect the mineral adsorption capacity. It is indisputable that the mineral adsorption mechanism plays an important role in soil organic carbon storage. It is beneficial to increase organic carbon storage in the soil to study the mechanism and factors of mineral adsorption of soil organic carbon. We have summarized previous studies related to soil organic carbon and soil minerals. The objectives of this study were to explore the correlation law of mineral immobilization of organic carbon in the soil and to provide a theoretical basis for increasing soil organic carbon storage and for mitigating the effects of climate warming on soil organic carbon storage.

The relationship between farmers’ cognitions, landscape heterogeneity and surface arthropods: based on the mediation effect model

BIAN Zhenxing, CHU Zhuoming, ZHANG Yufei, TONG Haoxuan, YU Miao

2022, 30(2): 184-193. doi: 10.12357/cjea.20210410

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Abstract:
At present, human activities are gradually increasing, and farmers’ activities have become a hot issue in research of protecting cultivated land and cultivated landscapes. The study encompassed survey data from 540 farmers in Jianping County, Liaoning Province to explore the impact of farmers’ cognition on the biodiversity of surface arthropods in farmland landscapes. Furthermore, it also examined the mediating effects of landscape heterogeneity. By constructing a mediation effect model, the logical relationship between farmers’ cognition, agricultural landscape heterogeneity, and surface arthropod diversity was studied aiming to provide a theoretical basis for landscape protection of farmland. The results showed that: 1) Differing cognition of farmers had varied effects on the diversity of surface arthropods in cultivated landscapes. Farmers’ cognition of pesticide and chemical fertilizer application, agricultural machinery, and ecological characteristics of cultivated landscapes had positive impacts on surface arthropod diversity. The better their cognition, the higher the diversity of surface arthropods in the farmland landscape is. Cognition of scale management and farmland protection policies had a negative impact. This manifested as better cognition leading to lower arthropod diversity. This conclusion differed from that which was expected. This further confirmed the important influence of farmers’ “effect expectations” on behavior. 2) Agricultural landscape heterogeneity had a significant mediating effect on farmers’ cognition affecting surface arthropod diversity. Farmers’ cognition could indirectly affect the diversity of surface arthropods by influencing the heterogeneity of agricultural landscapes. Based on this, the government should increase investment in rural education, build knowledge about agro-ecological protection, and improve awareness among farmers about cultivated land protection. It is also important to pay attention to optimization of cultivated land landscape patterns, appropriately increase non-farming habitats, to ultimately protect surface arthropod diversity, and enhance the ecological benefits of cultivated land.

Effects of organic nitrogen and indigenous AMF on growth and competitiveness of pepper-common bean intercropping

ZHOU Hongyin, ZHANG Shiying, ZHAO Qianxu, LI Bingxuan, BAO Li, YUE Xianrong, XIA Yunsheng

2022, 30(2): 194-202. doi: 10.12357/cjea.20210425

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Abstract:
In recent years, continuous pepper cropping and unreasonable application of high nitrogen (N) fertilizer have been the main factors inhibting pepper cultivation with high yield and quality. At present, many theories attempt to explain the interspecific competition in intercropping systems. Moreover, arbuscular mycorrhizal fungi (AMF) in soil has attracted increasing attention from scientists to improve interspecific competitive interactions. AMF can promote plant nutrient absorption, growth, and development. However, there are few systematic reports on the relationship between AMF on plant interspecific competition and its response to N fertilizer. Therefore, this study aimed to explore the effects of AMF on plant growth, interspecific complementarity, and nutrient competition in an intercropping system of pepper and common bean under different organic N application levels. This can lay down the foundation for diversified planting of protected vegetables and efficient utilization of nutrient resources. Pot experiments were conducted for three different planting modes: pepper-common bean intercropping, pepper monoculture, and common bean monoculture; and two native AMF treatments: without indigenous AMF (NM) and indigenous AMF inoculation (AMF); and two N treatments: no N (N0), organic N (glutamine, 120 mg·kg⁻¹, N120). The effects of inoculation of indigenous AMF, application of organic N and intercropping on plant growth, and interspecific competitiveness of pepper and common bean were studied. The results showed that the inoculation of indigenous AMF infected both common bean and pepper, and organic N application showed the promoting effects. Compared with NM, AMF inoculation significantly increased the aboveground biomasses, plant height of pepper and common bean. The N absorption efficiencies were also increased by 108% under N0 treatment and 98% under N120 treatment for intercropping common bean, and by 40% under N0 treatment and 22% under N120 treatment for intercropping pepper. The results showed that the response of N absorption efficiency to the planting mode was in the order of common bean > pepper, and the N absorption competition of common bean was stronger than that of pepper. Under NM conditions, the competitiveness of pepper to resources was stronger than that of common bean, the interspecific competitiveness of pepper relative to the common bean was 0.60, and pepper was in a dominant position. Under AMF conditions, the competitiveness of pepper to resources was lower than that of common bean, the interspecific competitiveness of pepper relative to the common bean was −0.37, and pepper was at a disadvantage position. Both were more obvious under the N120 condition and significantly increased by 125% and decreased by 19% compared with N0, respectively. It can be seen that the interspecific competitiveness of pepper and common bean was different under different treatments. In all composite treatments, inoculation of indigenous AMF and application of a certain amount of organic N can significantly promote the growth of pepper and common bean, and can also significantly change the interspecific competitiveness of pepper relative to common bean.

Comparison of irrigation strategies for summer maize under deficit irrigation: Grain yield and water use efficiency

ZHENG Mengjing, ZHANG Lihua, ZHAI Lichao, DONG Zhiqiang, JIA Xiuling

2022, 30(2): 203-215. doi: 10.12357/cjea.20210450

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Abstract:
The shortage of water resources in the North China Plain (NCP) poses a challenge to traditional agricultural irrigation methods. Adjusting and optimizing the irrigation mode is an important strategy for saving water and improving water use efficiency (WUE) and crop yield under water-limited irrigation conditions. Given this background, different irrigation modes were set in an automatic rainproof shed (to eliminate the effects of natural rainfall) in the two growing seasons of 2018 and 2019 to analyze the grain yield and WUE of summer maize. In this experiment, a randomized block design was adopted, and two irrigation methods were applied: border irrigation (BI) and micro-sprinkler irrigation (SI). Based on the total irrigation amount and frequency, sample plots were divided into two groups for comparison. Plots in the first group (SI-225 and BI-225) had the same total irrigation amount (50% of evapotranspiration, ET) but different irrigation frequencies. SI-225 was irrigated six times, namely at the emergent seedling stage (VE), sixth leaf stage (V6), tenth leaf stage (V10), thirteenth leaf stage (V13), tasseling stage (VT), and milk stage (R3). BI-225 was irrigated three times at VE, V10, and VT. Plots in the second group (SI-225, SI-280, SI-352, and BI-450) had the same irrigation frequency but different total irrigation amounts (50%, 60%, 80%, and 100% of ET). Among them, SI-225 and BI-450 received a fixed amount of water per irrigation event, whereas SI-280 and SI-352 underwent supplementary irrigation according to their soil moisture content. The results showed that, compared with those of BI-225, the grain yield of SI-225 increased by 17.7%−20.2% and its WUE increased by 9.2%−12.7%. Further analysis of physiological characteristics revealed that SI-225 showed an improved upper soil water status (0−40 cm), increased photosynthetic rate (P_n), leaf area index (LAI), and dry matter accumulation, and consequently higher yield and WUE due to modest but highly frequent irrigation. Under the same irrigation frequency, the grain yields of SI-225 and SI-280 decreased by 21.2% and 12.0%, respectively, compared with that of BI-450. However, total water consumption during the growth period was reduced due to the decrease in LAI and transpiration rate (T_r) of SI-225 and SI-280, which resulted in an improved WUE. The grain yield of SI-352 did not differ significantly from that of BI-450, but its ET decreased by 9.8% due to the optimization of LAI and T_r, its irrigation amount decreased by 21.8%, and its WUE increased by 5.1%. Therefore, under water-limited irrigation conditions (50% of ET), the yield and WUE of summer maize could be increased by increasing the irrigation frequency, with modest but highly frequent irrigation promoting the best results. Moreover, under moderate water limitation (80% of ET), the application of micro-spraying supplementary irrigation based on soil moisture content allowed to achieve a stable yield and a high WUE. These results provide a theoretical reference for improving the efficiency of agricultural water use in water-deficient areas of the NCP.

The impacts of cultivar maturity and meteorological factors on main quality of potato

ZHANG Jiaying, LI Yang, WANG Jing, HU Qi, HUANG Mingxia, LIU Xiaxia

2022, 30(2): 216-225. doi: 10.12357/cjea.20210561

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Abstract:
Meteorological factors and cultivar maturity are the two determining factors of potato tuber quality. Analyzing the relationship between meteorological factors during the potato growth period and potato quality is of great significance for ensuring food security and enriching people’s dietary structure. On the basis of 2 years × 3-planting dates × 3-cultivars field experiment conducted in Wuchuan, Inner Mongolia Autonomous Region, the relationships between meteorological factors during different potato growth periods and the main indices of potato quality were quantified. On the basis of hydrothermal requirements during different potato growth stages, we divided the entire growth period into two periods, namely the vegetative growth period (planting-tuberization) and the reproductive growth period (tuberization-maturity), and then divided the reproductive growth period into tuberization to tuber bulking, tuber bulking to maturity. With the addition of the whole growth period and the water critical period (10 days before to 15 days after tuberization), six growth periods were set as the study phases. Five meteorological factors, namely effective accumulative temperature, mean temperature, daily temperature range, precipitation, and sunshine hours during the six growth periods were used to assess the relationships with potato quality, using correlation analysis, variance analysis, and membership function. The results showed that the average contents of crude protein, vitamin C, soluble sugar, and starch were 100.1 g∙kg⁻¹, 19.64 mg∙(100g)⁻¹, 18.58 g∙(100g)⁻¹ and 31.48 g∙(100g)⁻¹, respectively. The coefficients of variation for the main potato quality indices were in the order of soluble sugar > starch > vitamin C > crude protein. On the basis of membership function, the early maturing cultivar (‘Favorita’) with early planting (April 27), the middle maturing cultivar (‘Connibeck’) with late planting (June 2), and the late maturing cultivar (‘Kexin_1’) with middle planting (May 15) achieved the best potato quality when compared with other combinations of planting date and cultivar maturity. Ultimately, the coupling of planting date and cultivar had a significant effect on potato quality. Furthermore, meteorological factors had significant effects on potato quality during different potato growth periods. The results showed that potato tuber quality was mainly determined by meteorological factors during the potato reproductive growth period (tuberization-maturity), especially during tuber bulking to maturity.

Effects of storage temperature on the post-harvest quality of chili pepper (Capsicum annum L.)

GAO Cheng’an, MAO Qi, WAN Hongjian, YAO Zhuping, ZHOU Guozhi, RUAN Meiying, WANG Rongqing, YE Qingjing, CHEN Shuangchen, CHENG Yuan

2022, 30(2): 226-235. doi: 10.12357/cjea.20210586

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Abstract:
This study explored the effects of different storage temperatures on the postharvest quality of pepper fruits. A pepper cultivar (P1808) bred by the Zhejiang Academy of Agricultural Sciences was used in this study. Pepper fruits at the green ripe stage were collected and kept at room temperature (RT, 20 °C) or high temperature (HT, 30 °C) for 24 h and 48 h. Thereafter, the quality-related parameters of pepper fruits, including firmness, water loss rate, as well as contents of capsaicinoids, vitamin C, and amino acid, were analyzed. The results showed that under RT storage, the capsaicinoid content increased by more than 50% after 24 h and then decreased after 48 h, respectively; and the chlorophyll content decreased and remained at the same level after 24 h and 48 h, respectively; however, the water loss rate, relative electrolyte leakage, and protein content showed a tendency of continuous accumulation up to 48 h. Under the HT storage treatment, the capsaicinoid content gradually increased by approximately 50% and 150% after 24 h and 48 h, respectively; while the chlorophyll content continuously declined. After 48 h, the fruit firmness decreased significantly, while other parameters, including the water loss rate, malondialdehyde content, relative electrolyte leakage, and total carotenoid content, increased. The results of amino acid composition and nutritional value analysis of the pepper fruits under different temperature storage treatments showed that both the RT and HT treatments promoted the accumulation of 17 amino acids after 48 h. Further analysis based on the functional classification of amino acids indicated that the RT treatment significantly increased the content of total amino acids, essential amino acids, amino acids essential for children, and flavor-related amino acids. From the perspective of the nutritional value of amino acids, methionine and cystine were proved to be the main limiting amino acids in the pepper fruits; after 48 h, both the RT and HT storage treatments led to a decreased pattern of valine and isoleucine compared to the amino acid pattern spectrum in the pepper fruits. Ultimately, this study provides theoretical and practical guidance for postharvest maintenance of the quality of pepper fruits.

Regulation of OsMYB57 gene expression in rice and its allelopathic suppression to weed

YANG Luke, WANG Hao, GAO Yujie, YAN Xue, MU Dan, LIN Wenxiong, FANG Changxun

2022, 30(2): 236-247. doi: 10.12357/cjea.20210550

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Rice allelopathy is a natural inhibitory phenomenon of some rice varieties against surrounding weeds. It is an eco-friendly method to control weeds, and it has become a popular research topic in the development of sustainable agriculture. Allelopathy is a quantitative trait regulated by a number of genes that are responsive to environmental changes. Previous studies have indicated that increasing the gene expression of the R2R3-MYB transcription factor MYB57 increases the expression of genes involved in the synthesis of phenolic acid allelochemicals, thereby enhancing the allelopathic effect of rice. This demonstrated that the transcription factor MYB57 efficiently regulates allelopathic weed suppression in rice; however, the regulatory network for MYB57 remains unknown. To further explore the transcriptional factors that regulate the gene expression of OsMYB57, an allelopathic rice accession (‘PI312777’) and a non-allelopathic accession (‘Lemont’) were used. The amplification of the promoter region of the OsMYB57 gene in ‘PI312777’ and ‘Lemont’ was conducted using specific biotin-labeled primers at the 5′ end. The proteins binding to the OsMYB57 gene promoter were co-precipitated using the DNA pull-down technique. Identification of these proteins using mass spectrometry showed that the gene expression of OsMYB57 was regulated by transcription factors (basic helix-loop-helix protein 009 [bHLH009], LOC_Os04g32590.1, and LOC_Os02g31160.1) and transcription regulators (LOC_Os03g25430.1 and LOC_Os03g50110.1), which were encoded by the OsMYC2, Os04g0397500, Os02g0516800, Os03g0370250, and Os03g0708800 genes, respectively. The transcript level of these genes was up-regulated in ‘PI312777’ and ‘Lemont’ when they were co-cultured with barnyardgrass (Echinochloa crusgalli L.) for 1, 3, 5, and 7 days; more specifically, the expression of OsMYC2, Os02g0516800, and Os03g0708800 was significantly up-regulated in rice that was co-cultured with barnyardgrass for 5 days when compared to control groups. Among these proteins, basic helix-loop-helix protein 009 is a positive regulator of the jasmonate (JA) signaling pathway. The gene expression level of OsMYC2, Os04g0397500, Os02g0516800, Os03g0370250, and Os03g0708800 in ‘PI312777’ and ‘Lemont’ was up-regulated after the rice was treated with 0.05 mmol∙L⁻¹ of exogenous methyl jasmonate (MeJA), which resulted in an increased allelopathic suppression to barnyardgrass. Results of western blotting demonstrated that the protein expression levels of MYB57, MAPK11, and PAL2;3 in ‘PI312777’ and ‘Lemont’ were increased under the induction of MeJA. Furthermore, when compared with the control group of barnyardgrass treated independently with MeJA, the root exudates of ‘PI312777’ and ‘Lemont’ induced by 0.05, 0.10, and 0.20 mmol∙L⁻¹ of MeJA exhibited an enhanced growth inhibitory ratio, and the inhibitory effect of the root exudates of ‘PI312777’ induced by MeJA was higher than that of ‘Lemont’. The inhibitory ratios of ‘PI312777’ exudates induced by 0.05 mmol∙L⁻¹ of MeJA on the plant height and root length of barnyardgrass increased by 25.82% and 17.01%, respectively; while the same treatment using ‘Lemont’ root exudates showed a 5.30% and 15.36% increased inhibitory ratio on barnyardgrass. These results indicated that the gene expression of OsMYB57 was transcriptionally regulated by bHLH009 (MYC2), and that a suitable concentration of MeJA promoted the gene expression of OsMYC2, thereby enhancing OsMYB57 expression and resulting in an increase in MYB57, MAPK11, and PAL2;3 expression, which led to systematically up-regulated and improved rice allelopathic weed suppression.

Effects of biological fumigation combined with microbial agents on fungi community structure in continuous watermelon cropping soil

CHANG Fangjuan, ZHANG Guiyun, ZHANG Liping, LYU Beibei, LIU Zhen, FAN Qiaolan, YAO Zhong

2022, 30(2): 248-257. doi: 10.12357/cjea.20210473

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Abstract:
The soil-borne disease caused by changes in soil microbial flora is an important factor restricting the healthy development of the watermelon industry. We examined the responses of soil fungal communities to biological fumigation combined with microbial agents by setting up different treatments, namely a control (CK), biological fumigation (R), and biological fumigation combined with microbial agents (RB) in a two-year continuous cropping watermelon field. On the basis of soil chemical property analysis and Illumina HiSeq high-throughput sequencing technology, the changes in the composition and diversity of soil fungal communities and their relationships with soil environmental factors were examined. The results showed that compared with CK, both R and RB increased the content of available nitrogen, available phosphorus, available potassium, total nitrogen, and organic matter in soil, while reducing soil pH. Moreover, the total nitrogen content was significantly (P<0.05) higher in R treatment compared to the other treatments. The alpha indexes of fungal community showed that R and RB treatments significantly decreased the abundance and diversity of soil fungal community and were in the order of R<RB<CK. When compared with CK, the ACE indexes of R and RB decreased by 4.86% and 3.15% and the Shannon index decreased by 12.65% and 10.88%, respectively, while the Chao1 and Simpson index showed no significant difference, it also decreased by varying degrees. A total of 794 operational taxonomic units were obtained from three watermelon soil samples, which included some unidentified or unknown fungi. In the identified fungal communities, Ascomycota, Basidiomycota, and Mortierellomycota were the dominant fungi phylums, contributing to 95.14%–96.17% of the total abundance, with Ascomycota displaying the highest relative abundance. The relative abundance of Ascomycota and Basidiomycota increased under R treatment, while RB treatment promoted an increase in the relative abundance of Ascomycota and a significant decrease in the relative abundance of Basidiomycota. At the family level, Chaetomiaceae was the dominant fungi, and R and RB treatments significantly increased the relative abundances of Chaetomiaceae and Microascaceae. In addition, RB treatment generated a significantly increased relative abundance of Nectriaceae and reduced relative abundance of Helotiaceae. Cluster analysis showed that the fungal community structures of RB and CK were significantly different from that of R treatment, while the differences between RB and CK were small. RDA analysis showed that there was a correlation between soil chemical properties and soil fungal abundance after bio-fumigation combined with microbial agents; moreover, soil organic matter, total nitrogen, available potassium, and pH were the important driving factors for the changes in soil fungal community structure. In conclusion, biological fumigation combined with microbial agents can improve soil quality, and compared with biological fumigation alone, it can also improve the abundance and diversity of soil fungal communities, as well as adjust the structure of the soil fungal community in a beneficial manner. This study provides effective measures for alleviating or overcoming the obstacles associated with watermelon continuous cropping and an important theoretical basis for a healthy and sustainable development of the watermelon industry.

Effect of chicken manure addition on humification of vegetable waste in composting process

ZHANG Lu, CAO Yubo, WANG Weishuai, ZHANG Xinyuan, WANG Xuan, YAO Peiqing, LIU Shuang, WANG Hong, MA Lin

2022, 30(2): 258-267. doi: 10.12357/cjea.20210536

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Abstract:
In the process of vegetable production and processing, a lot of wastes are produced. Vegetable waste is a potential organic fertilizer source, rich in organic matter, nitrogen, and phosphorus nutrients, and composting is an important way to realize vegetable wastes utilization. However, the high lignocellulose content restricts the composting process, and the addition of chicken manure can accelerate lignocellulose degradation. However, the effect of the chicken manure on the humification of vegetable wastes in the composting process is still unclear. It is necessary to investigate the effects of chicken manure on lignocellulose degradation and humification during vegetable waste composting. The yellowed and dried melon vines were used as raw material (CK), and different proportions of chicken manure (25%, 50%) were added for aerobic composting. By analyzing the temperature, carbon and nitrogen changes, lignocellulose, humus, and seed germination index in the composting process, the effects of active substances added from chicken manure on lignocellulosic degradation and humification in the composting process of vegetable wastes were discussed. The results showed that the addition of chicken manure increased the content of active carbon and nitrogen (dissolved organic carbon and soluble nitrogen) of the initial materials, accelerated the temperature rise of the compost, and prolonged the high-temperature period of composting. The addition of 25% (CM25) and 50% (CM50) chicken manure promoted the degradation of lignocellulose and organic matter, with the highest degradation rates of lignocellulose reaching 61% and 69%, and those of total organic matter reaching 53% and 64%, respectively. The ideal addition of chicken manure (25%) effectively promoted the generation of humic acid, and the content of humic acid in CM25 treatment increased by 56.7% and 48.6% compared with CK and CM50 treatment, respectively. Interestingly, the CM50 treatment significantly promoted the degradation of organic matter and lignocellulose, and the degradation rates of organic matter and lignocellulose increased by 18.5% and 16.9%, respectively, compared with CK. However, the humic acid content was not significantly increased when the addition dosage of chicken manure increased to 50% since the lignocellulose tended to be completely degraded to CO₂. The results showed that treatment with 25% chicken manure had achieved the best performance on maturity parameters, the humification index, degree of polymerization, and germination index reached 14%, 3.5, and 83%, respectively. RDA analysis showed that the degradation of soluble organic carbon, lignocellulose, fulvic acid, and the formation of humic acid were the key factors to promote compost maturity. Therefore, the addition of chicken manure could significantly promote the degradation of lignocellulose in vegetable wastes. However, adding excessive amount of chicken manure lead to the complete degradation of lignocellulose and mineralization and CO₂ emissions, which is not conducive to humic acid formation. Appropriate addition of chicken manure is the key to accelerating the lignocellulosic degradation and promoting the formation of humic acid in the composting process of melon straw. The results can provide a theoretical basis for industrial production.

Vertical distribution of antibiotic resistance genes and bacterial communities in soil of livestock manure stacking site

HAN Wanxue, WANG Fenghua, BAI Zhaohai, LI Wenyan, WANG Xinzhen, MA Lin

2022, 30(2): 268-275. doi: 10.12357/cjea.20210475

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Livestock manure has been regarded as an important reservoir of antibiotics and antibiotic resistance genes (ARGs). However, most livestock manure is stacked directly in the farm, which causes a potential threat to the surrounding soil and groundwater safety. In order to study the effect of long-term livestock manure stacking on the vertical distribution of ARGs and bacterial communities, 0−100 cm soil samples were collected from pig and chicken manure stacking sites, respectively. Real-time quantitative PCR results showed that pig and chicken manure stacking increased the detection ratio and abundance of tetracycline resistance genes (tetC, tetG, tetL, tetW) and sulfonamide resistance genes (sulI, sulII), and an integrase gene (intI1) in soil samples. This demonstrated that livestock manure stacking could lead to the contamination of ARGs in the surrounding soil. According to the cluster analysis, the abundance of ARGs and intI1 gene were decreased with increasing soil depth and mainly concentrated in the 0−30 cm soil layer, which posed a risk of migration of ARGs into the deep soil. In addition, intI1 gene had a significant and positive correlation with ARGs abundance, indicating that intI1 gene may play an important role in disseminating ARGs. Furthermore, the high-throughput sequencing results showed that both pig and chicken manure stacking significantly reduced and changed the diversity of bacterial communities in the 0−10 cm and 10−30 cm soil layers, compared with the control soil. The difference of bacterial community structure between livestock manure stacking site soil and control soil was higher in 0−30 cm than in deep soil. What’s more, both soil chemical properties and bacterial community affected the vertical distribution of ARGs in soil, with the shift of bacterial community structure representing the major driver shaping the ARGs distribution based on variation partitioning analysis. Taken together, our results provide insight into the control of ARGs pollution in livestock manure stacking stie soil around the farms.

Applicability evaluation of the nonparametric approach for estimating evapotranspiration on irrigated farmland in the North China Plain

ZHANG Xiaolong, ZHANG Yucui, SHI Jiali, WANG Yan, SHEN Yanjun

2022, 30(2): 276-289. doi: 10.12357/cjea.20210415

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Evapotranspiration (ET), generated by the evaporation of water from a natural surface into the atmosphere, is an important component of the water cycle and surface energy balance system, which is a fundamental information for agriculture, water resource management, and climate change research. In recent decades, the estimation of ET or latent energy (LE, which is the amount of heat required for ET) has remained one of the most challenging problems for researchers. A nonparametric approach for estimating ET may avoid the complex parameterization process and reduce the calculation uncertainties; therefore, it has broad application prospects. However, a more detailed applicability evaluation of the nonparametric approach in different regions or ecosystems is needed, as most of the current studies on the application of this approach focus on arid basins, with few applicability analysis reports focusing on irrigated farmland in sub-humid areas. In this study, the eddy covariance data modified by the energy residual closed correction method in three irrigated farmland stations (Luancheng Agroecosystem Experimental Station, Chinese Academy of Sciences; Yucheng Comprehensive Experimental Station, Chinese Academy of Sciences; and Guantao Experimental Station, Beijing Normal University) in the North China Plain were used as references, and the applicability of the nonparametric approach for estimating LE on irrigated farmland at different time scales (daily scale and 30 min scale) and seasons in the three stations was evaluated. The results showed that the nonparametric approach had reliable and robust performance for different crop types and time scales on irrigated farmland in the North China Plain. The estimated LE could ideally reflect seasonal and intraday variations, but these values were generally underestimated. Furthermore, the bias, coefficient of determination, root mean square error, and Nash-Sutcliffe coefficient at the daily (and 30 min) scale were −16.18 to −12.88 W∙m⁻² (−13.30 to −7.68 W∙m⁻²), 0.80 to 0.83 (0.88), 22.45 to 31.06 W∙m⁻² (39.22 to 42.15 W∙m⁻²), and 0.66 to 0.75 (0.86 to 0.87), respectively. The nonparametric approach significantly underestimated the latent heat flux when the water supply was sufficient or when crops were growing vigorously; moreover, this approach slightly or not underestimated the latent heat flux when the water supply was insufficient or when crops were sparse. In addition, the response of the nonparametric approach to irrigation activities was not considered sufficiently, and further improvement to the model structure may be required to improve the simulation accuracy of irrigated farmland. Finally, the parameter sensitivity of the nonparametric approach in irrigated farmland in the North China Plain, from high to low, was air temperature, surface temperature, net radiation, and soil heat flux, but the influence of soil heat flux can be ignored. Ultimately, this study not only provides a reference for the improvement of the nonparametric ET estimation approach but also helps further the understanding of ET fundamental theory.

Mapping soil available phosphorus of cultivated land in hilly region of southern China based on sparse samples

CAO Jiaping, ZHANG Liming, QIU Longxia, XING Shihe, MA Dan

2022, 30(2): 290-301. doi: 10.12357/cjea.20210565

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Abstract:
Spatial distribution mapping of topsoil available phosphorus content of cultivated land is essential for precise agricultural management and soil environmental assessment. Most research has focused on sufficient soil samples to map topsoil phosphorus content of cultivated land in flat areas. However, there are few studies on soil available phosphorus mapping based on sparse samples in the hilly areas of southern China. Jian’ou City was selected as the study area, which is a hilly area in southern China and has the largest cultivated land area among all county-level cities in Fujian Province. A total of 96 soil measurements, Sentinel-2 remote sensing data with a spatial resolution of 10 m, and climate and topographical variables were used to predict topsoil (0–20 cm) available phosphorus content. Random forest models with five combinations of environmental variables were constructed and their performance was compared for model prediction. Three assessment criteria, namely the coefficient of determination (R²), mean absolute error (MAE), and root mean square error (RMSE) were used to evaluate the performance of random forest models for five combinations of environmental variables. The results showed that the prediction accuracy of the random forest model using climate variables, topographic variables, and soil pH values significantly improved after adding remote sensing variables, with an R² increase from 0.36 to 0.59 and an RMSE decrease of 20.34%. In addition, the random forest model using all variables (remote sensing, topography, climate, and soil pH) obtained the optimal performance (R²= 0.59, MAE = 19.04 mg∙kg⁻¹, RMSE = 25.26 mg∙kg⁻¹) among five combinations of environmental variables. Therefore, remote sensing variables are of great value for the mapping of soil available phosphorus based on sparse samples, and we suggested that the use of remote sensing variables should be increased in future studies to improve prediction accuracy. Remote sensing variables, climate variables, topographic variables, and soil pH could explain 22.87%, 30.64%, 30.38%, and 16.11% of the topsoil available phosphorus content, respectively. Furthermore, the spatial distribution of soil available phosphorus content in the study area was found to be mainly affected by the mean annual temperature, soil pH, soil moisture index, and elevation. The spatial distribution maps of soil available phosphorus content by the five random forest models were similar. High values of topsoil available phosphorus content were distributed in the central and western regions, whereas low values were distributed in the eastern and southern regions. The spatial variation of the soil available phosphorus in the distribution map produced by the optimal random forest model with total environmental variables was the most precise. Therefore, a random forest model that uses all variables (i.e., soil pH, topographic, remote sensing, and climate) can be used as a robust method to resolve soil available phosphorus content mapping with sparse soil samples in the hilly regions of southern China. Thus, this research can provide some guidance for other researchers interested in mapping the soil available phosphorus content in the hilly regions of China.

Suitability evaluation of suitable-for-mechanization transformation of cultivated land based on topographic complexity in Chongqing, China

LI Lingli, LI Jiangwen, ZHONG Shouqin, YANG Chaoxian, WEI Chaofu

2022, 30(2): 302-313. doi: 10.12357/cjea.20210456

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Abstract:
Suitable-for-mechanization transformation is the fundamental way to promote the development of agricultural mechanization in hilly areas. Scientific evaluation of its suitability can reasonably plan the transformation process, which is significant in improving the efficiency and accuracy of agriculture mechanized transformation in hilly areas. The study selected three topographic limiting factors: elevation, slope and fragmentation with different districts and counties in Chongqing as evaluation units, to evaluate the suitability of suitable-for-mechanization transformation of cultivated land by integrating GIS spatial analysis function and data envelopment method (DEA). The results showed that: 1) the cultivated land plots in Chongqing was small and fragmented, mainly distributed in the central and western regions. The area and density of cultivated land in the eastern part of Chongqing were obviously less than that in other regions, consistent with the topography of high in the east and low in the west. The spatial distribution characteristics of paddy field and cultivated land were similar, and the terrain requirement of dryland was lower than that of paddy field. 2) The cultivated land was mainly distributed in the slope of 6°−15° and the elevation of 200−500 m, among which the cultivated land with the elevation of 300−400 m was the most ideal area for mechanization transformation, accounting for 48.88% of the main cultivated land. 3) According to the classification method of natural disjunctions (Jenks), the comprehensive topographical complexity index was segmented into six sections of the suitability degree of mechanization reconstruction in Chongqing City including very suitable, suitable, relatively suitable, relatively unsuitable, unsuitable and very unsuitable. The average value of terrain complexity index of each district and county was 0.925, and a total of 25 districts and counties were below that index, including 9 districts and counties in the very suitable area such as Tongnan District, 7 districts and counties in the suitable area such as Bishan District, and 9 districts and counties in the relatively suitable area such as Qijiang District, which were relatively suitable. The evaluation results, which consider the limiting factors of developing the agricultural mechanization of hilly areas, were highly coincident with the actual geomorphic layout of Chongqing City, which was conducive to group integrated development. So it is suggested that the places with high suitability should be given priority for mechanization reconstruction for further landing. Therefore, the suitability evaluation method based on the terrain complexity can effectively evaluate the suitability of hilly mountain land in reconstructing appropriate machine for cultivated land, with the support of GIS spatial analysis function. Futrthermore, the appropriate machine renovation for the cultivated land located in a region of gradient less than 15° will greatly improve the degree of agricultural mechanization in Chongqing municipality; thus, the appropriate machine reconstruction for cultivated land is potential.

Estimation method of daily global radiation under different sunshine conditions: A case study of Jiangsu Province

ZHANG Pei, GAO Ping, XIE Xiaoping, LA Ba, JIANG Xu, CHEN Shiyao, WU Hongyan

2022, 30(2): 314-324. doi: 10.12357/cjea.20210470

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Abstract:
Global radiation is a key factor affecting carbon exchange and the surface energy budget of agroecosystems. To accurately estimate the daily global radiation (GR) under different sunshine conditions and to improve the research carried out on agroecosystems, this study used daily meteorological and radiation data collected between 2005 and 2020 at three radiation observation stations in Jiangsu Province, namely Huai’an, Lüsi, and Nanjing, to divide the research samples into two categories, namely with and without sunshine, according to whether the number of hours of sunshine per day was zero. In total, 24 observable meteorological factors and 3 geographical factors were identified, with the main factors influencing GR under different sunshine conditions being determined using correlation analysis. Daily data from the three stations collected during odd-numbered years between 2005 and 2016 were selected as the modeling dataset, and the least-squares stepwise regression method was adopted to establish the GR estimation models for conditions with and without sunshine, with GR and the daily atmospheric transparency coefficient (ratio of GR to sky radiation [SR], GR/SR) representing the dependent variables. Daily data samples from the three stations collected during even-numbered years between 2005 and 2016 were selected as the between-group verification set, while daily data samples collected from 2017 to 2020 were selected as outside-group verification sets. The optimal GR estimation model for Jiangsu Province was determined by comparing the model fits and the estimation effects of the original models with the between-group and the outside-group verification sets. The results showed that first, GR was significantly correlated with most of the meteorological factors (P<0.01) regardless of the presence of sunshine. GR under sunshine conditions had the strongest correlation with sunshine factors, while GR under without sunshine condition had the strongest correlation with the daily maximum ground temperature (T_GMax). Furthermore, the correlation coefficient between GR and T_G_Max was higher than the correlation between GR and other temperature factors. Second, the estimation model with GR as the dependent variable and T_G_Max and daily dew point temperature as the independent variables was selected when the daily sunshine duration was zero; the coefficient of determination (R²) of this model was 0.650, and the estimation accuracy of GR was close to 75%. The estimation model with GR/SR as the dependent variable and daily percentage of sunshine and sunshine duration as the independent variables was selected when the daily sunshine duration was greater than zero; the R² of this model reached 0.769 and the average estimation accuracy of GR was 87.60%. On the basis of subsection of estimation models, the average accuracy of GR under different sunshine conditions in Jiangsu reached 84.71%, and the proportion of outliers in the total sample was 2.04%. The introduction of accurate GR estimation is greatly beneficial to carry out research on crop growth and yield simulation and soil moisture estimation, and ultimately provide a basis for related research on agroecosystems.

2022 Vol. 30, No. 2