中国生态农业学报(中英文)

Statistical characteristics of heat stress in early rice based on extreme value distribution in China

HE Liang, WU Menxin, HOU Yingyu, ZHAO Gang, JIN Ning, YU Qiang

2018, 26(11): 1601-1612. doi: 10.13930/j.cnki.cjea.180269

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Abstract:
Rice is one of the most important staple foods globally, eaten by more than half the world population. China is the largest producer of rice, accounting for 18.5% of the rice planted area globally and 28% of the global rice production. Rice is easily exposed to heat stress because of highly frequent heat-stress events in recent climate warming. Heat-stress is one of the main meteorological disasters causing yield loss in agriculture. Thus, it is essential to explore spatial and temporal characteristics along with extreme heat-wave distribution in early rice so as to develop measures for agricultural adaptation to climate change and to prevent and reduce natural disasters. Studies on heat-stress in rice have mainly focused on spatial and/or temporal distributions of heat-stress at provincial or catchment scales and on the relationship between heat-stress and yield production. However, spatial and temporal distributions of heat-stress at national scale and extreme heat-wave distribution have remained rarely explored. Extreme-value (outlier) theory is a branch of statistical deviation of median probability distribution, which is widely used in structural engineering, hydrology and traffic prediction. Here, we introduced extreme-value theory to analyze heat-stress in early rice and hypothesized that heat-stress in rice obeyed specific outlier distribution. Thus, using 214 meteorological data on early rice region in China, we studied spatial and temporal characteristics along with extreme-value distribution of heat-stress in early rice. Non-parametric methods (such as the Mann-Kendal trend test and extreme-value distribution) were used in this study. We found that:1) mean values of two heat-stress indices-ADHS (cumulative heat-stress days) and HDD (heat-stress degree days)-used to determine the extent of heat-stress were larger in the south and central Hunan Province, central Jiangxi Province, central Zhejiang and Fujian Provinces than that in other areas. This indicated that there were more severe heat-stress events in these areas. The two heat-stress indices significantly increased in more than a third of the investigated site (more than half of the sites in 1990-2015). This further indicated that early rice at these sites suffered from worsening heat-stress. 2) ADHS and HDD at more than half of the sites satisfied the extreme-value (outlier) distribution. ADHS at 56 sites obeyed the Gumbel distribution and at 82 sites satisfied the General extreme-value (outlier) distribution. HDD at 61 sites obeyed Gumbel distribution and at 58 sites satisfied the general extreme-value distribution. 3) The spatial distributions of the 10-, 50-and 100-year return periods of the two heat indices were similar to their mean values. It then meant that regions with larger mean values of the two heat-stress indices also had larger return periods. Furthermore, the return periods of the two heat-stress indices were not significantly correlated with longitude, latitude and altitude. The results improved our understanding of spatial and temporal distributions along with extreme-value (outlier) distributions of heat-stress in rice. It provided the scientific basis for adaptation to climate change and agricultural weather index insurance.

Effect of tillage method change on soil greenhouse gas emission and yield during winter-wheat growing season

ZHAO Liying, DONG Wenxu, HU Chunsheng, LI Jiazhen, CHEN Tuo

2018, 26(11): 1613-1623. doi: 10.13930/j.cnki.cjea.180219

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Abstract:
Under long-term rotary tillage, soil bulk density, carbon decomposition and nutrient in sub-surface soil in the shallow plow layer significantly increase, but wheat growth and soil carbon sequestration become limited. However, subsoiling and deep plowing can break the bottom of the plow layer and reduce soil bulk density, which are conducive for good growth of plant root and absorption of nutrients to ensure high crop yield. The objectives of this study were to analyze changes in greenhouse gases emission and wheat yield after 16 years (2001-2016) of rotary tillage (X) treatment and conversion into other tillage treatments, including rotary tillage-deep plowing (XF) and rotary tillage-subsoiling (XS) treatments in 2016, and to determine the best rational tillage strategy. Carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄)emission fluxes in the three tillage treatments were sampled and measured using static chamber-gas chromatography. Soil temperature at the 0 cm depth, soil gravimetric moisture content, soil bulk density at different depths and other related factors were monitored during wheat growth period and winter wheat yield analyzed after harvest. The experimental results showed prominent high fluxes of CO₂ and N₂O one week after the three tillage treatments and during harvest, with minimum emission fluxes of CO₂and N₂O during winter period. Compared with XF treatment, X and XS treatments significantly increased CO₂ emission fluxes from the start of the three tillage treatments to the end of October. Compared with X and XF treatments, N₂O fluxes under XS treatment were significant high after tillage treatment, fertilization and irrigation. CH₄ fluxes fluctuated from November 2016 to February 2017, and became more stable from March 2017. From January 2017 to the harvest season, soil uptake of CH₄ under XS treatment was higher than those under XF and X treatments. The fields under the three tillage treatments during winter wheat growth were the sources of CO₂ and N₂O. The cumulative fluxes of the three tillage treatments served as CH₄ sink. In winter wheat fields, cumulative CO₂ emission was in order of XS > X > XF, with total CO₂ emissions of 5 241 kg·hm^-2, 5 160 kg·hm^-2 and 4 840 kg·hm^-2, respectively. Cumulative N₂O emission was in order of XS > XF > X, with total N₂O emissions of 4.38 kg·hm^-2, 2.39 kg·hm^-2 and 2.26 kg·hm^-2, respectively. Cumulative CH₄ sink was in order of XS > XF > X, with total CH₄ absorptions of 6.14 kg·hm^-2, 5.64 kg·hm^-2 and 3.70 kg·hm^-2, respectively. The contribution of cumulative greenhouse gases to CO₂-equivalents was expressed as XS > X > XF, which were 6.23 t·hm^-2, 5.66 t·hm^-2 and 5.32 t·hm^-2, respectively. Using deep plowing and subsoiling, soil organic matter decreased in the 0-10 cm soil depth, but increased in the 10-20 cm soil depth. Soil organic carbon was the main source of CO₂. Reduction in soil organic matter led to reduction in CO₂. Winter wheat grain yield under X treatment was higher than that under XS and XF treatments. Considering the changes in soil physical properties, greenhouse gas emission and wheat yield, XF treatment was the most suitable tillage practice. However, more and longer research work was needed to determine an ideal tillage treatment to ensure future ecological benefits and grain yield.

Effects of intercropping and AMF inoculation on phosphorus forms in red soils

ZHONG Xiong, WANG Shuo, BAO Li, ZHANG Naiming, LIU Dahui, XIA Yunsheng, LI Jiahua

2018, 26(11): 1624-1633. doi: 10.13930/j.cnki.cjea.180407

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Abstract:
Arbuscular mycorrhizal fungi (AMF) can help host plants in the uptake of nutrients, especially phosphorus (P). Intercropping also can promote use efficiency of P in soils and increase crop yield. In order to study the effects of different P additions and AMF treatments on the absorption and utilization of different forms of P of intercropping corps in red soils, a pot simulation experiment was conducted using the three-compartment method. Under maize-soybean intercropping system, the hyphal compartments were treated with different forms of P-no P (P0), inorganic P (potassium dihydrogen phosphate-IOP50) and organic P (soy lecithin-OP50). Different AMF treatments, including no AMF (NM), inoculation with Funneliformis mosseae (FM), were performed in the root chamber. Intercropped maize and soybean, mono-cropped maize and soybean were planted in the experiment. The results showed that compared with mono-cropping-FM and IOP50 treatment, P uptake in maize increased by 150.2% and P uptake in soybean increased by only 24.5% under intercropping-FM and IOP50 treatment. Except mono-cropped soybean and P0 treatment, FM inoculation significantly decreased available P content in hyphal compartment soils. In addition to soybean mono-cropping-FM treatment, IOP50 application yielded the highest soil available P content under mono-cropping, and the lowest under intercropping conditions. AMF inoculation increased the contents of Ca₂-P, Al-P, Org-P, O-Al-P and Ca₁₀-P to a certain extent, while intercropping significantly increased crop uptake of Ca₂-P and Fe-P in the soil. Under combined intercropping, FM and IOP50, the contents of Ca₂-P, Org-P and O-Al-P in the soil were higher (P < 0.05) compared with other treatments. Correlation analysis showed that Ca₂-P was significantly negatively correlated with P uptake in maize, while O-Al-P was significantly negatively correlated with P uptake in soybean. In conclusion, FM inoculation, P fertilizer application and intercropping all promoted P absorption and accumulation of host crops to a certain extent. Among these, FM, IOP50 and intercropping was the best combination for the promotion of intercropped maize growth, P uptake and increased Ca₂-P, Org-P and O-Al-P of red soil. If applied to Dianchi watershed, it is expected to reduce the loss of P.

Effect of maize sowing date on yield and interspecific competition in soybean/maize intercropping system

ZHAO Jianhua, SUN Jianhao, LI Weiqi

2018, 26(11): 1634-1642. doi: 10.13930/j.cnki.cjea.180132

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Abstract:
A reasonable co-growth period between intercrop species can effectively improve the use efficiency of soil resources in time-space fabric. However, sowing date of intercrop plants directly determines the length of co-growth period of intercrop plants. This can directly affect intercropped plant productivity and interspecific interaction due to niche differentiation over time. Thus, a study was carried out to determine the effect of sowing date of intercropped maize on yield, productivity and interspecific competitiveness of crops of soybean/maize intercropping system. A total of three sowing dates of maize were set up, which were 24^th April (M1, co-growth period of maize and soybean was 165 days), 4^th May (M2, co-growth period of maize and soybean was 150 days) and 14^th May (M3, co-growth period of maize and soybean was 140 days). Then yield and dry matter accumulation of crops were investigated in both intercropping and sole systems, and system productivity and interspecific competitiveness also analyzed. The result showed that yield of soybean/maize intercropping was not affected by maize sowing date. Land equivalent ratio (LER) of all intercropping systems was greater than 1. However, LER value decreased with delay of sowing date of intercropped maize. The largest LER was for M1 (1.37) treatment. There were no significant differences in yields and yield components of intercropped soybeans with different maize sowing dates. Yield of intercropped maize and productivity of intercropping system decreased with delay of sowing date of intercropped maize. The 100-grain weight of intercropped maize decreased with delay of sowing date, 100-grain weight of M3 (26.1 g) was 71% that of M1 (36.6 g) treatment. The competitive ability of intercropped maize decreased during later co-growth period due to delay in sowing date. During early co-growth period, the competitive ability of soybean for growth resources was stronger than that of maize. However, in later co-growth period (from September to harvest), the competitive ability of maize significantly increased and was greater than that of soybean. However, the aggressiveness of soybean relative to maize (A_sm) under M3 was significantly higher than those under M1 and M2. Meanwhile, relative crowding coefficient of maize also was higher than that of soybean. This decreased with delay in sowing date of intercropped maize in the order of M1 > M2 > M3 and with competitive ratio values of M1 > M2 > M3. Therefore, the most reasonable sowing date of maize in soybean/maize intercropping system in Hexi Corridor of Gansu Province was on 24^th April. Here, yield of intercropped plants and the productivity of intercropping systems were maintained. The delayed sowing dates of maize decreased yield and productivity of intercropping system.

Effect of nitrogen reduction and soybean intercropping on nitrogen balance in sweet maize fields in South China

WANG Zhiguo, LIU Pei, SHAO Yuting, TANG Yiling, GUAN Aomei, WANG Jianwu

2018, 26(11): 1643-1652. doi: 10.13930/j.cnki.cjea.180121

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Abstract:
The increasing demand for fresh sweet maize (Zea mays L. saccharata) in South China has led to the prioritization of finding solutions to environmental pollution caused by continuous production of the crop and high inputs of chemical nitrogen fertilizer. A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes. Here, a field experiment was conducted at Experimental Center of South China Agriculture University for two years (2015-2016) to investigate nitrogen input, output and balance in sweet maize farmlands in South China under two nitrogen levels [reduced nitrogen dose of 300 kg·hm^-2 (N1) and conventional nitrogen dose of 360 kg·hm^-2 (N2)] and three cropping patterns [sole sweet maize (SS), sweet maize//soybean intercropping with sweet maize to soybean line ratios of 2:3 (S2B3) and 2:4 (S2B4)]. The purpose of the study was to provide scientific basis for reducing chemical nitrogen fertilizer input, improving nitrogen use efficiency and developing a sustainable sweet corn production model in South China. Results showed that:1) reduced nitrogen application and sweet maize//soybean intercropping decreased total nitrogen input and the proportion of chemical nitrogen input through soybean nitrogen fixation and straw return. Nitrogen fertilizer input under SS, S2B3 and S2B4 accounted respectively for 84.29%, 55.42% and 59.06% of total annual nitrogen input under N1 and for 87.53%, 49.93% and 53.70% under N2. 2) Accumulated nitrogen amount of grain under intercropping system was significantly higher than that under sole sweet maize. Average annual grain nitrogen accumulation of sweet maize//soybean intercropping was 2.18-2.43 times of that of SS. Sweet maize//soybean intercropping reduced ammonia volatilization significantly and thereby reduced the risk of nitrogen leaching. Compared with SS, S2B3 and S2B4 reduced annual ammonia volatilization and nitrogen leaching under N1 by 35.97% and 14.74%, 42.07% and 11.54%, respectively. Treatment S2B4-N1 had the lowest ammonia volatilization, which was 38.72 kg·hm^-2. Meanwhile, annual ammonia volatilization and average annual nitrogen leaching in S2B3 and S2B4 under N2 reduced respectively by 24.55% and 12.89%, 29.98% and 16.23% than that under N1 treatment. 3) Annual nitrogen surpluses under S2B3-N1, S2B3-N2, S2B4-N1 and S2B4-N2 were respectively 71.03 kg·hm^-2, 133.7 kg·hm^-2, 42.87 kg·hm^-2 and 100.64 kg·hm^-2, which were 81.27%, 64.75%, 88.69% and 73.47% lower than the average of SS under N1 and N2. Overall, the study demonstrated that intercropping combined with reduced-nitrogen rate maintained sweet maize production, reduced production cost, while also reducing environmental impact. Intercropping with soybean and reduced nitrogen application may be a more sustainable and environmentally friendly way for production of sweet maize in South China.

Soil respiration, carbon balance, and economic and environmental benefits of triple intercropping system of fava bean, maize and sweet potato under conservation tillage

XIONG Ying, WANG Longchang, ZHAO Linlu, DU Juan, ZHANG Sai, ZHOU Quan

2018, 26(11): 1653-1662. doi: 10.13930/j.cnki.cjea.180167

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Abstract:
Ridge tillage and straw mulching are suitable modes of conservation tillage that increase crop productivity and sequestrate carbon in the purple hilly region of Southwest China. A field experiment was conducted with six treatments-traditional tillage without straw mulching (T), ridge tillage without straw mulching (R), traditional tillage with straw mulching at 3 750 kg·hm^-2 (TS1), ridge tillage with straw mulching at 3 750 kg·hm^-2 (RS1), traditional tillage with straw mulching at 7 500 kg·hm^-2 (TS2) and ridge tillage with straw mulching at 7 500 kg·hm^-2 (RS2). The characteristics of soil respiration, carbon balance, crop yield, and economic and environmental benefits for the triple intercropping system of fava bean, maize and sweet potato were evaluated. The study provided the theoretical basis for quantifying carbon budget of farmland ecosystems in the region. It was noted that mean soil respiration rates during growth period of fava bean, maize and sweet potato were 3.704 μmol·m^-2·s^-1, 4.847 μmol·m^-2·s^-1 and 4.606 μmol·m^-2·s^-1, respectively. Ridge tillage reduced soil respiration rate during growth period of three crops, whereas straw mulching increased it (P < 0.05). Ridge tillage with straw mulching increased cumulative soil respiration and cumulative microbial respiration (P < 0.05). All treatments of conservation tillage improved carbon sequestration of crops in the triple intercropping system. The soil-crop system exhibited carbon sink and the treatments of RS2, TS2, RS1, TS1 and R significantly increased carbon sequestration respectively by 25.41%, 25.37%, 9.84%, 26.74% and 13.26%, compared with treatment T. Ridge tillage and straw mulching treatments increased total crop yield of the triple intercropping system, which was highest under RS2 (17 460.45 kg·hm^-2) and next TS2 (16 498.73 kg·hm^-2). The amount of CO₂ released from soil per 1 kg grain in the triple intercropping system was in the order of:T (1.88 kg·kg^-1) > TS1 (1.83 kg·kg^-1) > R (1.76 kg·kg^-1) > TS2 (1.75 kg·kg^-1) > RS1 (1.69 kg·kg^-1) > RS2 (1.68 kg·kg^-1). This meant that both ridge tillage and straw mulching increased the economic and environmental benefit index. The more straw was added during mulching, the more was the economic and environmental benefits. In conclusion, the RS2 treatment (ridge tillage + straw mulching at 7 500 kg·hm^-2) had the largest carbon sink capacity and the optimal economic and environmental benefits. Thus, it was recommended for adoption as tillage pattern to increase carbon sequestration and reduce carbon release in the study area.

Effects of spraying potassium fertilizer with surfactant on wettability, physiology and quality indexes of flue-cured tobacco

WANG Yahong, HAN Dan, GAO Sen, CAO Lijun, WANG Xiaoli, NIU Guiyan, REN Zhiguang, XU Zicheng

2018, 26(11): 1663-1671. doi: 10.13930/j.cnki.cjea.180585

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Abstract:
The 'K326' flue-cured tobacco variety was used to investigate the improvement of potassium fertilizer utilization and quality of tobacco leaf under combined application of surfactant and potassium fertilizer. While in the study the contact angle method was used to determine critical surface tension of tobacco leaf, the study critical micelle concentrations of surfactants of sucrose fatty acid ester, tea saponin and washing powder were measured by using surface tension method. By spraying water and potassium fertilizer as the control, the 3 surfactants were added to potassium fertilizer in the field spraying test. In the experiment, CK was the control involving water, CK1 was the control involving potassium fertilizer, T1 was the treatment involving potassium fertilizer plus sucrose fatty acid ester, T2 was the treatment involving potassium fertilizer plus tea saponin, and T3 was the treatment involving potassium fertilizer plus washing powder. The potassium content, antioxidant enzymes activities and plastid pigments contents of tobacco leaves in 5 treatments in different times were measured, and the chemical constituents of flue-cured tobacco leaf were determined. The effects of spraying potassium fertilizer with surfactant on the wettability, physiology and quality indexes of flue-cured tobacco leaf were determined. The results indicated that:1) critical surface tension of tobacco leaf was 30.41 mN·m^-1 indicating lower wettability of tobacco leaf. The critical micelle concentrations (CMC) of sucrose fatty acid ester and tea saponin were 1 000 mg·L^-1 and 5 000 mg·L^-1, with corresponding surface tensions of 32.64 mN·m^-1 and 40.33 mN·m^-1, respectively. When washing powder concentration was 2 000 mg·L^-1, its surface tension (30.30 mN·m^-1) was close to the critical surface tension of tobacco leaf. Under the addition of surfactant, the surface tension of potassium fertilizer solution decreased significantly while the wettability increased. 2) Surfactants promoted the absorption of potassium in tobacco leaf. Potassium contents under T1 and T2 treatments were higher than under CK1 during the growth period of tobacco. Application of potassium fertilizer with surfactant increased the activities of SOD and POD and decreased MDA content in tobacco leaf. This increased antioxidant capacity of tobacco leaf and reduced membrane lipid peroxidation. Also after the addition of surfactant, chlorophyll and carotenoid contents of tobacco leaf increased at the peak function stage. This enhanced photosynthesis of tobacco leaf which in turn was conducive for the synthesis and accumulation of photosynthetic products. 3) With the addition of surfactant, the contents of total nitrogen and nicotine decreased, while those of potassium, total sugar and reducing sugar increased in flue-cured tobacco leaf. The chemical constituents were more harmonious and the quality of tobacco leaf better. In summary, the addition of sucrose fatty acid ester had the best effect in terms of improving wettability of tobacco leaf, absorption of potassium fertilizer, physiology of tobacco and quality of tobacco leaf.

Effect of maize and gibberellic acid on sunflower broomrape germination, control and growth in sunflower field

WANG Yue, YE Xiaoxin, WANG Kai, LI Pufang, GUO Zhenguo, CHEN Fangjie, MA Yongqing

2018, 26(11): 1672-1681. doi: 10.13930/j.cnki.cjea.180090

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Abstract:
Sunflower broomrape (Orobanche cumana Wallr.) is a parasitic, herbaceous root plant that has severe effect on industrial crops like sunflower. In order to reduce the parasitic effect of sunflower broomrape on sunflower and sunflower broomrape seed bank, two generalized maize varieties ('Jingnuo No. 1', 'Xinyu No. 57') in Xinjiang Uygur Autonomous Region of China were used in a plug tray experiment to study the effects of application of two exogenous concentrations of gibberellin acid (10^-4 mol·L^-1 and 10^-5 mol·L^-1) at different periods (10 d and 15 d after germination) on maize growth and development, and secretion of stimulant of sunflower broomrape seed germination. The study screened out more capable maize variety for pot experiment by collecting and extracting root exudates of maize to stimulate sunflower broomrape seed germination after 24 days. Through applying GA₃(10^-4 mol·L^-1) at different times after planting, the study also explored the combined effects of maize and GA₃ on controlling sunflower broomrape seeds. Thus in the pot experiment, GA₃ was exogenously applied 20 and 40 days after planting maize, and plant samples (leaves, stems and roots) and rhizosphere soils collected at harvest (105 d) were used to further analyze sunflower broomrape seed germination. Sunflowers were planted in pots that were planted with maize in the past years. The epigaeous number of sunflower broomrape was counted and sunflower plants of agronomic index measured at harvest. The results showed the application of GA₃ in the plug tray experiment had a significant effect on maize height. In addition, there was no inhibiting effect on maize in terms of secreting germination stimulant of sunflower broomrape. Thus, it was productive to apply GA₃(10^-4 mol·L^-1 and 10^-5 mol·L^-1) during maize growth period. Moreover, 100-dilution of root exudate of 'Xinyu No. 57' maize variety showed more significantly stimulating effect on sunflower broomrape germination rate than 'Jingnuo No. 1', 'Xinyu No. 57' was finally used in the pot experiment. In the pot experiment, maize heights under 10^-4 mol·L^-1 GA₃ application after 20 and 40 days of maize planting were higher than that under the control (no application of GA₃), with respective increases of 22.5% and 19.1%. Sunflower was planted in the second year after maize, which was treated by GA₃at 20 days after planting. The diameter of sunflower disk increased by 57.1% compared with the control. Compared with control, the number of epigaeous sunflower broomrape was 1.3·plot^-1 and 1.8·plot^-1, which suggested decreases of 76.4% and 67.3%, respectively. In conclusion, the application of 10^-4 mol·L^-1 GA₃ to maize after 20 and 40 days of planting stopped sunflower broomrape seed germination and thereby reduced sunflower broomrape damage to sunflower.

The role of ionic interfacial behaviors in formation of soil organic-inorganic complexes

LI Shaobo, XU Yingde, GAO Xiaodan, ZHANG Yun, ZHANG Guangcai, LI Song, XU Chenyang, TIAN Rui, WANG Jingkuan

2018, 26(11): 1682-1691. doi: 10.13930/j.cnki.cjea.180376

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Abstract:
Interactions between soil organic matter and mineral surfaces are ubiquitous. Research on soil organic-inorganic complexes has received much attention. The association of soil organic matter and mineral has been related to the stability of soil carbon pool directly, and this is of great significance to the environmental sciences and agricultural resource utilization. However, the mechanism of the formation of soil organic-inorganic complexes has far remained from perfect, and the link of interaction mechanism at the macroscopic, mesoscopic, and microscopic scales of soil have not been reasonably explained. Therefore, this paper discussed the formation of organic-inorganic composite colloids (formation theory, action mechanism and influencing factors) and the interfacial behavior of ions in this process. It systematically combed the mechanism of ions in the formation of soil organic-inorganic complexes and recalled advanced technologies of studying the interaction between soil organic and inorganic components. Finally, the paper summarized the role of ion-specific effects on the formation of soil organic-inorganic complexes. In particular, different ions with the same valence had different effects on the properties and processes of soil systems. This meant that slight differences between the number and arrangement of the outer electrons were amplified in the strong electric field near the soil surface, which enhanced effective charge of ions and coulombic force on ions by polarization. The effective charge number of ions was used to quantify the strength of ion interaction at the interface during soil colloids association. The conclusions were that soil organic-inorganic complexes improved the complex formation theory of soil organic-inorganic aggregates, provided theoretical basis for soil fertility and bioremediation, promoted environmental chemistry regarding soil organic-inorganic complexes and advanced research on particulate pollutant migration dynamics.

Effects of planting apple trees on distribution of soil cementing materials in Weibei apple orchards

WEI Binmeng, WANG Yiquan, LI Zhonghui

2018, 26(11): 1692-1700. doi: 10.13930/j.cnki.cjea.180281

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Abstract:
The aim of this study was to explore the effects of planting apple trees on soil cementation substances, to determine the relationship between soil aggregate stability and soil cementation substances, to reveal the factors affecting soil aggregate state and to build theoretical basis for the scientific management of apple orchard in Weibei Plateau. Four replicates of 10-year-old and 20-year-old orchards and four farmlands (wheat-corn rotation, CK) were selected for the experiment in Binxian County, Shaanxi Province. Soil samples within two-thirds of the radius of apple tree canopy were collected. Four replicates of undisturbed core samples were taken by driving volumetric rings (100 cm³) into the 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm and 40-50 cm soil layers to determine soil aggregates. Another four replicates were collected from 10 cm and 20 cm intervals respectively over a depth of 0-60 cm and 60-100 cm in each plot to determine the soil contents of clay, organic matter (SOM) and calcium carbonate (CaCO₃) contents. The results showed that soil clay content increased with increasing depth in the 0-100 cm soil layer. The increase was in the order of farmland > 10-year-old orchard > 20-year-old orchard for the 0-40 cm soil layer and reverse order was noted for the 40-100 cm soil layer. Planting apple trees increased SOM content in the 0-100 cm soil layer of the orchard. However, SOM content decreased with increasing planting age of orchard. The content of soil CaCO₃ was in the order of 10-year-old orchard > farmland > 20-year-old orchard for the 0-40 cm soil layer, 20-year-old orchard > 10-year-old orchard > farmland for the 40-100 cm soil layer, and 10-year-old orchard > farmland > 20-year-old orchard for the 0-100 cm soil layer. Pearson correlation analysis showed that the quantity and mean weight diameter (MWD) of > 0.25 mm soil aggregates were closely link to soil clay, SOM and CaCO₃ contents. Macro aggregates (> 0.25 mm) and MWD of mechanically stable aggregates were mainly affected by CaCO₃ and SOM contents. However, the quantity and stability of water stable aggregates were mainly affected by soil clay and CaCO₃ contents. Overall, planting apple trees changed the evolution processes of soil clay, SOM and CaCO₃. Soil clay and CaCO₃ migrated to deep soil with increasing age of orchard. The total storage of SOM in orchard was higher than that in farmland, but decreased with increasing planting age. It was concluded that planting apple trees enhanced soil residual viscosity and calcification, which affected aggregation of surface soil and compaction and hardness of bottom soil.

Variations in soil moisture, heat and salt under year round mulching of white and black film

WU Xianzhong, LI Yi, GAO Zhiyong, DONG Jianguo

2018, 26(11): 1701-1709. doi: 10.13930/j.cnki.cjea.180245

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Abstract:
Plastic film mulching in agriculture is known as the "white revolution", which has played a decisive role in agriculture in semi-arid areas. With the wide application of black and white films in agro-forestry production, many scholars have focused on the studies of mechanisms and functions of film mulching. It was found that film mulching not only promote crop growth, but also accelerate soil moisture lose. However, previous studies were conducted on white mulch tests under condition of growing crops. In order to clarify the differences between black and white film mulching and the ecological benefits under continuous film mulching, the field experiment of continuous film mulching without crop were conducted in Mizhi, northern Shaanxi, from July 1^st, 2015 to June 30^th, 2017. The experiment included three treatments, white film mulching of ridge (WF), black film of ridge (BF) mulching and no mulching of ridge (CK). In the experiment, the ridge was 50 cm wide, 20 cm high with 20 cm wide furrow. Each treatment was repeated three times and soil moisture, temperature, and electrical conductivity were measured at depths of 5 cm, 15 cm, 30 cm, 50 cm, 75 cm, 100 cm, 125 cm and 150 cm using GS3 instrument. The results indicated that:1) after two consecutive years of film mulching, soil moisture contents under two film mulching treatments and CK were 16.9% in average and 13.6%, and soil water storage capacity were 314.56 mm and 204.44 mm. Soil moisture content under BF was higher at 0-15 cm (P < 0.05) and lower at 15-30 cm (P < 0.05) than that of WF. At 0-150 cm, the total water storage of WF and BF was not significantly different, but significantly different from that of CK (P < 0.05). During the crop growth period, the average soil water storage with film mulching was 60.8 mm higher than that of CK. The daily temperature difference near soil surface under WF was greater than that under BF. At 0-150 cm, there was no significant difference in the average soil temperature between WF and BF in two years, which was 1.3℃ higher than that of CK (P < 0.05). At higher temperatures, WF decreased the freeze-thaw time by 8 days and 24 days compared with BF and CK, respectively, which was more conducive for soil thawing and soil warming in early spring. Annual soil salt content was higher in shallow soil, and was in the order of BF > WF > CK at 0-30 cm soil layer, WF > BF > CK at 30-50 cm soil layer. The results also revealed that soil salt content was low and no difference among treatments below 50 cm depth. No salinization of soil was observed under CK, BF and WF treatments. Overall, WF was more beneficial for improving surface soil temperature than BF, but it was the opposite for soil water moisture. Film mulching may increase soil temperature and prolong crop growth time. The research results could provide a basis for reasonable soil water-heat-salt regulation by film mulching in semi-arid Loess Hilly Region, and also provide a reference for the continuous film mulching technique in orchard and woodland.

Dicranopteris dichotoma leaf stoichiometry in collapsing erosion areas in Southwest Fujian

CHEN Junjia, CHEN Zhibiao, CHEN Zhiqiang, JIANG Chao, CHEN Haibin, LIANG Meixia

2018, 26(11): 1710-1719. doi: 10.13930/j.cnki.cjea.180580

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Abstract:
Collapse mound is a form of widespread and severe soil erosion in granite areas in South China. As a typical pioneer plant in collapse mound areas, Dicranopreris dichotoma is critical for soil and water conservation in collapsing erosion areas in South China. Plant stoichiometric characteristics reflect the capacity of plants to absorb and store mineral nutrients from the soil. They also reflect the long-term stoichiometric distribution formed during plant adaptation to the environment. Therefore, analysis of the characteristics of ecological stoichiometry of D. dichotoma in collapsing erosion areas can provide an important guidance for ecological restoration in collapsing erosion areas. In order to clarify the characteristics of nutrient storage of D. dichotoma in extremely degraded collapse mound ecosystems, the characteristics of carbon (C), nitrogen (N), phosphorus (P) contents and C/N, C/P and N/P ratios for D. dichotoma leaf in three typical collapse mound areas with different erosion intensities in Southwest Fujian Province were analyzed. The ecological stoichiometry characteristics of D. dichotoma leaves in different erosion intensities of collapsing wall and collapse mound under the same erosion intensity in different erosion positions were also comparatively analyzed. The results showed that the average contents of C, N and P in the leaves of D. dichotoma in collapse mounds were 477.10 g·kg^-1, 6.45 g·kg^-1 and 0.25 g·kg^-1, respectively. The N and P contents were generally extremely low. The average ratios of C/N, C/P and N/P were 96.82, 2 097.20 and 27.67, respectively. Thus D. dichotoma growth was primary limited by P content. On the other hand, there were significant differences in C, N and P contents, and C/P and N/P ratios in collapsing wall leaves under different erosion intensities (P < 0.05). All the C content along with C/P and N/P ratios decreased with increasing erosion intensity. While N content was higher in collapsing walls with moderate erosion, P content increased with increasing erosion intensity. This showed that D. dichotoma had strong ability to adapt to collapse mound ecosystems with severe soil erosion. On the other hand, there were significant differences in P content, and C/P and N/P ratios in D. dichotom a leaves in different erosion positions of collapse mounds under the same erosion intensity (P < 0.05). P content was highest in the upper catchment and lowest on collapsing walls. All the C/P and N/P ratios on collapsing walls were significantly larger than in other erosion positions. Obviously, it was evident that the ability of D. dichotom a to assimilate carbon in collapsing walls was stronger than in other erosion positions of collapse mounds. In addition, P utilization efficiency in collapsing walls was significantly higher than that in other erosion positions. In conclusion, D. dichotom a had strong ability to assimilate C and use P efficiently in severely eroded gully ecosystems and was adaptive to environments with severe soil erosion and extreme nutrient deficiency by regulating C, N and P contents in its cells.

C, N and P stoichiometry of typical plants and soils in the Yellow River Delta Natural Reserve

LIU Xinghua, GONG Yanqing, CHEN Weifeng, HUANG Baohua, ZHU Rongsheng

2018, 26(11): 1720-1729. doi: 10.13930/j.cnki.cjea.171214

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Abstract:
The in-depth understanding of stoichiometry of plant and soil is beneficial for discovering convergence and divergence of ecosystem compositions, and forecasting response of ecosystem to environment change. The Yellow River Delta is an active and younger ecosystem, its' stoichiometry of plant and soil may impact ecosystem structure, function and stability. The aim of this study was to clarify the characteristics of carbon (C), nitrogen (N) and phosphorus (P) contents and stoichiometry of plants and soils in the Natural Reserve of Yellow River Delta. In the study, five vegetation communities from sea to inland were selected, which were Suaeda salsa, S. heteropter, Phragmites communis, Tamarix chinensis and Imperata cylindrical communities, to analyze contents of C, N and P of different organs of plants and soils. The results showed that C and P contents of plant leaf were higher than those of root, and those of stem were lowest for all the vegetation communities, except T. chinensis and I. cylindrica communitis. In I. cylindrica community, C and P contents were higher in plant stem than in root. N content of leaf was higher than of stem and that of root was lowest for all the vegetation communities. N:P ratio of leaf was lower than 12 and was not significantly different from that of root in all ecosystems. The average contents of soil organic C, total N and P were respectively 4.78 g·kg^-1, 0.32 g·kg^-1 and 0.53 g·kg^-1, with all lower than the national average. The differences in contents of soil C, N and P in different soil layers were insignificant. Soil stoichiometry ratio was significantly affected by vegetation type, but the spatial variability was insignificant. There was a significant correlation between contents of leaf organic C, N and P and stoichiometry ratios of C:N and C:P and then the contents of soil C and N in the 0-10 cm, 10-20 cm and 20-40 cm soil layers (P < 0.05). In conclusion, the results showed that the contents of C, N and P were stable in soil profile and lower than the national level. The low content of N affected the variations of C:N and C:P ratios. Consistent with C:P ratio of plant leaf and root, the cycles of the elements were stable in the ecosystem. Then N:P ratio of plant leaf was lower than 12. The findings in this study demonstrated that N was the limiting nutrient element in ecosystems of the Yellow River Delta Natural Reserve.

Inversion of Hg content in reed leaf using continuous wavelet transformation and random forest

LI Mengjie, ZHANG Manyin, CUI Lijuan, WANG Henian, GUO Ziliang, LI Wei, WEI Yuanyun, YANG Si, LONG Songyuan

2018, 26(11): 1730-1738. doi: 10.13930/j.cnki.cjea.180131

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Abstract:
Heavy metal pollution of plants is one of the most important eco-environmental problems in the world. Rapid and large-scale monitoring of heavy metal content in plants has always been an international problem and a key research topic. Due to its high resolution, multiple band and abundant data, hyperspectral technology could offer a rapid and accurate determination of heavy metal pollution in plants. It can be used to detect the absorption, reflection and transmission characteristics of spectral bands corresponding to phytochemical components and to quantitatively analyze weak spectral differences for large-scale determination of the growth and health of plants. However, researchers mostly construct sensitive spectral parameters (e.g., vegetation index) through simple spectral transformation techniques and continuous removal methods. Most of the inversion models are of univariate regression, multiple stepwise regression, principal component regression and other empirical or semi-empirical models. There have also been uses of artificial networks and support vector machine models. These models not only require more training sets, but also easily over-fit. Thus continuous wavelet transform (CWT) and Random Forest (RF) algorithms are used as more accurate models for inverting heavy metal pollution in plants. While CWT model can more clearly characterize spectral signals, RF has strong fitting ability and also has shorter iteration time. It has higher calculation efficiency for large datasets such as hyperspectral data and is superior in model construction. The heavy metal mercury (Hg) and the wetland plant reed (Phragmites communis) were used in this research to test the effectiveness off the CWT and RF models. CWT was used to decompose continuous wavelength at different scales in the original spectral reflectivity (R), first-order derivative reflectivity (FD) and de-envelope reflectivity (CR). Correlation analysis was used to determine sensitive bands of R, FD, CR, the spectral reflectance by continuous wavelet transform (R-CWT), the first derivative reflectivity by continuous wavelet transform (FD-CWT) and de-envelope reflectivity by continuous wavelet transform based on the correlation with leaf total Hg content. Then the sensitive bands and RF algorithm were used to establish the inversion model of reed leaf total Hg content. The results showed that sensitive bands of leaf total Hg content were mainly distributed in the visible regions of 419-522 nm, 664-695 nm and 724-876 nm, and the near-infrared regions of 1 450-1 558 nm and 1 972-2 500 nm. After CWT transformation, the absolute value of correlation coefficient between wavelet coefficient and leaf total Hg content increased by 0.04-0.18, the fitting effect (R²) of the prediction inversion model increased by 0.107-0.177 and the accuracy (RMSE) of the prediction inversion model increased by 0.008-0.013. The RF model which used continuum removal reflectance after wavelet transformation (CR-CWT) had optimal inversion precision and fitting effect (R²=0.713, RMSE=0.127). At the same time, it was more accurate and reliable to use RF model with CR-CWT to retrieve leaf total Hg content when soil total Hg content was about 20 mg·kg^-1 (R²=0.825, RMSE=0.051). Therefore, it was feasible to use RF algorithm to retrieve heavy metal content in plants. The inversion model constructed by CWT had a more reference value in terms of monitoring heavy metal content in plants. The model was widely used and provided methodological support for non-destructive and rapid monitoring of heavy metal pollution in ecosystems.

Environmental risk assessment and trend simulation of non-point source pollution of chemical fertilization in Sichuan Province, China

TIAN Ruoheng, HUANG Chengyi, DENG Liangji, FANG Conggang, XUE Chao, YANG Lianxin, LEI Yongjiang

2018, 26(11): 1739-1751. doi: 10.13930/j.cnki.cjea.180244

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Abstract:
Fertilizer-based pollution has been an important part of agricultural non-point source pollution. Systematic assessment of potential risks and hazards of excessive application of chemical fertilizers to the ecological environment can provide the data base for decision-making of the prevention and control of agricultural non-point source pollution. Sichuan Province is not only a predominant grain production base, but also a region with severe agricultural non-point source pollution in China. Due to excessive long-term fertilizer application, the agro-ecological environment in Sichuan Province has had tremendous pressure. Based on data on fertilizer application, grain sowing and cultivated land area, the spatio-temporal variations in environmental risk due to fertilizer application were evaluated. In the adoption of environmental risk model for fertilizer application in Sichuan Province during 2000-2015, many factors were considered. These included fertilization intensity, environmental safety threshold, fertilization efficiency, multiple cropping index and fertilizer effect on the environment. Using two scenarios (extension and policy intervention), the variation trend in environmental risk associated with fertilizer application under zero-growth chemical fertilizer was simulated for Sichuan for the 2016-2018. The results showed that the total amount of chemical fertilizers in Sichuan Province increased during 2000-2015. The intensity of chemical fertilizer application in Sichuan Province was 376.63 kg·hm^-2 in 2015, exceeding the ecological standard set for China's ecological city (250 kg·hm^-2). Based on the application structures of nitrogen, phosphorus and potassium fertilizers in 2015, the application of nitrogen fertilizer in Sichuan Province accounted for 57% of the total amount of chemical fertilizers. In Chengdu, Mianyang and Zigong, the proportion of nitrogen fertilizer application was the highest in the whole province. The proportions of phosphate and potash fertilizers were low, accounting respectively for 28% and 15%. This indicated that nitrogen fertilizer still played a dominant role in agricultural production in the region. In 2015, total environmental risk index due to fertilizer use in Sichuan Province was 0.69, which was a medium risk level. Specifically, the environmental risk indexes of nitrogen, phosphate and potash applications were respectively 0.69, 0.72 and 0.46. Only potassium fertilizer application had a safe level of environmental risk. The environmental risk areas of nitrogen and phosphate fertilizers were concentrated in the Chengdu Plain Economic Zone, Southern Sichuan Economic Zone and Northeast Sichuan Economic Zone. Under the extension scenario, the environmental risk index of fertilizer application in various regions of Sichuan Province was in the range of 0.48-0.69, showing an increasing trend. Compared with the extension scenario, environmental risk due to fertilizer use under the policy intervention scenario declined across 2016-2018. In 2018, the environmental risk index of fertilizer application decreased most significantly in Northeast Sichuan Economic Zone, which was 4.24% lower than that in 2015. However, in most areas of Sichuan Province, there were still different levels of excessive chemical fertilizer application. The risk of environmental pollution caused by chemical fertilizer application had obvious pressure on the local ecological environment. We suggested that monitoring non-point source pollution of fertilizers should be improved in Chengdu Plain Economic Zone and Northeast Sichuan Economic Zone. Fertilization plan for each area should take the focus so as to ensure coordination between food production and ecological protection.

Analysis of vulnerability of poor farmers using sustainable livelihood analysis framework: A case of Pingshang Village in Min County, Gansu Province

FENG Jiao, CHEN Yong, ZHOU Lihua, HOU Caixia, WANG Rui

2018, 26(11): 1752-1762. doi: 10.13930/j.cnki.cjea.180300

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Abstract:
Traditional researches have focused on the definition, measurement, root causes and reduction strategies of poverty. With the application of concepts such as "ability" and "risk" in the field of poverty research, vulnerability has become a hotspot of poverty research because of its forward-looking perspective. In the face of unfavorable external shocks, poor people generally have high vulnerability. The vulnerability of poverty research can predict the future of poverty, improve the efficiency of poverty reduction and take into account the risk of future shocks and ability to cope with risk. The vulnerability research based on livelihood capital can effectively be used to identify vulnerable groups and guide the formulation and adjustment of rural poverty alleviation policies. Studies of vulnerability to poverty are mainly aimed at the meaning and the measurement of poverty. Domestic literatures combined with actual situation have mostly drawn lessons on foreign to empirical tests with relevant survey data. Taking Pingshang Village in Minxian County as the research area, this paper constructed an evaluation index of vulnerability of poor households from three aspects-risk, livelihood capital and adaptability. We used household index data to analyze the key factors that affect the vulnerability of poor farmers based on the comprehensive index method and according to the divisions of sustainable livelihood framework of livelihood capital. The aim of the study was to provide references for effectively distinguishing vulnerable groups of poor farmers, and establishing and adjusting the policy of rural poverty alleviation. The results showed that:1) social and human capitals of Pingshang Village farmers were high and natural and material capitals low. 2) The farmers' natural disaster and economic activity risk indexes were high. 3) Adaptability was generally low and many adaptive measures to deal with the risk had no practical effect. 4) The vulnerability of farmers was negatively correlated with income and education levels. The vulnerability of young and middle-aged households was lowest, and households headed by the elderly were the most vulnerable. Risk and adaptability were closely related with capital status of farmers. If capital was reasonable, impact of risk was generally small, adaptability strong and fragility low. Half of rural households in the study area suffered high-risk shocks, severe lack of livelihood capital, low adaptive capacity and high levels of vulnerability. Based on the conclusions and actual situations in the study area, suggestions were put forward to reduce vulnerability of poor farmers. This included developing characteristic industries, changing traditional modes, expanding labor markets, improving network systems and establishing mutual help platforms. In order to identify vulnerability of disadvantaged groups at micro-scale, poverty alleviation policies needed to strengthen identification of vulnerable groups. The establishment of poverty vulnerability assessment indicators still needed further inspection and adjustment. Risk management, poverty forecasting and anti-poverty were key research priorities.

2018 Vol. 26, No. 11