中国生态农业学报(中英文)

Research status and application prospects of combined nitrogen fixation in gramineous plants

HU Mengyuan, LI Yaying, GE Chaorong, ZHANG Yingying, YAO Huaiying

2021, 29(11): 1815-1826. doi: 10.13930/j.cnki.cjea.210317

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Abstract:
Nitrogen is one of the most important factors restricting agricultural production. With the development of artificial nitrogen fixation technology, the application of nitrogen fertilizers can increase crop yields and solve problems related to the fulfilment of the basic human needs of food and clothing. However, it has also caused environmental problems, such as soil compaction, acidification, nitrogen loss, and greenhouse gas emissions (e.g., nitrous oxide, N₂O). Compared with synthetic ammonia, biological nitrogen fixation is a green and economical nitrogen fixation method, which entails symbiotic nitrogen fixation and non-symbiotic nitrogen fixation (autogenous nitrogen fixation and combined nitrogen fixation, respectively). Annually, biologically fixed nitrogen can account for more than 50% of the total fixed amount. Compared with symbiotic nitrogen fixation, non-symbiotic nitrogen fixation exists in many plants, for example, sugarcane, rice, maize, wheat, and other gramineous crops that carry out non-symbiotic nitrogen fixation (combined nitrogen fixation). This article reviewed the species of combined nitrogen-fixing bacteria in gramineous plants and their mechanism of action and nitrogen-fixing activity and regulation methods, as well as the resources and applications of these combined nitrogen-fixing bacteria. Compared with symbiotic nitrogen fixation, combined nitrogen-fixing bacteria are more vulnerable to indigenous microorganisms. Research on combined nitrogen-fixing bacteria is more difficult owing to the influence of environmental factors, such as nitrogen levels. It is necessary to screen and purify more combined nitrogen-fixing bacteria to provide optimum materials for research into the nitrogen fixation mechanism. Appropriate levels of nitrogen, phosphorus, molybdenum, iron, and other fertilizers can promote the nitrogen fixation efficiency of bacteria. Nitrogen-fixing bacteria not only increase the extent of soil nitrogen fixation but also facilitate the regulation of plant root hormones, thereby increasing plant disease resistance and stress resistance, promoting healthier plant growth. Finally, agronomic management measures for combined nitrogen fixation through gramineous plants and the practical application of the nitrogen-fixing bacteria are proposed to provide a theoretical basis for improving the efficiency of combined nitrogen fixation through gramineous plants and to promote the application of the nitrogen-fixing bacteria in agricultural production.

Effects of dazomet soil fumigation on characteristics of weed community in Codonopsis pilosula seedling cultivated fields

WANG Hongyan, CHEN Yuan, GUO Fengxia, JIAO Xusheng, ZHANG Biquan, LIU Huili

2021, 29(11): 1827-1837. doi: 10.12357/cjea.20210258

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Abstract:
The damage caused by weeds in fields affects the growth of Codonopsis pilosula seedlings, and the use of herbicides damages C. pilosula seedlings and has a poor effect. To explore available ways to control weeds in C. pilosula seedling fields in the main production areas of Gansu Province, dazomet was used to fumigate the soil before sowing (F) while using non-fumigated field as the control (CK). The dynamics and differences of weed communities in the seedling fields were systematically studied. The results showed that 1) during seedling cultivation, the similarity in weed community between F and CK fields was 83.3%, and the average WCs between weed communities in emergence stage and seedling growth stage in the fumigated field was 18.9% lower than that in the CK field. Fourteen species of weeds (10 families and 14 genera) occurred in the CK field, of which five (including two annual weeds of Myosoton aquaticum and Setaria viridis, and three perennial weeds of Cirsium arvense, Convolvulus arvensis, and Sonchus brachyotus) were dominant. Five weed species (Polygonum aviculare, S. viridis, S. brachyotus, Malva cathayensis, and Hypecoum leptocarpum) were reduced in the seedling stage of C. pilosula, and three weed species (P. aviculare, Chenopodium glaucum, and H. leptocarpum) were reduced during the whole growth of C. pilosula in the F field, which on an average decreased by 39.8%. 2) Soil fumigation decreased the diversity of primary weed communities in the early stage of C. pilosula seedlings, in which the weed richness index decreased by 0.68, Shannon-Wiener index decreased by 0.50, and Simpson’s index decreased by 0.36. Soil fumigation also reduced the population abundance of malignant weeds and significantly inhibited its regeneration. 3) Soil fumigation significantly reduced the occurrence density of primary weeds, reducing 477 primary weed plants per square meter in early June. In the F field, the density of primary weeds of seven families was less than 5 plants∙m⁻², and the distribution was uniform. Among 10 primary weeds in the CK field, Caryophyllaceae had the highest density, and it accounted for 67.6% of the total number of primary weeds in the field, which was significantly higher than that of other weeds. Polygonaceae, Amaranthaceae, and Gramineae accounted for 22.5%, 5.3%, and 2.2%, respectively, while the other six families in total accounted for only 2.4%. The primary amount of Caryophyllaceae, Polygonaceae, and Gramineae weeds was larger in the non-fumigated field. Soil fumigation reduced 143 regenerated weeds per square meter from late June to Oct and, thus, could reduce the density of regenerated weeds. The average weed density and fresh biomass significantly decreased by 89.0% and 77.5%, respectively. It obviously controlled the early sexually reproducing weeds, such as M. aquaticum and Fagopyrum gilesii, and the late perennial facultatively reproducing weeds such as S. brachyotus and Convolvulus arvensis. These results indicate that soil fumigation with 98% dazomet before sowing can effectively control and alleviate the damage caused by weeds in C. pilosula seedling fields. However, the perennial deep-rooted weeds should be controlled early.

Prediction of suitable climatic areas for Fortunella species in China

ZHANG Yi, XUE Shuai, HUANG Hongmei, LI Dazhi, TANG Shuai, KONG Weizheng, YI Zili

2021, 29(11): 1838-1845. doi: 10.12357/cjea.20210416

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Abstract:
Fortunella is one group of the citrus fruit trees in southern China, a kind of edible hesperidium with rich flavonoids, carotenoids, limonoids, coumarins, and the fruit of these evergreen trees also have ornamental value. In recent years, areas of growth of commercial species of Fortunella have been decreasing due to a low net interest of planting single species. Meanwhile, natural resources have also withered due to the Huanglong disease caused by gram-negative bacteria. National collection of germplasm resources of Fortunella has been completed in parts of China, including Hunan, Fujian, Guangxi, etc.; however, this work did not take the effects of climatic factors on their distribution into consideration, which could provide a scientific basis for protection and collection of natural resources of Fortunella species. In this study, we predicted suitable climatic areas for six species (F. hindsii Swingle, F. margarita Swingle, F. japonica Swingle, F. polyandra Tanaka, F. crassifolia Swingle, and F. obovata Tanaka) of Fortunella using the MaxEnt (the maximum entropy, MaxEnt 3.3.3) model and the ArcGIS (the geographic information, ArcGIS 10.3) system to analyze actual geographical distribution data and 18 climate factors affecting their distribution. The dominant climate factors were screened through Jackknife test. Results showed that the suitable climatic region for the six species analyzed were distributed mainly in the southern areas of Dabie—Daba Mountain. The suitable region for the six species covered 354 000 km² (F. hindsii Swingle), 276 100 km² (F. margarita Swingle), 495 800 km² (F. japonica Swingle), 613 600 km² (F. polyandra Tanaka), 474 400 km² (F. crassifolia Swingle), and 663 403 km² (F. obovata Tanaka). The optimum climate region for F. polyandra Tanaka mainly extended to Chongqing, Guangxi, Guangdong, Hainan, and south of Yunnan, while that for the other five species was predominantly distributed in Hunan, Jiangxi, Guangxi, Fujian, Zhejiang, and Guangdong; some favorable region for F. obovata Tanaka even extended to Chongqing. The main climatic factors affecting the growth of Fortunella include minimum temperature, precipitation, and isothermality. The major climatic factors affecting F. hindsii Swingle distribution included isothermality and precipitation in April and June, while for F. margarita Swingle such climatic factors comprised precipitation in April and June, minimum temperature in February and July, and isothermality and precipitation in the driest month. Similarly, geographical distribution of F. japonica Swingle was influenced by precipitation in April and June, minimum temperature in July, isothermality and precipitation in the driest month, and precipitation in the warmest quarter. Likewise, the major climatic factors affecting natural distribution of F. polyandra Tanaka comprised precipitation in July and in December, minimum temperature in February and June, isothermality, and mean precipitation in the warmest quarter. Similar analytical results demonstrated that the dominant climatic factors affecting the distribution of both F. crassifolia Swingle and F. obovata Tanaka were in terms of precipitation in June, and isothermality and mean precipitation of the warmest quarter. The area under the curve (AUC) value of the MaxEnt model for all six species exceeded 0.9 and their actual distribution areas were also integrated, which indicated that the predicted distribution range of this study was highly accurate. Consequently, these results are expected to provide scientific guidance for regional investigation and protection of wild species of Fortunella and promotion of its varieties.

Effect of nitrogen fertilizer amount on N₂O emission from wheat-maize rotation system in lime concretion black soil

LYU Jinling, GAO Yanbu, LI Taikui, KONG Haijiang, ZHANG Jinping, KOU Changlin

2021, 29(11): 1846-1856. doi: 10.12357/cjea.20210444

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Abstract:
Lime concretion black soil is an important medium and low-yield soil in the Huanghuaihai Plain. It is prone to cracks because containing a high clay and sand ginger layer, making it unique in nitrogen transport. This study used the wheat and corn rotation system in lime concretion black soil as the research object, researching the N₂O emission characteristics and key driving factors by static box-gas chromatography methods. The experiment included four treatments: no fertilization (CK), traditional fertilization (TR), optimized fertilization (OPT), and re-optimized fertilization (ZOPT). Results showed that the average emission flux of N₂O in the wheat season ranged from 14.2 to 21.6 μg∙m⁻²∙h⁻¹, and the cumulative emission amount ranged from 0.82 to 1.24 kg(N)∙hm⁻²; the average emission flux of N₂O in the corn season ranged from 14.4 to 24.5 μg∙m⁻²∙h⁻¹, the cumulative emission amount ranged from 0.42 to 0.71 kg(N)∙hm⁻²; the N₂O emission in the wheat season was higher than that in the corn season, and the N₂O emission in the top dressing period of the two seasons was higher than that in the basal fertilizer period, demonstrating that the wheat season and top dressing period were high N₂O emission periods for lime concretion black soil. The correlation analysis results showed that N₂O emission of CK showed a significant multiple linear correlation with soil temperature, water content, and NO₃⁻-N content (P<0.05); whereas that of TR, OPT, and ZOPT only showed a significant multiple linear correlation with soil nitrate (P<0.01). There was no significant correlation between soil temperature and soil water content (except in individual cases), indicating that under fertilization conditions, the level of soil nitrate content was the most critical factor affecting N₂O emissions from the farmland of lime concretion black soil. In addition, the cumulative N₂O emissions of different nitrogen application rates were significantly different (P<0.05), and the N₂O emissions of the TR treatment were the highest, which were 1.24 kg(N)∙hm⁻² and 0.71 kg(N)∙hm⁻², respectively, in the wheat and corn seasons, significantly higher than those of OPT treatment [0.99 kg(N)∙hm⁻² and 0.51 kg(N)∙hm⁻²] and ZOPT treatment [0.82 kg(N)∙hm⁻² and 0.42 kg(N)∙hm⁻²]. The cumulative emissions of N₂O in both the wheat and corn seasons showed an exponentially increasing trend with the increase in nitrogen application, with the correlation coefficients reaching 0.997 and 0.977 (P<0.05), respectively, indicating that the traditional lime concretion black soil nitrogen application had the problem of excessive emissions of N₂O. Overall, compared with other soils, although lime concretion black soil is not a high-emission soil of N₂O, the N₂O emission caused by higher nitrogen application cannot be ignored.

Effect of phosphorus fertilizer rate on phosphorus fractions contents in calcareous soil and phosphorus accumulation amount in crop

XU Xiaofeng, MI Qian, LIU Di, FU Senlin, WANG Xugang, GUO Dayong, ZHOU Wenli

2021, 29(11): 1857-1866. doi: 10.13930/j.cnki.cjea.210186

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Abstract:
Excessive application of phosphate fertilizer wastes phosphorus resources and induces eutrophication in lakes and rivers. To study the effect of reduction of phosphorus fertilizer on phosphorus fractions in calcareous soil and its relationship with crop phosphorus accumulation, three treatments were set up, i.e., phosphorus application rates of 150 kg∙hm⁻² (P150), 37.5 kg·hm⁻² (P37), and 0 kg∙hm⁻² (P0). After two consecutive years of “winter wheat-summer maize” crops rotation, the changes in the contents of soil phosphorus fractions were studied using Hedley soil phosphorus fractionation method, and the storage contribution rate and output contribution rate of each fraction were also estimated. The relationship between soil phosphorus fractions contents, phosphorus fertilizer application rate, and crop phosphorus uptake amount were explored by using regression analysis, path analysis, and structural equation model. The results showed that compared with P37, P150 led to a significant increase in soil total phosphorus content. The contents of inorganic phosphorus extracted with anion exchangeresin (resin_P_i), with NaHCO₃ (NaHCO₃_P_i), with NH₄OAc (NH₄OAc_P_i) and with NaOH-Na₂S₂O₆(Fe_P_i), and organic phosphorus extracted with NaHCO₃ (NaHCO₃_P_o) in P150 were significantly higher than those in P37, while the other fractions showed no significant change. P0 did not cause a significant decrease in the contents of soil phosphorus fractions. The storage contribution rates of soil inorganic phosphorus fractions and organic phosphorus fractions were 72.6% and 23.8%, respectively. Among them, the storage contribution rates of inorganic phosphorus extracted with HCl (HCl_P_i), Fe_P_i, NH₄OAc_P_i, resin_P_i, and organic phosphorus extracted with HCl (HCl_P_o) were 24.45%, 18.1%, 13.62%, 11.15%, and 9.30%, respectively. The output contribution rate of soil inorganic phosphorus fractions was 41.0%, and that of organic phosphorus fractions was 56.4%. Among them, the output contribution rates of HCl_P_o, Fe_P_i, and NH₄OAc_P_i were 39.44%, 17.36%, and 13.06%, respectively. The output contribution rates of HCl_P_i and resin_P_i were only 1.91% and 0.40%, respectively. In the structural equation model, the load factors of phosphorus fertilizer application rate on Fe_P_i, HCl_P_i, NH₄OAc_P_i, resin_P_i, organic phosphorus extracted with NH₄F (NH₄F_P_o), NaHCO₃_P_i, and NaHCO₃_P_o were 0.078, 0.077, 0.061, 0.036, 0.018, 0.015, and 0.012, respectively. The load factors of Fe_P_i, NH₄OAc_P_i, and HCl_P_o on crop phosphorus uptake were 0.355, 0.334, and −0.039, respectively. The above results show that in calcareous soil, Fe_P_i, NH₄OAc_P_i, and HCl_P_o were the key phosphorus fractions. Among them, Fe_P_i and NH₄OAc_P_i were easily consumed when no phosphorus fertilizer was applied, but they can be easily supplemented by phosphorus fertilizer application. However, HCl_P_o was available to the crop but was not easily replenished by phosphorus fertilizer application. The high storage contribution rate and low output contribution rate of HCl_P_i fraction were the important reasons for the low efficiency of phosphate fertilizer in the current season. It is suggested that the choice of phosphorus application rate should be based on the storage contribution rate of the key phosphorus fractions.

Effect of intercropping on balancing effect of absorption and desorption characteristics of phosphorus in red soil

ZHOU Long, SU Lizhen, WANG Sirui, WANG Ruixue, PU Zhengxian, ZHENG Yi, TANG Li

2021, 29(11): 1867-1878. doi: 10.13930/j.cnki.cjea.210312

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Abstract:
The migration and environment effect of phosphorus in soil are affected by its’ adsorption and desorption. Although the excessive application of phosphorus fertilizer causes phosphorus fixation and loss, reasonable intercropping promotes the absorption and utilization and decreases fixation of phosphorus. This study investigated the adsorption and desorption of phosphorus in red soil under intercropping and phosphorus application, it is signicant for promoting the efficient utilization of red soil phosphorus and balancing environmental effects. In this study, a two-factor split-plot block experiment was adopted through field trials, in which the first factor was the planting pattern, namely maize||soybean intercropping and maize monoculture; the second factor was phosphorus application levels: P0 (0), P60 [60 kg (P₂O₅)·hm⁻²], P90 [90 kg (P₂O₅)·hm⁻²], and P120 [120 kg (P₂O₅)·hm⁻²]. This study aimed to explore the effects of intercropping and application of phosphorus on the adsorption and desorption of phosphorus in red soil, and to quantitatively analyze the relative contribution of intercropping and phosphorus application to phosphorus adsorption and desorption by using the structural equation model, and to reveal the key intercropping effect factors on the adsorption/desorption of phosphorus in red soil by using the aggregated boosted tree methods. Results showed that: 1) the Langmuir isothermal adsorption equation was most suitable for fitting phosphorus adsorption in red soil. The adsorption amount of soil phosphorus increased first and then tended toward saturation with the increase in phosphorus concentration in the equilibrium solution, while the adsorption amount of phosphorus decreased gradually with the increase in phosphorus application. 2) Phosphorus adsorption and desorption in red soil were significantly affected by planting pattern, phosphorus application, and the interaction between planting pattern and application of phosphorus (P<0.01). Compared with monoculture, the maize||soybean intercropping increased the adsorption and desorption of phosphorus by 22.9% and 9.2%, respectively (P<0.05). Under four application rates of phosphorus, compared with monoculture, the adsorption of phosphorus in intercropping increased significantly by 13.0%, 19.4%, 41.5%, and 23.9% (P<0.05), respectively. The desorption of phosphorus increased significantly by 90.2% and 194.4% in P0 and P60 intercropping (P<0.05), but decreased by 52.1% and 34.1% in P90 and P120 intercropping, respectively (P<0.05). 3) Under different planting patterns and phosphorus application levels, the adsorption of soil phosphorus had a significant negative correlation with soil pH, organic matter, resin phosphorus, available phosphorus, total phosphorus, and degree of phosphorus saturation (P<0.01), and a significant positive correlation with free iron oxide, free alumina, and phosphate sorption index (P<0.01). However, the desorption of phosphorus from red soil had a significant negative correlation with a standard phosphorus requirement (P<0.01). The adsorption and desorption of phosphorus in the red soil were mainly affected by pH, organic matter, and free iron oxide. Intercropping of maize and soybean changed soil pH and contents of organic matter and free iron oxide, resulting in differences in the phosphorus adsorption and desorption from that of maize monoculture in red soil, improving the soil phosphorus buffering capacity. At a low phosphorus level, intercropping can accelerate a large amount of phosphorus desorption for plants to absorb and utilize; at high phosphorus levels, intercropping can promote phosphorus adsorption and effectively slow down the loss of phosphorus.

Effect of green manure on soil water and crop yield in the Loess Plateau of China: A Meta-analysis

ZHANG Shaohong, WANG Jun, RAJAN Ghimire, XING Wenchao, HU Yingming, ZHANG Nannan

2021, 29(11): 1879-1892. doi: 10.13930/j.cnki.cjea.210243

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Planting green manure is a long-established planting pattern in the dryland cropping areas across the Loess Plateau of China. However, due to limited precipitation, planting green manure may reduce soil water content and affect the succeeding crop yield. By combining data from 46 peer-reviewed publications, a Meta-analysis was carried out to assess the effect of green manure on precipitation storage efficiency (PSE) during the fallow period, soil water storage at succeeding crop planting (SWSP), succeeding crop yields, evapotranspiration (ET), and water use efficiency (WUE) in the Loess Plateau of China. Compared to fallow areas without green manure, area with green manure decreased PSE, SWSP and ET by 28.28% (P<0.05), 4.93% (P<0.05) and 2.51% (P<0.05), respectively, however, it increased succeeding crop yield and WUE by 2.37% and 8.97% (P<0.05), respectively. Green manure effect on soil water, crop yield, and soil water use varied with the interval between green manure termination and planting of succeeding crop, green manure biomass, and climatic conditions. Strong polynomial relationship was found between the response ratios (RRs) of PSE, SWSP and the interval between legume green manure termination and succeeding crop planting. Both PSE and SWSP maximized at an interval of 13 d. The RRs of crop yield and WUE were also correlated with legume green manure biomass in a polynomial way. Succeeding crop yield and WUE maximized when the legume green manure biomass was 2200 and 3100 kg∙hm⁻², respectively. Overall, introducing green manure during fallow period reduced soil water but enhanced succeeding crop production and water use in the Loess Plateau. Leaving a 12–14 d interval between legume green manure termination at a biomass of 2200–3100 kg∙hm⁻²,succeeding crop planting can be a reliable practice to mitigate soil water consumption in such dryland areas.

Effect of micro-nano bubbles on the yield of different rice types

QIAN Yinfei, CHEN Jin, SHAO Caihong, GUAN Xianjiao, QIU Caifei, CHEN Xianmao, LIANG Xihuan, XIE Jiang, DENG Guoqiang, PENG Chunrui

2021, 29(11): 1893-1901. doi: 10.13930/j.cnki.cjea.210194

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Increasing the rhizosphere oxygen in the rice paddy can influence the paddy field environment and improve the physiology, metabolism, and grain yield of rice. The traditional methods of mechanically or chemically aerating subsurface irrigation could produce large air bubbles, which can escape from the soil along the pores adjacent to the roots. Aerating irrigation efficiency improvement is an issue not yet to be resolved. One way is to use water rich in micro-nano bubbles (MNB). MNB are small air bubbles that cannot escape from the soil easily, thereby, supplying more oxygen. Different rice types vary in their ability to absorb and utilize oxygen. A pot experiment was carried out in which the experimental group was treated with MNB water and the control group with running water as check (CK) during 2019−2020 to determine the effect of MNB and CK on the growth and yield of two paddy rice varieties (inbred rice ‘Ganwanxian 37’ and super rice ‘Wufengyou T025’). The results showed that 1) MNB increased the dissolved oxygen concentration of soil solution, increased the number and volume of rice roots, enhanced α-NA oxidation, improved the total and active absorption area of root, promoted the SPAD and net photosynthetic rate (P_n) value of leaves, increased the biomass accumulation, raised the harvest index, improved the rice panicle characteristics such as length and number of grains per panicle, enhanced the number of primary and secondary branches and also the main spike-stalk, seed-setting rate on the primary and secondary branches and on spike-stalk, and enhanced the grain yield. 2) Compared to CK, MNB enhanced the yield of inbred rice by 8.46%–17.9% and super rice by 11.32%–22.09%, with the super rice showing higher grain yield than the inbred rice. 3) In case of inbred rice, MNB mainly increased the panicles (6.67%–16.67%), whereas in super rice it increased the spikelets per panicle (3.23%–7.2%) and the seed-setting rate (1.14%–6.57%). 4) The MNB enhanced the panicles number of inbred rice by promoting the tiller occurrence in the early growing period. The MNB enhanced the number of spikelets per panicle and the seed-setting rate in the super rice by increasing the rate of photosynthesis of leaves (improved the SPAD and P_n value). It also slowed down the leaf senescence, improved the bearing rate of tillers, biomass accumulation, increased the number and seed-setting rate in the secondary branches and the main spike-stalk, and it improved the harvest index. It was, thus, evident that MNB could improve the yield of both types of rice. In inbred rice, supplying MNB before the tillering stage increases the yield by increasing panicles number. In super rice, MNB supply after the earing stage increases the yield by producing more spikelets per panicle and through higher seed-setting rate.

Effect of seedling size on the medicinal properties of Codonopsis pilosula under organic cultivation

LIU Lanlan, GUO Fengxia, CHEN Yuan, CHEN Yongzhong, WANG Hongyan, ZHANG Biquan, GUO Aihui

2021, 29(11): 1902-1912. doi: 10.13930/j.cnki.cjea.210188

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Ecological organic cultivation is an increasing trend in the industrialized development of traditional Chinese medicine. The medicinal properties of Codonopsis pilosula vary with seedling size. To explore the effects of seedling size on medicinal formation in organic cultivated C. pilosula, seedlings were categorized as big (BS), middle (MS), small (SS), and slender (SLS) seedlings and transplanted under full organic conditions to comparatively evaluate the yield and medicinal characteristics of the medicinal roots. The results showed that the seedling sizes had an allometric growth pattern. After transplantation, bigger seedlings showed earlier regreening, greater growth at the early stages and weaker growth at the later stages with significant increases in lateral roots number, and higher water content of roots, and higher disease incidence. The smaller seedlings showed later regreening, faster growth at the mid and later stages with increased diameter, less root water content and lower disease incidence. These differences led to non-significant differences in the single root weight and total medicinal yield. The average fresh medicinal yields of MS (8225.1 kg·hm^–2) and SS (8125.0 kg·hm^–2) were the highest and second highest, respectively, increasing by 23.4% and 21.9% compared with the BS group and by 45.2% and 43.4% compared with the SLS group. The average dry medicinal yield of SS (2938.1 kg·hm^–2) and MS (2681.1 kg·hm^–2) was the highest and second highest, increasing by 37.8% and 25.7% compared with the BS group and by 53.6% and 40.1% compared with the SLS group, respectively. Among the four seedling sizes, the root disease incidence did not significantly differ, ranked as BS (6.4%) > MS (5.6%) > SS (3.9%)> SLS (3.6%). However, the disease severity showed significant differences, and the disease indices for MS and BS were 4.66% and 2.93%, respectively, both of which were significantly higher than those for SLS (1.32%) and SS (0.97%). The comprehensive evaluation indices were SS (0.734) > SLS (0.636) > MS (0.409) > BS (0.282). In summary, yield did not increase with seedling size largening. Plant seedlings have strong plasticity and manifest various strategies for establishment during the medicinal formation period. These results challenge the traditional selection and retention practices for plant seedlings, suggesting that the big seedlings should not be blindly chosen and that the slender seedlings should not be eliminated during production. Slender plants should be cultivated by increasing the transplantation density and controlling pests and birds to improve the regreening rate, whereas larger seedlings should be cultivated by decreasing the density. Together, these practices could improve the effectiveness of C. pilosula organic cultivation.

Growth promotion and mitigation of salt stress in wheat seedlings by a Kushneria bacterium

YUAN Lin, WANG Xinzhen, SUN Hongyong, LIU Xiaojing, LIU Binbin

2021, 29(11): 1913-1920. doi: 10.12357/cjea.20210144

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Globally, soil salinization is a major land degradation process, taking more than 1 million hectares of farmland out of production per year, threatening food security. In salt-affected soils, crop growth, development, and yield dramatically decrease due to salt toxicity in plants, reduced soil fertility and water availability to plants, and altered hydraulic properties of the soil. The rhizospheric microbiome is closely related to crop stress tolerance. Plants recruit specific groups of microbes in the rhizosphere, which provide nutrients and plant hormones that promote plant growth and stress tolerance. Kushneria indalinina JP-JH is a salt-tolerant and auxin-secreting bacteria strain isolated from the rhizosphere of Suaeda salsa. In this study, the effects of K. indalinina JP-JH on the growth and salt tolerance of wheat seedlings were investigated. The experiment was conducted using the wheat variety ‘Xiaoyan 60’ in a hydroponic system with Hoagland nutrient solution. The seedlings were inoculated with K. indalinina JP-JH under no salt (0 mmol∙L⁻¹), low salt (200 mmol∙L⁻¹), and high salt (400 mmol∙L⁻¹) conditions. Seeds without bacterial inoculation were prepared under the same conditions and used as control treatments. Plant growth parameters and organic acids contents in the root exudates were analyzed after 40 days of incubation. The results showed that the fresh weight of wheat seedlings in the treatments with K. indalinina JP-JH inoculation was significantly higher than that of the uninoculated group at all three salt concentrations. K. indalinina JP-JH inoculation significantly increased the plant dry weight of the whole plant under both salt-free and low salt-stressed conditions but had no significant effect on dry weight under high salt-stressed conditions. Meanwhile, K. indalinina JP-JH inoculation significantly increased plant height under high salt-stressed conditions but had no significant effect under salt-free and low salt-stressed conditions. Dry weight and plant height were negatively related to the salt concentration in the inoculated and uninoculated treatments. The concentrations of six organic acids (oxalic acid, tartaric acid, malic acid, citric acid, fumaric acid, and succinic acid) secreted from roots were determined for treatments with different salt concentrations, with or without bacterial inoculation. K. indalinina JP-JH inoculation significantly increased the contents of oxalic acid and tartaric acid in the root exudates under salt-stressed conditions (both low and high salt concentrations) but had no significant effect on organic acids secretion under salt-free conditions. This suggests that oxalic acid and tartaric acid may play important roles in regulating plant-microbe interactions and improving the salt tolerance of wheat variety ‘Xiaoyan 60’. Taken together, our results indicate that K. indalinina JP-JH promotes plant growth and development and improves the salt tolerance of wheat at seedling stage, which may be related to alterations in the root exudation potential and plant-microbe interactions. This study produced new experimental data on the mechanisms of microorganisms that promote plant growth and salt tolerance and provided biological resources for developing biofertilizers to enhance wheat growth under salt stress conditions.

Effects of different biogas slurries on soil microbial carbon metabolism

LI Yufei, XU Junxiang, LIU Bensheng, SUN Qinping, LI Jijin, LIU Jianbin, LANG Qianqian, SUN Renhua, JIN Hongyan

2021, 29(11): 1921-1930. doi: 10.12357/cjea.20210274

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Abstract:
Biogas slurry is a high-quality organic fertilizer, but different types of biogas slurries have different physical and chemical properties. To explore the effect of biogas slurries derived from different livestock and poultry wastes on the soil microbial community structure, a culture experiment was conducted in the laboratory with the following treatments: soil amended with biogas slurry from chicken manure (FS), pig manure (PS), and cow manure (CS), and an unamended control (CK). The experiment was conducted with equal nitrogen input for each treatment. Samples were collected after incubation of soil for 60 days. Changes in the carbon metabolism of microbial communities subjected to different treatments were examined using the Biolog microplate culture method. Compared to the control, the biogas slurry treatments exerted no significant effect on soil organic matter content, but improved soil pH, electrical conductivity, and contents of inorganic nitrogen, total nitrogen, available phosphorus, and available potassium to varying degrees. Soil microbial biomass carbon was highest in CS, whereas that in PS was significantly lower than that in CK (P<0.05). The highest carbon source utilization intensity was found in FS, while that in CS was similar to that in CK, and lower in PS. Carbohydrate utilization by soil microbes was highest in FS, where it showed a significant increase with respect to that of PS (P<0.05). The utilization of amino acids was inhibited by all biogas slurry treatments; however, such inhibition was significant only in PS when compared with CK (P<0.05). Carboxylic acid utilization was significantly higher in FS than that in the other treatments (P<0.05). The various treatments exerted three distinct effects on amine utilization: on the one hand, FS promoted amine utilization, which showed values significantly higher than those in CK and PS (P<0.05); on the other hand, PS treatment did not significantly affect amine utilization when compared to that of CK; and finally, there was no significant difference in amine utilization between microbial communities subjected to CS and the other treatments. When compared with the other treatments, FS resulted in soil microbial communities with significantly higher values of both Shannon and Simpson indices (P<0.05). The highest value of the McIntosh index was observed in the FS-treated community, with a significant increase with respect to that of PS. Amino acid utilization was the parameter showing the strongest correlations (P<0.05 or P<0.01) with various soil chemical properties. Particularly, significant negative correlations were observed with nitrate nitrogen content, total nitrogen content, available potassium content, and electrical conductivity. In contrast, there were no significant correlations between the diversity indices and soil chemical properties. Soil microbial biomass carbon was negatively correlated with nitrate and available potassium contents (P<0.05). Conversely, soil microbial biomass nitrogen was negatively correlated with the pH and electrical conductivity (P<0.05). Principal component analysis of microbial carbon metabolism showed that the microbial community of PS was differed from that of CK, while CS and FS had relatively small effects on microbial community metabolism. In summary, biogas slurry derived from different livestock and poultry wastes exerted different effects on soil microbial carbon metabolism. Nevertheless, future experiments are required to verify the long-term effects of different biogas slurries in the field.

Topsoil organic matter and its effect on the soil nutrients contents of Cunninghamia lanceolata plantations

YUWEN Ruinan, PAN Chang, GUO Jiahuan, FENG Huili, CHEN Jie, YU Yuanchun

2021, 29(11): 1931-1939. doi: 10.13930/j.cnki.cjea.210211

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Abstract:
Soil organic matter plays an important role in forest ecosystems and is an important index for estimating soil carbon storage and soil fertility and quality. In this study, the distribution of soil organic matter and its influence on soil nutrients were analyzed on a provincial scale and the impact of environmental factors on changes in the soil organic matter content of Chinese fir plantations (CFPs) was assessed to provide a theoretical basis for the sustainable management of CFPs. Data from 1092 forest farms in six provinces of China (Guangdong, Guangxi, Hunan, Jiangxi, Zhejiang, and Fujian) were used to characterize the distribution of soil organic matter and its effect on the soil nutrients in the topsoil (0–20 cm) in CFPs. The results showed that the average soil organic matter content of the CFPs was 31.02±13.44 g·kg⁻¹, the nutrient grade was at a medium level, and the coefficient of variation was 43.33%, which represented a moderate variation level. The available phosphorus (AP) content was 5.41±8.01 mg·kg⁻¹, the nutrient grade was rich, and the coefficient of variation was as high as 148.06%. The total phosphorus (TP) content was 0.49±0.38 g·kg⁻¹, which was extremely poor, and the coefficient of variation was 77.55%, being moderately variable. The soil organic matter content of different soil types varied greatly. The content in mountain yellow soil was the highest (46.63±16.88 g·kg⁻¹), and that in dark red soil was the lowest (15.81±4.38 g·kg⁻¹). Stand density, elevation, slope, and soil pH were the main factors that affected the soil organic matter content in the topsoil of CFPs, with relative contributions of −0.35, 0.28, 0.11, and 0.11, respectively. The contributions of soil organic matter to total nitrogen (TN), available nitrogen (AN), total potassium (TK), and available potassium (AK) were positive, with relative contributions of 0.17, 0.47, 0.16, and 0.21, respectively. However, soil organic matter contributes less to soil TP, with a relative contribution of −0.09. In general, the nutrient grade of soil organic matter in the surface layer of CFPs was medium. The main grading performance was mainly characterized by moderate to inferior levels, and few rich levels and no extremely poor levels were observed. Altitude, slope, and soil pH had positive effects on soil organic matter, whereas stand density had a negative effect. Soil organic matter had a positive effect on soil TN, AN, TK, and AK and a weak negative effect on TP. The contribution of soil organic matter to TP was low; therefore, the lack of phosphorus in the soil may be the main factor limiting Chinese fir growth.

Spatial and temporal variation characteristics of cultivated land in the upper Yellow River from 2002 to 2018 based on time series MODIS

HAN Chunlei, SHEN Yanjun, WU Lanzhen, GUO Ying, CHEN Xiaolu

2021, 29(11): 1940-1951. doi: 10.13930/j.cnki.cjea.210113

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Abstract:
The upper reaches of the Yellow River contribute 56.77% of the water resources in the whole basin, while agricultural water in the upper reaches accounts for more than 40% of the whole basin. Using MODIS data with medium-resolution remote sensing and crop phenology data, the cultivated land area in the upper reaches of the Yellow River from 2002 to 2018 was extracted, which provided basic data for studying the impact of cultivated land change in the upper reaches on water resource consumption in the basin. Using Harmonic Analysis of Time Series (HANTS) to smooth the cut and spliced MOD13Q1 data, the NDVI time series curve was easier to identify. Combined with the decision tree classification method and crop growth period and other phenological information, the decision tree rules were compiled, and then the smooth MOD13Q1 data were classified by using the classification rules. The distribution and change of cultivated land in the study area from 2002 to 2018 are obtained. Then, the confusion matrix verification of the extraction results was carried out by using the real ground sample data obtained from field investigation and the county-level statistical data in the study area. The extraction accuracy of cultivated land was above 75%, and R² reached 0.85. The main results showed that the cultivated land in the study area were increased from 2002 to 2018, with a total increase of 88.21×10⁴ hm². The most rapidly increased was Ningmeng Irrigation District, the total area of cultivated land in Ningxia increased by 64%, reaching 76.61×10⁴ hm² in 2018; and Inner Mongolia increased reaching 44.74×10⁴ hm², accounting for 44% of the total area; and Gansu section increased reaching 18.89×10⁴ hm²; Qinghai section showed an obvious trend of decrease in cultivated land, a total of 5.36×10⁴ hm². On the whole, the increase rate of cultivated land area is 5.18×10⁴ hm²·a⁻¹, in which the Qinghai section decreases at a rate of 0.2×10⁴ hm²·a⁻¹, the Gansu section increases at a rate of 1.05×10⁴ hm²·a⁻¹, the Ningxia section increases at a rate of 1.87×10⁴ hm²·a⁻¹, and the Inner Mongolia section increases at a rate of 2.46×10⁴ hm²·a⁻¹. Mann-Kendall analysis method was used to analyze the trend of NDVI change in the study area, and it was found that NDVI showed an increasing trend. In addition, compared with the change of precipitation, it also showed an increasing trend. Then using stepwise regression analysis to analyze the selected main indicators, the residents’ disposable income was the main factor affecting the change of cultivated land. Finally, using the collected data for qualitative analysis, it was concluded that water resources policy and engineering facilities construction are the factors affecting the change of cultivated land. The main conclusions of this paper were as follows. The cultivated land in the basin from Longyangxia to Hekou Town in the upper reaches of the Yellow River shows an increasing trend. The medium-resolution MODIS data can be used to extract the cultivated land in the upper reaches of the Yellow River. Water resources policy and local socio-economic environment change were the main driving factors for the change of cultivated land area in the study area.

An analysis of the spatial effect of agricultural science and technology investment on agricultural eco-efficiency

WANG Chenxuan, YAO Zuowen

2021, 29(11): 1952-1963. doi: 10.13930/j.cnki.cjea.210214

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Abstract:
With increasingly severe agricultural pollution, it is important to explore the effects of agricultural science and technology investments on agricultural ecological efficiency to alleviate rural ecological pressure and promote the healthy development of rural areas. This study used a super-efficiency slack-based measure (SBM) model to measure the agricultural ecological efficiency of provinces in eastern, middle, and western China from 2000 to 2018. According to the Moran index, the spatial autocorrelation of agricultural ecological efficiency and agricultural science and technology input were analyzed. The spatial spillover effect and threshold characteristics of the impact of agricultural science and technology input on agricultural ecological efficiency were explored by using the spatial econometric model. Results showed that from 2000 to 2018, the agro-ecological efficiency was high in the eastern and western regions and low in the middle region. The agro-ecological efficiency in the eastern, middle, and western regions fluctuated significantly from 2000 to 2018, with slight fluctuations in 2000–2003. Agricultural ecological efficiency declined slightly from 2004 to 2008 and then rose slightly from 2008 to 2010. In 2010, the agricultural ecological efficiency was 0.731, after which it declined slightly from 2011 to 2014. From 2015 to 2017, the national agricultural ecological efficiency dropped to 0.5894, 0.5839, and 0.5159, respectively. In 2018, the annual agricultural ecological efficiency increased to 0.5453. The impact of rural science and technology investments on agricultural ecological efficiency presented as an inverted U-shape, and the scale of agricultural science and technology investments had a significant spillover effect on agricultural ecological efficiency. The panel threshold regression showed that the threshold effect of agricultural science and technology investments in the eastern, middle, and western regions in China differed, and that in the eastern region had a positive promoting effect. The positive effect of agricultural science and technology input on agricultural ecological efficiency in the middle region was not as stable as that in the eastern region. The input of agricultural science and technology in the western region harmed agricultural ecological efficiency. The scientific and technological input in the agricultural development of the middle and western regions of China should consider economic and ecological efficiency. Therefore, China should vigorously promote the green and efficient technology mode, actively replace chemical fertilizers with organic fertilizers, accelerate the implementation of scientific fertilizer application techniques, pay close attention on demonstration, fertilizer reduction and fertilization efficiency, and improve agricultural ecological efficiency.

Actuality and factors influencing farmer adoption of mechanized harvesting in typical maize ecoregions

GUO Yinqiao, XU Wenjuan, WANG Keru, CHAI Zongwen, XIE Ruizhi, HOU Peng, MING Bo, LI Shaokun

2021, 29(11): 1964-1972. doi: 10.12357/cjea.20200807

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Abstract:
To understand the current situation and limiting factors of application of mechanical harvesting of maize, and improve the mechanization level of whole process of maize production in China, this paper investigated the adoption of mechanical harvesting of maize in the main maize planting ecological regions (Helongjiang and Jilin in Northeast region, Xinjiang in Northwest region and Henan in Huanghuaihai region) through questionnaire survey. The influencing factors of adoption of mechanical harvesting, key problems in different regions and of different maize producers (farmers, cooperatives and agricultural technicians) were discussed. The results showed significant differences among regions in the use of mechanical harvesting of maize; the proportion of area where mechanized harvesting was used was highest in Heilongjiang and Xinjiang, with a >83.11% adoption rate. The adoption rate of Henan was 54.72% and that of Jilin was 21.51%, which was the lowest. Mechanized kernel harvesting was largely used in Xinjiang and in some farms in Heilongjiang Agricultural Reclamation, which was mainly due to the large planting scale (>6.67 hm²), harvest convenience, and low cost. Mechanized ear harvesting and threshing after drying was the main form of maize harvesting in Youyi Farm of Heilongjiang Agricultural Reclamation, most areas in Heilongjiang, and part of Huanghuaihai. Factors limiting the application of mechanized kernel harvesting in these areas included unsuitable maize cultivars for mechanical harvesting, no professional kernel-harvesting machine, drying-storage needed for immature grains. However, in these area, the time- and labor-saving and harvested ears easily to be store promoted farmers to adopt mechanized ear harvesting. In Jilin and some areas with small planting scale, artificial harvest still was used due to scattered block and strong habit of traditional practices. Farmers with higher incomes, fixed occupation, ancillary revenue, or agricultural implements were willing to adopt mechanized harvesting. Small farmland, low planting benefit and low family income were the main reasons for the low adoption rate of mechanized harvesting in the investigated regions. The investigation results suggested that planting area, ratio of maize revenue to family income, years using mechanized ear harvesting, marketing ways significantly influenced the diffusion and extension of mechanized harvesting technology. Further expansion of planting area and facilitating direct-selling of grains after harvest will highly significantly affect the behavior of farmers adopting mechanized kernel harvesting. To sum up, the scale and benefit of cultivated land management is the key to the implementation of maize mechanical harvesting technology. The government, scientific institutions and enterprises should strengthen cooperation according to local conditions, and give assistance and guidance from policy, technology, economy and concept, gradually improve the harvest efficiency and the whole mechanization level of maize in China.

2021 Vol. 29, No. 11