Scientia Agricultura Sinica

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Influence of Medicago sativa Proportion on Its Individual Nitrogen Fixation Efficiency and Underlying Physiological Mechanism in Legume-Grass Mixture Grassland

LI Qiang, HUANG YingXin, ZHONG RongZhen, SUN HaiXia, ZHOU DaoWei

Scientia Agricultura Sinica 2020, 53 (13): 2647-2656. DOI: 10.3864/j.issn.0578-1752.2020.13.013

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【Objective】 The introduction of Nitrogen-fixing legumes into grasslands is the economical and ecological measurement to improve soil fertility and to increase forage yield and quality in grasslands. In legume-grass mixture grasslands, the proportion of legume plants is the key factor to determine their N fixation function. This research studied the influence of legume proportion on nitrogen fixation efficiency of Medicago sativa-Leymus chinensis mixture grassland and underlying physiological and ecological mechanism, aiming to improve our understanding to the relationship between community structure and biological N fixation in mixed grassland, and to assist the establishment and management of legume-grass mixture grassland for increasing the biological nitrogen fixation and soil fertility, and thus to improve the resources production and ecological stability of mixed grassland. 【Method】 In May 2017, using M. sativa and L. chinensis as experimental materials, a completely randomized block design with four repeats was applied to establish Medicago sativa-leymus chinensis mixture grassland with different legume proportion (25%, 50%, 75%, and 100%) in the field in Changling grassland farming research station. One year after establishment, based on the quadrat survey procedure, the changes in community structure, and growth status of leaf, shoot and root, physiological and metabolic characteristics were measured. After measuring nodulation of root, nitrogen fixation efficiency of M. sativa was measured using ¹⁵N natural isotope abundance method in mixed grasslands. Finally, the effect of legume proportion on biological nitrogen fixation of M. sativa and its mechanism were analyzed in combination with monitoring soil moisture. 【Result】 (1) One year after sowing, the observed proportions of legume plants were 11%, 27%, 53% and 100%, corresponding to initially sowed legume proportion of 25%, 50%, 75% and 100% in mixed grasslands, respectively. (2) Compared with the initial legume sowing proportions of 25%, 75% and 100%, the initial legume sowing proportion of 50% increased the mean soil moisture content within growing season by 21.4%, 36.4% and 51.7%, respectively. (3) M. sativa had greater shoot and root biomass, leaf number, leaf area, leaf thickness and leaf biomass under the legume sowing proportion of 50%. The minimum value of the above variables was found in the legume sowing proportion of 100%. (4) M. sativa had the greatest photosynthetic rate and the greatest starch concentrations in shoot and root, but the lowest soluble sugar concentration in shoot and root when legume sowing proportion was 50%. (5) Under initial legume sowing proportion of 50%, root nodule development of M. sativa was better and its biological nitrogen fixation capacity was increased by 13.5%, 44.6% and 79.2%, respectively, compared with initial legume sowing proportions of 25%, 75% and 100%. Regression analysis showed that the biological nitrogen fixation of M. sativa was positively correlated with soil water content following change in legume proportion. 【Conclusion】 In Medicago sativa-leymus chinensis mixture grassland, the relationship between biological nitrogen fixation and legume proportion was non-linear. M. sativa had the highest nitrogen fixation efficiency when the initial legume sowing proportion was 50% in mixed grassland. Legume proportion drived change in soil water availability, thus to regulate the growth and development of M. sativa and its root nodules via modification in leaf development and photosynthesis, which was the underlying mechanism for legume proportion to influence the biological nitrogen fixation. This study could help in determining the legume-grass ratio during establishment of mixed grasslands, and guiding the water management in mixed grasslands.

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Response of Alfalfa Production and Quality to Fertilization and Cutting Frequency and Benefit Analysis in Mollisol Agricultural Area in Cold Region

GONG Hao,YANG Liu,LI DanDan,LIU GuoFu,XIAO ZhiXin,WU QingYing,CUI GuoWen

Scientia Agricultura Sinica 2020, 53 (13): 2657-2667. DOI: 10.3864/j.issn.0578-1752.2020.13.014

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【Background】 The climate in the Mollisol area of Northeast China is cold and the growth period is short in the past, alfalfa was planted in degraded grassland or low-yield fields. In order to ensure safe wintering, it is generally only castrated three times a year. Under the background of “grain to feed”, the soil quality of the cultivated land in the Mollisol agricultural area in cold region is relatively fertile, and the field management is relatively standardized. 【Objective】 The purpose of this experiment is to explore the feasibility of alfalfa cutting four times a year under the condition of reasonable fertilization in the Mollisol agricultural area in cold region of northeast cold region. 【Method】 The second year of planting (Medicago sativa L. “Dongnong No.1”) was used as experimental material to study the one-time fertilization of soil 525 kg·hm ^-2 in the alfalfa spring before returning to green. The 525 kg·hm^-2 disposable soil fertilization (the self-developed Mollisol agricultural area in cold region special compound fertilizer, patent application number: 201101193040.0) was studied before the spring return to green, and then sprayed 15 days before each castration. Self-developed alfalfa special foliar fertilizer for Mollisol agricultural area in cold region (patent application number: 201010124670.2), nutrient quality and overwintering rate, and the economic benefit was analyzed. 【Result】 Fertilization can effectively improve the yield and quality of alfalfa. Under the condition of fertilization (soil fertilizer + foliar fertilizer), the annual total hay yield of four and three stubbles of alfalfa was 13 544.44 kg·hm^-2and 11 935.26 kg·hm^-2, which were 11.45% and 10.77% higher than that of the control, and the average crude protein content was 22.11%, 21.68%, 8.17% and 7.59% higher than that of the control. Increasing the number of cutting times under fertilization (soil fertilizer + foliar fertilizer) can effectively improve the yield and quality of grass, and has little effect on the overwintering rate. Compared with the three cropping, the annual hay yield and the average crude protein content of alfalfa were increased by 13.48% and 2%.And it had little effect on the overwintering rate, only reduced by 2 percentage points, from 96.70% to 94.84%. The output value and input-output ratio of four stubbles of alfalfa with fertilization and annual mowing were 24 380.01 yuan/hm² and 2.05, which increased the net income of three stubbles by 4 851.68 yuan/hm² compared with the three stubbles of alfalfa without fertilization. 【Conclusion】 It is feasible to cut four stubbles of alfalfa under reasonable fertilization conditions in Mollisol agricultural area in cold region by comprehensive comparative analysis.

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Effects of Fertilizing Time in Early Spring on Alfalfa (Medicago sativa) Production Performance and Nutritional Quality in Mollisol Area in Cold Region

XIAO ZhiXin,WANG Yang,LIU GuoFu,GONG Hao,LI DanDan,GONG Lin,BAI ZhenJian,CUI GuoWen

Scientia Agricultura Sinica 2020, 53 (13): 2668-2677. DOI: 10.3864/j.issn.0578-1752.2020.13.015

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【Background】 Planting of alfalfa in degraded meadow in cold mollisol area of Northeast China is an effective method for rapid vegetation restoration.Reasonable fertilization is an effective measure to improve the yield and quality of alfalfa. In order to reduce the rolling damage of soil and alfalfa plants by machinery in the process of fertilizing. It is generally advisable to fertilize the soil at one time before and after alfalfa plants have returned to green in spring. The turning green period of alfalfa in the mollisol area of Northeast China is from late April to early May, and in this time, fertilizer is often applied. However, there has been few studies on the effect of fertilizer on alfalfa at different time of early spring. 【Objective】 The purpose of this experiment was to study the effects of fertilizer application in different periods of early spring on the performance and nutritional quality of alfalfa, and to determine the best fertilizing period for alfalfa in early spring. In order to provide technical guidance for the restoration of degraded meadow by planting alfalfa in the mollisol area of cold region. 【Method】 Alfalfa in its second years after was used as the experimental material, and the type of fertilizer was self-developed special fertilizer for alfalfa (patent number: 201810193040.0). And the contents of N, P, K is 14.20%, 10.86%, 10.47%. A period of fertilizer was set up every 5 days from April 20 to May 15, and the amount of fertilizer was fixed at 525 mm. The alfalfa was mowed three times every year. The effects of fertilizer on the production performance and nutritional quality of alfalfa in different periods of early spring were investigated. 【Result】 Fertilizer as all time could significantly promote the growth at all cuts, among which earlier fertilizer trend to increase the plant height of the first cut and the average plant height over the whole year, and the late fertilizer trended to increase the plant height of the second and third cut, but the difference was not significant. Early fertilizer could significantly increase the hay yield of each cut, and the early application trend of increase the hay yield of the first cut while decrease the hay yield of the second and third cuts. The effect of different fertilizing time on the average hay yield in the whole year was not significant. The average crude protein content of each harvest and that of the whole year was significantly increased by fertilizer. But the effect of different fertilizing time periods on the annual average crude protein content was not significant. Compared with no fertilizer, the contents of NDF and ADF in all treatments were significantly decreased. Fertilizing early could reduce the contents of NDF and ADF significantly, in the first crop of alfalfa , and the decrease of the contents of NDF and ADF in the second crop was more obvious in the early spring than in the early spring. The difference between the contents of NDF and ADF in the third harvest was not significant. In the whole year, the contents of fiber in April 20 treatment was the lowest. The treatment of April 25 had little difference with the treatment of April 20. And difference between two treatments of April 20 and April 25 and treatments of others is significant. 【Conclusion】 Through the comprehensive analysis, in the mollisol area, the alfalfa which has been planted 2 years fertilizer near April 25 has great nutrition quality and annual output, when fertilizer was carried out once a year.

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Responses of Soil Organic Carbon Fractionation and Microbial Community to Nitrogen and Water Addition in Artificial Grassland

XU Meng,XU LiJun,CHENG ShuLan,FANG HuaJun,LU MingZhu,YU GuangXia,YANG Yan,GENG Jing,CAO ZiCheng,LI YuNa

Scientia Agricultura Sinica 2020, 53 (13): 2678-2690. DOI: 10.3864/j.issn.0578-1752.2020.13.016

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【Objective】 Establishment of artificial grassland provides one solution for releasing some of the grazing pressure on natural grassland, and thus is conducive to the restoration of degraded grassland. The present study aimed to investigate the effects of nitrogen (N) addition and water supplement on soil organic carbon (SOC) fractionation, composition and activity of soil microbial community on artificial grassland established in Hulunber region, so as to provide insight into the effect of management practices on SOC sequestration and stability of artificial grassland. 【Method Experimental plots were designed with two factors of N addition (0, and 150 kg N·hm^-2·a^-1) and water addition (0, and 60 mm), and were constructed under three types of artificial grasslands, i.e., alfalfa monoculture, smooth bromegrass monoculture, and the mixed cultivation of alfalfa and smooth bromegrass. Soil samples were collected from experimental plots and SOC of bulk soil was fractionated into different particulate-size fractions by wet-sieving method. The abundance, composition and activity of soil microbial community were measured by phospholipid fatty acids (PLFA) and extracellular enzyme activity. Then, the effects of N addition and watering treatments on SOC fractions and soil microbial community, and investigated the relationship between these two components were analyzed. 【Result】 Three years of N fertilization and water addition exerted significant impact on SOC fractionation. Addition of N generally increased the content of particulate organic carbon (POC) in soils of alfalfa monoculture and the mixed cultivation but decreased the content of mineral associated organic carbon (MAOC), while water addition significantly increased the content of coarse POC in soils of smooth bromegrass monoculture. The activities of four soil extracellular enzymes but not the abundance or composition of soil microbial community were significantly affected by N and water addition. Nitrogen application without water addition significantly inhibited the activity of β-N-acetylglucosidase (NAG) in soils of alfalfa monoculture, but promoted that in soils of smooth bromegrass monoculture. The activities of cellobiohydorlase (CB) and NAG were significantly decreased by water addition in soils of two monoculture grasslands. Nitrogen application with water addition significantly inhibited the activities of β-glucosidase (βG), CB and NAG in soils of alfalfa monoculture, but significantly promoted CB activity in soils of the mixed cultivation. The changes in PLFA concentration of total community and specific microbial groups were positively correlated with changes in content of POC, but negatively correlated with MAOC. There were negative correlations between the activities of βG and CB, as well as the ratio of enzyme C/N and C/P with changes in POC content, and these correlations were stronger under treatments with water addition. 【Conclusion】 Results of the present study showed that in artificial grassland established in semi-arid Hulunbeier region, the addition of N fertilization significantly promoted the accumulation of labile SOC fraction, but decreased the proportion of recalcitrant fraction, which reduced the stability of soil carbon sequestration. Nitrogen fertilization and water supplement induced significant changes in activity of soil microbial communities, and these changes in enzyme stoichiometric ratios were closely related to changes in SOC fractions. These results implied that the differential demands for C, N and P by microbial communities were crucial in regulating the turnover of labile SOC fraction in artificial grassland.

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Coupling Mechanism of Herbage-Water-Nitrogen Fertilizer in Abandoned Farmland in Meadow Steppe

LI Da,FANG HuaJun,WANG Di,XU LiJun,TANG XueJuan,XIN XiaoPing,NIE YingYing,Wuren qiqige

Scientia Agricultura Sinica 2020, 53 (13): 2691-2702. DOI: 10.3864/j.issn.0578-1752.2020.13.017

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【Objective】 The study was to investigate the effects of three factors, including water replenishment, nitrogen application, and pasture type, on the biomass, plant nutrient composition and soil quality of artificial grassland communities by planting artificial grassland with different planting patterns of Hulunber, and to reveal the retreat of Hulunbuir area and the water-fertilizer coupling mechanisms of cultivated land artificial grassland, so as to optimize the mode of planting management. 【Method】 The experiment was carried out at the Hulunber Grassland Ecosystem Observation and Research Station. On June 6, 2016, the experiment began with four blocks, each of which included three test factors pasture types (P) and nitrogen application level (N) and Irrigation (I); forage types included three treatments: alfalfa (P₁), awnless brome (P₂), and alfalfa and awnless brome 1:1 mixed sowing (P₃); nitrogen application levels included no nitrogen (N₀), low nitrogen (N₁: 75 kgN·hm^-2·a^-1) and high nitrogen (N₂: 150 kgN·hm^-2·a^-1). The hydration included two levels (I₀: no water, I₁: hydration). There were 72 test plots, each of which was 7 m×10 m, and the row spacing was 1 m; it replenished the water 3 times every year in June, July and August, and the water per unit area was 20 mm. The nitrogen application (chemical pure urea) was twice in the seedling (returning) and tillering stages, respectively. Grassland biomass, nutrients (plant crude protein, neutral detergent fiber and acid detergent fiber) and soil nutrients (soil total nitrogen, soil organic carbon and soil pH) were measured in 2016 and 2017. 【Result】 (1) The response of (N), (I), (P) and (P×I) to yield in the year of planting (2016) reached a significant level (P<0.05), and two measurements in 2017. The total yield of the production reached a significant level (P<0.05) in response to test factors such as (N), (P), (P×I), (P×N), (N×I×P), and mixed (P₃). Under low water (I₀) conditions, the yield of low nitrogen (N₁) was significantly higher than that of the other treatment groups (P<0.05), with an average of 17 801.19 kg·hm^-2. (2) The crude protein content in 2016 and 2017 were P₁ treatment>P₃ treatment>P₂ treatment, in 2016. P₁, P₂ and P₃ treatment showed that the CP content increased with the increase of nitrogen level when the hydration (I) conditions were the same, and P₁ was not replenished under water (I₀) conditions. The crude protein content under P₁N₂I₀ was significantly higher than that under P₁N₀I₀, P₁N₁I₀, and P₁N₁I₁ (P<0.05), reaching a maximum value of 19.08%; in 2017, under P₃ at I₀ conditions, the CP content of the lower N₁ level (15.12%) was significantly higher than that of N₀ (P<0.05). (3) Both nitrogen application and water addition promoted the negative growth of soil SOC content, positive TN content, and negative pH growth. The SOC growth of the topsoil and the bromegrass were significantly higher than that of the mixed seeding (P<0.05), and the TN growth of the topsoil was significantly higher than that of the bromegrass and mixed seeding (P<0.05); under the surface and subsurface of 2016, the ratio of soil carbon to nitrogen (C/N) was higher than that of 2017, the average surface layer was 17.39% higher, and the subsurface layer was 15.18% higher. The carbon and nitrogen ratio of surface soil was more obvious. The surface soil carbon and nitrogen ratio was P₁N₀I₁in 2016, with the highest value of 8.15; in 2017, the highest value under P₁N₂I₀ was 5.67. The carbon and nitrogen in the subsurface soil was 6.36 higher than that under P₁N₂I₁ in 2016, and the highest under P₃N₂I₁ in 2017 was 5.67. 【Conclusion】 In the second year of planting in Hulunber, the coupling effect of herbage, water and nitrogen fertilizer had a significant effect on the biomass of the grass. The coupling effect of water and nitrogen fertilizer had a synergistic effect on the nutrient accumulation of the grass. The construction of artificial grassland plant could reduce a C/N and soil quality to drop, and adding in different kinds of grass, and water and nitrogen levels all showed the 0-20 cm soil SOC content and pH value were lower and soil TN content increased, indicating that soil acidification occurs, bean-grain mixed soil pH lower amplitude was less than unicast, and high nitrogen and filling water could be reduced to a significantly increased the soil pH value.

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