CN113854069A

CN113854069A - Method for relieving corn drought stress by utilizing biogas slurry

Info

Publication number: CN113854069A
Application number: CN202111257352.1A
Authority: CN
Inventors: 杨建霞; 毛宁; 卜婷; 范小峰; 欧晓彬; 刘秀丽
Original assignee: Longdong University
Current assignee: Longdong University
Priority date: 2021-10-27
Filing date: 2021-10-27
Publication date: 2021-12-31

Abstract

The invention discloses a method for relieving corn drought stress by utilizing biogas slurry, which is to treat corn seedlings by adopting 50-75% of biogas slurry. According to the invention, the indexes of the overground parts such as the plant height, the stem thickness and the leaf area of the maize seedlings can be increased by spraying the biogas slurry on the leaf surfaces under drought stress, the dry matter accumulation of the leaves relative to the dry-wet weight ratio, the root crown ratio and the like is increased, the length of the root system is increased, the number of fibrous roots is increased, and fine and dense small roots are formed; meanwhile, the leaf surface spraying biogas slurry under drought stress can obviously improve the relative chlorophyll content SPAD, the photosynthetic rate, the transpiration rate, the stomatal conductance and the water utilization efficiency of the leaves, and reduce intercellular CO₂Photosynthetic performance indexes such as concentration and the like, thereby enhancing the dryness of the cornTolerance to drought stress.

Description

Method for relieving corn drought stress by utilizing biogas slurry

Technical Field

The invention belongs to the technical field of crop production, and particularly relates to a method for relieving corn drought stress by utilizing biogas slurry.

Background

Drought and water resource shortage become one of the limiting factors restricting the western agricultural production in China. Loess plateau belongs to a warm climate with half-humid to semi-arid climate, is cold and dry in winter and warm and humid in summer; the rainfall is rare and the water distribution is not uniform; particularly in summer, due to hot climate, the plant transpiration rate is high, the demand for water is increased, and the plant is easy to die due to insufficient water supply. Corn is one of important grain crops in loess plateau areas, and the position occupied in national economy is very important. In the arid region of loess plateau, the rainfall frequency and rainfall are less from the middle ten days of 5 months to the last 6 months, and are the periods most susceptible to drought stress in the seedling stage of corn, and the research on the water-saving drought-resisting technology is beneficial to improving the disaster prevention and reduction coping capability of corn growers, improving the utilization rate of water resources and improving the yield of main crops such as corn and the like. Agricultural water conservation not only has great potential, but also has profound significance for increasing the income of farmers, the development of rural economy and social stability.

Corn is one of the most widely distributed crops in the world and is also the main food crop in northwest. Drought is the major environmental factor responsible for crop loss, and statistical data from world banks shows that more than half of the annual crop yield losses are due to drought. In the crop production process, the research on the change of indexes such as plant morphology, physiology, biochemistry and the like under drought stress has important significance for protecting plants on the whole and improving the crop drought resistance mechanism.

Therefore, the problem to be solved by the technical personnel in the field is to provide a method capable of relieving the drought stress of the corn.

Disclosure of Invention

In view of the above, the invention provides a method for relieving corn drought stress by utilizing biogas slurry, and the method can ensure that corn seedling plant height, stem thickness, leaf area and other fields can be realized by spraying biogas slurry on leaf surfaces under drought stressThe upper index is increased, the dry matter accumulation such as the relative dry-wet weight ratio and the root cap ratio of the leaves is increased, the length of the root system is increased, the number of fibrous roots is increased, and fine and dense small roots are formed; meanwhile, the leaf surface spraying biogas slurry under drought stress can obviously improve the relative chlorophyll content SPAD, the photosynthetic rate, the transpiration rate, the stomatal conductance and the water utilization efficiency of the leaves, and reduce intercellular CO₂Concentration and other photosynthetic performance indexes, so as to enhance the drought stress tolerance of the corn.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for relieving corn drought stress by utilizing biogas slurry, which specifically comprises the following steps: the corn seedlings are treated by 50-75% of biogas slurry.

Preferably, the specific steps of the treatment are as follows:

(1) when the corn seedlings grow to have two leaves and one heart, directly brushing 50-75% of biogas slurry on the back of the leaves of the corn seedlings under drought stress, wherein the aim of preventing the biogas slurry from dripping on the back of the leaves is to ensure that the corn seedlings are not damaged by drought stress;

(2) when the corn seedlings grow to four leaves and one core, the pretreatment of root soaking is carried out by adopting 50-75% of biogas slurry;

(3) when the corn seedlings grow to 8-leaf stage, 50-75% biogas slurry is adopted for carrying out leaf surface spraying.

The biogas slurry is rich in various nutrients (such as nitrogen, phosphorus and potassium) required by crops. The biogas slurry sprayed on the leaf surface has the effects of regulating the growth metabolism of crops, promoting the growth balance, enhancing photosynthesis, supplementing nutrition and the like. The existing literature indicates that the biogas slurry can be sprayed in the whole growing season of crops, and the spraying effect is obvious when the crops or fruit trees enter a flowering period, a booting period, a filling period and a fruit expanding period. Tests show that 50-75% of leaf back smearing and leaf surface spraying are respectively carried out on the corn in the two-leaf one-heart stage, the four-leaf one-heart stage and the eight-leaf stage of the corn seedling stage, and the drought resistance physiological index and the photosynthetic performance parameter of the corn seedling stage can be well improved.

Preferably, the soaking time in step (1) is 1 d.

The biogas slurry contains multiple phytohormones such as plant growth hormone NAA and gibberellin GA₃And in addition, the biogas slurry contains various amino acids, B vitamins, organic acids, various trace elements and the like, and the soaking of the roots enables the plants to be more favorable for absorbing various bioactive components in the biogas slurry, so that a physiological basis is laid for the tolerance of the plants to adverse circumstances. The root soaking time is 1d because the root has a larger and more perfect absorption system than the leaf, and the total amount of nutrient absorbed by the root can be reached only by applying more than 10 times to the leaf surface according to the measurement on nutrient elements with large amount such as nitrogen, phosphorus, potassium and the like. Therefore, the soaking fertilization of the roots is carried out while the foliar fertilization, so that the uptake of the effective active ingredients in the biogas slurry by the corn seedlings can be quickly met. In addition, the root soaking time is 1d, because the corn seedlings in the two-leaf one-heart stage grow relatively tender and have undeveloped root systems, and if the soaking time is too long, biogas slurry can possibly burn the roots, so that the root soaking biogas slurry for the smaller seedlings is preferably 1d, the concentration of the biogas slurry is not too high, and the concentration is preferably 50% of the low concentration.

Preferably, the spraying method in the step (3) is that the foliar spraying is started at 9d before drought stress, and 50-75% biogas slurry is sprayed on the foliar every 3d, so as to completely wet the foliar and generate dropping liquid.

Preferably, the amount of spraying in step (3) is: spraying 20mL of biogas slurry on each plant once a day, wherein the spraying time is 17: 00-18: 00.

Because the corn seedlings in the two-leaf one-heart period grow relatively fragile and can damage corn leaves if being directly sprayed on the leaves, the biogas slurry is smeared on the backs of the leaves by using the soft hairbrush, so that the biogas slurry absorption efficiency of the leaves can be better improved, in addition, the number of air holes on the backs of the leaves is relatively small, the air holes cannot be blocked by smearing the soft hairbrush, and the transpiration effect of plants is better facilitated; the biogas slurry sprayed on the leaf surface has the effects of regulating the growth metabolism of crops, promoting the growth balance, enhancing photosynthesis, supplementing nutrition and the like. Therefore, the test of the invention finds that 50-75% biogas slurry is sprayed on the leaf surface in the early stage of drought stress (before 9 d), the spraying frequency is once every 3d, and the spraying frequency is high compared with that once of 7-10d of leaf surface in most data, so that the utilization efficiency of the effective components in the biogas slurry by the plant can be greatly improved, and a certain fertility foundation is provided for the later growth of the plant and the tolerance to adverse circumstances. In addition, when the biogas slurry is sprayed on the leaf surfaces, the pesticide is matched for spraying in advance, so that the effect of preventing and treating plant diseases and insect pests can be achieved, particularly, the corn biogas slurry is used for soaking seeds, and the corn biogas slurry has a certain killing effect on soil insects such as grubs and slugs.

Preferably, the method further comprises pregermination of the corn seeds with the biogas slurry.

The biogas slurry contains various active, resistant and nutritive substances, and has obvious effects of disease resistance, seedling strengthening and yield increase by soaking seeds with the biogas slurry. The biogas slurry seed soaking has a strong inhibiting effect on the northern leaf blight and southern leaf blight of the corn. Because the temperature of the feed liquid in the discharge chamber of the methane tank is generally 8-16 ℃, the pH value of the methane liquid fermented by cow dung is generally about 7.2, and the metabolism of seeds is facilitated. Therefore, the seed soaked in the biogas liquid has uniform and strong buds, high seedling rate, developed root system, vigorous growth vigor and stronger drought resistance and disease and insect resistance.

Preferably, the specific method for accelerating germination is as follows: selecting full corn seeds, soaking the corn seeds in 50-75% biogas slurry for 8h, transferring the corn seeds to a germination box with the bottom padded with wet filter paper (for supplying moisture), placing the germination box in a light incubator at 25 ℃ for dark culture for 48h, and reserving the corn seeds after germination.

Preferably, the biogas slurry is residual liquid of cow dung fermentation.

The cow dung has the advantages of fine texture, high water content, poor air permeability, slow decomposition and slow fertilizer efficiency, belongs to a cold fertilizer, has high carbon content, low nitrogen content and high carbon-nitrogen ratio, is safer to apply after decomposition fermentation than other animal dung, and can be used for chronically improving soil. Sheep manure and chicken manure belong to thermal fertilizers, and if the manure or the fermentation is not completely applied, seedlings can be directly burned. According to the existing literature reports, the contents of organic matters, total nitrogen, total potassium, water-soluble nitrogen, water-soluble potassium and the like in the cow dung fermented biogas slurry are higher than those of biogas slurry fermented by pig manure and chicken manure, except the contents of total phosphorus and water-soluble phosphorus.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, the indexes of the overground parts such as the plant height, the stem thickness and the leaf area of the maize seedlings can be increased by spraying the biogas slurry on the leaf surfaces under drought stress, the dry matter accumulation of the leaves relative to the dry-wet weight ratio, the root crown ratio and the like is increased, the length of the root system is increased, the number of fibrous roots is increased, and fine and dense small roots are formed; meanwhile, the leaf surface spraying biogas slurry under drought stress can obviously improve the relative chlorophyll content SPAD, the photosynthetic rate, the transpiration rate, the stomatal conductance and the water utilization efficiency of the leaves, and reduce intercellular CO₂Concentration and other photosynthetic performance indexes, so as to enhance the drought stress tolerance of the corn.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a graph showing the influence of biogas slurry spraying on chlorophyll content of corn seedling leaves under drought stress in an application example of the present invention;

FIG. 2 is a graph showing the effect of biogas slurry on SOD enzyme activity of corn seedlings under drought stress in an application example of the present invention;

FIG. 3 is a graph showing the effect of biogas slurry on POD enzyme activity of corn seedlings under drought stress in an application example of the present invention;

FIG. 4 is a graph showing the effect of biogas slurry on CAT enzyme activity of corn seedlings under drought stress in an application example of the present invention;

FIG. 5 is a graph showing the influence of biogas slurry on the MDA content of maize seedlings under drought stress in an application example of the present invention;

FIG. 6 is a graph showing the effect of biogas slurry on the proline content of corn seedlings under drought stress in an application example of the present invention;

FIG. 7 is a graph showing the effect of biogas slurry spraying on the soluble sugar content of corn seedlings under drought stress in an application example of the present invention;

FIG. 8 is a graph showing the effect of biogas slurry spraying on the content of soluble protein in maize seedlings under drought stress in an application example of the present invention;

FIG. 9 is a graph showing the effect of biogas slurry spraying on the dry-to-wet weight ratio of corn plants under drought stress in an application example of the present invention;

FIG. 10 is a graph showing the effect of biogas slurry on the length of corn roots and the number of fibrous roots under drought stress in an application example of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A method for relieving corn drought stress by utilizing biogas slurry comprises the following specific steps:

(1) firstly, soaking corn seeds for 8 hours by using 50-75% of biogas slurry respectively, then sowing the corn seeds into a germination box, placing the germination box in an illumination incubator at 25 ℃ for dark culture for 48 hours to perform germination acceleration treatment, sowing the seeds subjected to germination acceleration into plastic flowerpots (18cm multiplied by 45cm) containing nutrient soil (vermiculite: perlite: peat soil is 1: 1: 3) and fertilizers (10 g of quick-acting compound fertilizers are added into the culture soil of each flowerpot) which are uniformly mixed, irrigating 100mL of 10% PEG-6000 solution to simulate drought stress when corn seedlings grow to have two leaves and one heart, and simultaneously dipping 50% of biogas slurry into a soft brush to directly brush the back surfaces of the corn leaves on the basis of no-dropping biogas slurry on the back surfaces of the leaves;

(2) when the corn seedlings grow to be four leaves and one core, the corn seedlings are pretreated by soaking roots for 1d by adopting 100mL of 50% biogas slurry, and then the corn seedlings are sprayed on the leaves by adopting 50% biogas slurry (spraying is preferably performed to completely wet the leaves and generate dropping liquid). Description of the drawings: when the biogas slurry is used for spraying corn seedlings, insecticidal pesticide is added into the biogas slurry stock solution in advance, and the biogas slurry is diluted to 50% by clear water for later use;

Application example

The biogas slurry is taken from a biogas pool which normally produces biogas for more than 3 months, and is used after being filtered. The cow dung fermentation residue is provided by Hongxiang breeding professional cooperative society in Zhenyuan county, Qingyang city.

Testing the main fertilizer effect components of the biogas residues and the biogas slurry (quality supervision and inspection testing center of agricultural film of chemical fertilizer and pesticide in Lanzhou, university of supply and marketing, China):

(1) biogas slurry: organic matter 1.2%, total nutrient (N + P)₂O₅+K₂O) is 0.8 percent, the total nitrogen is 0.2 percent, the phosphorus is 0.2 percent, the potassium is 0.4 percent, the content of the heavy metals to be detected except Pb is 20mg/kg (less than or equal to 50), and the contents of other heavy metals As, Hg, Cd and Cr are all 0mg/kg (not detected), thereby meeting the national standard.

(2) Biogas residue: 2.4 percent of organic matter and total nutrient (N + P)₂O₅+K₂O) is 1.2 percent, the total nitrogen is 1.0 percent, the phosphorus is 0.6 percent, the potassium is 0.8 percent, the content of the heavy metals to be measured is 20mg/kg (less than or equal to 50) except Pb, and the contents of other heavy metals, namely As, Hg, Cd and Cr, are all 0mg/kg (not measured) and meet the national standard.

1. Influence of biogas slurry on physiological characteristics of corn seedlings under drought stress

The corn variety to be tested (Zeamays. L) is Zhengdan 958 and Xiuyu 335; fulvic acid (powder), an antitranspirant, available from dragon lantern biotechnology limited;

test design and method

Experiment pot culture experiments were carried out in artificial intelligent greenhouses in the farm science and technology park during 2018, 3-9 months.

Selecting plastic flowerpots with an upper opening diameter of 180mm, a lower opening diameter of 125mm and a height of 150mm, loading 1.2kg of growth matrix in each flowerpot, sowing corn seeds which are pre-germinated by biogas slurry and fulvic acid with different concentrations in the grouped flowerpots, performing conventional watering management, performing chemical treatment when the seedlings grow to 8-leaf stage, and performing chemical treatment by respectively using 25% biogas slurry, 50% biogas slurry, 75% biogas slurry and fulvic acid with a certain concentration (the fulvic acid and the biogas slurry are sprayed on leaf surfaces, and the spraying of the chemical is proper to completely wet the leaf surfaces and generate dropping liquid). 2 control groups CK and drought stress groups are set in the experiment, wherein CK is normal watering till the field water capacity, the drought control group is natural drought stress treatment for 7d (no biogas slurry spraying or fulvic acid treatment is carried out on the leaf surfaces in the period), other groups are that biogas slurry with different concentrations is sprayed on the leaf surfaces every 3 days 9 days before the drought stress treatment, the fulvic acid spraying is carried out on the leaf surfaces as a control, and the groups are treated after the natural drought stress for 7 d; after drought stress treatment for 7d, measuring the chlorophyll content, malondialdehyde content, proline content, soluble sugar and soluble protein content of the leaves of the seedlings and the activities of three antioxidant enzymes POD, CAT and SOD;

method for determining physiological and morphological indices

Selecting the 3 rd to 5 th fully-unfolded leaves at the top end of the corn, immediately putting the leaves into an ice box, taking the leaves back to a laboratory, and storing the leaves in a refrigerator at the temperature of minus 80 ℃ for measuring physiological indexes. The measurement of each index was repeated 3 times, and all the spectrophotometers used for the color comparison were ultraviolet-visible spectrophotometers (UV-5100B model, Shanghai Meta-analysis Instrument Co., Ltd.).

The following physiological indices were determined:

(1) measuring the chlorophyll content by adopting a 95% ethanol extraction method;

(2) several antioxidant enzyme activity assays: the activity of superoxide dismutase (SOD) is determined by a nitro blue tetrazole 5 method; peroxidase (POD) activity was measured by guaiacol colorimetry; the Catalase (CAT) activity was measured by the hydrogen peroxide method;

(3) determination of several osmolytes: the content of Malondialdehyde (MDA) is determined by a thiobarbituric acid color development method, referring to a method of Zhangliang and the like; the content of free proline is measured by an acid ninhydrin colorimetric method; measuring the content of soluble sugar and soluble protein;

the detection results are shown in figures 1-8, and as can be seen from figure 1, fulvic acid is a known plant antitranspirant and is widely applied to the aspects of drought resistance and water conservation of crops; the drought coerce forces the chlorophyll content of the corn leaves to be reduced, the trend of the chlorophyll content reduction can be remarkably relieved by spraying the biogas slurry with different concentrations on the leaf surfaces, and particularly, the treatment effect is better by using 75% biogas slurry and is compared with that of fulvic acid; the influence of the biogas slurry on the corn chlorophyll is positively correlated with the concentration of the corn chlorophyll under drought stress, the effect of relieving the drought stress by the biogas slurry with higher concentration is more obvious, and after the corn drought stress is 7d, the chlorophyll content can be better increased by spraying the biogas slurry with different concentrations on the leaf surfaces, so that the drought condition of the plants is relieved, and the biogas slurry has advantages in the aspects of water saving and drought resistance of the plants;

POD and CAT are plant cell clearance H₂O₂The major enzymes of (2); SOD has special physiological activity and is the first substance for eliminating free radicals in organisms; the level of SOD in the organism means the visual index of aging and death; as can be seen from fig. 3 and 4, the activity of both POD enzyme and CAT enzyme was increased to different extents in the corn plants treated with different concentrations of biogas slurry compared to the control group; the POD activity of the 50% biogas slurry treatment group is increased to the maximum, the CAT enzyme activity of the 75% biogas slurry treatment group is increased to the maximum, and compared with a maize plant sprayed with fulvic acid, the biogas slurry has the effect of better improving the POD and CAT enzyme activities in the plant body under the drought stress condition; the biogas slurry treatment can obviously improve the activity of POD and CAT enzymes, so as to improve the drought tolerance of the corn; from fig. 2, the SOD enzyme activities of the treated groups sprayed with 50% biogas slurry and fulvic acid were lower than those of the drought control group (no intervention of other measures after drought stress of 7 d), while the SOD enzyme activities were not significantly affected by spraying of 25% and 75% biogas slurry.

As can be seen from FIG. 5, the spraying of biogas slurry and fulvic acid does not reduce the MDA content in the corn leaves, the MDA content of each treatment group is higher than that of the normal watering and drought treatment groups, and the analysis is possibly interfered by the content of soluble sugar in plant tissues, because the maximum absorption wavelength of a chromogenic reaction product of sugar and thiobarbituric acid is 450nm, but the maximum absorption wavelength is also at 532nm, and the interference of the soluble sugar is not completely eliminated during the measurement.

Osmotic regulation is an important physiological mechanism of plants adapting to drought stress, and compatible substances for osmotic regulation mainly comprise proline, soluble sugar, betaine and the like. The free proline in the plant body can increase the cell permeability and promote the cells to absorb water to be prevented from being influenced by drought, and in addition, the self structure and the special physical and chemical properties of the free proline can also protect the activity, the structure and the function of enzyme in the cells when stressed, promote the protein solubility to be improved, reduce the precipitation of soluble protein, participate in chlorophyll synthesis and improve the plant resistance. As can be seen from fig. 6, compared with a control, the spraying of biogas slurry with different concentrations can significantly increase the proline content of a plant, especially the spraying of 75% biogas slurry has the most significant effect on the proline content of corn seedlings, and the effect is better than that of the known antitranspirant fulvic acid, which indicates that the effect of biogas slurry in improving the stress resistance of corn is better than that of fulvic acid;

the soluble sugar is an important constituent substance of a plant structure, and simultaneously, the soluble sugar also participates in various physiological metabolic processes in the plant body widely, and the increase of the content of the soluble sugar can accelerate the growth and metabolism of the plant; as can be seen from FIG. 7, compared with the control, the soluble sugar content of the plants treated by biogas slurry with different concentrations is increased to a certain extent, and the treatment effect is the best especially by 50% biogas slurry;

soluble protein is an essential important constituent substance in a plant structure, various physiological metabolic processes in a plant mostly need participation of the soluble protein, and researches show that the plant can accelerate the growth and metabolism of the plant by spraying an antitranspirant to improve the content of the soluble protein; as can be seen from FIG. 8, the soluble protein content in plants can be increased by biogas slurry treatment with different concentrations, and particularly the soluble protein content in corn leaves under drought stress is increased most remarkably by 50% biogas slurry treatment.

2. Influence of biogas slurry on growth of maize seedlings under drought stress

Soil conditions of the test field: the test field is selected to be carried out in an artificial intelligent greenhouse in a technical garden of agriculture of the Longdong institute, the previous crops are herbaceous flowers, the soil to be tested is sandy loam, loose in soil texture, permeable to air and water, sufficient in soil nutrients, more than 0.7% of organic matter, more than 0.05% of nitrogen content and 7.3 of soil pH; after earlier soil preparation, ridge making and base fertilizer application, the soil is flat, the irrigation and drainage are good, the soil fertility is medium, and the method is suitable for planting corn;

corn, test corn varieties were 'medium No. 2' (drought-sensitive corn variety, purchased from wuwei seed stations) and 'advanced corn 335' (drought-insensitive corn variety, purchased from fluvial south american agro-financing);

test method

Selecting 100 corn seeds with uniform size and full grains without diseases and insect pests, soaking for 24h, transferring to a culture dish, adding a proper amount of distilled water, and performing germination and seedling culture in an incubator, wherein the temperature of the incubator is set to 25 ℃; when the seedlings grow to have two leaves and one heart, selecting the seedlings with basically consistent growth conditions for treatment; the experiment was set with a total of 5 treatments: distilled water treatment (control, denoted by CK), 10% PEG treatment (drought, denoted by PEG), 25% biogas slurry + 10% PEG (denoted by 25% + PEG), 50% + 10% PEG (denoted by 50% + PEG), 75% + 10% PEG (denoted by 75% + PEG); 5 seedlings were used for each treatment, 5 replicates. Soaking roots in 100mL of biogas slurry with different concentrations of 25%, 50% and 75% for pretreatment for 1d, and treating with 100mL of liquid for both distilled water treatment (control) and 10% PEG treatment (drought); after pretreatment, 10% (W/V) solution prepared by PEG6000 is used for treating corn seedlings treated by biogas slurry with different concentrations and 1 group of corn seedlings treated by distilled water, each group is treated by 100mL of 10% PEG liquid, and the seedlings treated by distilled water are used as a reference; after drought treatment for 48h, respectively measuring various water physiological indexes of 5 groups of corn seedlings, and repeatedly measuring each index for 3 times;

wherein, the determination of the photosynthetic parameters: selecting corn seedling from the 3 rd leaf, completely unfolding the leaves at 9:00-11:30 in the morning on sunny day, and adopting LI-6400 type portable photosynthesis apparatus (LI-COR corporation) at 25 deg.C and illumination intensity of 400 μmol.m^-2·s^-1And the atmospheric concentration is 400 mu mol/mol^-1Under the condition, an empty place without people in the range of 200 m is selected, and the net photosynthetic rate (Pn) of leaves and intercellular CO are measured₂Concentration (Ci), stomatal conductance (Gs) and transpiration rate (Tr), each treatment being repeated 3 times; and calculating the water use efficiency WUE according to the following formula: water Use Efficiency (WUE) ═ Pn/Tr × 100%;

determination of chlorophyll relative content SPAD value: adopting a plant nutrient tester (TYS-3N, Topu Zhejiang instrument); measuring the leaves at the ear position, opening the machine, adjusting the blank of the machine for three times, and selecting the leaves with similar growth conditions for measurement; selecting the position of the blade deviating from the edge of the blade and the main vein of the blade during measurement, measuring 5 points at equal intervals from the base part to the tip part of the blade, and averaging; reading each leaf for 3-5 times, selecting 7-8 corns per treatment, and selecting 8-10 leaves per corn for measurement;

measurement of morphological index

Determination of root length: measuring the longitudinal length of the corn roots by using a graduated scale or a measuring tape, and measuring 9 plants;

the number of hair roots: 10 plants were measured for each treatment using direct counting;

and (3) measuring the dry-wet weight ratio of the leaves: collecting 5 well-grown corn leaves treated by each type, weighing by using an electronic analytical balance and recording the result (wet weight of the leaves); then subpackaging the weighed fresh weight leaves in a clean culture dish, putting the culture dish in an oven, deactivating enzymes at 105 ℃, adjusting to 70 ℃ after 15min, and treating to balance weight; after the dried blades are cooled, weighing and recording numerical values (dry weight of the blades), and calculating the dry-wet weight ratio of the blades according to a formula: leaf dry-to-wet weight ratio ═ leaf dry weight ÷ leaf wet weight;

root-to-crown ratio determination: the ratio of the fresh weight of the underground part of the plant to the fresh weight of the overground part of the plant;

investigation of growth conditions of seedlings: selecting 8 plants for each treatment, and respectively measuring the plant height, stem thickness and leaf area of each plant by 6 completely spread leaves;

measuring the plant height: measuring the distance from the plant ground to the top end of the corn seedling by using a meter ruler, and measuring 9 plants;

measurement of leaf area: measuring by adopting a PG-250 photoelectric leaf surface instrument, collecting fully-unfolded leaves, selecting 7-8 leaves for each treatment, and selecting 9-10 leaves without plant diseases and insect pests for each leaf;

stem thickness measurement: directly measuring and reading by using an electronic vernier caliper;

data processing: analyzing the data by adopting SPSS 20.0; carrying out data difference significance test (P <0.05) by adopting a Duncan method and single-factor analysis of variance, and using Excel2010 software to make a table; the data in the graph are mean values + -SD, and the results are shown in tables 1-3;

TABLE 1 influence of biogas slurry on the overground part of maize seedlings under drought stress

Note: the letters in the same column indicate significance of difference (P <0.05)

As can be seen from table 1, the PEG simulated drought stress treatment significantly decreased the SPAD values of the chlorophyll relative contents of both corn seedlings, i.e., jade 335 first and corn seedling No. 2 medium, especially, the SPAD value of jade 335 first was decreased by a larger amount, compared with CK; spraying 50% biogas slurry after drought stress for 7d obviously improves the relative chlorophyll SPAD content of the two corn seedlings, wherein the single No. 2 has a larger rising amplitude, compared with a CK and PEG treatment group; the results show that the application of the biogas slurry can improve the drought resistance of the corn by relieving the growth inhibition effect of drought stress on the corn seedlings, and the influence effect of the foliar spraying of the biogas slurry on the chlorophyll content of the No. 2 seedling in the corn is more obvious after the drought stress; when plants are subjected to drought stress, the stems often exhibit a robustly dwarfed appearance; the fact that the spraying of the biogas slurry can enhance the drought stress resistance effect of the corn seedlings or promote the growth of the leaves of the corn seedlings and reduce the influence of the drought stress on the height of the corn plants is shown, and the analysis can be carried out on the fact that the biogas slurry contains growth substances for promoting cell division and elongation, namely, the research of predecessors finds that the biogas slurry is rich in various bioactive substances, such as various amino acids, vitamins, gibberellin, auxin and other plant hormones and other bioactive substances;

TABLE 2 influence of biogas slurry on root growth and dry matter accumulation of maize seedlings under drought stress

The seedling stage of the corn is a vegetative growth stage, the root system is a growth center of the seedling stage, the underground part of the seedling grows vigorously, the overground part of the root system grows relatively slowly, and the high crown ratio indicates that the root system has strong activity and is weak. The corn is most sensitive to water in the growth process, the growth of the corn is forced to be hindered by slight drought, particularly, the fresh-to-heavy root-cap ratio of the plant is obviously influenced, and the root-cap ratio can reflect the growth and development conditions of the underground part and the overground part of the corn. Corn is a representative of plants with fibrous root systems, for which the root system is an organ that directly senses soil moisture signals and absorbs soil moisture, and a developed root system enables corn to have higher efficiency in absorbing and transporting moisture. As can be seen from Table 2, drought stress can cause significant reduction in the root length of both Jade 335 and Medium No. 2 maize seedlings, where the root length of Jade 335 is reduced by 16.4% and the root length of Medium No. 2 is reduced by 17%, but has no significant effect on the number of fibrous roots, compared to CK. And under drought stress, if 50% biogas slurry is sprayed on the leaf surfaces for treatment, the root length and the fibrous root number of the first jade 335 and the single No. 2 are both obviously increased, wherein the root length of the first jade 335 is increased by 48.1%, the fibrous root number is increased by 42%, the root length of the single No. 2 is increased by 56.1%, and the fibrous root number is increased by 32.3%, compared with the PEG treatment group;

in addition, as can be seen from table 2, PEG simulated drought stress treatment resulted in a significant increase in the root cap ratio of jadeite 335 and medium No. 2, with two varieties of maize seedlings having root cap ratios increased by 36% and 26.3%, respectively, compared to CK. However, if 50% of biogas slurry leaf surface spraying treatment is carried out under drought stress, the root-cap ratio of Yu 335 and Mi No. 2 is obviously reduced, and is respectively reduced by 33.3% and 30.2%, compared with the PEG treatment group, the biogas slurry leaf surface spraying treatment under drought stress can effectively promote the growth of the underground root system of the corn seedling and inhibit the increase of the root-cap ratio. Drought stress reduced the dry-to-wet weight ratio of the leaves of the first jade 335 seedling by 28.6%, but seemed to have no effect on the dry-to-wet weight ratio of the leaves of medium No. 2, compared to CK. If the biogas slurry leaf surface spraying treatment is carried out under drought stress, the dry-wet weight ratio of the jade 335 and the single No. 2 leaf is obviously increased by 80 percent and 42.9 percent respectively, compared with the PEG simulation drought treatment. Therefore, drought stress enables the root cap ratio of the first jade 335 and the single No. 2 seedling to be obviously promoted, and the dry-wet weight ratio of leaves to be obviously inhibited (except for the single No. 2 seedling), but under the drought stress, if the leaf surface spraying biogas slurry treatment is carried out, the increase of the dry-wet weight ratio of the leaves of the corn seedling can be obviously promoted, and the increase of the root cap ratio of the corn seedling is inhibited, and the results show that the biogas slurry leaf surface spraying can improve the drought resistance of the corn plant by promoting the growth of the root system of the corn plant and the accumulation of dry matters on the ground part.

In conclusion, the growth inhibition phenomenon of the corn can be relieved by spraying the biogas slurry on the leaf surfaces under drought stress, so that the tolerance of the corn to the drought stress can be effectively improved by increasing indexes such as the plant height, the stem thickness, the leaf area, the root length, the root number and the like of the corn seedlings and increasing the accumulation of dry matters on the overground parts of the corn, and further, the effects of the drought stress on the growth and development of the underground and overground parts of the corn can be reduced or the growth of the underground parts of the corn seedlings can be promoted by spraying the biogas slurry, so that the drought resistance of the corn can be enhanced and the water saving effect of the corn can be improved.

TABLE 3 influence of biogas slurry on photosynthesis characteristics of maize seedling leaves under drought stress

Note: the letters in the same column indicate significance of difference (P <0.05), and the same applies below

As can be seen from Table 3, drought stress caused both Pn of the first maize seedling 335 and Pn of the middle single No. 2 maize seedling to decrease by 25.6% and 16.4%, respectively, compared to the control CK; the Pn of the prime jade 335 and the single No. 2 corn seedling can be significantly increased if the foliar spray treatment with 50% biogas slurry is adopted under drought stress, wherein the Pn of the prime jade 335 and the single No. 2 seedling is increased by 47.4% and 42.9%, respectively, compared with the PEG treated group. The drought stress causes the transpiration rates Tr of the corn seedlings of Yu 335 and Midan No. 2 to be increased, so that the Tr of the two corn seedlings is respectively reduced by 17.8% and 15.6%, compared with CK; if the leaf surface spraying treatment is carried out by 50% biogas slurry under drought stress, Tr of two corn seedlings is further increased, and the increase amplitudes respectively reach 26.4% and 11.5%, compared with the PEG treatment group. In addition, drought stress resulted in Xiuyu 335 and Zhongdan No. 2 maize seedling leavesThe stomatal conductance Gs of the corn seedlings are reduced, wherein the Gs of the two corn seedlings are reduced by 19.3 percent and 23.2 percent respectively, and compared with CK. And under drought stress, if 50% biogas slurry is used for foliar spraying treatment, the Gs of the corn seedlings 335 of Yu first can be increased by 7.3%, but the Gs of the corn seedlings of single No. 2 are further reduced by 19.1%, compared with the PEG treated group. While drought stress results in intercellular CO of single No. 2 maize seedlings₂The concentration is increased by 7.3 percent, so that intercellular CO of the corn seedlings of the Xiyu 335 is increased₂The concentration is reduced by 11.9%, compared with CK, if 50% biogas slurry is sprayed on the leaf surface under drought stress, the first jade 335 and intercellular CO of the single No. 2 are sprayed₂The concentration Ci decreased by 7.6% and 29.4%, respectively, compared to the PEG treated group. Therefore, the biogas slurry sprayed on the leaf surfaces under drought stress can improve the photosynthetic rate, the transpiration rate and the stomatal conductance (except for single No. 2), and reduce intercellular CO₂The concentration Ci and other indexes, thereby enhancing the drought resistance of the corn.

As can be seen from table 3, drought stress resulted in a decrease in water use efficiency WUE of the corn seedling leaves of jadei 335 and medium No. 2, by 36.9% and 27.9%, respectively, compared to CK. However, under drought stress, if the foliar spray treatment with 50% biogas slurry was used, the WUE of the two corn seedlings increased by 16.4% and 28.3% respectively, relative to the PEG treated group.

In conclusion, the WUE of the corn seedlings can be improved by applying biogas slurry under drought stress, and compared with a PEG treatment group, the effect of the treatment of spraying biogas slurry on the leaf surfaces under drought stress on the WUE with the water utilization efficiency of No. 2 in the corn seedlings is obviously greater than that of the treatment of the WUE with Yu 335.

3. Influence of biogas slurry on growth and yield of corn plants under drought stress

Test method

The test was conducted in the open field of a farm-oriented technical park. Selecting full corn seeds with regular shape, sowing by a dibbling method, wherein the test area is 5m multiplied by 1m, the total number of the rows is 4, the row spacing is 70cm, each row is 3 columns, and the column spacing is 33.33 cm. Four treatments were designed for the experiment, each treatment was replicated three times: normal watering (CK); drought stress 7 d; spraying 75% biogas slurry after drought stress for 7 d; spraying 1.0g/L fulvic acid after drought stress for 7d, wherein the concentration of the selected biogas slurry and fulvic acid is selected in the early-stage preliminary experiment.

And performing a preliminary experiment before the experiment, aiming at screening out the optimal biogas slurry concentration. The test corns are planted in the test field, and the test corns are tested when the corns grow to 5-leaf stage. A total of 10 treatments were designed, each treatment being repeated 3 times, respectively: watering normally; drought stress 7 d; after drought stress for 7 days, 25%, 50%, 75% and 100% biogas slurry are sprayed. After the test is finished, after the morphological index and the physiological and biochemical index of the biogas slurry are measured, the concentration of 50% of biogas slurry is found to be the optimum concentration for the test, so that the subsequent test takes 50% of biogas slurry as the application standard.

After the test is subjected to early treatment, pouring bottom water in 2019 in 4 and 2 days, sowing in 2019 in 4 and 15 days, covering soil for about 1cm, and covering a mulching film on the upper layer for heat preservation and moisture preservation; the corn seedlings emerge in 24 days in 4 months, and the management among the seedlings is normally carried out; and in 13 days after 5 months, all the corn seedlings grow to 5-6 visible leaves, except CK, the drought stress is carried out for seven days, no treatment is carried out for 7d according to the experimental design in the drought stress period, and the biogas slurry (50%) is sprayed on the leaf surfaces of the corn seedlings in the rest period. And (5) finishing the field test after 21 days after 9 months, and determining the agronomic characters (fresh weight root-crown ratio, plant height, leaf area, stem thickness, fibrous root number, ear length and hundred grain weight) of the corn plants.

Measurement of dry-wet weight ratio of leaves: 5 leaves are collected in each cell by S-shaped septa, and the results are weighed and recorded by an analytical balance respectively. Respectively putting the weighed leaves into a clean beaker, putting the beaker into an oven, deactivating enzyme at 105 ℃ for 15min, and adjusting the temperature of the oven to 70 ℃ to process the leaves until the weight of the leaves is constant. And (5) weighing and recording the numerical value after the dried blade is cooled. The Root-crown ratio (Root-toparatio) of the fresh weight of the corn is measured by a one-thousandth balance; a scale for measuring plant height; measuring the leaf area by using a length multiplied by width product coefficient method; vernier calipers are used for measuring stem thickness; the number of fibrous roots is measured by natural counting.

Leaf area determination: collecting 8 fully extended leaves without plant diseases and insect pests, finding a piece of white paper, preferably A4 paper, cutting into a square, weighing the paper, measuring its side length and recording data, then placing the leaves on the cut square paper, drawing the shape of the leaves on the paper along the edges of the leaves, cutting along the edges to be marked, and finally weighing the cut paper, thereby calculating the area of the leaves and making 3 repetitions per cell.

And (3) measuring the plant height: measuring the plant height and the fruit crown height by using a tape measure;

measuring the weight of hundred grains and the number of single fruit grains: collecting mature corns in different processing districts, manually threshing, drying in a vacuum drying oven at 70 ℃, counting 100 corns, and weighing and recording; the single fruit grain number refers to that 8 fruits are randomly selected from each processing cell, threshed respectively, counted and averaged to be used as a single fruit grain record;

the results are shown in FIGS. 9-10 and Table 4:

as can be seen from fig. 9, under drought stress, the dry-wet weight ratio (root, stem, leaf) of corn is reduced, and compared with CK, spraying 50% biogas slurry on the leaf surface can relieve the tolerance of corn to drought stress, which is shown in that the dry-wet weight ratio of root, stem and leaf is improved compared with PEG (drought), and especially the dry-wet weight ratio of leaf is improved more remarkably;

TABLE 4 influence of biogas slurry on physiological characteristics of maize plants under drought stress

As can be seen from Table 4, under drought stress, the plant height, leaf area and crown height of the corn are all significantly reduced, and compared with CK, the 4 physiological indexes of the corn under drought stress can be effectively improved by spraying biogas slurry on the leaf surfaces. The 50% biogas slurry spraying can effectively improve the drought tolerance of the corn, and the indexes are improved even higher than CK group except plant height.

Meanwhile, as shown in table 4, PEG simulation drought treatment reduces the number of grains per ear of corn, while biogas slurry spraying increases the number of grains per ear of corn, but has little effect on thousand seed weight (after mature harvest), indicating that biogas slurry has a certain effect on the yield of corn under drought stress, and can improve the increase of the number of grains per ear of corn, even higher than control CK treatment.

As can be seen from FIG. 10, under drought stress, the corn root length and the number of fibrous roots are reduced, and compared with the control CK, the corn root length can be remarkably improved by spraying 50% biogas slurry on the leaf surfaces, but the influence on the number of fibrous roots is small. The biogas slurry can relieve the drought tolerance of the corn and improve the drought resistance of the corn within a range.

4. Influence of biogas slurry leaf surface spraying on photosynthetic physiological characteristics and water-saving effect of corn plants under PEG drought treatment

Test method

Material cultivation and treatment: selecting corn variety Yu 335 seed, sterilizing with 10% sodium hypochlorite for 10min in 2019, 12 months and 30 days, repeatedly washing with distilled water for 2-3 times, and soaking for 8 hr. Placing in a germination accelerating box, and placing in an illumination incubator at 25 deg.C for dark germination accelerating for 48 h. The germinated seeds were sown in plastic pots (18cm by 45cm) containing nutrient soil (perlite: nutrient soil: 6:2: 2). When the corn seedlings of each treatment group grow to the two-leaf one-heart stage, 3 treatment groups are respectively designed and marked as 1, 2 and 3. Wherein No. 1 is clear water control group, and watering is performed normally; no. 2 is poured by 10 percent PEG-6000 solution; no. 3 is a group of 50% biogas slurry and PEG treatment, namely the biogas slurry with the concentration of 50% is sprayed to the blades while the PEG is stressed. After each group is continuously processed for 3d, measuring each index in the 3 rd step;

measurement of photosynthetic characteristic parameters: measured using a Yaxin-1101 photosynthesis meter, at 10 am on treatment 3 d: 00 selection of fully expanded inverted Trifolium for determination of Net photosynthetic Rate (Pn), intercellular CO₂Concentration (Ci), stomatal conductance (Gs), transpiration rate (Tr) and the like, and the Water Use Efficiency (WUE) (ratio of net photosynthetic rate (Pn) to transpiration rate (Tr)) was calculated. The leaf stomata limit (Ls) is calculated as 1-Ci/Ca, and Ca is environmental CO₂Concentration, Water Use Efficiency (WUE) ═ Pn/Tr.

And (3) root activity determination: adopting a TTC method;

leaf Relative Water Content (RWC): shearing the middle upper part of mature leaves by a drying method, repeating for 3 times, wiping the materials, weighing Fresh Weight (FW), soaking in distilled water overnight, taking out the wiped surface water, immediately weighing the weight (T) after the water absorption saturation, placing the dried leaves in an oven for deactivation of enzymes at 120 ℃ for 30min, drying the leaves at 80 ℃ to constant weight, and weighing Dry Weight (DW). The relative water content was calculated according to the following formula:

relative water content (%) ═ ((FW-DW)/(T-DW)) × 100;

chlorophyll relative content (SPAD) assay: adopting a plant nutrient tester (TYS-3N, Topu Zhejiang instrument);

the results are shown in tables 5-7:

TABLE 5 Effect of biogas slurry on Relative Water Content (RWC) of maize seedlings under drought stress%

As shown in Table 5, compared with the control, the drought stress obviously reduces the relative water content of the leaves and the root systems of the maize seedlings, the water content of the leaves is reduced by 10.91%, and the root systems are reduced by 14.8%; the relative water content of the leaves and the root systems can be obviously improved by spraying 50% biogas slurry on the leaf surfaces; the fact shows that the spraying of the biogas slurry can influence the water balance of leaves and root systems, improve the relative water content of the leaves and the root systems, and further improve the drought resistance.

TABLE 6 influence of biogas slurry on drought corn seedling root vigor/(TTF. mu. g.g)^-1.h^-1)

As shown in Table 6, drought significantly enhanced the root activity of maize seedlings compared to the control, which increased 0.71TTF μ g.g compared to the control^-1.h^-1(ii) a Compared with single drought treatment, the root activity of the seedlings pretreated by 50% biogas slurry is obviously improved; the root system activity of the seedlings under the drought is increased, and the seed is soaked by the biogas slurry to further improve the root system activity of the corn seedlings and improve the water absorption capacity of the root system under the drought, so that the drought resistance is enhanced.

TABLE 7 influence of biogas slurry on photosynthetic characteristics of maize plant leaves under drought stress

As shown in Table 7, drought forces leaf photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂The concentration (Ci) (except single No. 2) and the Water Use Efficiency (WUE) were both decreased, and the transpiration rate was increased, compared to CK; but the biogas slurry treatment can relieve the reduction of Pn, Gs, WUE and the like, and compared with the PEG treatment group, the biogas slurry treatment method shows that the drought resistance of the corn can be enhanced by improving the photosynthetic rate, the stomatal conductance and the water utilization efficiency of the corn leaves by spraying 50% biogas slurry on the leaf surfaces under drought stress; the SPAD value and the single plant biomass of the corn functional leaves are in a descending trend under the same drought stress, compared with a control, the index is relieved by spraying 50% of biogas slurry, and compared with the single drought stress, the chlorophyll content (SPAD value) of the plant leaves is obviously improved by spraying the biogas slurry, so that the plant photosynthetic rate and the single plant biomass are obviously improved.

In conclusion, drought stress treatment resulted in reduced biomass of Jade 335 and single No. 2 maize seedlings, limited plant growth and reduced photosynthetic rate, stomatal conductance, intercellular CO₂The concentration is less influenced by the transpiration rate, and the growth of the corn seedlings under the drought condition can be promoted after 50% biogas slurry is applied, so that the photosynthetic rate, the transpiration rate, the water utilization efficiency and the porosity conductivity (except for the single No. 2), the water-saving effect is realized, the drought resistance of the corn is improved, and the drought-resisting and water-saving effects on the early corn 335 seedling with strong drought resistance are better. Therefore, the biogas slurry applied under the drought stress condition can fully utilize the biogas fertilizer resource, improve the comprehensive utilization efficiency of the biogas slurry, promote the increase of the corn yield, more importantly realize the water-saving effect, have guiding significance to the production practice, and can be popularized and applied to the corn production

The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for relieving corn drought stress by utilizing biogas slurry is characterized by specifically comprising the following steps: the corn seedlings are treated by 50-75% of biogas slurry.

2. The method for relieving corn drought stress by utilizing biogas slurry as claimed in claim 1, wherein the specific steps of the treatment are as follows:

3. The method for alleviating corn drought stress using biogas slurry as claimed in claim 2, wherein the soaking time in step (2) is 1 d.

4. The method for relieving corn drought stress by utilizing biogas slurry as claimed in claim 2, wherein the spraying method in the step (3) is as follows: the leaf surface spraying is started 9d before drought stress, and 50-75% biogas slurry is sprayed on the leaf surfaces every 3d, so that the leaf surfaces are completely moistened and dropping liquid is generated.

5. The method for relieving corn drought stress by utilizing biogas slurry as claimed in claim 2, wherein the spraying amount in the step (3) is as follows: spraying 20mL of biogas slurry on each plant once a day, wherein the spraying time is 17: 00-18: 00.

6. The method for alleviating corn drought stress using biogas slurry as claimed in claim 1, further comprising pregerminating the corn seeds with the biogas slurry.

7. The method for relieving corn drought stress by utilizing biogas slurry as claimed in claim 6, wherein the specific method for accelerating germination is as follows: selecting full corn seeds, soaking the corn seeds in 50-75% biogas slurry for 8h, transferring the corn seeds to a germination box with the bottom padded with wet filter paper in advance, placing the germination box in a light incubator at 25 ℃ for dark culture for 48h, and reserving the corn seeds after germination.

8. The method for relieving corn drought stress by utilizing biogas slurry as claimed in claim 1, wherein the biogas slurry is residual liquid of cow dung fermentation.