Method and application of root-leaf complementary nitrogen fertilization to promote corn growth under salt stress conditions

Abstract

The present invention belongs to the technical field of fertilization, and specifically relates to a method and application for promoting corn growth under salt stress conditions through complementary root-leaf nitrogen fertilization. The present invention provides a method for promoting corn growth under salt stress conditions through complementary root-leaf nitrogen fertilization. Corn is planted in saline soil and subjected to soil nitrogen fertilization and foliar nitrogen fertilization. The amount of soil nitrogen fertilization is a soil nitrogen fertilization threshold, and the amount of foliar nitrogen fertilization is a foliar nitrogen fertilization threshold. Because corn roots are hindered from absorbing nutrients under salt stress conditions, the present invention utilizes complementary soil and foliar nitrogen fertilization to supplement the insufficient nitrogen fertilizer absorbed by the corn roots through foliar nitrogen fertilization, thereby improving corn nitrogen absorption, enhancing corn stress resistance, and promoting corn growth.

Description

Technical Field

[0001] The present invention relates to the technical field of fertilization, and in particular to a method and application of promoting corn growth by complementary nitrogen application of roots and leaves under salt stress conditions. Background Art

[0002] Salt stress is a key environmental factor restricting crop growth. In salinized soils, high concentrations of salt ions (such as sodium and chloride) increase soil osmotic pressure, inhibiting water and nutrient absorption by plant roots. It also triggers ion toxicity and oxidative stress, destabilizing cell membranes and severely impacting plant growth and development.

[0003] Traditional nitrogen fertilizer application methods typically supplement nitrogen through soil basal application or irrigation topdressing. However, salt stress can increase soil osmotic pressure, making it difficult for plant roots to absorb water, triggering physiological drought, changing root cell membrane permeability, weakening metabolic activity, and significantly reducing the roots' active nitrogen absorption capacity. In addition, plant transpiration is weakened, reducing the ability of xylem sap flow to transport nitrogen, resulting in a decrease in the efficiency of nitrogen distribution to the aboveground parts. Salt stress can also induce a burst of reactive oxygen species (ROS), destroy chloroplast structure, reduce photosynthetic capacity, and reduce the plant's energy supply for converting nitrogen into biomolecules such as amino acids and proteins. In addition, irrational application of nitrogen fertilizers can cause nitrogen residues in the soil, further exacerbating the saline soil environment.

[0004] Corn is one of the world's most important crops, but its growth and yield are severely hampered by salt stress, posing a challenge to agricultural productivity. Nitrogen plays a crucial role in improving corn plants' stress tolerance. While recent studies have attempted to enhance salt tolerance through modified nitrogen fertilizer types (such as slow-release and coated fertilizers), these efforts are costly and complex, and they fail to address the core issue of synergistic regulation of nitrogen uptake and corn stress tolerance in saline soils. Therefore, optimizing nitrogen supply to simultaneously enhance corn seedling nitrogen uptake efficiency, stress tolerance, and growth rate under salt stress has become a critical technical challenge in saline-alkali land agriculture. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and application of root-leaf complementary nitrogen application to promote corn growth under salt stress conditions. The method of the present invention can promote corn nitrogen absorption under salt stress conditions, improve corn stress resistance, and ultimately promote corn growth.

[0006] In order to solve the above technical problems, the present invention proposes the following technical solutions:

[0007] The present invention provides a method for promoting corn growth by complementary nitrogen fertilization with roots and leaves under salt stress conditions, comprising the following steps:

[0008] Plant corn in saline soils and apply soil and foliar nitrogen fertilizers;

[0009] The amount of soil nitrogen application is the soil nitrogen application threshold, and the amount of foliar nitrogen application is the foliar nitrogen application threshold;

[0010] The soil nitrogen application threshold is the minimum nitrogen application rate at which the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted no longer significantly increase, and the oxidation marker index no longer significantly decreases;

[0011] The foliar nitrogen application threshold is the minimum foliar nitrogen application rate when the soil nitrogen application threshold is used as the application rate of soil nitrogen fertilizer in the soil where corn is to be planted, so that the growth index, nutrient absorption index, and antioxidant enzyme index of the corn no longer increase significantly and the oxidation marker index no longer decreases significantly.

[0012] Preferably, the nitrogen fertilizer for foliar nitrogen application includes liquid nitrogen fertilizer; the nitrogen fertilizer for soil nitrogen application includes one or more of ammonium nitrogen fertilizer, nitrate nitrogen fertilizer and amide nitrogen fertilizer, the ammonium nitrogen fertilizer includes one or more of ammonium sulfate, ammonium chloride and ammonium bicarbonate, the nitrate nitrogen fertilizer includes potassium nitrate and / or calcium nitrate, and the amide nitrogen fertilizer includes urea.

[0013] Preferably, the growth index includes fresh weight and dry weight; the nutrient absorption index includes total nitrogen content; the antioxidant enzyme index includes superoxide dismutase; and the oxidation marker index includes malondialdehyde and hydrogen peroxide.

[0014] Preferably, the method for determining the soil nitrogen application threshold comprises: in the planting year, performing soil testing on the soil to be planted with corn and calculating the nitrogen application amount, taking the calculated soil nitrogen application amount as a benchmark of 100%, applying different amounts of nitrogen fertilizer to the soil, and measuring the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of the corn;

[0015] The nitrogen fertilizer application rate for the selected soil was determined based on the standard that the growth indicators of corn no longer significantly improved. The lowest nitrogen fertilizer application rate at which the nutrient absorption indicators and antioxidant enzymes of corn no longer significantly increased and the oxidation marker indicators no longer significantly decreased under the selected soil nitrogen fertilizer application rate was the soil nitrogen application rate threshold.

[0016] The method for determining the foliar nitrogen application threshold comprises: in the planting year, in the soil where corn is to be planted, using the soil nitrogen application threshold as the soil nitrogen fertilizer application rate, determining the foliar nitrogen fertilizer application rate based on 0.25% to 0.26% of the nitrogen application rate of the calculated soil test formula, using the determined foliar nitrogen fertilizer application rate as a benchmark of 100%, and applying different foliar nitrogen fertilizer amounts to the corn at the same time, and measuring the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of the corn;

[0017] The selected foliar nitrogen application rate is determined based on the standard that the growth indicators of corn no longer increase significantly; the lowest foliar nitrogen application rate when the nutrient absorption indicators and antioxidant enzymes of corn no longer increase significantly and the oxidation marker indicators no longer decrease significantly under the selected foliar nitrogen application rate is the foliar nitrogen application rate threshold.

[0018] Preferably, the different nitrogen fertilizer amounts are 10% to 130% of the soil nitrogen application rate;

[0019] The different foliar nitrogen fertilizer amounts are 70% to 190% of the foliar nitrogen fertilizer application standard.

[0020] Preferably, the first fertilization time for soil nitrogen application and corn foliage nitrogen application is the corn three-leaf stage.

[0021] Preferably, the soil nitrogen application is performed 2 to 5 times, with a time interval of 4 to 6 days between each application; the foliar nitrogen application is performed 2 to 4 times, with a time interval of 14 to 16 days between each application.

[0022] The present invention provides an application of the method described in the above technical solution in at least one of the following 1) to 3),

[0023] 1) Improve the stress resistance of corn;

[0024] 2) Promote corn growth under salt stress conditions;

[0025] 3) Improve the nitrogen absorption rate of corn under salt stress.

[0026] Preferably, promoting corn growth includes increasing at least one of fresh weight, dry weight, plant height, stem diameter and chlorophyll content of corn.

[0027] Preferably, the improving stress resistance of corn comprises improving the antioxidant enzyme activity of corn under salt stress and reducing at least one of malondialdehyde and hydrogen peroxide content; the antioxidant enzyme comprises superoxide dismutase and / or peroxidase.

[0028] Beneficial effects of the present invention: The present invention provides a method for promoting corn growth by complementary root-leaf nitrogen application under salt stress conditions. Under salt stress conditions, the corn root system is hindered from absorbing nutrients. Therefore, in order to promote the absorption of fertilizers by corn, a method combining soil nitrogen application and foliar nitrogen application is adopted at an appropriate concentration. By applying foliar nitrogen fertilizer, nutrients are directly introduced into the mesophyll cells from the leaf stomata or penetrate into the cuticle and cellulose wall of the leaf epidermis through free diffusion, thereby allowing nutrients to enter the corn body from the leaves and directly participate in the metabolism of corn and the synthesis of organic matter, thereby solving the problem of insufficient nutrient absorption by the corn root system under salt stress conditions. The method of complementary soil and foliar nitrogen application provided by the present invention sets appropriate soil nitrogen application amounts and foliar nitrogen application amounts, and uses foliar nitrogen fertilizer to supplement the insufficient nitrogen fertilizer absorption by the corn root system, thereby improving corn nitrogen absorption, improving corn stress resistance, and promoting corn growth. DETAILED DESCRIPTION

[0029] The present invention provides a method for promoting corn growth by complementary nitrogen fertilization with roots and leaves under salt stress conditions, comprising the following steps:

[0030] Planting corn in saline soils with soil and foliar nitrogen applications;

[0031] The amount of soil nitrogen application is the soil nitrogen application threshold, and the amount of foliar nitrogen application is the foliar nitrogen application threshold;

[0032] The soil nitrogen application threshold is the minimum nitrogen application rate at which the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted no longer significantly increase, and the oxidation marker index no longer significantly decreases;

[0033] The foliar nitrogen application threshold is the minimum foliar nitrogen application rate when the soil nitrogen application threshold is used as the application rate of soil nitrogen fertilizer in the soil where corn is to be planted, so that the growth index, nutrient absorption index, and antioxidant enzyme index of the corn no longer increase significantly and the oxidation marker index no longer decreases significantly.

[0034] As an optional embodiment, the growth indicators of the present invention include fresh weight and dry weight; the nutrient absorption indicators include total nitrogen content; the antioxidant enzyme indicators include superoxide dismutase; and the oxidation markers include malondialdehyde and hydrogen peroxide. The method for determining the soil nitrogen application threshold and the foliar nitrogen application threshold provided by the present invention is simple and efficient, and can accurately determine the optimal nitrogen fertilizer application rate in combination with the specific properties of the soil, thereby improving the utilization rate of nitrogen fertilizer, maximizing the utilization rate of nitrogen fertilizer, and reducing the residual nitrogen in the soil, thereby reducing production costs and achieving environmental protection. The present invention uses growth indicators as macroscopic indicators for evaluating the soil nitrogen application threshold and the foliar nitrogen application threshold of corn, and uses nutrient absorption indicators, antioxidant enzyme indicators and oxidation markers as microscopic indicators for evaluating the soil nitrogen application threshold and the foliar nitrogen application threshold. The present invention uses a method combining macroscopic indicators and microscopic indicators to improve the accuracy of determining the soil nitrogen application threshold and the foliar nitrogen application threshold.

[0035] The present invention uses the soil nitrogen application threshold as the soil nitrogen application amount and the foliar nitrogen application threshold as the foliar nitrogen application, thereby realizing foliar nitrogen fertilizer supplementary fertilization and further supplementing the nutrient absorption of corn under salt stress.

[0036] As an optional embodiment, the present invention does not specifically limit the salt content of the salinized soil; salinized soils of any salt content can be applied to the fertilization scheme of the present invention to improve the salt tolerance of corn. In a specific embodiment of the present invention, the soil used for the test was moderately salinized soil with an EC of 6 ds / m.

[0037] As an optional embodiment, the method for determining the soil nitrogen application threshold of the present invention includes: in the planting year, performing soil testing on the soil to be planted with corn and calculating the nitrogen application amount, using the calculated soil nitrogen application amount as a benchmark of 100%, applying different amounts of nitrogen fertilizer to the soil, and measuring the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of the corn;

[0038] The nitrogen fertilizer application rate for the selected soil is determined based on the standard that the growth indicators of corn no longer increase significantly; the lowest nitrogen fertilizer application rate when the corn nutrient absorption indicators and antioxidant enzymes no longer increase significantly and the oxidation marker indicators no longer decrease significantly under the selected soil nitrogen fertilizer application rate is the soil nitrogen application threshold.

[0039] The present invention performs soil testing and formula nitrogen application calculation on the soil for planting corn, and uses the calculated soil nitrogen application amount as a benchmark of 100%. As an optional embodiment, the calculation of the soil testing and formula nitrogen application amount described in the present invention is performed in accordance with the "Technical Specifications for Soil Testing and Formula Fertilization" (NY / T-2911-2016), an agricultural industry standard of the People's Republic of China. In a specific embodiment of the present invention, the soil testing and formula nitrogen application amount is used as a benchmark of 100%, and the determined soil nitrogen application benchmark of 100% is 250 kg / ha in terms of pure nitrogen. As an optional embodiment, the different nitrogen fertilizer amounts described in the present invention are 10% to 130% of the soil nitrogen application benchmark.

[0040] When the base ratio of different nitrogen fertilizer amounts described in the present invention is selected from 10% to 130%, the selected base ratio needs to be dispersed in 10% to 130%. In a specific embodiment of the present invention, 10%, 40%, 70%, 100% and 130% of the base ratio of soil nitrogen application are selected when determining the soil nitrogen application threshold value, and other base ratios can also be used. The present invention needs to set at least 5 base ratios of fertilizer application amounts to obtain trend curves of corn growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index as the fertilizer application amount changes. The trend curve includes valley values, peak values ​​and inflection point values, from which the soil nitrogen application amount at which the corn growth index, nutrient absorption index, antioxidant enzyme index no longer significantly increases and the oxidation marker index no longer significantly decreases is selected as the soil nitrogen application threshold value. When the present invention no longer significantly increases or no longer significantly decreases, the growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index of adjacent concentrations of corn are subjected to difference significance analysis, and the significance analysis is based on a T-test P value less than 0.05 as the standard, the same below.

[0041] To ensure the accuracy of the soil nitrogen application threshold data, at least four parallel experiments were conducted at different nitrogen fertilizer concentration gradients, and at least three biological replicates were performed when measuring corn data indicators. The soil nitrogen application threshold of the present invention is related to the nitrogen content of the soil itself. Therefore, the soil nitrogen application threshold needs to be determined each time nitrogen fertilizer is applied using the technical solution of the present invention.

[0042] After determining the soil nitrogen application threshold, the present invention determines the foliar nitrogen fertilizer application rate. As an optional embodiment, the method for determining the foliar nitrogen application threshold of the present invention includes: in the planting year, in the soil to be planted with corn, using the soil nitrogen application threshold as the soil nitrogen fertilizer application rate, and determining the foliar nitrogen fertilizer application rate based on 0.25% to 0.26% of the nitrogen application rate of the calculated soil test formula; using the determined foliar nitrogen fertilizer application rate as a benchmark of 100%, simultaneously applying different foliar nitrogen fertilizer amounts to the corn, and measuring the corn's growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index;

[0043] The selected foliar nitrogen application rate is determined based on the criterion that corn growth indicators no longer significantly improve. The lowest foliar nitrogen application rate at which corn nutrient absorption indicators and antioxidant enzymes no longer significantly increase, and oxidation marker indicators no longer significantly decrease, under the selected foliar nitrogen application rate is the foliar nitrogen application threshold. The foliar nitrogen fertilizer application rate benchmark (100%) of the present invention is 0.25% to 0.26% of the soil nitrogen application rate calculated using the soil testing and formulation method, more preferably 0.253%. In a specific embodiment of the present invention, the soil nitrogen fertilizer application rate is determined using the "Technical Specification for Soil Testing and Formulated Fertilization" (NY / T-2911-2016): 250 kg / ha of pure nitrogen, with the foliar nitrogen application rate accounting for 0.253%, resulting in a foliar nitrogen application rate of 632.5 g / ha. Therefore, the foliar nitrogen application rate benchmark (100%) is determined to be 632.5 g / ha.

[0044] As an optional embodiment, after obtaining the foliar nitrogen fertilizer application rate benchmark of 100%, the present invention applies different foliar nitrogen fertilizer amounts to the soil to be planted with corn. The different foliar nitrogen fertilizer amounts are 70% to 190% of the foliar nitrogen fertilizer application rate benchmark. The foliar nitrogen fertilizer amounts selected by the present invention need to be dispersed within 70% to 190% of the benchmark. In a specific embodiment of the present invention, when determining the soil nitrogen application rate threshold, 70%, 100%, 130%, 160% and 190% of the foliar nitrogen fertilizer application rate benchmark are selected, and other benchmark proportions can also be used. The present invention needs to set at least 5 fertilizer application rates of the benchmark proportions to obtain a trend curve of corn growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index as the fertilizer application rate changes. The trend curve includes a valley value, a peak value and an inflection point value. The foliar nitrogen application rate at which the corn growth index, nutrient absorption index, antioxidant enzyme index no longer significantly improve and the oxidation marker index no longer significantly decreases is selected to determine the foliar nitrogen application rate threshold.

[0045] In a specific embodiment of the present invention, different nitrogen fertilizer amounts are set as 70%, 100%, 130%, 160% and 190% of the benchmark, the nitrogen absorption rate of corn is measured, and the foliar nitrogen fertilizer application concentration with a high nitrogen absorption rate of corn is selected. Taking into account that saline-alkali stress will lead to a reduction in nitrogen absorption by the corn root system, a gradient of more than 100% foliar nitrogen fertilizer is set. The foliar nitrogen application threshold value of the present invention is related to the nitrogen content of the soil itself. Therefore, it is necessary to measure the foliar nitrogen application threshold value each time fertilization is performed using the technical solution of the present invention. By foliar application of nitrogen fertilizer, nutrients are directly entered into the mesophyll cells through the stomata of the leaves or penetrate into the cuticle and cellulose wall of the leaf epidermis through free diffusion, so that nutrients can enter the body from the leaves and directly participate in the metabolism of crops and the synthesis process of organic matter, thereby solving the problem of insufficient nutrient absorption by the corn root system under salt stress conditions.

[0046] As an optional embodiment, the present invention has no particular limitation on the specific variety of corn, and conventional crops can be applied to the fertilization scheme of the present invention. In a specific embodiment of the present invention, the effect of the fertilization scheme is verified by taking "Zhengdan 958" corn as an example.

[0047] As an optional embodiment, the nitrogen fertilizer for foliar nitrogen application of the present invention includes liquid nitrogen fertilizer. The present invention has no special limitation on the source of the liquid nitrogen fertilizer, and conventional products can be used.

[0048] As an optional embodiment, the nitrogen fertilizer for soil nitrogen application described herein includes ammonium nitrogen fertilizer, nitrate nitrogen fertilizer, and amide nitrogen fertilizer. The ammonium nitrogen fertilizer includes one or more of ammonium sulfate, ammonium chloride, and ammonium bicarbonate; the nitrate nitrogen fertilizer includes potassium nitrate and / or calcium nitrate; and the amide nitrogen fertilizer includes urea. The present invention does not particularly limit the source of the nitrogen fertilizer; conventional products can be used.

[0049] As an optional embodiment, the first time of soil nitrogen application and corn foliar nitrogen application according to the present invention is the three-leaf stage of corn. As an optional embodiment, the number of soil nitrogen applications according to the present invention is 2 to 5 times, more preferably 4 times; the time interval between each two soil nitrogen applications is 4 to 6 days, more preferably 5 days; the amount of soil nitrogen applied each time according to the present invention is the soil nitrogen application threshold. The number of foliar nitrogen applications according to the present invention is 2 to 4 times, more preferably 3 times; the time interval between each two applications is 14 to 16 days, more preferably 15 days. The amount of foliar nitrogen applied each time according to the present invention is the foliar nitrogen application threshold. In a specific embodiment of the present invention, the first fertilization is performed when the third leaf grows 10 to 15 days after corn sowing.

[0050] Under salt stress conditions, the nutrient absorption of corn roots is hindered, resulting in insufficient nutrient absorption by the corn. The present invention solves the problem of insufficient nitrogen fertilizer absorption by the corn roots by simultaneously applying soil nitrogen fertilization and foliar nitrogen fertilization, utilizing foliar nitrogen fertilizer absorption to improve nitrogen absorption of corn, thereby improving corn stress resistance and promoting corn growth.

[0051] The present invention provides an application of the fertilization method described in the above technical solution in at least one of the following 1) to 3),

[0052] 1) Improve the stress resistance of corn;

[0053] 2) Promote corn growth under salt stress conditions;

[0054] 3) Improve the nitrogen absorption rate of corn under salt stress.

[0055] As an optional embodiment, the present invention promotes corn growth by increasing at least one of fresh weight, dry weight, plant height, stem diameter, and chlorophyll content. Example results demonstrate that simultaneous application of foliar nitrogen fertilizer and soil nitrogen fertilizer can increase the fresh weight, dry weight, plant height, stem diameter, and chlorophyll content of corn seedlings.

[0056] As an optional embodiment, the present invention's method for improving corn stress resistance includes increasing antioxidant enzyme activity and reducing at least one of malondialdehyde and hydrogen peroxide content in corn under salt stress; the antioxidant enzymes described herein include superoxide dismutase and / or peroxidase. The results of the examples demonstrate that simultaneous application of foliar and soil nitrogen fertilizers can increase peroxidase and superoxide dismutase activity in corn seedlings and reduce malondialdehyde and hydrogen peroxide content.

[0057] As an optional embodiment, the present invention's method of increasing the nitrogen absorption rate of corn under salt stress includes increasing the total nitrogen content in the aboveground part and / or the total nitrogen content in the underground part of the corn. The results of the examples demonstrate that simultaneous application of foliar nitrogen fertilizer and soil nitrogen fertilizer can increase the nitrogen content in both the aboveground and underground parts of corn seedlings.

[0058] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] The test materials and test methods used in the following examples are:

[0060] 1. Test materials

[0061] Corn, an important global food and feed crop, is particularly sensitive to salt stress during its seedling stage. Salt-induced conditions can easily lead to blocked nitrogen absorption, leaf yellowing, biomass reduction, and reduced stress resistance, directly impacting later yield. Therefore, corn was selected as the research subject.

[0062] The corn seeds used were “Zhengdan 958”, which were obtained from a seed dealer in Beijing, China.

[0063] The soil nitrogen fertilization treatment used urea (Kunningwang brand) with a nitrogen content of ≥46.0%. The foliar nitrogen fertilization treatment used liquid nitrogen fertilizer 422-0-0 (422 g / L or more) purchased from Shandong Cangyuan Biotechnology Co., Ltd. Both urea and foliar liquid nitrogen fertilizers are commonly used in farmers' fields.

[0064] 2. Determination method

[0065] Before collecting corn samples, the plant height and stem diameter of corn were measured using a ruler and vernier caliper.

[0066] Chlorophyll content and stomatal exchange were measured on the third fully expanded leaf of the maize top using a portable SPAD meter (Zhejiang Top Yunnong Technology Co., Ltd.) and a portable stomatal conductance meter LI-600 photosynthesis system (Li-COR Biosciences, Lincoln, Nebraska, USA).

[0067] Seedlings were randomly collected and washed with deionized water, their fresh weight was determined using an electronic balance, and their dry weight was measured after drying in an oven at 70 °C for 48 h.

[0068] The total nitrogen content in corn leaves was determined using sulfuric acid-hydrogen peroxide digestion and a Kjeldahl nitrogen analyzer (Alva fully automatic Kjeldahl nitrogen analyzer KN520) (Gmitrowicz-Iwan Joanna, Ligęza Sławomir, Pranagal Jacek, SmalHalina, Wójcikowska-Kapusta Anna. Improving acidic sandy soil properties for plant growth with dam reservoir sediments in the face of soaring fertiliser prices[J]. Soil&Tillage Research, 2023, 234).

[0069] A certain amount of leaf tissue was weighed, added to 1 ml of the extract, and homogenized on ice. The mixture was centrifuged for 10 minutes (8000 g at 4°C). The supernatant was collected and placed on ice for analysis. The supernatant was used to measure peroxidase (POD), superoxide dismutase (SOD), malondialdehyde (MDA), and hydrogen peroxide (H2O2) using kits (Nanjing Mofan Biotechnology Co., Ltd.) and a full-wavelength microplate reader (SpectraMax 190, Molecular Devices, USA).

[0070] When determining the nitrogen application threshold, the dry weight and fresh weight of plant growth indicators were used as evaluation criteria. The candidate fertilization concentration at which no significant increase in growth was determined. The total nitrogen content, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide levels of the plants at these candidate fertilization concentrations were then compared. The lowest fertilization concentration at which no significant increase in total nitrogen content and superoxide dismutase activity, and no significant decrease in hydrogen peroxide and malondialdehyde levels, was deemed the optimal threshold.

[0071] Soil testing and formula fertilization are carried out in accordance with the Agricultural Industry Standard of the People's Republic of China "Technical Specifications for Soil Testing and Formula Fertilization" (NY / T-2911-2016).

[0072] Example 1 Soil nitrogen fertilizer-urea

[0073] 1. Overview of potting soil

[0074] The soil type was sandy loam, collected from the surface soil (0–20 cm) of farmland in Beijing. The soil pH was 7.79, the EC was 1.55 mS / cm, the organic matter content was 14.10 g / kg, the cation exchange capacity was 10.46 g / kg, the total nitrogen content was 0.82 g / kg, the available phosphorus content was 14.69 g / kg, and the available potassium content was 175.82 g / kg. Prior to the potting experiment, the collected soil was air-dried and sieved to 2 mm (referred to as the sieved soil).

[0075] 2. The corn pot experiment was conducted using pots 22 cm high and 20 cm in diameter. Each pot was filled with an equal weight of sieved soil and seeded with corn seeds, with six seeds per pot. The seedlings were thinned to four plants per pot, ensuring uniform growth, and fertilized.

[0076] After that, it is divided into the following 6 processes:

[0077] (1) CK: no fertilizer;

[0078] (2) SD-10: Fertilizer application rate is 10% of the soil urea base;

[0079] (3) SD-40: Fertilizer application rate is 40% of the soil urea base;

[0080] (4) SD-70: Fertilizer application rate is 70% of the soil urea base;

[0081] (5) SD-100: The fertilizer application rate is 100% of the soil urea base;

[0082] (6) SD-130: The fertilizer application rate is 130% of the soil urea base.

[0083] Among them, the soil urea benchmark is determined as follows: the nitrogen fertilizer application rate of the test soil is calculated according to the soil testing and formula fertilization method, specifically the pure nitrogen application rate per hectare is 250 kg, and the nitrogen application rate required during the jointing stage of corn is 20% of the entire period. Therefore, a total of 50 kg of nitrogen fertilizer is required per hectare during the jointing stage; and the nitrogen content of urea is 46%. Therefore, if urea is used as a nitrogen fertilizer, a total of 108.7 kg of urea is required per hectare. Per hectare, with a row spacing of 60 cm and a plant spacing of 20 cm, 83,333 corn plants are planted. The urea content applied to each corn plant during the jointing stage is 1.304 g, and a total of 5.216 g of urea is applied to the four plants. The nitrogen fertilizer is applied in four times, so a total of 1.304 g of urea is applied to the four corn plants each time, and 1.304 g of urea is used as the soil urea benchmark. Therefore, the urea application rates for each of the four corn plants were: 0.1304 g for SD-10, 0.5216 g for SD-40, 0.9128 g for SD-70, 1.304 g for SD-100, and 1.6952 g for SD-130. The specific fertilizer application rates for the different treatments are shown in Table 1.

[0084] All experimental treatments were replicated four times. Nitrogen fertilizer was applied to the soil in each pot by dissolving the required urea and sodium chloride in deionized water (0.6% sodium chloride) and then applying it to the soil. The saturated electrical conductivity of the soil after application was 6 dS / m. Soil moisture was maintained at 50%–60% of field capacity until the end of the experiment.

[0085] The experiment lasted for 40 days. The first fertilization was applied 15 days after sowing, at the three-leaf stage. Fertilization was applied every 5 days, with the fourth fertilization applied 30 days after sowing. The corn seedlings were harvested on the 40th day after sowing. The fertilizer application rates are shown in Table 1. Growth and physiological indicators of the harvested corn seedlings were measured.

[0086] Table 1 Soil nitrogen fertilizer application plan (urea amount per pot)

[0087]

[0088] 3. The results are as follows:

[0089] (1) Effects of different soil nitrogen application rates on the growth and photosynthetic performance of corn seedlings

[0090] The effects of different soil nitrogen application rates on the fresh weight, dry weight, plant height, and stem diameter of maize seedlings were significantly different, as shown in Table 2. Compared with the control (CK), fresh weight was significantly increased in the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments. When the soil nitrogen application rate reached SD-70, SD-100, and SD-130, the fresh and dry weights of maize no longer increased significantly with increasing fertilizer application rates. There were no significant differences in plant height among the different fertilizer application rate treatments. When the soil nitrogen application rate reached SD-40, maize stem diameter no longer increased significantly with increasing fertilizer application rates. There were no significant differences in chlorophyll content among the treatments. When the soil nitrogen application rate reached SD-70, the stomatal conductance of maize no longer increased significantly with increasing nitrogen application rates.

[0091] Table 2 Effects of different soil nitrogen fertilizer application rates on the growth and photosynthetic performance of corn seedlings

[0092]

[0093] (2) Effects of different soil nitrogen application rates on total nitrogen, antioxidant enzymes, and oxidative markers in the aboveground parts of maize seedlings

[0094] Different soil nitrogen application rates significantly affected aboveground total nitrogen, antioxidant enzymes, and oxidative markers in maize seedlings, as shown in Table 3. Compared with the CK, aboveground total nitrogen, superoxide dismutase (SOD) activity, and peroxidase activity were significantly increased in the SD-40, SD-70, SD-100, and SD-130 treatments. Compared with the CK, aboveground malondialdehyde (MDA) content was significantly reduced in the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments. Compared with the CK, aboveground hydrogen peroxide content was significantly reduced in the SD-70, SD-100, and SD-130 treatments. When the soil nitrogen application rate reached SD-40, aboveground total nitrogen content no longer increased significantly. Superoxide dismutase activity peaked at the SD-70 and SD-100 application rates and then decreased. Peroxidase activity no longer significantly increased at the SD-70 application rate. With the increase of fertilizer application rate, the content of malondialdehyde and hydrogen peroxide showed a trend of first decreasing and then increasing. When the fertilizer application rate was SD-70, the content of malondialdehyde and hydrogen peroxide, two markers of oxidative damage, was the lowest.

[0095] Table 3 Effects of different soil nitrogen application rates on total nitrogen, antioxidant enzymes and oxidation markers in the aboveground parts of maize seedlings

[0096]

[0097] (3) Effects of different soil nitrogen application rates on total nitrogen, antioxidant enzymes, and oxidative markers in the underground part of maize seedlings

[0098] Different soil nitrogen application rates also significantly affected total nitrogen, antioxidant enzyme activity, and oxidative marker content in the underground parts of maize seedlings. As shown in Table 4, compared with the CK, the total nitrogen content in the underground parts of the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments did not increase significantly. Compared with the CK, the superoxide dismutase activity of the SD-40 and SD-70 treatments was significantly increased. Compared with the CK, the peroxidase content in the underground parts of the SD-40 and SD-70 treatments was significantly increased. Compared with the CK, the malondialdehyde content in the SD-10 and SD-40 treatments was significantly reduced. Compared with the CK, the hydrogen peroxide content in the SD-70 treatment was significantly reduced. With increasing fertilizer application, total nitrogen and superoxide dismutase activity no longer increased significantly with SD-70. At SD-100, peroxidase activity no longer increased with increasing fertilizer application. Both malondialdehyde and hydrogen peroxide content were lowest at SD-70. According to Tables 2 to 4, salt stress will limit the absorption of nitrogen fertilizer by corn roots. With the increase of fertilizer application, the absorption of nitrogen fertilizer by corn roots will reach a certain threshold, and the nitrogen absorption, antioxidant properties and growth indicators of corn will no longer increase significantly.

[0099] Table 4 Effects of different soil nitrogen application rates on total nitrogen, antioxidant enzymes and oxidation markers in the underground part of maize seedlings

[0100]

[0101] In summary, Table 2 shows that with increasing nitrogen fertilizer concentrations, maize fresh weight and dry weight no longer significantly increased at soil nitrogen fertilizer concentrations of SD-70, SD-100, and SD-130. Therefore, SD-70, SD-100, and SD-130 were selected as candidate soil nitrogen fertilizer concentrations. Furthermore, based on the test results of aboveground total nitrogen, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide indices for maize (Table 3) and belowground total nitrogen, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide indices for maize (Table 4), a comprehensive consideration of aboveground and belowground indices determined that the SD-70 nitrogen fertilizer concentration was the threshold for maize total nitrogen and superoxide dismutase activity, and for malondialdehyde and hydrogen peroxide.

[0102] Example 2 Foliar nitrogen fertilizer + soil nitrogen fertilizer

[0103] The optimal SD-70 dosage of 0.9128 g / pot, determined in Example 1, was used as the soil nitrogen application rate, followed by foliar nitrogen fertilization. Foliar nitrogen fertilization was performed between 7 and 8 a.m. daily. To minimize the impact of foliar spraying on the soil environment, the potting soil and the main stem of the corn were covered with paper, and liquid nitrogen fertilizer was sprayed on the corn.

[0104] 1. Potting soil overview: Same as step 1 in Example 1.

[0105] 2. The corn pot experiment was conducted using pots 22 cm high and 20 cm in diameter. Each pot was filled with an equal weight of sieved soil and seeded with corn seeds, with six seeds per pot. The seedlings were thinned to four plants per pot, ensuring uniform growth, and fertilized.

[0106] Six treatments were designed: FS-0, FS-70, FS-100, FS-130, FS-160, and FS-190. The 100% foliar nitrogen base (FS-100) was determined by calculating the foliar nitrogen rate based on the soil nitrogen application rate obtained using the soil testing and fertilization formula method. Specifically, the pure nitrogen application rate was 250 kg per hectare, and the foliar nitrogen application rate was 0.253% of the soil nitrogen application rate, or 632.5 g of pure nitrogen. The nitrogen content of the applied liquid urea was 422 g / L, resulting in a foliar nitrogen application rate of 1.5 L / ha. With 83,333 maize plants planted per hectare, with a row spacing of 60 cm and a plant spacing of 20 cm, the foliar nitrogen application rate was 0.018 mL per plant. For a pot with four maize plants, the application rate was 0.072 mL, which was diluted 100-fold to 7.2 mL. This was recorded as the foliar nitrogen base.

[0107] The fertilizer application rates for different treatments are as follows:

[0108] FS-0: no fertilizer;

[0109] FS-70: Foliar nitrogen fertilizer application rate is 70% of the foliar nitrogen fertilizer standard (i.e. 7.2mL);

[0110] FS-100: Foliar nitrogen fertilizer application rate is 100% of the foliar nitrogen fertilizer standard (i.e. 7.2mL);

[0111] FS-130: Foliar nitrogen fertilizer application rate is 130% of the foliar nitrogen fertilizer standard (i.e. 7.2mL);

[0112] FS-160: Foliar nitrogen fertilizer application rate is 160% of the foliar nitrogen fertilizer standard (i.e. 7.2mL);

[0113] FS-190: Foliar nitrogen fertilizer application rate is 190% of the foliar nitrogen fertilizer standard (i.e. 7.2mL).

[0114] Soil nitrogen fertilizer: Apply once every 5 days at 0.9128 g / pot for a total of 4 applications. Foliar nitrogen fertilizer: Apply once every 15 days for a total of 2 applications. For the second and third fertilizations, only soil nitrogen fertilizer is applied. For the first and fourth fertilizations, both soil and foliar nitrogen fertilizers are applied. See Table 5 for details.

[0115] All experimental treatments were replicated four times. Nitrogen fertilizer was applied to the soil in each pot by dissolving the specified amount of urea and sodium chloride in deionized water (0.6%). The saturated electrical conductivity of the soil after urea and sodium chloride application was 6 dS / m. Soil moisture was maintained at 50%–60% of field capacity until the end of the experiment.

[0116] The experiment lasted for 40 days. The first foliar nitrogen fertilizer application was carried out on the 15th day after sowing, when three leaves appeared. The second foliar nitrogen fertilizer application was carried out on the 30th day after sowing. The corn seedlings were harvested on the 40th day after sowing for measurement.

[0117] Table 5 Fertilization plan

[0118]

[0119] (4) Effects of different foliar nitrogen fertilizer application rates on the growth and photosynthetic performance of corn seedlings

[0120] The effects of different foliar nitrogen fertilizer application rates on the fresh weight, dry weight, plant height, and stem diameter of maize seedlings were significantly different, as shown in Table 6.

[0121] Table 6 Effects of different foliar nitrogen fertilizer application rates on the growth and photosynthetic performance of corn seedlings

[0122]

[0123] (5) Effects of different foliar nitrogen fertilizer application rates on total nitrogen, antioxidant enzymes, and oxidative markers in the aboveground parts of maize seedlings

[0124] The effects of different foliar nitrogen fertilizer application rates on total nitrogen content, superoxide dismutase and peroxidase activities, and malondialdehyde and hydrogen peroxide contents in the aboveground parts of corn seedlings were significantly different. As shown in Table 7, compared with FS-0, the aboveground total nitrogen content and peroxidase activity of FS-160 and FS-190 significantly increased. Compared with FS-0, the aboveground superoxide dismutase activity of FS-100, FS-130, FS-160, and FS-190 significantly increased. When the foliar nitrogen fertilizer application rate was FS-160, the aboveground total nitrogen content, superoxide dismutase activity, and peroxidase activity no longer increased significantly with increasing foliar nitrogen fertilizer application rates. The aboveground malondialdehyde and hydrogen peroxide contents were lowest when FS-160 was used.

[0125] Table 7 Effects of different foliar nitrogen fertilizer application rates on total nitrogen, antioxidant enzymes and oxidation markers in the aboveground parts of maize seedlings

[0126]

[0127] (5) Effects of different foliar nitrogen fertilizer application rates on total nitrogen, antioxidant enzymes, and oxidative markers in the underground part of corn seedlings

[0128] The effects of different foliar nitrogen fertilizer rates on total nitrogen content, superoxide dismutase (SOD) and peroxidase (POD) activities, and malondialdehyde (MDA) and hydrogen peroxide (HPO) contents in the underground part of maize seedlings were significantly different. As shown in Table 8, compared with FS-0, the total nitrogen content of FS-190 in the underground part was significantly increased. Compared with FS-0, the SOD activity of FS-100, FS-130, FS-160, and FS-190 was significantly increased. Compared with FS-0, the POD activity of FS-70, FS-100, FS-130, FS-160, and FS-190 in the underground part was significantly increased. With increasing foliar nitrogen fertilizer rates, the total nitrogen content and SOD activity in the underground part gradually increased. When the foliar nitrogen fertilizer rate was FS-160, the peroxidase activity in the underground part no longer increased significantly with increasing fertilizer application, and the MDA and HPO contents in the underground part were the lowest.

[0129] Table 8 Effects of different foliar nitrogen fertilizer application rates on total nitrogen, antioxidant enzymes and oxidation markers in the underground part of corn seedlings

[0130]

[0131] Table 6 shows that with increasing foliar nitrogen fertilizer concentrations, corn fresh weight and dry weight no longer significantly increased at soil and foliar nitrogen fertilizer concentrations of FS-130, FS-160, and FS-190. Therefore, FS-130, FS-160, and FS-190 were selected as candidate foliar nitrogen fertilizer concentrations. Furthermore, based on the test results of aboveground total nitrogen, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide indices (Table 7) and belowground total nitrogen, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide indices (Table 8), and taking into account the aboveground and belowground indices, the FS-160 concentration was determined to be the threshold for foliar nitrogen application, at which total nitrogen and superoxide dismutase activity no longer significantly increased, and malondialdehyde and hydrogen peroxide no longer significantly decreased.

[0132] According to Tables 6 to 8, when the root system is limited in nutrient absorption, foliar application of nitrogen fertilizer can alleviate the problem of insufficient nitrogen fertilizer absorption by the corn root system and quickly supplement the nitrogen demand of corn during the seedling stage.

[0133] In summary, the nitrogen fertilizer application method provided by the present invention can accurately input nitrogen fertilizer, reduce nitrogen fertilizer residue in the soil, and significantly improve corn nitrogen absorption and antioxidant capacity, further ensuring the growth of corn in the seedling stage.

[0134] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for promoting corn growth by complementary nitrogen fertilization with roots and leaves under salt stress conditions, characterized in that: Here are the steps: Plant corn in saline soils and apply soil and foliar nitrogen fertilizers; The amount of soil nitrogen application is the soil nitrogen application threshold, and the amount of foliar nitrogen application is the foliar nitrogen application threshold; The soil nitrogen application threshold is the minimum nitrogen application rate when the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted with corn no longer significantly increase and the oxidation marker index no longer significantly decreases; the method for determining the soil nitrogen application threshold is: in the planting year, the soil to be planted with corn is tested and the nitrogen application rate is calculated, and the calculated soil nitrogen application rate is used as a benchmark of 100%, different nitrogen fertilizer amounts are applied to the soil, and the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of corn are measured; the soil nitrogen application rate to be selected is determined based on the standard that the growth index of corn no longer significantly increases; the minimum nitrogen application rate when the nutrient absorption index and antioxidant enzyme of corn no longer significantly increase and the oxidation marker index no longer significantly decrease under the soil nitrogen application rate to be selected is the soil nitrogen application threshold; The foliar nitrogen application threshold is the minimum foliar nitrogen application rate when the soil nitrogen application threshold is used as the application rate of soil nitrogen fertilizer in the soil to be planted with corn, so that the growth index, nutrient absorption index, and antioxidant enzyme index of the corn no longer increase significantly and the oxidation marker index no longer decreases significantly; the method for determining the foliar nitrogen application threshold is as follows: in the planting year, in the soil to be planted with corn, the soil nitrogen application threshold is used as the application rate of soil nitrogen fertilizer; the foliar nitrogen application rate is determined based on 0.25% to 0.26% of the nitrogen application rate of the calculated soil test formula, and the determined foliar nitrogen application rate is used as the benchmark 100%; different foliar nitrogen fertilizer amounts are applied to the corn at the same time, and the growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index of the corn are measured; the selected foliar nitrogen application rate is determined based on the standard that the growth index of the corn no longer increases significantly; the minimum foliar nitrogen application rate when the nutrient absorption index and antioxidant enzyme of the corn no longer increase significantly and the oxidation marker index no longer decreases significantly under the selected foliar nitrogen application rate is the foliar nitrogen application threshold; The growth index is fresh weight and dry weight; the nutrient absorption index is total nitrogen content; the antioxidant enzyme index is superoxide dismutase content; and the oxidation marker index is malondialdehyde content and hydrogen peroxide content.

2. The method according to claim 1, characterized in that The foliar nitrogen fertilizer includes liquid nitrogen fertilizer; the soil nitrogen fertilizer includes one or more of ammonium nitrogen fertilizer, nitrate nitrogen fertilizer and amide nitrogen fertilizer; the ammonium nitrogen fertilizer includes one or more of ammonium sulfate, ammonium chloride and ammonium bicarbonate; the nitrate nitrogen fertilizer includes potassium nitrate and / or calcium nitrate; and the amide nitrogen fertilizer includes urea.

3. The method according to claim 1, characterized in that The different nitrogen fertilizer amounts are 10% to 130% of the soil nitrogen application rate; The different foliar nitrogen fertilizer amounts are 70% to 190% of the foliar nitrogen fertilizer application standard.

4. The method according to claim 1, wherein The first time to apply soil nitrogen and foliar nitrogen is when the corn is in its three-leaf stage.

5. The method according to claim 1 or 4, characterized in that The number of soil nitrogen applications is 2 to 5 times, with a time interval of 4 to 6 days between each application; the number of foliar nitrogen applications is 2 to 4 times, with a time interval of 14 to 16 days between each application.

6. Use of the method according to any one of claims 1 to 5 in at least one of the following 1) to 3), 1) Improve the stress resistance of corn; 2) Promote corn growth under salt stress conditions; 3) Improve the nitrogen absorption rate of corn under salt stress.

7. The use according to claim 6, characterized in that Promoting corn growth includes increasing at least one of fresh weight, dry weight, plant height, stem diameter and chlorophyll content of corn.

8. The use according to claim 6, characterized in that The method for improving the stress resistance of corn comprises improving the antioxidant enzyme activity of corn under salt stress and reducing at least one of malondialdehyde and hydrogen peroxide content; the antioxidant enzyme comprises superoxide dismutase and / or peroxidase.

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