Method for promoting corn growth through root-leaf complementary nitrogen application under salt stress condition and application

Abstract

The invention belongs to the technical field of fertilization, and particularly relates to a method for promoting corn growth through root-leaf complementary nitrogen application under the salt stress condition and application. The invention provides a method for promoting corn growth by root-leaf complementary nitrogen application under a salt stress condition, corn is planted in saline soil, soil nitrogen application and leaf surface nitrogen application are performed, the soil nitrogen application amount is a soil nitrogen application amount threshold value, and the leaf surface nitrogen application amount is a leaf surface nitrogen application amount threshold value. As nutrient absorption of corn roots is blocked under the salt stress condition, nitrogen fertilizer is applied through soil and leaf surface complementation, and the nitrogen fertilizer is applied through leaf surfaces to supplement insufficient nitrogen fertilizer absorption of the corn roots, so that nitrogen absorption of the corn can be improved, stress resistance of the corn is improved, and growth of the corn is promoted.

Description

Technical Field

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

[0002] Salt stress is one of the important environmental factors restricting crop growth. In saline-alkali soil, high concentrations of salt ions (such as sodium ions and chloride ions) will cause an increase in soil osmotic pressure, inhibit the absorption of water and nutrients by plant roots, and at the same time trigger ion toxicity and oxidative stress, damaging the stability of cell membranes and seriously affecting plant growth and development.

[0003] Traditional nitrogen fertilizer application methods usually supplement nitrogen through soil basal application or irrigation topdressing. However, salt stress will cause an increase in soil osmotic pressure, making it difficult for plant roots to absorb water, leading to physiological drought, changing the permeability of root cell membranes, weakening metabolic activities, and significantly reducing the active absorption capacity of roots for nitrogen. In addition, the transpiration of plants weakens, reducing the transport capacity of xylem sap for nitrogen, resulting in a decrease in the distribution efficiency of nitrogen to the above-ground parts. Salt stress also induces the burst of reactive oxygen species (ROS), damages the chloroplast structure, reduces photosynthetic capacity, and reduces the energy supply for plants to convert nitrogen into biomolecules such as amino acids and proteins. In addition, unreasonable application of nitrogen fertilizer will also cause nitrogen residues in the soil, further deteriorating the saline-alkali soil environment.

[0004] Maize is one of the most important crops in the world, but its growth and yield are severely hindered by salt stress, posing a challenge to agricultural productivity. Nitrogen plays an important role in improving the stress resistance of maize plants. Although recent studies have tried to improve salt tolerance by modifying nitrogen fertilizer types (such as slow-release fertilizers and coated fertilizers), the cost is high, the operation is complex, and the core problem of the coordinated regulation of nitrogen absorption in saline-alkali soil and maize stress resistance has not been solved. Therefore, how to optimize the nitrogen supply method to simultaneously improve the nitrogen absorption efficiency, stress resistance, and growth rate of maize seedlings under salt stress has become a technical difficulty that urgently needs to be overcome in saline-alkali land agriculture. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and application for promoting maize growth by complementary nitrogen application between roots and leaves under salt stress conditions. The method of the present invention can promote nitrogen absorption in maize, improve the stress resistance of maize, and ultimately promote maize growth under salt stress conditions.

[0006] In order to solve the above technical problems, the present invention proposes the following technical solutions: The present invention provides a method for promoting maize growth by complementary nitrogen application between roots and leaves under salt stress conditions, including the following steps: Plant maize in saline-alkali soil, and apply nitrogen to the soil and foliar nitrogen application. The amount of nitrogen applied to the soil is the threshold value of the nitrogen application amount for the soil, and the amount of nitrogen applied by foliar spraying is the threshold value of the nitrogen application amount by foliar spraying; The threshold value of the nitrogen application amount for the soil is the lowest nitrogen application amount when the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted with corn no longer increase significantly and the oxidation marker index no longer decreases significantly; The threshold value of the nitrogen application amount by foliar spraying is the lowest nitrogen application amount by foliar spraying when, in the soil to be planted with corn, using the threshold value of the nitrogen application amount for the soil as the application amount of soil nitrogen fertilizer, the growth index, nutrient absorption index, and antioxidant enzyme index of corn no longer increase significantly and the oxidation marker index no longer decreases significantly.

[0007] 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. The amide nitrogen fertilizer includes urea.

[0008] 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; the oxidation marker index includes malondialdehyde and hydrogen peroxide.

[0009] Preferably, the method for determining the threshold value of the nitrogen application amount for the soil includes: in the planting year, calculating the soil nitrogen application amount by soil testing and formula fertilization for the soil to be planted with corn, taking the calculated soil nitrogen application amount as the 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 corn; Determining the candidate soil nitrogen application amount based on the criterion that the growth index of corn no longer increases significantly; the lowest nitrogen application amount when the nutrient absorption index and antioxidant enzyme of corn under the candidate soil nitrogen application amount no longer increase significantly and the oxidation marker index no longer decreases significantly is the threshold value of the nitrogen application amount for the soil; The method for determining the threshold value of the nitrogen application amount by foliar spraying includes: in the planting year, in the soil to be planted with corn, using the threshold value of the nitrogen application amount for the soil as the application amount of soil nitrogen fertilizer, determining the foliar nitrogen fertilizer application amount according to 0.25% - 0.26% of the calculated soil testing and formula fertilization nitrogen application amount, taking the determined foliar nitrogen fertilizer application amount as the benchmark of 100%, and at the same time applying different amounts of foliar nitrogen fertilizer to corn, and measuring the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of corn; Determining the candidate foliar nitrogen application amount based on the criterion that the growth index of corn no longer increases significantly; the lowest foliar nitrogen application amount when the nutrient absorption index and antioxidant enzyme of corn under the candidate foliar nitrogen application amount no longer increase significantly and the oxidation marker index no longer decreases significantly is the threshold value of the nitrogen application amount by foliar spraying.

[0010] Preferably, the different nitrogen fertilizer amounts are 10% - 130% of the soil nitrogen application amount benchmark; The different foliar nitrogen fertilizer amounts are 70% - 190% of the foliar nitrogen fertilizer application amount benchmark.

[0011] Preferably, the first fertilization time for soil nitrogen application and corn foliar nitrogen application is the three - leaf stage of corn.

[0012] Preferably, the number of times of soil nitrogen application is 2 - 5 times, and the time interval between every two times is 4 - 6 days; the number of times of foliar nitrogen application is 2 - 4 times, and the time interval between every two times is 14 - 16 days.

[0013] The present invention provides the application of the method described in the above technical solution in at least one of the following 1) - 3): 1) Improving the stress resistance of corn; 2) Promoting the growth of corn under salt stress conditions; 3) Improving the nitrogen absorption rate of corn under salt stress.

[0014] Preferably, promoting the growth of corn includes increasing at least one of the fresh weight, dry weight, plant height, stem diameter, and chlorophyll content of corn.

[0015] Preferably, improving the stress resistance of corn includes increasing at least one of the antioxidant enzyme activities of corn under salt stress and reducing the content of malondialdehyde and hydrogen peroxide; the antioxidant enzymes include superoxide dismutase and / or peroxidase.

[0016] The beneficial effects of the present invention: The present invention provides a method for promoting the growth of corn by complementary root - leaf nitrogen application under salt stress conditions. The nutrient absorption of corn roots is blocked under salt stress conditions. Therefore, in order to promote the absorption of fertilizers by corn, a method of combining soil nitrogen application and foliar nitrogen application is adopted at an appropriate concentration. By applying foliar nitrogen fertilizer, nutrients directly enter mesophyll cells through leaf surface stomata or penetrate into the cutin layer and cellulose wall of the leaf surface epidermis through free diffusion, so that the nutrients enter the corn body from the leaf part and directly participate in the metabolism and organic matter synthesis process of corn, solving the problem of insufficient nutrient absorption by corn roots under salt stress conditions. The method of complementary application of nitrogen fertilizer in soil and on the leaf surface 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 absorption of corn roots, thereby being able to improve the nitrogen absorption of corn, improve the stress resistance of corn, and promote the growth of corn. Detailed implementation mode

[0017] The present invention provides a method for promoting the growth of corn by complementary root - leaf nitrogen application under salt stress conditions, including the following steps: Plant corn in saline - alkali soil, and carry out soil nitrogen application and foliar nitrogen application; The amount of nitrogen applied to the soil is the threshold value of the nitrogen application amount to the soil, and the amount of nitrogen applied by foliar spraying is the threshold value of the nitrogen application amount by foliar spraying; The threshold value of the nitrogen application amount to the soil is the lowest nitrogen application amount when the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted with corn no longer increase significantly and the oxidation marker index no longer decreases significantly; The threshold value of the nitrogen application amount by foliar spraying is the lowest nitrogen application amount by foliar spraying when the growth index, nutrient absorption index, and antioxidant enzyme index of corn no longer increase significantly and the oxidation marker index no longer decreases significantly by using the threshold value of the nitrogen application amount to the soil as the application amount of soil nitrogen fertilizer in the soil to be planted with corn.

[0018] As an optional implementation manner, the growth index described in the present invention includes fresh weight and dry weight; the nutrient absorption index includes total nitrogen content; the antioxidant enzyme index includes superoxide dismutase; the oxidation markers include malondialdehyde and hydrogen peroxide. The method provided by the present invention for determining the threshold value of the nitrogen application amount to the soil and the threshold value of the nitrogen application amount by foliar spraying is simple and efficient, can accurately determine the optimal nitrogen fertilizer application amount in combination with the specific properties of the soil, can improve the utilization rate of nitrogen fertilizer, while maximizing the utilization rate of nitrogen fertilizer, reduce the nitrogen residue in the soil, and achieve the purpose of environmental protection while reducing production costs. The present invention uses the growth index as a macroscopic index for evaluating the threshold value of the nitrogen application amount to the soil and the threshold value of the nitrogen application amount by foliar spraying of corn, and uses the nutrient absorption index, antioxidant enzyme index, and oxidation markers as microscopic indexes for evaluating the threshold value of the nitrogen application amount to the soil and the threshold value of the nitrogen application amount by foliar spraying. The method of combining macroscopic indexes and microscopic indexes in the present invention improves the accuracy of determining the threshold value of the nitrogen application amount to the soil and the threshold value of the nitrogen application amount by foliar spraying.

[0019] The present invention uses the threshold value of the nitrogen application amount to the soil as the nitrogen application amount to the soil and the threshold value of the nitrogen application amount by foliar spraying as the nitrogen application by foliar spraying to realize supplementary fertilization by foliar spraying of nitrogen fertilizer, thereby supplementing the nutrient absorption of corn under salt stress.

[0020] As an optional implementation manner, the present invention does not have special limitations on the salt content of the salinized soil, and the fertilization scheme of the present invention can be applied to salinized soil with any salt content to improve the salt tolerance of corn. In a specific embodiment of the present invention, the soil during verification is moderately salinized soil with EC = 6 ds / m.

[0021] As an optional implementation manner, the method for determining the threshold value of the nitrogen application amount to the soil described in the present invention includes: in the year of planting, calculating the soil testing formula nitrogen application amount for the soil to be planted with corn, using the calculated nitrogen application amount to the soil as 100% of the benchmark, 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 corn; The nitrogen application rate for the soil to be selected is determined based on the criterion that the growth indicators of corn no longer increase significantly; the lowest nitrogen application rate when the nutrient absorption indicators and antioxidant enzymes of corn under the nitrogen application rate for the soil to be selected no longer increase significantly and the oxidation marker indicators no longer decrease significantly is the nitrogen application rate threshold for the soil.

[0022] The present invention calculates the soil nitrogen application rate for soil where corn is to be planted, and takes the calculated soil nitrogen application rate as the benchmark of 100%. As an alternative embodiment, the calculation of the soil nitrogen application rate of the present invention is carried out according to the Agricultural Industry Standard of the People's Republic of China "Technical Regulations for Soil Testing and Formula Fertilization" (NY / T - 2911 - 2016). In a specific embodiment of the present invention, with the soil nitrogen application rate as the benchmark of 100%, the determined soil nitrogen application rate benchmark of 100% is 250 kg / ha in terms of pure nitrogen. As an alternative embodiment, the different nitrogen application rates of the present invention are 10% - 130% of the soil nitrogen application rate benchmark.

[0023] When the benchmark proportion of the different nitrogen application rates of the present invention is selected within 10% - 130%, the selected benchmark proportion needs to be distributed dispersedly within 10% - 130%. In a specific embodiment of the present invention, when determining the soil nitrogen application rate threshold, 10%, 40%, 70%, 100% and 130% of the soil nitrogen application rate benchmark are selected, and other benchmark proportions can also be used. The present invention needs to set at least 5 fertilization amounts with benchmark proportions to obtain the trend curves of corn growth indicators, nutrient absorption indicators, antioxidant enzyme indicators and oxidation marker indicators with the change of fertilization amount. The trend curves include valley values, peak values and inflection point values, and the soil nitrogen application rate when the corn growth indicators, nutrient absorption indicators and antioxidant enzyme indicators no longer increase significantly and the oxidation marker indicators no longer decrease significantly is selected as the soil nitrogen application rate threshold. When the present invention mentions no longer increasing significantly or no longer decreasing significantly, a significance analysis of the growth indicators, nutrient absorption indicators, antioxidant enzyme indicators and oxidation marker indicators of corn at adjacent concentrations is carried out. The significance analysis is based on the criterion that the P value of the T - test is less than 0.05, and the same applies hereinafter.

[0024] To ensure the accuracy of the soil nitrogen application rate threshold data, at least 4 groups of parallel experiments are set under different nitrogen application concentration gradients, and at least 3 groups of biological replicates are set when measuring the data indicators of corn. The soil nitrogen application rate threshold of the present invention is related to the nitrogen element content of the soil itself. Therefore, it is necessary to measure the soil nitrogen application rate threshold every time the technical scheme of the present invention is used for nitrogen application.

[0025] After determining the threshold of soil nitrogen application rate, the present invention determines the foliar nitrogen application rate. As an alternative embodiment, the method for determining the threshold of foliar nitrogen application rate of the present invention includes: in the year of planting, in the soil of the corn to be planted, using the threshold of soil nitrogen application rate as the application rate of soil nitrogen fertilizer, and determining the foliar nitrogen application rate according to 0.25% - 0.26% of the calculated nitrogen application rate of soil testing and formulated fertilization; taking the determined foliar nitrogen application rate as the benchmark 100%, and simultaneously applying different amounts of foliar nitrogen fertilizer to the corn, and measuring the growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index of the corn; Determine the candidate foliar nitrogen application rate based on the criterion that the growth index of the corn no longer increases significantly; the lowest foliar nitrogen application rate when the nutrient absorption index and antioxidant enzyme of the corn under the candidate foliar nitrogen application rate no longer increase significantly and the oxidation marker index no longer decreases significantly is the threshold of foliar nitrogen application rate. The benchmark 100% of the foliar nitrogen application rate of the present invention is 0.25% - 0.26% of the soil nitrogen application rate calculated by the soil testing and formulated fertilization method, and more preferably 0.253%. In a specific embodiment of the present invention, using the "Technical Regulations for Soil Testing and Formulated Fertilization" (NY / T - 2911 - 2016), the determined application rate of soil nitrogen fertilizer: calculated as pure nitrogen is 250 kg / ha, and the proportion of foliar nitrogen application rate is 0.253%, then the foliar nitrogen application is 632.5 g / ha, that is, the determined benchmark 100% of the foliar nitrogen application rate is 632.5 g / ha.

[0026] As an alternative embodiment, after obtaining the benchmark 100% of the foliar nitrogen application rate, the present invention applies different amounts of foliar nitrogen fertilizer to the soil of the corn to be planted. The different amounts of foliar nitrogen fertilizer are 70% - 190% of the benchmark of the foliar nitrogen application rate. The selected foliar nitrogen fertilizer amounts of the present invention need to be distributed dispersedly among 70% - 190% of the benchmark. In a specific embodiment of the present invention, 70%, 100%, 130%, 160% and 190% of the benchmark of the foliar nitrogen application rate are selected when measuring the threshold of soil nitrogen application rate, and it can also be other benchmark ratios. The present invention needs to set at least 5 fertilization amounts with benchmark ratios to obtain the change trend curve of the growth index, nutrient absorption index, antioxidant enzyme index and oxidation marker index of the corn with the change of the fertilization amount. The change trend curve includes valley value, peak value and inflection point value, and select the foliar nitrogen application rate when the growth index, nutrient absorption index and antioxidant enzyme of the corn no longer increase significantly and the oxidation marker index no longer decreases significantly to determine the threshold of foliar nitrogen application rate.

[0027] In specific embodiments 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. Considering that saline-alkali stress will lead to a reduction in nitrogen absorption by corn roots, a gradient of more than 100% of foliar nitrogen application is set. The foliar nitrogen application threshold of the present invention is related to the nitrogen element content in the soil itself. Therefore, it is necessary to measure the foliar nitrogen application threshold every time the fertilization technology of the present invention is used. By applying nitrogen fertilizer to the leaves, nutrients can directly enter the mesophyll cells through the leaf stomata or penetrate into the cutin layer and cellulose wall of the leaf epidermis through free diffusion, enabling the nutrients to enter the body from the leaves and directly participate in the crop's metabolism and the synthesis process of organic matter, thus solving the problem of insufficient nutrient absorption by corn roots under salt stress conditions.

[0028] As an alternative embodiment, the present invention has no special limitation on the specific variety of the corn, and the fertilization scheme of the present invention can be applied to conventional crops. In specific embodiments of the present invention, the "Zhengdan 958" corn is taken as an example to verify the effect of the fertilization scheme.

[0029] As an alternative embodiment, the nitrogen fertilizer for foliar nitrogen application in 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.

[0030] As an alternative embodiment, the nitrogen fertilizers for soil nitrogen application in the present invention include ammonium nitrogen fertilizers, nitrate nitrogen fertilizers, and amide nitrogen fertilizers. The ammonium nitrogen fertilizers include one or more of ammonium sulfate, ammonium chloride, and ammonium bicarbonate. The nitrate nitrogen fertilizers include potassium nitrate and / or calcium nitrate. The amide nitrogen fertilizer includes urea. The present invention has no special limitation on the source of the nitrogen fertilizer, and conventional products can be used.

[0031] As an alternative embodiment, the first fertilization time for soil nitrogen application and foliar nitrogen application to corn in the present invention is the three-leaf stage of corn. As an alternative embodiment, the number of times of soil nitrogen application in the present invention is 2 to 5 times, more preferably 4 times; the time interval between every two soil nitrogen applications is 4 to 6 days, more preferably 5 days; the amount of soil nitrogen application each time in the present invention is the soil nitrogen application threshold. The number of times of foliar nitrogen application in the present invention is 2 to 4 times, more preferably 3 times; the time interval between every two times is 14 to 16 days, more preferably 15 days. The amount of foliar nitrogen application each time in the present invention is the foliar nitrogen application threshold. In specific embodiments of the present invention, the first fertilization is carried out when the third leaf grows 10 to 15 days after corn sowing.

[0032] Under salt stress conditions, the nutrient uptake of corn roots is hindered, and the nutrient uptake of corn is insufficient. The present invention solves the problem of insufficient nitrogen uptake by corn roots by simultaneously applying soil nitrogen fertilizer and foliar nitrogen fertilizer, thereby improving nitrogen uptake of corn, enhancing the stress resistance of corn, and promoting the growth of corn.

[0033] The present invention provides the application of the fertilization method described in the above technical solution in at least one of the following 1) to 3): 1) Enhancing the stress resistance of corn; 2) Promoting the growth of corn under salt stress conditions; 3) Increasing the nitrogen absorption rate of corn under salt stress.

[0034] As an alternative embodiment, the promotion of corn growth in the present invention includes increasing at least one of the fresh weight, dry weight, plant height, stem diameter, and chlorophyll content of corn. The results of the examples show that by simultaneously applying foliar nitrogen fertilizer and soil nitrogen fertilizer, the fresh weight, dry weight, plant height, stem diameter, and chlorophyll content of corn seedlings can be increased.

[0035] As an alternative embodiment, the enhancement of the stress resistance of corn in the present invention includes increasing the antioxidant enzyme activity of corn under salt stress and reducing at least one of the malondialdehyde and hydrogen peroxide contents; the antioxidant enzymes in the present invention include superoxide dismutase and / or peroxidase. The results of the examples show that by simultaneously applying foliar nitrogen fertilizer and soil nitrogen fertilizer, the peroxidase activity and superoxide dismutase activity of corn seedlings can be increased, and the malondialdehyde and hydrogen peroxide contents of corn seedlings can be reduced.

[0036] As an alternative embodiment, the increase in the nitrogen absorption rate of corn under salt stress in the present invention includes increasing the total nitrogen content in the above-ground part and / or the total nitrogen content in the underground part of corn. The results of the examples show that by simultaneously applying foliar nitrogen fertilizer and soil nitrogen fertilizer, the nitrogen content in the above-ground part and the underground part of corn seedlings can be increased.

[0037] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with examples, but they should not be construed as limiting the protection scope of the present invention.

[0038] The test materials and measurement methods applied in the following examples: 1. Test materials As an important global food and feed crop, corn is particularly sensitive to salt stress during its seedling stage. Salt stress conditions can easily lead to hindered nitrogen uptake, yellowing of leaves, decreased biomass, and weakened stress resistance, directly affecting the later yield. Therefore, corn is used as the research object.

[0039] Corn seeds of the variety "Zhengdan 958" were obtained from a seed dealer in Beijing, China.

[0040] In the soil nitrogen application treatment, the nitrogen fertilizer is urea with N≥46.0% and the brand is Kunningwang. In the foliar nitrogen application treatment, the nitrogen fertilizer used is liquid nitrogen fertilizer 422-0-0 with total nitrogen ≥422 g / L, which is purchased from Shandong Cangyuan Biotechnology Co., Ltd. Both urea and foliar liquid nitrogen fertilizer are common nitrogen fertilizer types used by farmers in the fields.

[0041] 2. Measurement methods Before collecting corn samples, a ruler and vernier caliper were used to measure the plant height and stem diameter of the corn.

[0042] A portable SPAD meter (Zhejiang Top Cloud-Agri Technology Co., Ltd.) and a portable stomatal conductance meter LI-600 photosynthesis system (Li-COR Biosciences, Lincoln, Nebraska, USA) were used to measure chlorophyll content and stomatal exchange on the third fully expanded leaf at the top of the corn.

[0043] Seedlings were randomly collected, washed clean with deionized water, and the fresh weight was measured with an electronic balance. After drying in an oven at 70°C for 48 h, the dry weight was measured.

[0044] Sulfuric acid-hydrogen peroxide digestion was used, and a Kjeldahl nitrogen analyzer (Alva automatic Kjeldahl nitrogen analyzer KN520) was used to measure the total nitrogen content in corn leaves (Gmitrowicz-Iwan Joanna, Ligęza Sławomir, Pranagal Jacek, SmalHalina, Wójcikowska-Kapusta Anna. Improving acidic sandy soil properties forplant growth with dam reservoir sediments in the face of soaring fertiliserprices[J]. Soil&Tillage Research, 2023, 234).

[0045] A certain amount of leaf tissue was weighed, 1 ml of extraction solution was added, and homogenized in an ice bath. After centrifugation for 10 min (8000 g, 4°C), the supernatant was taken and placed on ice for further measurement. The supernatant was used to measure peroxidase (POD), superoxide dismutase (SOD), malondialdehyde (MDA), and hydrogen peroxide (H2O2), all using kits (Nanjing Mofan Biotechnology Co., Ltd.), and measured with a full-wavelength microplate reader (SpectraMax190, Molecular Devices, USA).

[0046] When determining the nitrogen application rate threshold, the dry weight and fresh weight of plant growth indicators are used as evaluation indicators, and the candidate fertilization concentrations that no longer increase significantly are determined through the growth indicators. Then, the total nitrogen content, superoxide dismutase activity, malondialdehyde, and hydrogen peroxide content of the plants under the candidate fertilization concentrations are compared. When the total nitrogen content and superoxide dismutase activity of the plants no longer increase significantly and the hydrogen peroxide content and malondialdehyde content no longer decrease significantly, the lowest fertilization concentration is the optimal threshold.

[0047] Soil testing and formulated fertilization are carried out according to the Agricultural Industry Standard of the People's Republic of China, "Technical Regulations for Soil Testing and Formulated Fertilization" (NY / T - 2911 - 2016).

[0048] Example 1 Soil Nitrogen Fertilization - Urea 1. General Situation of Potting Soil The soil type is sandy loam, and the soil is taken from the surface soil (0 - 20 cm) of farmland in Beijing; the soil pH is 7.79, EC is 1.55 ms / cm, organic matter is 14.10 g / kg, cation exchange capacity is 10.46 g / kg, total nitrogen is 0.82 g / kg, available phosphorus is 14.69 g / kg, and available potassium is 175.82 g / kg. Before the pot experiment, the collected soil is naturally air - dried and sieved to 2 mm, which is recorded as the sieved soil.

[0049] 2. The corn pot experiment is carried out using flowerpots. The flowerpots are 22 cm high and 20 cm in diameter. The same weight of sieved soil is filled into each flowerpot, and corn seeds are sown in the flowerpots. 6 seeds are sown in each pot. Based on the consistent growth of corn seedlings, the seedlings in each pot are thinned to 4 plants, and fertilization treatment is carried out.

[0050] After that, it is divided into the following 6 treatments, namely: (1) CK: No fertilization; (2) SD - 10: The fertilization amount is 10% of the soil urea benchmark; (3) SD - 40: The fertilization amount is 40% of the soil urea benchmark; (4) SD - 70: The fertilization amount is 70% of the soil urea benchmark; (5) SD - 100: The fertilization amount is 100% of the soil urea benchmark; (6) SD - 130: The fertilization amount is 130% of the soil urea benchmark.

[0051] Among them, the determination method of the soil urea baseline is as follows: Calculate the nitrogen fertilizer application rate of the tested soil according to the soil testing and formulated 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 that during the whole period. Therefore, a total of 50 kg of nitrogen fertilizer needs to be applied per hectare during the jointing stage; and the nitrogen content of urea is 46%. Therefore, if urea is used as the nitrogen fertilizer, then a total of 108.7 kg of urea needs to be applied per hectare. According to a row spacing of 60 cm and a plant spacing of 20 cm per hectare, 83,333 corn plants are planted. After conversion, 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 4 plants. The nitrogen fertilizer is applied in 4 times, so a total of 1.304 g of urea is applied to 4 corn plants each time. Taking 1.304 g of urea as the soil urea baseline. Therefore, the amount of urea applied to 4 corn plants each time is as follows: 0.1304 g for the SD-10 treatment, 0.5216 g for the SD-40 treatment, 0.9128 g for the SD-70 treatment, 1.304 g for the SD-100 treatment, and 1.6952 g for the SD-130 treatment. The specific fertilization amounts for different treatments are shown in Table 1.

[0052] All experimental treatments were set with 4 replicate experiments. When applying nitrogen fertilizer to the flowerpot soil of each treatment, dissolve the required urea and NaCl of each treatment completely in deionized water and then apply it to the soil. The mass concentration of sodium chloride in the deionized water is 0.6%, and the saturated conductivity of the soil after application is 6 dS / m. The soil water content in the flowerpots was maintained at 50% - 60% of the field water holding capacity until the end of the experiment.

[0053] The experiment was set for a total of 40 days. 15 days after sowing the corn, the first fertilization was carried out at the three-leaf stage, and fertilization was carried out every 5 days. The 4th fertilization was at the 30th day after sowing, and the corn seedlings were harvested on the 40th day after sowing. The fertilization amounts are shown in Table 1. The harvested corn seedlings were measured for growth indicators and physiological indicators.

[0054] Table 1 Soil nitrogen fertilizer application plan (amount of urea per pot)

[0055] 3. The results are as follows: (1) Effects of different soil nitrogen application rates on the growth and photosynthetic performance of corn seedlings The effects of different nitrogen application rates in the soil on the fresh weight, dry weight, plant height, and stem diameter of maize seedlings were significantly different, as shown in Table 2. Compared with CK, the fresh weights of the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments were significantly increased. When the nitrogen application rate in the soil reached SD-70, SD-100, and SD-130, the fresh weight and dry weight of maize did not increase significantly with the increase in the fertilization rate. There was no significant difference in plant height among the different fertilization rate treatment groups. When the nitrogen application rate in the soil reached SD-40, the stem diameter of maize did not increase significantly with the increase in the fertilization rate. There was no significant difference in chlorophyll content among the treatments. When the nitrogen application rate in the soil reached SD-70, the stomatal conductance intensity of maize did not increase significantly with the increase in the nitrogen fertilizer application rate.

[0056] Table 2 Effects of Different Nitrogen Application Rates in the Soil on the Growth and Photosynthetic Performance of Maize Seedlings

[0057] (2)Effects of Different Nitrogen Application Rates in the Soil on the Total Nitrogen, Antioxidant Enzymes, and Oxidative Markers in the Shoot of Maize Seedlings The effects of different nitrogen application rates in the soil on the total nitrogen, antioxidant enzymes, and oxidative markers in the shoot of maize seedlings were significantly different, as shown in Table 3. Compared with CK, the total nitrogen in the shoot of the SD-40, SD-70, SD-100, and SD-130 treatments was significantly increased, the superoxide dismutase activity in the shoot was significantly increased, and the peroxidase activity in the shoot was significantly increased. Compared with CK, the malondialdehyde content in the shoot of the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments was significantly decreased. Compared with CK, the hydrogen peroxide content in the shoot of the SD-70, SD-100, and SD-130 treatments was significantly decreased. When the nitrogen application rate in the soil reached SD-40, the total nitrogen content in the shoot did not increase significantly. The superoxide dismutase activity was the highest when the fertilization rate was SD-70 and SD-100, and then decreased. When the fertilization rate was SD-70, the peroxidase activity did not increase significantly. With the increase in the fertilization rate, the malondialdehyde and hydrogen peroxide contents showed a trend of first decreasing and then increasing. When the fertilization rate was SD-70, the contents of the oxidative harmful markers malondialdehyde and hydrogen peroxide were the lowest.

[0058] Table 3 Effects of Different Nitrogen Application Rates in the Soil on the Total Nitrogen, Antioxidant Enzymes, and Oxidative Markers in the Shoot of Maize Seedlings

[0059] (3)Effects of Different Nitrogen Application Rates in the Soil on the Total Nitrogen, Antioxidant Enzymes, and Oxidative Markers in the Root of Maize Seedlings Different nitrogen application rates in the soil also had significant effects on the total nitrogen in the underground part, antioxidant enzyme activities, and the contents of oxidation markers of maize seedlings. As shown in Table 4, compared with CK, the increase in the total nitrogen content in the underground part under the SD-10, SD-40, SD-70, SD-100, and SD-130 treatments was not significant. Compared with CK, the activities of superoxide dismutase under the SD-40 and SD-70 treatments were significantly increased. Compared with CK, the contents of peroxidase in the underground part under the SD-40 and SD-70 treatments were significantly increased. Compared with CK, the contents of malondialdehyde under the SD-10 and SD-40 treatments were significantly decreased. Compared with CK, the content of hydrogen peroxide under the SD-70 treatment was significantly decreased. With the increase in the fertilization rate, when the fertilization rate was at SD-70, the total nitrogen and the activity of superoxide dismutase no longer increased significantly with the increase in the fertilization rate. At SD-100, the activity of peroxidase no longer increased with the increase in the fertilization rate. The contents of malondialdehyde and hydrogen peroxide were the lowest when the fertilization rate was at SD-70. According to Tables 2 to 4, salt stress would limit the absorption of nitrogen fertilizer by maize roots. With the increase in the fertilization rate, the absorption of nitrogen fertilizer by maize roots would reach a certain threshold, and the nitrogen absorption, antioxidant performance, and growth indicators of maize would no longer increase significantly.

[0060] Table 4 Effects of Different Nitrogen Application Rates in the Soil on Total Nitrogen, Antioxidant Enzymes, and Oxidation Markers in the Underground Part of Maize Seedlings

[0061] In summary, according to Table 2, it can be seen that with the increase in the nitrogen fertilizer application concentration, the fresh weight and dry weight indexes of maize no longer increased significantly under the soil nitrogen fertilizer application concentrations of SD-70, SD-100, and SD-130. SD-70, SD-100, and SD-130 were used as the candidate concentrations for soil nitrogen fertilizer application. Then, based on the detection results of the total nitrogen index, superoxide dismutase activity index, malondialdehyde index, and hydrogen peroxide index in the above-ground part of maize (Table 3) and the detection results of the total nitrogen index, superoxide dismutase activity index, malondialdehyde index, and hydrogen peroxide index in the underground part (Table 4), considering the above-ground and underground indexes comprehensively, it was determined that under the nitrogen fertilizer application concentration of SD-70, the total nitrogen index and superoxide dismutase activity index of maize no longer increased significantly, and the malondialdehyde index and hydrogen peroxide index no longer decreased significantly. That is, the nitrogen fertilizer application rate of SD-70 (70% soil urea) was used as the soil nitrogen application threshold.

[0062] Example 2 Foliar Application of Nitrogen Fertilizer + Soil Application of Nitrogen Fertilizer The optimal SD-70 of 0.9128 g / pot determined in Example 1 was used as the soil nitrogen application rate, and then foliar application of nitrogen fertilizer was carried out. In the foliar application of nitrogen fertilizer, the application method was as follows: Soil application of nitrogen fertilizer and foliar application of nitrogen fertilizer were carried out at 7-8 am every day. To avoid the additional impact of foliar spraying on the soil environment, the potted soil and the main stem of maize were covered with paper, and liquid nitrogen fertilizer was sprayed on maize.

[0063] 1. General situation of potted soil. Follow the steps of Example 1.

[0064] 2. The corn potted experiment is carried out using flowerpots with a height of 22 cm and a diameter of 20 cm. The same weight of sieved soil is filled into each flowerpot, and corn seeds are sown in the flowerpots, with 6 seeds sown in each pot. Taking the consistent growth of corn seedlings as the standard, the seedlings in each pot are thinned to 4 plants, and fertilization treatment is carried out.

[0065] A total of 6 treatments are set, denoted as FS-0, FS-70, FS-100, FS-130, FS-160, and FS-190. Among them, the determination method of the foliar nitrogen fertilizer benchmark of 100% (i.e., FS-100) is as follows: Calculate the foliar nitrogen fertilizer application amount according to the soil nitrogen fertilizer application amount obtained by the soil testing and formulated fertilization method. Specifically, the application amount of pure nitrogen per hectare is 250 kg, and the application amount of foliar nitrogen fertilizer is 0.253% of the soil nitrogen fertilizer application amount, that is, 632.5 g of pure nitrogen. The nitrogen content of the liquid urea applied is 422 g / L, that is, the application amount of foliar liquid nitrogen fertilizer is 1.5 L / ha. According to a row spacing of 60 cm and a plant spacing of 20 cm per hectare, 83,333 corn plants are planted. The dosage per plant is 0.018 mL, and the dosage for 4 corn plants in each pot is 0.072 mL. After dilution by 100 times, it is 7.2 mL, which is denoted as the foliar nitrogen fertilizer benchmark.

[0066] The fertilization amounts of different treatments are as follows: FS-0: No fertilization; FS-70: The foliar nitrogen fertilizer application amount is 70% of the foliar nitrogen fertilizer benchmark (i.e., 7.2 mL); FS-100: The foliar nitrogen fertilizer application amount is 100% of the foliar nitrogen fertilizer benchmark (i.e., 7.2 mL); FS-130: The foliar nitrogen fertilizer application amount is 130% of the foliar nitrogen fertilizer benchmark (i.e., 7.2 mL); FS-160: The foliar nitrogen fertilizer application amount is 160% of the foliar nitrogen fertilizer benchmark (i.e., 7.2 mL); FS-190: The foliar nitrogen fertilizer application amount is 190% of the foliar nitrogen fertilizer benchmark (i.e., 7.2 mL).

[0067] Soil nitrogen fertilizer application: Once every 5 days, 0.9128 g / pot, for a total of 4 times. Foliar nitrogen fertilizer application: Once every 15 days, for a total of 2 times. Only soil nitrogen fertilizer is applied for the second and third fertilizations, and both soil nitrogen fertilizer and foliar nitrogen fertilizer are applied simultaneously for the first and fourth fertilizations. See Table 5 for details.

[0068] All experimental treatments were set with 4 replicated experiments. When applying nitrogen fertilizer to the flowerpot soil of each treatment, the amount of urea and NaCl applied to each treatment were dissolved completely in deionized water and then applied to the soil. The mass concentration of sodium chloride in the deionized water was 0.6%, and the saturated conductivity of the soil after applying urea and NaCl was 6 dS / m. The soil water content in the flowerpots was maintained at 50% - 60% of the field capacity until the end of the experiment.

[0069] The experiment was set for a total of 40 days. On the 15th day after the emergence of three leaves after maize sowing, the first foliar nitrogen application was carried out, and the second foliar nitrogen application was carried out on the 30th day after sowing. The maize seedlings were harvested on the 40th day after sowing for measurement.

[0070] Table 5 Fertilization scheme

[0071] (4)Effects of different foliar nitrogen application rates on the growth and photosynthetic performance of maize seedlings The effects of different foliar nitrogen application rates on the fresh weight, dry weight, plant height and stem diameter of maize seedlings were significantly different. As shown in Table 6.

[0072] Table 6 Effects of different foliar nitrogen application rates on the growth and photosynthetic performance of maize seedlings

[0073] (5)Effects of different foliar nitrogen application rates on the total nitrogen, antioxidant enzymes and oxidative markers in the above-ground parts of maize seedlings The effects of different foliar nitrogen application rates on the total nitrogen content, superoxide dismutase and peroxidase activities, malondialdehyde and hydrogen peroxide contents in the above-ground parts of maize seedlings were significantly different. As shown in Table 7, compared with FS-0, the total nitrogen content and peroxidase activity in the above-ground parts of FS-160 and FS-190 were significantly increased. Compared with FS-0, the superoxide dismutase activities in the above-ground parts of FS-100, FS-130, FS-160 and FS-190 were significantly increased. When the foliar nitrogen application rate was FS-160, with the increase of the foliar nitrogen application rate, the total nitrogen content, superoxide dismutase activity and peroxidase activity in the above-ground parts no longer increased significantly. The contents of malondialdehyde and hydrogen peroxide in the above-ground parts were the lowest at FS-160.

[0074] Table 7 Effects of different foliar nitrogen application rates on the total nitrogen, antioxidant enzymes and oxidative markers in the above-ground parts of maize seedlings

[0075] (5)Effects of different foliar nitrogen application rates on the total nitrogen, antioxidant enzymes and oxidative markers in the underground parts of maize seedlings The effects of different foliar nitrogen application rates on the total nitrogen content, superoxide dismutase and peroxidase activities, and malondialdehyde and hydrogen peroxide contents in the underground parts of maize seedlings were significantly different. As shown in Table 8, compared with FS-0, the total nitrogen content in the underground part of FS-190 was significantly increased. Compared with FS-0, the superoxide dismutase activities of FS-100, FS-130, FS-160 and FS-190 were significantly increased. Compared with FS-0, the peroxidase activities of FS-70, FS-100, FS-130, FS-160 and FS-190 in the underground parts were significantly increased. With the increase of foliar nitrogen application rate, the total nitrogen content and superoxide dismutase activity in the underground part gradually increased. When the foliar nitrogen application rate was FS-160, with the increase of fertilizer application rate, the peroxidase activity in the underground part no longer increased significantly, and the malondialdehyde and hydrogen peroxide contents in the underground part were the lowest.

[0076] Table 8 Effects of different foliar nitrogen application rates on total nitrogen, antioxidant enzymes and oxidation markers in the underground parts of maize seedlings

[0077] It can be seen from Table 6 that with the increase of foliar nitrogen application concentration, under the soil nitrogen fertilizer application concentration and foliar nitrogen application concentration of FS-130, FS-160 and FS-190, the fresh weight and dry weight indexes of maize no longer increased significantly. FS-130, FS-160 and FS-190 were used as the candidate concentrations of foliar nitrogen application concentration. Then, according to the detection results of the total nitrogen index, superoxide dismutase enzyme activity index, malondialdehyde index and hydrogen peroxide index in the above-ground part of maize (Table 7) and the detection results of the total nitrogen index, superoxide dismutase enzyme activity index, malondialdehyde index and hydrogen peroxide index in the underground part (Table 8), considering the corresponding above-ground and underground indexes comprehensively, it was determined that under the fertilization concentration of FS-160, the total nitrogen index and superoxide dismutase enzyme activity index of maize no longer increased significantly, and the malondialdehyde index and hydrogen peroxide index no longer decreased significantly. That is, the fertilization concentration of FS-160 (11.52 mL foliar nitrogen fertilizer) was used as the foliar nitrogen application amount threshold.

[0078] It can be seen from Tables 6-8 that under the condition of limited nutrient absorption by roots, foliar application of nitrogen fertilizer can alleviate the problem of insufficient nitrogen fertilizer absorption by maize roots and quickly supplement the nitrogen demand of maize during the seedling stage.

[0079] In summary, by using the nitrogen fertilizer application method provided by the present invention, the amount of nitrogen fertilizer input can be accurately controlled, the residue of nitrogen fertilizer in the soil can be reduced, and the nitrogen absorption and antioxidant properties of maize can be significantly improved, further ensuring the growth of maize during the seedling stage.

[0080] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on this embodiment without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for promoting maize growth by complementary nitrogen application between roots and leaves under salt stress conditions, characterized in that, It includes the following steps: Plant corn in saline soil and apply nitrogen to the soil and foliar nitrogen application. The amount of nitrogen applied to the soil is the threshold of soil nitrogen application amount, and the amount of foliar nitrogen application is the threshold of foliar nitrogen application amount. The threshold of soil nitrogen application amount is the lowest nitrogen application amount when the growth index, nutrient absorption index, and antioxidant enzyme index of corn in the soil to be planted with corn no longer increase significantly and the oxidation marker index no longer decreases significantly. The threshold of foliar nitrogen application amount is the lowest foliar nitrogen application amount when the growth index, nutrient absorption index, and antioxidant enzyme index of corn no longer increase significantly and the oxidation marker index no longer decreases significantly by using the threshold of soil nitrogen application amount as the application amount of soil nitrogen fertilizer in the soil to be planted with corn.

2. The method according to claim 1, wherein The nitrogen fertilizer for foliar nitrogen application 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; the amide nitrogen fertilizer includes urea.

3. The method according to claim 1, characterized in that The growth index includes fresh weight and dry weight; the nutrient absorption index includes total nitrogen content; the antioxidant enzyme index includes superoxide dismutase; the oxidation marker index includes malondialdehyde and hydrogen peroxide.

4. The method according to claim 1, wherein The method for determining the threshold of soil nitrogen application amount includes: in the planting year, calculate the soil nitrogen application amount by soil testing and formulated fertilization for the soil to be planted with corn, take the calculated soil nitrogen application amount as 100% of the benchmark, apply different amounts of nitrogen fertilizer to the soil, and measure the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of corn; determine the candidate soil nitrogen application amount based on the criterion that the growth index of corn no longer increases significantly; the lowest nitrogen application amount when the nutrient absorption index and antioxidant enzyme of corn under the candidate soil nitrogen application amount no longer increase significantly and the oxidation marker index no longer decreases significantly is the threshold of soil nitrogen application amount. The method for determining the threshold of foliar nitrogen application amount includes: in the planting year, in the soil to be planted with corn, use the threshold of soil nitrogen application amount as the application amount of soil nitrogen fertilizer; determine the foliar nitrogen fertilizer application amount according to 0.25% - 0.26% of the calculated soil nitrogen application amount by soil testing and formulated fertilization, and take the determined foliar nitrogen fertilizer application amount as 100% of the benchmark; at the same time, apply different amounts of foliar nitrogen fertilizer to corn, and measure the growth index, nutrient absorption index, antioxidant enzyme index, and oxidation marker index of corn; determine the candidate foliar nitrogen application amount based on the criterion that the growth index of corn no longer increases significantly; the lowest foliar nitrogen application amount when the nutrient absorption index and antioxidant enzyme of corn under the candidate foliar nitrogen application amount no longer increase significantly and the oxidation marker index no longer decreases significantly is the threshold of foliar nitrogen application amount.

5. The method according to claim 4, characterized in that The different amounts of nitrogen fertilizer are 10% - 130% of the soil nitrogen application amount benchmark. The different amounts of foliar nitrogen fertilizer are 70% - 190% of the foliar nitrogen fertilizer application amount benchmark.

6. The method according to claim 1, wherein The first fertilization time for soil nitrogen application and foliar nitrogen application is the three - leaf stage of corn.

7. The method according to claim 1 or 6, characterized in that The number of times of soil nitrogen application is 2 - 5 times, and the time interval between every two times is 4 - 6 days; the number of times of foliar nitrogen application is 2 - 4 times, and the time interval between every two times is 14 - 16 days.

8. Use of the method according to any one of claims 1 to 7 in at least one of the following 1) to 3): 1) Improving the stress resistance of maize; 2) Promoting the growth of maize under salt stress conditions; 3) Increasing the nitrogen absorption rate of maize under salt stress.

9. The application according to claim 8, characterized in that, Promoting the growth of maize includes increasing at least one of the fresh weight, dry weight, plant height, stem diameter, and chlorophyll content of maize.

10. The application according to claim 8, wherein The improvement of the stress resistance of maize includes increasing the antioxidant enzyme activity of maize under salt stress and reducing at least one of the malondialdehyde and hydrogen peroxide contents; the antioxidant enzymes include superoxide dismutase and / or peroxidase.

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