AU2020101690A4 - Method for Nitrogen Application Via Drip Irrigation for Improving Nitrogen Use Efficiency (NUE) of Flue-Cured Tobacco - Google Patents

Abstract

The present invention relates to a method for nitrogen application via drip irrigation for improving nitrogen use efficiency (NUE) of flue-cured tobacco. In the method, nitrogen application via drip irrigation is combined with split nitrogen application to decrease a proportion of base fertilizer nitrogen, increase a proportion of top-dressed fertilizer nitrogen, and supply nutrients in accordance with nitrogen requirements of flue-cured tobacco, achieving integration of water and fertilizer and a reduction of the loss of nitrogen fertilizer. The NUE in this present invention is increased by more than 20% compared with that in the conventional technology. DRAWINGS 60 - a 50 -b b EOTi bcE 0T2 40d dd de 0T e *TT 30 20 *T6 *T7 10 UT8 *T9 TI T2 T3 T4 T5 T6 T7 T8 T9 Treatment FIG. 1 15

Description

DRAWINGS

- a

-b b EOTi bcE 0T2 d dd de 0T e *TT

*T6 *T7 10 UT8

*T9 TI T2 T3 T4 T5 T6 T7 T8 T9 Treatment

FIG. 1

METHOD FOR NITROGEN APPLICATION VIA DRIP IRRIGATION FOR IMPROVING NITROGEN USE EFFICIENCY (NUE) OF FLUE-CURED TOBACCO

TECHNICAL FIELD The present invention relates to the technical field of nitrogen fertilizer application, in particular to a method for nitrogen application via drip irrigation for improving nitrogen use efficiency (NUE) of flue-cured tobacco.

BACKGROUND Flue-cured tobacco (Nicotianatabacum L.) is the largest type of tobacco cultivated in China and the world and is the main raw material of Chinese cigarettes. The flue-cured tobacco plant is tall and big with sparse and uniformly distributed leaves. Proper application of nitrogen fertilizer is one of the main measures to improve the yield and quality of tobacco. In the current flue-cured tobacco production, nitrogen fertilizers are mainly applied by hole application or side-dressing. The hole method of fertilizer application was achieved by digging a hole of about several centimeters away from each plant and fertilizer was put into the hole and covered with soil, which is laborious and time-consuming. The side dressing is labor-saving, but because the nitrogen fertilizer is applied to the ridge bottom at one time, the release of fertilizer is inconsistent with the nutrient requirement of flue-cured tobacco, and the NUE is low. In the prior art, the application rate of nitrogen fertilizer is improper, with 70% nitrogen fertilizer applied as base fertilizer and 30% nitrogen fertilizer applied as topdressing. The existing "one-time nitrogen supply and fertilization method capable of improving NUE of flue-cured tobacco" (CN 201010297119.1) is achieved by increasing the amount of organic fertilizer and reducing the amount of chemical fertilizer at southern rainy regions such as Guangdong and the like, and only has a NUE of 33%-43%, but not suitable for northern arid and semi-arid tobacco-growing regions. Besides, "a fertilization method for improving NUE of flue-cured tobacco" has previously been disclosed in Chinese patent No. 201501799063.2, which improves the NUE with 44% on yellow loam soil and over 50% on the rice soil, but is laborious and time-consuming because of cumbersome fertilizing steps. At present, there is no suitable and simple method of nitrogen application for improving NUE of flue-cured tobacco in the Huang-Huai region and northern tobacco-growing regions.

SUMMARY The present invention aims to provide a method for integrated water-fertilizer application to improve NUE of flue-cured tobacco in the -luang-Huai region and northern tobacco-growing regions. The present invention provides a method for nitrogen application via drip irrigation for improving NUE of flue-cured tobacco, where a nitrogen fertilizer solution is formed by dissolving a water-soluble nitrogen fertilizer in water, and applied via drip irrigation several times. Preferably, the nitrogen fertilizer solution is applied via drip irrigation two or three times. Preferably, when the drip irrigation is performed two times, the nitrogen fertilizer solution is applied as base fertilizer nitrogen when the drip irrigation is performed for the first time, where the base fertilizer nitrogen accounts for less than 10%-50% of the total nitrogen in the entire nitrogen application period and is applied 2 days after transplanting, and the residual nitrogen fertilizer is top-dressed 30 days after transplanting; Preferably, when the drip irrigation is performed two times, the base fertilizer nitrogen accounts for 10%-30% of the total nitrogen mass and the residual nitrogen fertilizer accounts for %-90% of the total nitrogen mass. Preferably, when the drip irrigation is performed three times, the base fertilizer nitrogen is applied 2 days after transplanting; the residual nitrogen fertilizer accounts for 50%-90% of the total nitrogen mass, and the residual nitrogen fertilizer is top-dressed twice, 30 days and 44 days after transplanting. Preferably, when the drip irrigation is performed three times, the nitrogen fertilizer solution is applied as base fertilizer nitrogen when the drip irrigation is performed for the first time, and the residual top-dressed fertilizer nitrogen accounts for 50%-55% of the total nitrogen mass; the first top-dressed nitrogen fertilizer accounts for 33%-42% of the total nitrogen mass, and the second top-dressed nitrogen fertilizer accounts for 13%-17% of the total nitrogen mass. Preferably, a drip irrigation kit is a gravity drip irrigation kit, a transverse distance between an emitter of the drip irrigation kit and a flue-cured tobacco plant is 6-10 cm, and a drip speed of the drip irrigation kit is 0.95-1.05 L-h1 Preferably, clear water is applied via drip irrigation before and after the nitrogen fertilizer solution application via drip irrigation. Preferably, the time for two-time clear water application via drip irrigation is independently 0.4-0.6 h. Preferably, the time for each nitrogen fertilizer solution application via drip irrigation is 1.5-2.5 h. The present invention has the beneficial effects that: in the method for nitrogen application via drip irrigation for improving NUE of flue-cured tobacco, the nitrogen application via drip irrigation is combined with split nitrogen application to supply nutrients in accordance with nitrogen requirements of flue-cured tobacco. With the decrease in a proportion of base fertilizer nitrogen and an increase in a proportion of top-dressed fertilizer nitrogen, achieving an integration of water and fertilizer, and a reduction in the loss of nitrogen fertilizer was achieved. The NUE in the present invention is increased by more than 20% compared with that in the conventional technology.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows NUE of flue-cured tobacco subjected to different nitrogen application treatments in Example 1 of the present invention.

DETAILED DESCRIPTION The present invention provides a method for nitrogen application via drip irrigation for improving NUE of flue-cured tobacco, where a nitrogen fertilizer solution is formed by dissolving a nitrogen fertilizer in water, and applied via drip irrigation several times. In the present invention, the method for nitrogen application via drip irrigation is preferably applicable to a brown soil region, and more preferably applicable to the Huang-Huai region and northern tobacco-growing regions. In the specific implementation process of the present invention, flue-cured tobacco seedlings are preferably cultivated by a floating system, and the plant height of the tobacco plant used for transplanting is preferably 7-9 cm, more preferably 8 cm. In the present invention, the tobacco plants are preferably planted in a PVC container after being transplanted, a width of upper opening of which is preferably 35-45 cm, more preferably 40 cm; a width of lower bottom of which is preferably 25-35 cm, more preferably 30 cm; a height of which is preferably 25-30 cm, more preferably 28 cm. The addition amount of the brown soil in the PVC container is preferably -70 kg, more preferably 65 kg; one flue-cured tobacco plant is preferably planted in the single PVC container of the size described in the above technical solution. In the present invention, when flue-cured tobacco plants are transplanted, a base fertilizer is applied, where the base fertilizer includes a nitrogen fertilizer, a phosphorus fertilizer and a potassium fertilizer. The nitrogen fertilizer form is preferably anmnonium sulfate, the phosphorus fertilizer is preferably calcium superphosphate, the potassium fertilizer is preferably potassium sulfate, and a mass ratio of ammonium sulfate to calcium superphosphate to potassium sulfate is preferably 1:1:3. In the present invention, the phosphorus fertilizer and the potassium fertilizer are mixed and applied with soil when flue-cured tobacco plants are transplanted. In the present invention, a mass of the phosphorus fertilizer applied to the soil is preferably 3-5 g/plant, more preferably 4 g/plant; the potassium fertilizer is preferably 10-14 g/plant, more preferably 12 g/plant. Specifically, the phosphorus fertilizer, the potassium fertilizer and the brown soil are mixed and loaded into the PVC container before the flue-cured tobacco plants are transplanted. In the present invention, the nitrogen fertilizer is applied via drip irrigation, and the solid-phase nitrogen fertilizer is formulated into a nitrogen fertilizer solution, where a concentration of the nitrogen fertilizer solution is preferably 1-3 g/L, more preferably 2 g/L. In the present invention, the nitrogen fertilizer is preferably applied via drip irrigation two or three times. In the present invention, when the drip irrigation is performed two times, preferably the base fertilizer nitrogen is applied 2 days after transplanting, and the residual nitrogen fertilizer is top-dressed after transplanting, which preferably is top-dressed 30 days after transplanting. In the present invention, when the drip irrigation is performed two times, a mass ratio of the base fertilizer nitrogen to the total nitrogen is preferably 10%-50%, more preferably 10%-30%. Preferably a mass ratio of the residual nitrogen fertilizer to the total nitrogen is greater than or equal to 50%, and more preferably 70%-90%. In the present invention, when the drip irrigation is performed three times, preferably the base fertilizer nitrogen is applied 2 days after transplanting, the residual nitrogen fertilizer is top-dressed twice, preferably the residual nitrogen fertilizer is top-dressed 30 days and 44 days after transplanting. In the present invention, when the drip irrigation is performed three times, a mass ratio of the base fertilizer nitrogen to the total nitrogen is preferably 10%-50%; a mass ratio of the residual nitrogen fertilizer to the total nitrogen is preferably greater than or equal to 50%; the first top-dressed nitrogen fertilizer preferably accounts for 33%-42% of the total nitrogen mass, more preferably 35%; the second top-dressed nitrogen fertilizer preferably accounts for 13%-17% of the total nitrogen mass, more preferably 15%. In a process of nitrogen application via drip irrigation, a drip irrigation kit is preferably a gravity drip irrigation kit, a distance between an emitter and a flue-cured tobacco plant is preferably 6-10 cm, more preferably 8 cm; and a drip speed of the drip irrigation kit is preferably 0.95-1.05 Lhf1, more preferably 1.0 L-h. In the present invention, specific steps of the drip irrigation are preferably as follows: firstly, clear water is applied via drip irrigation, then a nitrogen fertilizer solution is applied via drip irrigation, and finally clear water is applied via drip irrigation again. According to the present invention, the water for clear water application via drip irrigation is preferably irrigation water, and the time for clear water application via drip irrigation is preferably 0.4-0.6 h, more preferably 0.5 h; after the clear water application via drip irrigation, preferably a nitrogen fertilizer solution is applied, and the time for each nitrogen fertilizer solution application via drip irrigation is preferably 1.5-2.5 h, more preferably 2 h; a concentration of the nitrogen fertilizer solution is preferably 1-3 g- L1; more preferably 2 g L-. According to the present invention, after the nitrogen fertilizer solution application via drip irrigation, preferably clear water is applied via drip irrigation again, and the water consumption and time are the same as that for the first time, which will not be repeated here. The first clear water application via drip irrigation, the nitrogen fertilizer solution application via drip irrigation and the last clear water application via drip irrigation are continuously performed without time interval. Other measures in the present invention are conventional technical means in the art without other special requirements. In the present invention, the flue-cured tobacco plants are preferably topped in a full-bloom stage, preferably leaving 20-30 leaves per plant, more preferably leaving 24 leaves. In the present invention, a Kjeldahl method is used to determine the total nitrogen content of each organ, and NUE is calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100. The method for nitrogen application via drip irrigation for improving NUE of flue-cured tobacco described in the present invention will be described in further detail below with reference to specific examples. The technical solutions of the present invention include but are not limited to the following examples. Example 1 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) : m(P205): m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting and 30 days after transplanting, with 50% of nitrogen applied 2 days after transplanting and 50% of nitrogen applied 30 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants was 1895.72 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (1895.72-666.06)/4000x100=30.74%. Example 2 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) :m(P205) m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 50% ofnitrogen applied 2 days after transplanting, 35% of nitrogen applied 30 days after transplanting, and 15% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants in the nitrogen application regions was 2838.48 mg/plant, so that the NUE (%)= (2838.48-666.06)/4000x100=54.31%.

Example 3 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) : m(P205) m(K20) =1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting and 30 days after transplanting, with 30% of nitrogen applied 2 days after transplanting and 70% of nitrogen applied 30 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants was 2500.75 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, nitrogen application rate was 4000 mg/plant, so that the NUE (%)= (2500.75-666.06)/4000x 100=45.87%. Example 4 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h 1 , and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) : m(P205): m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer.

Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 30% of nitrogen applied 2 days after transplanting, 55% of nitrogen applied 30 days after transplanting, and 15% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%)= (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants was 2322.88 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2322.88-666.06)/4000x100=41.42%. Example 5 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h1 , and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) :m(P205): m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 30% of nitrogen applied 2 days after transplanting, 40% of nitrogen applied 30 days after transplanting, and 30% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants was 2109.72 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2109.72-666.06)/4000x100=36.09%. Example 6 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) :m(P205): m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting and 30 days after transplanting, with 10% of nitrogen applied 2 days after transplanting and 90% of nitrogen applied 30 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. In this example, NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100; in this example, the total nitrogen uptake by plants was 2513.66 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2513.66-666.06)/4000x100=46.19%. Example 7 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) :m(P205): m(K20) = 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 10% of nitrogen applied 2 days after transplanting, 75% of nitrogen applied 30 days after transplanting, and 15% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application ratex100; in this example, the total nitrogen uptake by plants was 2185.17 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2185.17-666.06)/4000x100=37.98%. Example 8 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, withm(N) :m(P205) m(K20)= 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 10% of nitrogen applied 2 days after transplanting, 60% of nitrogen applied 30 days after transplanting, and 30% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in nitrogen-free regions)/nitrogen application rate x 100. In this example, the total nitrogen uptake by plants was 2032.94 mg/plant in the nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2032.94-666.06)/4000x100=34.17%. Example 9 A container for planting flue-cured tobacco was a PVC square pot with a width of upper opening of 40 cm, a width of lower bottom of 30 cm, and a height of 28 cm; each pot contained kg of brown soil and one tobacco plant, with 24 tobacco plants per treatment group. Drip irrigation was performed by using a gravity drip irrigation kit, with a distance between an emitter and a tobacco plant of 8 cm, and drip speed of 1.0 L-h, and each tobacco plant was provided with one drip irrigation kit. 4 g of pure nitrogen was applied for each plant, with m(N) : m(P205): m(K20) = 1:1:3, a nitrogen fertilizer form being ammonium sulfate, a phosphorus fertilizer being calcium superphosphate, and a potassium fertilizer being potassium sulfate, and the phosphorus and potassium fertilizers were uniformly mixed with soil to be applied as a base fertilizer. Nitrogen was applied via drip irrigation 2 days after transplanting, 30 days after transplanting, and 44 days after transplanting, with 10% of nitrogen applied 2 days after transplanting, 45% of nitrogen applied 30 days after transplanting, and 45% of nitrogen applied 44 days after transplanting. In a process of nitrogen application, firstly drip irrigation was performed with clear water for 0.5 h, and then nitrogen fertilizer from each treatment group was dissolved in 2 L water, the nitrogen was applied with a gravity drip irrigation kit for 2 h, and finally drip irrigation was performed with clear water for 0.5 h. A soil moisture content was determined by using agrometeorological monitoring system V 3.0 (TNHY-12G, Zhejiang Top Instrument Co., Ltd.) combined with a drying method; flue-cured tobacco from each treatment group was topped in a full-bloom stage, leaving 24 leaves per plant. The Kjeldahl method was used to determine the total nitrogen content of each organ, and the NUE was calculated. NUE (%) = (total nitrogen uptake by plants in nitrogen application regions) - (total nitrogen uptake by plants in the nitrogen-free region)/nitrogen application rate x 100. In this example, the total nitrogen uptake by plants was 2066.09 mg/plant in nitrogen application regions and 666.06 mg/plant in the nitrogen-free regions, and nitrogen application rate was 4000 mg/plant, so that the NUE was calculated as = (2066.09-666.06)/4000x100=35.00%. The comparisons of the NUE of Examples 1 to 9 in the present invention are shown in FIG. 1. As can be seen from FIG. 1, the NUE is the highest in Example 2, followed by Example 6, and the lowest in Example 1. In the treatment of one-time nitrogen topdressing, the NUE increased with the increase of nitrogen topdressing ratio. The NUE in Example 3 and Example 6 are 15.13 and 15.45 percents higher than that of Example 1, respectively. In the treatment of two-time nitrogen topdressing, the NUE is the highest in Example 2, followed by Example 4, and the lowest in Example 8. In the treatment of applying 50% of nitrogen during transplanting, the NUE in Example 2 is 23.57 percents higher than that of Example 1. The nitrogen application rate is % or 10% during transplanting, the NUE in the treatment of two-time nitrogen topdressing is lower than that in the one-time nitrogen topdressing via drip irrigation, and the increase of nitrogen topdressing rate shows a decreasing tendency at 44 days after transplanting. In the present invention, drip irrigation is controlled according to the soil water content condition, and the soil water content in the root extension period, vigorous growth period and mature period of each treatment respectively reach 60%-70%, 70%-80% and 60%-70% of the maximum field capacity (27.14%) through drip irrigation. By adopting the nitrogen application method disclosed by the present invention, drip irrigation is combined with split nitrogen application and postponing nitrogen application to decrease a proportion of base fertilizer nitrogen, increase a proportion of top-dressed fertilizer nitrogen, and supply nutrients in accordance with nitrogen requirements of flue-cured tobacco. Thus achieving integration of water and fertilizer and a reduction of the loss of nitrogen fertilizer. The NUE is increased by more than 20% compared with that in the conventional technology, and the NUE in the optimal example of the present invention is increased by 8.12-23.57 percents compared with that in other examples. The above descriptions are merely preferred implementations of the present invention. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present invention, but such improvements and modifications should be deemed as falling within the protection scope of the present invention.

Claims (1)

1. What is claimed is: 1. A method for nitrogen application via drip irrigation for improving nitrogen use efficiency (NUE) of flue-cured tobacco, wherein a nitrogen fertilizer solution is formed by dissolving a water-soluble nitrogen fertilizer in water and applied several times using a drip irrigation kit in a water-fertilizer integration manner, the drip irrigation kit is a gravity drip irrigation kit, a transverse distance between an emitter of the drip irrigation kit and a flue-cured tobacco plant is 6-10 cm, and a drip speed of the drip irrigation kit is 0.95-1.05 L-h1

   . 2. The method according to claim 1, wherein the nitrogen fertilizer solution is applied via drip irrigation two times, the nitrogen fertilizer solution is applied as base fertilizer nitrogen when the drip irrigation is performed for the first time, the base fertilizer nitrogen accounts for 10%-50% of total nitrogen in the entire nitrogen application period and is applied 2 days after transplanting, and a top-dressed nitrogen fertilizer is top-dressed 30 days after transplanting. 3. The method according to claim 2, wherein when the drip irrigation is performed two times, the base fertilizer nitrogen accounts for 10%-30% of the total nitrogen mass in the entire nitrogen application period and the top-dressed nitrogen fertilizer accounts for 70%-90% of the total nitrogen mass. 4. The method according to claim 1, wherein when the drip irrigation is performed three times, the nitrogen fertilizer solution is applied as base fertilizer nitrogen when the drip irrigation is performed for the first time, the base fertilizer nitrogen is applied 2 days after transplanting; the top-dressed nitrogen fertilizer accounts for 50%-90% of the total nitrogen mass in the entire nitrogen application period, and the residual nitrogen fertilizer is top-dressed twice, respectively days and 44 days after transplanting. 5. The method according to claim 4, wherein when the drip irrigation is performed three times, the top-dressed fertilizer nitrogen accounts for 50%-55% of the total nitrogen mass in the entire nitrogen application period; the first top-dressed nitrogen fertilizer accounts for 33%-42% of the total nitrogen mass, and the second top-dressed nitrogen fertilizer accounts for 13%-17% of the total nitrogen mass.