A device for recycling nitrogen in cattle farm manure to prepare liquid nitrogen fertilizer, a preparation method and application thereof

Abstract

A device for recovering nitrogen in cow farm manure to prepare liquid nitrogen fertilizer, a preparation method and applications thereof, the specific scheme is: placing cow manure in the compost shed, setting a water leakage net below the manure, filtering the liquid in the manure into a water receiving tray, pumping the ammonia gas generated by the fermentation of the manure into a gas washing tank by a gas pump, adding a dilute sulfuric acid solution with a concentration of 16.66 g / L in the gas washing tank, and after the pH value of the solution approaches neutral and remains stable, the gas pump is automatically closed, and the liquid nitrogen fertilizer is prepared. The liquid nitrogen fertilizer prepared by using cow manure and the like can realize efficient recovery of nitrogen resources and provide high-quality nitrogen nutrients for production. When applied to rice production, it can reduce the loss of nitrogen volatilization in manure, realize the organic combination of nitrogen recycling and efficient fertilization of rice.

Description

Technical Field

[0001] This invention belongs to the field of efficient nitrogen recovery for nitrogen fertilizer production and crop-livestock cycle technology, and particularly relates to an apparatus, preparation method and application for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer. Background Technology

[0002] my country's dairy farming industry continues to develop towards intensification and large-scale operations. This large-scale farming model leads to a high concentration of manure production. Fresh dairy manure contains a large proportion of ammonium nitrogen, which, after fermentation, produces large amounts of ammonia, nitrous oxide, and other gases. In rice cultivation, increased nitrogen fertilizer application ensures high and stable yields. Nitrogen, as a core nutrient element required for crop growth, enhances the nutritional value and yield of grains, making it crucial for grain production and supporting nearly half of all grain output. Summary of the Invention

[0003] To address the problem of nitrogen volatilizing in the form of ammonia nitrogen from large-scale cattle farm excrement, which is both wasteful and causes odor pollution, this application provides a method for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer and its application. Experimental results show that the recovered liquid nitrogen fertilizer from large-scale cattle farm excrement can serve as an effective nitrogen source for rice, and replacing commercial fertilizer in base fertilizer with the recovered liquid nitrogen fertilizer can improve rice growth and yield.

[0004] The technical solution provided by this invention is: an apparatus for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer, comprising a composting shed and manure inside the composting shed, an air collecting net installed inside the manure, a temperature sensor installed on the air collecting net, the manure placed on a water-leaking net, the water-leaking net being connected to a water receiving pan below it, an ammonia gas pipe connected to the upper part of the water receiving pan, an air pump and a one-way valve installed on the ammonia gas pipe, the outlet end of the ammonia gas pipe being connected to the lower part of a gas washing tank, a pH meter installed on the side wall of the gas washing tank, and an acid addition hopper and a gas balance pipe A installed on the upper cover of the gas washing tank.

[0005] The aforementioned gas washing tank has a finished product discharge valve installed on the discharge pipe at the bottom. The end of the discharge pipe connected to the bottom of the gas washing tank is a flexible hose, and the outlet end of the flexible hose is located above the finished product tank, which is located inside the hoisting cage.

[0006] The outlet end of the aforementioned water receiving tray is connected to the lower part of the water collection tank. The water collection tank is equipped with a submersible pump and a liquid level float switch. An air balance pipe B extends from the upper surface of the water collection tank. An activated carbon filter layer B and a rain cap B are provided at the upper end of the air balance pipe B.

[0007] The upper end of the aforementioned air balance pipe A is equipped with an activated carbon filter layer A and a rain cap A.

[0008] A method for preparing liquid nitrogen fertilizer by recovering nitrogen from cattle farm manure using the device described in claim 1 includes the following steps: Step (1) The dairy cow manure is placed in a composting shed, and the liquid in the manure is filtered through a drain net below and then enters a water receiving tray; Step (2) The ammonia gas produced by the fermentation of the manure is drawn into a gas washing tank through an ammonia pipe and a gas pump; Step (3) A dilute sulfuric acid solution with a concentration of 16.66 g / L is added to the gas washing tank. After the pH value of the solution in the gas washing tank is close to neutral and remains stable, the gas pump is automatically turned off, and the liquid nitrogen fertilizer ammonium sulfate is prepared; Step (4) The liquid nitrogen fertilizer ammonium sulfate is placed in a finished product tank through a discharge pipe, a finished product discharge valve, and a hose, and stored at room temperature for use as fertilizer; The nitrogen content of the liquid nitrogen fertilizer is 5.92%, and the pH value is neutral.

[0009] The fermentation temperature of the above-mentioned manure should be maintained at around 60 degrees Celsius. If the temperature is too high, it needs to be stirred to prevent the fermentation temperature from being too high and affecting the ammonia production.

[0010] An application of liquid nitrogen fertilizer prepared from nitrogen in cattle farm manure, which is then used in rice production, is presented as an organic combination with efficient fertilizer use in rice production.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] This application utilizes dilute sulfuric acid to absorb nitrogen from manure, converting volatile ammonia into stable ammonium sulfate, thereby reducing the nitrogen content of liquid nitrogen fertilizer to 5.92% and effectively recovering nitrogen from manure. The cost of dilute sulfuric acid for this recovery process is 0.66 yuan / m³. 3 Each liter of liquid nitrogen fertilizer can fix approximately 71.9g of ammonia, demonstrating superior overall performance compared to other acidifying agents. Liquid nitrogen fertilizer prepared using recycled manure from dairy farms and other livestock farms achieves efficient nitrogen resource recovery and provides high-quality nitrogen nutrients for crop production. Its application in rice production reduces nitrogen volatilization losses from manure, achieving an organic combination of nitrogen recycling and efficient rice fertilization. Attached Figure Description

[0013] Figure 1 It is a nitrogen recovery device.

[0014] Figure 2 This is a bar chart showing the effects of different fertilization treatments on rice yield. Detailed Implementation

[0015] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0016] Example 1: An apparatus for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer, comprising a composting shed 1 and manure 2 within the composting shed 1. The manure 2 ferments in the composting shed 1 to produce ammonia. A gas collecting net 4 is installed inside the manure 2 to facilitate the collection of ammonia. A temperature sensor 3 is installed on the gas collecting net 4 to monitor the temperature inside the manure 2. The fermentation temperature of the manure is maintained at approximately 60 degrees Celsius. If the temperature is too high, the manure 2 needs to be stirred to prevent excessive fermentation temperature from affecting ammonia production. The manure 2 is placed on a draining net 5, which is connected to a water receiving tray 6 below it. The liquid in the manure 2 is filtered through the draining net 5 and collected by the water receiving tray 6. To avoid environmental pollution, an ammonia gas pipe 9 is connected to the upper part of the water receiving tray 6. An air pump 10 and a one-way valve 11 are installed on the ammonia gas pipe 9. The outlet end of the ammonia gas pipe 9 is connected to the lower part of the gas washing tank 8. The ammonia gas produced by the fermentation of manure sludge 2 is pumped into the gas washing tank 8 through the ammonia gas pipe 9 by the air pump 10. The gas washing tank 8 contains a dilute sulfuric acid solution that reacts with the ammonia gas to produce liquid nitrogen fertilizer, ammonium sulfate. A pH meter 12 is installed on the side wall of the gas washing tank 8 to monitor the pH inside. When the pH in the gas washing tank 8 shows neutral or near-neutral, the reaction is complete, and the one-way valve 11 closes. An acid addition hopper 15 and a gas balance pipe A 17 are installed on the upper cover of the gas washing tank 8. Dilute sulfuric acid solution is added to the gas washing tank 8 through the acid addition hopper 15. An activated carbon filter layer A 19 and a rain cap A 18 are installed on the upper end of the gas balance pipe A 17.

[0017] The lower part of the gas washing tank 8 is equipped with a finished product discharge valve 16 on the discharge pipe. The end of the discharge pipe connected to the lower part of the gas washing tank 8 is a flexible hose 24. The outlet end of the flexible hose 24 is located above the finished product tank 23. The finished product tank 23 is located inside the hoisting rail 25. Liquid nitrogen fertilizer ammonium sulfate is placed inside the finished product tank 23.

[0018] The outlet end of the water receiving tray 6 is connected to the lower part of the water collection tank 7. The liquid collected by the water receiving tray 6 flows into the water collection tank 7. The water collection tank 7 is equipped with a submersible pump 13 and a liquid level float switch 14. When the liquid in the water collection tank 7 reaches a certain height, the liquid level float switch 14 responds, and the submersible pump 13 starts to pump out the liquid. An air balance pipe B 20 extends from the upper end of the water collection tank 7. The upper end of the air balance pipe B 20 is equipped with an activated carbon filter layer B 22 and a rain cap B 21. The gas in the water collection tank 7 is adsorbed by the activated carbon filter layer B 22 and discharged through the air balance pipe B 20.

[0019] Example 2: A method for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer, comprising the following steps:

[0020] Step (1): The cow manure is placed in the composting shed to ferment and produce ammonia. The liquid in the manure is filtered through the drain net below and then collected in the water collection tray 6.

[0021] Step (2): The ammonia gas produced by the fermentation of manure is drawn into the gas washing tank 8 through the ammonia gas pipe 9 and the gas pump 10.

[0022] Step (3): Add a dilute sulfuric acid solution with a concentration of 16.66 g / L to the gas washing tank. The dilute sulfuric acid solution reacts with ammonia. When the pH value of the solution in the gas washing tank is close to neutral and remains stable, it indicates that the reaction is complete. The gas pump will automatically shut off, and the liquid nitrogen fertilizer ammonium sulfate will be prepared.

[0023] Step (4): Place the liquid nitrogen fertilizer ammonium sulfate into the finished product tank 23 through the discharge pipe, finished product discharge valve 16, and hose 24, and store it at room temperature for use as fertilizer; the nitrogen content of the liquid nitrogen fertilizer is 5.92%, and the pH value is neutral.

[0024] Example 3: Application of the liquid nitrogen fertilizer described above. The liquid nitrogen fertilizer is applied to rice production. The liquid nitrogen fertilizer obtained in this application, abbreviated as LN, is applied to rice production:

[0025] The commercial nitrogen fertilizer is Yangfeng potassium sulfate compound fertilizer, abbreviated as PN, with an organic matter content ≥45%, N-P2O5-K2O: 14-16-15, a nitrogen content of 14.0%, and a neutral pH value. The recovered liquid nitrogen fertilizer prepared in this application is abbreviated as LN.

[0026] The experiment employed a randomized block design, dividing the field into 6 plots (2 basal fertilizer plots, 2 topdressing fertilizer plots × 3 replicates) in a 2 × 6 configuration, with each plot randomly arranged. Each plot was separated by a water-resistant partition, and the plant spacing was 13.5 cm × 30.0 cm. Four treatments were established: T1 (basal fertilizer: PN + topdressing: PN), T2 (basal fertilizer: PN + topdressing: LN), T3 (basal fertilizer: LN + topdressing: PN), and T4 (basal fertilizer: LN + topdressing: LN). Topdressing was applied twice, once before heading and once 5 days after heading. Field management, including irrigation, weeding, and pest and disease control, was carried out according to local conventional rice planting standards.

[0027] 3.1 Determination of agronomic indicators for rice:

[0028] Following transplanting, agronomic indicators such as plant height, tiller number, and leaf color were measured every two weeks. Plant height was measured from the ground to the highest point of the rice plant. Tiller number was determined by randomly selecting nine plants from each treatment area. Leaf color was measured on the flag leaf or uppermost leaf using a SPAD-502 chlorophyll meter, with three measurements taken at the midpoint of the leaf, and the average value was used as the leaf color observation data. After harvest, nine plants from each treatment group were collected to measure aboveground dry weight, brown rice weight, thousand-grain weight, paddy yield, straw yield, and crude protein (CP), among other yield and quality indicators.

[0029] Data processing: Experimental data were processed using Excel 2020. SPSS 23.0 statistical software was used for one-way ANOVA and Duncan's multiple comparisons. P < 0.05 was considered statistically significant. The results are shown in Tables 1, 2, and 3.

[0030] Table 1 Effects of different fertilization treatments on rice plant height

[0031]

[0032] Note: Different lowercase letters indicate significant differences between different fertilization treatments (P < 0.05), the same applies to the following table.

[0033] Table 1 shows that there were no significant differences in plant height among the different treatments at the seedling and tillering stages. At the jointing and booting stages, the T4 treatment had the lowest plant height (67.45 cm and 80.55 cm, respectively), significantly lower than the T1 and T2 treatments (P<0.05), indicating that the T4 treatment had the least impact on plant height at these stages. At the grain-filling stage, the T4 treatment had the lowest plant height (89.47 cm), significantly lower than the other treatments (P<0.05). At harvest, the T1 treatment had the highest plant height (95.86 cm), significantly higher than the other treatments (P<0.05). The growth trend of rice plant height was basically consistent throughout the entire growth period under different treatments: rapid growth from the seedling to the jointing stage, slower growth from the jointing to the grain-filling stage, and essentially ceasing growth from the grain-filling to harvest. At different stages, the plant height of the PN basal fertilizer treatment was 1.84%, 0.97%, 5.78%, 5.98%, 2.97%, and 3.03% higher than that of the LN basal fertilizer treatment, respectively.

[0034] Table 2. Effects of different fertilization treatments on the number of tillers in rice.

[0035]

[0036] Table 2 shows that the number of tillers in each treatment increased rapidly from the seedling stage to the jointing stage, with the rate of increase being slow at first and then fast, gradually stabilizing at the booting stage. The tillering stage was the period of rapid increase in the number of tillers, with the T3 treatment having the highest number of tillers (18), which was 20.0% higher than the T4 treatment. Each treatment reached its peak at the jointing stage, with the T1 and T2 treatments having slightly higher numbers of tillers than the T3 and T4 treatments, and the T4 treatment having the fewest. During the subsequent growth process, ineffective tillers disappeared, and the number of tillers in the T2 treatment remained at a high level. At the harvest, the number of tillers in each treatment was as follows: T2 > T1 > T3 > T4, indicating that the T2 fertilization treatment was beneficial in maintaining the needs of rice for subsequent growth and development.

[0037] Table 3 Effects of different fertilization treatments on rice leaf color

[0038]

[0039] Table 3 shows that the SPAD values ​​of rice under different fertilization treatments all exhibited a trend of first increasing and then decreasing. The leaf color values ​​of each treatment reached their peak at the tillering stage, and then gradually decreased as the growth progressed. This pattern of change is basically consistent with the physiological characteristics of nitrogen absorption and translocation during rice growth and development. At the seedling stage, the T1 treatment was slightly higher than the other treatments, while the values ​​of the other treatment groups were relatively similar. SPAD values ​​increased during the tillering stage, with increases of 4.45%, 6.75%, 0.80%, and 3.43% for treatments T1 to T4, respectively, with the T2 treatment showing the most significant increase. From the jointing stage to harvest, the values ​​gradually decreased, with decreases of 13.58%, 11.29%, 5.30%, and 7.80% for treatments T1 to T4, respectively. At harvest, the SPAD values ​​for each treatment were: T1 > T3 > T4 > T2.

[0040] The effects of different fertilization treatments on rice yield are shown in the figure. Figure 2 ,Depend on Figure 2 As shown in Figure a, regarding the total weight of the aboveground parts, there were no significant differences among treatments T1, T2, and T3, but all were significantly higher than treatment T4 (P<0.05). Treatment T3 increased yield by 1.49%, 3.36%, and 15.18% compared to the other treatments, respectively. The yield distribution was as follows: T3 (1025.34 kg) > T1 (1010.32 kg) > T2 (992.01 kg) > T4 (890.21 kg). Rice yield is a direct indicator of fertilization effectiveness. Figure 2 b indicates that treatments T3 and T1 had higher rice yields, with no significant difference between them, but treatment T3 was slightly higher than treatment T1. Treatment T2 was next, with no significant difference compared to treatments T1 and T3. Treatment T4 had the lowest rice yield, significantly lower than treatments T1, T2, and T3 (P<0.05). Treatment T3 increased yield by 1.28%, 4.34%, and 13.51% compared to the other treatments, respectively. The yield distribution was: T3 (570.77 kg) > T1 (563.55 kg) > T2 (547.05 kg) > T4 (502.87 kg). Rice straw yield reflects the growth status of vegetative organs. Figure 2 c indicates that there were no significant differences among treatments T1, T2, and T3, but all were significantly higher than treatment T4 (P<0.05). Treatment T3 had the highest straw yield, exceeding the other treatments by 1.75%, 2.16%, and 17.35%, respectively. The order of yield was: T3 (454.57 kg) > T1 (446.77 kg) > T2 (444.96 kg) > T4 (387.34 kg). Figure 2As shown in Figure d, the brown rice yield did not differ significantly among treatments T1, T2, and T3, but was significantly higher in T3 than in T4 (P<0.05). The yield distribution was as follows: T3 (473.81 kg) > T1 (465.60 kg) > T2 (451.55 kg) > T4 (411.99 kg). Thousand-grain weight is a crucial factor in yield composition. Figure 2 As shown in the data, the thousand-grain weight of each treatment was: T3 (24.21 g) > T4 (23.83 g) > T1 (23.70 g) > T2 (23.17 g), with no significant differences among the treatments. CP content is an important indicator for evaluating the nutritional quality of rice. Figure 2 f indicates that treatments T1 and T2 were significantly higher than treatment T3 (P<0.05), while treatment T4 did not show significant differences compared to other treatments. The crude protein content of each treatment was as follows: T1 (8.25%) > T2 (8.24%) > T4 (8.02%) > T3 (7.91%).

[0041] The results showed that, in terms of agronomic traits, the plant height of group T1 at harvest was higher than that of other groups (P<0.05), the number of tillers was in the order of T2>T1>T3>T4, group T2 was more conducive to maintaining the subsequent growth and development needs of rice, and the chlorophyll content (SPAD) value was in the order of T1>T3>T4>T2. In terms of rice yield, the total weight of aboveground parts, brown rice yield and paddy yield of groups T1, T2 and T3 were all higher than those of group T4 (P<0.05).

[0042] 3.2 The costs and benefits of rice cultivation under different fertilization treatments are shown in Table 4:

[0043] Table 4. Costs and benefits of rice cultivation under different fertilization treatments

[0044]

[0045] Note: PN: 3.2 yuan / kg (market reference price), LN: 1.5 yuan / kg (including 0.66 yuan / m³ of dilute sulfuric acid absorbent treatment cost and application cost); rice purchase price: 2.6 yuan / kg, rice straw income: 0.4 yuan / kg; base fertilizer labor cost: including transplanting and base fertilizer application labor; topdressing cost: including two topdressings, with a single topdressing cost of 15 yuan / mu; field management cost: including pesticides, irrigation and drainage, weeding, etc. The increase in income is compared with T1 treatment (all commercial fertilizer), and the calculation formula is: Increase in income = Treatment profit - T1 profit.

[0046] As shown in Table 4, treatment T3 yielded the highest profit at 1305.1 yuan / mu, an increase of 10.5 yuan / mu compared to treatment T1. Treatment T1 yielded a profit of 1294.6 yuan / mu, slightly lower than treatment T3, but it had the lowest fertilizer cost due to its high PN nutrient content and low application rate per unit area. Treatment T2 yielded a profit of 1239.6 yuan / mu, a decrease of 55.0 yuan / mu compared to treatment T1. Treatment T4 had the lowest yield, with a profit of only 1090.2 yuan / mu, a decrease of 204.4 yuan / mu compared to treatment T1.

[0047] Effects of fertilization treatments on rice growth traits: Plant height is an important growth trait reflecting the growth status and nutritional status of rice populations. Its variation is closely related to nitrogen supply levels. Nitrogen fertilizer can promote the growth and development of rice, enhance photosynthesis, and LN replacing traditional fertilizers can increase rice plant height. Appropriate nitrogen fertilizer can improve soil physicochemical properties, enhance soil water and fertilizer retention capacity, promote root growth and nutrient absorption, and provide sufficient materials and energy for stem elongation. In this application, treatments T1 and T2 showed relatively high levels at all rice growth stages, while treatment T3 showed no significant difference from treatment T2, indicating that the effect of LN as basal fertilizer or topdressing mixed with PN was not significantly different from that of PN.

[0048] Rice exhibits tillering behavior, and the number of tillers determines the number of panicles, photosynthetic area, and panicle formation rate, thus affecting rice yield. The number of tillers peaks at the jointing stage, with the T4 treatment having the fewest tillers, which was also the lowest at harvest, possibly due to nutrient loss from ln (live nitrogen). Ln can promote early and effective root development in rice, encouraging early tillering and rapid growth. When PN (phosphorus nitrogen) is mixed with Ln fertilizer, the difference in tiller number is minimal.

[0049] Leaf color is an important indicator reflecting the nitrogen nutritional status and physiological metabolic activity of rice. Increased chlorophyll content reduces the attenuation rate in the later stages of plant growth and can delay leaf senescence. Chlorophyll content is related to the accumulation of dry matter at rice maturity. In this application, treatment T1 maintained the highest SPAD value at both the jointing and harvest stages, demonstrating good leaf function maintenance ability. Treatment T2 showed the largest increase in SPAD value at the tillering stage, but the largest decrease from the jointing to harvest stage, possibly related to the faster nitrogen translocation to grains in the later stages of growth. Treatment T4 showed an increased decrease in chlorophyll content during the booting stage, similar to plant height, presumably because LN is in liquid form and is lost during later topdressing, indicating that its nutrient retention and supply stability are significantly weaker than other treatments, making it prone to rapid loss of key nutrients such as nitrogen and phosphorus due to field water leaching or runoff. Insufficient nutrient supply stability of LN in the later stages leads to inhibited chlorophyll synthesis and accelerated degradation. Other treatments, which combined PN and LN, showed significant improvements in plant height, tiller number, and leaf color. Rice cannot obtain a continuous supply of nutrients during its critical growth period. Different fertilizers hinder the synthesis and accelerate the degradation of chlorophyll in rice, while plant height growth is also limited due to insufficient nutrients.

[0050] The effects of different fertilization treatments on rice yield, planting costs, and profits: Rice yield is determined by both growth and nutrient supply. In this study, treatments T1, T2, and T3 showed significantly higher total aboveground weight, brown rice yield, and paddy yield than treatment T4. This result is consistent with the results regarding plant height, tiller number, and leaf color. This indicates that the combined application of nitrogen (LN) and phosphorus (PN) or pure PN treatment can effectively promote dry matter accumulation and yield formation in rice, while the yield-increasing effect of pure LN treatment is relatively limited. Treatment T4, due to the weak retention and supply stability of LN nutrients, resulted in the loss of nitrogen and phosphorus nutrients in the later stages of growth. This not only accelerated chlorophyll decay during the booting stage and resulted in a persistently low tiller number, but also ultimately restricted dry matter accumulation and yield formation, which is consistent with previous hypotheses regarding LN nutrient loss. Treatment T3 yielded the highest rice yield, increasing by 13.51% compared to treatment T4. Calculations showed a high grain-to-straw ratio, indicating that the combined application of LN as basal fertilizer and PN as topdressing effectively coordinates vegetative and reproductive growth, promoting the distribution of photosynthetic products to the grains. Analysis of thousand-grain weight, grain-to-straw ratio, and CP content showed that treatments T3 and T4 had relatively higher thousand-grain weights, but treatment T4 experienced a reduced yield due to insufficient tiller numbers. Treatments T1 and T2 had the highest CP content, reflecting superior grain protein content or seed setting rate, further demonstrating the advantages of combined PN and LN application.

[0051] LN can serve as an effective nitrogen source for rice, and the combined application of PN and LN is more effective than LN alone. In terms of growth traits, treatments T2 and T3 showed no significant differences or only minor differences compared to treatment T1 in terms of plant height, tiller number, and leaf color, indicating that LN, whether used as basal fertilizer or top dressing, can achieve growth-promoting effects similar to pure PN when applied together. Regarding yield, the rice yields of treatments T2 and T3 were not significantly different from those of treatment T1, and were significantly higher than those of treatment T4, further validating the feasibility of combining LN and PN. The treatments using the combined fertilizers showed significant advantages in both yield and growth indicators, suggesting that the combined fertilizer provides a more stable nutrient supply, ensuring continuous nutrient supply during key growth stages of rice and promoting the accumulation and translocation of photosynthetic products. The lower yield in treatment T4, which used LN throughout the growing season, validates the earlier hypothesis that LN is easily lost in the field. In practical applications, the application method of LN should be optimized to improve fertilizer utilization and the stability of rice yield.

[0052] Whether ln (nitrogen) can be accepted by rice farmers depends on its economic benefits. The mixed application treatments T2 and T3 can guarantee rice yield while reducing the amount of commercial nitrogen fertilizer used, with planting benefits roughly equivalent to the all-commercial fertilizer treatment T1, although the profit of treatment T3 is higher than that of treatment T1. In a market where PN (nitrogen peroxide) prices are high, the mixed application of ln and PN can not only effectively reduce fertilizer input costs but also guarantee and slightly improve planting benefits. Existing research shows that replacing some chemical fertilizers with bio-fertilizers, organic fertilizers, and recycled fertilizers can significantly improve the economic benefits of rice cultivation. Pure ln treatments, due to the easy loss of nutrients, result in a significant decrease in both yield and profit. Therefore, it is not advisable to replace PN alone in actual production; the application method of ln should be further optimized to improve fertilizer utilization and the stability of rice yield. Different fertilization treatments affect yield formation by regulating the rice growth and development process and nutrient supply efficiency. The mixed application of PN and ln can achieve a synergistic effect of high yield and efficient nutrient utilization.

[0053] The results showed that the optimal application scheme for liquid nitrogen fertilizer recovered from dairy cow manure in rice production is "commercial nitrogen fertilizer + liquid nitrogen fertilizer," and the dosage can be flexibly adjusted according to crop needs during application. This application provides data and technical reference for the use of liquid nitrogen fertilizer prepared from recovered manure in large-scale dairy farms for the production of crops such as rice, reducing nitrogen loss and environmental pollution caused by ammonia volatilization, achieving cost reduction and efficiency improvement, and promoting green agricultural development through integrated crop and livestock farming.

Claims

1. An apparatus for recovering nitrogen from cattle farm manure to prepare liquid nitrogen fertilizer, comprising a composting shed (1) and manure (2) within the composting shed (1), characterized in that: A gas collection net (4) is installed inside the feces (2). A temperature sensor (3) is installed on the gas collection net (4). The feces (2) is placed on a water leakage net (5). The water leakage net (5) is connected to the water receiving pan (6) below it. An ammonia pipe (9) is connected to the upper part of the water receiving pan (6). An air pump (10) and a one-way valve (11) are installed on the ammonia pipe (9). The outlet end of the ammonia pipe (9) is connected to the lower part of the gas washing tank (8). A pH meter (12) is installed on the side wall of the gas washing tank (8). An acid addition hopper (15) and a gas balance pipe A (17) are installed on the upper end cover of the gas washing tank (8).

2. The apparatus for preparing liquid nitrogen fertilizer from cattle farm manure according to claim 1, characterized in that: The gas washing tank (8) is equipped with a finished product discharge valve (16) on the discharge pipe at the bottom. The end of the discharge pipe connected to the bottom of the gas washing tank (8) is a flexible hose (24). The outlet end of the flexible hose (24) is located above the finished product tank (23). The finished product tank (23) is located inside the hoisting railing (25).

3. The apparatus for preparing liquid nitrogen fertilizer from cattle farm manure according to claim 1, characterized in that: The outlet end of the water receiving tray (6) is connected to the lower part of the water collection tank (7). The water collection tank (7) is equipped with a submersible pump (13) and a liquid level float switch (14). An air balance pipe B (20) extends from the upper surface of the water collection tank (7). An activated carbon filter layer B (22) and a rain cap B (21) are provided at the upper end of the air balance pipe B (20).

4. The apparatus for preparing liquid nitrogen fertilizer from cattle farm manure according to claim 1, characterized in that: The upper end of the gas balance pipe A (17) is equipped with an activated carbon filter layer A (19) and a rain cap A (18).

5. A method for preparing liquid nitrogen fertilizer by recovering nitrogen from cattle farm manure using the apparatus of claim 1, comprising the following steps: Step (1): Place the cow manure in the composting shed. The liquid in the manure is filtered through the drain net below and then enters the water collection tray (6). Step (2): The ammonia gas produced by the fermentation of manure is drawn into the gas washing tank (8) through the ammonia gas pipe (9) and the gas pump (10); Step (3): Add a dilute sulfuric acid solution with a concentration of 16.66 g / L to the gas washing tank. After the pH value of the solution in the gas washing tank is close to neutral and remains stable, the gas pump will automatically shut off, and the liquid nitrogen fertilizer ammonium sulfate will be prepared. Step (4): Place the liquid nitrogen fertilizer ammonium sulfate into the finished product tank (23) through the discharge pipe, finished product discharge valve (16), and hose (24), and store it at room temperature for fertilization; the nitrogen content of the liquid nitrogen fertilizer is 5.92%, and the pH value is neutral.

6. The method for preparing liquid nitrogen fertilizer from cattle farm manure using the apparatus according to claim 5, characterized in that: The fermentation temperature of manure should be maintained at around 60 degrees Celsius. If the temperature is too high, it needs to be stirred to prevent the fermentation temperature from being too high, which would affect the loss of ammonia and thus the amount of nitrogen recovered.

7. The application of the method for preparing liquid nitrogen fertilizer from cattle farm manure according to claim 5, wherein the liquid nitrogen fertilizer is applied to rice production, can reduce the loss of nitrogen volatilization in manure and realize the organic combination of nitrogen recycling and efficient fertilization of rice.

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