CN113024327B

CN113024327B - Method for increasing organic carbon content of soil by applying inorganic nutrients to straw returning field

Info

Publication number: CN113024327B
Application number: CN202110564048.5A
Authority: CN
Inventors: 蔡岸冬; 武红亮; 肖婧; 王斌; 万云帆; 高清竹; 李玉娥
Original assignee: Institute of Environment and Sustainable Development in Agriculturem of CAAS
Current assignee: Institute of Environment and Sustainable Development in Agriculturem of CAAS
Priority date: 2021-05-24
Filing date: 2021-05-24
Publication date: 2021-09-21
Anticipated expiration: 2041-05-24
Also published as: CN113024327A

Abstract

The invention discloses a method for increasing the content of organic carbon in soil by returning straws to a field and applying inorganic nutrients. Belongs to the field of straw returning technology. Applying the following components in soil to be improved: 12.5g/kg of straws, 16.3-49.0 mg/kg of ammonium nitrate, 12.2-36.5 mg/kg of monopotassium phosphate and 3.3-10.0 mg/kg of ammonium sulfate. Compared with the prior art, the invention has the following beneficial effects: the invention considers that the difference of the composition of the straw and the soil element limits the high-efficiency humification process of the straw. Therefore, the invention adds inorganic nutrients while returning the straws to the field, and the nutrient requirement proportion of C: N: P: S =10000:860:169:129 is followed in the conversion of the straws C. The addition of nutrients and exogenous organic materials can enhance the mineralization and decomposition effects of natural SOC, and meanwhile, the straw carbon can form new soil SOC according to a constant carbon-nutrient ratio.

Description

Method for increasing organic carbon content of soil by applying inorganic nutrients to straw returning field

Technical Field

The invention relates to the technical field of straw returning, in particular to a method for increasing the content of organic carbon in soil by returning straw to field and applying inorganic nutrients.

Background

Soil carbon sequestration in agroecological systems is a major measure to mitigate climate change, and small changes in soil carbon reserves can significantly affect the biogeochemical cycle of carbon. Crop straw returning has been widely recommended as an effective field management practice to improve Soil Organic Carbon (SOC).

At present, the understanding of sustainable contribution of straw returning to soil new carbon generation (conversion of straw carbon into soil carbon) is not enough, and even research shows that the improvement of the input amount of crop straws on the improvement of SOC in soil with different fertility is still low, and even no obvious improvement effect exists.

In conclusion, how to provide a method for driving a larger proportion of straw carbon to be transferred into soil new carbon is a problem to be solved urgently by the technical personnel in the field.

Disclosure of Invention

In view of the above, the invention provides a method for increasing the organic carbon content of soil by returning straws to fields and applying inorganic nutrients.

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

a method for increasing the content of organic carbon in soil by returning straws to the field and applying inorganic nutrients comprises the following steps: 12.5g/kg of straws, 16.3-49.0 mg/kg of ammonium nitrate, 12.2-36.5 mg/kg of monopotassium phosphate and 3.3-10.0 mg/kg of ammonium sulfate.

12.5g/kg of straw, i.e. 1kg of soil to be improved (dry weight of soil), is applied with 12.5g of straw.

The beneficial effects are as follows: from the aspect of element composition and proportion, the straw is rich in carbon and less nutrients, wherein the proportion of C to nutrient elements is obviously higher than the element proportion in the soil (straw C: N: P: S =10000:225:29: 32). The invention considers that the difference of the composition of the straw and the soil element limits the high-efficiency humification process of the straw. Therefore, the invention adds inorganic nutrients while returning the straws to the field, and the nutrient requirement proportion of C: N: P: S =10000:860:169:129 is followed in the conversion of the straws C. The addition of nutrients and exogenous organic materials can enhance the mineralization and decomposition effects of natural SOC, and meanwhile, the straw carbon can form new soil SOC according to a constant carbon-nutrient ratio.

Further, the ammonium nitrate, the monopotassium phosphate and the ammonium sulfate are added in the form of a nutrient solution.

Further, the pH value of the nutrient solution is 7.

Further, the pH regulator of the nutrient solution is used for regulating the pH value of the nutrient solution by using a 10M sodium hydroxide solution.

Further, the straw is corn straw.

Furthermore, the straws are dried straws and cut into 2mm fragments.

Furthermore, the total carbon content in the straws is 42.8% w/w, the total nitrogen content is 0.97% w/w, the total phosphorus content is 0.12% w/w, and the total sulfur content is 0.11% w/w.

Further, the soil moisture content was 60%.

According to the technical scheme, compared with the prior art, the invention has the following beneficial effects: the invention considers that the difference of the composition of the straw and the soil element limits the high-efficiency humification process of the straw. Therefore, the invention adds inorganic nutrients while returning the straws to the field, and the nutrient requirement proportion of C: N: P: S =10000:860:169:129 is followed in the conversion of the straws C. The addition of nutrients and exogenous organic materials can enhance the mineralization and decomposition effects of natural SOC, and meanwhile, the straw carbon can form new soil SOC according to a constant carbon-nutrient ratio.

Drawings

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

FIG. 1 is a graph showing the relationship between the total carbon and total nitrogen, organic phosphorus, and total sulfur of soil stabilizing organic components in example 1 of the present invention, wherein (a) is a C: N result, (b) is a C: P result, and (C) is a C: S result;

FIG. 2 is a graph showing the change in the content of the soil-stabilizing organic component before and after acid washing in example 1 of the present invention, wherein (a) is a result of the carbon component, (b) is a result of the nitrogen component, (c) is a result of the organic phosphorus component, and (d) is a result of the sulfur component;

FIG. 3 is a graph showing the soil respiration during the cultivation of princess ridge (a) and Helen (b) in example 2 of the present invention;

FIG. 4 is a graph showing the effect of the addition or non-addition of straw and nutrients on (a) new carbon formation and (b) old carbon decomposition in example 2 of the present invention.

Detailed Description

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

The medicament required by the embodiment of the invention is a conventional experimental medicament purchased from a commercially available channel; the experimental methods not mentioned in the examples are conventional experimental methods, and are not described in detail herein.

Example 1

(1) Sample collection

Selecting four typical farmland soil areas with different reclamation years and carbon levels as sampling points on a northeast long and narrow black land belt, wherein the four typical farmland soil areas comprise: in a thick-layer black soil area, the cultivation is carried out for 40-60 years, and the variation range of the soil SOC level is 3.23-4.61%; helen: in the medium-thick black soil area, the cultivation is carried out for 80-100 years, and the organic carbon level of the soil is changed within the range of 2.73-4.62%; double cities: a middle-layer black soil area is cultivated for 100-150 years, and the organic carbon change range of the soil is 1.62-2.77%; princess ridge: in a shallow black soil area, the cultivation period is more than 200 years, and the organic carbon variation range of soil is 1.10-1.76%.

After the crop is harvested in 2017, soil of a farmland plough layer is collected by using a soil drill from north to south in 4 sampling areas (Beian (40 sampling points), Heilong (39 sampling points), Shuangcheng (32 sampling points) and princess ridge (41 sampling points)) to be tested to be used as a soil sample. And selecting sampling points of the same field according to a snake-shaped sampling method according to the principles of random, equivalent and multipoint mixing. The specific method comprises the following steps: selecting more than 10 basic sample points in the same field, wherein the sample point interval is more than 100m, the sampling depth is 0-20 cm, and uniformly mixing the soil samples into one soil sample after multi-point sampling. And at the same time of sampling, the environmental conditions, soil fertility, production management level and black soil reclamation utilization history of each sampling point are investigated in detail, and GPS positioning is carried out.

(2) Grouping of soil samples

After the soil sample is air-dried, the soil sample is lightly rolled and crushed along the soil aggregate weakening texture layer by hand and then passes through a sieve with the diameter of 2 mm. Carefully remove all identifiable gravel, debris and vegetable-like material (coarse organic matter component, ≧ 2 mm) from the top of the screen. The fraction passing through the 2mm sieve was then further sieved using a 0.4 mm sieve and carefully cleaned of any visible vegetable-like light fraction (coarse organic fraction, ≧ 0.4 mm) above the 0.4 mm sieve. And finally, mixing the coarse organic components with the diameters of more than or equal to 2mm and more than or equal to 0.4 mm to obtain coarse organic matters (CF-SOM), and taking the rest components as stable organic matters (FF-SOM).

(3) Index and method of measurement

And selecting a sub-sample of the coarse organic components and the stable organic components of the soil sample at each point, and passing the sub-sample through a 0.15 mm sieve to perform CNPS element determination. Wherein, the contents of C, N and S in the soil are measured by using an element analyzer (Hanan, Germany); the total phosphorus of the soil is determined by a sodium carbonate melting-molybdenum-antimony colorimetric resistance method, and the organic phosphorus of the soil is determined by a burning-sulfuric acid leaching method. In order to obtain an accurate metering ratio of C to N to P to S of soil and avoid overestimating the NPS content in soil stable organic matters, on the basis of measuring all organic components of undisturbed soil, meanwhile, typical soil stable organic matters under long-term straw returning and centralized optimization management in 4 points of Bei' an, Hailong, Shuangcheng and princess mountains are washed by 0.1 mol/L hydrochloric acid, and the CNPS content of the soil after acid washing is measured by adopting the same method.

(4) Data analysis

All data were collated using Excel 2016 (Microsoft, Redmond, WA, USA). Values in the results are reported as the mean of the three replicates ± standard error. Firstly, one-way analysis of variance (ANOVA) and duncan multivariate comparison (P < 0.05) were used to determine the significant differences in element content and element ratio in the organic components of the soil before and after pickling. Soil C was then linearly regressed with N, P and S by SPSS version 20 (IBM, Chicago, IL, USA) to determine the strength of the C: N, C: P and C: S linear relationships. Finally, the exact N, P and S contents required for assimilation of the unit mass C in the stabilized SOM were determined by comparing the CNPS content and the elemental ratio in the organic components of the soil before and after pickling.

(5) Results

(51) Element composition characteristics of different organic components of black soil

TABLE 1 content and metering ratio of different organic components CNPS in each soil point

Note: the numbers after "±) are the standard error of the mean (n = 3). Significant differences in different organic matter fractions in each soil are indicated by different lower case letters (P < 0.05).

Coarse organic matters are removed from soil at each point to obtain stable organic matters, and the mass ratio of the two components to undisturbed soil is 1.42% (1.28% -1.62%) and 98.58% (98.38% -98.72%) respectively. The content ranges of C, N, P, S in the coarse organic matter of the soil at each point are respectively 7.3-10.0%, 0.36-0.54%, 0.04-0.07% and 0.04-0.06%, and the average values of the C, N, P, S and the C, N, P, S are respectively 3.1 times, 2.2 times, 1.3 times and 1.7 times of the content of C, N, P, S in the stable organic matter. The proportion of C to N, particularly C to P and C to S in the rough organic matter of the soil at different points is obviously different and is obviously higher than that of C to N, P and S in the stable organic matter. The content of C in the soil stable organic matter is gradually increased from south to north (princess ridge, double cities, Helen and Beian) on a black soil zone, the change range is 1.4-3.8%, and the change trends of nutrients N, P and S are similar to the change trends. The ratio of C to N, C to P and the ratio of C to S in the soil stabilizing organic matter at each point are maintained in a relatively stable and narrow range, and the ratio is 11-13, 65-73 and 69-80 respectively. It can be seen that the element proportion of C, N, P and S in the soil stabilized organic matter is relatively stable and is obviously lower than that of the coarse organic matter, and the content of NPS element which can be stably supported by organic carbon with unit mass in the stabilized organic matter is higher than that of the coarse organic matter.

(52) CNPS (carbon black polystyrene) metering ratio of stable organic components in black soil

The ratio of total carbon to total nitrogen, organic phosphorus, and total sulfur in the soil stabilizing organic components is shown in FIG. 1.

An undifferentiated significant relation (R) exists between N, S and C in the soil stable organic matter at each point²=0.9163 and 0.9040, P<0.001). Data and fitting equations show that C of unit mass in each point soil stable organic matter is obviously related to a certain proportion of N or S. The invention relates to a method for establishing a relation between soil total phosphorus and soil carbon by replacing the total phosphorus with organic phosphorus. Establishing a regression relationship between C and P of each point soil stable organic matter, and finding that the content of C in the soil stable organic matter per unit mass and the content of organic phosphorus also have an obvious linear relationship (R)²= 0.7636). The linear relation strength of N, S and C in the soil stabilized organic matter is superior to that of P and C. In addition, the linear relation strength of P and C in the soil stable organic matter at each point position which is independently established is weaker (R)²=0.2646~ 0.6882). As can be seen, stable C: N, C: S and C: P proportion relation can exist in the black soil stable organic matter.

(53) Content variation of stabilized organic component (acid-washed) CNPS in Black soil

The change in the contents of carbon (a), nitrogen (b), phosphorus (c) and sulfur (d) which are organic components for soil stabilization before and after pickling is shown in FIG. 2.

The C, N and S element contents of the soil stabilized organic matter sample after acid washing are obviously reduced compared with those before acid washing (P is less than 0.05, and figure 2). The content of stable organic matter C in the double city and Helen soil after acid washing is slightly reduced by 2.0 percent and 2.9 percent respectively, which are reduced by 4 percent and 3 percent compared with the content before acid washing. The C content in the stabilized organic matter of the princess ridge and the Beian soil has no obvious change before and after acid cleaning. The N content of the post-washing organic acid stabilized by the soil of princess mountain, Shuangcheng, Helen and Beian is respectively 0.13%, 0.16%, 0.23% and 0.27%, which are respectively reduced by 11%, 8%, 6% and 5% compared with the N content of the post-washing organic acid stabilized by the soil of princess mountain, Shuangcheng, Helen and Beian. The contents of S in the post-washing organic acid stabilized by the soil of princess mountain, Shuangcheng, Helen and Beian are respectively 0.022%, 0.025%, 0.036% and 0.046%, which are respectively reduced by 11%, 13%, 16% and 10% compared with the contents before acid washing. Due to the special adsorption and fixation states of the phosphorus in the soil, the content of organic phosphorus in the stabilized organic matter of each point soil has no obvious change before and after acid cleaning.

(54) Accurate metering ratio of elements of stable organic components of black soil

TABLE 2 content ratio of carbon, nitrogen, phosphorus and sulfur in organic components stabilized in soil before and after pickling

Note: the numbers after "±) are the standard error of the mean (n = 3). Significant differences in the ratios of the individual soil elements are indicated by different lower case letters (P < 0.05). Indicates that the proportion of elements increased after washing with the hydrochloric acid solution.

The changes of the average ratio of C to N, C to P and C to S in the soil stable organic matter at each point before and after pickling are shown in Table 2. After the soil is washed by hydrochloric acid, the proportion of C to N, C to P and the proportion of C to S in the soil stable organic matter have no obvious difference between different point positions (excluding the proportion of C to P in Helen soil). After acid washing, the ratio of C to N, C to P and C to S in the soil stabilized organic matter is improved to different degrees, which shows that the inorganic nutrients, especially the inorganic N and S nutrients in the soil stabilized organic matter can be removed by hydrochloric acid washing. After acid washing, the proportion of C to S in the stable organic matters of the soil at each site is remarkably improved (P is less than 0.05), and the proportions of C to S in the stable organic matters of the soil at each site are respectively improved by 7.6%, 10.6%, 15.4% and 9.2% at princess mountains, double cities, Helen and North Ann sites. The C to N ratio of the soil at the princess ridge and the double-city point is respectively improved by 8.4 percent and 6.8 percent. Before and after acid washing, the ratio of the stable organic matter C to P in the soil is relatively stable, which is consistent with no significant change before and after acid washing of the organic phosphorus content shown in FIG. 2. In a word, after the inorganic nutrients are removed by acid washing, the ratio of C elements to nutrient elements is improved by 6.8-15.4%.

The typical farmland soil in different areas of a black soil area and within the reclamation age is taken as a research object, the relatively stable C: N: P: S metering ratio in the soil stable organic matter is disclosed, and the nutrient content of N, P and S required by carbon sequestration in the soil stable organic matter can be avoided from being overestimated through acid washing, so that the more accurate C: N: P: S metering ratio is obtained. The coefficient of variation of the ratios of C: N, C: P and C: S in the coarse black soil organic matter is higher (compared with the stable organic matter), and is respectively 7.1%, 22.2% and 12.3%. This result illustrates that there is no relatively stable and narrow interval for the C: N, C: P and C: S ratios due to the coarse organic matter instability characteristics of soils (primarily of vegetable material origin). However, there is a relatively stable ratio of C: N, C: OP and C: S in soil stabilized organic matter, which is supported by the strong linear relationship of C to N, OP and S in soil stabilized organic matter. Inorganic nutrients, particularly N and S, in the soil can be effectively removed through acid washing, so that N and S nutrients required by carbon assimilation per unit mass in the soil stabilized organic matter are avoided being overestimated, and C: N: P: S in the soil stabilized organic matter is accurately obtained. The invention provides favorable evidence for the relatively stable C: N: P: S metering ratio in the soil stable organic matter, and provides scientific basis for improving the assimilation efficiency of exogenous carbon and establishing the connection with the availability of soil nutrients.

Example 2

(1) Soil sample collection and preparation

In 2018 in 10 months, two long-term positioning tests of returning crop straws to the field in a northeast black soil area are selected, and soil with the surface layer of 0-20 cm is collected to serve as a soil sample to be tested: (1) jilin princess ridge (northern latitude 43 ° 30 ', east longitude 124 ° 48'); (2) heilongjiang Helen (47 ° 27 'north latitude, 126 ° 55' east longitude). Both sites were field-returning tests with crop straw and chemical nitrogen, phosphorus and potassium fertilizer applications since 1990 (see table 3 for details). Before the positioning test was conducted, the princess's mountains and the point of the herons had been agricultural for at least 150 years and 60 years, respectively. The collected soil samples were air dried naturally in a cool, ventilated place while soil aggregates were gently crushed by hand along the edges of the weakened texture and then passed through a 2mm sieve. While sieving, all identifiable gravel, debris and vegetable-like material (coarse fraction of SOM, CF-SOM. gtoreq.2 mm) were carefully removed. The soil sample passed through the 2mm sieve was further sieved through a 0.4 mm sieve to remove the remaining CF-SOM on the top of the 0.4 mm sieve according to the method described by Kirkby et al. The invention takes the soil (small part of SOM) left after removing CF-SOM as a research object. The basic physicochemical properties of the soil samples are shown in Table 4.

TABLE 3 Long-term location of test points straw and fertilizer application management introduction

Table 4 summary of test points and soil base attributes

Note: the numbers after "±) are the standard error of the mean (n = 3).

An appropriate amount of soil sample was selected through a 0.15 mm sieve and analyzed for C, N and S content using an elemental analyzer (Hanau, Germany). Soil organophosphorus was determined by calcination-extraction (alignment-extraction) procedure. The soil was analyzed for atom% using an elemental analyzer (Sercon Ltd, Cheshire, UK) coupled to a PDZ Europa 20-20 isotope mass spectrometer¹³C. The soil pH was measured with an electrode pH meter at a soil to water ratio of 1: 5.

(2) Straw and nutrient treatment

To highlight the differential change in soil new carbon formation, we set the corn stover addition to 12.5g kg⁻¹soil dry weight (equivalent to 7.5 tha of 0-20 cm soil body)⁻¹Twice the equivalent of returning the straws to the field (the soil volume weight is 1.24 t m)⁻³). By harvesting¹³CO₂The aerial parts of the mature corns marked by the pulses are used as rich standard straw donors and are dried at the constant temperature of 60 ℃. Corn stover was chopped into 2mm long pieces before mixing with the soil sample.¹³The final chemical analysis of the C-labeled straw was: total carbon is 42.8%; total nitrogen 0.97%; total phosphorus 0.12%; total sulfur 0.11% and atom%¹³C 1.48％。

Five treatments are set for each soil: soil control (S), soil + straw (S + St), soil + straw + low nutrient (S + St + Lnu), soil + straw + medium nutrient (S + St + Mnu) and soil + straw + high nutrient (S + St + Hnu) (table 5). The nutrient gradient was set based on the following findings: n, P and S nutrient supplement can enhance the humification efficiency of the straw-C. The addition level of low amount of nutrients is based on 30% humification (idealized rot rate) in straw C to form new soil carbon and follows the ratio of C: N: P: S =10000:860:169:129 nutrient demand in straw C conversion. Medium and high nutrient addition levels were set at 2 and 3 times the low nutrient addition levels, respectively. The nutrients N, P and S are added as a nutrient solution prepared from ammonium nitrate, potassium dihydrogen phosphate and ammonium sulfate. The pH of the nutrient solution was adjusted to 7 with 10M sodium hydroxide solution.

TABLE 5 straw and nutrient addition treatment

(3) Culture set-up

The prepared straws and soil are evenly mixed on a smooth and soft plastic plate. First, nutrient solution was added or not to the mixture of soil and straw, then distilled water was added to ensure that the soil achieved 60% field capacity. The soil samples with different nutrient additions at two places are placed in a constant temperature incubator (25 ℃) and are cultured for 84 days in a dark place. Each treatment contained 15 replicate samples of 40 g soil, each replicate sample being placed in a round plastic tube with two open ends, the tube having a diameter of 50 mm and a height of 60 mm. The bottom of each plastic tube was wrapped with nylon cloth (0.074 mm) to prevent the soil sample from overflowing, but to allow gas exchange. The plastic tube containing the soil sample was placed in a 500 ml Meisen flask equipped with a three-way valve. Distilled water was applied to the bottom of each flask to prevent water loss during the culture. The plastic tube was supported above the water surface by a circular support (diameter 50 mm, height 30 mm). Each mixed soil and straw sample was first added with nutrient solution and then distilled water to obtain a field capacity of 60%. The mixture was periodically injected into 50 ml syringes (No. 1, 7, 14, 28, 56,84 days) carbon dioxide gas was collected from each of the three replicate samples treated and detected using gas chromatography (6890, Agilent, USA). Each sampling period CO₂The discharge amount is calculated by the following formula:

F=[(Q_t-Q₀) ×V×M×273×1000×24)]/[22.4×m×t×(273+T)]

wherein F is CO₂Emission (mg CO)₂ kg⁻¹ soil day⁻¹），Q_tAnd Q₀Is CO detected at room temperature₂Concentration (CO)₂ /Air，×10⁻¹ mol mol⁻¹) V is the volume of the Messen flask (L), M is the dry weight of the soil sample (kg), t is the closed cultivation time (h), M is CO₂Molar mass (g mol)⁻¹) And T is the incubation temperature.

After the gas was collected, the mixture from each sample tube was spread onto a soft, smooth plastic plate and mixed again uniformly. The soil moisture was then readjusted with distilled water to maintain a constant weight of the sample tube. In addition, ambient air was repeatedly injected into the meisen bottle using a 100 ml syringe before the vial was replaced.

(4) Soil sample analysis and soil new carbon calculation

And after the culture is finished, selecting a part of culture samples for natural air drying. Removing residual partially degraded straw residues by a dry screening-air separation method. Each 3 replicate samples were passed through a 0.15 mm sieve and analyzed for total C and atom% according to the method described in step (1)¹³C (Table 3). We define the carbon of the straw carbon transfer into the soil as soil new carbon (NFC) and calculate using equations (1), (2) and (3):

NFC= (Net-¹³C ×100 – Net-C × atom%¹³C_soil)/(atom%¹³C_residue – atom%¹³C_soil) (1)

wherein Net-¹³C（mg kg⁻¹soil) is sample atom%¹³A net change in C; Net-C (mg kg)⁻¹soil) is the net change in the stable SOC of the sample；atom％¹³C_soil(%) is atom% of the original soil¹³C；atom％¹³C_residue(%) is the atom% of the original straw¹³C。

Net-¹³C = [(C_sample × atom%¹³C_sample – C_soil × atom%¹³C_soil) ×1000]/100 (2)

Net-C = (C_sample – C_soil) ×1000 (3)

Wherein C is_sample（g kg⁻¹) Is the stable SOC content, atom% of the sample¹³C_sample(%) is the atom% of the sample¹³C，C_soil（g kg⁻¹) Is the initial soil stabilization SOC content.

TABLE 6 soil sample atom% after completion of culture¹³C and SOC content

Note: the numbers after "±) are the standard error of the mean (n = 3).

(5) Statistical analysis

All data were entered into Excel 2016 and collated (Microsoft, Redmond, WA, USA). All results are presented as mean ± standard error of triplicates.

(6) Results

(61) Respiration of soil

The CO in the soil at two points during the whole culture period₂The emission is relatively low (0.4-1.0 mg CO)₂–C kg⁻¹soil day⁻¹) (FIG. 3). In the early culture stage (day 1 to day 28), straws are added into soil or CO at two points after N, P and S nutrient supplement₂The discharge rate is obviously increased, and the whole discharge level is 4.5 times that of the control soil (the variation range is 2.5-6.5 times). In the later period of culture (day 56, day 84), the respiration rates of the soils treated with different nutrients at each locus gradually became uniform. Adding straw or nutrient, and making into sea-lun soilCO at soil pre-culture stage (day 1 to day 14)₂CO with discharge rate higher than that of princess ridge soil₂The emission rate of the catalyst is 2.2-6.5 mg CO₂–C kg⁻¹ soil day⁻¹The variation range of the emission rate of the latter is 1.9-5.2 mg CO₂–C kg⁻¹ soil day⁻¹。

(62) New carbon change of soil

The addition of straw increased the formation of new soil carbon in both soils compared to the control soil, while causing mineralization of the original soil SOC (figure 4). Compared with the Helen soil, the N, P and S nutrient are added to improve the generation strength of new carbon in the soil of the princess mountains. By increasing the nutrient addition level, the generation amount of new carbon in the soil of the princess ridge is increased gradually from 1155.9 mg kg⁻¹The soil was raised to 1722.4 mg kg⁻¹soil (from low nutrient to high nutrient addition). Under the high nutrient addition level, the new carbon generation amount of the soil accounts for 30.4 percent of the input straw carbon. The nutrient supplement also enhances the generation amount of new carbon in the Helen soil, and the change range of the new carbon is 725.1-1067.5 mg kg⁻¹And the soil accounts for 12.8-18.8% of the total amount of the carbon added into the straws. It can be seen that the input of straw and nutrients leads to the mineralization of the original SOC of the soil, while further increasing the strength of the formation of new carbon in the soil (fig. 4).

The amount of new carbon generated in soil at each point accounts for 10.7-14.9% of the total carbon input amount of the straws. In addition, the mineralization effect of original SOC is also intensified by artificial nutrient management and straw addition, and the average proportion of the original SOC mineralization amount of the soil at two point positions to the total carbon input amount of the straw is 6.6-7.6%. Therefore, the addition of exogenous straws usually causes the mineralization decomposition of the original SOC and the generation of new soil carbon, thereby influencing the turnover of the new soil carbon and old soil carbon

Compared with the method of adding straws alone, the strength of new carbon generation of soil is increased by 1.2-2.0 times along with the increase of the nutrient supplement level (figure 4). By increasing the addition level of nutrient elements, PE can intensify the loss (mineralization) of original SOC of soil; meanwhile, the straw carbon and available nutrients are synergistically transformed according to the stable C: N: P: S metering ratio. Under the comprehensive action of the factors, the humification efficiency of the added straws is improved, so that the generation amount of new carbon in the soil is increased. Compared with the method of adding straws alone, N, P and S nutrients are supplemented in the mixture of the soil and the straws (from a low addition level to a high addition level), the mineralization quantity of the original SOC of the soil is improved by 13-81%, and the new carbon production quantity of the soil is increased by 20-103%. Thus, the increased availability of N, P and S nutrients increases the consumption of C in the soil' S original SOM by microbial activity, while the main microbial taxa involved in straw decomposition grow rapidly and form more soil new carbon by building their own microbial biomass.

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

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

Claims

1. A method for increasing the content of organic carbon in soil by returning straws to the field and applying inorganic nutrients is characterized in that the following components are applied to the soil to be improved: 12.5g/kg of straws, 16.3-49.0 mg/kg of ammonium nitrate, 12.2-36.5 mg/kg of monopotassium phosphate and 3.3-10.0 mg/kg of ammonium sulfate;

the ammonium nitrate, the monopotassium phosphate and the ammonium sulfate are added in the form of nutrient solution; the pH value of the nutrient solution is 7;

the total carbon content in the straws is 42.8% w/w, the total nitrogen content is 0.97% w/w, the total phosphorus content is 0.12% w/w, and the total sulfur content is 0.11% w/w;

the water content of the soil is 60%;

the method is characterized in that the content of organic carbon in the soil is improved to improve the generation amount of new carbon in the soil, the new carbon is defined as new carbon in the soil, is expressed by NFC and is calculated by the following formulas (1), (2) and (3):

NFC＝(Net-¹³C×100–Net-C×atom％¹³C_soil)/(atom％¹³C_residue–atom％¹³C_soil) (1)；

wherein Net-¹³C(mg kg^-1soil) is sample atom%¹³A net change in C; Net-C (mg kg)^-1soil) is the net change in the sample's stable SOC; atom%¹³C_soil(%) is atom% of the original soil¹³C；atom％¹³C_residue(%) is the atom% of the original straw¹³C；

Net-¹³C＝[(C_sample×atom％¹³C_sample–C_soil×atom％¹³C_soil)×1000]/100 (2)；

Net-C＝(C_sample–C_soil)×1000 (3)；

The new carbon generation amount accounts for 10.7-14.9% of the total carbon input amount of the straws.

2. The method for increasing the content of organic carbon in soil by applying inorganic nutrients to straw returning fields as claimed in claim 1, wherein the pH regulator of the nutrient solution is a 10M sodium hydroxide solution used for regulating the pH value of the nutrient solution.

3. The method for increasing the organic carbon content of soil by applying the inorganic nutrients to the straw returning field as claimed in claim 1, wherein the straw is corn straw.

4. The method for increasing the organic carbon content in soil by applying inorganic nutrients to straw returning fields as claimed in claim 1, wherein the straw is dried straw and cut into 2mm pieces.