Method for evaluating potential risk of phosphorus loss of outdoor vegetable crops

Abstract

A method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops. An observation database is established based on observed data and evaluation factors for phosphorus loss are cla

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops and belongs to the technical field of phosphorus loss evaluation. BACKGROUND

[0002] Phosphorus is a main limiting factor for the growth of most freshwater algae and therefore has become a critical substance that decides water eutrophication. The input and continuous accumulation of farmland nutrients cause the major output substance phosphorus of agricultural non-point source pollution to be the main source of phosphorus in water. A phosphorus index (PI) method is a method for evaluating a potential risk of phosphorus loss in combination with geographic information system (GIS). By PI evaluation, areas at a high potential risk of phosphorus loss can be found such that the management and control of phosphorus are efficient, thereby reducing an economic input. The selection of evaluation factors is one of key techniques of the PI method, which is highly operable. However, due to differences in farmland crop types and soil backgrounds, the selection of evaluation factors and PI calculation are highly difference, and outdoor vegetable crops are crops in need of high phosphorus input and are at the risk of environmental loss.

[0003] Therefore, a method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops is proposed. It is essential to formulate a calculation method for evaluating a potential risk of phosphorus loss by selecting PI evaluation factors for the phosphorus loss characteristic of outdoor vegetable crops and through overall consideration. SUMMARY

[0004] To overcome the problems in the background art, according to the present disclosure, a phosphorus index (PI) evaluation factor is selected for phosphorus loss characteristics of outdoor vegetable crops, and an evaluation method is formulated by overall consideration according to monitored data of a long-term locating point; an outdoor vegetable PI evaluation system is divided into a particulate phosphorus loss index and a dissolved phosphorus loss index and each index is composed of a source factor and a transport factor; and a surface runoff index is introduced as the transport factor, rendering each index more suitable for calculating a phosphorus loss risk on farmland scale. Therefore, the fit and accuracy of calculation of the phosphorus loss risk of outdoor vegetable soil are improved.

[0005] To overcome the problems in the background art, the present disclosure is implemented by the following technical solutions.

[0006] A method for evaluating potential risk of phosphorus loss of outdoor vegetable crops includes the following steps:

[0007] step 1: collecting and processing information, establishing an observation database based on observed data of a long-term vegetable locating planting observation point, and classifying evaluation factors for phosphorus loss;

[0008] step 2: determining affecting factors for the loss of particulate phosphorus and dissolved phosphorus of outdoor vegetable crops, and determining a formula for calculating a phosphorus loss index of the outdoor vegetable crops based on the affecting factors;

[0009] step 3: calculating a source loss index for particulate phosphorus and a source loss index for dissolved phosphorus according to the affecting factors and the formula obtained in step 2, and entering data in a phosphorus loss index evaluation system database;

[0010] step 4: calculating a transport loss index for particulate phosphorus and a transport loss index for dissolved phosphorus according to the affecting factors and the formula obtained in step 2, and entering data in the phosphorus loss index evaluation system database;

[0011] step 5: calculating the phosphorus loss index from calculation results of the affecting factors of steps 3 and 4, and entering data in the phosphorus loss index evaluation system database; and

[0012] step 6: analyzing an outdoor vegetable phosphorus loss index by contrast with the phosphorus loss index evaluation system database of step 5, and determining a phosphorus loss risk of outdoor vegetable crops.

[0013] Preferably, step 1 may specifically include:

[0014] step 1.1: analyzing collected data of different farmland crop types and soil backgrounds, classifying the evaluation factors into a source loss index and a transport loss index for particulate phosphorus loss and a source loss index and a transport loss index for dissolved phosphorus loss; and

[0015] step 1.2: performing analysis on the collected data of different farmland crop types and soil backgrounds, selecting the most representative farmland crop type and soil background with rich information, and entering total phosphorus and rapidly available phosphorus grades of soil, an application amount and an application method of chemical fertilizer phosphorus, an application amount and an application method of organic fertilizer phosphorus, annual and monthly rainfalls, a soil loss amount, a land cover and management factor, soil mechanical composition, an organic matter content, a soil structure, a slope length and a slope gradient of land, a surface runoff, and a phosphorus acting distance of an observation point so as to form an observation database.

[0016] Preferably, step 2 may specifically include:

[0017] step 2.1: determining, based on an affecting type of a phosphorus index affecting factor, affecting factors for a source loss index for phosphorus loss as the total phosphorus and rapidly available phosphorus grades of soil, the application amount and the application method of chemical fertilizer phosphorus, and the application amount and the application method of organic fertilizer phosphorus, and affecting factors for a transport loss index for phosphorus loss as the annual and monthly rainfalls, the soil loss amount, the land cover and management factor, the soil mechanical composition, the organic matter content, the soil structure, the slope length and the slope gradient of land, the surface runoff, and the phosphorus acting distance, and allocating an affecting factor weight based on the collected data of step 1; and

[0018] step 2.2: deriving the formula for calculating the phosphorus loss index of the vegetable planting land based on a magnitude of the affecting factor weight in step 2.1:

[0019] calculation of values of source loss indexes:

[0020] source loss index for particulate phosphorus = value of total phosphorus grade of soil x a * corresponding weight + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index

[0021] source loss index for dissolved phosphorus = value of rapidly available phosphorus grade of soil x a x corresponding weight + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index, where a represents phosphorus in soil equivalent to a chemical fertilizer being applied to the soil in a deep placement manner as a base fertilizer. Calculation of values of transport loss indexes:

[0022] transport loss index for particulate phosphorus = soil erosion grade x corresponding weight x acting distance grade x corresponding weight;

[0023] transport loss index for dissolved phosphorus = surface runoff grade x corresponding weight x acting distance grade x corresponding weight; and

[0024] calculation of the phosphorus loss index:

[0025] PI = (Si ■ W.) x (Tj ■ Wj) (1)

[0026] where PI represents the phosphorus loss index; St represents a corresponding grade score of a source factor evaluation indicator i; W, represents a corresponding weight of the source factor evaluation indicator i; Tj represents a corresponding grade score of a transport factor evaluation indicator]; Wj represents a corresponding weight of the transport factor evaluation indicator].

[0027] Preferably, extremely low, low, medium, high, and extremely high total phosphorus grades of soil are defined according to total phosphorus and rapidly available phosphorus content data obtained based on average values of the observed data of the long-term vegetable locating planting observation point, and put in phosphorus index evaluation system tables of particulate phosphorus and dissolved phosphorus, respectively;

[0028] the chemical fertilizer phosphorus input index includes extremely low, low, medium, high, and extremely high grades defined according to the application amount data of chemical fertilizer phosphorus of the long-term vegetable locating planting observation point; the application method of chemical fertilizer phosphorus includes no application, deep placement of a base application, base fertilizer + top application, full top application, and surface application before seeding, which are put in two tables described above; the chemical fertilizer phosphorus input index is calculated by:

[0029] chemical fertilizer phosphorus input index = application amount grade of chemical fertilizer phosphorus * application method grade of chemical fertilizer phosphorus;

[0030] grades of the organic fertilizer phosphorus input index and the application method of organic fertilizer phosphorus are the same with chemical fertilizer phosphorus; and the organic fertilizer phosphorus input index is calculated by:

[0031] organic fertilizer phosphorus input index = phosphorus source coefficient x application amount grade of organic fertilizer phosphorus x application method grade of organic fertilizer phosphorus.

[0032] Preferably, for the soil erosion grade, a soil erosion amount is calculated by a revised universal soil loss equation (RUSLE) widely used at present by the following formula:

[0033] A=RxKxLS*CxP (2)

[0034] where A represents the soil loss amount; R represents an erosivity factor; K represents a soil erosion factor; LS represents a slope gradient and slope length factor; C represents the land cover and management factor; and P represents a protective measure factor; after the soil erosion amount is obtained, the soil erosion of the farmland is graded with reference to the standards for classification and gradation of soil erosion issued by the ministry of water resources.

[0035] Preferably, phosphorus loss indexes are ranked by comparing phosphorus loss index calculation results of step 5 so as to obtain an environmental risk report of phosphorus loss of outdoor vegetable planting.

[0036] The present invention has the following beneficial effects:

[0037] According to the present disclosure, the PI evaluation factor is selected for the phosphorus loss characteristics of outdoor vegetable crops, and the evaluation method is formulated by overall consideration according to the monitored data of the long-term locating point; the outdoor vegetable PI evaluation system is divided into the particulate phosphorus loss index and the dissolved phosphorus loss index and each index is composed of the source factor and the transport factor, making the outdoor vegetable PI evaluation system highly operable. Thus, the calculation of the phosphorus loss indexes is more efficient and the calculation results are more accurate. Moreover, a reasonable fertilizer application scheme is formulated according to phosphorus loss index risk evaluation; the economic input is reduced; and the control efficiency of phosphorus loss is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. lisa block diagram of calculation according to the present disclosure.

[0039] Reference numerals:

[0040] 1-Block diagram of outdoor vegetable PI evaluation system

[0041] 2-Establishment of phosphorus loss index

[0042] 3-Establishment of particulate phosphorus loss index

[0043] 4-Source factor

[0044] 5-Soil total phosphorus grade

[0045] 6-Chemical fertilizer phosphorus input index (application amount and method)

[0046] 7-Organic fertilizer phosphorus input index (application amount and method)

[0047] 8-Determined according to measured values of a long-term monitoring point

[0048] 9-Chemical fertilizer phosphorus input index = application amount grade of chemical fertilizer phosphorus x application method grade of chemical fertilizer phosphorus

[0049] 10-organic fertilizer phosphorus input index = application amount grade of organic fertilizer phosphorus x application method grade of organic fertilizer phosphorus

[0050] 11-Transport factor

[0051] 12-Soil erosion grade

[0052] 13-Acting distance grade

[0053] 14-Calculated according universal soil equation (RUSLE), A=RxKxLSxCxP

[0054] 15-Acting distance (distance from drainage ditch) / m

[0055] 16-Source factor index value = soil total phosphorus grade value x 2 + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index

[0056] 17-Transport factor index value = soil erosion grade x acting distance grade

[0057] 18-Particulate phosphorus loss index = source factor index value x transport factor index value

[0058] 19- Establishment of dissolved phosphorus loss index

[0059] 20-Source factor

[0060] 21-Soil rapidly available phosphorus grade

[0061] 22-Chemical fertilizer phosphorus input index (application amount and method)

[0062] 23-Organic fertilizer phosphorus input index (application amount and method)

[0063] 24-Determined according to measured values of a long-term monitoring point

[0064] 25-Chemical fertilizer phosphorus input index = application amount grade of chemical fertilizer phosphorus x application method grade of chemical fertilizer phosphorus

[0065] 26-Organic fertilizer phosphorus input index = 0.45 x application amount grade of organic fertilizer phosphorus x application method grade of organic fertilizer phosphorus

[0066] 27-Transport factor

[0067] 28-Surface runoff grade

[0068] 29-Acting distance grade

[0069] 30-Surface runoff index (runoff depth / mm)

[0070] 31-Acting distance (distance from drainage ditch) / m

[0071] 32-Source factor index value = soil rapidly available phosphorus grade x 2 + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index

[0072] 33-Transport factor index value = surface runoff grade x acting distance grade

[0073] 34-Dissolved phosphorus loss index = source factor index value x transport factor index value DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] In order to make the objective, technical solutions, and beneficial effects of the disclosure clearer, the preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings to facilitate understanding by those skilled in the art.

[0075] A method for evaluating potential risk of phosphorus loss of outdoor vegetable crops includes the following steps:

[0076] step 1: collect and process information, establish an observation database based on observed data of a long-term vegetable locating planting observation point, and classify phosphorus loss indexes;

[0077] step 2: determine affecting factors for the loss of particulate phosphorus and dissolved phosphorus of outdoor vegetable crops, and determine a formula for calculating a phosphorus loss index of the outdoor vegetable crops based on the affecting factors;

[0078] step 3: calculate a source loss index for particulate phosphorus and a source loss index for dissolved phosphorus according to the affecting factors and the formula obtained in step 2, and enter data in a phosphorus loss index evaluation system database;

[0079] step 4: calculate a transport loss index for particulate phosphorus and a transport loss index for dissolved phosphorus according to the affecting factors and the formula obtained in step 2, and enter data in the phosphorus loss index evaluation system database;

[0080] step 5: calculate the phosphorus loss index from calculation results of the affecting factors of steps 3 and 4, and enter data in the phosphorus loss index evaluation system database; and

[0081] step 6: analyze an outdoor vegetable phosphorus loss index by contrast with the phosphorus loss index evaluation system database, and determine a phosphorus loss risk of outdoor vegetable crops.

[0082] Step 1 specifically includes:

[0083] step 1.1: analyze collected data of different farmland crop types and soil backgrounds, classify the evaluation factors into a source loss index and a transport loss index for particulate phosphorus loss and a source loss index and a transport loss index for dissolved phosphorus loss; and

[0084] step 1.2: perform analysis on the collected data of different farmland crop types and soil backgrounds, select the most representative farmland crop type and soil background with rich information, and enter total phosphorus and rapidly available phosphorus grades of soil, an application amount and an application method of chemical fertilizer phosphorus, an application amount and an application method of organic fertilizer phosphorus, annual and monthly rainfalls, a soil loss amount, a land cover and management factor, soil mechanical composition, an organic matter content, a soil structure, a slope length and a slope gradient of land, a surface runoff, and a phosphorus acting distance of an observation point so as to form an observation database.

[0085] Step 2 specifically includes:

[0086] step 2.1: determine, based on an affecting type of a phosphorus index affecting factor, affecting factors for the source loss index for particulate phosphorus loss and the source loss index for dissolved phosphorus loss as the total phosphorus and rapidly available phosphorus grades of soil, the application amount and the application method of chemical fertilizer phosphorus, and the application amount and the application method of organic fertilizer phosphorus, and affecting factors for the transport loss index for particulate phosphorus loss and the transport loss index for dissolved phosphorus loss as the annual and monthly rainfalls, the soil loss amount, the land cover and management factor, the soil mechanical composition, the organic matter content, the soil structure, the slope length and the slope gradient of land, the surface runoff, and the phosphorus acting distance.

[0087] In steps 2 and 3, extremely low, low, medium, high, and extremely high total phosphorus grades of soil are defined according to total phosphorus (g kg4) and rapidly available phosphorus (mg-kg-1) obtained based on average values of the observed data of the long-term vegetable locating planting observation point, and put in phosphorus index evaluation system tables (Table 3 and Table 4) of particulate phosphorus and dissolved phosphorus, respectively.

[0088] The application amount / (kghm-2) and the application method of chemical fertilizer phosphorus each include extremely low, low, medium, high, and extremely high grades defined according to the application amount data of chemical fertilizer phosphorus of the long-term vegetable locating planting observation point; and the application method of chemical fertilizer phosphorus includes no application, deep placement of a base application, base fertilizer + top application, full top application, and surface application before seeding, which are put in two tables (Table 3 and Table 4) described above.

[0089] The chemical fertilizer phosphorus input index is calculated by:

[0090] chemical fertilizer phosphorus input index = application amount grade of chemical fertilizer phosphorus x corresponding weight x application method grade of chemical fertilizer phosphorusx corresponding weight.

[0091] Taking three treatments (no application, organic fertilizer application, and organic fertilizer + chemical fertilizer) in the farmland for example, no application means no any fertilizer being added; organic fertilizer application means only an organic fertilizer (i.e., organic fertilizer phosphorus 100 kg / hm2) is applied; and organic fertilizer + chemical fertilizer represents organic fertilizer phosphorus 27 kg / hm2 and chemical fertilizer phosphorus 73 kg / hm2. The chemical fertilizer phosphorus input indexes of particulate phosphorus and dissolved phosphorus chemical fertilizers are calculated as 0x0.75x0x0.5=0, 0x0.75x0x0.5=0, and 2x0.75x2x0.5=1.5.

[0092] The application amount / (kghnr2) and the application method of organic fertilizer phosphorus each include extremely low, low, medium, high, and extremely high grades defined according to the application amount data of organic fertilizer phosphorus of the long-term vegetable locating planting observation point; and the application method of organic fertilizer phosphorus includes no application, deep placement of a base application, base fertilizer + top application, full top application, and surface application before seeding, which are put in the two tables (Table 3 and Table 4) described above.

[0093] The organic fertilizer phosphorus input index of particulate phosphorus is calculated by:

[0094] organic fertilizer phosphorus input index = application amount grade of organic fertilizer phosphorus x corresponding weight (1) x application method grade of organic fertilizer phosphorus x corresponding weight; and

[0095] the organic fertilizer phosphorus input index of dissolved phosphorus is calculated by:

[0096] organic fertilizer phosphorus input index = application amount grade of organic fertilizer phosphorus x corresponding weight (0.45) x application method grade of organic fertilizer phosphorus x corresponding weight;

[0097] where 0.45 is the phosphorus source weight coefficient of the organic fertilizer, representing a contribution ratio of the organic fertilizer phosphorus to dissolved phosphorus loss.

[0098] Similarly, taking three treatments (no application, organic fertilizer application, and organic fertilizer + chemical fertilizer) in the farmland for example, no application means no any fertilizer being added; organic fertilizer application means only an organic fertilizer (i.e., organic fertilizer phosphorus 100 kg / hm2) is applied; and organic fertilizer + chemical fertilizer represents organic fertilizer phosphorus 27 kg / hm2 and chemical fertilizer phosphorus 73 kg / hm2. The organic fertilizer phosphorus input index of particulate phosphorus is calculated as 0* 1x0* 1=0, 6x1x2x1=12, and 2xlx2xi=4. The organic fertilizer phosphorus input index of dissolved phosphorus is calculated as 0x0.45x0x1=0, 6x0.45x2x1=5.4, and 2x0.45x2x1=1.8.

[0099] Calculation of a value of a source loss index:

[00100] source loss index for particulate phosphorus = value of total phosphorus grade of soil x 2 x corresponding weight (1) + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index,

[00101] where 2 represents phosphorus in soil equivalent to a chemical fertilizer being applied to the soil in a deep placement manner as a base fertilizer, with reference to Table 3.

[00102] Similarly, taking three treatments (no application, organic fertilizer application, and organic fertilizer + chemical fertilizer) in the farmland for example, the source loss index for particulate phosphorus is calculated as 4x2x 1+0+0=8, 8x2+0+12=28, and 6x2+1.5+4=17.5.

[00103] source loss index for dissolved phosphorus = value of rapidly available phosphorus grade of soil x 2 x corresponding weight (1) + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input index,

[00104] where 2 represents phosphorus in soil equivalent to a chemical fertilizer being applied to the soil in a deep placement manner as a base fertilizer, with reference to Table 4.

[00105] Similarly, taking three treatments (no application, organic fertilizer application, and organic fertilizer + chemical fertilizer) in the farmland for example, the source loss index for dissolved phosphorus is calculated as 4x2xl+0+0=8, 8x2+0+5.4=21.4, and 6x2+1.5+1.8=15.3.

[00106] Step 2-4, calculation of the transport factor: for the soil erosion factor, soil erosion is one of main ways for soil nitrogen and phosphorus loss. A soil erosion amount is calculated herein by a revised universal soil loss equation (RUSLE) widely used at present by the following formula:

[00107] A=RxKxLSxCxP (2)

[00108] where A represents the soil loss amount, t km^ a’1; R represents an erosivity factor; K represents a soil erosion factor; LS represents a slope gradient and slope length factor; C represents the land cover and management factor; and P represents a protective measure factor.

[00109] After the soil erosion amount is obtained, the soil erosion of the farmland is graded with reference to the standards for classification and gradation of soil erosion issued by the ministry of water resources, as shown in Table 3.

[00110] For rainfall erosivity factor R, by querying annual and monthly rainfalls of county and municipal level of local statistical yearbook, R (MJ-mm-hm’2-h4-a4) is calculated with a mean annual rainfall and multi-year mean rainfall by the following formula: P-

[00111] R = (1.735 x 10(15° (3)

[00112] where P represents the mean annual precipitation (mm); and Pi represents a monthly precipitation (mm).

[00113] Taking mean rainfall data of 14 years in Dali for example, by querying the rainfall yearbook, the calculated value of Ris 127.71 to 478.18 MJ mm hnr2 h4 a4.

[00114] For the soil erosion factor K, K (t hm2 h hnr2 MJ4 mm4) is related to soil mechanical composition, an organic matter content, a soil structure, and the like, and is calculated using an estimation method for a K value in a cognitive model EPIC in combination with an actual situation in a study area by the following formula: 1001151K = {0.2 + 0.3exp[ - 0.0256Sa(l - [1 - " -----—-----] (4) Sn + exp( 5.51+22.9Sn) J v ’

[00116] where Sn = l-Sa / 100; Sa represents a sand grain content (%); Si represents a silt content (%); Cl represents a clay grain content (%); and C represents the organic matter content (%).

[00117] Taking soil in the study area, Sn = 0.5, Sa = 50%, Si = 35%, Cl = 15%, C = 3.8%; and the calculated K value is 0.22 t hm2 h hm’2 MJ4 mm4.

[00118] The slope gradient and slope length factor LS refers to a ratio of a soil loss amount on a slope surface of a certain slope gradient and a certain slope length to a soil loss amount on a typical slope surface in a standard runoff plot, and includes a slope length factor L and a slope gradient factor S.

[00119] L represents the slope length factor; a calculation formula for the slope length factor based on identification of a key resource area of agricultural non-point source pollution in Songhuaba watershed is used herein; and different indexes are selected for different slope gradients, where the slope gradients are divided into four grades: <1%, 1-3%, 3-4.5%, and >4.5%.

[00120] S represents the slope gradient factor. The slope gradient factor S is calculated by a continuity formula further improved based on previous studies.

[00121] L = (—— / 22.13 ] (5)

[00122] S =- 1.5 + (1+ei,"li,je) (6)

[00123] In the formulas (4) and (5), X represents a slope length; m represents a slope gradient index; and 0 represents a slope gradient.

[00124] Taking for example X being 6 m, 6 being 0 degree, and corresponding m values being 0.2, 0.3, 0.4, and 0.5, respectively, by calculation, L = 0.59 and S = 0.33.

[00125] The land cover and management factor C depends on a vegetation type, site conditions, growth vigor, crop rotation, crop (harvest) residue availability, and management and tillage activities, and changes very obviously in different seasons and months. A value of C is obtained with reference to Table 1 according to a C value determination method based on small-watershed nitrogen and phosphorus loss risk evaluation. Taking plain dry land for example, the value of C is 0.006.

[00126] Table 1 Values of C for Different Land Utilization Types

[00127] Land Utilization Type Paddy Field Mountainous Dry Land Hilly Dry Land Plain Dry Land Dense Forest Land Open Forest Land Value of C 0.18 0.22 0.16 0.006 0.004 0.06 Land Utilization Type Other forest land High-coverage grassland Medium-coverage grassland Low-coverage grassland River water surface Rural residential area Value of C 0.1 0.1 0.15 0.24 0 0 Land Utilization Type Urban land Wetland Bare land Bare rock Value of C 0 0.05 1 0

[00128] For the protective measure factor P, P in the soil loss equation RUSLE is a ratio of soil loss caused by the use of a particular protective measure to soil loss caused by planting along a slope. The values of P for different land utilization types in the present disclosure are obtained with reference to the following table according to a P value determination method based on small-watershed nitrogen and phosphorus loss risk evaluation of nitrogen and phosphorus indexes. Taking dry land for example, the value of P is 0.6.

[00129] Table 2 Values of P for Different Land Utilization Types

[00130] Land Paddy Irrigable Dry Garden Forest Grassland Water Construction Utilization Field Land Land Land Land Area Land Value of P 0.35 0.47 0.6 0.8 1 1 1 1

[00131] The surface runoff factor, factors affecting the occurrence of a surface runoff include rainfall, landform (e.g., slope gradient) and soil permeability, soil moisture content, and the like, and a volume of runoff is directly obtained by a rainfall-runoff conversion experience formula to reflect an occurrence degree of the runoff. Since a monitoring station has long-term monitored data of runoffs, the magnitudes of average annual flow volumes of a plurality of years are converted into runoff depths that can reflect the influence degrees of the surface runoffs on dissolved phosphorus loss.

[00132] For the acting distance factor, an acting distance refers to a distance of a pollutant from a loss site to a river. Since phosphorus is continuously diluted and trapped during transport. A contribution of a phosphorus source area far away from the river to a phosphorus loss amount is generally smaller than that of a phosphorus source area close to the river, and a distance between a source of pollution and receiving water is incorporated into the transport factor to better reflect the loss situation of the phosphorus element. An acting distance factor grade indicator for an observation point is formulated for length division and contribution grades of acting distances in the present disclosure, as shown in Table 3 and Table 4.

[00133] Table 3 Particulate Phosphorus Index Evaluation System

[00134] Relative Value of Particulate Phosphorus Loss Factor Weight Extremely low Low Medium High Extremely high Source factor Soil total phosphorus / g'kg1 1 Test value <1.5 1.5-1.7 1.7-1.9 1.9-2.1 >2.1 Grade 2 4 6 8 10 Chemical fertilizer phosphorus / kg • hm‘2 0.75 Application amount 0 45-80 80-114 114-140 >140 Grade 0 2 4 6 8 Chemical fertilizer application method 0.5 Method No application Deep placement of base fertilizer Base fertilizer + top application Full top application Surface application before seeding Grade 0 2 4 6 8 Organic fertilizer phosphorus / kg • hm'2 1 Application amount 0 25-55 55-85 85-115 >115 Grade 0 2 4 6 8 Application method of organic fertilizer phosphorus 1 Method No application Deep placement of base fertilizer Base fertilizer + top application Full top application Surface application before seeding Grade 0 2 4 6 8 Transport factor Soil erosion / tkm^a'1 1 Calculated value <200 200 2500-5000 5000-8000 8000-15000 Grade 1 4 6 8 10 Acting distance (distance from drainage ditch) / m 1 Determined value >300 200-300 100-200 50-100 <50 Grade 1 4 6 8 10

[00135] Table 4 Dissolved Phosphorus Index Evaluation System

[00136] Relative value of dissolved phosphorus loss Factor Weight Extremely low Low Medium High Extremely high Source factor Soil rapidly available phosphorus / gkg'1 1 Test value <80 80-114 114-140 140-185 >185 Grade 2 4 6 8 10 Chemical fertilizer phosphorus / kg • hnr2 0.75 Application amount 0 45-80 80-114 114-140 >140 Grade 0 2 4 6 8 Chemical fertilizer application method 0.5 Method No application Deep placement of base fertilizer Base fertilizer + top application Full top application Surface application before seeding Grade 0 2 4 6 8 Organic fertilizer phosphorus;'kghnr2 0.45 Application amount 0 25-55 55-85 85-115 >115 Grade 0 2 4 6 8 Application method of organic fertilizer phosphorus 1 Method No application Deep placement of base fertilizer Base fertilizer + top application Full top application Surface application before seeding Grade 0 2 4 6 8 Transport factor Surface runoff index (runoff depth / mm) 1 Calculated value <250 250-300 300-350 350-400 >400 Grade 2 4 6 8 10 Acting distance (distance from drainage ditch) / m 1 Determined value >300 200-300 100-200 50-100 <50 Grade 1 4 6 8 10

[00137] Calculation of values of transport loss indexes:

[00138] transport loss index for particulate phosphorus = soil erosion grade * corresponding weight x acting distance grade x corresponding weight;

[00139] according to the foregoing embodiments, the transport loss index for particulate phosphorus is calculated as lxlxlxi=i; transport loss index for dissolved phosphorus = surface runoff grade x corresponding weight x acting distance grade x corresponding weight.

[00140] According to the foregoing embodiments, the transport loss index for dissolved phosphorus is calculated as 6xlxixi=6, 4xlxixi=4j and 8xlxjxi=8.

[00141] According to the above formulas, the phosphorus loss index is calculated by:

[00142] Pl = (S, ■ Wj) x (Tj ■ Wj) (1)

[00143] That is, particulate phosphorus loss index = source loss index x particulate phosphorus transport loss index; dissolved phosphorus loss index = source loss index x dissolved phosphorus transport loss index; and phosphorus loss index = particulate phosphorus loss index x dissolved phosphorus loss index,

[00144] where PI represents the phosphorus loss index; Si represents a corresponding grade score of a source factor evaluation indicator i; W, represents a corresponding weight of the source factor evaluation indicator i; 7, represents a corresponding grade score of a transport factor evaluation indicator]; Wj represents a corresponding weight of the transport factor evaluation indicator].

[00145] According to the foregoing embodiments, the calculation results of the above indexes are as shown in Table 5 in detail.

[00146] Table 5 Phosphorus Index Evaluation System

[00147] Treatment Particulate Phosphorus Loss Index Dissolved Phosphorus Loss Index Phosphorus Loss Index Phosphorus Loss Index Ratio Soil residual phosphorus Content (kg ha4yr') Source Loss Index Transport Loss Index Source Loss Index Transport Loss Index No application 8 1 8 6 56.0 1.0 -50 Organic fertilizer 28 1 21.4 4 113.6 2.0 130 Organic fertilizer + Chemical fertilizer 17.5 1 15.3 8 139.9 2.5 120

[00148] By comparing the above treatments (Table 5), it is found that the phosphorus loss indexes are ranked as organic fertilizer + chemical fertilizer (139.9) >organic fertilizer (113.6) >no application (56.0), indicating that the environmental risk of phosphorus loss is the highest when the organic fertilizer + chemical fertilizer is applied in planting outdoor vegetable crops. With no application as control, a ratio of phosphorus loss index ratio to the treatment with no application, the treatment with organic fertilizer, and the treatment with organic fertilizer + chemical fertilizer is 1:2:2.5. The soil residual phosphorus contents are -50, 130, and 120 kg ha4yr4, respectively.

[00149] As can be seen from Table 5, after the source loss indexes in the particulate phosphorus loss indexes and the dissolved phosphorus loss indexes of three treatments are assigned with different weights, the source loss index is the highest in the treatment with organic fertilizer and the transport loss index is the highest in the treatment with organic fertilizer + chemical fertilizer. The transport loss index having a high surface runoff grade causes a difference. The transport loss index for dissolved phosphorus loss in the treatment with organic fertilizer + chemical fertilizer is relatively high, and principally, the surface runoff index is high. The reason may be that the soil structure changes after a chemical fertilizer is added for a long time and the organic matter content is reduced (42.37g kg4) relative to the treatment with application of single organic fertilizer (59.92 g kg4). Therefore, the application amount of the chemical fertilizer may be determined according to the specific nutrient absorption condition of vegetables to avoid the environmental risk of phosphorus loss due to reasonable fertilizer application.

[00150] Finally, it should be noted that the foregoing preferred embodiments are only intended to illustrate rather than limit the technical solutions of the present disclosure. Although the present disclosure has been described through the foregoing preferred embodiments, those of ordinary skill in the art will understand that various changes can be made to forms and details without departing from the scope of the present disclosure defined by the appended claims. 06 03 25

Claims

1. A method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops, comprising the following steps:step 1.1: analyzing collected data of different farmland crop types and soil backgrounds, classifying evaluation factors for phosphorus loss into a source loss index and a transport loss index for particulate phosphorus loss and a source loss index and a transport loss index for dissolved phosphorus loss; andstep 1.2: performing analysis on the collected data of different farmland crop types and soil backgrounds, selecting the most representative farmland crop type and soil background with rich information, and entering total phosphorus and rapidly available phosphorus grades of soil, an application amount and an application method of chemical fertilizer phosphorus, an application amount and an application method of organic fertilizer phosphorus, annual and monthly rainfalls, a soil loss amount, a land cover and management factor, soil mechanical composition, an organic matter content, a soil structure, a slope length and a slope gradient of land, a surface runoff, and a phosphorus acting distance of an observation point so as to form an observation database;step 2.1: determining, based on an affecting type of a phosphorus index affecting factor, affecting factors for a source loss index for phosphorus loss as the total phosphorus and rapidly available phosphorus grades of soil, the application amount and the application method of chemical fertilizer phosphorus, and the application amount and the application method of organic fertilizer phosphorus, and affecting factors for a transport loss index for phosphorus loss as the annual and monthly rainfalls, the soil loss amount, the land cover and management factor, the soil mechanical composition, the organic matter content, the soil structure, the slope length and the slope gradient of land, the surface runoff, and the phosphorus acting distance, and allocating an affecting factor weight based on the collected data of step 1; andstep 2.2: deriving the formula for calculating the phosphorus loss index of the vegetable planting land based on a magnitude of the affecting factor weight in step 2.1:calculation of values of source loss indexes:source loss index for particulate phosphorus = value of total phosphorus grade of soil x a x corresponding weight + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input indexsource loss index for dissolved phosphorus = value of rapidly available phosphorus grade of soil x a x corresponding weight + chemical fertilizer phosphorus input index + organic fertilizer phosphorus input indexwherein a represents phosphorus in soil equivalent to a chemical fertilizer being applied to the soil in a deep placement manner as a base fertilizer06 03 25calculation of values of transport loss indexes:transport loss index for particulate phosphorus = soil erosion grade x corresponding weight x acting distance grade x corresponding weight;transport loss index for dissolved phosphorus = surface runoff grade x corresponding weight x acting distance grade x corresponding weight; andcalculation of the phosphorus loss index:P^^iCSi-WOxn^Tj-Wj) (1)wherein PI represents the phosphorus loss index; Si represents a corresponding grade score of a source factor evaluation indicator i; Wi represents a corresponding weight of the source factor evaluation indicator i; Tj represents a corresponding grade score of a transport factor evaluation indicator j; Wj represents a corresponding weight of the transport factor evaluation indicator jstep 3: calculating source loss indexes for particulate phosphorus and dissolved phosphorus, and transport loss indexes for particulate phosphorus and dissolved phosphorus for each of fertilizer treatments according to the affecting factors and formula obtained in steps 2.1 and 2.2, and storing the source loss indexes for particulate phosphorus and dissolved phosphorus, and the transport loss indexes for particulate phosphorus and dissolved phosphorus in a phosphorus loss index evaluation system database; wherein the fertilizer treatments comprise no application, organic fertilizer application, and organic fertilizer and chemical fertilizer application;step 4: calculating phosphorus loss indexes for each of the fertilizer treatments from the source loss indexes for particulate phosphorus and dissolved phosphorus, and the transport loss indexes for particulate phosphorus and dissolved phosphorus of step 3 and formula (1) obtained in step 2.2, and storing the phosphorus loss indexes in the phosphorus loss index evaluation system database; andstep 5: ranking the phosphorus loss indexes by comparing the phosphorus loss indexes of step 4 so as to obtain an environmental risk report of phosphorus loss of outdoor vegetable planting, and determining a phosphorus loss risk of outdoor vegetable crops based on the environmental risk report; and adjusting the application amount of the chemical fertilizer according to the determined phosphorus loss risk of outdoor vegetable crops.

2. The method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops according to claim 1, wherein extremely low, low, medium, high, and extremely high phosphorus grades of soil are defined according to total phosphorus and rapidly available phosphorus content data obtained based on average values of the observed data of the long-term vegetable locating planting observation point, and put in phosphorus index evaluation system tables of particulate phosphorus and dissolved phosphorus, respectively;the chemical fertilizer phosphorus input index comprises extremely low, low, medium, high,06 03 25and extremely high grades defined according to the application amount data of chemical fertilizer phosphorus of the long-term vegetable locating planting observation point; the application method of chemical fertilizer phosphorus comprises no application, deep placement of a base application, base fertilizer + top application, full top application, and surface application before seeding, which are put in two tables described above; the chemical fertilizer phosphorus input index is calculated by:chemical fertilizer phosphorus input index = application amount grade of chemical fertilizer phosphorus x application method grade of chemical fertilizer phosphorus;grades of the organic fertilizer phosphorus input index and the application method of organic fertilizer phosphorus are the same with chemical fertilizer phosphorus; and the organic fertilizer phosphorus input index is calculated by:organic fertilizer phosphorus input index = phosphorus source coefficient x application amount grade of organic fertilizer phosphorus x application method grade of organic fertilizer phosphorus.

3. The method for evaluating a potential risk of phosphorus loss of outdoor vegetable crops according to claim 1, wherein for the soil erosion grade, a soil erosion amount is calculated by a revised universal soil loss equation (RUSLE) widely used at present by the following formula:A=RxKxLSxCxP (2)wherein A represents the soil loss amount; R represents an erosivity factor; K represents a soil erosion factor; LS represents a slope gradient and slope length factor; C represents the land cover and management factor; and P represents a protective measure factor; after the soil erosion amount is obtained, the soil erosion of the farmland is graded with reference to the standards for classification and gradation of soil erosion issued by the ministry of water resources.

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