P = The Factor for Support Practices - USDA › references › Agency › ...The .p. factor value...

P = The Factor for Support Practices

Step 1 - Determine the "P" subfactor forcontouring on-grade.

A series of tables and charts are required todetermine the appropriate .p. factor to creditthe support practices (contour farming, cross-slope farming, buffer strips, stripcropping,and terraces) planned or applied to the field.

a. Using the 10-year . EI . value, ridgeheight, hydrologic soil group, and cover.management condition, select theappropriate section of Table P-8.

b. Select the value that represents thehydrologic soil group for the % slope beingevaluated. This value is the .p. subfactorvalue for contouring on-grade.

The .p. factor value used in the RUSLEequation is a combination of subfactors thatrepresents the actual field conditions. Afterdetermining the contour on-grade .p. factor,adjustments with subfactors are made.These adjustments may increase .p. due toridge/furrow grade and/or when the actualfield slope length exceeds the critical slopelength for effectiveness of contouring.Stripcropping, buffer strip, and terrace .p.subfactors reduce the .p. factor for on-gradecontouring or as adjusted for ridge/furrowgrade.

Step 2 - Adjust contouring "P" subfactorfor ridge/furrow grade.

Determine the appropriate .p. factor usingthe instructions and tables presented in thissection.

a. Calculate the ratio of the field averageridge/furrow grade to the landscape profileslope used to describe the fieldtopographic factor. (divide the %ridge/furrow grade by the slope % andround to the nearest 0.1.) For ratio values0.05. go to Table P-3.

c. In the left column of Table P-3, locate the.p. value for on-grade contouring obtainedfrom Step 2 above. If the .p. factor valueis an odd number, round up or down tothe nearest even number. Round in theopposite direction from that used whenrounding the ridge/furrow grade tolandscape profile slope ratio to thenearest 0.1.

The following information is required:

Identify the hydrologic soil group for the soilmap unit(s) on the selected landscape profile.

Determine the slope length "L" and slopesteepness .S" of the landscape profile, andgrade along the ridges/furrows that resultfrom tillage, planting, and/or row cultivationoperations.

Identify the 10-year storm erosivity (10-yr. .EI .) value for the site from the map inFigure P-1.

Select the cover-management condition fromTable P-1.

d. On the located row, move right to thecolumn for the appropriate ratio ofridge/furrow grade to slope steepness ofthe landscape profile. This value is the.p. subfactor value for off-gradecontouring where the slope is less thanthe critical slope. Beyond the critical slopelength, the practice effectivenessdecreases quickly with increasing slopelength.

Select the appropriate ridge height using theguidelines shown in Table P-2.

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USDA-NAGSSection

P = The Factor for Support Practices, page 2

subfactor value. This subfactor value isthe corrected "P" subfactor value forcontouring and applies to the entirelandscape profile slope length.

Step 3 - Determine the critical slopelength.

a. In Kansas, exceeding the critical slopelength is usually only a concern withcover management codes 5, 6, or 7. Step 5 - Compute rotational contouring

IIp'' subfactor where cover-managementconditions and/or ridge heights changefrom year to year during the life of a croprotation.

b. Refer to Figure P-3 and select theapplicable figure for the hydrologic soilgroup and cover-management condition.

a. Calculate the contour .p. subfactor foreach year in the crop rotation following theappropriate Steps 1 to 4 above.

c.

b. Add the contour .p. subfactor values forall years in the rotation and divide by thetotal years in the rotation to determine aweighted average annual contour .p.subfactor value.

"P" Subfactor Values forStripcropping

Enter the selected figure at the landscapeprofile slope percent on the horizontalaxis and project a vertical line up tointersect the 10-year EI value for the site.From that intersection point, project ahorizontal line to the left and read thecritical slope length. This is the criticalslope length or the maximum slopelength for which the previouslydetermined .p. subfactor value applies.If the landscape profile slope length forthe site is less than the critical slopelength, use the previously determined .p.subfactor The following information is required:

d. Stripcropping increases the effectivenessof contouring. If stripcropping is beingused in conjunction with contouring,increase the critical slope length bymultiplying by 1.5.

Note: Some of the infonnation is the same asused for evaluating contouring.

a. Identify the hydrologic soil group for thesoil map unit(s) on the selectedlandscape profile.Step 4 - Adjust the contouring "P"

subfactor where the landscape profileexceeds the critical slope length.

Determine the slope length .L. and slopesteepness .S. of the landscape profileand grade along the ridges/furrows thatresult from tillage, planting, and/or rowcultivation operations.

b.

a.

Identify the 1 a-year storm erosivity (10-year 8 EI 8) value for the site from the

map in Figure P-1.

c.

When landscape profile slope lengthexceeds the critical slope length,calculate the ratio by dividing thelandscape profile slope length by thecritical slope length (increase the criticalslope length before making thiscalculation if stripcropping applies).

Determine the number of strips that canbe laid across the landscape profile slopelength "L," A minimum of two full stripwidths must fit on the slope,

d.Go to Figure P-4. Select the appropriatefigure for the land use and the site slopesteepness.

b.

From the actual slope length/critical slopelength ratio on the horizontal axis of theselected figure, project a vertical line tointersect the "P" subfactor valuedetermined in step 2 or 3 above. Fromthat intersection, project a horizontal lineto the left and read the effective "P"

c. For a strip pair. select the cover-management conditions that will beopposite each other during the life of thecrop rotation using Table P-1. For sod-based rotations, it is also importantwhether or not hay is established by

8.

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P = The Factor for Support PractK:es. page 3

direct seeding or seeding is done with anurse crop. The seeding year with anurse crop introduces a third cover-management condition.

Table P-5 for field stripcroppingsubfactors

Table P-6 for buffer strip subfactorsDetermine whether the support practiceis one of the following: b. locate the stripcropping subfactor value

at the intersection of the number of stripsand the cover-management conditions ofthe strips. For buffer strips. enter thecorrect column for ratio of cultivated cropstrip to buffer strip. The value is thestripcropping .p. subfactor for slopeswhere the landscape profile slope lengthdoes not exceed the critical slope length.

A contour stripcropping layout withstrip boundaries as close to level aspossible - Sediment retarding stripsand erosion-Prone strips on contourlayouts switch positions on thelandscape profile during the croprotation.

Step 2 - Detennine critical slope length.8. Refer to Figure P-3 and select the

applicable figure for the hydrologic soilgroup and cover-management condition

A field stricropping layout with stripboundaries markedly off-contour -Sediment retarding strips and erosionprone strips on field stripcroppinglayouts switch positions on thelandscape profile during the life of thecrop rotation. Use the most erosive cover-management

condition of the opposing strip pairs onthe slope to determine the critical slopelength for stripcropping.

b

A buffer strip layout with narrow sodcross slope strips alternating withwider tilled strips - Sod strips aremaintained in a permanent location. c.

g. For buffer strip la~ut using Figure P-2.determine the percentage of landscapeprofile to be occupied by buffer strips atleast 15 feet wide. Table P-6 is set up for1 0 and 20 percent of the landscapeprofile. Table P-6 presents these as cropstrip to buffer strip ratios of 9:1 and 4:1respectively. Note from Table P-6 thatthere is little to be gained by going to 20percent from a sheet and rill erosionstandpoint. The minimum landscapeprofile length that can benefit from bufferstrips is 150 feet.

Enter the selected figure at the profileslope on the horizontal axis and project avertical line up to intersect the 1G-year .EI . value for the site. From thatintersection, project a horizontal line tothe left and read the critical length.Stripcropping increases the effectivenessof the contouring. Therefore, adjust thecritical slope length from the figure bymultiplying the value by 1.5.

d,

Step 1 - Determine the "P" subfactor for

stripcropping.

The adjusted critical length is themaximum slope length for which thepreviously determined stripcropping .p.subfactor value applies. Use thepreviously determined stripcropping .p.subfactor value where the landscapeslope is equal to or less than the adjustedcritical slope length.

a. Determine the type of stripcropping Ia~ut,number of strips on the slope length .L,.cover-management condition pairings,and (for buffer strips) the percent of slopelength .L. occupied by butter strips.Select the appropriate table:

Step 3 - Adjust the stripcropping .p.subfactor where the landscape profileexceeds the critical slope length.

a Where landscape profile slope lengthexceeds the critical slope length,calculate the slope actual length to criticalslope length ratio by dividing the

Table P-4 for contour stripcroppingsubfactors

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TG Notice KS-251 , 1/00

P = The Factor for Support Practices. page 4

composite .p. factor for the conservationmanagement subsystem.

landscape profile slope length by thecritical slope length. Increase the criticalslope length before making thiscalculation for stripcropping. RUSLE "P" Subfactor Values for

TerracingUse the same rilVinterrili ratio aspreviously used in determining thetopographic .LS. factor at the site. Usemedium for cultivated cropland and otherland uses with moderately consolidatedsoil conditions.

b.The following information is required:

Detennine the slope steepness of thelandscape profile. Will it change withconstruction of terrace? If yes, detenninenew slope steepness.

8.

From Figure P-4, select the appropriatefigure for the land use rilVinterrili ratio andthe site slope steepness.

c.

b. Determine what supporting conservationpractice will accompany the terraces,contouring, cross-slope farming, bufferstrips, or contour stripcropping.d

c. Decide whether terrace will have an openor closed outlet.

From the actual slope length/critical slopelength ratio on the horizontal axis of theselected figure, project a vertical line tointersect the .p. subfactor valuedeten-nined in Step 2 above. From thatintersection, project a horizontal line tothe left and read the effective .p.subfactor value. This subfactor value isthe corrected .p. subfactor value forstripcropping and applies to the entirelandscape profile slope length.

d If the terrace has an open outlet,detennine the channel grade of terrace atoutlet end. The terrace outlet for thisdetennination is defined as the lesser ofthe 300 feet or 1/3 of the terrace closestto the outlet. If channel grade is 0.8 orgreater, the practice factor equals 1.0. Inthis case, skip Step 2 below and proceedwith Step 3 below.

Step 4 - Multiply the contour Hp" subfactortimes the stripcropplng "pH subfactor toget the composite HpH factor for the sheetand rill erosion conservation managementsubsystem.

Step 1 - Determine terrace "P" subfactor.

When the critical slope is not exceededfor stripcropping, use the unadjusted .L.for slope length contour .p. subfactorvalue determined earlier using thecontour .p. subfactor instructions. Takethe .p. subfactor for stripcropping timesthe contour .p. subfactor to get thecomposite .p. factor for the conservationmanagement subsystem.

a.From Table P-7, select the appropriatehorizontal spacing interval. Read acrossthe row to the selected outlet type. If anopen outlet is used. then select theterrace channel grade range column thatdescribes the design terrace channelgrade. Read the .p. subfactor value atthe row-column intersection.

b.

Step 2 - If terrace horizontal spacinginterval is less than landscape profileslope length, recalculate the ilLS" value toreflect a shorter sheet and rill erosion flowlength.

a. If significant earthmoving will cause achange in landscape profile slope,recompute landscape profile slopesteepness and length and record for usein Step 2.

When the critical slope is exceeded forstripcropping, adjust the contour .p.subfactor value using the ratiodetermined by dividing the total slopelength by the critical slope length forstripcropping. From Figure P-4, enterappropriate figure with this ratio anddetermine adjusted contour .p.subfactor. Take this adjusted contour .p.subfactor times the adjusted .p.subfactor for stripcropping to get the


six percent slope. Read the .p. subfactorvalue of 0.53 for on-grade contouring.

b. Determine new "LS" value fromappropriate "LS" table. For croppedagricultural land. use Table L5-1.

Step 3 - Adjust contouring "P" subfactorfor ridge/furrow grade.Step 3 - Determine composite .pH factor

for te~cing when used In combinationwith contouring a/one or with contouringand strlpcropping.

The ridge/furrow to field slope steepnessratio is calculated by dividing 1 % by 6% =0.167 rounded up to 0.2.

8.

a. When terraces are used in conjunctionwith contouring or cross-slope farming,multiply terrace .p. subfactor times thepreviously determined contouring .p.subfactor to get the composite .p. factor.

Go to Table P-3 as ridge/furrow to fieldslope ratio >0.05 indicates a correctionapplies.

b.

Since Table P.3 does not have an on-grade contour line for 0.53, round thevalue up or down to 0.52 or 0.54. Sincethe ridge/furrow to slope grade ratio wasrounded up, round down this time to 0.52.

cb. When terraces are used in conjunction

with contouring, buffer strips, orstripcropping, multiply atl applicable .p.subfactors together to get the composite.p. factor.

Enter Table P-2 with the on-gradecontouring .p. subfactor value of 0.52and read across to the ridge/furrow toslope grade ratio of 0.2. The value is0.73. This is the .p. subfactor value foroff-grade contouring where the slope isless than the critical slope.

d.

Example A: Contour "P" FactorDetermination

Step 1 - Gather information.Hydrologic Soil Group B8,


Landscape profile slope steepness = 6percent, slope length = 250 feet, andridge/furrow grade = 1 percent

b.

From Figure P-7 for Hydrologic SoilGroup B. Cover-Management Condition6. at the 6 percent slope" EI "-10 = 100intersect. read a critical length of 300feel The critical slope exceeds the 250-foot slope length at the site so the "P"subfactor value of 0.73 applies to theentire landscape profile slope length.

The 1D-year. EI. = 100 from Figure Pc

The crop rotation is continuous comusing conventional clean tillage. FromTable P-1 this is Cover-ManagementCondition 6.

d.

Ridges and furrows created during complanting are 2 to 3 inches in depth or lowridges from Table P-2.

e Step 5 - Determine the critical slopelength.

Select from Figure P-3 Hydrologic SoilGroup C and Cover-ManagementCondition 6

aStep 2 - Determine the IIp'' subfactor forcontouring on-grade.

From Table P-8, 10-year. EI. = 100 andCover-Management Condition 6. selectthe table for low ridge height (2- to 3-inchridges).

a Enter with the 6 percent slope, read up tothe intersection of 10-year "Er = 80 andacross to find a critical length of 300 feet.The new profile slope length of 150 feetwith terraces does not exceed the criticalslope length so no adjustment of the "P-subfactor is needed.

b.

Find the row for Hydrologic Soil Group Band the value in the intersect column for

b.


Step 6 - Determine composite "P" factor. c.Multiply terrace .p. subfactor 0.77 timesoff-contour .p. subfactor 0.67. Thecomposite "p. factor. 0.52.

Example B: Contour "P" FactorDetermination When Actual SlopeLength Exceeds Critical SlopeLength

Since Table P-3 does not have a line for0.53, round the value up or down to 0.52or 0.53. Since the ridge/furrow to slopegrade ratio was rounded up, round downthis time to 0.52. Enter Table P-3 withthe on-grade contouring .p. subfactorvalue of 0.52 and read across to theridge/furrow to slope grade ratio of 0.2.The value is 0.73. This is the .p.subfactor value for off-grade contouringwhere the slope is less than the criticalslope.

Step 1. Gather information.Step 4 - Determine the critical slopelength.Hydrologic Soil Group C

a. Select Figure P-3 Hydrologic Soil GroupC and Cover-Management Condition 6.

Landscape profile slope = 6 percent,slope length = 450 feet, and ridge/furrowgrade = 1 percent.

b.

b. Enter with the 6 percent slope, read up tointersection of . EI .-10 = 80 and across

to find a critical length of 300 feet. Theprofile slope length of 450 feet exceedsthe critical slope length so adjust the .p.subfactor value of 0.73.

The 1Q-year. EI. = 80 from Figure P-1c.

d, The crop rotation is com-soybeansproduced using conventional cleantillage. From Table P-1 this is Cover-Management Condition 6.

Example C: Contour "P" FactorDetermination for a Crop Rotationwith Varying Ridge Height

A ridge height of 2 to 3 inches is formedby tillage and planting equipment on thissoil. From Table P-2 this is a low ridge.

9.

Step 1 - Assemble information about thecrop rotation. Include the crops grown,ridge height as applicable, and the covermanagement condition for each year Inthe rotation. Select ridge height andcover management condition based onthose conditions during the seedbed andplanting period.

Step 2 - Determine the "P" subfactor forcontouring on-grade.

In Table P-8. . EI . = 80 and Condition 6.

select the table for low ridge height (2- to3-inch ridges).

8.

Find the row for Hydrofogic Soil Group Cand the value in the intersect column for6 percent slope. Read the .p. subfactorvalue of 0.53.

b.

Crop rotation is six years (Cg-Cg-Og-HH-H).

a

b.Step 3 - Adjust contouring .p. subfactorfor rldge/furrow grade.

Calculate the ridge/furrow to field slopesteepness ratio by dividing 1 % by 6% =0.167. Round to 0.2.

a

Crops and tillage practices aremoldboard plow com after hay; mulch tillcom after corn, 50 percent cover; mulchtill oats after com, 30 percent cover;followed by three years of alfalfa.intermediate wheatgrass hay production.Com after hay is row cultivated within 30days of planting.Go to Table P-3 as ridge/furrow to field

slope ratio >0.05 indicates a correctionapplies.

b.Landscape profile is 10 percent slopesteepness, slope length = 400 feet,ridge/furrow grade = 1 percent, 10-year

c

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TG Notice KS-251 , 1/00USDA-NRCS

p. The Factor for Support Practices, page 7

8EI 8 - 90, and Hydrologic Soil Group is

B. Add the values in Step 2 and divide bythe number of years in the crop rotation.The result is the weighted averageannual contour .p. subfactor for the croprotation.

8.

d. Ridge height = 3 to 4 inches for com afterhay, 2 to 3 inches for mulch till com aftercom, 0.5 to 2 inches for oats after com,and 3 years of a"a"a-wheatgrass hay =no ridges. + 0.63 + 0.79 + 1.0 + 1.0 + 1.0 8

5.27/6 years .0.88b.

Cover management condition of comafter hay = 6, com after com = 4, oatsafter com = 5, and alfalfa-wheatgrasshay/hayiage = 2.

e.

Example D: Stripcropping "P"Factor Determination

Step 1 - Gather required information.Step 2 - Calculate the "p. subfactor foreach year where cover managementcondition or ridge height change. Makeadjustments as needed when actual slopelength exceeds the critical slope length.

a. Landscape profile = 10 percent slopesteepness, slope length = 400 feet, 10-year. EI . = 90. Hydrologic Soil Group is

B, and strip boundary grade = 1 percent.

a. Ridge/furrow to profile grade = 10/0divided by 10% = 0.1 for all annual cropswhere ridges are formed.

b

b. Com after hay, on-grade .p. = 0.37 fromTable P-8. Off-grade .p. = 0.56 fromTable P-3. Critical slope length = 190feet from the graphs in Figure P-3.Corrected contour .p. subfactor = 0.85from Figure P-4 for exceeding criticalslope length where actual slopelength/critical slope length is 400 dividedby 190 = 2.1.

Four contour strips are planned withalternating Cover-Management Condition2 for established hay that was seededwith a nurse crop and Cover-Management Condition 6 for clean-tilledcom. Acreage of com and hay is nearlyequal in every year of the crop rotation.

Step 2 - Determine stripcropping "p.subfactor.

From Table P-4, select the contourstripcropping practice .p. subfactor tablefor sod-based rotations and hayestablished with a nurse crop. This tablehas a ridge/furrow grade of 0.5 percent(close to the 1 percent actual row grade).

a

c. Com after com, on-grade .p. = 0.46 fromTable P-8. Off.grade .p. = 0.63 fromTable P-3. From the graphs in FigureP-3, the critical slope length = > 1000 feet.Thus, no adjustment for exceedingcritical slope length is required.

b,

Oats after com, on-grade .p. = 0.70 fromTable P-8. Off-grade .p. = 0.79 fromTable P.3. From the graphs in FigureP-3. the critical slope length = 420 feet.No adjustment for exceeding criticalslope length is required.

d

Locate the intersection of four strips andCover-Management Condition Pairings =2-(6.5). The value of 0.69 is thestripcropping .p. subfactor that appliesfor slopes less than or equal to the criticalslope length.

Step 3 - Determine critical slope length.From Figure P-7 for 10-year. EI. = 90,Cover-Management Condition 6,Hydrologic Soil Group 8, and the 10percent slope, the critical length is 190feet.

aAlfalfa-intermediate wheatgrass hay, noridges present, contour .p. subfactor =1.0.

e

Step 3 - Calculate the weighted averageannual contour "p,. subfactor for therotation.

-USDA-NRCSSection I - General Resource References

TG Notice KS-251 , 1/00


b.b. Multiply 1.5 times 190 to calculate thestripcropping critical length of 285 feet.The 400-foot slope length at the site isgreater than the critical length.

Step 4 - Adjust the stripcropping "P"subfactor for critical slope length.

The crop rotation is com-soybeansproduced using conventional cleantillage. This is Cover-ManagementCondition 6 from Table P-1. A ridgeheight of 2 to 3 inches is formed by tillageand planting equipment on this soil. Thisis a "low ridge- from Table P-2.Contouring will be used. Row grades willparallel terrace channel.Actual slope length/critical slope length is

400/285 = 1.4. From Figure P-4 thecorrected stripcropping .p. subfactor forexceeding the critical slope length is0.83.

Landscape profile (slope steepness) willnot change with terrace construction.

c.

d. Horizontal spacing interval selected is150 feet to split original landscape profileslope length (450 feet) into thirds.Step 5 - Multiply contour "P" subfactortimes stripcropping "P" Subfactor to get

composite "P" factor. Open outlet design with terrace channelgrade at 0.4 percent.

e.a. From Example C, the contouring .p.

subfactor was determined to be 0.56 +0.63 = 0.60. This is an average of thecontour .p. subfactors for the two comyears of the crop rotation.

Step 2 - Determine IIp'' subfsctor forte"scing.

In Table P-7 find Horizontal Intervalrange (terrace spacing) of 150 feet andread across to Open Outlets. withpercent grade of 0.4. Read the terrace.p. subfactor value of 0.77.

Note: This is the contour .p. subfactorfor the com with appropriate cover-management condition beforeadjustment for critical slope and not aweighted average .pH subfactor for comand hay cover-management conditions.Corn cover management conditions arepresent on the field profile a majority ofthe time and alternate positionally backand forth between strip pairs.

Step 3 - Adjust ilLS" value.Slope length after terrace installation is150 feet. Adjust .LS. factor value and re-enter new value into the general RUSLE

equation.

a.

b. From Table LS-1, find the column for 150feet of slope length and the value in theintersected row for 6 percent slope.Read the new .LS. value of 0.93. Enterthis new value Into the general RUSLE

equation.

b.From this example, the contourstripcropping .p. subfactor was 0.83.

Multiply the two subfactors together, 0.60times 0.83 = 0.50. The .p. factor for thisfield's contour stripcropping system is0.50.

c.

Step 4 - Adjust contouring "P" subfactorfor ridgelfurrow grade.

Example E: Terrace "P" FactorDetermination

Contour .p. subfactor is based on a lowridge (2 to 3 inches high), 6 percentslope, 10-year . EI . = 80, and HydrologicSoil Group of C. On-grade .p. = 0.53.

Step 1 - Gather required information.Landscape profile = 6 percent slopesteepness. slope length = 450 feet, 10-year. EI . = BO, and Hydrologic Soil

Group is C.

8.

For 0.4 percent row grade, calculate theridge/furrow to field slope steepness ratioby dividing 0.4% by 6% = 0.066. Roundto 0.1. Go to Table P-3 as ridge/furrow to

b.


field slope ratio >0.05 indicates acorrection applies.


c. Since Table P-3 does not have a line for0.53, round the value up or down to 0.52or 0.54. Since the ridge/furrow to slopegrade ratio was rounded up, round downthis time to 0.52. Enter Table P-3 withthe on-grade contouring .p. subfactorvalue of 0.52 and read across to theridge/furrow to slope grade ratio of 0.1.The adjusted ~P' subfactor value is 0.67.This is the .p. subfactor value for off-grade contouring where the slope is lessthan the critical slope.

a. Select Figure P-3 for Hydrologic SoilGroup C and Cover-ManagementCondition 6.

b. Enter with the 6 percent slope, read up tointersection of 1D-year . EI . = 80 and

across to find a critical length of 300 feet.The new profile slope length of 150 feetwith terraces does not exceed the criticalslope length so no adjustment of the .p.subfactor is needed.

Step 6 - Detennine composite "P" factor.Multiply terrace .p. subfactor 0.77 timesoff-contour .p. subfactor 0.67.Composite .p. factor = 0.52.

Section I - General Resource ReferencesTG Notice KS-251. 1/00

USDA-NAGS

P = The Factor for Support Practices. page 10

Figure P-1 -10-Year Frequency, Single Storm EI Map

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"EI" is an abbreviation for "energy times intensity" and equals the total storm energy times themaximum 30-minute intensity. Storm energy indicates the volume of rainfall and runoff; a long, slowrain may have the same E value as a shorter rain at a much higher intensity. The energy of arainstorm is a function of the amount of rain and of all the storm's component intensities.

Section I - General Resource ReferencesTG Notice KS-251. 1/00

U50A-NRCS


Table P-1 - Cover Management Conditions

Select the cover management condition that best describes the land surface conditions during spring seedbedpreparation and planting when rainfall and runoff are most erosive and the soil is most susceptible to erosion.Use the following descriptions of cropland cover-management conditions for estimating "P" factor values.

DescriptionCover-Management Conditions

The grass cover is dense and runoff is very slow--theslowest under any vegetative condition. When mowed andbaled, this condition is Code 2.

Code 1. Established grass/legume cover

Hay is a mixture of grass and legume just before cutting.The vegetation is a good grass/legume stand and isharvested for hay. When harvested, this cover conditionbecomes a Code 4 until regrowth occurs.

Code 2. Established hay under harvest management

Ground cover for this condition is about 65 to 95 percentas with no-till planting. Roughness depressions wouldhave the appearance of being 7 inches deep and deeper

Code 3. Heavy cover and/or very rough

The ground cover for this condition is about 40 to 65percent. Roughness depressions would have theappearance of being about 4 to 6 inches deep.

Code 4. Moderate cover and/or rough

I Code 5. Light cover and/or rough Ground surface cover is between 10 to 40 percent.Roughness depressions would have the appearance ofbeing on the order of 2 to 3 inches deep.

Code 6. No cover and/or minimal roughness This condition is very much like the condition typicallyfound in row-cropped fields after the field has been plantedand exposed to a moderately intense rainfall. Groundcover is less than about 10 percent and the roughnesscharacteristic of a good seedbed for corn or soybeans.The surface is rougher than that of a finely pulverizedseedbed for seeding vegetables or grass.

Code 7. Clean-tilled. smooth fallowThis condition is essentially bare with a cover of 5 percentor less. The soil has not had a crop grown on it in the last6 months or more. Many residual effects of previouscropping have disappeared. The surface is smooth, muchlike the surface that develops on a finely pulverizedseedbed exposed to several intense rainfalls. Thiscondition is found in fallow and vegetable fields or in newlyseeded lawns.

USDA-NRCS TG NoticeGeneral Resource ReferencesSectionKS-251. 1/00


Table P-2 - Guidelines for Selecting Ridge Heights

Select the ridge height that best describes the condition during the spring seedbed preparation andplanting when rainfall and runoff are most erosive. and the soil is most susceptible to erosion.

",:'

-Plants not closely spaced but with a slight ridge height-No-till planted row crops-Fields that have been rolled. pressed. or dragged after planting-Spring planted conventionally drilled crops-Direct seeded forage crops that leave a very low ridge

I'~'

-No-till drilled crops-Mulch tilled row crops-Clean tilled row crops with no row cultivation-Transplanted crops, widely spaced

3.

~

-Clean tilled row crops with row cultivation-High yielding winter small grain crops when erosive rains are concentrated in the late springafter plants have developed a stiff, upright stem-Transplanted crops that are closely spaced and/or in narrow rows

~~

.1j

4. .. rill

~

-Ridge tilled crops with high (4-6") ridges during periods of erosive rain

5. Very High (Greater than 6 Inch) Ridges '.." c"':'.;...c""":r?; .;"c'",'.. c,

-Ridge tilled crops with very high (6+") ridges during periods of erosive rains-Hipping, bedding. or ridging with very high ridges during periods of erosive rains

Section I - General Resource ReferencesTG Notice KS-251 , 1/00

USDA-NAGS


Table P-3 - Contouring "P" Subfactor Value Adjusted for Ridge/Furrow Grade

1.001.001.001.00

0.900.900.900.90

0.950.950.950.95

0.780.790.790.80

0.840.850.850.85

0.650.650.660.67

0.720:720.730.74

0.570.570.580.59

:0.340.360.370.38

0.470.480.490.50

0.040.060.080.10

1.001.001.001.001.00

0.950.960.960.960.96

o.o.o.o.o.

0.910.910.910.910.92

0.740.750.750.760.77

0.800.810.810.820.82

0.600.610.620.630.64

0.680.680.690.700.71

0.400.410.430.440.45

0.510.520.540.550.56

0.120.140.160.180.20

1.001.001.001.001.00

0.920.920.920.920.93

0.960.960.960.960.96

0.870.880.880.880.89

0.710.720.730.740.74

0.770..780.780.790.79

0.820.830.830.840.84

0.650.660.670.670.68

0.470.480.490.510.52

0.570.580.590.600.61

0.220.240.260.280.30

0.970.970.970.970.97

1.001.001.001.001.00

0.930.930.930.930.94

0.800.810.810.820.82

0.850.850.860.860.86

o.o.o.o.o.

0.750.760.760.770.78

0.620.640.650.660.67

o.o.o.o.o.

o.o.o.o.o.

0.540.550.560.580.59

0.970.970.970.970.97

1.001.001.001.001.00

0.910.910.910.920.92

o.o.o.o.o.

0.830.840.840.850.85

0.870.870.880.880.89

0.790.790.800.810.82

o.o.0..o.o.

0.680.690.700.710.72

0.740.750.760.760.77

0.420.440.440.480.50

0.980.980.980.980.98

1.001.001.001.001.00

0.890.900.900.910.91

0.920.920.930.930.93

o.o.o.o.o.

0.820.830.840.850.85

0.860.870.870.880.88

0.730.750.760.770.78

0.780.790.800.810.82

0.520.540.560.580.60

0.670.690.700.710.73

0.980.980.980.980.98

1.001.001.001.001.00

0.940.940.940.950.95

o.o.o.o.o.

0.890.890.900.910.91

0.910.920.920.930.93

o.o.o.o.o.

o.o.o.o.o.

0.740.750.170.780.79

0.790.800.810.820.83

o.o.o.o.o.

0.990.990.990.990.99

1.001.001.001.001.00

0.950.960.960.960.97

0.970.970.970.980.98

0.920.920.930.940.94

0.940.940.950.950.95

0.870.880.890.900.91

0.900.900.910.920.93

0.810.820.840.850.86

0.850.860.870.880.89

0.720.740.7~0.780.80

USDA-NAGSSection I - General Resource ReferencesTGNotice KS-251 , 1/00

8686868787

8989909090

6970717273

3234363840

9494949595

6062636466

9595959696

9696969797

8384858686

8687888889

6264666870


Table P-3 - Contouring "P" Subfactor Value Adjusted for Ridge/Furrow Grade (continued)

0.970.970.980.980.98

0.980.980.990.990.99

0.990.990.990.990.99

1.001.001.001.001.00

0.920.930.940.950.95

0.930.940.950.960.96

0.950.950.960.960.97

0.960.960.970.970.98

0.820.840.860.880.90

0.880.890.900.920.93

0.900.910.920.930.94

0.990.990.991.001.00

0.990.991.001.001.00

1.001.001.001.001.00

1.001.001.001.001.00

0.960.970.980.991.00

0.970.980.990.991.00

0.980.980.990.991.00

0.980.990.991.001.00

0.920.940.960.981.00

10.0.'

10.lO., 1.'

0.960.970.980.991.00

Section I - General Resource ReferencesTG Notice K5-251. 1/00

-USDA-NRCS

9596979900


Table P-4 - Contour Stripcropping Practice "P" Subfactor

This table is based on an average row gradient of 0.5 percent, low ridge height (2 to 3 inches), 12 percent RUSLEslope gradient with the number of strips listed spanning 100 percent of the RUSLE slope length, and only 2 cover-management conditions being on the RUSLE slope at any given time.

Y Rotations where cross-slope sod strips are alternated with cross-slope cultivated strips down the slope -Sediment deposition is induced by the sod.

gI Sod-based rotations where hay crop is established in the spring without a nurse or companion crop of smallgrain - Ha" of the strips are always in hay, which is condition 2.

~I Sod-based rotations where a companion crop of small grain is sown with hay seed, or hay crop is sown instubble after small grain harvest - Ha" of the strips are always in hay.

,41 Rotations where cross-slope strips of contrasting residue amounts or surface roughness are ahemated down theslope or strips of small grain ahemate with clean-tilled row crops - Sediment deposition is induced by a strip thatis either rougher surfaced or more residue-covered or has standing small grain or small grain stubble. Seasonalshifts in location of the sediment trapping versus sediment-producing strip during the cropping year areacceptable as long as the contrasting cover strip types ahemate at all times.

.§.I Rotations where strips with greater than 75 percent residue cover or roughness depressions 7 inches or deeperalternate with strips of lesser cover or shallower tillage depressions at all times

§/ Rotations where strips with greater than 40 percent but less than 75 percent residue cover or surface roughnessdepressions, 4 to 6 inches deep, or strips of growing small grain or small grain stubble, ahemate with strips oflesser cover or shallower tillage depressions at all times

~

P = The Factor for Suppon PractIces, pa9~ ) 0

Table P-5 - Field Stripcropping Practice liP" Subfactor

This table is based on an average row gradient of 3.0 percent. low ridge height (2 to 3 inches), 12 percent RUSLEslope gradient with the number of strips listed spanning 100 percent of the RUSLE slope length, and only 2 cover-management conditions being on the RUSLE slope at any given time.

1/ Rotations where cross-slope sod strips are alternated with cross-slope cultivated strips down the slope -Sediment deposition is induced by the sod.

?! Sod-based rotations where hay crop is established in the spring Without a nurse or companion crop of smallgrain - Half of the strips are always in hay, which is condition 2.

'J/ Sod-based rotations where a companion crop of small grain is sown With hay seed. or hay crop is sown instubble after small grain harvest - Half of the strips are always in hay.

~ Rotations where cross-slope strips of contrasting residue amounts or surface roughness are alternated down theslope or strips of small grain alternate With clean-tilled row crops - Sediment deposition is induced by a strip thatis either rougher surfaced or more residue-covered or has standing small grain or small grain stubble. Seasonalshifts in location of the sediment trapping versus sediment-producing strip during the cropping year areacceptable as long as the contrasting cover strip types alternate at all times.

§! Rotations where strips with greater than 75 percent residue cover or roughness depressions 7 inches or deeperaltemate with strips of lesser cover or shallower tillage depressions at all times

§! Rotations where strips with greater than 40 percent but less than 75 percent residue cover or surface roughnessdepressions, 4 to 6 inches deep, or strips of growing small grain or small grain stubble, alternate with strips oflesser cover or shallower tillage depressions at all times

- -Section I - General Resource References

TG Notice KS-251 , 1/00USDA-NRCS

P = The Factor for Support P

Table P-6 - Buffer Stripcropping Practice "P" Subfactor

~

~ This table is based on an average row gradient of 0.5 percent, low ridge height (2 to 3 inches), 12 percent RUSLEslope gradient with the number of strips listed spanning 100 percent of the RUSLE slope length. a continuous cover-management condition on all cultivated crop strips, and the position of the buffer/crop strips on the slope as shownbelow. Use the upper portions of this table for buffer strips that are left in an unharvested condition. Use the lowerportion of this table for buffer strips that are mowed and/or harvested for forage.1/ Ratio of cultivated crop strip to perennial sod (buffer) strip - A ratio of 9:1 means 10 percent of the RUSLE slope

length is in buffer strip(s). A ratio of 4:1 is 20 percent of the RUSLE slope length in buffer strip(s).

,,-..

The actol lor Support Prac :es, page 1

Figure P-2 - Buffer Strip Systems

oSITION OF STRIPS ON RUSLE SLOPE

(TOP OF SLOPE)

POSITION OF STRIPS ON RUSLE SLOPE

(TOP OF SLO,

CROP

.-,BUFFERCROP

CROP

'~FFeecSUFFER

(BOTTOM OF SLOPE**..****.***

(BOTTOM OF SLOPE,*******************************

flv:E-STijlP SYST~POSITION OF STRIPS ON RUSLE SLOPE

(TOP OF SLC.OPE

IPE

(TOP ( SLOPECROP

CROP,i:; B'"r~ R~~:.;:Ufjl;i~c'

BUFFER

CROFB UFFE R r~".

,..

~OPtPE~OTTOM

.**********F Sl'r*****

(BOTTOM OF SLOPE'*********************

be expE anditior .trips herE 'WErela

'-NRC - General ResoulTG Notice KS-25'

iectior erence


Table P-7 - Terrace "P" Subfactor

;~~\;t,. ~~ ..j~~, ~..

~

~~i .::\!;;~~. $,:;:' ...'~;~:

~

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