Crop Database Record Development

Introduction

In the plant growth submodel of the Wind Erosion Prediction System (WEPS), biomass is converted from solar radiation and partitioned to root and shoot parts (Fig. 1.34). The shoot mass is partitioned into leaf, stem, and reproductive masses. Finally, the reproductive mass is partitioned into grain and chaff parts. Development of the crop in WEPS is a function of the heat-unit index, which is the ratio of the heat units (growing degree days) at any time during the growing season to the total amount of heat units required to grow a crop from planting to maturity. The heat-unit index is 0 at planting, and the crop reaches maturity when the heat-unit index is 1.

To perform these and other operations, crop growth in WEPS is configured by a set of parameters that define and drive the growth processes represented in the model code. Reasonable crop growth in different environments is achieved by setting the appropriate parameter values for the type of crop being grown. The purpose of this guide is to define and describe the process of obtaining reasonable parameter values based on knowledge of crop characteristics.

After estimating a parameter value, specific WEPS output can be examined to see if the parameter setting gives reasonable results. Not all WEPS output is available through the WEPS interface output reports. Therefore, the user is sometimes referred to other output files, such as 'crop.out' which contains daily output for many crop variables and 'decomp.out', which contains daily output for many decomposition variables. A parameter should be adjusted if a related simulated variable does not look reasonable. After adjusting the parameter(s), run WEPS again and inspect the variable again to see if it matches what is expected. If not, continue to adjust the parameter values on this trial-and-error basis. Be sure to look at simulation output for more than one growing season.

Crop Database Structure Files and Definitions

Crop database records are stored in an XML format file with the extension .crop for use by the WEPS interface. Supporting files that define the database structure are part of the MCREW configuration files. New individual crop database records are most directly created by using MCREW to edit an existing crop file and saving it to a new name. New files can also be created with a text editor to edit the .crop file directly. The parameter descriptions herein provide the keys to enable the reader to know which parameter is being edited by either method.

The parameters are defined with units and are identified by a Parameter Prompt, which is the text that appears in the MCREW Crop drill-down screen. Some parameters have Parameter Choices, a list of choices that will be displayed when the parameter is defined as a discrete set of values, often integer flags. The parameters are grouped according to similar function, just as they are grouped by tabs on the Crop drill-down screen. Some parameters have both primary and alternate units which, along with a conversion factor, are given in Table 1.2.

Note that for NRCS most parameter choices will not be editable by Field Office Users. NRCS will use a database manager to adjust and distribute new or revised database file.

Table 1.2. Parameters having both primary and alternate units. The WEPS science model uses the primary units. Alternate units are used if English units are selected in the WEPS configuration. To convert from primary units to alternative units multiply by the given conversion factor (and add 32 where indicated).

Parameter Prompt	Primary Units	Alternative Units	Conversion Factor
Plant population	#/m2	#/acre	4046.7
Planted mass, dry weight	mg/plant	ounce/plant	3.5274*10-5
Root storage mass required for each regrowth shoot	mg/shoot	ounce/shoot	3.5274*10-5
Heat units to maturity	°C day	°F day	1.8
Minimum temperature for plant growth	°C	°F	1.8 + 32
Optimum temperature for plant growth	°C	°F	1.8 + 32
Maximum growth diameter of a single plant	m	ft	3.281
Residue : Yield intercept	kg/m2	lb/acre	8921.8
Maximum root depth	m	ft	3.2808
Maximum crop height	m	ft	3.2808
Lower temperature	°C	°F	1.8 + 32
Higher temperature	°C	°F	1.8 + 32
Stalk diameter	m	inches	39.3696
Mass to cover factor	m2/kg	acre/lb	0.00011209

Crop Parameter Definitions

Shoot Tab

The emergence of plant shoots, from either seeds, stored root mass, or the pseudo emergence of transplants, is controlled by four crop parameters: "Planted mass, dry weight", mp , "Root storage mass required for each regrowth shoot", msh, "Ratio of leaf mass/stem mass in shoot", rls, and "Ratio of stem diameter to stem length", rdl, and two parameters described later in this document: "Stem silhouette area coefficient a" and "Stem silhouette area coefficient b". Note that the "Root storage mass required for each regrowth shoot" is mostly used in regrowth calculations. If the "Planted mass, dry weight" is greater than the "Root storage mass required for each regrowth shoot", then multiple shoots per plant will be generated. The number of shoots per plant, nsh, that will grow from the planted (stored) mass, is calculated from:

where nms is the "Maximum number of shoots per plant" and Nsh is the number of shoots per square meter. Note that nsh does not have to be an integer. The shoot growth subroutines assume a 70% conversion efficiency from stored to live biomass. When growth is from seed or a transplant, 40% of growth biomass will become roots. The stem length at full extension is calculated as:

where mst is the mass of stem generated in the complete emergence process, Ast is the silhouette area of a single stem, and lst is the length of stem generated at full extension. Full extension has been realized when all of the planted (stored) mass (mp) has been converted to generated shoot mass. Emergence occurs when lst is greater than the "Starting depth of growing point". An error message is generated if emergence never occurs.

Parameter Prompt: Crop Type

Parameter Choices:	1 - Warm-season legume (soybeans, etc.)

2 - Cool-season legume (peas, etc.)

3 - Perennial legume (alfalfa, etc.)

4 - Spring seeded and warm-season annuals (spring wheat, cotton, sunflowers, corn, etc.)

5 - Cool-season annuals (winter wheat, winter canola)

6 - Perennials (pasture, etc.)

This selection determines crop growth processes, such as vernalization (crop types 2 and 5 implement a vernalization delay to overwinter heat-unit accumulation), and the ability to regrow after cutting (crop types 3 and 6 will regrow if sufficient root or crown storage has been accumulated).

Parameter Prompt: Transplant or Seed flag

Parameter Choices:	0 - Seeds planted in field

1 - Transplants planted in field (mass immediately divided into root, leaf, stem).

This flag is set to indicate that plant growth begins with a transplant or with a seed being placed in the field. If growth begins with a transplant (as opposed to grown from seed), a number of additional parameters need to be adjusted: the length of the growing season will need to be shortened, by either days or heat-units, to represent the time from transplant to maturity; the planted mass, dry weight, should be adjusted to represent the size of the transplant; and the heat-unit index at (pseudo) emergence, should be adjusted to represent a reasonable transplant-shock recovery time.

Parameter Prompt: Plant population, Np ( #/m2)

The number of plants expected in a normal stand. This should be the estimated plant population after germination. If the maximum number of shoots per plant (next parameter) is set to one, then this is the total number of stems expected.

Parameter Prompt: Maximum number of shoots per plant, nms (#/plant)

Growth of multiple shoots occurs when this value is greater than one and root (crown) storage mass is greater than "Root storage mass required for each regrowth shoot" at the time regrowth commences. The number of stems produced can be examined by viewing the number of stems per square meter (the variable '#stems' in the output file 'crop.out') and comparing it with the "Plant Population" (previous parameter).

Parameter Prompt: Starting depth of growing point (m)

Crop growth begins at this depth in the soil. Root extension proceeds downward from this depth, while shoot extension proceeds upward from this depth at equal rates. It is necessary that the shoot growth parameters result in a shoot length greater than this depth or seedlings will not emerge. This depth is used as the depth from which regrowth begins for crop types 3 and 6 at all times. For crop types 1 and 4, the growing point is moved to the surface at the completion of seedling emergence. For crop types 2 and 5, the growing point is moved to the surface after the initiation of spring growth.

Parameter Prompt: Planted mass, dry weight, mp (mg/plant)

At planting time, total plant biomass is initialized to this value. From the time of growth initialization until the completion of emergence, this mass is allocated to roots, stems, and leaves. For a crop grown from a seed, the mass should be set to the individual seed weight. For a crop that is placed in the field as a transplant, the total plant dry weight, including roots, should be entered.

Parameter Prompt: Root storage mass required for each regrowth shoot, msh (mg/shoot)

As described previously, the number of shoots that grow from stored root mass is calculated based on this parameter. For crops that can regrow from stored root or crown mass, this value is used, along with the "Maximum number of shoots per plant" and the stored root mass of the crop to determine how many shoots will re-sprout. The partitioning of mass to be stored for regrowth is set by using the parameters "Fraction of leaf mass partitioning diverted to root storage", "Fraction of stem mass partitioning diverted to root storage", and "Fraction of standing store mass partitioning diverted to root storage". The quantity stored varies depending on growth conditions.

Parameter Prompt: Ratio of leaf mass/stem mass in shoot, rls

This is the ratio at full extension. When the growth of a shoot from stored mass occurs, as in germination, regrowth after cutting, or the pseudo growth used to initialize a transplant, mass is divided into leaf and stem according to this ratio. This value should be large enough to generate the leaf area required to get crop growth started. If a crop does not grow adequately, examine the variable 'eff_lai' in the output file 'crop.out'. It should show a value of 0.01 or greater at the heat-unit index at emergence.

Parameter Prompt: Ratio of stem diameter to stem length, rdl

This is the ratio at full extension. When the growth of a shoot from stored mass occurs, as in germination, regrowth after cutting, or the pseudo growth used to initialize a transplant, stem length is calculated from stem mass according to this ratio. This parameter is the prime candidate for adjustment to ensure that plant emergence occurs when growing from seed.

Parameter Prompt: Heat-unit index at emergence

Setting this value to zero will cause the program to fail.

Growth Tab

Parameter Prompt: Crop maturity measurement method

Parameter Choices:	0 - Crop matures on average in Days shown

1 - Crop matures in Heat Units shown

For some types of crops, corn being the best example, the length of the growing season is genetically manipulated, and the average length of the crop growth period for that area is expressed in days, not heat units. When this option is set to 0, the average weather for the location being simulated is used to find the heat unit accumulation from the planting day through the number of days shown in the "Days to maturity" parameter. The simulation is then run using this heat unit total as the season length. For option 1, the value entered for "Heat units to maturity" is used directly, regardless of location. Because the effect of vernalization on the calculation of average heat units is not implemented, all crop types 2 (cool season legumes like peas) and 5 (cool season annuals like winter wheat and winter canola) should be configured to use option 1.

Parameter Prompt: Days to maturity (days)

For annual grain crops, the average number of days from planting to maturity of seed. For vegetable, fruit, and root crops; sugarcane; and tobacco, it is the number of days from planting (or ratooning) to harvest. For perennials (e.g., alfalfa), it is the number of days from spring growth to maturity of seed.

Parameter Prompt: Heat units to maturity (oC day)

For annual grain crops, the average seasonal heat units from planting to maturity of seed. For vegetable, fruit, and root crops; sugarcane; and tobacco, it is the average seasonal heat units from planting (or ratooning) to harvest. For perennials (e.g., alfalfa), it is the average seasonal heat units from spring growth to maturity of seed.

Parameter Prompt: Heat unit index at start of senescence (fraction)

This is the fraction of the growing season (expressed as heat-unit index) during which plant senescence begins. Examine the variable 'eff_lai' in the output file 'crop.out' to see the effect of adjusting this parameter.

Parameter Prompt: Minimum temperature for plant growth (oC)

The average daily air temperature below which the model will not allow plant growth (full temperature stress). This is commonly known as the minimum cardinal growth temperature and forms the base temperature for calculating heat-unit accumulation.

Parameter Prompt: Optimum temperature for plant growth (oC)

The average daily air temperature at which the model will allow maximum growth (no temperature stress). This is commonly known as the maximum cardinal growth temperature and forms the upper temperature for calculating heat unit accumulation. When the average daily air temperature exceeds this value, heat-units accumulate at the maximum rate for the day, and temperature stress increases.

Geometry Tab

Parameter Prompt: Maximum growth diameter (m) of a single plant

Some cropping systems use plant densities that do not result in canopy closure. In these systems, the plant will grow to cover a ground area that is characteristic of the plant. WEPS assumes that the covered ground area is round. This parameter is the diameter of the circle that encloses the covered area. Biomass production is reduced by the decrease in intercepted light (some of the light reaches the soil), unless the reduced densities are used to reduce water stress for the remaining plants.

Parameter Prompt: Stem silhouette area coefficient a

Parameter Prompt: Stem silhouette area coefficient b

For many crops, the relationship of stem silhouette area to its mass is described well by a 2-parameter power function, which is used to compute stem silhouette area from stem mass: SSA = a Mb, where SSA is stem silhouette area (m2 / plant), M is stem mass (kg / plant), and a and b are coefficients. Retta and Armbrust (1995) obtained values for alfalfa, corn, sorghum, oat, winter wheat, and soybean.

Parameter Prompt: Specific leaf area (m2 / kg)

For many crops, the relationship of leaf area to its mass is described well by a linear relationship, which is used to compute leaf area from leaf mass: LA = a M, where LA is leaf area (m2 / plant), M is leaf mass (kg / plant), and a is specific leaf area (m2 / kg).

Parameter Prompt: Light extinction coefficient

Canopy light utilization is specified by an exponential relationship for the attenuation of light with distance into the canopy. Combined with the leaf-area index, this coefficient determines the amount of light interception by the canopy according to the relationship:

where fraction is the ratio of photosynthetically active radiation (PAR) that is intercepted by the crop and total PAR received above the crop canopy, k is light extinction coefficient, and LAI is leaf area index (Fig. 1.35). A higher number indicates more light interception by a given leaf area index, as occurs with broadleaf plants with a horizontal leaf orientation, such as cotton. A lower number indicates decreased light interception by a given leaf area index, as occurs with narrow leaf plants with a vertical leaf orientation, such as the grasses.

Parameter Prompt: Biomass Conversion Efficiency (t/ha) / (MJ/m2)

The unstressed (potential) growth rate per unit of intercepted photosynthetically active radiation. EPIC values were used as a starting point for the major crops. Literature searches revealed that this value is difficult to measure exactly. This parameter is key to making the crop grow correctly.

Partitioning Tab

The daily converted (grown) biomass is partitioned between root and shoot mass (Figure 1.34). The shoot mass (above-ground biomass) is further partitioned into leaf, stem, and reproductive mass (Figure 1.36). Both the leaf curve and the reproductive curve are defined by a 4-parameter function. The remaining mass is considered stem mass. The three fractions always add to 1.0.

Specify the four parameters for the leaf curve (Figure 1.37):

Parameter Prompt: Leaf fraction coefficient a

The lower asymptote.

Parameter Prompt: Leaf fraction coefficient b

The range between the upper and lower asymptote.

Parameter Prompt: Leaf fraction coefficient c

The heat-unit index at the inflection point. The leaf mass / shoot mass ratio at the inflection point is half way between the lower and upper asymptote (a + b/2).

Parameter Prompt: Leaf fraction coefficient d

Determines the slope of the curve. A negative d produces a descending curve (leaf) and a positive d gives an ascending curve (reproductive).

Specify the four parameters for the reproductive curve:

Parameter Prompt: Reproductive mass coefficient a

The lower asymptote.

Parameter Prompt: Reproductive mass coefficient b

The range between the upper and lower asymptote.

Parameter Prompt: Reproductive mass coefficient c

The heat-unit index at the inflection point.

Parameter Prompt: Reproductive mass coefficient d

Determines the slope of the curve at the inflection point.

For a new crop, the four leaf parameters can be adjusted on the basis of total leaf mass development (the variable 'total leaf' in the output file 'crop.out'). Check total stem mass development by inspecting the variable 'total stem' in the output file 'crop.out'. If stem mass development seems unsatisfactory, adjust both leaf and reproductive parameters to change the stem partitioning curve.

Reproductive mass should be equal to zero before time of flowering. This may be used as a point on the reproductive partitioning curve. Inspect the variable 'standing store' in the output file 'crop.out'. If 'standing store' is greater than zero before flowering is expected, partitioning to reproductive mass starts too early in the growing season. Adjust the reproductive parameters accordingly.

By default (option Y1), WEPS does not use the reproductive parameters. WEPS will only use them if the Y0 option is specified. If using the reproductive parameters for partitioning then harvest index is also something to look at. Adjust partitioning parameters if the harvest index seems incorrect. Remember that adjusting leaf and/or reproductive parameters will automatically affect stem mass partitioning.

The default method for partitioning and to calculate crop yield from total above-ground biomass uses parameters r and b to specify the relationship between yield and residue, where yield (at market-standard moisture content) plus residue (dry weight) equals total above-
ground biomass. The equation is:

where b is the minimum above ground biomass required for a crop to generate any yield, and r is the incremental increase in residue for each additional unit of yield in excess of the minimum. The two parameters were estimated for the major crops from field data gathered for this purpose.

Parameter Prompt: Residue : Yield ratio (kg/kg)

Parameter r. As defined for the residue equation, this is the incremental increase in residue for each additional unit of yield in excess of the minimum (i.e., yield mass / residue mass).

Parameter Prompt: Residue : Yield intercept (kg/m2 or lbs/ac)

Parameter b. As defined for the residue equation, this is the minimum biomass required for a crop to generate any yield.

Biomass is estimated to be stored in the root (or crown) storage pool on the basis of the values of the following three parameters. They are tied to the three biomass partitioning components (leaf, stem, reproductive) of plant growth, allowing the modeling of plants that store biomass during different periods of the growing season (Fig. 1.34).

Parameter Prompt: Fraction of leaf mass partitioning diverted to root storage

For crops that store biomass early in the growth season, set this value greater than zero.

Parameter Prompt: Fraction of stem mass partitioning diverted to root storage

For crops that store biomass in the middle of the growth season, set this value greater than zero.

Parameter Prompt: Fraction of reproductive mass partitioning diverted to root storage

For crops that store biomass late in the growth season, set this value greater than zero. For root crops, this value should be very close to 1, indicating that most reproductive biomass is stored below ground.

Size Tab

Parameter Prompt: Maximum root depth (m)

The maximum depth of roots attained by the crop under ideal (unstressed) growth conditions. The main modeling impact of this value is the depth of soil water extraction. Examine the variable 'rootd' in the output file 'crop.out' to see the effect of adjusting this parameter.

Parameter Prompt: Maximum crop height (m)

The maximum height attained by the crop under ideal (unstressed) growth conditions. For a new crop, this parameter can be adjusted based on the crop height (the variable 'height' in the output file 'crop.out'). If WEPS simulates a crop that is too tall (inspect 'height'), then decrease the parameter value. After adjustment, inspect the height variable again to see if it matches what is expected. If not, continue to adjust the parameter values on this trial-and-error basis. Be sure to look at simulation output for more than one growing season. Note that the crop height at the end of the growing season will usually be less than this maximum crop height. Only if the crop grows under unstressed conditions for the entire growing season will the crop height at the end of the season be equal to the maximum crop height.

Crop height development through the growing season, as it would be without any stresses (potential), is defined by a 2-parameter function (Figure 1.38). This curve should be in harmony with the partitioning curves discussed earlier (i.e., the greatest increase in plant height should coincide with the greatest stem partitioning ratio).

Specify the two parameters for the crop height development curve (Figure 1.38):

Parameter Prompt: Crop height coefficient a

The heat unit index at the inflection point.

Parameter Prompt: Crop height coefficient b

Determines the slope of the curve at the inflection point. A negative b produces an ascending curve.

For a new crop, the two crop height parameters can be adjusted based on the crop height (the variable 'height' in the output file 'crop.out'). If WEPS simulates a crop that is too tall too early in the growing season (inspect 'height'), then increase the "a" parameter value. If WEPS simulates too gradual a crop height increase (inspect 'height'), then increase the "b" parameter value (make b less negative). Changing a and/or b may cause the final crop height to change. This can be adjusted by changing the maximum plant height.

Cold Tab

In WEPS, freezing temperatures can reduce green leaf area. This reduction is calculated from a curve (Figure 1.39). For example, using Figure 1.39, if the daily minimum temperature of the top soil layer equals -15 oC, the green leaf area is reduced by 95% on this day.

The user can specify the frost damage curve by specifying two points on the curve. The curve for corn in Figure 1.39 is specified by the points (-5, 0.01) and (-15, 0.95). Use the Excel spreadsheet tool to visualize the curve after specifying two points on the curve. The following four parameters specify the two points:

Parameter Prompt: Higher temperature (oC)

This is -5 oC (23 oF) for the example in Figure 1.39.

Parameter Prompt: Reduction in green leaf area at higher temperature (fraction)

This is 0.01 (1%) for the example in Figure 1.39.

Parameter Prompt: Lower temperature (oC)

This is -15 oC (5 oF) for the example in Figure 1.39.

Parameter Prompt: Reduction in green leaf area at lower temperature (fraction)

This is 0.95 (95%) for the example in Figure 1.39.

For a new crop, these four parameters can be adjusted based on the green leaf area (the variable 'eff_lai' in the output file 'crop.out'). Example: the new crop is a winter crop. If WEPS simulates too much reduction in green leaf area over the winter (inspect eff_lai), then adjust the four parameter values so that there is less reduction in green leaf area for the same freezing temperatures.

Parameter Prompt: Thermal delay coefficient pre-vernalization

For winter annual crops (crop types 2 and 5), the rate of heat-unit accumulation is reduced if the plants have not been exposed to cool temperatures. The method implemented is from Ritchie, J.T. (1991). For crops that do not experience vernalization, the value is set to 0.0. A crop requiring a high degree of vernalization would have a value around 0.04. Examine the variable 'hu_del' in the output file 'crop.out' to see the effect of adjusting this parameter. This variable is 0.0 when vernalization has not yet started, and it is 1.0 when the crop is fully vernalized.

Harvest Tab

Parameter Prompt: Which plant component is (partly) harvested?

Parameter Choices:	0 - constant fraction of reproductive mass (grain+)

1 - increasing fraction of reproductive mass (grain)

2 - all or fraction of aboveground biomass

3 - all or fraction of the leaf mass

4 - all or fraction of the stem mass

5 - all or fraction of underground mass

Crop harvesting operations remove parts of plants that are not explicitly specified as a plant part in the model. To compensate for this, a mass fraction can be specified (see parameter "Harvested fraction of plant component") to divide the plant component into harvested fraction (fraction removed from the field) and fraction left in the field. For example, the reproductive component of wheat is divided into grain and chaff during harvest, and only the grain is removed from the field. This entry specifies the plant component that will be divided if that plant component is harvested. Choice 1 specifies a type of crop in which early-season reproductive development is all chaff and awns, not grain. If the crop is harvested before maturity, grain development is incomplete. The model internally, increases the actual harvested fraction from zero early in the season, until the value entered in "Harvested fraction of plant component" is reached at maturity.

Examples:

0 - Stripper cotton, for which all the reproductive mass is removed from the field. In this instance, the "Harvested fraction of plant component" for this example would be set to 1. Expression of final yield in bales of lint then requires accounting for the amount of trash and seed in the yield conversion factor;

1 - harvested grains, such as wheat, oats, barley, milo, corn. For a crop like corn, ear corn would have a larger value for the "Harvested fraction of plant component" than shelled corn has, for which the cob is left in the field;

2 - hay or forage crops, green vegetable crops. The "Harvested fraction of plant component" in most instances would be 1.0, indicating that all above-ground biomass above the cutting height is removed from the field. It should be less than 1.0 for a crop in which significant portions of the above-ground biomass above the cutting height are left behind in the field. This comment also applies to choices 3 and 4.

3 - tobacco and similar crops;

4 - Sugarcane and similar crops;

5 - Potatoes, peanuts, sugar beets.

In all crops, this setting and the corresponding "Yield fraction of harvested yield component" should be used to divide mass removed from mass left in the field, NOT mass removed from mass actually counted as yield. The parameter "Harvested yield conversion factor" should be used to account for post-harvest processing into marketable components.

Parameter Prompt: Harvested fraction of plant component (grain fraction etc.)

See parameter "Which plant component is (partly) harvested" for a full explanation.

Parameter Prompt: Units for reporting harvested yield

This field contains the units label that will be displayed for yield reporting. It should match the "Harvested yield conversion factor (kg/m2 to units shown)" value that is entered.

Parameter Prompt: Moisture content for reporting harvested yield (%)

In WEPS, all biomass values are tracked as oven-dry weight. Crop yields are normally reported at a "standard" moisture content other than oven dry weight. For yield reporting, oven-dry weight is converted to the moisture content entered in this field. To match yield numbers from other sources, this value should be the "standard" moisture content used for this product.

Parameter Prompt: Harvested yield conversion factor (kg/m2 to units shown)

This parameter should match the "Units for reporting harvested yield" value that is entered. The conversion factor is applied to the WEPS internal yield amount units (which is in kilograms per square meter) to report the yield in the units that are specified. This conversion is applied directly to the material removed from the field, as defined in "Which plant component is (partially) harvested?" and "Harvested fraction of plant component" and implemented by the appropriate harvest operation. If the component removed from the field is post-processed into a marketable product and a byproduct, and the yield reported in units of marketable product (cotton lint yield is an excellent example), the fraction of marketable product should be included in this conversion factor.

Decomposition Tab

For a better understanding of the decomposition parameters, also consult the Residue Decomposition Sub-model technical documentation.

Parameter Prompt: Residue size/toughness class

Parameter Choices:	1 - Fragile, very small residue (e.g., soybeans)

2 - Moderately tough, short residue (e.g., wheat)

3 - Non-fragile, medium residue (e.g., corn)

4 - Woody, large residue (sticks, hard wood)

5 - Gravel, rock

This class is used to determine what percentage of residue should be buried by certain management operations. For example, a tillage operation such as disking will bury a larger percentage of small, fragile residue and a smaller percentage of large, woody residue.

Parameter Prompt: Decomposition days after which stalks begin to fall (day)

The Number of days after which stalks begin to fall under optimum moisture and temperature conditions. After this threshold has been reached, stalks will begin to fall at the rate discussed. Example: a threshold of 20 decomposition days means that standing stalks begin to fall 20 days after harvest if moisture and temperature conditions are optimum during these 20 days. If conditions are not optimum, the number of days that stalks remain standing increases.

For a new crop, this parameter can be adjusted based on the number of stalks in residue pool 1 (the variable 'stem1' in the output file 'decomp.out'). Example: the new crop is a winter crop that is harvested in July. It is known that, on average, stalks begin to fall down in the middle of October. If WEPS simulates that stalks begin to fall down only in the next Spring (inspect stem1), then decrease the parameter value to start stem fall earlier. Increase the parameter value if WEPS makes the stalks fall too early.

Parameter Prompt: Fall rate for standing stalks (day-1)

The rate at which standing stalks fall to a flattened (horizontal) position on the soil surface. A larger number means that stalks fall faster. Only after a threshold has been reached, will stalks begin to fall at this rate. Example: a fall rate of 0.12 day-1 means that 12% of the total number of standing stalks fall down per day if moisture and temperature conditions are optimum on this day. If conditions are not optimum, the fall rate is reduced.

For a new crop, this parameter can be adjusted based on the number of stalks in residue pool 1 (the variable 'stem1' in the output file 'decomp.out'). Example: the new crop is a winter crop that is harvested in July. There is a fallow period of 14 months in which it is known that, on average, 50% of the stalks fall down. If WEPS simulates that less than 50% falls down (inspect stem1), then increase the parameter value to increase stem fall. Decrease the parameter value if WEPS makes the stalks fall too fast. Adjust 'Decomposition days after which stalks begin to fall' before adjusting this parameter.

Parameter Prompt: Decomposition rate for standing stalks (kg kg-1 day-1)

The rate at which standing stalks decompose under optimum conditions. A larger number means faster decomposition. Example: a decomposition rate of 0.02 kg kg-1 day-1 means a 2% standing stalk mass loss per day if moisture and temperature conditions are optimum for decomposition on this day. If conditions are not optimum, the rate is reduced. Leaves, if any are present, decompose at 3 times the rate of stalks, and reproductive material, if any is present, decomposes at 1.5 times the rate of stalks. Other models, such as WEPP and RUSLE, simulate the effect of moisture and temperature on decomposition differently from WEPS (see WEPS technical documentation). Thus, the same parameter value results in different rates of decomposition. Therefore, if a new WEPS crop already exists in one of these other models, this parameter value should not be used in WEPS.

For a new crop, this parameter can be adjusted based on the amount of standing residue biomass in residue pool 1 (the variable 'stand1' in the output file 'decomp.out'). Be sure to look at this variable only before stalks start falling. After stalks start falling, stand1 decreases due to two things: decomposition and stem fall. Example: the new crop is a winter crop that is harvested in July. It is known that, on average, stalks begin to fall down in the middle of the next April. Inspect stand1 between July and April. If stand1 is decreasing too rapidly, then decrease the parameter value. Increase the parameter value if stand1 decreases too slowly.

Parameter Prompt: Decomposition rate for surface (flat) stalks (kg kg-1 day-1)

The decomposition rate (under optimum conditions) of stalks that have fallen to a flattened (horizontal) position on the soil surface. For a new crop, this parameter can be adjusted based on the amount of flat residue biomass in residue pool 1 (the variable 'flat1' in the output file 'decomp.out'). Be sure to only look at this variable before stalks start falling. After stalks start falling, flat1 is affected by two things: decomposition and stem fall. It will actually increase if the mass received from the standing pool exceeds the flat mass that is decomposed. Example: the new crop is a winter crop that is harvested in July. It is known that, on average, stalks begin to fall down in the middle of the next April. Inspect flat1 between July and April. If flat1 is decreasing too rapidly, then decrease the parameter value. Increase the parameter value if flat1 decreases too slowly.

Parameter Prompt: Decomposition rate for buried stalks (kg kg-1 day-1)

The decomposition rate (under optimum conditions) of stalks that have been buried below the soil surface by tillage. For a new crop, this parameter can be adjusted based on the amount of buried residue biomass in residue pool 1 (the variable 'belo1' in the output file 'decomp.out').

Parameter Prompt: Decomposition rate for roots (kg kg-1 day-1)

The rate at which roots decompose under optimum conditions. For a new crop, this parameter can be adjusted based on the amount of root residue biomass in residue pool 1 (the variable 'root1' in the output file 'decomp.out').

In WEPS, the four parameters (decomposition rate for standing, flat, buried, and root mass) currently have the same values for a given crop. It is recommended to also do this for new crops, unless there is solid research data to do otherwise. For these six decomposition parameters, be sure to look at a no-till situation, because tillage operations will also make stalks fall down.

Parameter Prompt: Stalk diameter (m)

Stalk diameter at the base (at the soil surface) of a fully grown plant.

Parameter Prompt: Mass to cover factor (m2 kg-1)

WEPS calculates soil cover from flat residue mass:

where Cf is flat residue cover (m2 m-2), b is mass-to-cover factor (m2 kg-1), and Mf is flat residue mass (kg m-2) (Figure 1.40, 43).

Use the Excel spreadsheet to estimate a b value for a new crop, comparing with curves for crops that already exist in WEPS. If reliable mass and cover data are available for the new crop, the spreadsheet can be used to calculate a b value from this data.

RUSLE also uses the mass-to-cover equation to calculate soil cover from flat residue mass. Therefore, if a new WEPS crop already exists in RUSLE, and there is a high degree of confidence in the value of the RUSLE b parameter, this value could be used in WEPS.

Crop residue laying flat on the soil surface has the effect of reducing the water evaporation rate from the soil surface. Research done by Steiner (1989) showed that the effect varied for different crops. The data from Steiner for cotton, sorghum, and wheat, was refit to an exponential power relationship

where re is the ratio of evaporation from residue covered soil to bare soil evaporation and Mf is flat residue mass (kg/m2). This equation has better mathematical properties than the curve used by Steiner. If additional research is available, intermediate curves can be developed by using the "evaporation suppression" tab within the spreadsheet "howtopcropdb.xls" (available from WERU). Otherwise, use the numbers for the crop that most closely characterize the evaporation-suppression characteristics of the crop you are developing.

Parameter Prompt: Residue Evaporation Suppression multiplier coefficient a

Parameter Prompt: Residue Evaporation Suppression multiplier coefficient b

Calibration Tab

Parameter Prompt: Crop growth calibration selection

Parameter Choices:	0 - Crop NOT selected for calibration

1 - Select Crop for calibration to match target harvested yield

This flag is only effective when the model is run in calibration mode. It should be set to zero for all crop records.

Parameter Prompt: Target harvested yield

This value is only used when the model is run in calibration mode. It should be set to 0 for all crop records. NRCS will add RUSLE yield values as a starting point for calibration.

Parameter Prompt: Biomass adjustment factor

Multiplier used with the "Yield/biomass ratio adjustment factor" to enhance or suppress the conversion of solar radiation to biomass. This is the factor that is automatically adjusted when calibrating a crop. When developing a new crop record, this value should be set to 1.0. Locally adjusted records can be saved with numbers other than 1.0.

Parameter Prompt: Yield/biomass ratio adjustment factor

Intended use has not been implemented. Was to allow adjusting the ratio between total yield and total biomass for calibration purposes. Set to 1.0 for all crop records.

We created a new crop (flax), and documented the process in Appendices A and B. Appendix A is a list of questions about flax that was given to people with knowledge about how flax grows. Some questions are directly related to a parameter; others are more indirectly related. Appendix B shows how the answers to these questions were used to determine parameter values for flax.

References

Retta, A. and D.V. Armbrust. 1995. Estimation of leaf and stem area in the Wind Erosion Prediction System (WEPS). Agron. J. 87:93-98.

Ritchie, J.T. 1991. Wheat Phasic development. In: J. Hanks and J.T. Ritchie eds. Modeling plant and soil systems. Agronomy Monograph 31, pp. 34-36.

Steiner, J.L. 1989. Tillage and surface residue effects on evaporation from soils. Soil Sci. Soc. Am. J. 53:911-916.

Appendix A: Flax (seed) questions for WEPS crop growth model

The Wind Erosion Prediction System (WEPS) includes a crop-growth model that simulates a few dozen crops (Table 1.3). It does not yet include flax (seed). The USDA-NRCS has requested the inclusion of flax in WEPS. The following questions are meant to give information needed to include flax (seed) in the WEPS model. For these questions, we are always asking for the average, if not specified otherwise (e.g., average plant population, average planting depth, etc). Similar questions can be asked if other crops are developed for the WEPS model.

In general, which one of the current WEPS crops (Table 1.3) is flax (seed) most similar to? Please list only one crop.

For the following questions, you may not always know the answer (value) in an absolute sense, but you may know it in a relative sense. For this reason, we always ask: Which of the current WEPS crops are similar to flax (seed) regarding the aspect being discussed? Please list more than one current WEPS crop if applicable. Even if you know the answer in an absolute sense, please also list current WEPS crops that are similar.

What is the plant population ( #/m2)? Please give the number of plants expected in a normal stand. This should be the estimated plant population after germination. Which of the current WEPS crops have a similar plant population?

What is the planting depth? Which of the current WEPS crops have a similar planting depth?

Dry weight of one planted seed? Which of the current WEPS crops have a similar dry weight per planted seed?

What is the ratio leaf mass/stem mass in the shoot after seed mass has been converted to root and shoot? Which of the current WEPS crops have a similar ratio?

What is the ratio stem diameter/stem length after seed mass has been converted to root and shoot? Which of the current WEPS crops have a similar ratio?

How many days after planting (DAP) do plants emerge?

Does the crop regrow? If yes:

•	At what growth stage will it regrow?

•	What do regrowth shoots look like (size, length)?

•	What is the maximum number of shoots per plant?

Number of days from planting to maturity of seed? Which of the current WEPS crops have a similar number of days?

When (DAP) does senescence start (when do green leaves start to turn yellow/brown)?

Minimum temperature for plant growth? Which of the current WEPS crops have a similar minimum temperature?

Optimum temperature for plant growth? Which of the current WEPS crops have a similar optimum temperature?

Some cropping systems use plant densities that do not result in canopy closure. In these systems, the plant will grow to cover a ground area that is characteristic of the plant. WEPS assumes that the covered ground area is round. What is the diameter of the circle that encloses the area covered by a full-grown plant? Which of the current WEPS crops have a similar diameter?

Ratio of leaf area to leaf mass (m2 / kg)? Which of the current WEPS crops have a similar ratio?

Ratio of stem silhouette area to stem mass (m2 / kg)? Which of the current WEPS crops have a similar ratio?

Canopy light utilization is specified by an exponential relationship for the attenuation of light with distance into the canopy. Combined with the leaf area index, this coefficient determines the amount of light interception by the canopy, according to the relationship:

where fraction is the ratio of photosynthetically active radiation (PAR) that is intercepted by the crop and total PAR received above the crop canopy, k is light extinction coefficient, and LAI is leaf area index. A larger number indicates increased light interception by a given leaf area index, as occurs with broadleaf plants with a horizontal leaf orientation, such as cotton. A smaller number indicates decreased light interception by a given leaf area index, as occurs with narrow-leaf plants with a vertical leaf orientation, such as the grasses.

What is k? Which of the current WEPS crops have a similar k (similar light interception at a given amount of leaf area)?

Biomass conversion efficiency (t/ha) / (MJ/m2) is the unstressed (potential) growth rate per unit of intercepted photosynthetically active radiation. What is the biomass conversion efficiency? Which of the current WEPS crops convert light (PAR) to biomass with a similar efficiency?

Throughout the growing season, the above-ground biomass is partitioned into leaf, stem, and reproductive mass. In the beginning of the season most, of the above-ground biomass is allocated to leaf mass, and at the end of the season most is allocated to reproductive mass. Which of the current WEPS crops show a similar pattern of partitioning?

What are the growth stages? How many days for each of these stages?

What is the harvest index? Which of the current WEPS crops have a similar harvest index?

We use the equation:

where yield plus residue equals total above-ground biomass, b is the minimum above-ground biomass required for a crop to generate any yield, and r is the incremental increase in residue for each additional unit of yield in excess of the minimum. Do you have field data that can be used to estimate r and b? Which of the current WEPS crops have a similar relationship (similar r and b)?

The maximum depth of roots attained by the crop under ideal (unstressed) growth conditions? Which of the current WEPS crops have a similar rooting depth?

The maximum height attained by the crop under ideal (unstressed) growth conditions? Which of the current WEPS crops have a similar height?

When (DAP) does the crop reach 25%, 50%, 75% of its final height? Which of the current WEPS crops have a similar pattern of crop height development through the growing season?

In WEPS, freezing temperatures can reduce green leaf area. Which of the current WEPS crops experience a similar amount of damage caused by freezing temperatures?

Fraction of reproductive mass that is harvested (grain fraction)? Which of the current WEPS crops have a similar grain fraction?

Market-standard moisture content? Which of the current WEPS crops have a similar market-
standard moisture content?

How many pounds per bushel at market-standard moisture content?

Residue size/toughness class?

Choices:	1 - Fragile, very small residue (e.g., soybeans)

2 - Moderately tough, short residue (e.g., wheat)

3 - Non fragile, medium residue (e.g., corn)

4 - Woody, large residue (sticks, hard wood)

5 - Gravel, rock

Which of the current WEPS crops have a similar residue size/toughness?

Which of the current WEPS crops have a similar rate of residue decomposition?

Stem diameter at the base (at the soil surface) of a fully grown plant? Which of the current WEPS crops have a similar stem diameter?

Crop residue laying flat on the soil surface provides a certain amount of cover to the soil surface. Which of the current WEPS crops provide a similar amount of soil surface cover for a given mass of flat (not standing) residue?

Crop residue laying flat on the soil surface has the effect of reducing the water evaporation rate from the soil surface. Which of the current WEPS crops cause a similar amount of evaporation reduction for a given mass of flat (not standing) residue?

Please contact us if you have any questions. Thank you very much for helping us to include flax (seed) in our model.

USDA-ARS Wind Erosion Research Unit

1515 College Avenue

Manhattan, KS 66502

phone: (785) 537-5559

fax: (785) 537-5507

E-mail: office@weru.ksu.edu

Table 1.3. Crops currently simulated by the WEPS crop submodel.

Alfalfa

Asparagus

Barley, spring

Barley, winter

Bean, field, dry

Bean, green snap

Bean, lima

Beans, garbonzo

Bluestem, old world

Brassicas, forage

Broccoli

Bromegrass

Buckwheat

Cabbage

Camelina

Canola, spring

Canola, winter

Cantaloupe, Muskmelon, Honeydew

Carrot

Cauliflower

Celery

Chickpea

Chile, green, direct seed

Chile, green, transplant

Clover, alsike

Clover, red

Clover, sweet

Collard, greens

Corn, grain

Corn, pop

Corn, silage

Corn, sweet

Cotton

Cucumber

Eggplant

Flax

Garlic

Grama, sideoats

Grass seed, cool season

Grass seed, warm season

Horseradish

Lentils

Lettuce, head

Lettuce, leaf

Millet, foxtail

Millet, proso

Mint

Mustard seed, spring

Mustard, cover crop

Mustard, greens

Oats, fall

Oats, spring

Oats, winter

Onion

Peanut, runner

Peas, field, dry

Peas, forage

Peas, green

Peppers, bell

Peppers, chili

Pineapple, transplants

Potato, early, harvest

Potato, late, harvest

Potato, sweet

Pumpkin

Radish

Rice

Rye, cereal

Rye, spring

Rye, winter,cover

Rye, winter, grain

Rye, winter, silage

Safflower

Sorghum, forage

Sorghum, grain

Sorghum, sudangrass

Soybean, group 0 and I

Soybean, group II, III and IV

Soybean, groups V, VI, VII, and VIII

Spinach

Squash

Strawberry

Sugarbeet, sugar

Sugarcane

Sunflower

Switchgrass, biomass prod

Tall Fescue

Timothy

Tobacco, burley

Tobacco, dark

Tobacco, flue cured

Tomato

Triticale

Turfgrass

Vetch, hairy

Watermelon

Wheat, spring

Wheat, winter

Appendix B. Documentation of crop parameter values for flax (seed)

This appendix documents crop parameter values for flax (seed) and describes how knowledge about flax is used to determine flax parameter values. We started the database record for flax with a copy of the record for spring oats (Myers, 2005). Whenever there are no flax parameter values shown in the example, we use the same value as for spring oats.

We used the WEPS DB Viewer to create the flax crop from spring oats:

Select Spring Oats

Right click

Select 'Create a copy of this crop'

You are prompted to give it a name. Enter: 'flax'

You have now a crop named 'flax' with the same parameter values as spring oats.

To be able to change parameter values, select Options - Allow Changes on the menu.

Shoot Tab

Parameter Prompt: Crop type: 4 - Spring Seeded

Parameter Prompt: Transplant or Seed flag: 0 - Seeds planted in field

Parameter Prompt: Plant population: 3,000,000/ac

3,040,000/ac (Tanaka, 2005)

2,800,000 (Myers, 2005)

3,500,000/ac (Berglund, 2005)

30-70/ft2 (Berglund and Zollinger, 2002)

(70/ft2 = 3,050,000/ac)

Parameter Prompt: Maximum number of shoots per plant, nms (#/plant)

no regrowth (Berglund, 2005)

Parameter Prompt: Starting depth of growing point: 2 cm planting depths:

•	1 in (Berglund, 2005)

•	0.75-1.5 in (Tanaka, 2005)

•	<= 1 in (Martin et al., 1976)

•	0.75-1.5 in (Berglund and Zollinger, 2002)

•	2.5-3.2 cm (Duke, 1983)

•

At first, the simulated crop did not emerge. A flax seed is much smaller than a wheat seed. To ensure emergence, a value of 2 cm was used. Also, the value for 'Ratio of stem diameter to stem length' was adjusted, by using the Excel spreadsheet, to ensure emergence.

Parameter Prompt: Planted mass, dry weight: 5.5 mg/plant

180 seeds/g for flax seed (Martin et al., 1976)

5.7 mg/seed (Tanaka, 2005)

5 mg/seed (Myers, 2005)

3-12 g/1000 seeds (Duke, 1983)

3.8-7.0 g/1000 seeds (Martin et al., 1976)

Parameter Prompt: Root storage mass required for each regrowth shoot, msh (mg/shoot)

no regrowth (Berglund, 2005)

Parameter Prompt: Ratio of leaf mass/stem mass in shoot: 0.111

ratio = 1/9 = 0.111 (Myers, 2005)

Parameter Prompt: Ratio of stem diameter to stem length: 0.01

Reduced 0.015 (spring oats) to 0.01 to ensure emergence. See comments under 'Starting depth of growing point'

diameter = 1-2 mm, stem length = 25 mm (Myers, 2005). This would translate to a ratio of 1.5/25 = 0.06, but we don't get emergence with this value.

Parameter Prompt: Heat unit index at emergence: 0.05

Plants emerge 5 - 10 days after planting (Berglund, 2005)

Plants emerge 7 - 14 days after planting (Tanaka, 2005)

Plants emerge 5 - 8 days after planting (Myers, 2005)

The USDA-NASS (1997) planting and harvest dates were used for Foster County, ND (east-
central ND, in the heart of flax growing country [Martin et al., 1976]). Ten (10) cycles of the crop were simulated. The simulated emergence date can be found by finding the first day that the crop height (variable 'height' in the output file 'crop.out') is greater than 0.0. For 10 cycles, the earliest emergence date was 5 days after planting and the latest, 10 days after planting. Thus, the parameter value of 0.05 for spring oats works for flax.

Growth Tab

Parameter Prompt: Crop maturity measurement method: 0 - Crop matures, on average, in days shown

Parameter Prompt: Days to maturity (days): 100

95 days (Berglund, 2005)

110 days (Tanaka, 2005)

110 days (Myers, 2005)

50+25+35 = 110 days (Berglund and Zollinger, 2002)

90 to 120 days (Duke, 1983)

planting date:

•	25 May for North Dakota (USDA-NASS, 1997)

•	desired: April or early May for Minnesota and North Dakota (Duke, 1983)

•	desired: same as wheat (Duke, 1983)

•	as soon after possible after planting of small grains is completed (Duke, 1983)

•	desired: late April (Berglund and Zollinger, 2002)

harvest date: 17 Sept. for North Dakota (USDA-NASS, 1997)

In all 10 simulated cycles, the crop reached maturity before being harvested (the variable 'heatui' in the output file 'crop.out' reached 1.0 before being harvested). Also, the crop was not harvested too late: the earliest maturity date (variable 'doy') was 245, the latest was 254, with a harvest date 260 (17 Sept.). Thus, 100 days for 'days to maturity' works well. Note that, on the basis of the planting date of 25 May (day 145), we would expect the crop to mature, on average, on day 245. But the simulations show an average maturation date of about 250 (range is from 245 to 254). This discrepancy is caused by different methods of heat-unit calculation in WEPS. So, to get this parameter value correct, do not only look at the planting and harvest dates. Always inspect 'crop.out', as discussed here.

Parameter Prompt: Heat units to maturity (oC day)

Parameter Prompt: Heat-unit index at start of senescence: 0.85

Senescence starts 85 to 90 days after planting (Tanaka, 2005)

Leaves stay green long. In North Dakota, senescence starts late July or early August (Myers, 2005)

With the 0.85 value in our simulations for North Dakota, senescence started, on average, 80 days after planting (variable 'eff_lai' is at a maximum). This is in the middle of August.

Parameter Prompt: Minimum temperature for plant growth: 40 oF

40 oF (Berglund, 2005)

similar to spring wheat (Tanaka, 2005)

Parameter Prompt: Optimum temperature for plant growth: 70 oF

65 -75 oF (Berglund, 2005)

similar to spring wheat (Tanaka, 2005)

Geometry Tab

Parameter Prompt: Maximum growth diameter (m) of a single plant: 0.3 m

1 ft (Myers, 2005)

Parameter Prompt: Stem silhouette area coefficient a

Parameter Prompt: Stem silhouette area coefficient b

Parameter Prompt: Specific leaf area: 20.6 m2 / kg

like crimson clover (Myers, 2005)

Parameter Prompt: Light extinction coefficient: 0.45

This coefficient (k) is much lower than that of any small grain. There is never complete shading (Myers, 2005).

Simulated biomass production is very sensitive to k. Using the default k-value of spring oats resulted in yield and residue values similar to those of spring wheat. But, field data shows that flax yield and residue is about half that of spring wheat yield and residue (Tanaka et al., 2001; USDA-NASS, 2005). Using a k of 0.45 resulted in simulated biomass that matches this observation. Using a k of 0.40 resulted in too little biomass.

Parameter Prompt: Biomass Conversion Efficiency (t/ha) / (MJ/m2)

Partitioning Tab

Parameter Prompt: Leaf fraction coefficient a: 0.0006

Parameter Prompt: Leaf fraction coefficient b: 0.7149

Parameter Prompt: Leaf fraction coefficient c: 0.4297

Parameter Prompt: Leaf fraction coefficient d: -0.072

Parameter Prompt: Reproductive mass coefficient a: -0.0195

Parameter Prompt: Reproductive mass coefficient b: 0.995

Parameter Prompt: Reproductive mass coefficient c: 0.5077

Parameter Prompt: Reproductive mass coefficient d: 0.0849

Partitioning is like spring canola (Myers, 2005)

50 days vegetative + 25 days flowering + 35 days maturing (Berglund and Zollinger, 2002)

Parameter Prompt: Residue : Yield ratio (kg/kg): 0.82

Parameter Prompt: Residue : Yield intercept (kg/m2): 0.168

Used values of spring wheat (none available for flax, spring canola, or spring oats)

Parameter Prompt: Fraction of leaf mass partitioning diverted to root storage

no regrowth (Berglund, 2005)

Parameter Prompt: Fraction of stem mass partitioning diverted to root storage

no regrowth (Berglund, 2005)

Parameter Prompt: Fraction of reproductive mass partitioning diverted to root storage

no regrowth (Berglund, 2005)

Size Tab

Parameter Prompt: Maximum root depth: 40 in

40 in (Berglund and Zollinger, 2002)

short, flax gets its moisture largely from the top 2 ft (Martin et al., 1976)

shallow rooted (Duke, 1983)

not deep, like spring canola (Myers, 2005)

Parameter Prompt: Maximum crop height: 36 in

36 in (Berglund and Zollinger, 2002)

30 in for flax seed (Martin et al., 1976)

30 in (Myers, 2005)

Parameter Prompt: Crop height coefficient a

Parameter Prompt: Crop height coefficient b

Cold Tab

Parameter Prompt: Higher temperature: -5 oC

Parameter Prompt: Reduction in green leaf area at higher temperature: 0.01

Parameter Prompt: Lower temperature: -15 oC

Parameter Prompt: Reduction in green leaf area at lower temperature: 0.95

Freeze damage similar to that of spring canola (Myers, 2005)

Parameter Prompt: Thermal delay coefficient pre-vernalization: 0

Harvest Tab

Parameter Prompt: Which plant component is (partly) harvested: 1 - increasing fraction of reproductive mass (grain)

Parameter Prompt: Harvested fraction of plant component (i.e., grain fraction): 0.9

grain fraction = 90% (Myers, 2005)

Parameter Prompt: Units for reporting harvested yield: bu/ac

Parameter Prompt: Moisture content for reporting harvested yield: 8%

7.1-8.3% (Carter, 2005)

8-9% (Berglund, 2005)

10% (Tanaka, 2005)

8% (Myers, 2005)

Parameter Prompt: Harvested yield conversion factor (kg/m2 to units shown): 159.4 Pounds per bushel at market standard moisture content:

56 lbs/bu (Martin et al., 1976)

56 lbs/bu (Berglund, 2005)

Using 56 lbs/bu:

Decomposition Tab

Parameter Prompt: Residue size/toughness class: 3

3 - Non fragile, medium residue (e.g., corn) (Berglund, 2005; Myers, 2005).

2 - Moderately tough, short residue (e.g., wheat) (Tanaka, 2005)

Parameter Prompt: Decomposition days after which stalks begin to fall (day)

Parameter Prompt: Fall rate for standing stalks (day-1)

Parameter Prompt: Decomposition rate for standing stalks (kg kg-1 day-1)

Parameter Prompt: Decomposition rate for surface (flat) stalks (kg kg-1 day-1)

Parameter Prompt: Decomposition rate for buried stalks (kg kg-1 day-1)

Parameter Prompt: Decomposition rate for roots (kg kg-1 day-1)

Parameter Prompt: Stalk diameter (m)

Parameter Prompt: Mass to cover factor: 3.0 m2 kg-1

like proso millet (Myers, 2005)

Parameter Prompt: Residue Evaporation Suppression multiplier coefficient a: -1.20379

Parameter Prompt: Residue Evaporation Suppression multiplier coefficient b: 0.604887

like proso millet (Myers, 2005)

References

Berglund, D.R. 2005. Personal communication (answers to questions in appendix 1).

Berglund, D.R. and R.K. Zollinger. 2002. Flax production in North Dakota. North Dakota State University Extension Service. A-1038 (Revised). http://www.ext.nodak.edu/extpubs/plantsci/crops/a1038.pdf

Carter, J. 2005. Flaxseed as functional food for people… and as feed for other animals. Dept. of Plant Sciences, North Dakota State University, Fargo, North Dakota. http://www.ag.ndsu.nodak.edu/plantsci/flaxseed.htm

Duke, J. A. 1983. Handbook of energy crops. Unpublished. http://www.hort.purdue.edu/newcrop/duke_energy/Linum_usitatissimum.html

Martin, J.H., W.H. Leonard, and D.L. Stamp. 1976. Principles of field crop production. Third edition. Macmillan, New York.

Myers, R. Thomas Jefferson Agricultural Institute. Columbia, MO. 2005. Personal communication (answers to questions in appendix 1).

Tanaka, D.L. USDA-ARS, Mandan, ND. 2005. Personal communication (answers to questions in appendix 1).

Tanaka, D.L., J.M. Krupinsky, S.D. Merrill, R.E. Ries, M.A. Liebig, and J.R. Hendrickson. 2001. Dynamic Cropping Systems: Crop Production and Crop Sequences. CD. Annual Meeting Abstracts, SSSA, CSSA, ASA, Madison, WI.

USDA-NASS. 1997. Usual planting and harvesting dates for U.S. field crops. Agricultural Handbook 628. http://usda.mannlib.cornell.edu/reports/nassr/field/planting/uph97.pdf

USDA-NASS. 2005. Agricultural Statistics Database. http://www.nass.usda.gov:81/ipedbcnty/sso-mapc.htm