former_yield <- 70 # units = cwt/ac
former_moisture <- 12.5 / 100
standard_moisture <- 14 / 100
yield_adjusted_uscs <- former_yield * (1 - former_moisture) / (1 - standard_moisture)Adjusting Crop Yield
Methods 5.0
Adjusting yield to standard moisture and back again.
Introduction
Harvested crops differ by moisture content at the time of harvest and need to be adjusted to a standard moisture (Mulvaney and Devkota 2020). Differences in moisture content would affect any sustainability metrics expressed on a production basis1. Using standardized yields allows for proper interpretation of results. Adjusting crop yield to a standard moisture content is one of the first calculations in the Fieldprint Platform. Here is the formula when moisture content at harvest (\(M\)) is expressed as a decimal:
1 For example, GHG emissions per kg of crop. Some metrics are expressed on an area basis, like ton/ac of soil lost to erosion.
\[ Y_s = \frac{Y(1-M)}{1-M_s} \tag{1}\]
where \(Y_s\) = standardized yield, \(Y\) = yield at harvest, \(M\) = moisture content at harvest, \(M_s\) = standard moisture
If using percentages:
\[ Y_s = \frac{Y(100-M)}{100-M_s} \tag{2}\]
For most crops, the Fieldprint Platform expects the user to report yield at standard moisture content (\(Y = Y_{s}\)). For other crops, like alfalfa and sugar beets, some yield adjustment is needed.
Default Method
| Input | Value | Units | Symbol |
|---|---|---|---|
| Crop type | User entry | ||
| Harvest yield | User entry | See Table 1 | \(Y\) |
| Yield (standardized) | Calculated | kg ha-1 | \(Y_{s}\) |
| Acres per hectare | 2.47105 | ac ha-1 | |
| Kilograms per pound | 0.4535929 | kg lb-1 |
Formula
If crop yield is entered on a standard moisture basis, then no conversions are needed. The following is the default calculation for most crops:
\[ Y_s = Y \tag{3}\]
Note
In the case of irrigated crops, the “non-irrigated yield” should receive the same adjustment to a standard moisture, which will be used in the calculation of the metric for Irrigation Water Use.
Example: Corn🌽
Standardize the reported corn yield of 160 bu/acre (56 lbs/bu).
NoteAnswer
Because the Calculator assumes the user is entering yield at a standard moisture, the adjusted yield is 160 bu/ac or 10,043 kg/ha.
Rice🌾
Beginning with version 5.0, the user is expected to enter rice yield at standard moisture (14%). This is the common value used in reporting grain yield globally across Asia, Europe, Africa, and in parts of the United States like California.
Previously in version 4, the Platform allowed users to choose between two ways of entering rice yield :
- “dry basis” (already at a standard moisture of 12.5%)
- “wet/green basis” along with entering the % moisture at harvest2
2 For example, 75 cwt at 19% moisture.
In v5 as with v4, the user will still enter the percent moisture removed during drying, from which the moisture at harvest can still be derived.
Example: Converting rice yield at 12.5% to 14%
Using Equation 1, we can convert former standard yields in v4 to the new standard yield at 14% moisture.
NoteAnswer
The new yield in version 5 would be 71.2 cwt.
Sugar Beets
Standardize the yield as mass of sugar per area by multiplying the yield of beets by the percentage sugar.
Inputs
| Input | Value | Units | Symbol |
|---|---|---|---|
| Sugar beet yield | User entry | See Table 1 | \(Y\) |
| Percent sugar | User entry | %, as decimal | \(\%Sugar\) |
Formula
\[ Y_s = Y\times \%_{sugar} \]
Example: Sugar beets
For a sugar beet field with a yield of 25 tons/acre of beets with 15.9% sugar
# Inputs
yield <- 25 # ton beets/acre
pct_sugar <- 15.9 / 100 # percent sugar as decimal
# USCS units
yield_adjusted_uscs <- yield * pct_sugar # ton sugar/acre
# SI units
yield_adjusted <- yield_adjusted_uscs * ton_kg / ac_ha # convert denominator ac->ha[1] "3.98 ton/acre sugar or 8,911 kg/ha sugar"Alfalfa
Inputs
| Input | Value | Units | Symbol |
|---|---|---|---|
| Alfalfa yield of single cutting | User entry | See Table 1 | \(Y_1,Y_2,...,Y_n\) |
| Harvest moisture at baling | User entry | %, as decimal | \(M_1, M_2,...M_n\) |
| Alfalfa standard moisture | 12% = 0.12 | %, as decimal | \(M_s\) |
Formula
If the crop is alfalfa, calculate dry hay equivalent for cuttings where moisture level is greater than 12% and sum the dry hay equivalent yield for all cuttings. Note that each cutting will have a different moisture percentage; correction is only required if \(M > 12\%\) .
Standardized alfalfa yield
\[ Y_{1_s} = \frac{Y_1(1-M_1)}{1-M_{s}} = \frac{Y_1(DM_1)}{\%DM_{s}} \]
Total alfalfa yield
\[Y_s = \sum_{n=1}^{n}{Y_{n_s}}\] where
\(n\) = number of hay cutting in the year.
Example: Alfalfa
An alfalfa field had 2 cuttings, where the first cut yielded 3 ton/ac and the second cut yielded 2.2 ton/ac. Harvest moisture (i.e., at baling) was 20% and 18%, respectively.
# Inputs
alf_cut_1_yield <- 3 # ton/acre
alf_cut_2_yield <- 2.2 # ton/acre
# First calculate the dry hay equivalent of the second cut
alf_cut_1_moisture <- 20 # percentage
alf_cut_2_moisture <- 18 # percentage
# Lookups
standard_moisture <- tbl_yield |> filter(crop == "Alfalfa") |> pull(standard_moisture)
yield_1_adjusted <- alf_cut_1_yield * (1 - alf_cut_1_moisture / 100) / (1 - standard_moisture)
yield_2_adjusted <- alf_cut_2_yield * (1 - alf_cut_2_moisture / 100) / (1 - standard_moisture)
# USCS units Total yield
yield_adjusted_uscs <- yield_1_adjusted + yield_2_adjusted # ton/acre
# SI units
yield_adjusted <- yield_adjusted_uscs * ton_kg / ac_ha # convert denominator ac->ha[1] "4.78 ton/ac"[1] "10,709 kg/ha"Cotton👕
In the case of cotton, the user enters the lint yield, or yield based on lint only. The user should not enter the seed cotton yield (weight of lint + seed + residues). A conversion factor adjusts lint yield to seed cotton yield for certain calculations that rely on total weight. (see Section 6.2)
Convert from standardized yield to harvest yield
For some crops in the Fieldprint Calculator, like corn and other grains, the reported harvest yield is assumed to be at standard moisture. In this case, there is a need to convert the standardized yield back to a harvest yield at harvest moisture in order to estimate the true mass of crop harvested. This information is used in other calculations such as the energy expended in transporting the mass of harvested crop to a storage or drying facility. To convert back to a harvest moisture, the Calculator uses the percentage points of moisture removed in drying.
Default
The following is the default method for crops that do not have an harvest moisture entry, for which the reported yield is assumed to already be at standard moisture (e.g., corn, rice, barley, etc).
Formula
\[ Y = \frac{Y_s(1 - M_s)}{1 - M_s + M_{removed}} \tag{4}\]
Example: Rice🌾
The reported rice yield was 70 cwt/ac. The grain elevator removed 6% of water from the harvested grain. What was the “wet” yield, or yield at harvest moisture?
# Inputs
yield <- 70 # cwt/ac at standard moisture of 14% or 0.14
moisture_removed <- 6 / 100 # as decimal
# Lookup conversion
cwt_lb <- filter(tbl_yield, crop == "Rice") |> pull(lb_per_unit)
standard_moisture <- tbl_yield |>
filter(crop == "Rice") |>
pull(standard_moisture)
# USCS units
yield_adjusted_uscs <- yield
yield_harvest_uscs <- yield_adjusted_uscs * (1 - standard_moisture) / (1 - (standard_moisture + moisture_removed))
yield_harvest <- yield_harvest_uscs * cwt_lb * lb_kg / ac_ha # convert denominator ac->ha
NoteAnswer
The “wet/green” yield at harvest was 75.2 cwt/ac or 8,434 kg/ha, assuming the harvest moisture was 20 %.
Cotton
The reported yield for cotton is assumed and intended to be lint yield only. The seed cotton yield, or mass of the lint plus the seed and debris harvested along with the lint, is not reported. However, we can use an average lint content (Internal data, Cotton Incorporated).
Inputs
| Input | Value | Units | Symbol |
|---|---|---|---|
| Seed cotton yield conversion factor | 0.365 | units of lint per unit of seed cotton |
Example: Cotton
The reported cotton lint yield was 1000 lbs/ac. What was the seed cotton yield (lint + seed + debris)?
# Inputs
yield <- 1000 #lb-lint/ac
# Lookup
seed_lint <- 0.365 # seed to lint
# Calculations
yield_adjusted_uscs <- yield
yield_harvest_uscs <- yield_adjusted_uscs / seed_lint
yield_harvest <- yield_harvest_uscs * lb_kg / ac_ha # convert denominator ac->ha[1] "2,740 lb/ac seed cotton"[1] "3,071 kg/ha seed cotton"Tables
| crop | uscs_units | lb_per_unit | kg_per_uscs_unit | standard_moisture |
|---|---|---|---|---|
| Alfalfa | ton | 2000 | 907.184000 | 0.120 |
| Barley | bushel | 48 | 21.772416 | 0.145 |
| Chickpeas (garbanzos) | lb | 1 | 0.453592 | 0.160 |
| Corn (grain) | bushel | 56 | 25.401152 | 0.155 |
| Corn (silage) | ton | 2000 | 907.184000 | 0.650 |
| Cotton | lb | 1 | 0.453592 | 0.080 |
| Dry Beans | lb | 60 | 27.215520 | 0.160 |
| Dry Peas | lb | 60 | 27.215520 | 0.160 |
| Fava Beans | lb | 1 | 0.453592 | 0.160 |
| Lentils | lb | 1 | 0.453592 | 0.160 |
| Lupin | lb | 1 | 0.453592 | 0.160 |
| Peanuts | lb | 1 | 0.453592 | 0.090 |
| Potatoes | cwt | 100 | 45.359200 | 0.800 |
| Rice | cwt | 100 | 45.359200 | 0.140 |
| Sorghum | bushel | 56 | 25.401152 | 0.140 |
| Soybeans | bushel | 60 | 27.215520 | 0.130 |
| Sugar beets | ton sugar | 2000 | 907.184000 | 0.850 |
| Wheat (durum) | bushel | 60 | 27.215520 | 0.135 |
| Wheat (spring) | bushel | 60 | 27.215520 | 0.135 |
| Wheat (winter) | bushel | 60 | 27.215520 | 0.135 |
References
Mulvaney, Michael J., and Pratap J. Devkota. 2020. “Adjusting Crop Yield to a Standard Moisture Content: SS-AGR-443/AG442, 05/2020.” EDIS 2020 (3). https://doi.org/10.32473/edis-ag442-2020.