DWR_2807910

• Title: STATE AND DIVISION ENGINEER'S FORUM ENGINEERING ASSUMPTIONS - ATTACHMENT: CROP COEFFICIENT MEMO
• Author/Source: DEAN SANTISTEVAN, P.E.
• Author/Source: DIVISION OF WATER RESOURCES
• Keywords: CROP COEFFICIENT, CROP GROWTH
• Document Type - Reference Library: Presentations
• Document Date: 4/15/2014
• Year: 2014
• Team/Office: Division 1 Office

MEMORANDUM
December 13, 2013
Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney
Page 11 of 34

Corn (Grain). The crop growth stag
three data sets provided in ARS 1275
the following locations:

Location
Phoenix
Davis
Mandan
Table

IDSCU reports the growing season for silage corn
Phoenix, AZ shows a growing season of up to
Arizona were excluded from the
relationship to SCS TR-21 (R2 = 0.198

Figure 7 - kc vs. month for C

The SCS TR-21 crop curve for corn closely resemble
analysis shows a strong correlation (R
upwards by 0.34, the curves follow closely with one another.
corn from Mandan, ND was reported to be 0.5 in May. This is the same value that the SCS TR
starts at. It would appear that the SCS felt it was necessary to shift this curve upward.
Task Memo 59.1 suggests that the SCS adjustment upwards
data shows a stronger relationship to SCS TR
probable that the TR-21 coefficients reflect corn

It is interesting to note that the SCS TR
of the growing season. In fact, the first part of the growing season trends more closely with the Task
Memo 59.1 data presented for the upper plains coefficients.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
4 5
Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney-Criddle Eqn.
crop growth stage coefficients in TR-21 for grain corn were compared to
ARS 1275, identified as only “corn.” Data from ARS 1275 were reported from
Elevation
Location State Crop (m) (ft)
Phoenix AZ corn 340 1,117
Davis CA corn 16 52
Mandan ND corn 502 1,647
Table 10 – Locations of corn data from ARS 1275
growing season for silage corn as being around 110 days. ARS 1275 data
shows a growing season of up to 120 days, which may reflect silage corn. Th
analysis. The data from ARS 1275 did not sh
198) as shown in Chart 5.
vs. month for Corn (grain)
for corn closely resembles the curve from Davis, CA and a simple regression
analysis shows a strong correlation (R2 = 0.980) as shown in Chart 6. If the Davis, CA curve is shifted
by 0.34, the curves follow closely with one another. It is interesting to note that the k value for
ND was reported to be 0.5 in May. This is the same value that the SCS TR
that the SCS felt it was necessary to shift this curve upward. A comparison with
Task Memo 59.1 suggests that the SCS adjustment upwards may have been warranted.
shows a stronger relationship to SCS TR-21 when shifted upwards and may suggest that it is more
21 coefficients reflect corn with adjustment.
It is interesting to note that the SCS TR-21 curve does not trend with the Davis, CA data for the first part
of the growing season. In fact, the first part of the growing season trends more closely with the Task
Memo 59.1 data presented for the upper plains coefficients.
6 7 8 9
SCS TR-21 Corn Grain
Davis, CA
Mandan, ND
Task Memo 59.1
Average of ARS 1275
Criddle Eqn.
were compared to two out of
Data from ARS 1275 were reported from
ARS 1275 data from
reflect silage corn. The data from
not show a substantial

and a simple regression
. If the Davis, CA curve is shifted
It is interesting to note that the k value for
ND was reported to be 0.5 in May. This is the same value that the SCS TR-21 curve
A comparison with
warranted. The Davis, CA
and may suggest that it is more
not trend with the Davis, CA data for the first part
of the growing season. In fact, the first part of the growing season trends more closely with the Task
10