Structural Conservation Practices in U.S. Corn Production: Evidence on Environmental Stewardship by Program Participants and Non-Participants

Table 3. Model II estimated GEE coefficients for corn field-acreage allocation equations by field
structural practice (technology), and by conservation program participation.

[Model II: (Aj,p) = f(normalized input prices, technology class, installation, & socio-environmental variables)].

Equation/Variable____________________	________Program Non-Participants_______		Program Participants
Equation/Variable____________________	_________Estimate_______	T-Tests ^b	Estimate	T-Tests
Model II
Constant	2.5478	1.04	4.4805	1.30
Corn Field Acres Planted (with):
EQ1: No structural practices: ^a
N price	119.9414 *	3.64	- 41.1041	- 0.62
Ag. wage	0.4437 ***	1.56	- 2.2255 *	- 4.25
Diesel price	- 21.7852 *	- 3.37	15.5230	1.30
EQ2: Only infield structures: ^a
N price	- 68.3726 *	- 2.56	4.6041	0.10
Ag. wage	0.1951	0.77	0.3661	0.75
Diesel price	9.3637 **	1.96	- 4.5506	- 0.51
EQ3: Only perimeter-field structures: ^a
N price	- 14.6446	- 0.94	29.8064	0.91
Ag. wage	- 0.3468 *	- 3.54	1.2607 *	4.37
Diesel price	6.1154 **	1.97	- 12.9867 *	- 2.20
EQ4: Both structural practices: ^a
N price	- 5.4257	- 0.98	- 25.2886	- 1.37
Ag. wage	0.1431	0.93	0.2792	0.71
Diesel price	________2.4690_______	1.20	0.8440	_________0.19
Technology class variables:	Units_________________	Estimate	______T-tests
Only infield structures	(Yes = 1)	- 0.9789	- 0.25
Only perimeter-field structures	(Yes = 1)	- 4.1142	- 1.43
Both structures	(Yes = 1)	- 4.5246 ***	- 1.71
Installation dummy variables:
Installed in 2005	(Yes = 1)	0.0080	0.12
Installed within last 10 years	(Yes = 1)	- 0.0088	- 0.20
Installed prior to 1990	(Yes = 1)	0.0213	0.19
Socio-Environmental Variables:
Farm tenure rate	(owned/operated acres)	0.0735	1.04
Farm cropland acres	(acres)	0.0001 *	3.06
Crop rotation	(Yes = 1)	- 0.2240 *	- 2.46
Gully erosion on field	(Yes = 1)	0.1264 ***	1.52
Field next to water body	(Yes = 1)	- 0.1150 **	- 1.98
Surface drainage	(Yes = 1)	0.1811 *	2.75
Improve wildlife habitat	(Yes = 1)	- 0.1356	- 1.25
Log Likelihood Value (L2) = - 2872.0891	R² = 0.10 Likelihood Ratio (L1:L2) = 68.10, d.f. = 7,			p = .05

^a State average per unit prices (2005) for nitrogen ($/lb.), agricultural wage ($/hr.), and diesel ($/gal.) were normalized using State average
2005 corn price ($/bu.).

^b Critical values for the t tests are 1.52 (***), 1.76 (**), and 2.14 (*) for the 15 %, 10 %, and 5 % significance levels, respectively.

Standard errors were computed using the delete-a-group Jackknife approach (Dubman, 2000).

Note: Infield conservation structural practices included terraces, grassed waterways, vegetative buffers, contour buffers, filter strips, and grade
stabilization structures. Perimeter-field conservation structural practices included hedgerow plantings, stream-side forest buffers, stream-
side herbaceous buffers, windbreaks or herbaceous wind barriers, field borders, and critical area plantings.

Source: 2005 CEAP-ARMS Phase II data (for corn), Economic Research Service, USDA.

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