1. Alabama’s Cullars Rotation: The Oldest, Continuous Soil Fertility Experiment in the South
C.C. Mitchell*, D.P. Delaney (Auburn Univ.) & K.S. Balkcom (USDA-ARS)
Soil Profile K after 90 years of K fertilization
M1 Extractable K (mg/kg) 25 50
100 75
Soil depth (cm) 20 40 80 60
Horizon Ap E
B22t
B2t AB
No K
1/3 K
2/3 K
Std. K
4/3 K
Std. K (no S)
Seed Cotton Yields
Standard
No P
No K
No lime
Crop Rotation Since 1956
1) Cotton followed by a winter legume (crimson clover)
2) Corn planted into clover residue in April followed by a winter crop of rye or wheat planted in October.
3) Small grain harvested in late May or early June followed by soybean; winter fallow.
Before 1997, all crops were planted and cultivated using conventional tillage. Since 1997, all crops have been planted using in-row subsoiling and high residue, conservation tillage. The experiment is non-irrigated.
Cullars Rotation Soil: Marvyn loamy sand (fine-loamy siliceous, thermic Typic Kanhapludults)
Limestone Valley
National Register of Historical Places
The Cullars Rotation experiment (circa 1911) on the campus of Auburn University in Alabama was placed on the National Register of Historical Places in April, It joins the nearby Old Rotation experiment (circa 1896) as one of only 5 field crop research sites in the U.S. to receive this honor. It is America’s oldest cotton fertility experiment, the oldest soil fertility study in the South, and the second oldest, continuous cotton study in the world.
History of the Cullars Rotation
Mr. J.A. Cullars and his family owned and farmed this property in the late 1800s. Mr. Cullars allowed Professor George F. Atkinson of the Agricultural and Mechanical College of Alabama (now Auburn University) to conduct numerous early cotton fertility experiments on this property. Professor Atkinson’s research on this site led to the discovery that "cotton rust" was caused by a deficiency of potassium. An appropriation by the Alabama Legislature in 1911 enabled the Alabama Agricultural Experiment Station to conduct on-farm research throughout the state. Alabama Agric. Exp. Sta. Bulletin 219 (1923) summarized 226 experiments on farmers' fields throughout Alabama. An extensive cotton, corn, and legume fertility test begun in 1911 on the Auburn farm of Mr. Cullars is the only one of these experiments that has been continued.
In 1938, the farm was sold to Alabama Polytechnic Institute (now Auburn University) by heirs of J.A. Cullars. The Cullars Rotation experiment with a 40-foot border (approx. 4 acres) has been preserved.
Long-term Objective
The Cullars Rotation preserves a replicated experiment for monitoring nutrient accumulation and loss and soil quality changes and their effects on long-term sustainability of an intensive crop rotation system. This experiment is one of the few sites where controlled nutrient deficiencies can be observed on 5 different crops during the course of a year.
Appalachian Plateau
Piedmont
Black Belt Prairie
Corn Grain Yields
Standard
No P
No K
No lime
Coastal Plain
Soil Fertility Treatments since 1911 and Mean Soil Test Results in 2006
Although K leaches beyond 1m in this sandy, Coastal Plain soil (CEC= 3.0 cmol/kg) under high K fertilization, significant K remains in the upper profile and is plant available.
Mehlich -
1 extractable nutrients*** P K Mg Ca
Plot
no.
Treatment*
Soil
pH**
mg/kg A
No N/ + winter legume
6.1
VH 73
H 84
H 25
406 B
No N/ no winter legume
6.3
VH 65
H 72
H 17
263 C
No soil amendment 5. 1
VL 6
L 22
L 8 82
Complete fertilization/ no winter leg.
H 41
M 60
H 50
243 2
No P
5.8
H 23
176 3
Complete fertilization
VH 54
H 70
H 38
353 4
4/3 K
5.9
VH 87
H 82
H 45
513 5
Rock phosphate
EH 276
H 76 6
No K EH
101
L 18
419 7
2/3 K
VH 68
M 57
402 8
No lime
4.5
VH 79
M 45
L 7 72 9
No S
VH 94
405 10
Complete fertilization +
micronutrients (B, Zn, Cu, Mn)
VH 82
H 66
H 29
350 11
1/3 K
M 36
H 39
330
*P rate = 112 kg P O
/ha per 3
yr rotation as TSP
K rate = 302 kg K
O/ha per 3
yr rotation as muriate of potash
Cotton N rate = 100 kg/ha in split applications
Corn N rate = 134 kg/ha in split applications
Small grain N rate = 67 kg/ha in February
**All plots except C and
8 are limed to pH 6.5 when pH drops below
5.8.
*** Soil test rating for cotton:
VL= very low; L = low; M = medium; H = high; VH = very high;
EH = excessively high
Site Description and Methods
Mean crop yields relative to the standard fertilization treatment, 6 C B A 5 4 3 2 1 11 10 9 8 7
East Tier
Middle Tier
West Tier
97 m
102 m N
Standard
No P
No K
No lime
Soybean Yields
Summary
The Cullar’s Rotation experiment continues to document long-term trends in non-irrigated crop yields and soil changes due to variable rates of P, K, S, micronutrients and lime. It provides a valuable and accessible teaching tool for monitoring crop nutrient deficiences. It also is a source of uniform soil with variable fertility conditions for related studies. No other such resource exists in the Coastal Plain of the southern United States. The Cullars Rotation was placed on the National Register of Historical Places in 2003.
Each plot on the Cullars Rotation is 6m wide x 30m long with a 1m alley between plots and a 6m alley between tiers. Plots 1 through 11 were begun in 1911 and plots A, B and C were added in Each plot is a different soil fertility treatment replicated 3 times in a non-randomized manner in the three tiers. Each tier is planted to a different crop in the rotation sequence.
Five-year average yields in four treatments illustrate the increasing gap due to nutrient deficiencies since the experiment began. Cotton and corn yields trend upward under standard fertilization but soybean yields are static. Note that cotton is most sensitive to low K whereas corn and soybean are most sensitive to low P.