Proc. 57th Southern Pasture and Forage Crop Improvement Conference, Athens, GA April 23-25, 2002
The Salem Road Study: Restoration of Degraded Land with Pasture
–Experimental Layout and Animal Responses
John A. Stuedemann, Alan J. Franzluebbers and Dwight H. Seman
USDA-Agricultural Research Service, 1420 Experiment Station Road, Watkinsville, GA 30677
Summary
The general goal of the following study was to identify sustainable cattle production systems that are highly productive, that minimize negative environmental impacts, and that improve soil quality in degraded landscapes. The experimental site was a 15-ha upland field near Farmington, GA that had previously been cropped for several decades prior to grassland establishment by sprigging of Coastal bermudagrass [Cynodon dactylon (L.) Pers.] in 1991.
The experimental design was a randomized complete block with treatments in a split plot arrangement in each of three blocks, which were delineated by landscape feature (i.e., slight, moderate, and severe erosion classes). Main plots were pasture fertilization treatments (n = 3) and split plots were harvest methods (n = 4). Fertilizer treatments consisted of (a) inorganic only, (b) crimson clover cover crop plus supplemental inorganic fertilizer, and (c) broiler litter. This paper discusses only the two harvest methods that involved grazing, i.e., the high forage mass (low intensity grazing) and low forage mass (high intensity grazing) treatments.
Yearling Angus steers (Bos taurus) were managed in a put-and-take grazing system with three “tester” steers assigned to each paddock and “grazer” steers added or removed at 28-day intervals. Except on rare occasions, three tester steers grazed each of the paddocks. From 1994-1998, steers grazed the paddocks for a 140-day period from mid-May until early October each year.
Steer average daily gain (ADG) during this five-year period was excellent, irrespective of treatment. Steers grazing the clover plus inorganic N treatment had higher (P<.05) ADG than cattle grazing either inorganic N or broiler littered pastures. The inorganic N treatment supported the highest (P<.05) number of steers per ha across the five-year period.
For some time, there has been general concern in agriculture that we must develop production systems that are sustainable, i.e., those that maintain or enhance our natural resource base while reducing our dependency on external inputs including pesticides and inorganic fertilizers. All of this must be put in the context of profitability and a time dimension that implies that it could endure indefinitely (Lockeretz 1988). Parr et al. (1990) stated that the primary objectives of U. S. farmers in achieving sustainability are to develop farming systems that (a) maintain or improve the natural resource base, (b) protect the environment, (c) ensure profitability, (d) conserve energy, (e) improve food quality and safety, and (f) create a more viable socioeconomic infrastructure for farms and rural communities. It is within this general context that the following experiment was implemented.
The experiment was conducted in the Southern Piedmont Land Resource Area, which extends from northern Virginia southwestward through the Carolinas, Georgia and into Alabama. It is a rolling upland plateau lying between the Blue Ridge Mountains and the Coastal Plains covering about 17 million hectares. Elevation of the Southern Piedmont Region ranges from about 500 m above sea level near the mountains to about 100 m at the southeastern edge near the Coastal Plain. The climate is relatively mild and humid, and favorable for crops, forests, grasses and livestock enterprises. The area is also favorable for human habitation. The infrastructure of the region, including the interstate highway system, has resulted in rapid urbanization. The soil erosion hazard is generally severe which necessitates the use of conservation farming practices. Soils have typically undergone severe erosion as a result of historically intensive conventional tillage for crop production. In recent years the land area devoted to row crop production has decreased with much of it being converted to forest or pasture
Whether soil restoration, as determined by soil quality factors such as soil organic C can occur under pasture conditions has not been adequately established. Furthermore, the impact of alternative nutrient sources, such as broiler litter, or clover-N and different grazing strategies such as grazing to different available forage masses, on the restoration process are not well defined.
The general goal of the experiment was to identify sustainable cattle production systems that are highly productive, that minimize negative environmental impacts, and that improve soil quality in degraded landscapes. Specific objectives were to: 1) determine cattle performance and production, 2) determine forage mass, botanical composition and quality, 3) determine soil chemical properties including surface residue C and N, total organic C and N, particulate organic C and N, available soil P accumulation and deep soil nitrate accumulation, 4) determine soil physical properties including soil bulk density, steady state water infiltration and water-stable aggregate distribution and stability, 5) determine soil biological properties including soil microbial biomass C, and potentially mineralizable C and N, 6) determine spatial distribution of soil properties, 7) determine water runoff and quality, 8) determine the number and diversity of internal parasites of cattle, and 9) determine if the area could be maintained parasite free.
Site characteristics
A 15-ha upland field (33o 22’N, 83o 24’W) in the Greenbrier Creek subwatershed of the Oconee River watershed near Farmington, GA had previously been conventionally cultivated with cotton (Gossypium hirsutum L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) for several decades prior to grassland establishment by sprigging of Coastal bermudagrass [Cynodon dactylon (L.) Pers.] in 1991. Mean annual temperature is 16.5oC, rainfall is 1250 mm, and potential evaporation is 1560 mm, and elevation is 205 to 215 m above sea level.
Experimental design
The experimental design was a randomized complete block with treatments in a split plot arrangement in each of three blocks, which were delineated by landscape feature (i.e., slight, moderate, and severe erosion classes). Main plots were pasture fertilization treatments (n = 3) and split plots were harvest methods (n = 4). Individual paddocks ranged from .65 to .75 ha. Paddock shape minimized runoff contamination among paddocks and an animal handling and service alley followed the top of the landscape. Each paddock contained a 3 x 4 m shade, a mineral feeder, and a water trough placed in a 15 m line near the top of the landscape.
Fertilizer treatments consisted of (a) inorganic or mineral only (~200 kg N ha-1 yr-1 as NH4NO3 broadcast in split applications in May and July), (b) crimson clover cover crop plus supplemental inorganic fertilizer (~200 kg N ha-1 yr-1 with one-half of the N assumed fixed by clover biomass and the other half as NH4NO3 broadcast in July), and (c) broiler litter (~200 kg N ha-1 yr-1 broadcast in split applications in May and July). Phosphorus and K applications varied among treatments because excess P and K were applied with broiler litter (124 +/- 40 kg P ha-1 yr-1 and 167 +/- 48 kg K ha-1 yr-1) to meet N requirements, while diammonium phosphate and potash were applied based on soil test recommendations (16 +/- 11 kg P ha-1 yr-1 and 52 +/- 41 kg K ha-1 yr-1 for inorganic
Harvest methods were (a) unharvested (biomass cut and left in place at the end of the growing season), (b) high forage mass or low grazing intensity (put-and-take system of grazing to maintain a target forage mass of 3000 kg ha-1), (c) low forage mass or high grazing intensity (put-and-take system of grazing to maintain a target forage mass of 1500 kg ha-1), and (d) hayed monthly to remove aboveground biomass at 4-cm height. The objective of this report concerns all pasture fertilization treatments, but only the two harvest methods that involve grazing, i.e., the high forage mass (low intensity grazing) and low forage mass (high intensity grazing) treatments
Yearling Angus steers (Bos taurus) were managed in a put-and-take grazing system with three “tester” steers assigned to each paddock and “grazer” steers added or removed at 28-day intervals except during periods of rapid forage mass changes when steers were added or removed at 14-day intervals. Except on rare occasions, three tester steers grazed each of the paddocks. Mean initial steer weights of testers for each year are presented in Table 1.
Grazer steers not on experimental paddocks were placed on adjacent parasite-free pastures. Steers were randomly allotted to paddocks such that the number one tester was randomly selected from the group of 18 steers close to the mean weight of the total number of steers available. Likewise the number two and three tester steers were allotted from groups of 18 steers on either side of the number one tester steers. The stocking density for a given paddock was computed by assuming that each steer would consume 1 kg of dry matter per 45.45 kg of body weight. The number of steers that could be supported on a given paddock was calculated by dividing the forage mass (kg ha-1) by the estimated average daily intake and then dividing by 28 (the number of days in the grazing period).
|
Year |
N |
Weight, kg |
SD |
Minimum |
Maximum |
|
1994 |
51 |
261 |
14.6 |
227 |
286 |
|
1995 |
54 |
273 |
15.8 |
243 |
313 |
|
1996 |
54 |
258 |
13.8 |
227 |
286 |
|
1997 |
54 |
245 |
18.7 |
197 |
279 |
|
1998 |
54 |
247 |
12.9 |
218 |
272 |
Table 2. Average Above-Ground Forage Mass (Mg ha-1) by
Nitrogen Treatment and Grazing Intensity
|
Nitrogen Treatment |
Grazing Intensity |
||||
| Year |
Clover |
Litter |
Mineral |
High |
Low |
| 1994 |
5.3 |
5.7 |
6.2 |
4.3 |
7.2 |
| 1995 |
3.8 |
3.5 |
3.9 |
2.6 |
4.8 |
| 1996 |
3.4 |
3.3 |
3.3 |
2.2 |
4.5 |
| 1997 |
3.7 |
3.4 |
4.0 |
2.3 |
5.1 |
| 1998 |
2.2 |
2.4 |
2.6 |
1.5 |
3.3 |
| Mean |
3.7a |
3.7a |
4.0b |
2.6c |
5.0d |
c,d Values with different superscripts across grazing intensity differ, P<.05. Year*grazingintensity interaction was significant, P<.0001.
Anthelmintic treatment
Estimates of forage mass were made prior to stocking the paddocks and at 28-day intervals except during those times when adjustments were made at 14-day intervals. Estimates of forage mass were made by clipping a .25 m2 area to ground level at 30 m grid sites. Average above ground forage masses (Mg ha-1), during the experimental period, for each fertilization and grazing intensity treatment for each of the five years are presented in Table 2. Steers grazed the paddocks for a 140-day period from mid-May until early October each year except during the first year of treatment implementation (1994) when grazing began in mid-July due to repairs to infrastructure following a tornado. Shrunk weights (16 h off water) were obtained initially and at 28-day intervals except when stocking rate adjustments were made at 14-day intervals.
Anthelmintic treatment included pour-on ivermectin on day –21, albendazole on day –7, and injectable ivermectin 48 hours prior to stocking of pastures, with the cattle remaining in drylot during the 48-hour period. All steers received only one series of treatments during any given year.
Statistical analysis
Results of the experiment were analyzed by using the MIXED Procedure of SAS. The study was analyzed as a randomized complete block with repeated measures and block and block*grazing intensity*fertilizer specified as random. Different covariance structures were evaluated using the Schwartz’s Bayesian Criterion to indicate the best fit. Effects of fertilizer treatment, grazing intensity and their interaction were tested with the interaction of block, fertilizer and grazing intensity. Effects of year and its two-way interactions with fertilizer and grazing intensity were tested with residual error.
Results and discussion
Steer performance
Average daily gain (ADG) of tester steers for each of the five years and overall are presented in Table 3. Among the pasture fertilization treatments, steers grazing the clover plus nitrogen treatment had higher (P<.05) ADG than those on either of the other treatments. There is no obvious explanation for these differences in ADG. There was very little clover available for consumption, other than some residue in the early part of the grazing season, because the clover was mowed approximately one month before grazing began each year. Steers grazing at the low forage mass (high intensity) had lower (P<.05) ADG than those grazing at the high forage mass (low intensity). This difference could be attributed to greater selection potential for steers grazing the high forage mass.
The steer ADG during this five-year period was excellent, irrespective of treatment. These results could partly by attributed to the fact that these pastures were free of nematode parasites (see the paper in this proceedings by R. Kaplan for details of this aspect of the study).
The average number of steers per ha over the five years was highest (P<.05) for the mineral fertilizer treatment with no difference between the clover N plus inorganic N and the broiler litter treatment (Table 4). Other than the slower availability of plant nutrients, we have no explanation as to why the inorganic fertilizer treatment supported more steers than the other treatments. The average number of steers grazing the high intensity treatment exceeded (P<.05) that of the low intensity.
Literature Cited
Lockeretz, W. 1988. Open questions in sustainable agriculture. Am. J. Alternative Agriculture 3(4), 174-181.
Parr, J. F., Papendick, R. I., Youngberg, I. G., Meyer, R. E., 1990. Sustainable agriculture in the United States. In: Edwards, C. A., Lal, R., Madden, P., Miller, R. H., House, G. (eds.), Sustainable agricultural systems. Soil and Water Conservation Society, Ankeny, Iowa, U. S. A., pp. 50-67.
|
Nitrogen Treatment |
Grazing Intensity |
||||||
|
Litter |
Mineral |
High |
Low |
||||
| 1994 |
1.10 |
.86 |
.84 |
.74 |
1.13 |
||
| 1995 |
.67 |
.62 |
.57 |
.56 |
.68 |
||
| 1996 |
.85 |
.65 |
.77 |
.72 |
.79 |
||
| 1997 |
.75 |
.67 |
.77 |
.58 |
.88 |
||
| 1998 |
.84 |
.80 |
.85 |
.75 |
.91 |
||
| Mean |
.84a |
.72b |
.76b |
.67c |
.88d |
||
a,b Values with different superscripts across nitrogen treatments differ, P<.05.
Year*nitrogen treatment interaction was significant, P=.0203.
c,d Values with different superscripts across grazing intensity differ, P<.05. Year*grazing
intensity interaction was significant, P<.0001.
|
Nitrogen Treatment |
Grazing Intensity |
||||
| Year |
Clover |
Litter |
Mineral |
High |
Low |
| 1994 |
6.61 |
8.01 |
9.60 |
11.43 |
4.71 |
| 1995 |
6.48 |
6.66 |
8.06 |
8.09 |
6.04 |
| 1996 |
6.81 |
7.09 |
7.48 |
7.73 |
6.53 |
| 1997 |
7.68 |
7.24 |
8.77 |
9.48 |
6.31 |
| 1998 |
5.38 |
5.78 |
6.63 |
6.61 |
5.25 |
| Mean |
6.59b |
6.96b |
8.11a |
8.67c |
5.77d |
a,b Values with different superscripts across nitrogen treatments differ, P<.05.
c,d Values with different superscripts across grazing intensity differ, P<.05. Year*grazing
intensity interaction was significant, P<.0001, and Year*nitrogen treatment interaction was significant P=.0030.