Agroforestry silvopastural systems are not a new concept. Orchardists have long grazed livestock among their mature trees during seasons when the animals were not a threat to the fruit crop. Southern pecan growers commonly graze cattle among mature native trees.
However, there has been little experience with grazing livestock among young trees in plantations of nut trees. Almost nothing has been recorded about the potential damage animals would inflict on the trees at various stages of growth.
With the support from a Sustainable Agriculture Research and Education grant and in cooperation with the Center for Agroforestry at the University of Missouri, a research and demonstration project was initiated in 1999.
Although the primary objective of the project was to determine the amount and type of damage cattle would inflict on a black walnut plantation, two secondary objectives also were included. One was closely related to the damage aspect by measuring compaction from cattle traffic in grazed areas versus non-grazed areas. The other objective was to demonstrate potential profitability of such a silvopastoral practice and compare it with production of hay between the tree rows.
The demonstration site selected was on HarperHill Farms located near Butler, Missouri, in west central Missouri near the Kansas border. Owner/operator Larry Harper conducted the trials with the help of part time employees. HarperHill Farms has nearly 120 acres of black walnut plantations planted 40 feet between the rows and 20 feet between the trees within the rows. Trees range from 10 to 15 years old and most all are grafted to improved nut producing varieties.
The site selected for the demonstration was 15 acres containing trees from 12 to 15 years of age. Nearly all are grafted to improved varieties. However, a few trees have been left ungrafted to compare production characteristics. The trees had been herbicided in a four-foot strip down both sides during the first three years after planting and in alternating years until they were about eight years old. They had not been herbicided in the last four years prior to and during the experiment. An additional six acres of big bluestem grass in an open pasture was included in the system for use in July when the bromegrass became less productive. All trees, including the one-acre check area, received 60 pounds of nitrogen in the form of ammonium nitrate in April of each year prior to grazing.
In April of 1999 and 2000, 25 steer calves weighing an average of 585 pounds were purchased and placed on the grass. The 21 acres had been divided into paddocks of from one to two acres each by using single strand electric polywire. The polywire was movable by rolling it on reels so only a limited amount of fencing was necessary. The electric fence was powered by a low impedance charger commonly referred to as the New Zealand system of electric fencing.
With this management intensive grazing system, all 25 steers would graze a single paddock for one day and then be moved to the next paddock. With 18 paddocks, they would be grazing each paddock every 18 to 24 days, depending on the regrowth of the forage.
The steers were short grazed for only 100 days and sold the first week of August. They received no additional feed other than forage. Salt and mineral were kept before them at all times. The cattle received a pour-on treatment before entering the grazing system to discourage external parasites and corresponding tree rubbing. Flies were controlled with insecticide ear tags.
In the third year of the study (2001) the forage between the rows was harvested for hay and sold to achieve a comparison of the profit potential of these agroforestry systems. The forage between the tree rows consists mostly of smooth bromegrass with some legumes. A small portion of the grazed area is covered by invading Kentucky 31 fescue.
Measurements of both diameter and height of the trees were taken in the spring of 1999 prior to first grazing, again in the spring of 2000 and finally in the spring of 2001.
Densiometer readings to determine compaction effects of trampling were taken in three places (3 feet, 12 feet and 25 feet) on each side of selected tree rows in both the check area and grazed area. These sites joined so soil conditions were similar.
The management intensive grazing system was chosen not only for its potential of reducing animal traffic and exposure of trees to damage, but for its other potential benefits to both trees and forage as well. With this fast rotation grazing system the cattle are constantly grazing forage that is at or near its optimum feeding value. It is convenient for cattle to graze and may keep them from overgrazing favorite spots and thus increasing pressure on the adjacent trees. This system promotes even distribution of manure over the grazing area as the animals graze the whole area more evenly. This self management of fertility should be beneficial to the trees over the long term. It also is possible to control where cattle are grazing during wet times and keep them from doing additional damage to trees in wet pastures.
In the spring of 1999, the control area trees averaged 2.56 inches in diameter. By the spring of 2000 they had grown .4 inch in diameter. Between 2000 and 2001 the diameter growth was an additional .43 of an inch. These trees were 12 years old in 2000.
In the grazed area adjacent to the control area the trees also are 12 years old. In 1999 these trees averaged 2.99 inches in diameter. By the spring of 2000 they increased in diameter by .30 inches. Between 2000 and 2001 they had an additional growth of .34 inches. These finding are similar to those reported by J. W. Lehmkuhler and Monty Kerley of the University of Missouri Center for Agroforestry (“Comparison of continuous and rotational silvopastoral systems for established walnut plantations” submitted to Agroforestry Systems). At most, the grazed trees may have diameter growth suppressed by 20% to 25%.
A second grazed area adjacent to the first grazing area is populated with 15-year-old trees, a few of which are natives and have not been grafted. In this area of slightly older trees the increase in diameter for both years was .39 inches or almost as much growth as the control area.
Measurements on height growth did not show major differences between the control area and the grazed areas. Between 1999 and 2000 the control area trees increased in height by 43.6 inches. Between 2000 and 2001 the increase was 11.3 inches.
For the 12-year-old trees in the grazed area next to the control area, the increase in height the first year was 36.2 inches and 11.7 inches the second year — very similar to the control area growth. In the 15-year-old tree grazing area, the increased heights were 49.1 inches and 15.9 inches — again a similar growth as the control area. A similar height growth record was noted by researchers at the University of Missouri (Lehmkuhler et al.). This supports the conclusion that height growth is little affected by cattle grazing under management intensive grazing practices.
Compaction has been a concern of grazing livestock, especially cattle, in orchards. However, results from this trial indicate that it is a non-issue. A densiometer probe that measures pounds of pressure necessary to push the probe into the soil was used to make a comparative measurement. The probe was pushed four inches into the ground, then eight inches at three distances from the tree row on each side of the row. Results indicate that there was slight compaction in the upper four inches. However, the increased pressure necessary to penetrate the soil to eight inches was deemed no more than what is required to overcome normal friction.
Miscellaneous physical damage to trees also was noted. A few trees (7 of 116) were killed by the cattle. All of these trees were less than four feet tall when the cattle entered the grazing area in 1999. The most prevalent cause of damage was rubbing, especially to alleviate the effects of face flies. Cattle were observed browsing branches from the trees, but this seemed to be more mischief than desire for food. However, this browsing caused damage by ripping off strips of bark with the small branches. Most of these wounds have healed over. An overall browse line was noted at about the five-foot height.
From these observations, it can be concluded that trees must be 10 to 12 feet tall and have a diameter of at least three inches if they are to be safely grazed under this system with cattle of this size. To overcome the browsing effects and stripping of bark, it might be wise to prune the trees to at least the five-foot height. That would leave half or more of the crown in place as is generally recommended by most foresters.
However, in other trials at HarperHill Farms and in trials conducted by Monty Kerley at the University of Missouri Horticulture and Agroforestry Research Center, it has been shown that by using a single strand of electric polywire four feet on either side of the tree row, grazing can begin immediately after planting. Cost of the electric fencing is reasonable, especially when rolled on reels and moved with the cattle from paddock to paddock.
From the results, it can be assumed that it is practical to combine steer grazing in a black walnut agroforestry system. Potential damage to the trees by the animals can be overcome by management techniques. Slight decreases in growth of the trees are more than offset by the income potential of the cattle operation, especially in the early years when there is no income from the nut crop. Given this, it provides more opportunity for diversifying the farm products and income over time. Where before, a farmer may have had only an annual income with hay while waiting 15 years for walnut production, there is now an opportunity for a second annual income with the sale of the cattle.
In most years, cattle will be more profitable than selling the hay crop. The trick is knowing which years. Historically, grazing has been somewhat profitable seven out of 10 years.
A silvopastoral practice also offers the opportunity to promote rotational grazing (MIG). Cattle grazing is known to help build the fertility and health of the soil and forage when managed correctly, such as with MIG. Alternating steers with hay production may be a practical option. Because of the synergistic effects of short grazing steers among the trees, overall profit potential is increased. Trees also provide shade in the summer and cattle will graze even during the hot hours of the day, which helps them maintain their weight. Further, they tend to spread out along the shade line, rather than congregating under a single tree or group of trees.
There was great interest in this application among farmers (approximately 90 total) who attended the two field days held by Larry Harper at HarperHill Farm. The expectation is that farmers, as they learn more about the practice, will adopt it.
The economics and profit potential of a grazing system of this type totally depends on each operator’s equity position, their ability to buy and sell steers and their comparative good or bad luck. However, “walking off” the forage through cattle rather than incurring the expense of owning or hiring machinery likely will be the most profitable, most years.
During the two years of experience with this project HarperHill Farms recorded a gross profit per steer of between $50 and $75. Since less than one acre (.84 acre) was required per steer for the grazing season this figure can be translated into a $60 to $89 gross profit per acre. This profit figure does not include costs of land, labor or fertilizer. Land and fertilizer costs are charged to the primary enterprise of growing trees for nuts. Labor was not charged because the same labor used for 25 steers could suffice for a herd of 100, even 300, head under a management intensive grazing system.
It is interesting to note that short grazing steers can be a most complementary enterprise with a black walnut or other nut production agroforestry system. By removing the cattle the first of August, the grass has ample time to recover before nut harvest in September. The manure has time to dry and disappear so it will not affect nut quality. And, the cattle price trends for the past 20 years show that selling 750 to 800 pound steers the first week of August avoids a traditional late summer price slump. It also is advantageous because the cattle are not carried through the August gain slump, or even reversal.
During both years of the demonstration, the cattle at HarperHill gained an average of 1.5 pounds per day for 100 days. It was observed that the grass was improving in growth and condition during the second year, likely due to application of fertilizer and manure. Stimulation of the grass by the movements of the cattle also contributed to a healthier sward. It is likely that gains would either increase in successive years or, more likely under a management intensive grazing system, more steers could be grazed on fewer acres thus contributing more income to the system.
In 2001, the forage was baled for hay and sold. The hay yielded two tons per acre. Half the hay was given to the custom hay operator to pay for harvesting. The other half was sold for $45 per ton. This was a gross profit or $45 per acre without land or fertilizer charges.
An additional “profit” must be noted with either of these systems. At least one and possibly two annual mowings of the plantation are eliminated. At $12 per acre per mowing, that makes a considerable contribution to the bottom line.
A field day (summer 1999) was held to demonstrate the agroforestry silvopasture practices, and was attended by over 40 farmers and 60 other extension and natural resource agency personnel.
A second field day was held (summer 2000) and about 50 farmers attended. At least one farmer has adopted this practice since seeing the demonstration; yet, there was great interest especially since it can produce short-term and long-term income.
Educational & Outreach Activities
Stories appeared in The Green Horizons, a newsletter publication of the University of Missouri Center for Agroforestry, which is sent to over 2000 subscribers. Attached are copies of Vol. 4, No. 3, Autumn 1999 (“Cattle vs. Trees Revisited”) and Vol. 6, No. 3, Winter 2001 (“Grazing cows in a walnut agroforestry practices: Results from on farm research”).
Larry Harper was also featured as a farmer participant in a video “Silvopasture: An Agroforestry Practice,” a copy of which is being sent with this report to the NCR-SARE office.
Areas needing additional study
Studies that focus on the carrying capacity of cows/acre in silvopasture practices would be of interest, as would studies that measure the impacts of shade on a cow’s weight gain.
Lehmkuhler, J.W., M.S. Kerley, H.E. Garrett, B.E. Cutter, and R.L. McGraw. 1999.
Comparison of continuous and rotational silvopastoral systems for established walnut plantations in southwest Missouri USA. Agroforestry Systems 44:267