This demonstration showed that legumes can meet the pecan trees’ N requirement even if grazed. However, increasing N application by 10% in grazed orchards likely would be a good long term investment to offset loss to grazing. Legumes may offer the greatest benefit on grazed sites that tend to have less native forage, e.g. flood prone sites, as they offer grazing benefits as well as nitrogen fixing benefits. Higher yield of both pecans and beef in the non-flood site suggests the need to correct drainage problems or, if that is not possible, to focus management inputs on those trees with the greatest production potential.
Demonstrate the effects of a legume based grazed native pecan orchard management system on soil N fixation, soil characteristics and beneficial insect attraction.
Demonstrate trapping and weather monitoring to schedule pecan weevil and scab spray programs compatible with livestock.
Demonstrate a fully integrated and sustainable legume based beef and native pecan production system.
Quantify treatment effects on changes to the plant community.
Quantify the economic benefits of legumes, weevil trapping, scab monitoring and grazing in a native pecan system.
History and folklore have recorded incidences of Native Americans, and early explorers as well, surviving exceptionally hard winters on the tasty, high energy kernels from native pecans. Pecan kernels consist of 70-75% fat. In these diet conscious times all fat was considered bad until the “good fat” concept i.e. unsaturated fat, was discovered. The good news for pecans is that from 92% to 97% of the fat in pecans is unsaturated. Recent studies (Loma Linda Univ. and New Mexico State University) have shown that pecan oils in a heart healthy diet result in lower cholesterol.
Management requirements for native and variety pecans vary somewhat depending on the variety in question. In comparison to improved varieties native pecan trees generally have better pest resistance and require fewer inputs but they produce smaller nuts and are less efficient with more yield variation and lower value per pound. Variety selection is critical to success in pecan management particularly if the variety is to be managed in conjunction with a larger stand of native trees. A typical management program for native pecans might consist of 100 lbs of nitrogen per acre, zero to one pecan nut casebearer spray and zero to two sprays for pecan scab.
Sustainable pecan management is a viable alternative for native pecans and for varieties suitable for a native pecan management system. Sustainable management is fully compatible with double crop systems including livestock and pecan production. If management techniques are properly applied native pecans can be managed with minimum external inputs. In order to achieve maximum benefit from a management program the trees must be in condition to utilize the inputs provided.
A legume based orchard floor management system can provide all the nitrogen needed by the trees. Even if grazed, legumes can contribute to the N needs of the trees while increasing animal gain per acre. Cool season legumes are best. Annual or perennial, they can be seeded in September and make a good harvest surface in late fall. They grow while the pecan is dormant and are most competitive in the spring when moisture is generally ample for both trees and forage. They also can be harvested by mid July which allows deferment from grazing before pecan harvest. A good stand of legumes can contribute up to 150 pounds of actual N per acre if not harvested and 60 lbs or more N if harvested for hay or by grazing. Legumes can contribute 2 to 4 tons of forage production per acre without nitrogen fertilizer.
Perennials such as white or red clover are functional over a wide range of soils. White Clover is the most tolerant of flooding and generally best suited to grazing. Red Clover is short lived but fixes the most N. Of the annual clovers arrowleaf produces the most forage while crimson fixes the most nitrogen. Clovers are small seeded and must have short residue for establishment in the fall.
Native pecan fertilization is usually minimal value without other management actions. Trees that are crowded or standing on waterlogged soil may give little or no positive response to added fertilizer.
Each native tree is genetically different. As such, there is much variability from tree to tree. Long term development of a native orchard is benefited by grafting smaller trees to pecans of known performance. Use only low input varieties which are scab resistant with medium nut size which mature early enough to avoid early fall freezes. Proven selections from native trees in the area are frequently good choices for grafting. They are likely to be best adapted to the area and have management requirements compatible with the other trees.
This project was initiated in 1999 with plots at Haydon Farms near Okemah, OK and at Santifer Farms near Texarkana, Arkansas. The Oklahoma component consisted of eight plots either grazed or un-grazed, seeded to cool season legumes or left to native vegetation, on a site prone to natural flooding or not. Grazed plots were 10 acres each and un-grazed plots were 2 acres each for a total of 48 acres. Plots were identified to contain about 32 square feet of trunk cross sectional area per acre and were fenced with electric fence to include or exclude cattle. The Arkansas demonstration included only four plots as it did not have a flood component.
A mixture of crimson, white and red clover was seeded with a pasture drill in September, 1999 and over seeded as needed each September to maintain the stand. About ten percent of the trees in each plot were identified at random and labeled for collection of individual tree yield and growth data. The plots were harvested with commercial harvesting equipment and yield determined by weighing. Fall rains in OK prevented harvest in 2000 so yield for that year was estimated based on crop estimates on the 10% sample trees. Grade was determined from a sample of nuts from each plot.
Leaf and soil samples were collected each year from each plot. Native vegetation plots were fertilized in accordance with leaf sample results. Legume plots received no supplementary fertilization other than zinc added to spray solutions. All vegetation from un-grazed plots was mowed and left in place. Pest management was accomplished as specified by Oklahoma Cooperative Extension Service recommendations.
Grazing was accomplished with steers in OK and heifers in AR from about mid April until mid July in 2000, 2001 and 2002. Gain was calculated from individual animal weights at the beginning and end of each grazing period. The stocking rate was based on forage availability and averaged 0.8 and 1.5 animals per acre in flood and non-flood plots, respectively.
Objective 1. Grazing reduced tree leaf N content whether flooded or not. The reduction ranged from 6.3% in flooded legume plots to 3.1% in flooded native vegetation plots. Trees in legume plots maintained minimum recommended leaf N levels without supplementary fertilization whether grazed or flooded. Supplemental N fertilization in amounts ranging up to 150 lbs N per acre, was required on native plots to maintain tree leaf N content above minimum level of 2.4%.
Pecan aphid populations were slightly greater and beneficial organisms were slightly lower in native forage areas than in legume plots. Pecan nut casebearer adult populations were similar in flooded or un-flooded areas of the orchard but greater in grazed than un-grazed plots. Adult casebearer populations were greater in legume plots than native vegetation plots. Pecan nut casebearer damage was similar across all treatments.
Objective 2. Pesticide application was accomplished only as dictated by threshold calculation. During 2000 pecan weevil populations tended to be greater in the non-flood areas than in the flood plane. Weevil numbers recovered were also greater in grazed than in un-grazed sites. Pecan aphid populations were greater in flood areas than in un-flooded sites and higher in grazed than un-grazed plots. Pecan aphid populations were slightly greater and beneficial organisms were slightly lower in native forage areas than in legume plots.
Disease management focused on demonstration of best management practices for control of pecan scab. Scab was effectively controlled and maintained at an economic level in OK with minimum fungicide applications made according to the Oklahoma pecan scab model. Arkansas plots used the phenology scab spray model.
Objective 3. Comparison benefits from the AR demonstration were reduced due to expression of what appeared to be the so called “barnyard effect”, essentially a severe zinc deficiency, in the grazed, native vegetation plot and to tree damage in all plots resulting from a severe ice storm in December 2000.
Natural flooding in the Oklahoma flood prone plot was consistent with the intent of the project. Harvest data were collected for four years at both sites. Grazing data were collected for three years at both sites.
Average pecan yield over 4 years ranged from 483 lbs. per acre in non flood native vegetation plots to 698 pounds per acre in non flood grazed plots. Legume plots produced higher nut yield than native vegetation plots whether grazed or flooded. Nut yield from non-grazed plots in the AR test varied. In grazed plots, trees with legumes out yielded those with native vegetation. Nut yield in the Arkansas plots were too variable for conclusion due to ice storm damage and nutritional disorder.
In the OK trial average beef gain was highest (307 lbs/A) on non-flood plots with native vegetation. In flood prone plots beef gain was highest (226 lbs/A) on legume forage. Data from the July thru August grazing period revealed little or no gain probably due to excessive heat and associated effects on the cattle. The summer grazing period can serve essentially as a holding area for the cattle to take advantage of the microclimate among trees as it likely does no harm to the trees. Cattle must be removed by Sept 1 in preparation for pecan harvest.
Average pecan yield ranged from under 500 to nearly 700 lbs of nuts per acre. Yield from legume plots was higher whether grazed or not. Yield from non-flood plots was higher than flood plots except for the non-grazed native vegetation plot which was the least productive plot in the test.
Average beef gain ranged from 167 to 307 pounds per acre. Greater gain from the non-flood plots was likely due to the greater amount of forage available and resultant higher stocking rate in those plots. Native vegetation plots in non-flood area produced more beef gain while the reverse was true in the flood prone area. The seeded legumes provided good grazing in the absence of alternate forage. Higher pecan yield from legume plots in the flood site also suggest increased benefit from legumes on flood prone sites.
Leaf nitrogen was used as an indicator of grazing effect on tree nutrition. Grazing consistently reduced average leaf nitrogen in the trees. The greatest reduction was in trees in the flood prone site, 6 percent in the case of grazed legumes (Table 3). This nitrogen reduction did not significantly affect the trees, at least for the term of this test, since nut yield was higher from legume plots whether grazed or not (Table 1). A longer term study may have revealed a “mining” effect of grazing on tree nutrition. The fact that the legumes, even though grazed, could provide for the nitrogen needs of the trees without supplementary N fertilization is a strong testament to their benefits.
The grazing period and stocking rate for the Texarkana plots were about one 400 pound heifer per acre from April through June. Forage crude protein averaged nearly 19% in legume plots compared to about 15% in native plots whether grazed or not. Grazing results revealed from 125 to 150 pounds of gain per acre from grazing in the Texarkana test.
Harvest data from the Texarkana plots showed variable results. Yield exceeded 650 lbs per acre in 1999 and trees on native plots returned an increased yield in 2000 after the big year in 1999. Yield for 2001 reflect storm damage in 2000. This stand could include more trees without reducing per tree yields substantially.
Objective 4. We were unable to complete this objective due to relocation of the ecologist assigned to the project.
Objective 5. Mr. Jason Lopez, PhD student under the direction of Dr. Joe Schatzer in the OSU Department of Agricultural Economics is nearing completion of his PhD program which includes in depth analysis of data generated from this project. Detailed analysis will be available as part of his dissertation.
Educational & Outreach Activities
The publication budget from this project was leveraged with funds from other sources to support development of the Oklahoma Pecan Management eLearning course, a unique pecan educational vehicle now available at http://pecan.okstate.edu
Results obtained from this SARE project formed the basis for the native pecan section in that unique educational tool. A total of 10 growers from 4 states have registered to take the course which was posted in February, 2004. This project represents a major innovation in Extension program delivery and was made possible in large part by this SARE project.
OCES Current Report 6250, Use of Legumes in Pecan Orchards and Fact Sheet 2585, Forage Legumes for Oklahoma are both are available from OSU County Extension office or on the Internet at http://pearl.agcomm.okstate.edu/hort/fruits/index.html
Additional presentations covering results of this project were made at numerous public meetings including the Kerr Center for Sustainable Agriculture Alternative Agriculture Symposium, county extension meetings, the National Pecan Scientists Research and Extension Forum, the Texas Pecan Orchard Management Short Course and other similar meetings throughout the native pecan region.
This project was highly successful. The OK demonstration served as an excellent field day site with over 300 persons in attendance in June 2000. A field day at the AR site in April 2002 attracted 20 people. Results of the project were presented at the Langston University Small Farm and Alternative Agriculture Symposium on the Langston University campus during August, 2001. Over 150 growers of various crops were in attendance. A summary of the results was presented at the Kerr Center for Sustainable Agriculture’s “Future Farms 2002″ conference in Oklahoma City with over 200 in attendance and at the annual Oklahoma Pecan Growers’ Association meeting with over 175 growers in attendance. The project was also featured as the cover story in the SARE annual report for 2003.
Over 2400 pecan industry surveys were mailed with nearly 700 returns. Results were presented at the annual Oklahoma Pecan Growers’ Association meeting in Oklahoma City in June 2003. The highest attended OPGA annual meeting in the last 5 years was the Haydon Farms field day in June 2000 which featured reports on this SARE demonstration. Over 40% of survey respondents attended that field day. Other SARE educational activities with percent attendance included the Miller County, Arkansas field day (2%) and the Langston University small farm field day (1%). The survey also verified that over 80% of native pecan producers also graze livestock in their orchards.
Economic analysis of this project will receive wide dissemination as part of a PhD project. Results will be reported before the Agricultural Economics section held annually in connection with the Southern Association of Agricultural Scientists.
Results of the study were presented at the annual meeting of the Oklahoma Pecan Growers’ Association in Oklahoma City, June 2003 before 150 pecan growers. Audience acceptance and interest were among the highest of subjects presented.
Survey of pecan growers revealed that approximately 80% on native pecan growers graze their orchards and 5% use a legume mix in their orchard floor management program. Of those, 22% use white, crimson or red clovers which are the species shown to be the most beneficial to the beneficial insect population as well as pecan tree nutritional status.
Areas needing additional study
A significant incidental result from this study was increased pecan yield from grazed plots. The design of this study did not lend itself to explaining this result. Therefore, additional study is needed to explain this result and to determine the optimum stocking rate in a legume based grazed native pecan system.