Water was withheld from 2-year-old seedlings or rooted cuttings of four birch genotypes (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. ‘Cully’, and B. papyrifera Marsh.) until the combined weight of the container and plant decreased below 40% of its original value to induce plant predawn water potential between −1.5 MPa and −2.1 MPa, after which plants were supplied with a requisite amount of water to reach 40% of its original value for 5 weeks under controlled conditions to investigate changes in gas exchange, osmotic solutes, leaf abscission, and growth compared with well-watered (WW) plants. Observations indicated that three of the four genotypes (except B. papyrifera) expressed three stages of photosynthetic response during water deficit: 1) a stress stage, 2) an acclimation stage, and 3) an adapted (or tolerance) stage. The stages were characterized by decreasing, increasing, and stabilized Pnws/ww (net photosynthesis presented as a ratio of water-deficit stressed (WS) plants to WW plants), respectively. A strong relationship between Pn and g S observed in the WS plants of the four genotypes, suggested inhibition of Pn by stomatal closure. After exposure to water deficit for 5 weeks, Pnws/ww recovered to 70% of the initial value for B. alleghaniensis and B. nigra ‘Cully’ and 98% for B. davurica and B. papyrifera. WS plants had higher foliar concentrations of chlorophyll a and b (nmol/g) and potassium (%) than the WW plants. Increased levels of polyols (mg/g) were detected only in the WS plants of B. allegahaniensis. Increased levels of carbohydrates or organic acid under water deficit were not detected. A significant increase in leaf abscission in the WS plants of B. papyrifera compared with the other genotypes could be a morphological adaptation to water deficit conditions and facilitate recovery of Pnws/ww during the acclimation stage.
Mengmeng Gu, Curt R. Rom, James A. Robbins, and Derrick M. Oosterhuis
N. Mays, K.R. Brye, Curt R. Rom, M. Savin, and M.E. Garcia
Orchards established on weathered, acidic mineral soils in the Ozark Highlands must be managed to meet tree nutritional requirements. However, a common characteristic of Ozark Highland soils is a relatively low soil organic matter (SOM) concentration, a condition that can have detrimental effects on orchard productivity. Organic orchard management poses specific challenges to managing competitive under-tree vegetation and supplying appropriate supplemental nutrition to maintain tree growth and cropping. In Mar. 2006, an experimental apple orchard was established to evaluate the effects of under tree, in-row groundcover management system (i.e., shredded paper, wood chips, municipal green compost, and mow-blow), and nutrient source (i.e., non-fertilized control, composted poultry litter, and pelletized organic commercial fertilizer) on SOM, carbon (C), and nitrogen (N) concentration, and soil C and N sequestration over time in an organically managed orchard in the Ozark Highlands region of northwest Arkansas. Soil organic matter, total C, and total N concentrations (soil weight basis) and contents (area basis) in the top 7.5 cm increased in all groundcover management systems from 2006 to 2011. The greatest differences were observed with municipal green compost treatments. Significant interactions between groundcover management treatment and nutrient source were only observed for SOM concentration, whereas nutrient source did not affect total C and total N concentrations or contents. Soil C sequestration rates were 0.9, 1.0, and 2.8 Mg·ha−1 per year under the shredded paper, wood chip, and green compost treatments, respectively, whereas total C content did not change over time under the mow-blow treatment. The green compost treatment was the only treatment that had significant total N sequestration occur (0.25 Mg nitrogen/ha/year). Results of this study indicate that organic cultural methods can significantly augment near-surface soil C and N contents, which will likely increase productivity, of apple orchards in the Ozark Highlands over a relatively short period time after establishment. This study has implications for orchards in similar soils or environmental circumstance and for both organic and conventional management systems.
Curt R. Rom, H. Friedrich, D. Johnson, J. Popp, B. Bellows, M. Savin, and D. Miller
Fruit production in the Southern region has declined in the last several decades. Further, although certified organic fruit production has increased significantly in other regions of the US in the past decade, there has been very little growth of that industry in this region. It is presumed that the lack of production is based upon the lack of research, out-reach, and science-based information available to growers which make organic production possible. Based on planning grant funding from the Southern IPM Center program and the Sustainable Agriculture Research and Education program a Southern Organic Fruit Working Group is being formed. The projects are collaborative efforts of horticulturists, entomologists, plant pathologists, soil scientists, and agricultural economists in Arkansas, Georgia, Kentucky, North Carolina, South Carolina, and Tennessee. In each state, a coordinator is hosting stake-holder focus groups of producers, marketers, processors, extension workers, consultants, organic certifiers, etc. The purpose of focus group meetings is to identify challenges and opportunities in production and marketing organic fruit, especially apples, blackberries, blueberries, and peaches, in the Southern Region. Coordinators are combining findings from state focus group meetings to establish priorities for research and outreach to support organic production, and will work collaborative to addresses those priorities. Because of the similarity in climate, geography and demographics of growers and markets among the states of the region, this is a project best addressed as a regionally collaborative effort.
Mengmeng Gu, Curt R. Rom, James A. Robbins, and Hyun-Sug Choi
The genus Betula consists of approximately 50 deciduous species throughout northern hemisphere. Net CO2 assimilation ([A]) of four birch taxa (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. `Heritage', and B. papyrifera Marsh.) was measured with a portable gas exchange system, CIRAS-I. Light was increased from 0 to 2000 μmol· m-2·s-1 at increments of 25, 50, 100, 250, 500, 750, 1000, 1250, 1500, 1750, 2000 μmol·m–2·s–1 to create an [A] light-response curve. CO2 concentration was gradually increased to 1100 ppm in increments 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 ppm to create an [A]-Ca (ambient CO2) curve. B. davurica had significantly higher potential A capacity than the other taxa under high CO2 conditions. Betula nigra `Heritage' had the highest carboxylation efficiency among four taxa. B. davurica and B. nigra `Heritage', had higher [A] when ambient CO2 is 0ppm. Betula davurica and B. nigra `Heritage', had higher light-saturated rate of gross [A] than B. alleghaniensis and B. papyrifera.
Jessica Chitwood, Ainong Shi, Michael Evans, Curt Rom, Edward E. Gbur Jr., Dennis Motes, Pengyin Chen, and David Hensley
Breeding heat-tolerant spinach is an important project to meet the demand of increasing spinach production in heat conditions. Seed germination is the early stage to test, screen, and develop heat-tolerant spinach genotypes. The objective of this research was to determine temperature effect on the seed germination percentage and to select heat-tolerant spinach genotypes. A total of nine spinach genotypes were used in this research. The germination experiment was conducted using seven temperatures: 10, 15, 20, 25, 30, 32, and 35 °C under growth chambers. The temperature trials were conducted using completely randomized design (CRD) with three replicates. Spinach seed germination percentage varied among the nine spinach genotypes under the seven temperatures, indicating that genetic variation for heat tolerance existed in the nine spinach genotypes. ‘Donkey’, ‘Marabu’, and ‘Raccoon’ showed higher seed germination percentage with over 70% at 30 and 32 °C, indicating the three spinach genotypes had heat tolerance for germination. However, all spinach genotypes except ‘Ozarka II’ dropped their germination percentages sharply to less than 30%; ‘Ozarka II’ had 63% germination under 35 °C, indicating it is a good source of heat tolerance for seed germination. The higher germination percentages above 30 °C of ‘Ozarka II’, ‘Donkey’, ‘Marabu’, and ‘Raccoon’ may indicate their potential as donors of heat-tolerant traits in spinach breeding program.
Heather Friedrich, Curt Rom, Jennie Popp, Barbara Bellows, Donn Johnson, Dan Horton, Kirk Pomper, David Lockwood, Steve McArtney, and Geoffrey Zehnder
Southern organic fruit production is limited by a lack of regionally appropriate, scale-neutral, and market-focused research and technology. There has been limited research, outreach, and cooperation among universities on organic fruit crops in the southern region. Organic research and outreach activities, based on producer input, must be focused on the most limiting areas of the organic system in order to allow southern producers to receive the economic and environmental benefits that organic agriculture can provide. With funding from USDA-SARE and USDA-SRIPMC, researchers at the University of Arkansas have collaborated with scientists, extension specialists, growers, and representatives of the organic industry in Arkansas, Georgia, Kentucky, North Carolina, South Carolina, and Tennessee to create a Southern Region Organic Fruit Working Group (SROFWG). The SROFWG conducted in-state focus group meetings through which barriers to production and marketing, and opportunities for organic fruit in the region were identified. Prioritized research and outreach needs that were identified in the focus groups included use and understanding of organic fertilizers and nutrient management; methods, knowledge and awareness of pest disease and weed control including orchard floor management; information on transition to organic; consumer awareness and market development and the economics of organics. The planning activities of the SROFWG support the development and submission of grants for cooperative and collaborative research and outreach programs to sustain and expand organic fruit production in the southern region.
Jayesh B. Samtani, Curt R. Rom, Heather Friedrich, Steven A. Fennimore, Chad E. Finn, Andrew Petran, Russell W. Wallace, Marvin P. Pritts, Gina Fernandez, Carlene A. Chase, Chieri Kubota, and Brad Bergefurd
Strawberry (Fragaria ×ananassa) production practices followed by growers in the United States vary by region. Understanding the challenges, needs, and opportunities in each region is essential to guide research, policy, and marketing strategies for the strawberry industry across the country, and to enable the development of general and region-specific educational and production tools. This review divided the United States into eight distinct geographic regions and an indoor controlled or protected environment production system. Current production systems, markets, cultivars, trends, and future directions for each region are discussed. A common trend across all regions is the increasing use of protected culture strawberry production with both day-neutral and short-day cultivars for season extension to meet consumer demand for year-round availability. All regions experience challenges with pests and obtaining adequate harvest labor. Increasing consumer demand for berries, climate change-induced weather variability, high pesticide use, labor and immigration policies, and land availability impact regional production, thus facilitating the adoption of new technologies such as robotics and network communications to assist with strawberry harvesting in open-field production and production under controlled-environment agriculture and protected culture.