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Dario Stefanelli and Ronald L. Perry

One of the main problems facing organic horticulture is orchard ground floor management. Several works report that ground floor management affects root architecture of fruit trees, changing the position and depth of the roots. The purpose of this work is to study the effects of orchard ground floor management systems (GFMS) in an apple orchard under organic protocol in Michigan. The research was conducted at the Clarksville Horticultural Experimental Station of Michigan State University, in the organically certified (by OCIA) orchard of `Pacific Gala' grafted on M9 NAKB 337, established in May 2000. The GFMS being studied are: 1) mulch (MU) made of alfalfa hay on the tree rows, with a width of 2 m; 2) “Swiss Sandwich System” (SSS) that consists in superficial tillage of two strips 90 cm wide at each side of the tree row, leaving a 40-cm strip in the middle (under the canopy) where volunteer vegetation is allowed to grow; 3) flaming (FL) of the weeds in a 2-m strip underneath the tree canopy by a propane burner. Root architecture was studied in Sept. 2005 through the frequency of roots by the profile wall method. Trenches (3.36-m long × 1.32-m deep) were dug in the soil 45 cm from the tree trunk. Two 158 cm × 130 cm metal grid frames divided by strings into a 28 cm × 22 cm grid were placed against the profile faces to facilitate the counting and mapping of the root distribution. The GFMS did affect the root distribution of the two classes of roots under study (<2 mm and >2mm). In the FL and MU treatments, roots were noticed to be superficial and their frequency was higher close to the tree. In SSS, root frequency was similar until 80 cm deep in the soil profile and they extended farther from the tree.

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Dario Stefanelli*, Giovambattista Sorrenti, and Ronald L. Perry

Soil organic matter is a critical component which is fundamental in plant growth. Several soil factors are influenced by organic matter such as slow release of nutrients, increased water holding capacity, improved soil physical characteristics and improved environment for soil microorganisms. The aim of this work is to investigate the physical effect of organic matter content in the soil on apple root growth and development. Twenty five two-year old apple trees (Malus domestica, Borkh) cv. `Buckeye Gala' on M.9 NAKB 337 rootstock were planted in completely transparent acrylic boxes. Plants have been grown in a green house to avoid external rain in a complete randomized design. Trees were planted in a sandy-mix soil amended with soil high in organic matter, “muck”, at four incremental levels. Treatments compared were a control (sandy soil with 0% organic matter) and 1%, 2%, 4% and 8% soil organic matter. The amount of water applied by automatic drip irrigation was comparable for all the treatments to avoid high fluctuation of soil moisture on root dynamics. All treatments have been fertilized with the same amount of mineral fertilizer to avoid the nutrition effect on root dynamics. Digital photos of roots were taken to study their dynamics every one to two weeks during a period of five months. Roots have been highlighted with Photoshop and then analyzed with WinRhizo to measure root length, area, lifespan and dynamics. At the end of the growing period plants have been harvested and fresh and dry weight was evaluated to asses the root/shoot ratio. The effects of the treatments on root length, area, lifespan and dynamics, and root/shoot ratio will be discussed.

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Ronald L Perry*, Dario Stefanelli, and Gail Byler

Trees of Gala were planted in 1994 on 18 rootstocks at the Clarksville Horticulture Experiment Station as one cooperating site of 26 North American sites organized by the NC-140 Regional Pome and Stone fruit rootstock committee. One tree each of seven rootstock treatments and two on B.9 and B.491 have died since establishment. Death has been caused by wind (brittle union) on most of the trees in replication one, on the western exterior of the plot which is exposed to strong wind. The most vigorous trees in this planting are those on V.1 and M.26 and least vigorous on M.27 and P.22. Cropping in 2003 was highest on Pajam 2, Ottawa 3 and M.9 NAKB 337, yielding an average of between 60 to 70 kg per tree. Cropping over the years has been highest on PJ.2, M.9 EMLA, and O.3. Cumulative yield efficiency in this plot is highest on P.16, followed by P.22 and B.491. Trees on M.26 are the least efficient over the years. Average fruit weight was highest in 2003 on V.1 and PJ.2. M.9 NAKB 337, the dominant international an national standard M.9 clonal rootstock is not as productive and as precocious as many other M.9 clonal stocks in this trial. After 10 years of evaluation, there appears to be no significant difference in cropping, cumulative yield, for `Gala' among the top eight rootstocks led by M.9 Pajam 2. M.9 NAKB 337 is not among the top eight rootstocks at this site. Pajam 2 is impressive from the view that while it is the top cropping stock, it is the rootstock in 2003 which also averaged the largest fruit. Among the M.9 clonal rootstocks, PJ 2 is also the most vigorous which for North American commercial apple orchards, has excellent commercial potential to withstand field and production stresses.

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Dario Stefanelli, Roberto J. Zoppolo, Ronald L. Perry, and Franco Weibel

In organic apple production systems, orchard floor management is of prime importance because it determines weed management and soil fertility. In this experiment, we evaluated the response of the cultivar Pacific Gala on three rootstocks of different vigor: M.9 NAKB 337, M.9 RN 29, and Supporter 4 (in respective order of vigor from dwarfing to semivigorous). The rootstocks were also evaluated for the response to three orchard floor management systems (OFMSs): mulching using alfalfa hay, flame burning, and shallow strip tillage using the Swiss sandwich system (SSS). The experiment was conducted in an experimental orchard planted in 2000.

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Dario Stefanelli, Roberto J. Zoppolo, and Ronald L. Perry

Fine root dynamics, timing of the events, and their relationship with soil conditions are of major interest because the understanding of these phenomena will permit a better synchronicity between nutrients and plant uptake. The goal of this research is to study the effect of different soil conditions, generated from two ground floor management systems, on fine root dynamics of apple trees under organic protocol in Michigan. The research has been conducted at the Clarksville Horticultural Experimental Station (CHES) of Michigan State University (MSU), in the organically certified (by OCIA) orchard of “Pacific Gala” grafted on M9 NAKB 337, established in May 2000. The orchard floor management systems being studied are: 1) a mulch made of alfalfa hay on the tree rows, with a width of 1.8 m and 2) the “Swiss Sandwich System” (SSS) that consists in superficial tillage of two strips 80 cm wide at each side of the tree row, leaving a 40 cm strip in the middle (on the tree row, under the canopy) where volunteer vegetation is allowed to grow. Root dynamics are studied on four replicas of two trees per each of the two ground treatments (16 in total) in a block design. For each tree in the trial four clear butyrate minirhizotrons have been installed (64 in total) at a 45° angle facing the tree, in the summer of 2002. Root dynamics, measured through pictures taken with a Bartz Technology digital camera and analyzed with a new software under development at MSU. During the 2003 season differences between the two systems have been found depending on the parameter taken in consideration. Mulch had different root distribution compared to SSS. Mulch treatment showed shallower roots even if below 90 cm the two systems didn't show any difference.

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Thomas G. Beckman, Ronald L. Perry, and James A. Flore

The effects of short-term soil flooding on gas exchange characteristics of containerized sour cherry trees (Prunus cerasus L. cv. Montmorency /P. mahaleb L.) were studied under laboratory conditions. Soil flooding reduced net CO2 assimilation (A) within 24 hours. Net CO2 assimilation and residual conductance to CO2(gr′) declined to ≈30% of control values after 5 days of flooding. Effects on stomatal conductance to CO2 (gS) and intercellular CO2 (Ci) were not significant during the 5 days of treatment. Apparent quantum yield (Φ) gradually declined to 52% that of controls during these 5 days. In a second experiment, CO2 response curves suggested that, initially, stomatal and nonstomatal limitations to A were of about equal importance; however, as flooding continued, nonstomatal limitations became dominant.

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Rodney T. Fernandez, Ronald L. Perry, and James A. Flore

`Imperial Gala' on M.9 EMLA, MM.111 and Mark rootstocks were planted in a rain exclusion shelter. Two drought stress periods lasting approximately 1 month each were imposed during 1991. Water was supplied at 2 liters per day per tree before and after each drought cycle while water was withheld from half of the trees during the drought stresses. Maximal and variable chlorophyll fluorescence and fluorescence quenching were significantly reduced by the drought stress with M.111 generally affected first and with the largest difference between drought and control followed by Mark and then M.9. Leaf and stomatal conductance, assimilation and transpiration usually occurred first and were lowest for M.9 followed by Mark and then M.111 during the first stress cycle while Mark responded more rapidly and to a greater extent than M.9 and M.111 during the second stress. Water potential was lower for the stressed trees during both stress periods but osmotic and turgor potentials were reduced only during the first stress period. Changes in water relations were noticed first and to a greater extent for Mark followed by M.9 with M.111 exhibiting the least sensitivity and differences.

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R. Thomas Fernandez, Ronald L. Perry, and James A. Flore

`Imperial Gala' apple trees (Malus ×domestica Borkh.) on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Water relations, gas-exchange parameters per unit leaf area and per tree, chlorophyll fluorescence, and leaf abscisic acid content were determined during each stress and recovery period. Whole-plant calculated gas exchange best indicated plant response to drought stress, with consistent reductions in CO2 assimilation, transpiration, and leaf conductance. Variable and maximal chlorophyll fluorescence and fluorescence quenching were not as sensitive to stress. Other fluorescence parameters showed little difference. The most consistent decreases due to stress for gas exchange per square meter were in transpiration and leaf conductance, with few differences in CO2 assimilation and fewer for mesophyll conductance, internal CO2 concentration, and water-use efficiency. Leaf water potential was consistently lower during drought stress and returned to control values upon irrigation. Leaf abscisic acid content was higher for drought-stressed trees on M.9 EMLA than control trees during the stress periods but inconsistently different for the other rootstock treatments. Trees on M.9 EMLA were least affected by drought stress, MM.111 was intermediate, and Mark was the most sensitive; these results are consistent with the growth data.

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R. Thomas Fernandez, Ronald L. Perry, and James A. Flore

`Imperial Gala' apple (Malus domestica Borkh.) trees, trained to two shoots, on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Leaf growth rate, leaf area, leaf emergence, shoot length, and trunk cross-sectional area were measured during each stress and recovery period. Leaf growth rate was reduced during both stress periods but most consistently during the second drought stress. Length of the less-vigorous shoot was reduced most consistently due to drought stress but did not recover upon irrigation. Leaf emergence and trunk cross-sectional area increment were inconsistent in response to stress. Tree growth was reduced by drought stress to the greatest extent for trees on Mark, with MM.111 intermediate and M.9 EMLA least affected. At termination, the plants were separated into roots, current-season shoot growth, previous-season shoot growth, and rootstock, and dry weights were measured. Dry weights confirmed the growth measurements taken during the experiment with a 16%, 27%, and 34% reduction in total plant dry weight for drought-stressed trees on M.9 EMLA, MM.111, and Mark, respectively, compared to corresponding controls. It was concluded that Mark was the most sensitive of the three rootstocks followed by MM.111; M.9 EMLA was the most drought resistant.

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R. Thomas Fernandez, Ronald L. Perry, and David C. Ferree

Root distribution of `Starkspur Supreme Delicious' on nine apple (Malus domestics Borkh.) rootstock grown in two different soil types in the 1980 NC-140 Uniform Apple Regional Rootstock Trial (Michigan and Ohio sites) was determined using the trench profile method. Based on the number of roots counted per tree, rootstock could be separated into five groups for the Marlette soil from most to least: MAC.24 > OAR1 > M.26EMLA = M.9EMLA > M.7EMLA = 0.3 = M.9 = MAC.9 > M.27EMLA. For the Canfield soil, rootstock were ranked for number of roots counted from most to least as follows: MAC.24 > OAR 1. MAC.9 = M.7EMLA > M.26EMLA = O.3 = M.9 EMLA = M.9. Root distribution pattern by depth was affected by soil type with roots fairly well distributed throughout the Marlette soil but restricted primarily above the fragipan in the Canfield soil. Two rootstock performed differently from others in adapting to soil conditions at the different sites. MAC.9 had the second lowest number of total roots/dm2 in the Marlette soil yet the second most in the Canfield soil, while the opposite was found for M.9EMLA. Regression analysis demonstrated positive correlations between number of roots counted and vigor and yield of the scion.