Groundcover Management Systems Research Articles

Orchard floor management practices that maintain vegetative or biomass groundcover stimulate soil microbial activity and alter soil microbial community composition

Groundcover management systems (GMS) are important in managing fruit-tree orchards because of their effects on soil conditions, nutrient availability, tree growth and yields. We employed a polyphasic approach, incorporating measures of soil microbial abundance, activity and community composition, to study the long-term effects of different GMS on biotic and abiotic factors in an orchard soil. Four GMS treatments – Pre-emergence residual herbicides (Pre-H), post-emergence herbicide (Post-H), mowed-sod (Grass), and hardwood bark mulch (Mulch) – were established in 2-m-wide strips within tree rows in an apple orchard in 1992, and have been maintained and monitored annually until the present. We have measured soil water and nutrient availability, tree growth, and yields annually from 1993 to 2003. Soil nematode numbers and trophic groups were evaluated in July and Oct. 2001, and Sept. 2003. Numbers of culturable bacteria and fungi, soil respiratory activity, eubacterial and fungal community composition were determined in May and Sept. 2003. The Pre-H treatment soil had the fewest culturable bacteria, while the Grass treatment had the largest population of culturable fungi. Soil nematode population size and diversity were also affected by GMS treatments; the Pre-H treatment had the lowest ratio of (bacteriovores + fungivores) to plant parasitic nematodes. Soil respiration rates were higher in the Mulch than in other treatments during a 40-day incubation period. Hierarchical cluster dendrograms of denaturing gradient gel electrophoresis (DGGE) fingerprints for eubacterial community 16S rRNA genes indicated that Post-H and Grass treatments clustered together and separately from the Pre-H and Mulch treatments, which were also grouped together. The influence of GMSs on the fungal community, as assessed by PCR-DGGE of the internal transcribed spacer (ITS) region, was not as pronounced as that observed for bacteria. Soil fungal community composition under the Mulch differed from that under other treatments. The effects of GMS on soil microbial community abundance, activity, and composition were associated with observed differences in soil organic matter inputs and turnover, nutrient availability, and apple tree growth and yields under the different GMS treatments.

Groundcover Management Systems Influence Soil Microbial Community Composition in an Apple Orchard

An apple (Malus domestica cv. Empire on M9/MM111 rootstock) orchard groundcover management systems (GMSs) study has been underway since 1992 in Ithaca, N.Y. Four GMS treatments are applied each year in 2-m wide tree-row strips: Pre-emergence herbicides (Pre-H: diuron + norflurazon + glyphosate); Post-emergence herbicide (Post-H: glyphosate); mowed-sod (Grass); and composted hardwood bark mulch (Mulch) treatment. The soil (silty clay loam) physical and chemical conditions have been monitored continuously. In May and Sept. 2003, we sampled topsoil beneath trees in each GMS and used PCR-DGGE combined with sequencing to characterize soil microbial community composition. Mulch had more culturable soil bacteria than the Pre-H treatment. Soil in Grass plots had the most culturable soil fungi. Soil microbial respiration rates were higher in Mulch than Grass and herbicide GMSs. Surface vegetation in the Grass and Post-H plots strongly influenced soil bacterial community composition. In Principal Component Analyses, Post-H and Grass treatments comprised one variance cluster, and Pre-H and Mulch treatments another. The soil fungal community was less diverse (fewer DGGE bands) than the bacterial community, and was less affected by GMS. Treatments with more surface vegetation (Post-H and Grass) also had more free-living and phytonematodes than Pre-H and Mulch. A total of 47 clones from 12 DGGE bands yielded 31 unique DNA sequences. Of these, 15 were novel sequences with no matches in the GenBank (NCBI) database. Another 10 (27 clones) could be matched with known fungal species at 96-100% identity. The primer pair used, ITS1F/ITS2, amplified a considerable number of Basidiomycetes and Ascomycetes, but there was no amplification for Zygomycetes and Oomycetes.

Effects of groundcover management on ground beetles (Coleoptera: Carabidae) in an apple orchard

A field experiment was conducted in a cider-apple orchard to evaluate the effect of six groundcover management systems (pine-bark, plastic and straw mulches, tillage, herbicide and natural soil) on the occurrence of ground beetles (Coleoptera: Carabidae). Eight species of carabids were collected in pitfall traps. The three most common beetles, Steropus gallega Fairmaire (65.8%), Pseudophonus rufipes (DeGeer) (18.2%) and Poecilus cupreus L. (14.6%), represented more than 98% of the total catches. The specific dominance depended on the sampling date. The soil management treatment significantly affected the following parameters. (1) The overall carabid catch: the plastic mulch (5.6% of the total catches) negatively affected total carabid collection, which was higher in the tilled (24.3%) and herbicide-treated (21.4%) plots, although not significantly different from the natural soil (16.5%), straw mulch (16.3%) and pine-bark mulch (15.9%) treatments. (2) The specific preferences of the three most common carabids: the plastic cover adversely affected the catches of S. gallega whilst P. rufipes was collected in greater numbers in tilled areas and P. cupreus in the herbicide treatments. (3) The structure of the carabid community: based on species richness, diversity and evenness indices, herbicide and tillage provided the most diverse carabid community and the straw mulch the poorest. It was concluded that groundcover management in apple orchards may affect the activity density of epigeic predators which may contribute to the natural control of pests.

Soil physical conditions in a New York orchard after eight years under different groundcover management systems

An experiment was conducted near Ithaca, New York, to compare orchard soil and groundcover management systems (GMSs) in a silty clay loam soil (mixed, mesic, Glosaquic Hapludalf). Three replications of four GMS treatments were randomly assigned to 12 plots and maintained since 1992 in 2 m-wide strips within tree rows: (1) Sod: Red fescue (Festuca rubra) turfgrass mowed biweekly; (2) Post-HBS: Post-emergence applications of glyphosate herbicide in May and July annually; (3) Pre-HBS: Pre-emergence applications of paraquat, diuron and norflurazon herbicides each May; and (4) Mulch: A 15-cm depth layer of shredded hardwood bark mulch, renewed triennially. After eight years of continuous treatments, we compared soil physical conditions and hydraulic properties in these GMSs. Bulk density was lower and soil porosity greater under Mulch than other GMSs. Infiltration was more rapid under Mulch than other GMSs, and under Post-HBS than Sod. Saturated hydraulic conductivity ranged from 6 × 10−4 m.s−1under Sod to 12 × 10−4 m.s−1 under Mulch plots, and was equivalent in Sod and Pre-HBS, lower in Sod than Post-HBS or Mulch treatments, higher in Post-HBS than Pre-HBS, and higher in Mulch than all other GMSs. Volumetric soil water content at field capacity ranged from 0.47 under Mulch to 0.40 under Sod, and was not significantly different among GMSs between 0.99 and 39.22 kPa of pressure. GMS treatments and related management practices at this orchard had substantially different long-term effects on soil physical conditions. Compaction and reduced infiltration in Sod compared with other GMSs were attributed to tractor wheel traffic during mowing. Mulch treatments improved soil conditions relative to other GMSs. Greater infiltration rates and hydraulic conductivity under Post-HBS compared with Pre-HBS suggest relative advantages of post-emergence herbicides.

Orchard Groundcover Management Systems Affect Meadow Vole Populations and Damage to Apple Trees

Meadow vole (Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple (Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m2 was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)

Orchard Groundcover Systems Affect Meadow Vole Populations and Damage to Apple Trees.

Meadow vole (Microtus pennsylvanicus L.) populations, feeding activity, and damage to young apple (Malus domestica Borkh.) trees were monitored by direct observation, trap counts, and a feeding activity index in different groundcover management systems (GMSs) for five years in a New York orchard. Vole populations differed greatly among GMSs, with consistently higher populations and more damage to tree trunks in crownvetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.)sodgrass GMSs. Vole populations were highest in the fall and lowest during the spring seasons each year. Anticoagulant rodenticides and natural predation did not result in adequate control of voles in GMSs that provided favorable habitat for nesting and feeding of this pest. The percent of soil surface vegetation coverage was not, but the amount of groundcover biomass was, a significant predictor of vole populations and damage to trees, independent of groundcover vegetation species. Trunk applications of thiram fungicide were less effective than 40-cm-high plastic mesh trunk guards, but better than no protective measures for controlling vole depredation in groundcover management systems (GMSs) with high rodent populations. A combination of late fall vole trapouts, close and consistent mowing of orchard floor vegetation, tree trunk protection with mesh guards, ample surrounding habitat for natural predators of voles, and suppression of tree row groundcover species with herbicides provided adequate control of meadow voles without the use of rodenticides at this orchard.

Groundcover Management Systems Influence Fungicide and Nitrate-N Concentrations in Leachate and Runoff from a New York Apple Orchard

Commercial apple (Malus domestica Borkh.) orchards in the northeastern United States receive heavy pesticide inputs and are often located on well-drained soils near surface and groundwater resources. Nonpoint-source water pollution by agrichemicals has been monitored in agronomic crop systems and simulated using computer models and laboratory soil columns, but inadequately studied at field scale in orchards. We monitored the concentrations of agrichemical tracers, nitrate-N, and benomyl fungicide in water samples from two apple orchards under mowed sodgrass (Mowed-Sod), shredded bark mulch (Bark-Mulch), preemergence residual herbicides (Resid-Herb), and postemergence herbicide (Post-Herb) groundcover management systems (GMSs). In one orchard, we evaluated subsurface spatial patterns and flow rates of a weakly adsorbed blue dye (pesticide analog) and potassium bromide (nitrate analog) under trees after six years of Post-Herb and Mowed-Sod treatments. Nitrate and pesticide tracers leached more rapidly and in higher concentrations under Post-Herb treatments, apparently via preferential macropore flowpaths such as root channels, soil cracks, and macrofauna burrows. At another orchard, we monitored subsurface leaching and surface runoff of benomyl and nitrate-N on a whole-field scale. Peak concentrations of benomyl (up to 29 mg·liter-1) and nitrates (up to 20 mg·liter-1) were observed in subsoil leachate under Resid-Herb plots during 1993. In 1994, nitrate concentrations were greater in leachate from all GMSs, with upper ranges from 48 to 66 mg·liter-1, while benomyl concentrations were lower in all GMSs compared with the previous summer. In surface water runoff during 1993, the highest benomyl concentrations (387 mg·liter-1) and most frequent outflows occurred in Resid-Herb plots. During 1994, benomyl runoff was more frequent in both herbicide GMSs, with concentrations up to 61 mg·liter-1 observed in the Post-Herb plots. Weather patterns, irrigation intensity, differing soil conditions under each GMS, and the turfgrass/clover drive lanes affected the relative frequency and concentrations of benomyl and nitrate leaching and runoff. Preferential bypass flow appeared to be a major subsurface leaching pathway, and erosion sediment an important factor in surface movement of these agrichemicals. Our studies suggest that nitrate-N and benomyl fungicide may be more prone to leaching or runoff from orchard soils under some herbicide GMSs in comparison with mowed sodgrass or biomass mulch systems.

Orchard Groundcover Management Systems Influence Surface Runoff and Subsoil Leaching of Agrichemicals

Non-point source water pollution by agrichemicals is a recognized problem that has been studied in agronomic crop systems, and simulated using computer models or artificial soil columns, but rarely measured at field scale in orchards. For three growing seasons, we monitored the movement of nitrate and pesticide analogs and a widely used fungicide (benomyl) in two apple orchards under four different groundcover management systems (GMSs), including turfgrass, wood-chip mulch, residual pre-emergence herbicides, and post-emergence herbicide treatments. In subsoil lysimeter samplers at one orchard, we observed that nitrate and pesticide analogs leached more rapidly and in higher concentrations under herbicide plots compared with turfgrass plots. At another orchard where subsoil leaching and surface runoff of benomyl and nitrate-N were monitored in replicated GMS plots, we observed higher concentrations of benomyl (up to 30 μg·liter–1) and nitrate-N up to 50 μg·liter–1) leaching under herbicide GMS. The highest benomyl concentrations (375 μg·liter–1) and most frequent runoff of this pesticide were observed in the residual pre-emergence herbicide plots. Yearly weather patterns, irrigation, and development of different soil physical conditions under the four GMSs determined the relative magnitude and frequency of agrichemical leaching and runoff in both orchards. The agrichemicals apparently leached by mass flow in preferential flowpaths such as old root channels and soil cracks, while surface chemical runoff occurred mostly adsorbed on eroding soil sediment. These observations indicate that orchard GMSs can have a significant impact on leaching and runoff of pesticides and nutrients.

Compost Mulch, Canola Cover Crops, and Herbicides affect soil Fertility, Apple Tree Yield, and Nutrition

Three orchard groundcover management systems (GMSs) were established in a newly planted apple (Malus domestica cvs. Liberty, Nova Easygro, and NY84828-12 on Malling 9 rootstock) orchard on a silty-clay loam soil (Aeric Ochraqualf). The GMSs were applied in 2-m-wide strips within tree rows as follows: 1) a 6-cm-thick mulch layer of composed manure, straw, sawdust, and vegetable plant wastes applied in May 1992 and 1994; 2) a “green manure” cover crop of canola (Brassica campestris cv. Humus) seeded in mid-August each year and tilled under the following May; and 3) Post-emergence applications of N-(phosphonomethyl) glycine (glyphosate) herbicide (2.0 kg a.i./ha) in mid-May and July each year. After 3 years of GMS treatments, apple tree growth and trunk cross-sectional area were similar in all three systems. Fruit yield and yield efficiency were greater in glyphosate and compost than in canola GMSs, and `Liberty' was the most productive cultivar. Topsoil N, P, K, Ca, Mg, Zn, and organic matter content were all substantially greater in the compost GMS. Leaf N, K, and P concentrations were consistently greater in trees in compost plots; leaf Ca, Mg, Cu, and Zn concentrations were lower in compost GMS. Weed growth was rank and difficult to control in the compost mulch, but this GMS substantially enhanced orchard soil fertility.

Comparing Mulches, Herbicides, and Cultivation as Orchard Groundcover Management Systems

Natural (hay, wood chips, recycled paper pulp) and synthetic (polypropylene film and polyester fabric) mulches were compared with mechanical tillage and residual herbicides as orchard groundcover management systems (GMSS). In two New York orchards-the Clarke farm and Hudson Valley Lab (HVL—GMSS were applied from 1990 to 1993 in 1.8-m-wide strips under newly planted apple (Malus domestica; `Liberty', `Empire', `Freedom', and advanced numbered selections from the disease-resistant apple breeding program at Geneva, N.Y.) trees. GMS impacts on soil fertility, tree nutrition and growth, yields, crop value, and vole (Microtus spp.) populations were evaluated. After 3 years at the Clarke orchard, extractable NO3, Mn, Fe, B, and Zn concentrations were greater in soil with herbicides than synthetic mulches; soil K and P concentrations were greater with herbicides and wood chips than synthetic mulches. At the HVL orchard, topsoil NO3, K, and Mg concentrations were greater with hay mulch than herbicides or other mulches; Mg, Fe, and B concentrations were lower in soil with wood chips than other GMSs. Soil organic matter content was not affected by GMS. Apple leaf N, K, Cu, and Zn concentrations were greater with herbicides, hay mulch, and polypropylene mulch than cultivation or recycled paper mulch at the HVL orchard during hot, dry Summer 1991. Despite transient differences among GMSS during the initial years, after 4 years of treatments there were no consistent GMS trends in cumulative tree growth or gross yields. The higher establishment and maintenance costs of several mulches were offset by their prolonged efficacy over successive years; crop market values from 1992 to 1994 were considerably greater for trees with polypropylene film, polyester fabric, and hay mulches than herbicides, cultivation, or other mulches. Voles caused more serious damage to trees in synthetic and hay mulches, despite the use of mesh trunk guards and rodenticide bait.

604 PB 220 GROUNDCOVER MANAGEMENT SYSTEMS AND PREPLANT FERTILIZERS INFLUENCE PEACH TREE GROWTH, YIELD, MICRONUTRIENT AVAILABILITY AND UPTAKE

Growth, nutrient uptake, and yield of peach (Prunus persica) trees was evaluated in various groundcover management systems (GMSs) for three years, with and without preplant soil additions of Zn, B, and Cu. In July 1990, micronutrients (none, or 135kg Zn·ha-1+100kg Cu·ha-1+1.1kg B·ha-1) were incorporated into the upper 20 cm of a silty clay-loam soil (pH 6.7, 4% organic matter), and a fine-leaf fescue (Festuca ovina) turf was established. Trees were planted Apr. 1991, and four GMS treatments (wood-chip mulch, pre-emergence herbicide, post-emergence herbicide, and mowed turf) were superimposed upon the “+/-” micro-nutrient preplant treatments. Extractable Zn, Cu and B concentrations were greatly increased in soil of plots which had received preplant amendments. Peach leaf content of Zn, Cu and B was also greater in preplant fertilized plots in the year of planting. However, in subsequent years only leaf B (in 1992) and leaf Zn (in 1993) continued to respond positively to preplant soil treatments. No significant interactions were observed between GMS and micronutrient availability or uptake. Peach growth and yield were not affected by preplant treatments, but were substantially greater in mulch and pre-emergence herbicide plots compared with the mowed fescue turfgrass.

073 A COMPARISON OF NATURAL AND SYNTHETIC MULCHES WITH CONVENTIONAL ORCHARD-FLOOR MANAGEMENT SYSTEMS

In several northeastern USDA Low-Input Sustainable Agriculture (LISA) projects, we compared natural (hay-straw, wood-chips, recycled newspaper pulp) and synthetic (polypropylene films and polyester fabrics) mulch materials with mowed sodgrass, tillage, and residual herbicides, as orchard groundcover management systems (GMS). Treatments were applied in 2m-wide strips under newly planted apple (Malus domestica cvs. Liberty, Empire, Freedom. and others) trees on MARK rootstock, planted at 3 by 5m spacing, in 1990. Edaphic, economic, tree nutritional and fruit yield impacts of these GMS were evaluated for four years in five Hudson Valley orchards. All the mulches cost more to establish and maintain ($450 to 4500/ha) than mowed sod ($150/ha), tillage ($120/ha), or residual herbicide ($50/ha) systems. There were few differences in soil water or nutrient availability, leaf nutrient content, tree growth or fruit yield in the mulch systems compared with herbicide or tillage GMS. Meadow voles (Microtus spp.) caused considerable damage to trees in the synthetic and straw mulches, despite the use of trunk guards. Wood-chips were the most enduring, least expensive, and most effective natural mulch. There were insufficient short-term benefits to offset the greater costs of synthetic mulch fabrics or films, in comparison with conventional herbicide snip systems for orchard floor management.

Orchard Groundcover Management Impacts on Soil Physical Properties

This study was conducted to compare various orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of post-emergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during the first 6 years in a newly established apple (Malus domestica Borkh.) planting. Mean soil water potential at 5 to 35 cm deep varied substantially among treatments each summer, and treatment × year interactions were observed. During most growing seasons from 1986 to 1991, soil water availability trends were STMCH > NDPQT > GLY2.5 > GLY1.5 > tilled > GRSOD > MWSOD > CNVCH. Soil organic matter content increased under STMCH, CNVCH, and MWSOD and decreased under NDPQT and tilled treatments. Water infiltration and saturated hydraulic conductivity after 4 years were lower under NDPQT and tilled, and soil under STMCH and GRSOD retained more water per unit volume at applied pressures approximating field water capacity. Mid-summer soil temperatures at 5 cm deep were highest (25 to 28C) in tilled and NDPQT plots, intermediate (22 to 24C) under GRSOD, and lowest (16 to 20C) under CNVCH and STMCH. These observations indicate that long-term soil fertility and orchard productivity may be diminished under pre-emergence herbicides and mechanical cultivation in comparison with certain other GMSs.

Orchard Groundcover Management Impacts on Apple Tree Growth and Yield, and Nutrient Availability and Uptake

This study compared various conventional and alternative orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of postemergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during 6 years in a newly established apple (Malus domestica Borkh.) planting. Trunk cross-sectional area and fruit yield were higher in STMCH, GLY, and NDPQT, intermediate in tilled, and lower in GRSOD, MWSOD, and CNVCH treatments after 5 years. Despite N and K fertilizer applications, extractable soil N and leaf N concentrations were reduced under MWSOD and GRSOD, and soil K, P, and B concentrations were greater under STMCH. Leaf K concentrations were usually highest in STMCH trees, even when heavily cropped; leaf K declined below the sufficiency range in GLY, NDPQT, and tilled trees as they began to bear fruit. Leaf Ca was marginally deficient in all trees and was unaffected by GMS. Foliar Mn, Zn, and B concentrations declined rapidly in all treatments during 2 years without micronutrient fertilizers. Leaf Cu was higher in herbicide and tilled treatments where seasonal soil water content was intermediate (22% to 27%) and lower where soil was very wet or dry for most of the 1988 growing season. Multiple regression analysis indicated that leaf N and B and soil organic matter in 1990, and mean soil water content during the unusually dry Summer 1988, were the best predictors of fruit yield in 1990. Phytophthora root rot and meadow vole depredation were serious problems in STMCH and CNVCH trees. GMSs greatly affected tree establishment, nutrition, and yield; each system involves tradeoffs among important short- and long-term impacts on the orchard agroecosystem.

ALTERNATIVE STRATEGIES FOR SMALL FRUIT PRODUCTION

This LISA project involves four state universities and the USDA, and has the objective of developing and evaluating non-conventional production and pest management strategies for raspberries and strawberries. Production goals are divided between cropping systems and pest management. The evaluation of trellising systems for cropping efficiency, ease of harvest, and spray distribution is an example of a production related objective. Groundcover management systems for strawberries are being evaluated for their effects on both the pest complex and production system. Biological control strategies for root diseases are also being studied. Evaluations involve field performance, economics, and impacts on pesticide use. In addition, grower attitudes towards adoption of non-traditional production practices have been assessed. The project supports the publication of a newsletter that is distributed to 450 growers. The major goal of our work has been to improve production efficiency and provide growers with economical, dependable tools that can be used to prevent pest problems before chemical intervention is required.

ALTERNATIVE ORCHARD GROUNDCOVER MANAGEMENT SYSTEMS AFFECT APPLE QUALITY AND MATURITY INDICES

Alternative groundcover management systems (GMS) beneath establishing 'Jonagold' apple trees have been evaluated since 1986 in an orchard field test Tree-row GMS being studied include post-emergence herbicide (glyphosate) “killed sods”, pre-emergence herbicides (norflurazon and diuron). a crownvetch “living mulch”, hay-straw mulch, monthly cultivation, and a closely mowed sodgrass. Trees in herbicide and straw-mulch plots produced the most fruit in 1990, but in 1991 there were no GMS-related differences in crop load. Fruit were larger in herbicide and straw-mulch plots in 1990 and 1991, and red color development was better in sod and crownvetch GMS. Starch-to-sugar conversion was advanced in apples from sodgrass and straw mulched plots. The ethylene climacteric was delayed in fruit from crownvetch and straw-mulch GMS, and peaked rapidly as mean starch indices approached 4.0 in all GMS treatments. Differences in soil moisture and nutrient availability under alternative GMS may have influenced fruit quality and maturity.

COMPETITIVE VEGETATIVE ORCHARD COVERS REDUCE PEACH ROOTING

Peach trees (`Biscoe'/Lovell) were planted in March, 1988 in ten different ground cover management systems. The trees were planted at the Sandhills Research Station in Southeastern North Carolina on a Candor sand and Eunola sandy loam. In December, 1991 the trench profile method was used to evaluate root distribution under the six orchard floor management systems of nimblewill, bare ground control, centipedegrass, brome, bahiagrass, and weedy control. Trenches were dug parallel to the tree row 60 cm from the center of the row on both sides of the tree. Grids 1 meter square, sectioned into 10 cm squares, were placed on the profile walls and root distribution (in three size categories) was recorded for 1 meter on each side of the tree in each trench. Root numbers were greatly reduced under the vegetative covers that provided the greatest suppression of vegetative tree growth. Total root densities under the trees in the vegetative covers were ranked into three size categories which were correlated with the amount of vegetative tree growth.

ALTERNATIVE GROUNDCOVER MANAGEMENT SYSTEMS AFFECT ORCHARD SOIL FERTILITY AND APPLE LEAF NUTRIENT CONTENT.

Eight groundcover management systems (GMS) have been evaluated since 1986 in an apple orchard replant site. Tree-row GMS have included post-emergence herbicide (glyphosate) “killed sods,” pre-emergence herbicide (norflurazon + diuron) strips, a crownvetch “living mulch,” hay-straw mulch, monthly cultivation, a close-mowed sod, and an unmowed, chemically growth-regulated (maleic hydrazide + 2,4-D) sodgrass. Soil organ&matter content, surface aggregate structure, and water infiltration have improved under vegetative groundcovers relative to herbicide treatments. Extractable soil N, K, P and B have increased under straw mulch. Except for K, foliar nutrient content (dry wt basis) has not been closely coupled with soil nutrient content. Leaf K, P and B contents have increased, while leaf N, Mg and Zn, have decreased in trees in sodgrass relative to herbicide GMS.

ALTERNATIVE ORCHARD GROUNDCOVER MANAGEMENT SYSTEMS INFLUENCE EARLY APPLE YIELDS AND MORTALITY.

Eight groundcover management systems (GMS) have been studied since 1986 in an apple orchard replant site. Tree-row GMS consisted of post-emergence “killed sods” and pre-emergence herbicide strips, a crownvetch “living mulch,” hay-straw mulch, clean cultivation, a close-mowed sod, and an unmowed but chemically growth-regulated sodgrass. Trees initially grew best in the straw-mulch treatment, but nearly 40% have succumbed to Phytophthora crown rot since 1988, apparently due to excessive soil moisture. Meadow vole populations have been higher, and vole injury to lower trunks has been more frequent and severe on trees in crownvetch and straw-mulch GMS, despite routine rodenticide baiting. Cumulative yields per tree have been highest in straw-mulched trees, but yields per acre have been much lower, because of the increased tree mortality in this treatment.

EFFECTS OF GROUNDCOVER MANAGEMENT SYSTEMS AND WATER DEFICIT STRESS ON QUALITY OF APPLE

A field study was initiated in 1981 in western North Carolina to determine the influence of eight groundcover management systems on quality of `Redchief Red Delicious' apple (Malus domestica) grafted onto rootstock of M VIIA. Management systems included: bare soil, Secale cereale mulch, minimal cultivation, Festuca arundinacea, Dactylis glomerata, Poa pratensis, Muhlenbergia schreberi and Rubus sp. Thus far, fruit quality data indicate that fruits produced in plots of cool-season grasses are smaller and less mature than those produced in vegetation-free plots or plots of warm-season grasses. A negative correlation was noted between high fruit quality and water deficit stress as measured by water potential and stomatal conductance.