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  • Author or Editor: Ian A. Merwin x
  • Journal of the American Society for Horticultural Science x
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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.

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One-year-old potted `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on scion invigorating Malling-Merton 111 (MM.111) and scion dwarfing Malling 9 (M.9) rootstocks were grown outdoors in containers under three levels of water availability (irrigated at -20, -80, and -200 kPa) to investigate the effects of soil water availability on combined soil/root (rhizosphere) respiration rates, and developmental morphology of root systems. Rhizosphere respiration was measured with a portable infrared gas analyzer, and root biomass was estimated by electrical capacitance. These nondestructive measurements were compared with final root dry weights of harvested trees, to determine their reliability for estimating relative differences in root biomass. Water stress reduced final biomass similarly for both rootstocks, but the relative reduction in shoot growth was greater for MM.111. Root to shoot ratios were higher and average specific root respiration was lower for M.9 rootstock compared with MM.111. M.9 appeared to be more tolerant of water stress then MM.111, due to reduced canopy transpiration relative to root system mass. Water stress increased root to shoot ratios, specific root length, and the carbohydrate costs of root maintenance as indicated by specific respiration rates. Root dry weight (DW) was better correlated to rhizosphere respiration than to root electric capacitance. The observed r 2 values between root capacitance and root DW were as high as 0.73, but capacitance measurements were also influenced by soil water content and rootstock type. Electrical capacitance estimated total root biomass more accurately for M.9 than for MM.111.

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Abstract

Growth chamber evaluations of soil from an orchard replant site showed severe stunting of ‘Northern Spy’ apple (Malus domestica Borkh.) seedlings grown in field soil (FS) compared with pasteurized soil (PS) from the same site. The FS : PS seedling dry weight ratio of 0.44 indicated a serious replant problem. Leaf nutrient content was generally higher in PS than FS seedlings. Multiple-regression analysis indicated that leaf K and root-lesion nematode (Pratylenchus penetrans Filipjev) primary inoculum accounted for 75% of the variation in FS seedling dry weight. Apple seedling dry weight in FS was 97% of that in PS following a marigold (Tagetes patula L. cv. Sparky) cover crop, and 75% following oats (Avena sativa L. cv. Saia). Root-lesion nematodes were nearly eliminated from the plots with marigold. Other cover crops and a weed-free fallow period were less effective in controlling apple replant disease and/or phytonematodes.

Open Access

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.

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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.

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A 2-year field study of `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] on `Malling 9' (M.9) rootstock was conducted to observe root growth in situ, and compare patterns of root growth, root maturation and turnover rates, and soil-root respiration. Rhizosphere respiration was monitored with a portable chamber connected to an infrared gas analyzer; root emergence, browning, and turnover rates were measured by direct observation through minirhizotron tubes inserted in the root zone. Negligible root growth was observed before the onset of shoot growth in mid-May. In both years, a main peak of new root emergence in late June and early July coincided partially with major phases of shoot and fruit growth. A smaller peak of root emergence during August to September 1997 consisted primarily of new roots at 20 to 45 cm soil depths. Most roots remained <1 mm in diameter and developed in the upper 25 cm soil profile; no roots were observed at any time below 50 cm, due to a compacted soil layer at that depth. The cumulative survivorship of new roots was 38% in 1996 and 64% in 1997, and 50% of emergent white roots turned brown or senesced within 26 days in 1996 and 19 days in 1997. Root turnover rates were highest in mid-August both years. Rhizosphere respiration was correlated (r 2 = 0.36 and 0.59, P = 0.01 and 0.004) with soil temperatures in 1996 and 1997, with Q10 values of 2.3 in both years. The Q10 for root-dependent respiration (the difference between soil only and combined soil-root respiration) in 1997 was 3.1, indicating that roots were more sensitive than soil microflora to soil temperature. The temporal overlap of high rates of shoot, root and fruit growth from late May to mid-July suggests this is a critical period for resource allocations and competition in temperate zone apple trees.

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