A leach collection unit (LCU) was assembled to capture all leachate draining from a nursery container. An injection molded 2.8-L nursery container was plastic welded into the lid of a 7.6-L black plastic collection bucket so that the bottom 2.5 cm of the nursery container protruded through the lid. The LCU was designed to track total N release from CRFs without confounding effects of plant uptake or N immobilization. Total N released between any two sampling periods is determined by multiplying the N concentration in a leachate subsample × total leachate volume. The LCU were placed in a container nursery area with overhead irrigation. LCU were thoroughly leached before sampling the leach solution. To study the effects of substrate on N leach rates, Osmocote 18.0N–2.6P–9.9K (8 to 9 months 21 °C) was incorporated at 1.8 kg N/m3 using a locally available, bark-based substrate or medium-grade quartz sand. The experiment was conducted at Scotts Research locations in Apopka, Fla., and Marysville, Ohio. Osmocote incorporated into either a bark-based substrate or sand resulted in similar N release profiles. Although substrate did not affect N leach rate, quartz sand was recommended as the substrate in the leach collection system for polymer-coated CRFs. Quartz sand is chemically and biologically inert, does not immobilize nutrients and has low ion exchange capacity compared to bark-based potting substrates. More than 90% of the total nitrogen applied from Osmocote was recovered from leachate and unreleased N in fertilizer granules. This research has demonstrated the leach collection system as a reliable means to quantify nitrogen release rate of a polymer-coated CRF under nursery conditions. The LCU, when used with a crop plant, allows nutrient budget and nutrient uptake efficiency to be determined for CRFs.
Brian A. Birrenkott, Joseph L. Craig, and George R. McVey
Steven A. Weinbaum, R. Scott Johnson, and Theodore M. DeJong
Over-fertilization (i.e., the application of fertilizer nitrogen (N) in excess of the tree or vine capacity to use it for optimum productivity) is associated with high levels of residual nitrate in the soil, which potentially contribute to groundwater and atmospheric pollution as a result of leaching, denitrification, etc. Overfert-ilization also may adversely affect productivity and fruit quality because of both direct (i.e., N) and indirect (i.e., shading) effects on flowering, fruit set, and fruit growth resulting from vegetative vigor. Pathological and physiological disorders as well as susceptibility to disease and insect pests also are influenced by the rate of applied N. Over-fertilization appears to be more serious in orchard crops than in many other crop species. The perennial growth habit of deciduous trees and vines is associated with an increased likelihood of fertilizer N application (and losses) during the dormant period. The large woody biomass increases the difficulty in assessing the kinetics and magnitude of annual N requirement. In mature trees, the N content of the harvested fruit appears to represent a large percentage of annual N uptake. Overfertilization is supported by a) the lack of integration of fertilizer and irrigation management, b) failure to consider nonfertilizer sources of plant-available N in the accounting of fertilizer needs, c) failure to conduct annual diagnosis of the N status, and d) the insensitivity of leaf analysis to over-fertilization. The diversity of orchard sites (with climatic, soil type, and management variables) precludes the general applicability of specific fertilization recommendations. The lack of regulatory and economic penalties encourage excessive application of fertilizer N, and it appears unlikely that the majority of growers will embrace recommended fertilizer management strategies voluntarily.
Don Merhaut and Julie Newman
Four types of media [coir, 1 coir: 1 peat (by volume), peat, and sandy loam soil] were evaluated for their effects on plant growth and nitrate (NO – 3) leaching in the production of oriental lilies (Lilium L.) `Starfighter' and `Casa Blanca'. Twenty-five bulbs were planted in perforated plastic crates and placed on the ground in temperature-controlled greenhouses. The potential for NO – 3 leaching was determined by placing an ion-exchange resin (IER) bag under each crate at the beginning of the study. After plant harvest (14 to 16 weeks), resin bags were collected and analyzed for NO – 3 content. Plant tissues were dried, ground, and analyzed for N content. Results indicated that the use of coir and peat did not significantly influence plant growth (shoot dry weight) relative to the use of sandy loam soil; however, substrate type influenced the amount of NO – 3 leached through the media and N accumulation in the shoots for `Starfighter', but not `Casa Blanca'.
Jeff Million, Tom Yeager, and Claudia Larsen
subirrigation watering ( Barrett, 1991 ; Dole et al., 1994 ). Similarly, reduced controlled-release fertilizer (CRF) rates are recommended when capillary mat irrigation is used ( Havis, 1982 ). When leaching is reduced or eliminated, buildup of fertilizer salts
Chris Wilson, Joseph Albano, Miguel Mozdzen, and Catherine Riiska
's ionic structure and has a high potential for moving with water once dissolved. Leaching of NO 3 from containers is enhanced by the low anion-holding capacity of most media used for plant production. Much research has focused on documenting leaching of
John R. Young, E. Jay Holcomb, and Charles W. Heuser
Though high electrical conductivity (EC) levels are commonly held to be the primary limiting factor for using spent mushroom compost (SMC) as a growing substrate, EC can be reduced by leaching. This allowed SMC to be successfully used for growing plants. Leaching reduced EC of the substrate solution from as high of 30 dS·m-1 (mmhos·cm-1) to 2 to 3 dS·m-1, a level acceptable for growing plants. The initial EC and container capacity determined the number of leachings and total volume of water required to lower EC of SMC substrates to acceptable levels. As the concentration of SMC was increased, a higher number of leachings or larger volume of water were required to adequately reduce EC levels. In trials spanning 2.5 years, SMC was effectively used as a substrate in the production of marigold (Tagetes patula) `Yellow Girl'. Benefits to plant growth from SMC incorporation included a slow release of nutrients as the SMC decomposed and a good air-filled pore space/water-holding capacity when amended with a commercial nursery mix. From these trials, it is recommended that SMC be incorporated at rates of 25% to 50%. It is not recommended that SMC be used in concentrations over 50% because the EC may be too difficult to manage and the high levels of air-filled pore space of SMC. Though season may affect the initial EC level of SMC, such variation is minimized by leaching while differences in plant response are more likely to be attributed to environmental conditions. No differences in plant growth were observed among SMC sources.
Julián Miralles-Crespo and Marc W. van Iersel
leaching and runoff of water and fertilizer, which may cause eutrophication and algal blooms ( Conover and Poole, 1992 ; Majsztrik et al., 2011 ). More efficient irrigation practices can also reduce energy use and CO 2 emissions. To achieve more efficient
Marc W. Van Iersel, Sue Dove, Jong-Goo Kang, and Stephanie E. Burnett
(2008) , Kim and van Iersel (2009) , and Nemali and van Iersel (2006) also reported that the total irrigation volume increases with increasing θ threshold, although not necessarily linearly. None of the applied irrigation water leached from the
Charles A. Sanchez
The low desert region of Arizona is the major area of lettuce (Lactuca sativa L.) production in the United States during the winter. Lettuce is commonly grown on the loam, clay loam, and clay soils of the alluvial river valleys. There is some interest in moving a portion of the vegetable production onto the sandy soils of the terraces (mesa) above the alluvial river valley to partially relieve the intensive production pressure being placed on lands in the valley. Of major concern in these sandy soils is water and N management. Studies were conducted during two seasons to evaluate the response of crisphead lettuce to sprinkler irrigation and N fertilizer and to evaluate the potential for leaching of nitrate-N on a coarse-textured soil. Lettuce yields increased in response to water and N, and were maximized by 55 cm of water and 271 kg·ha–1 N in 1991–92 and 76 cm water and 270 kg·ha–1 N in 1992–93. These water and N rates exceeded those typically required on finer-textured alluvial valley soils. At N and water rates required for maximum yields, 88% and 77% of the applied N was not recovered in the aboveground portions of the plant during the 1991–92 and 1992–93 seasons, respectively. Overall, data for the amount of N fertilizer not recovered, estimates of nitrate-N leaching determined during one growing season, and analysis of soil samples collected after harvest indicate the potential for large N leaching losses on this coarse-textured soil. Alternative production methods that enhance water and N use efficiencies, such as drip irrigation and/or the use of controlled-release fertilizers, should be considered on this sandy soil.
Michael A. Arnold, Don C. Wilkerson, Bruce J. Lesikar, and Douglas F. Welsh
Studies were conducted using Zea mays L. and Taxodium distichum L. seedlings as model systems to study Cu leaching from Cu(OH)2-treated containers. Initial experiments developed Cu toxicity curves (as CuSO4) in an inorganic (sand) or organic (bark-sand) medium with single (acute) or multiple (chronic) applications. A second pair of experiments investigated short-term (35 days) Cu accumulation and plant responses to irrigation with water (125 mL/plant per day) recycled through a fixed reservoir volume (9.5 L) from 0.7-L Cu(OH)2-treated containers filled with an inorganic or organic medium. Finally, plant responses and Cu leaching were monitored during growth in 2.3-L Cu(OH)2-treated containers filled with two organic media fertigated with high (8.0) or low (6.5) pH solutions. Different Cu(OH)2 concentrations and application methods were tested. Leachate data from the latter studies were used to calculate potential Cu concentrations in nursery runoff using various water application methods and pot spacings. Expression of Cu toxicity symptoms depended on exposure, concentration, and medium for each species. Plants subjected to chronic exposure and grown in an inorganic medium developed toxicity symptoms at lower doses than plants subjected to acute exposure and grown in an organic medium. Several measures of plant growth were greater for both species when grown in 0.7-L Cu(OH)2-treated containers, but not in 2.3-L containers. Plants in Cu(OH)2-treated containers seldom exhibited Cu toxicity symptoms in shoot tissues, even with an inorganic medium. Soluble Cu content of the recycled solution from Spin Out-treated containers increased slightly (<1.2 mg·L-1) during the 35-day experiment. Longer-term studies with nonrecycled leachate from 2.3-L containers indicated that Cu leaching increased after 60 to 90 days. Copper leaching was greater with the combination of applied solution of pH 6.5 and bark-sand-peat medium than with the combination of applied solution of pH 8.0 and bark-sand medium, and increased with greater concentrations of Cu(OH)2 in container wall treatments or when containers were filled before latex carrier was dried. Calculations of potential nursery runoff indicated that the levels of soluble Cu in effluent for most concentrations and spacings projected were below EPA action levels for potable water (1.3 mg·L-1) when overhead irrigation was used.