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Dennis C. Odero, Jose V. Fernandez, and Nikol Havranek

soils (Histosols) that were formed under flooded conditions, which precluded decomposition of organic matter, allowing those materials to form organic soils with up to 85% or more organic matter ( Snyder, 1994 ; Wright and Hanlon, 2009 ). About 3200 ha

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Sean M. Westerveld, Alan W. McKeown, and Mary Ruth McDonald

An understanding of nitrogen (N) uptake and the partitioning of N during the season by the carrot crop (Daucus carota subsp. sativus [Hoffm.] Arkang.) is required to develop more efficient N fertilization practices. Experiments were conducted on both organic and mineral soils to track the accumulation of dry matter (DM) and N over the growing season and to develop an N budget of the crop. Treatments included two carrot cultivars (`Idaho' and `Fontana') and 5 N rates ranging from 0% to 200% of the provincial recommendations in Ontario. Foliage and root samples were collected biweekly from selected treatments during the growing season and assessed for total N concentration. Harvest samples were used to calculate N uptake, N in debris, and net N removal values. Accumulation of DM and N in the roots was low until 50 to 60 days after seeding (DAS) and then increased linearly until harvest for all 3 years regardless of the soil type, cultivar, and N rate. Foliage dry weight and N accumulation were more significant by 50 to 60 DAS, increased linearly between 50 and 100 DAS, and reached a maximum or declined slightly beyond 100 DAS in most cases. The N application rates required to maximize yield on mineral soil resulted in a net loss of N from the system, except when sufficient N was available from the soil to produce optimal yield. On organic soil, a net removal of N occurred at all N application rates in all years. Carrots could be used as an N catch crop to reduce N losses in a vegetable rotation in conditions of high soil residual N, thereby improving the N use efficiency (NUE) of the crop rotation.

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Dennis C. Odero and Alan L. Wright

Snap bean ( Phaseolus vulgaris L.) is an important crop cultivated in the EAA of south Florida for the processing market. The EAA is dominated by organic soils (histosols) with up to 85% organic matter underlain by limestone bedrock ( Snyder, 1994

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Shawna Loper, Amy L. Shober, Christine Wiese, Geoffrey C. Denny, Craig D. Stanley, and Edward F. Gilman

from a depth of 122 to 213 cm (Hills Dirt Pit, LLC.). Composted dairy manure solids (compost; Agrigy, Palm Harbor, FL) were applied as an organic soil amendment at a rate of 508 m 3 ·ha −1 (5-cm depth, equaling ≈256 Mg·ha −1 ) in combination with two

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Brent K. Harbaugh, David A. DeVoll, and R. Zalewski

Phosphorus is considered a major pollutant of lakes in central Florida, and growers producing crops in the Lake Okeechobee watershed are being challenged to reduce use of P fertilizer. Caladium (Caladium×hortulanum Birdsey) tubers are produced on organic soils within this area. This study was done to determine if current commercial P fertilization rates could be reduced or eliminated, since these organic soils have high levels of water extractable P (Pw). Two farms were selected with low (Farm A 19 lb/acre; 21 kg·ha-1) or high (Farm B 59 lb/acre; 66 kg·ha-1) preplant Pw levels. Production of caladium tubers with the standard grower P fertilization practice (Farm A = P at 39.2 lb/acre; 43.9 kg·ha-1, or Farm B = P at 15.9 lb/acre; 17.8 kg·ha-1) was compared to production with either one-half the standard grower rate of P or no P. The percentage of harvested tubers in each of five grades and the estimated harvested tuber value index were similar irrespective of the amount of P fertilizer used on either farm. These results indicate that P could be eliminated from the fertilization program for caladium tuber production on organic soils.

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Sean M. Westerveld, Mary Ruth McDonald, and Alan W. McKeown

The Nutrient Management Act (NMA) established in the province of Ontario in 2002 has prompted a re-evaluation of nitrogen (N) management practices. However, N management research in Ontario is currently outdated. The experiment in this 3-year study was designed to establish the yield response of carrot (Daucus carota) to N fertilization on mineral and organic soils and identify the relative yield effects of preplant and residual soil N. In 2002, N was applied at 0%, 50%, 100%, 150%, and 200% of recommended N application rates in Ontario as ammonium nitrate (organic soil: 60 kg·ha-1 preplant; mineral soil: 110 kg·ha-1 split 66% preplant/33% sidedress). Experimental units were split in half in 2003 and 2004, and N was applied to one half in 2003 and both halves in 2004 to identify the effects of residual N from the previous season on yield. Crop stand, yield, and quality were assessed at harvest, and storability was assessed by placing carrots into cold storage for 6 months. Nitrogen application rate had no effect on the yield, quality, or storability of carrots grown on organic soil. On mineral soil there were no effects of applied N in the first year of the 3-year study. In the second and third year on mineral soil, yield increased in response to increasing N, up to 200% and 91% of the recommended application rate, respectively, based on the regression equations. Yield declined above 91% of the recommended application rate in the third year due to a decrease in stand at higher N application rates. There were no effects of N on carrot quality or storability on mineral soil. On mineral soil, residual N from the 2002 season had more effect on yield at harvest in 2003 than N applied in 2003. This major effect of residual soil N on yield provides an explanation for the lack of yield response to preplant N application in previous studies conducted in temperate regions. These results indicate that there is no single N recommendation that is appropriate for all years on mineral soil. Assessing the availability of N from the soil at different depths at seeding is recommended to determine the need for N application.

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Wei Qiang Yang, Barbara L. Goulart, K. Demchak, and Yadong Li

The ability of mycorrhizal and nonmycorrhizal `Elliott' highbush blueberry (Vaccinium corymbosum L.) plants to acquire soil N under different preplant organic soil amendment regimes (forest litter, rotted sawdust, or no amendment) was investigated in a field experiment using 15N labeled (NH4)2SO4. Plants inoculated with an ericoid mycorrhizal isolate, Oidiodendron maius Dalpé (UAMH 9263), had lower leaf 15N enrichment and higher leaf N contents than noninoculated plants but similar leaf N concentrations, indicating mycorrhizal plants absorbed more nonlabeled soil N than nonmycorrhizal plants. Mycorrhizal plants produced more plant dry weight (DW) and larger canopy volumes. The effect of preplant organic amendments on the growth of highbush blueberry plants was clearly demonstrated. Plants grown in soil amended with forest litter produced higher DW than those in either the rotted sawdust amendment or no amendment. Plants grown in soils amended preplant with sawdust, the current commercial recommendation, were the smallest. Differences in the carbon to nitrogen ratio were likely responsible for growth differences among plants treated with different soil amendments.

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D. Brault, K.A. Stewart, and S. Jenni

Optical properties of paper and plastic mulches were determined in experiments on mulched head lettuce (Lactuca sativa L.) grown in organic soil in 1997-98. Mulches used in 1997 were a coextruded white/black polyethylene, a beige paper coated with latex on both sides and a black paper coated with latex on both sides. Three supplementary mulches were added in the 1998 experiment: beige paper coated with a biodegradable polymer either coated on the underside, on the top side or on both sides. Optical properties of the polyethylene mulch remained stable over the course of the experiment. As the paper mulches aged, they changed structurally, spectrally, or both, but remained in place until harvest. The black paper was the only mulch that offered complete weed control, although the weeds under the other mulches did not develop beyond the cotyledonary or two-true-leaf stage.

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D. Brault, K.A. Stewart, and S. Jenni

Lettuce plants (Lactuca sativa L. cv. Ithaca) were transplanted into organic soil and onto beige paper, black paper, and coextruded white/black polyethylene mulches in 1997 and 1998. A weeded bare ground plot was also tested. Transplanting in 1997 occurred in July under warm and dry conditions. Plants grown on mulch established better when the mean air temperature during the week after transplanting was 22.5 °C. The mortality rates of the bare ground control were 30%. All mulches significantly reduced plant mortality in 1997. In 1998, air temperature during the week after transplanting (June) was 14.6 °C. Plant mortality in 1998 was 1.3% for the control and 1.5% for the mulched plots. For both years, plants grown on mulched plots had higher relative growth rates than the control at the start of the season. Head fresh weight was 3.6 times (1997) and 1.2 times (1998) greater for lettuce grown on mulch compared with lettuce grown in a weeded control. Soil bulk density was lower under mulch than in the control plots in 1997.

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Kathleen Delate and Vincent Lawson

Organic farming has increased to a $6 billion industry in the U.S. and continues to expand 20% annually. In Iowa, organic acreage for all crops has increased from 13,000 in 1995 to 130,000 in 1999. Most organic farmers rely on crop rotations, compost, or manure applications, and cover crops to maintain soil fertility. In our trials at the Iowa State Univ. Muscatine Island Research Farm, a cover crop of hairy vetch (Vicia villosa) and rye was seeded in the fall and incorporated 2 weeks prior to transplanting `Lantern' pepper plants. Other organic and conventional soil treatments were applied at transplanting and at 3 weeks post-planting. Four replications of 40 peppers transplanted at 31 × 61-cm spacing under seven fertilization treatments were observed for plant growth and yields. The fertilization goal was to obtain equivalent nitrogen and calcium rates in the organic and conventional systems. Plants fertilized with the compost at 88 kg/ha N plus BioCal® (a liming industry by-product) were not significantly greater in leaf biomass than plants conventionally fertilized with equal amounts of N. All organic and conventional treatments had greater biomass and yield than the organic and conventional controls (no fertilizer), respectively (P = 0.05). Pepper fresh weight was greater in the vetch-strips treatment than in the vetch-incorporated, and the 44 kg/ha N compost treatment, but significantly less than the conventionally fertilized plants. Second year results demonstrated similar results to the 1998 trial where the greatest yields in the organic system occurred in the compost at 88 kg/ha N plus BioCal® treatment, demonstrating to organic farmers that comparable yields can be obtained in systems employing alternatives to synthetic nitrogen fertilizer.