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Ben A. Faber, A. James Downer, Dirk Holstege, and Maren J. Mochizuki

Soil testing is an important component of a plant nutrient management program and has been standard practice for growers to aid in adjustment of fertilizer applications ( Reisenauer, 1978 ). Soil testing is performed not only to improve plant growth

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Amy J. Compton and Paul V. Nelson

Soil and tissue standards and procedures have not been developed for plug seedlings. Turn-around time for foliar analysis is often adversely long for timely crop corrections. Visual assessment occurs after damage has occurred. Many plug growers have tried but abandoned soil testing due to erratic results. Of the three monitoring systems, soil testing offers the best potential, but can it be effectively refined for plugs? Petunias were grown in 288-plug trays under six fertilizer regimes. Fertilization or waterings were applied at 9:00 am, and 1 hour later, soil solutions were squeezed out and analyzed. Soil levels after fertilization and watering were too variable to inscribe a curve, while levels after fertilization formed a curve consistent with growth of the seedlings. Twice, soil samples were taken 1, 4, 8, and 24 hours after a fertilizer application. Some soil solution concentrations 1 and 4 hours after fertilization were 51 and 36 ppm for NH4-N, 46 and 32 ppm for PO4-P, and 147 and 84 ppm for NO3-N, respectively. Soil testing can be used for plug production, but samples must be taken after a fertilizer application and at a specified length after the application.

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Stephanie C. Hamel and Joseph R. Heckman

Recent changes in soil testing methodology, the important role of P fertilization in early establishment and soil coverage, and new restrictions on P applications to turf suggest a need for soil test calibration research on Kentucky bluegrass (Poa pratensis L.), tall fescue (Festuca arundinacea Schreb), and perennial ryegrass (Lolium perenne L.). Greenhouse and field studies were conducted for 42 days to examine the relationship between soil test P levels and P needs for rapid grass establishment using 23 NJ soils with a Mehlich-3 extractable P ranging from 6 to 1238 mg·kg–1. Soil tests (Mehlich-1, Mehlich-3, and Bray-1) for extractable P were performed by inductively coupled plasma–atomic emission spectroscopy (ICP). Mehlich-3 extractable P and Al were measured to evaluate the ratio of P to Al as a predictor of need for P fertilizer. Kentucky bluegrass establishment was more sensitive to low soil P availability than tall fescue or perennial ryegrass. Soil test extractants Mehlich-1, Bray-1, or Mehlich-3 were each effective predictors of need for P fertilization. The ratio of P to Al (Mehlich-3 P/Al %) was a better predictor of tall fescue and perennial ryegrass establishment response to P fertilization than soil test P alone. The Mehlich-1, Bray-1, and Mehlich-3 soil test P critical levels for clipping yield response were in the range of 170 to 280 mg·kg–1, depending on the soil test extractant, for tall fescue and perennial ryegrass. The Mehlich-3 P/Al (%) critical level was 42% for tall fescue and 33% for perennial ryegrass. Soil test critical levels, based on estimates from clipping yield data, could not be determined for Kentucky bluegrass using the soils in this study. Soil testing for P has the potential to aid in protection of water quality by helping to identify sites where P fertilization can accelerate grass establishment and thereby prevent soil erosion, and by identifying sites that do not need P fertilization, thereby preventing further P enrichment of soil and runoff. Because different grass species have varying critical P levels for establishment, both soil test P and the species should be incorporated into the decision-making process regarding P fertilization.

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J.M. White, C.A. Neal, E.A. Hanlon, and S. Cox

A cooperative project between the Univ. of Florida Cooperative Extension Service, USDA Natural Resources Conservation Service, and Consolidated Farm Services Agency to address farm nutrient use and water management in the Lake Apopka hydrologic unit area of Florida began in 1991. This area was selected due to the vegetable production on the organic soils (muck) and sandy soils north of Lake Apopka, Florida's most polluted large lake. Discharge of nutrient-laden water into the lake from the 4050-ha vegetable production area has been implicated as a major contribution to the hypereutrophic status of the lake. Changes in cultural practices including water management, which would lead to a reduction in nutrient loading, should aid in the restoration of the lake. A grower survey of fertilizer application rates was conducted each year for 4 years with the baseline established by the 1991 survey. Demonstration plots using soil tests as the basis for fertilizer rates compared to normal grower rates of fertilizer were established for carrots, sweet corn, and celery. In 1995, muck growers had reduced their total application of N by 16%, P 52%, and K 32%, without reducing yields or quality. Nutrient applications were reduced by over 656 t/year over the years surveyed. Farms have saved fertilizer and reduced environmental risks.

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C.A. Sanchez and N.M. El-Hout

This research was funded in part by the Southern Florida Soil Test Advisory Board. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked

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George Hochmuth, Pete Weingartner, Chad Hutchinson, Austin Tilton, and Dwight Jesseman

Phosphorus (P) fertilization studies were conducted on four commercial farms and at the University of Florida Institute of Food and Agricultural Sciences Hastings Research and Education Center in Hastings. All sites were in the potato (Solanum tuberosum) production area of northeastern Florida. Preplant Mehlich-1 soil test P was very low at one commercial site and very high at the other four sites. The yield of marketable size A tubers, the desired tuber category, did not respond to P fertilization from 0 to 66 lb/acre (74.0 kg·ha-1) of P at any site. The average yield across all sites was 324 cwt/acre [16.2 ton/acre (36.3 t·ha-1)]. Leaf-P concentration at midseason did not respond to P fertilization. Leaf-P concentration averaged 0.38%, which was sufficient for potato. Potato tuber specific gravity averaged 1.075 and responded slightly to P fertilization only at one site.

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John R. Clark, Kelly M. Irvin, and Richard Maples

Nitrogen rates (using urea) of 22, 67 and 135 kg/ha were applied to mature mulched and unmulched highbush blueberries over a 5 year period. Soil samples were taken each year at budbreak (prior to fertilization) and post-harvest at the suggested time of foliar sampling (approx. Aug.1) to determine N rate effects within and among years. Data analysis revealed that the most common soil test variables affected by N rate and date of sampling were pH, electrical conductivity (EC) and nitrate. For unmulched plants, a significant reduction in soil pH was found each year between budbreak and Aug. 1 for the 67 and 135 kg/ha rates, but not usually for the 22 kg/ha rate. For mulched plants, pH reduction within N rate among sample dates was usually not significant. Overall soil pH reduction was greatest for the 135 kg/ha rate over the 5 years, and the pH reduction for the 67 kg/ha rate was similar to the 135 kg/ha rate for the unmulched plants. For mulched plants, 22 and 67 kg/ha rates had a similar trend of only a slight pH reduction over the 5 years. EC and nitrate trends were very similar, with the highest levels of each on the unmulched plants.

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George J. Hochmuth, Jeffrey K. Brecht, and Mark J. Bassett

Potassium (K) is required for successful carrot (Daucus carota) production on sandy soils of the southeastern United States, yet there is little published research documenting most current university Cooperative Extension Service recommendations. Soil test methods for K in carrot production have not been rigorously validated. Excessive fertilization sometimes is practiced by carrot growers to compensate for potential losses of K from leaching and because some growers believe that high rates of fertilization may improve vegetable quality. Carrots were grown in three plantings during the winter of 1994-95 in Gainesville, Fla., to test the effects of K fertilization on carrot yield and quality on a sandy soil testing medium (38 ppm) in Mehlich-1 soil-test K. Large-size carrot yield was increased linearly with K fertilization. Yields of U.S. No. 1 grade carrots and total marketable carrots were not affected by K fertilization. K fertilizer was not required on this soil even though the University of Florida Cooperative Extension Service recommendation was for 84 lb/acre K. Neither soluble sugar nor carotenoid concentrations in carrot roots were affected by K fertilization. The current K recommendation for carrots grown on sandy soils testing 38 ppm Mehlich-1 K could be reduced and still maintain maximum carrot yield and root quality.

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George Hochmuth, Osmar Carrijo, and Ken Shuler

Tomato (Lycopersicon esculentum Mill.) was grown in southeastern Florida on sandy soils that tested very high in Mehlich-1 P to evaluate the yield response to P fertilization. One location was used in 1995–96, another in 1996–97. Prefertilization soil samples contained 290 (location 1) and 63 (location 2) mg·kg–1 Mehlich-1 P. Both soil test results were interpreted as very high in P, and P fertilizer was not recommended for the crop. Fertilizer treatments at both sites were 0, 25, 50, 100, 150, and 200 kg·ha–1 P. Neither total marketable yield nor yield in any fruit size category was affected by P fertilization in either season. Amounts of cull (undersized or misshapened) fruits increased quadratically with P fertilization in the second season. Whole-leaf P concentrations increased linearly or quadratically with P application, depending on sample periods, and were always above sufficiency values. Although many tomato growers apply P fertilizer irrespective of soil test recommendations, our results showed that added P was not needed on soils testing very high in P. Furthermore, withholding P applications to soils with high P concentrations will minimize potential P pollution of surface water and groundwater.

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Joseph R. Heckman

Yield responses of `Blue Vantage' cabbage (Brassica oleracea L.) to P fertilizer and two commercially available biostimulants—ROOTS and ESSENTIAL-were evaluated on soils very high in P fertility. Head yield was not increased with P fertilizer when cabbage was transplanted into soil with Mehlich-3 soil test P indexes ≥ 112 ppm (112 mg·kg-1). Neither of the biostimlants applied as a root drench at transplanting influenced head yield or plant tissue nutrient analysis.