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William B. Evans and Mark A. Bennett

A significant portion of the Great Lakes region's processing tomato crop is used to make whole fruit and diced products, where fruit color and textural uniformity are important. Soil and fertilizer studies were undertaken to better understand the role of soil fertility and potassium application on the color disorder known as internal white tissue (IWT) under this region's conditions and in area soils. During 2 years of replicated potassium rate trials in Ohio, tomato yield was not significantly altered by broadcast potassium applications. Potassium application rate was inversely correlated with frequency and severity of IWT in each season, and positively correlated with titratable acidity. The ability of split applications to influence IWT severity was not significantly different than that of preplant applications. IWT symptom frequency and severity was correlated with elemental concentrations in the fruit, leaves, and soil. In 1998, severity of IWT symptoms was positively correlated with shoulder tissue calcium and sodium concentrations, and negatively correlated with concentrations of phosphorus, magnesium, and nitrogen. Correlations for other nutrients, including potassium, were less clear. A companion study of six grower fields during the second year, using grid sampling techniques and the IWT-susceptible Peto 696 cultivar, found significant variability of IWT symptoms within and among fields. Variability within fields was correlated with soil nutrient concentrations. These data indicate researchers may be able to develop recommendations for field mapping and precision management strategies that can reduce the levels of IWT for area growers.

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Teresa Olczyk, Yuncong Li, Waldemar Klassen and Qingren Wang

Summer cover crops can improve soil fertility by adding organic matter, supplying nutrients through mineralization, reducing nutrient leaching, and improving soil water and nutrient holding capacity. Other benefits include weed suppression and reduction of soil parasitic nematodes. A series of field experiments have been conducted at the UF IFAS Tropical Research and Education Center in Homestead, Florida to evaluate several summer cover crops for use in vegetable production in South Florida followed by field demonstrations conducted in the growers' fields. Best performing cover crops were legumes: velvet bean (Macuna deeringiana) and sunn hemp (Crotalaria juncea L. `Tropic Sun') providing 13 and 11 Mt of dry matter/ha, respectively. Sunn hemp supplied 330 kg N/ha followed by velvet been with 310 kg N/ha. Traditional summer cover crop sorghum-Sudan produced 4 Mt of dry matter/ha and retained only 36 kg N/ha. In addition Sunn hemp significantly reduced soil parasitic nematodes for successive crops. Limitations in use of Sunn hemp by more vegetable growers in South Florida include cost and availability of seeds.

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Robert O. Miller, Steven E. Newman and Janice Kotuby-Amacher

The accuracy of soil and plant analytical results are occasionally called into question by laboratory clientele. Although laboratories generally conduct internal quality assurance procedures, there are few external performance testing programs for the industry. In 1994, a proficiency testing program was initiated for soil and plant samples for agricultural laboratories in the western United States to provide an external quality control for the lab industry. The program involves the quarterly exchange of soil and plant samples on which soil salinity, soil fertility, and plant nutrition analyses are conducted. One hundred laboratories are annually enrolled in the program from 24 states and Canadian provinces. Results of 3 years of the program indicate soil nitrate, soil pH, extractable potassium, soil and organic matter are reproducible within 10% between laboratories. Soil-extractable phosphorus (by five methods), soil-extractable boron, and soluble chloride were only reproducible within 15% to 20% between laboratories. Plant nitrogen and phosphorus results were consistent across samples, laboratories, and methods. Variability in plant nitrate increased with decreasing tissue concentrations. Overall accuracy and precision of reported results, based on the use of NIST certified reference botanical samples, were excellent for N, P, K, Ca, and Cu. Generally, for any given analysis, the results of ≈10% of the laboratories exceed two standard deviations from the mean. Overall, significant improvement was noted in the laboratory industry proficiency through the course of the program.

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Y.C. Li, P.J. Stoffella, A.K. Alva, D.V. Calvert and D.A. Graetz

Compost amendment to agricultural soils has been shown to either reduce disease incidence, conserve soil moisture, control weeds or improve soil fertility. Application of compost can range from 5 to 250 Mt·ha–1 (N content up to 4%). Large application of compost with high N and P levels may result in excessive leaching of nitrate, ammonium, and phosphate into groundwater. It could be a serious concern on the east coast of Florida with its high annual rainfall and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were collected from different facilities throughout Florida. Composts were applied on a surface of 15-cm sandy soil columns at the rate of 100 Mt·ha–1 on the surface basis and leached with deionized water by 300 ml·d–1 for 5 days (equivalent to 34 cm rainfall). The concentrations of NO3-N, NH4-N, and PO4-P in leachates reached as high as 246, 29, and 142 mg·L–1, respectively. The amount of N and P leached following 5-day leaching events accounted for 3.3% to 15.8% of total N and 0.2% to 2.8% of total P as inorganic forms.

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Tina Gray Teague and Gail S. Lee

Soil fertility studies conducted in commercial vegetable fields to examine alternative uses of mid-south agricultural wastes as soil amendments included work with poultry litter, cotton gin trash, and rice hulls. Poultry litter applications ranging from 0.3 to 0.9 Mg·ha–1 resulted in significant increases in spinach, cabbage, turnip greens, and collard yields grown in soils damaged by precision leveling or in sandy soils with low organic matter; however, positive yield response to litter applied to undamaged soils was variable. Raw rice hulls applied at rates ranging from 2 to 44 Mg·ha–1 resulted in reduced cabbage yield. Trials with cotton gin trash and cover crops on yield of cabbage, broccoli, southern pea, snap bean, and cucumber indicate significant problems with weeds following use of raw gin trash. Composting alleviated most weed problems, but no yield response was apparent at composted gin trash rates ≤9.6 Mg·ha–1. High rates (60 Mg·ha–1) of composted gin trash on damaged soil significantly improved cabbage yield. There were increases in soil pH and Ca levels. Research was supported by a SAREIACE grant.

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Hector Valenzuela, Ted Goo, Ted Radovich and Susan Migita

As many farmers transition toward organic farming, research-based information is required to determine the appropriate rates and timing for the application of available organic fertilizers. Four experiments were conducted over a 3-year period in Oahu, Hawaii, to evaluate the effect of five different organic amendments on the growth and yield of edible ginger. Fertilizer amendments, applied at a rate of 30–60 t·ha-1, included bone meal, a locally available commercial chicken manure-based compost, a commercial Bokashi compost, aged chicken manure, synthetic fertilizer (farmer's practice at 300 kg·ha-1 N), and a control. Each treatment plot consisted of a 10-m row with 15 plants per plot, and five replications per treatment. Ginger was planted in April of every year, and harvested from February to March of the following year. Data collected included soil fertility before initiation and after experiment completion, tissue nutrient levels, plant stands, plant height, and stem number, individual tops and root weight of 5–10 plants per treatment, as well as nematode counts before and after experiment completion. The data showed that similar or greater root weight yields and quality were obtained with the use of organic amendments compared to the use of synthetic fertilizer. Increased yields were obtained when organic amendment and fertilizer applications were split over the growing season. Data will be presented with regard to initial plant stands, tissue levels, and yield trends in response to the several amendments used in these experiments, and management considerations for farmers will be discussed.

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Ian A. Merwin, Warren C. Stiles and Harold M. van Es

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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Mongi Zekri and Robert C.J. Koo

Controlled-release sources of N and K were compared with soluble sources on young `Valencia' orange trees (Citrus sinensis [L.] Osb.). The effects of these fertilizers on leaf mineral concentration, soil chemical analysis, and tree growth were evaluated for 3 years. Soluble fertilizers were generally more readily available but had shorter residual effects on leaves and soil than controlled-release fertilizers. In the top 30 cm of soil, the plots treated with controlled-release N had 23% more total N than those treated with soluble N sources, while the plots fertilized with controlled-release K contained 56% more extractable K than those that received soluble K. Different effects on leaf and soil N between the two controlled-release N sources, sulfur-coated urea (SCU) and methylene urea (MU), were also found. With the use of controlled-release fertilizers, application frequency was reduced from a total of 15 to six applications with no adverse effects on tree growth, leaf mineral composition, or soil fertility during the first 3 years. Combining soluble and controlled-release fertilizers in a plant nutrition program offers an economical and effective strategy for citrus growers.

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James B. Calkins and Bert T. Swanson

Media fertility, nutrient availability, and subsequently plant nutrition are critical factors that can be modified by growers to produce quality container-grown plants. The trend in container fertility has been toward incorporation of slow-release fertilizers; however, fertility release curves are variable and fertilizer longevity for many fertilizers is limited. Seventeen slow-release fertilizers were compared for longevity and plant performance over a 2-year production cycle using deciduous and evergreen plant materials. Plant growth was quantified based on height, volume, branching, dry weight, and quality. Soil fertility levels based on leachates were followed. Nutrient release for the incorporated fertilizers evaluated was variable. Fertility treatment effects were species-dependent. Several incorporated, slow-release fertilizers, especially those high in nitrogen and having extended release curves, including Nutricote 20–7–10, Scotts Experimental 24–6–10 and 26–6–11, Scotts Prokote Plus 20–3–10, Sierra 17–6–10, Sierra High N 24–4–6, Sierra Experimental 24–4–8, Woodace 21–4–10, Woodace 23–7–12, and Woodace Briquettes 23–2–0, show promise for use in 2-year container production systems.

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Qingren Wang, Waldemar Klassen, Yuncong Li, Merlyn Codallo and Aref A. Abdul-Baki

Intensive rainfall during summer causes substantial nutrient leaching in a subtropical region, where most vegetable lands lay fallow during this period. Also, an excessive amount of irrigation water supplied during the winter vegetable growing season leads to soil nutrient loss, which greatly impacts vegetable yields, especially in soils that possess a low capacity to retain soil water and nutrients. A 2-year field experiment was carried out to evaluate the effects of various summer cover crops and irrigation rates on tomato yields and quality, and on soil fertility in a subtropical region of Florida. The cover crops were sunn hemp [Crotalaria juncea (L.) `Tropic Sun'], cowpea [Vigna unguiculata (L.) Walp, `Iron Clay'], velvetbean [Mucuna deeringiana (Bort.) Merr.], and sorghum sudangrass [Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.], with a weed-free fallow as a control. The cover crops were planted during late Spring 2001 and 2002, incorporated into the soil in the fall, and tomatoes [Lycopersicon esculentum (Mill.) `Sanibel'] were grown on raised beds during Winter 2001–02 and 2002–03, respectively. Irrigation in various treatments was controlled when tensiometer readings reached –5, –10, –20, or –30 kPa. The cover crops produced from 5.2 to 12.5 Mg·ha–1 of above ground dry biomass and 48 to 356 Mg·ha–1 of N during 2001–02 and from 3.6 to 9.7 Mg·ha–1 of dry biomass and 35 to 277 kg·ha–1 of N during 2002–03. The highest N contribution was made by sunn hemp and the lowest by sorghum sudangrass. Based on 2-year data, tomato marketable yields were increased from 14% to 27% (p ≤ 0.05) by growing cover crops, and the greatest increase occurred in the sunn hemp treatment followed by the cowpea treatment. Irrigation at –10, –20, and –30 kPa significantly improved marketable yields by 14%, 12%, and 25% (p ≤ 0.05) for 2001–02, and 18%, 31%, and 34% (p ≤ 0.05) for 2002–03, respectively, compared to yields at the commonly applied rate, –5 kPa (control). Irrigation at –30 kPa used about 85% less water than at –5 kPa. Yields of extra-large fruit in the sunn hemp and cowpea treatments from the first harvest in both years averaged 12.6 to 15.2 Mg·ha–1, and they were significantly higher than yields in the fallow treatment (10.2 to 11.3 Mg·ha–1). Likewise at –30 kPa yields of extra-large fruit from the first harvest for both years were 13.0 to 15.3 Mg·ha–1 compared to 9.8 to 10.7 Mg·ha–1 at –5 kPa. Soil NO3-N and total N contents in sunn hemp and cowpea treatments were significantly higher than those in fallow. The results indicate that growing legume summer cover crops in a subtropical region, especially sunn hemp and cowpea, and reducing irrigation rates are valuable approaches to conserve soil nutrients and water, and to improve soil fertility and tomato yields and quality.