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G.J. Hochmuth

Petiole sap N and K quick tests offer fast and accurate in-field analysis for N and K and have been calibrated for some vegetable crops in Florida. This paper summarizes 10 years of research conducted in Florida on petiole sap testing for N and K. Petiole sap nitrate-N and K concentrations correlated highly with whole-leaf N and K concentrations and decreased through the season for all vegetable crops tested. Optimum early season fresh sap nitrate-N and K concentrations were highest for pepper, and optimum late-season concentrations were lowest for tomato. Petiole sap nitrate-N and K concentrations were not affected by storing petioles on ice for up to 16 h or freezing them for 24 h.

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G.J. Hochmuth

Fertilizer application by drip irrigation is becoming a common practice for many vegetable crops, especially in Florida. Vegetable producers view drip irrigation as a tool to reduce water use, increase fertilizer efficiency, and improve profits, while simultaneously reducing the potential risk to the environment due to nutrient enrichment of surface and groundwater. This paper presents the current Univ. of Florida recommendations for fertilizer management with drip irrigation for vegetables in Florida. These recommendations are based on more than 15 years of research on water and nutrient management with drip irrigation. Although these recommendations were developed for largely sandy soils from mostly Florida research, they should be easily adaptable for other U.S. vegetable regions on sandy soils.

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S. J. Locascio and G. J. Hochmuth

Watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai] were grown with three rates each of lime, gypsum, and K during two seasons to evaluate their effects on fruit production and mineral concentration. The first experimental site was a recently cleared Sparr fine sand with an initial pH of 5.4 and Mehlich I extractable K of 32 ppm (low) and 948 ppm Ca. The second site was a virgin Pomona fine sand with a pH of 4.8, 28 ppm K, and 612 ppm Ca. `Crimson Sweet' fruit yield was reduced 10% with an increase in lime rate from to 4.48 Mt·ha-1 in the first season. In the second season, lime rate had no effect on yield. In both seasons, fruit yields were reduced 14% by an increase in Ca from gypsum from 0 to 1.12 Mt·ha-1. Fruit yields were not influenced by K rates from 90 to 224 kg·ha-1. Application of lime and gypsum increased leaf tissue Ca concentrations and decreased K. An increase in K application significantly increased leaf K and decreased Mg in the first season but not significantly in the second season. Fruit firmness and soluble solid content were not consistently affected by treatment.

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S.J. Locascio and G.J. Hochmuth

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] were grown with three rates each of lime, gypsum, and K during two seasons to evaluate their effects on fruit production and mineral concentration. The first experimental site was a recently cleared Sparr fine sand with an initial water pH of 5.0 and Mehlich I extractable K of 8 mg·kg-1 (very low) and 20 mg·kg-1 Ca (very low). The second site was a virgin Pomona fine sand with a water pH of 4.8, 28 mg·kg-1 K (low), and 612 mg·kg-1 Ca (high). `Crimson Sweet' fruit yields were reduced 10% with an increase in lime rate from 0 to 4.48 t·ha-1 in the first season. In the second season, lime rate had no effect on yield. In both seasons, fruit yields were reduced 14% with an increase in Ca from gypsum from 0 to 1.12 t·ha-1. On the soil testing very low in K, yield increased with an increase in K rate from 90 to 224 kg·ha-1 with no lime or gypsum. On the soil testing low in K, greatest yields were obtained with 90 kg·ha-1 K with no lime and gypsum. Application of lime and gypsum increased Ca and decreased K in seedlings but not consistently in older leaf and fruit tissues. An increase in K application increased leaf K in the first season but not in the second. Fruit firmness and soluble solids content were not consistently affected by treatment during the two seasons. Thus, on soils low in toxic elements (Mn and Al) such as used in this study, watermelon will grow well and tolerate a wide range of soil pH values without additional Ca from lime or gypsum.

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T.K. Hartz and G.J. Hochmuth

Drip irrigation provides an efficient method of fertilizer delivery virtually free of cultural constraints that characterize other production systems. Achieving maximum fertigation efficiency requires knowledge of crop nutrient requirements, soil nutrient supply, fertilizer injection technology, irrigation scheduling, and crop and soil monitoring techniques. If properly managed, fertigation through drip irrigation lines can reduce overall fertilizer application rates and minimize adverse environmental impact of vegetable production.

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C. Jasso-Chaverria, G.J. Hochmuth, R.C. Hochmuth and S.A. Sargent

Two greenhouse cucumber (Cucumis sativus) cultivars with differing fruit types [European (`Bologna') and Beit-alpha (`Sarig')] were grown during two seasons in a perlite medium in black plastic nursery containers in a passively ventilated greenhouse in northern Florida to evaluate fruiting responses to nitrogen (N) fertilization over the range of 75 to 375 mg·L–1. Fruit production, consisting mostly of fancy fruits, increased quadratically with N concentration in the nutrient solution, leveling off above 225 mg·L–1 for both cucumber cultivars. Fruit length and diameter were not affected by N concentration in the nutrient solution. Leaf N concentration, averaged over three sampling dates, increased linearly with N concentration in the nutrient solution from 46 g·kg–1 with 75 mg·L–1 N to 50 g·kg–1 with 375 mg·L–1 N. Fruit firmness decreased with increasing N concentration and there was little difference in firmness between the two cultivars. Firmness was similar across three measurement dates during the spring harvest season, but increased during the season in the fall. Fruit color responses to N concentration were dependent on the specific combination of experiment, sampling date, and cultivar. For most combinations of experiment, sampling date, and cultivar, cucumber epidermal color was greener (higher hue angle) with increased N concentration. The color was darkest (lowest L* value) and most intense (highest chroma value) with intermediate to higher N concentrations.

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G. Hochmuth, S. Locascio, R. Hochmuth, Jennifer Hornsby, D. Haman, B. McNeal and J. Kidder

Nitrate concentrations in the springs and rivers in northern Florida have been increasing, and several state agencies are interested in implementing nitrogen management programs on farms to reduce N entering the groundwater. Watermelon was grown in the first season of a six-season project under various cultural and fertilization programs to investigate the relationship of N management with N leaching. Treatments were a factorial arrangement of two cultural systems (polyethylene mulch with drip-irrigated beds and unmulched, overhead irrigated beds) and three N fertilization programs [N at the extension-recommended rate, N at the commercial-watermelon-producer rate (1.5 times recommended), or N at the recommended rate with 50% of N from poultry manure]. Nitrate in the soil beneath the watermelon crop was monitored at the 2-m depth with porous-crop suction lysimeters and soil sampling. Yields were greater with the mulch/drip irrigation system compared with the unmulched/sprinkler cultural system; however, fertilization program had no effect on yield. Nitrate-N concentrations in the soil solution at the 2-m depth with all fertilizer treatments were only slightly elevated (3 to 5 mg·L-1) above that in the unfertilized soil (< 1.0 mg·L-1) early in the season when no rain fell. Later in the season, soil solution nitrate-N concentrations at the 2-m depth increased to >50 mg·L -1 with the unmulched treatment and with the greater fertilization rate. Polyethylene mulch, drip irrigation, and recommended N rate combined to maintain groundwater nitrate-N concentration below 10 mg·L-1 for most of the production season and only slightly above 10 mg·L-1 during the summer off-season when rainfall was frequent.

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G.J. Hochmuth, R.C. Hochmuth, M.E. Donley and E.A. Hanlon

`Classic' eggplant (Solanum melongena L.) responses to K fertilization were evaluated in Spring and Fall 1991 at Live Oak, Fla., on soils testing low in Mehlich-1 extractable K. Total season yield leveled off at 51.1 t·ha-1 with 94 kg K/ha fertilization in spring and at 53.3 t·ha-1 with 60 kg K/ha in fall. Critical K concentrations (in grams per kilogram) in whole leaves were ≈45 at first flowering, 35 at early fruiting, 30 during harvest, and 28 at the end of seven harvests. Fresh petiole-sap K critical concentrations (in milligrams per liter) were ≈4500 to 5000 before harvest and 4000 to 4500 during harvest. Less than 3500 mg K/liter in fresh sap indicated K deficiency in fruiting plants. The Mehlich-1 soil extractant procedure predicted similar responses at the two sites; however, yield responses showed that the two sites differed in fertilization requirements. Fertilizer recommendations for K at both sites exceeded eggplant K requirements.

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S.J. Locascio, G.J. Hochmuth, S.M. Olson, R.C. Hochmuth, A.A. Csizinszky and K.D. Shuler

Tomato (Lycopersicon esculentum Mill.) was grown with polyethylene mulch at five locations during a total of nine seasons to evaluate the effects of K source and K rate on fruit yield and leaf K concentration with drip and subsurface irrigation. K sources evaluated were KCl, K2SO4, and KNO3, and K rates varied from 0 to 400 kg·ha-1. Preplant soil K concentrations by Mehlich-1 extraction on the sandy soils and loamy sands used in the study varied from 12 mg·kg-1 (very low) to 60 mg·kg-1 (medium). In seven of the eight studies, K source did not significantly influence fruit yield or leaf K concentration. In the other study with subsurface irrigation at Bradenton in Spring 1992, marketable yields were significantly higher with KNO3 than with KCl as the K source. Tomato fruit yield responded to the application of K in all studies. At Gainesville, Quincy, and Live Oak, with drip irrigation on soils testing low to medium in K, maximum yields were produced with 75 to 150 kg·ha-1 K where the K was broadcast preplant. These rates were 25% to 30% higher than those predicted by soil test. At Bradenton and West Palm Beach on soils testing low to very low in K, where all or part of the K was applied in double bands on the bed shoulder with subsurface irrigation, yield responses were obtained to 225 to 300 kg·ha-1 K. These rates exceeded the maximum recommended K rate of 150 kg·ha-1. Tomato leaf tissue K concentrations increased linearly with increased rates of K application, but were not influenced by K source. These data suggest that the recommendation for K on soils testing low in K be increased from 150 to 210 kg·ha-1 and that this increase should suffice for tomatoes grown with either drip or subsurface irrigation.

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Puffy Soundy, D.J. Cantliffe, G.J. Hochmuth and P.J. Stoffella

`South Bay' lettuce transplants were grown in F392A styrofoam Speedling® flats at different levels of N to evaluate the effect of N on transplant quality and subsequent yield and head quality in the field. Plants were irrigated eight times over a 4-week growing period by floating flats for 30 min in nutrient solution containing eight 0, 15, 39, 45, or 60 mg·liter–1 N supplied from NH4NO3. Dry shoot mass, leaf area, and plant height increased linearly with increasing N rates and dry root mass and stem diameter increased in a quadratic fashion. Transplants with the greatest plant biomass were, therefore, produced with 60 mg·liter–1 N. Plants from the 15, 30, 45 and 60 mg·liter–1 N treatments were planted in sandy soil in plastic-mulched beds under drip irrigation. To optimize lettuce head maturity among the treatments, plants from the N treatments were harvest 53, 56, and 59 days after transplanting (DAT). The optimum time to harvest was determined to be 56 DAT. There was no yield response (measured in terms of head mass) or quality response (measured in terms of head height, head diameter, head compactness or core length) to N applied during transplant production. This indicated that transplants produced with 15 mg·liter–1 N gave equally good yield to those produced with 30, 45, or 60 mg·liter–1 N when N was applied via flotation irrigation.