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Darryl D. Warncke

Available for $15 from the Council on Soil Testing and Plant Analysis, Georgia University Station, P.O. Box 2007, Athens, GA 30623-2007.

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Sean M. Westerveld, Alan W. McKeown, Mary Ruth McDonald, and Cynthia D. Scott-Dupree

Nutrient management legislation has prompted an evaluation of alternative nitrogen (N) management techniques. SPAD (Soil Plant Analysis Development) chlorophyll and Cardy nitrate (NO3 -) meters were evaluated for their potential as tissue nitrogen tests in cabbage (Brassica oleracea var. capitata), onions (Allium cepa), and carrots (Daucus carota subsp. sativus). Cabbage, carrots, and onions were grown on both organic and mineral soils in Ontario, Canada in 2000 and 2001. Nitrogen was applied at five rates to cabbage and carrots and three rates to onions ranging from 0 to 200% of current provincial recommended N rates. In an additional treatment, 50% of the recommended rate was applied preplant and sidedress N applications of 40 kg·ha-1 (35.7 lb/acre) were applied when SPAD chlorophyll meter readings fell below 95 (2000) and 97% (2001) of the highest N rate treatment. Yields were generally unaffected by N rate, except in cabbage in 2000, suggesting adequate N was present in most treatments. SPAD chlorophyll meter readings were highly variable among soil types, cultivars, and years. Chlorophyll readings reached a plateau in adequately fertilized crops in many instances. Cardy readings were less variable among soil types, cultivars, and years. The relationship between N rate and sap NO3-N concentration was generally linear. The results suggest that the use of a well-fertilized reference plot is most appropriate for the SPAD meter on these vegetable crops, while the use of region-specific critical NO3-N concentrations was most appropriate for the Cardy NO3-meter. Both meters would be cost advantageous when over 500 samples are tested. The meters were generally easy to use, except for the SPAD meter on carrots. The meters have potential for N management of vegetable crops under Ontario growing conditions.

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H.G. Taber

Tomato (Lycopersicon esculentum) response to potassium (K) fertilization on a well-drained, central Iowa loam soil testing low in exchangeable K was evaluated over a 3-year period. Each year the experimental design was a factorial, split-plot randomized complete block with K rate as the whole unit (0 to 332 lb/acre). The subunit was cultivar, either `Mountain Spring' (determinate growth habit) or `Jet Star' (indeterminate growth habit). Fruit harvest began the first week of August and continued weekly for 5 to 8 weeks. For all years there was a significant K rate and cultivar effect for all parameters, but no interaction except for marketable fruit size and unmarketable fruit produced. Increasing the K rate to 103 lb/acre increased fruit size of both cultivars to a maximum of 8.9 oz, but year accounted for greater fruit size difference than the choice of cultivar. Maximum marketable yield for both cultivars occurred at 220 lb/acre K with `Jet Star' producing 13% more fruit than `Mountain Spring', 359 vs. 319 cwt/acre, respectively. Cullage was high, mostly as a result of blotchy ripening disorders, with `Jet Star' consistently producing more culls than `Mountain Spring'. Increasing K rate did not reduce the percentage of culls, which remained constant at about 29% of total yield. Whole-leaf K and leaf petiole sap K levels linearly increased with additional K rate for the two sample periods at flowering and mid-harvest. The whole-leaf K sufficiency level for both cultivars at the flowering stage of growth was determined to be 3.15% and dropped to 1.30% K by mid-harvest. Critical petiole leaf sap K values (using a dilution of 1:1 sap to water) could not be determined at flowering, but at mid-harvest the critical value was about 2200 to 2800 ppm K.

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V.P. Grubinger, P.L. Minotti, H.C. Wien, and A.D. Turneti

Unmulched and polyethylene-mulched tomatoes (Lycopersicon esculentum Mill.) were grown with and without starter fertilizer (SF) in four field experiments. The fields varied as to residual P level and the amount of P incorporated before planting. No benefits from SF were obtained on a soil with high residual P that was moderately fertilized with P before transplanting or on a soil with low residual P that was heavily fertilized with P. A positive effect from SF was observed only when residual P was low and no P was broadcast, and this was true in mulched and umnulched plots. No significant SF by mulch interaction was obtained in these experiments even though mulching consistently increased shoot P concentrations and fruit yield. The mulch was beneficial even under conditions where unmulched tomato leaves contained 0.4 % P 3 weeks after transplanting, indicating that factors in addition to improved P nutrition are also involved in the mulch effect.

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Sean M. Westerveld, Alan W. McKeown, Cynthia D. Scott-Dupree, and Mary Ruth McDonald

With the introduction of nutrient management legislation in Ontario, there is a need to improve the efficiency of nitrogen (N) utilization. One possibility is to use critical nutrient concentrations in plant tissue as an indicator of the N nutritional status of the crop. Plant tissue analysis was used to determine the total N and nitrate-N (NO3-N) concentrations of cabbage (Brassica oleracea var. capitata L.), carrots (Daucus carota L.), and onions (Allium cepa L.) grown in Ontario. The tissue samples were collected from plants as part of N fertilization studies from 1999 to 2001 on the organic soils in the Holland/Bradford Marsh area and the mineral soils near Simcoe, Ontario. Yield was assessed at harvest as an indicator of the N requirement of the crop. Testing the usefulness of critical NO3-N concentrations to indicate the N requirement of the crop was problematic because: 1) few published references were available to indicate a critical level of NO3-N in these crops; 2) tissue NO3-N concentrations were highly variable; and 3) field data rarely matched published references. Tissue total N concentrations from the trials corresponded to published critical N concentrations in some cases, however, the use of published critical N concentrations would have resulted in either over or under-application of fertilizer to the crops. Cultivar, soil type, and climate were shown to affect tissue N concentrations. Based on these results it was concluded that local research and field verification is required before tissue N critical nutrient concentrations become useful for determining fertilizer needs of cabbage, carrots, and onions grown in Ontario.

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L. Espinoza, C.A. Sanchez, and T.J. Schueneman

Four field experiments were conducted during two production seasons to evaluate soil-test P fertilizer recommendations for celery (Apium graveolens var. dulce) produced on Histosols, which often are linked hydrologically to environmentally sensitive wetlands, and to evaluate band placement as a strategy for improving P fertilizer-use efficiency in celery in such areas. Phosphorus was applied (broadcast or banded) at 0,50, 100,150, and 200 kg P/ha. Broadcast P was surface-applied and disked into the soil ≈ 15 cm deep 1 day before planting. Banded P was applied 5 cm below the soil surface and 5 cm to the side of each celery row. Total above-ground mass, marketable trimmed yield of celery, and yield of the larger grade sizes increased with P rate in all experiments. Band P placement was not a viable strategy for improving P fertilizer-use efficiency for celery. However, our results indicate that previous soil-test-based P fertilizer recommendations for celery were too high for the cultivars grown currently, and improved P fertilizer-use efficiency can be obtained with revised soil-test calibrations.

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C.A. Sanchez, S. Swanson, and P.S. Porter

Five field experiments were conducted from 1986 to 1989 to compare broadcast and band P fertilization of crisphead lettuce (Lactuca sativa L.) on Histosols. Rates of P were 0, 50, 100, 200, and 300 kg P/ha applied broadcast or banded. Broadcast P was surface-applied and disked into the soil 1 day before bedding and planting. Banded P was placed in strips 8 cm wide, 5 cm below the lettuce seeds at planting. Lettuce yields were significantly(P < 0.01) increased by P rate in all experiments. However, significant rate-by -placement interactions indicated that response of lettuce to P varied by placement. Lettuce yields were generally optimized with a band P rate one-third of that required with broadcast placement. Analysis of soil samples collected in the lettuce bed after fertilization indicated that banded P increased available P in the lettuce root zone compared to broadcast fertilization. Lettuce leaf P concentration increased with P rate and generally was greater when P was banded. The critical concentration of P in lettuce leaf tissue at the six- to eight-leaf stage was 0.37%. Banding P fertilizer did not reduce the availability of other essential nutrients, as indicated by tissue analysis.

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P.L. Minotti, D.E. Halseth, and J.B. Sieczka

We report three N rate experiments conducted on a gravelly loam soil to assess the N status of potato (Solanum tuberosum L.) using a Minolta SPAD-502 chlorophyll meter. Highly significant linear and quadratic trends were obtained for the regression of N rate on marketable tuber yields and SPAD readings. SPAD readings were taken at four times during the growing season and decreased as plants aged. Based on regression analysis, the early season SPAD readings, associated with N rates giving maximum marketable tuber yields, ranged from 49 to 56 units depending on year, variety, and location. Potato variety significantly affected SPAD values in eight of the 12 situations where readings were obtained. Precision in interpretation was improved when the highest N rates were considered “reference strips” to standardize the SPAD readings across varieties and growing seasons. Our results suggest that field SPAD readings can readily identify severe N deficiency in potatoes, have the potential to identify situations where supplementary sidedressed N would not be necessary, but would be of limited value for identifying situations of marginal N deficiency unless reference strips are used.

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Tim C. Knowles, Billy W. Hipp, and Mary Ann Hegemann

We examined responses of Salvia farinacea Benth. (mealy blue sage, a water- and nutrient-efficient native landscape plant for the southern United States) to slow-release (8- to 9-month), resin-coated urea (39N-0P4K) preplant-incorporated at 0.5, 1, 2, or 3 kg N/m3 in 2 perlite: 1 vermiculite (PV) or 2 pine bark: 1 fine sand (BS) (both by volume). This slow-release fertilization was compared to weekly fertigation at 100 mg N/liter from ammonium nitrate (34N-0P4K). After 21 weeks of greenhouse culture in 3.8-liter containers, shoot dry weight was higher in BS than PV when these media received fertigation or contained slow-release fertilizer at 21 kg N/m3. Shoot dry weight and shoot quality were not increased by exceeding 1 kg N/m3 in PV or 2 kg N/m3 in BS. Fertigation resulted in shoot dry weight and shoot quality equal to the highest values achieved with slow-release fertilizer. Cate-Nelson analysis showed that shoot N concentration should be ≥ 4.0% for this element not to limit plant growth.

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C.A. Sanchez, M. Lockhart, and P.S. Porter

Five field experiments were conducted from 1986 through 1988 to evaluate the response of radish (Raphanus sativus L.) to rate and source of P (triple superphosphate and phosphoric acid) and to rate of K (KC1) on Histosols. Marketable radish root yields increased with P fertilization when the soil tested <13 mg P/dm3 using a test for water-soluble P. No significant differences were due to P source. Results of leaf tissue analysis suggested that the critical concentration of P in radish leaves was 0.45%. Radish did not respond to K fertilization in any of the five experiments, even though preliminary soil-test K levels ranged from 20 to 102 K/dm3. Histosols used for crop production in Florida rarely test below 20 mg K/dm3; thus, radish rarely would require supplementary K fertilization for optimal yield.