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M. Lamarre and M.J. Lareau

During 1993 and 1994, the day-neutral strawberry cultivar Tribute was subjected to two rates of N (50 and 100 kgha–1), four rates of K (0, 60,120, and 180 kgha–1), and three rates of Mg fertilization (0, 25, and 50 kgha–1) from June to September through trickle irrigation. The objective of this experiment was to determine the best N, K, and Mg fertilization rates in the production of day-neutral `Tribute' strawberry. The N treatments had no significant influence on yield and fruit size for the two years. We observed the same situation for K as for N. For Mg treatments, fruit size was increased by adding 25 kgha–1 during the first picking in 1993, and they had no effect in the second year. For both years, the Mg had no effect on the yield.

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John M. Swiader and William H. Shoemaker

Field experiments were conducted over a 5-year period (1994-98) to determine the effect of various cropping systems (rotations) on fertilizer N requirements in processing pumpkins [Cucurbita moschata (Duchesne ex Lam.) Duchesne ex Poir.] on medium- to fine-textured soil. Treatments consisted of a factorial combination of five N fertilization rates (0, 56, 112, 168, 224 kg·ha-1 N) and four pumpkin cropping systems: 1) pumpkins following corn (Zea mays L.); 2) pumpkins following soybeans [Glycine max (L.) Merrill]; 3) pumpkins following 2-years corn; and 4) pumpkins following fallow ground. Cropping systems were chronologically and spatially arranged in two complete cycles, with pumpkin studies taking place in 1996 and 1998. Averaged over the two studies, the optimal N fertilization rate for highest total weight of ripe fruit following soybeans was estimated at 109 kg·ha-1 N, compared to 128 kg·ha-1 N following fallow ground, even though yields were similar, suggesting a soybean N-credit of 19 kg·ha-1 N. Concurrently, the N fertilizer rate for highest total ripe fruit weight following corn was estimated at 151 kg·ha-1 N, and 178 kg·ha-1 following 2-years corn, indicating a negative rotation effect on pumpkin N requirements of 23 and 50 kg·ha-1 N, respectively. Minimum N fertilizer requirements, the N fertilizer rate associated with a ripe fruit yield of 50 t·ha-1, were calculated at 45, 37, 69, and 47 kg·ha-1 N in the respective cropping systems. Negative effects from excessive N fertilization were greater in pumpkins following soybeans than in pumpkins following corn or 2-years corn, with reductions in total ripe fruit weight of 21%, 9%, and 3%, respectively, at the highest N rate. A critical level for preplant soil NO 3-N of 17.6 mg·kg-1 was identified above which there was little or no pumpkin yield response to N fertilization.

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Kimberly A. Klock-Moore and Timothy K. Broschat

Two experiments were conducted to compare the growth of `Ultra White' petunia (Petunia ×hybrida) plants in a subirrigation system versus in a hand-watered system. In Expt. 1, petunia plants were watered with 50, 100, or 150 ppm (mg·L-1) of N of Peter's 20-10-20 (20N-4.4P-16.6K) and in Expt. 2, Nutricote 13-13-13 (13N-5.8P-10.8K) type 100, a controlled release fertilizer, was incorporated into the growing substrate, prior to transplanting, at rates of 3, 6, or 9 lb/yard3 (1.8, 3.6, or 4.5 kg·m-3). In both experiments, there was no difference in petunia shoot dry mass or final flower number between the irrigation systems at the lowest fertilization rate but differences were evident at the higher fertilization rates. In Expt. 1, shoot dry mass and flower number of subirrigated petunia plants fertilized with 100 ppm of N was greater than for hand-watered plants fertilized at the same rate. However, subirrigated petunia plants fertilized with 150 ppm of N were smaller with fewer flowers than hand-watered petunia plants fertilized with 150 ppm of N. Substrate electrical conductivity (EC) concentrations for petunia plants subirrigated with 150 ppm of N were 4.9 times greater than concentrations in pots hand-watered with 150 ppm of N. In Expt. 2, subirrigated petunia plants fertilized with 6 and 9 lb/yard3 were larger with more flowers than hand-watered plants fertilized at the same rates. Although substrate EC concentrations were greater in subirrigated substrates than in hand-watered substrates, substrate EC concentrations of all hand-watered plants were about 0.35 dS·m-1. Subirrigation benches similar to those used in these experiments, appear to be a viable method for growing `Ultra White' petunia plants. However, the use of Peter's 20-10-20 at concentrations greater than 100 ppm of N with subirrigation appeared to be detrimental to petunia growth probably because of high EC concentrations in the substrate. On the other hand, the use of subirrigation with Nutricote 13-13-13 type 100 incorporated at all of the rates tested did not appear to be detrimental to petunia growth.

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Z.L. He, D.V. Calvert, A.K. Alva, and Y.C. Li

Fertilization is among the most important factors influencing fruit quality of citrus. Effects of Individual element such as N, P, or K on fruit quality have been well-documented. Much less has been done on the interactions of N, P, and K in relation to citrus fruit quality. A field experiment was conducted from 1994 to 1999 in a commercial grove on a Riviera fine sand (Loamy, siliceous, hyperthermic Arenic Glossaqualf) to investigate the effects of fertilizer rates and sources on fruit quality of 26-year-old `White Marsh' grapefruit trees (Citrus paradisi Macfad.) on Sour Orange rootstock (Citrus aurantium Lush). Fertilizer was applied as water-soluble dry granular broadcast (three applications/year) at N rates of 0, 56, 112, 168, 224, and 336 kg/ha per year using a N;P:K blend (1.0:0.17:1.0). There was a quadratic relationship between fruit weight or peel thickness and fertilizer rates. Fruit weight per piece increased with fertilizer rates from 0 to 168 kg N/ha per year, but decreased from 168 to 336 kg N/ha per year. Fruit size was small at zero or low fertilizer rates due to nutrient deficiencies. Large fruit sizes of `White Marsh' grapefruit in the sandy soil were achieved at fertilizer rate around 168 kg N/ha per year. Increasing fertilizer application rates higher than 168 kg/ha per year greatly increased the number of fruit per tree, but decreased the size of fruit. Peel thickness, which is related to the fruit size, declines at higher fertilizer rates. Increase in fertilizer rate from 0 to 336 kg N/ha per year increased solids content and fruit acid concentration of the grapefruit. Fertilization rate effect on fruit Brix concentration was more complicated. Brix concentration was not affected by increasing fertilizer rates from 0 to 168 kg N/ha-per year, but was increased at higher fertilization rates (168 to 336 kg N/ha per year). As a result, the Brix/acid ratio was, in general, decreased by increasing fertilizer rates.

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Paolo Sambo*, Daniele Borsato, and Giorgio Gianquinto

Research at Padova Univ., Italy, during Summer 2003, was carried out to determine the effect on nitrogen fertilization on yield and canopy reflectance of sweet bell pepper (Capsicum annuum). Pepper var. Tolomeo LRP 4993 (Syngenta) was transplanted into plots (24 m2) on 20 May, maintaining 40 cm between plants and 75 cm between rows (3.3 plant per m2). The experimental design was a randomized block with four replicates. Treatments were 6 nitrogen fertilization rates ranging from 0 to 300 kg·ha-1. Nitrogen was distributed at planting and as top dressing, 44 days after planting. All other production techniques were typical of pepper production in the Veneto region. Beginning the second week after transplanting, canopy reflectance was measured weekly using a multispectral radiometer MSR 87 (Cropscan Rochester, Minn.). Fruits were harvested at breaking color stage starting from 21 July to 9 Oct. (8 harvests). At harvest, total and marketable yield, fruit averaged weight and nitrogen content were determined. Maximum yield was recorded at the 120 kg·ha-1 nitrogen treatment, while higher rates proved ineffective at increasing production. Nitrogen rates positively affected fruit weight. The nitrate content of fruits also increased with the nitrogen rates although it remained below the level dangerous for human health. Canopy reflectance was able to detect the different nitrogen treatments only during the late stages of the growth cycle making difficult its use as a tool to drive nitrogen fertilization.

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Zhongchun Jiang

Information about micronutrient concentrations of plants in general can be found in botany and plant physiology textbooks, but micronutrient concentrations in field-grown lettuce is hard to find and so are concentrations of heavy metals. Lettuce consumers may be concerned with heavy metal concentrations and information about heavy metal concentrations may help consumers make a choice. This study examined the concentrations of eight micronutrients and five heavy metals in field-grown lettuce with different fertilization programs. Under the field conditions, different NPK fertilizers and fertilization rates did not differ in the leaf concentrations of micronutrients and heavy metals. The overall means of Fe, Na, Mo, and Ni concentrations in the lettuce were 663, 710, 0.9, and 1.9 μg·g–1 of dry leaves, respectively. These values were significantly higher (over 500% greater) than the values found in textbooks for plants in general. Mean Mn, Cu, B, and Zn concentrations were 55.5, 7.3, 23.7, and 28.4 μg·g–1 of dry leaves, respectively, which are in general agreement with textbook values. Mean concentrations of heavy metals Cd, Co, Cr, and Pb were 1.5, 1.0, 2.9, and 4.5 μg·g–1 of dry leaves, respectively, whereas mean Al concentration was 498.5 micrograms per gram of dry leaves. These results indicate that concentrations of some elements in lettuce leaves can be high under certain field conditions. It would be beneficial for lettuce growers and consumers to have this information.

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Timothy K. Broschat and Kimberly A. Moore

Salvia (Salvia splendens) `Red Vista' or `Purple Vista,' french marigold (Tagetes patula) `Little Hero Orange,' bell pepper (Capsicum annuum) `Better Bell,' impatiens (Impatiens wallerana) `Accent White,' and wax begonia (Begonia ×semperflorens-cultorum) `Cocktail Vodka' were grown in 0.95-L (1-qt) containers using a 5 pine bark: 4 sedge peat: 1 sand substrate (Expts. 1 and 2) or Pro Mix BX (Expt. 2 only). They were fertilized weekly with 50 mL (1.7 fl oz) of a solution containing 100, 200, or 300 mg·L-1 (ppm) of nitrogen derived from 15N-6.5P-12.5K (1N-1P2O5-1K2O ratio) or 21N-3P-11.7K (3N-1P2O5-2K2O ratio) uncoated prills used in the manufacture of controlled-release fertilizers. Plants grown with Pro Mix BX were generally larger and produced more flowers or fruit than those grown with the pine bark mix. With few exceptions, plant color, root and shoot dry weights, and number of flowers or fruit were highly correlated with fertilization rate, but not with prill type. There appears to be little reason for using the more expensive 1-1-1 ratio prills, since they generally did not improve plant quality and may increase phosphorous runoff from bedding plant nurseries.

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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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Russell Johnston, Vernon Shattuck, and John Seliga

The influence of various crop rotations on the marketable yield of processing tomatoes (Lvcopersicon esculentum) in southwestern Ontario was investigated. The study was conducted for three years using nine and eight crop rotations at Leamington and Dresden, respectively. Four rates of nitrogen, 0, 45, 90, and 135 kg/ha were applied to each rotation. The treatments were arranged in a split-plot experimental design. Tomato yields were generally higher at both locations for all rotations compared to continuously grown tomatoes (control). The highest yields were obtained when tomatoes were grown in an alfalfa (Medicago sativa) rotation and rotations involving rye (Secale cereale) or winter wheat (Triticum aestivum). Tomato yields from the soybean (Glycine max) rotation and from continuously grown tomatoes were similar. At both locations, yields from continuously grown tomatoes increased with increasing rates of nitrogen fertilizer. Optimal yields for each rotation varied with each individual rate of nitrogen. Tomatoes grown in the alfalfa rotation showed the least response to higher rates of applied nitrogen. Our data indicates that certain crop rotations and nitrogen fertilization rates can be used together to enhance the yield of processing tomatoes.

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San-Gwang Hwang, Hsiao-Chien Chao, and Huey-Ling Lin

Global surface temperatures are predicted to increase by 1 to 4 °C by the year 2100. To unravel the risks from rising temperature to Taiwan’s summer leafy vegetable production, the phenotypical and physiological responses of two leafy crops, pak choi (Brassica chinensis L. cv. Quanzhou) and edible amaranth (Amaranthus tricolor L. cv. White leaf), were compared under an elevated temperature. A temperature increase from 28 to 32 °C resulted in lower leaf calcium, magnesium, and manganese concentrations (dry weight basis) in pak choi without significant changes in shoot dry weight, suggesting potential negative effects of the elevated temperature on pak choi leaf nutrient status. However, increased temperature promoted both root and leaf growth in edible amaranth, which may be beneficial to its yield, making edible amaranth a potential summer leafy vegetable crop for Taiwan. Furthermore, a temperature change from 28 to 32 °C resulted in a higher leaf nitrate concentration in edible amaranth, because of the lower nitrate reductase activity (NRA). Thus, suitable nitrogen fertilization rates and programs under elevated temperature conditions should be reconsidered in the future. To sum up, a future rise in summer temperatures may impose negative impacts on pak choi leaf nutrient status but positive impacts on edible amaranth production.