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P.L. Preusch and T.J. Tworkoski

93 POSTER SESSION 11 (Abstr. 159–188) Crop Physiology Tuesday, 25 July, 1:00–2:00 p.m.

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William E. Klingeman, Gregory R. Armel, Henry P. Wilson, Thomas E. Hines, Jose J. Vargas and Philip C. Flanagan

of mugwort. Mesotrione and topramezone impede carotenoid biosynthesis by inhibiting the enzyme p -HPPD ( Norris et al., 1998 ). Mesotrione is registered for preemergence (PRE) and POST applications in corn and turfgrass ( BASF, 2013 ; Mitchell et al

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P.R. Johnstone and T.K. Hartz*

Heavy P fertilization of vegetable crops in the Salinas Valley of California have increased soil P levels, with > 50 mg·kg-1 bicarbonate-extractable P (Pbc) now common. To evaluate the response of lettuce (Lactuca sativa L.) to P fertilization in fields with elevated soil P levels, 12 trials were conducted in commercial fields during 2002-2003. Pbc at the trial sites varied from 53-171 mg·kg-1. In each trial four replicate plots receiving the growers' P application were compared with paired plots in which no P was applied. Leaf P was monitored at cupping stage and at harvest. At harvest mean whole plant mass and % of marketable plants were recorded. The correlation of Pbc to bioavailable P (Pba) was evaluated using 30 representative Salinas Valley soils; Pbc varied among these soils from 15-177 mg·kg-1. Pba was estimated by P adsorption on an anion resin membrane during a 16 h incubation. The effect of temperature on P bioavailability in 6 of these soils was estimated by conducting the Pba incubation at 5, 15 and 25 °C. A significant increase in lettuce yield with P fertilization was achieved at only one trial site, a spring planting where Pbc was 54 mg kg-1 ; at all other sites, including 3 with Pbc < 60 mg kg-1, P application resulted in no agronomic benefit. P application resulted in only a marginal increase in plant P uptake. Pba was highly correlated with Pbc (r = 0.89). Pba increased approximately 40% across soils with each 10 °C increase in soil temperature.

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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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M. K. Schon and M. P. Compton

Experiments were conducted to determine the optimum levels of N and P for use in greenhouse cucumber (Cucumis sativus L. `Vetomil') production. Plants were grown in rockwool slabs using a double-stem pruning method. Treatment 1 plants were fed 90 ppm N until N in the growing slabs was depleted (averaged <10 ppm); N was then increased to 175 ppm. Treatment 2 and 3 plants were given a constant 175 or 225 ppm N, respectively. Plants in all treatments depleted N in the slabs by three to four weeks after transplant (WAT); N remained low in Treatment 1, but recovered to adequate levels in Treatments 2 and 3. Phosphorus was provided at a constant 50 ppm and was depleted to <10 ppm in the slabs of all three treatments by four WAT. Fruit yield increased significantly with each increase in solution N. Similar results in a second trial indicated that N and/or P may have been limiting factors even at the highest levels tested. Research will continue to determine optimum levels of N and P for maximizing yield.

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Audrey I. Gerber, Karen I. Theron and Gerard Jacobs

1 To whom reprint requests should be addressed. Current address: Ovens Research Station, P.O. Box 235, Myrtleford, VIC 3737, Australia. E-mail address: 2 Associate Professor. 3 Professor. This paper is a portion

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Gerry H. Neilsen, Denise Neilsen, Sung-hee Guak and Tom Forge

trees were not nutrient limited, and following optimum industry recommendations, trees received annual NPKB fertigation. N was fertigated daily as calcium nitrate (15.5N–0P–0K) for 6 weeks after bloom to provide 75 g N/tree. Subsequent research indicated

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R. Paul Schreiner

western Oregon use foliar sprays of B (often mixed with fungicides) early in the season or postharvest to ensure that vines are not limited by this nutrient. Foliar sprays of macronutrients [nitrogen (N), phosphorus (P), potassium (K) calcium (Ca

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G.H. Neilsen, E.J. Hogue and P. Parchomchuk

Application of high rates of P in the year of planting increased the number of flower clusters and fruit set the subsequent year on newly planted `Macspur McIntosh', `Summerland Red McIntosh', `Jonagold', and `Jonamac' apple (Malus domestica Borkh.) on dwarfing rootstock (M.26 and M.9) in three separate experiments. The effect occurred whether P was applied at rates of 36 or 48 g P/tree as granular monoammonium phosphate (11 N-23.6 P-0K) uniformly mixed with 100 or 180 liter of soil in the planting hole or at rates of 17.5 and 35 g P applied as soluble ammonium polyphosphate (10N-14.6P-0K) with the irrigation water. A leaf P concentration range between 0.20% and 0.36% was associated with the acceleration of fruiting.

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Rebecca G. Bichsel, Terri W. Starman and Yin-Tung Wang

Oral Session 10—Floriculture 2 28 July 2006, 10:00 a.m.–12:00 p.m. Bayside A Moderator: Ying-Tung Wang