HORTSCIENCE VOL. 40(5) AUGUST 2005 1190 Fruit Nitrogen Content of Sixteen Strawberry Genotypes Grown in an Advanced Matted Row Production System Brent L. Black, 1 Stan C. Hokanson, 2 and Kim S. Lewers United States Department of Agriculture, Agricultural Research Service, Henry A. Wallace Beltsville Agricultural Research Center, Fruit Laboratory, Building 010A, 10300 Baltimore Avenue, Beltsville, MD 20705-2350 Additional index words. Fragaria ×ananassa, nitrogen Abstract. In the perennial strawberry production system, removal of the harvested crop represents a loss of nitrogen (N) that may be influenced by cultivar. Eight strawberry (Fragaria ×ananassa Duch.) cultivars and eight numbered selections grown in advanced matted row culture were compared over three seasons for removal of N in the harvested crop. Replicated plots were established in 1999, 2000, and 2001 and fruited the following year. ‘Allstar’, ‘Cavendish’, ‘Earliglow’, ‘Honeoye’, ‘Jewel’, ‘Northeaster’, ‘Ovation’, and ‘Latestar’ and selections B37, B51, B244-89, B683, B753, B781, B793, and B817 were compared for yield and fruit N concentration. Harvest removal of N (HRN) was calculated from total season yield and fruit N concentration at peak harvest. There were significant differences in HRN among genotypes, ranging from 1.80 to 2.96 g N per meter of row for numbered selections B781 and B37, respectively. Among cultivars, HRN ranged from 2.01 to 3.56 g·m –1 for ‘Ovation’ and ‘Jewel’, respectively. The amount of HRN was largely determined by yield, however, there were also significant genotype differences in fruit N concentration, ranging from 0.608 to 0.938 mg N per gram fresh weight for B244-89 and ‘Jewel’, respectively. These differences indicate that N losses in the harvested crop are genotype dependent. Efforts to improve the sustainability of food production practices have resulted in increased interest in the conservation of soil and water resources, including the reduction of soil and nutrient losses. Many states in the northeastern U.S. have enacted nutrient management legislation to encourage reduced nutrient run-off and leaching from agricultural lands (Lea-Cox and Ross, 2001). These plans focus on nitrogen and phosphorus. Central to improving nutrient management practices is the quantification of the nutrients added to, and lost from an agricultural system. In the case of nitrogen, losses from the agroecosystem can occur through several pathways, includ- ing volatilization of reduced N, microbial denitrification, removal in the harvested crop, surface run-off and leaching. The latter two are primary concerns in determining nonpoint source nutrient pollution. Commercial practices for N fertilization of strawberry differ depending on soil type, cultivar, and cropping system. In an annual hill system using fertigation, annual rates can range from 85 to 450 kg·ha –1 with much of this applied during cropping (Campbell and Miner, 1996; May and Pritts, 1990). For perennial matted row culture where N fertilizer is broadcast- applied in both spring and fall, N fertilization rates ranging from 56 to 110 kg·ha –1 have been reported (May and Pritts, 1990; Pritts, 1998; Strik et al., 2004). However, some reports have suggested that fertilizer N additions during the establishment year do not increase yield in the first fruiting year (Archbold and MacKown, 1995; Breen, 1979). In general, strawberry requires less N than do many vegetable and agronomic crops. A number of published stud- ies have investigated efficiency of nitrogen acquisition by strawberry plants (Archbold and MacKown, 1988, 1995; Peterson et al., 1986; Strik et al., 2004). Several studies have provided estimates of nitrogen removed in the harvested crop, both for a winter production system in Florida (Albregts and Howard, 1978, 1980) and for conventional matted row management (Archbold and MacKown, 1988; Strik et al., 2004). However, previous studies estimating the fate of fertilizer N involved the use of only one or several cultivars, and the primary focus was not on cultivar comparison. Further, the cultivars used in many of these studies are no longer grown commercially in the U.S. The purpose of this study was to deter- mine the amount of nitrogen removed in a strawberry crop using modern production practices and cultivars, and to determine the extent to which harvest removal of N varied among genotypes. Materials and Methods The strawberry breeding program at the USDA–ARS Fruit Laboratory, Henry A. Wal- lace Beltsville Agricultural Research Center, conducts replicated trials of advanced selec- tions and commercial cultivars. New plantings are established each year and cropped for a single season. Plots are evaluated for plant health, fruit yield, fruit size and quality. These trials are conducted in two production systems, a cold-climate annual hill system (plasticul- ture), and a modified or advanced matted row (AMR) system. Both of these systems have been described previously (Black et al., 2002). During the 2000–02 harvests, fruit samples were collected from the AMR selection trial to compare HRN among genotypes. The AMR system involves the use of raised beds, subsurface drip irrigation, and a killed cover crop mulch. For this study, raised beds were formed and a mixed cover crop consist- ing of hairy vetch (Vicia villosa Roth), grain rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) was seeded over the beds in late August, at seeding rates of 45, 78, and 34 kg·ha –1 , respectively. Drip irrigation tape (T-tape brand irrigation tape; Trickl-eez Co., Biglerville, Pa.; 30 cm emitter spacing, 56 mL·min –1 ·m –1 flow rating) was placed in the center of the bed, 5 to 8 cm below the surface. The cover crop was killed in April and dormant bare-root plants were transplanted through the cover crop mulch. Weed control was by directed herbicide application and some hand weeding. For the research plots, bed spacing was 1.5 m between row centers. However, typical spacing in a commercial planting would be about 1.2 m. In 1999, 2000, and 2001, plots were es- tablished in three separate locations within the same field. Two soil types are found in the field, a Matawan-Hammonton Loamy Sand (Aquic Hapludult, silicios, mesic) and an Elkton-Keyport Silt Loam (Typic Endoaquult, mixed mesic). Within each year, four replicate plots of each genotype were established in a randomized complete block design, with blocking by location in the field to account for variation in soil type and other field char- acteristics. In a typical year, the AMR trial contains 12 to 18 numbered selections, and 6 to 10 named cultivars, however, genotypes are added to and dropped from the selection trials each year. Only those cultivars and selections that were present in at least two of the three years were included in the comparison of HRN (Table 1). The four replicate plots of each genotype were established by planting cold-stored dor- mant plants at 0.3 m spacing in a single row down the center of the bed, with four plants per plot. Starting two weeks after planting, am- monium nitrate fertilizer was applied through the irrigation system in weekly applications at a rate of 210 mg N per row meter for 16 weeks, providing a season total of 3.36 g·m –1 . With a row spacing of 1.5 m, 3.36 g·m –1 is equiva- lent to 22.4 kg·ha –1 as a broadcast rate. With a matted row width of 0.45 m, 3.36 g·m –1 is equivalent to 75 kg·ha –1 on the basis of treated HORTSCIENCE 40(5):1190–1193. 2005. Received for publication 24 Nov. 2004. Accepted for publication 15 Jan. 2005. The authors gratefully acknowledge the technical assistance of Ingrid Fordham, Adrienne Labega and John Enns. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products or vendors that may be suitable. 1 To whom reprint requests should be addressed; e-mail blackb@ba.ars.usda.gov. 2 Present address: Department of Horticultural Science, University of Minnesota, St. Paul, MN 55108.