Research has shown that plant analysis can determine the N needs of many crops (Gardner, 1989a; Gardner and Pew, 1972). Regular tissue analysis should enable farmers to recognize and correct an incipient nutrient deficiency, but this is impractical for vegetables like pac choi (Brassica rapa L. Chinensis group) with a short growth period. Petiole sap nitrate is a highly sensitive indicator of plant nutrient status, and testing for it is simple, practical, and fast (Amor et al., 2006; Drews and Fischer, 1992; Hochmuth et al., 1991). Need for a reliable method of testing N to improve yield, avoid over- and underfertilization, and to reduce the extra cost with excessive fertilizer has encouraged research on the nitrate test for petiole sap in vegetables. Petiole sap nitrate-nitrogen (PSNN) levels associated with maximum growth rate or yield have been determined for vegetable crops like cabbage (Brassica oleracea L. Capitata group) (Gardner, 1989a; Schulbach et al., 2007); broccoli (Brassica oleracea L. Italica group) (Gardner, 1989b; Hochmuth, 1994); lettuce (Lactuca sativa L.) (Schulbach et al., 2007); and collards (Brassica oleracea L. Acephala group) (Hochmuth, 1994), but not for pac choi. The objectives of this study were to: 1) determine if petiole sap tests can be used to identify N sufficiency in pac choi; 2) determine if fertilization system (organic and inorganic) affects the potential use of petiole sap tests for N management; and 3) evaluate petiole sap response to a fertilization regime in field and high tunnel environments.
Albright, L. 2010 Pak choi handbook. Cornell University. Biological and environmental engineering. Sept. 2010. <http://www.cornellcea.com/Pakchoi_Handbook/pc_biological_significance.htm>
Amor, F.M. del, Espinosa, M.F., Molina, S., Varo, P., Camara, J.M. & Lopez, Y.A. 2006 Evaluation of methods for the determination of N in pepper crops Horticultura, Revista de Industria, Distribucion y Socioeconomia Horticola 196 14 20
Cavins, T.J., Whipker, B.E. & Fonteno, W.C. 2008 Pourthru: A method for monitoring nutrition in the greenhouse. Acta Hort. (ISHS) (779):289
Drews, M. & Fischer, S. 1992 Standards for nitrate and potassium in press sap analysis of greenhouse tomatoes and cucumbers Gartenbauwissenschaft 57 145 150
Elfar Altamimi, M. 2010 Nitrate-nitrogen sufficiency ranges in leaf petiole sap of pac choi grown with organic and conventional fertilizers. Master of Science, Kansas State University, KS
Evans, L. 2006 Salinity tolerance in irrigated crops. Sept. 2010. <http://www.dpi.nsw.gov.au/agriculture/resources/soils/salinity/crops/tolerance-irrigated>
Gardner, B.R. 1989a Midrib nitrate concentration as a means for determining nitrogen needs of cabbage. Marcel Dekker, New York, NY
Gardner, B.R. 1989b Midrib nitrate concentration as a means for determining nitrogen needs of broccoli. Marcel Dekker, New York, NY
Gardner, B.R. & Pew, W.D. 1972 Response of fall grown head lettuce to nitrogen fertilization. Univ. Arizona Tech. Bul. 199.
Hartz, T.K., Johnstone, P.R. & Williams, E.S. 2007. Establishing lettuce leaf nutrient optimum ranges through DRIS analysis. The Society, Alexandria, VA.
Hochmuth, G.J. 1994 Efficiency ranges for nitrate-nitrogen and potassium for vegetable petiole sap quick tests HortTechnology 4 218 222
Hochmuth, G.J., Maynard, D., Vavrina, C., & Hanlon, E. 1991. Plant tissue analysis and interpretation for vegetable crops in Florida (No. SS-VEC-42). Univ. Florida Special Publication
Knewtson, J.S. 2008 Studies in vegetables and high tunnel production on the central great plains. Doctor of Philosophy, Kansas State University, KS
Lyons, D.J., Rayment, G.E., Nobbs, P.E. & McCallum, L.E. 1994 Nitrate and nitrite in fresh vegetables from Queensland J. Sci. Food Agr. 64 279
Marr, C.W., Morrison, F.D. & Whitney, D.A. 1998 Fertilizing gardens in Kansas. MF-2320. Kansas State University Agricultural Experiment Station and Cooperative Extension Service
Parks, S.E., Huett, D.O., Campbell, L.C. & Spohr, L.J. 2008 Nitrate and nitrite in Australian leafy vegetables Aust. J. Agr. Res. 59 632 638
Proietti, S., Moscatello, S., Leccese, A., Colla, G. & Ballistelli, A. 2004 The effect of growing spinach (spinacia oleracea L.) at two light intensities on the amounts of oxalate, ascorbate, and nitrate in their leaves J. Hort. Sci. Biotechnol. 79 606
Schulbach, K., Smith, R., Hartz, T. & Jackson, L. 2007 Guide to nitrogee quick-tests for vegetables with ‘Cardy’ nitrate meter (No. 95-0582). CDFA, CA
Scuderi, D., Giuffrida, F. & Noto, G. 2009 Effects of nutrient solutoon EC on yield, quality and shelf-life of lettuce grown in floating system Acta Hort. 807 221 226 (ISHS)
Talavera-Bianchi, M. 2009 Sensory alanlysis of pak choi and tomato grown under organic and conventional systems. Doctor of Philosophy, Kansas State University, KS
Warman, P.R. & Havard, K.A. 1997 Yield, vitamin, and mineral contents of organically and conventionally grown carrots and cabbage Agr. Ecosyst. Environ. 61 155 162
Westerveld, S.M., McKeown, A.W., Scott-Dupree, C.D. & McDonald, M.R. 2004 Assessment of chlorophyll and nitrate meters as field-tissue nitrogen tests for cabbage, onions, and carrots HortTechnology 14 179 188
Wright, A.F. & Bailey, J.S. 2001 Organic carbon, total carbon, and total nitrogen determinations in soils of variable calcium carbonate contents using a Leco CN-2000 dry combustion analyzer Commun. Soil Sci. Plant Anal. 32 3243