Sugarbeet Agronomy Journal  Volume 102, Issue 1  2010 17 Published in Agron. J. 102:17–22 (2010) Published online 2 Nov. 2009 doi:10.2134/agronj2009.0041 Copyright © 2010 by the American Society of Agronomy, 677 South Segoe Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. R eduction in sugar content and processing quality of sugarbeet at harvest is a common problem for farmers of the Po River Valley, Italy. Sugar content refers to the sugar (sucrose) percentage (w/w) in the commercial roots and determines the sugarbeet price. High sugar content is consid- ered a key factor for enhancing the extraction capacity of the factories (Dutton and Huijbregts, 2006). Processing quality is a combination of chemical and physical traits of the roots afecting the sugar extraction rate (Burba and Schiewek, 1993). Being a rather complex characteristic, processing quality is routinely evaluated by quantifying three important nonsugars: K, Na, and α-amino N (Campbell, 2005). Potassium and Na are present in roots in appreciable amounts and interfere with sugar crystallization (McGinnis, 1982). α-amino N is a mix of amino acids with the NH 2 group linked to the carbon chain in the α position, and represents numerous N components of the root including betaine, amino acids (glutamine, glycine, alanine), amides, and nitrate (Burba, 1996). hese substances react or decompose during the processing and are detrimental because they induce formation of ammonia, of-colors, and organic acids in the juices (Dutton and Huijbregts, 2006). Low sugar content and poor processing quality of the beets are among the causes of the high costs sustained by the Italian sugar industry. he reduction in sugar content and quality dur- ing harvest, common in Mediterranean countries, occur also when the soil N exceeds the crop uptake, suggesting that excess N might contribute to these losses in ields where otherwise adequate fertility recommendations have been applied (Mar- chetti et al., 2002). Nitrogen in the soil is present in diferent forms. Organic N is a mixture of compounds at di ferent stages of oxidation and molecular weight. Mineral N is the sum of NH 4 –N and NO 3 –N, and represents the bulk of N readily available for crops (Cariolle and Duvall, 2006). Ammonium N displays a very low mobility in the soil and can be absorbed by clay particles becoming unavailable for plants (Marschner, 2003). In the upper part of the soil proile, the concentration of NO 3 –N is usually much greater than NH 4 –N and represents the major N source for sugarbeet (Draycott, 1972). Nitrate N moves easily into the soil and can be leached by percolat- ing water. For deep-rooted crops, mineral N accumulation in the deeper soil layers is a potentially important source of N (horup-Kristensen, 2006). Excess N is more harmful to sug- arbeet than to most other crops (Biancardi et al., 1998) because it stimulates vegetative growth, severely reducing both sugar content and quality (Cariolle and Duvall, 2006). Sugarbeet ibrous roots can extend to a depth of 2.8 to 3.0 m in good soil conditions (Märländer and Windt, 1996; Biancardi et al., 1998), and a study using labeled 15 N showed that the crop can accumulate N from depths > 1.8 m (Peterson et al., 1979). Other experiments utilizing 15 N demonstrated that sugarbeet absorbed between 50 and 80% of applied N from depths down to 1.2 m (Haunold, 1983; Broeshart, 1983). Deep ibrous roots, despite being a small fraction of entire sugarbeet root system (Vamerali et al., 2003), are critical in depleting deep mineral N, ABSTRACT he loss of sugar content and processing quality during the harvest period happens frequently in sugarbeet (Beta vulgaris L. ssp. vulgaris ) grown in the Po Valley of Italy. he aim of this study was to assess the consequences on sugar content and quality of excess mineral N in the deep soil explored by the roots. Soil mineral N concentration and other chemical properties to a 3-m depth were correlated with sugar content and processing quality of sugarbeet in 27 sites sampled in 2000–2003. At each site, 12 soil samples with 0.25-m depth increments were collected and analyzed separately. Organic matter as high as 10% and mineral N as much as 100 mg kg -1 frequently were found between 2 and 3 m, corresponding to the maximum depth of the sugarbeet root system. Signiicant negative relationships were observed between mineral N at the 2.5- to 3-m depth and sugar content (r = –0.63) and quality (r = –0.72). his study indicates both the utility of soil sampling to the depth reached by the roots, and the need of more complete analyses of mineral N, which should include not only nitrate N, but also ammonium N and organic matter. To reduce the losses of sugar content and quality, the presence of organic layers in the rooting zone should be avoided, or adequately considered in the fertilizer management of the crop. P. Stevanato and M. Saccomani, Dep. of Agricultural Biotechnology, Univ. of Padua, viale dell’Università 16, 35020 Legnaro (PD), Italy; C. Zavalloni, Dep. of Agricultural and Environmental Sci., Univ. of Udine, Via delle Scienze 208, 33100, Udine, Italy; R. Marchetti, CRA-Experimental Institute for Crop Sci., viale Caduti in Guerra 133, 44100 Modena, Italy; J.M. McGrath, USDA-ARS, 494D Plant and Soil Sci. Bldg., Michigan State Univ., East Lansing, MI 48824-1325; L.W. Panella, USDA-ARS Crop Research Laboratory, 1701 Center Avenue, Fort Collins, CO 80526; M. Bertaggia and E. Biancardi, CRA-Experimental Institute for Industrial Crops, viale Amendola 82, 45100 Rovigo, Italy. Received 30 Jan. 2009. *Corresponding author (stevanato@unipd.it). Relationship between Subsoil Nitrogen Availability and Sugarbeet Processing Quality Piergiorgio Stevanato,* Costanza Zavalloni, Rosa Marchetti, Marco Bertaggia, Massimo Saccomani, J. Mitchell McGrath, Leonard W. Panella, and Enrico Biancardi