Effects of Nitrogen and Planting Seed Size on Cotton Growth, Development, and Yield

Published in Agron. J. 105:1853–1859 (2013) doi:10.2134/agronj2013.0154 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford 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. arborescent perennials that can be highly indeterminate in growth and reproduction patterns (Donald and Hamblin, 1976; Bednarz and Nichols, 2005). Partitioning of N in cotton is affected by genetics, environment, and the availability of N (Mullins and Burmeister, 1990; Boquet et al., 1993; Boquet and Breitenbeck, 2000; Fritschi et al., 2003). Cotton varieties that receive supraoptimal N may produce excessive vegetative growth and fewer reproductive structures than cotton receiving less N (Boquet et al., 1994; Boquet and Breitenbeck, 2000). Increasing N fertilization may increase cottonseed yield more than lint yields (Egelkraut et al., 2004; Fritschi et al., 2003). Pre-sidedress soil nitrate tests (PSNT) have shown promise in predicting N fertilizer needs for other crops. Spellman et al. (1996) reported that critical levels for PSNT NO3 – for corn production were lower in semiarid areas of the western United States than in more humid environments. Similar results were reported in Australia where soil NO3 – levels sampled to a depth of 30 cm before planting were closely correlated to cotton N uptake in plots that received no applied N fertilizer (Constable and Rochester, 1988). While soil NO3 – testing is not currently used to a great extent for cotton production, this type of testing could prove to be economically beneficial in areas where residual NO3 – is present. Cotton lint is comprised of fibers growing from the cotton seed surface. Because a large number of small seed can have more surface area than do a few large seed, greater lint yields might be achieved by selecting for reduced seed size and increasing seed numbers (Harrell and Culp, 1976). Such a result could accrue from simple selection for high gin turnout, the fraction of lint obtained from harvested seed cotton. In fact the mean seed size of cotton varieties has been decreasing for the last 30 yr (Bednarz et al., 2007). AbStrACt A standardized experiment was conducted during 2009 and 2010 at 20 location-years across U.S. cotton (Gossypium hirsutum L.)producing states to compare the N use requirement of contemporary cotton cultivars based on their planting seed size. Treatments consisted of three cotton varieties with planting seed of different numbers of seed per kg and N rates of 0, 45, 90, and 134 kg ha–1. Soil at each trial location was sampled and tested for nitrate presence. High levels of soil nitrate (>91 N-NO3 – kg ha–1) were found in Arizona and western Texas, and soil nitrate in the range of 45 to 73 kg N-NO3 – ha–1 was found at locations in the central United States. Cotton lint yield responded to applied N at 11 of 20 locations. Considering only sites that responded to applied N, highest lint yields were achieved with 112 to 224 kg ha–1of applied plus pre-plant residual soil NO3—translating to an optimal N requirement of 23 kg ha–1 per 218 kg bale of lint produced. Among the varieties tested those with medium-sized seed produced higher yields in response to N than did larger and smaller seeded varieties. Varieties with larger seed had longer and stronger fibers, higher fiber length uniformity than small seeded varieties and decreased micronaire. Seed protein and oil increased and decreased slightly in response to increasing amounts of soil nitrate plus applied N, respectively.