CROP SCIENCE, VOL. 53, NOVEMBER– DECEMBER 2013 WWW.CROPS.ORG 2659 RESEARCH U pland rice ( Oryza sativa L.), which is cultivated in Asia, Africa, and the Americas, has been increasing in global importance because of the decreasing availability of water for lood-irrigated varieties (Tao et al., 2006; Crusciol et al., 2013; Nascente et al., 2013). Because available water resources have been reduced owing to the competing demands of industry and population, alternatives are being sought that allow a greater eiciency of water usage (Saito et al., 2005; Tao et al., 2006). Some alternatives include growing rice under aerobic conditions such as no-tillage systems (NTS) that allow better conservation of soil moisture with the use of cover crops (Curran et al., 1996; Dabney et al., 2001; Nascente et al., 2011). Because grain crops when used as cash crops do not normally produce enough straw to allow yearlong soil coverage, perennial forage species such as Brachiaria and Panicum, which produce large amounts of straw and remain longer on the soil surface because of their high C/N ratio (Crusciol et al., 2012; Nascente et al., 2012), have attracted interest and have been used either in rotation with cash crops or as a cover crop. These grasses also grow quickly and create aggressive root systems that favor nutrient cycling by improving the physical properties and increasing the biological activity and the organic matter of the soil (Dabney et al., 2001; Cover Crop Termination Timing on Rice Crop Production in a No-Till System A. S. Nascente,* C. A. C. Crusciol, T. Cobucci, and E. D. Velini ABSTRACT Measuring shikimic acid accumulation in response to glyphosate applications can be a rapid and accurate way to quantify and pre- dict glyphosate-induced damage to sensitive plants. The objective of this paper was to evalu- ate the effect of cover crop termination timing by glyphosate application on rice (Oryza sativa L.) yield in a no-till system. A factorial experi- ment, arranged in a split-plot design, was con- ducted for 2 yr. Treatments consisted of cover crops (main plots) and timed herbicide applica- tions (subplots) to these cover crops (30, 20, 10, and 0 d before rice planting). There was a decrease in rice yield from 2866 kg ha -1 to 2322 kg ha -1 when the herbicide was applied closer to the rice planting day. Glyphosate application on cover crops increased shikimate concen- trations in rice seedlings cultivated under pali- sade grass (Brachiaria brizantha), signal grass (B. ruziziensis), guinea grass (Panicum maxi- mum), and weedy fallow (spontaneous vegeta- tion) but not under millet (Pennisetum glaucum), which behaved similarly to the control (clean fallow, no glyphosate application). Glyphosate applications in the timing intervals used were associated with stress in the rice plants, and this association increased if cover crops took longer to completely dry and if higher amounts of biomass were produced. Millet, as a cover crop, allowed the highest seedling dry matter for upland rice and the highest rice yield. Our results suggest that using millet as a cover crop, with glyphosate application far from upland rice planting day (10 d or more), was the best option for upland rice under a no-tillage system. A.S. Nascente and T. Cobucci, Brazilian Agricultural Research Corporation (EMBRAPA), Rice and Beans Research Center, P.O. Box 179, 75.375-000, Santo Antônio de Goiás, Goiás, Brazil; C.A.C. Crusciol and E.D. Velini, São Paulo State Univ. (UNESP), College of Agricultural Science, Dep. of Crop Science, P.O. Box 237, 18.610-307, Botucatu, São Paulo, Brazil. Received 22 Jan. 2013. *Corresponding author (adriano.nascente@embrapa.br). Abbreviations: a.i., active ingredient; NTS, no-till system; SOM, soil organic matter. Published in Crop Sci. 53:2659–2669 (2013). doi: 10.2135/cropsci2013.01.0047 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA 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. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.