Carbon Sequestration and Soil Aggregation in Center-Pivot Irrigated and Dryland Cultivated Farming Systems

SSSAJ: Volume 71: Number 3 • May–June 2007 Soil Sci. Soc. Am. J. 71:1020–1028 doi:10.2136/sssaj2006.0215 Received 8 June 2006. *Corresponding author ([email protected]). © Soil Science Society of America 677 S. Segoe 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. Increasing the amount of C sequestered in cropland through improved agricultural management has become an important part of the strategy to mitigate CO2 emissions to the atmosphere (Lal et al., 1998; Intergovernmental Panel on Climate Change, 2001). Examples of management practices that enhance soil C stocks are reduced tillage and increasing cropping intensity (Paustian et al., 2000), but also irrigation is believed to be a potential benefi cial management for increasing soil C stocks (Follett, 2001). Carbon sequestration rates through irrigation have been estimated to reach as high as 50 to 150 kg ha−1 yr−1 (Lal et al., 1998). These estimates, however, are based solely on increased C inputs due to enhanced biomass production on irrigation. Yet, irrigation can affect the soil C balance in several other ways as well. For example, irrigation can greatly stimulate microbial activity in regions suffering from drought. In a study of Churchman and Tate (1986), irrigation led to a decrease of C stocks in soils under pasture, suggesting that its effect on microbial activity and SOM decomposition was potentially more dominant than its effect on C input. Besides increasing C input and microbial activity, irrigation can also affect soil structure. Many studies have reported a negative impact of irrigation on physical properties such as bulk density, porosity, and hydraulic conductivity (Moreno et al., 1986; Elnaim et al., 1987; Poznyak, 1990; Al-Nabulsi, 2001), Carbon Sequestration and Soil Aggregation in Center-Pivot Irrigated and Dryland Cultivated Farming Systems