Potential contribution by corn and Bollgard II cotton roots to soil carbon stocks in a furrow-irrigated Vertisol

摘要

Potential contribution by roots of corn and genetically-modified Bollgard II cotton to soil carbon stocks was evaluated in two experiments near Narrabri, north-western NSW. In one experiment a Bollgard~(TM) II-Roundup Ready~(TM)-Flex~(TM) variety wascompared with a Roundup Ready~(TM)-Flex~(TM) variety, and in another, corn grown as a monoculture was compared with corn sown in rotation with cotton. Root growth in the surface 0.10 m was measured with the core-break method, and that in the 0.10 to 1.0m depth with a minirhizotron and I-CAP image capture system. These measurements were used to derive root length per unit area (L_A), root C added to soil through intra-seasonal root death (C_(lost)), C in roots remaining at end of season (C_(root)) and root C potentially available for addition to soil C (C_(total)). C_(total) averaged 5.0 t/ha with cotton-corn and 9.3 t/ha with corn monoculture, with average C_(lost) accounting for 11%. In contrast, C_(total) with genetically-modified cotton ranged from0.6 to 0.9 t/ha with Q_(lost) contributing 43%. Intra-seasonal root death makes a significant contribution to soil carbon stocks by cotton roots whereas only a small proportion was contributed through this pathway by corn. L_A was higher with corn monoculture than with cotton-corn, and was higher in Bollgard II cotton which was resistant to the Helicoverpa moth larvae than in cotton which did not possess the Bollgard II gene.