Frank Hons, Javier Betran, and Teresa Salvatore Wilson. Texas A&M Univ, Soil & Crop Dept, Heep Bldg, TAMU 2474, College Station, TX 77843-2474
US farmers produced 1.1 billion bushels of corn (Zea mays L.) in 2005, approximately 35% from Bt-modified varieties. About one ton of stover is produced for every ton of grain and most is returned to the soil; the rate at which these residues decay impacts carbon sequestration/soil fertility. Trials were conducted at two locations in South-central Texas with 4 commercial hybrids (DKC6971, DKC6972, DKC6410 and DKC6411) to evaluate the impact of the Cry1Ab transgene on corn stover degradation rate. Whole plants, without ears, were harvested at maturity and separated into the upper (U) (up to the last node), middle (M) (next to the last to third node) and lower (L) (first 3 nodes, no roots). Plant parts were dried, ground and incubated in Weswood silt loam soil. Degradation rate (measured by CO2 evolution) of the transgenic isoline was lower than its corresponding non-transgenic counterpart for both varieties. Degradation rate order for both non-Bt varieties, DKC6972 and DKC6410, was U>M>L; while for transgenic plants, DKC6971 was L>U>M and DKC6411 –a high fermentable corn variety- was M> L>U. Stover samples were analyzed for crude protein, starch, cellulose, lignin and, silica concentration to determine if chemical composition could also account for the variation observed in the degradation rates.
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