Abstract: By using ELISA test kits, a field investigation was conducted on the degradation dynamics of Cry1Ab protein in the rhizosphere soil of Bt corn MON810 at its different growth stages and in the MON810 straws returned into field after harvest. Three models (shiftlog model, exponential model, and biexponential model) were used to fit the degradation dynamics of the Cry1Ab protein from the straw debris, and the DT₅₀ and DT₉₀ values were estimated. There existed great differences in the Cry1Ab protein content in the rhizosphere soil of MON810 at its different growth stages, but overall, the Cry1Ab protein content was decreased remarkably with the growth of MON810. The degradation of Cry1Ab protein from the straws covered on soil surface and buried in soil showed the same twostage pattern, i.e., more rapid at early stage and slowstable in later period. Within the first week after straw return, the degradation rate of the Cry1Ab protein from the straws covered on soil surface was significantly higher than that from the straws buried in soil. At 10 d, the degradation rate of the Cry1Ab protein from the straws covered on soil surface and buried in soil was basically the same, being 88.8% and 88.6%, respectively. After 20 days, the degradation of Cry1Ab protein entered slowstable stage. Till at 180 d, a small amount of Cry1Ab protein could still be detected in the straw debris. All of the three models used in this study could  fit the decay pattern of the Cry1Ab protein from the straw debris in field. By comparing the correlation coefficient (R) and the consistency between the measured and calculated DT₉₀, biexponential model was considered to be the best.

Key words: Bt corn, Cry1Ab protein, rhizosphere soil, straw return, degradation in field, simulation model.