Models with capabilities to simulate plant responses to strategies of sustainable agriculture such as conservation tillage are useful for making management decisions. This study evaluated the cotton (Gossypium hirsutum L.) crop simulation model, GOSSYM, for its ability to simulate cotton growth and yield under no-till and mulch-till systems with a winter rye (Secale cereale L.) cover crop and poultry litter (PL) as a nitrogen source. The soil is a Decatur silt loam (clayey, kaolinitic thermic, Typic Paleudults) in northern Alabama. Cotton lint yield under no-till was 7 to 24% greater than that under conventional till. Simulated phenology data were closer to measured data in 1997. In 1998, simulated durations to first square and first flower were 7 to 16 days shorter than observed data, while simulated duration to maturity was up to 15 days longer than observed data. The model generally simulated cotton plant height, LAI, and root dry weight well up to the first flower growth stage. Thereafter, simulated data were significantly lower than measured data. Simulated lint yields were 130 to 390 kg ha^-1 lower than measured lint yields. These relatively lower values simulated by the GOSSYM model can be attributed to its inability to simulate no-till, cover cropping, and PL effects on water conservation. These treatments conserved 10 to 56% more soil moisture compared to conventional till, ammonium nitrate and no cover cropping. To properly simulate the effects of sustainable cotton production practices such as no- till, GOSSYM needs appropriate modifications in the sub-routines dealing with soil moisture availability.