Maintaining Soil Health after Remediated Agroecostems Are Returned to Traditional Cropping Systems.

Intensively tilled cotton (Gossypium hirsutum L.) monoculture systems, although profitable and well-adapted to the semiarid climate of the Texas High Plains in the U.S., have contributed to the degradation of inherently low soil organic matter (SOM).  We conducted a two-phase study (2003-2010) focused on: I) Initially improving soil health by incorporating up to three times more residue annually by including haygrazer (Hay), sorghum (Srg) and/or rye winter cover crops into different cropping systems; and, II) After soil health parameters were significantly improved (five years),  increasing the frequency of cotton cropping (i.e., at least two out of three years) in all systems to test if the increases in these parameters would be maintained and if cotton yields would be improved.  The soil health parameters evaluated (0-5cm) were microbial biomass C& N, fatty acid profiling to describe changes in microbial community composition (i.e., fungal vs. bacterial populations), and enzyme activities (EAs) involved in biogeochemical cycling and SOM dynamics.  During the first year of Phase II (2008), all plots were planted in cotton, and higher cotton yields (73-137%) corresponded to the rotation (Hay-Rye>Srg-Ctn=Ctn-Rye-Srg) with higher soil microbial biomass C&N (10-26%) and EAs (15-97%) involved in C (b-glucosidase, a-galactosidase), C&N (b-glucosaminidase), P (alkaline phosphatase, phosphodiesesterase) and S (arylsulfatase) cycling. A year of rotation crops during 2009 was followed by the second year of cotton in 2010, in which no differences were found in yields, but soil under Hay-Rye was still found to have higher microbial biomass (20-45%) and enzyme activities (33-83%, except phosphodiesterase).  The geometric mean of these EAs was significantly decreased for Hay-Rye (32%) due to the incorporation of cotton into the cropping system during Phase II of the study; however, all cropping systems established in Phase I continue to show improved soil health compared to continuous monoculture cotton.