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Cropping Systems Effects on Improving Soil Carbon Stocks of Exposed Subsoil

Dep. of Agronomy, Iowa State Univ., Ames, IA 50010-1010

View larger version (20K): [in this window] [in a new window]   Fig. 1. Monthly (a) maximum air temperature and (b) precipitation distribution during 2003 and 2004 growing seasons for the research site from a nearby weather station.

View larger version (27K): [in this window] [in a new window]   Fig. 2. (a) Soil moisture, (b) soil temperature, and (c) CO2–C emission rate measured in exposed subsoil planted to three cropping systems in 2003: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation with corn planted in 2003. Soil temperature and soil moisture were measured at the 5-cm depth. * Dates CO2–C emissions were different at P 0.05.

View larger version (29K): [in this window] [in a new window]   Fig. 3. (a) Soil moisture, (b) soil temperature, and (c) CO2–C emission rate measured in exposed subsoil planted to three cropping systems in 2004: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation with soybean planted in 2004. Soil temperature and soil moisture were measured at the 5-cm depth. * Dates CO2–C emissions were different at P 0.05.

View larger version (35K): [in this window] [in a new window]   Fig. 4. Cumulative soil CO2–C emissions from exposed subsoil planted to three cropping systems during the growing seasons of 2003 and 2004: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. The crop was corn in 2003 and soybean in 2004 in the corn–soybean rotation. Means with the same letter within each year are not different at P 0.05.

View larger version (11K): [in this window] [in a new window]   Fig. 5. Microbial biomass C content in the 0- to 15-cm depth of exposed subsoil planted to three cropping systems: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. The crop was soybean for the corn–soybean rotation when the field was sampled. Means with the same letter are not different at P 0.05.

View larger version (20K): [in this window] [in a new window]   Fig. 6. Soil CO2–C emission rates of subsoil planted to three cropping systems during a 77-d laboratory incubation study: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. * Days CO2–C emissions were different at P 0.05.

View larger version (11K): [in this window] [in a new window]   Fig. 7. Cumulative soil CO2–C emissions from exposed subsoil planted to three cropping systems after a 77-d laboratory incubation study: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. The crop was soybean for the corn–soybean rotation when the field was sampled. Means with the same letter are not different at P 0.05.

View larger version (11K): [in this window] [in a new window]   Fig. 8. Net organic N mineralization calculated from pre- and post 77-d soil incubation of exposed subsoil planted to three cropping systems: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. Means with the same letter are not different at P 0.05.