Wednesday, November 15, 2006

Terrestrial carbon sequestration in north central Montana cropland.

Ross Bricklemyer and Perry Miller. Montana State University, 102 Greentree Dr., 102 Greentree Dr., Belgrade, MT 59714, United States of America

This on-farm study was initiated to provide robust regional C sequestration rates in north central Montana cropland by comparing two tillage systems (i.e., tillage and no-till) and two cropping intensities (i.e., fallow-wheat and legume-wheat).  Experimental sites were established at six cooperative farm sites.  The effects of treatments on carbon sequestration rates and crop production were compared on 32-ha fields split into four contiguous 8-ha fields at each farm site. In the continuous crop system (i.e., legume-wheat) a crop was seeded every year and managed according to seasonal water availability. Crops are sampled annually at maturity to estimate crop yield and aboveground biomass, and soil is sampled biannually within each plot. Soil organic C is measured to a depth of 50cm (0-10, 10-20, and 20-50cm) using a five-pointed star pattern with a 10-m diameter. Baseline soil carbon values showed greater variability than soil texture and pH values.  Analysis of carbon change between 2002 and 2004 shows inconclusive results after only two years of a management change.  The plots are scheduled for a four year SOC sampling after harvest in 2006.  Agronomic effects of the treatments showed no statistically significant differences (α = 0.1) in legume crop biomass in 2003.  Wheat crop biomass in 2004 showed that no-till was 9% greater than the tilled system and the continuous cropping system was 72% of the fallow-wheat system.  The 2004 wheat yield results showed similar trends in results as wheat biomass. Wheat protein tended to be higher in tilled and continuously cropped plots.  Crop biomass differences are likely attributable to soil water status differences between treatments. No differences in legume crop biomass or yield occurred between tillage systems 2005.  The amount of cumulative crop residue carbon returned to the soil 2003-5 was greatest in NT and continuous crop plots.