Machado, Stephen (Oregon State University, OSU, CBARC, Box 370, Pendleton, OR, 97801; Phone: 541-278-4416; Fax: 541-278-4188; Email: firstname.lastname@example.org)
S. Machado *, S. Petrie, K. Rhinhart
Soil carbon (C) is essential for sustaining crop productivity. In agricultural lands, carbon (C) sequestration is directly influenced by cropping systems. Tillage, crop rotations, and cropping intensity influence the rate at which C is added and removed. Cropping systems that result in the C gain and sustained soil productivity should be developed. Determinations of sustainability, however, take many years and require long term experimentation. The Columbia Basin Agricultural Research Center (CBARC), near Pendleton Oregon, is home to the oldest agricultural experiments in the Pacific Northwest (PNW) with some of the experiments dating back to 1931. These experiments have different tillage, cropping intensity, and crop rotation treatments that can shed light on soil productivity and sustainability. To determine the effect of these cropping systems on sustainability, soil samples were taken at 0-10, 10-20, 20-30, and 30-40-cm soil depth profile from the grass pasture (GP) that has not been cultivated since 1931, fertilized (100 kg N ha-1) and unfertilized plots of the continuous conventional tillage winter wheat (CTWW) monoculture initiated in 1931, the conventional tillage wheat/fallow (CTWF) experiment initiated before 1984, and from the fertilized (112 kg N ha-1) and unfertilized plots of continuous no-till winter wheat (NTWW) experiment initiated in 1997. The samples were analyzed for soil organic matter (SOM) at AgriCheck (Umatilla, OR), a commercial soil testing laboratory. Soil organic C (SOC) was estimated by dividing % soil organic matter by 1.724. In the 0-10-cm soil depth profile, uncultivated plots had higher SOC than tilled plots. The highest level of SOC (3.0%) was observed in GP, followed by fertilized NTWW (2.0%), unfertilized NTWW (1.93%), fertilized CTWW (1.86%), unfertilized CTWW (1.78%), and CTF (1.47%) in the 0-10-cm soil depth profile. Fertilized CTWW had the highest SOC (2.07%) followed by GP (1.80%), unfertilized CTWW (1.73%), the NT plots (1.36-1.41%) and lastly the CTF (1.09%) in the 10-20-cm soil depth profile. The trend was similar for the 30- and 40-cm depth profiles. Results indicate that NT cropping systems sequestered more C in the top soil than tillage treatments. More C was stored at lower depths in continuous cropping systems under tillage. Fertilization increased SOC by an average of 0.34%. Among tillage systems, continuous cropping significantly increased SOC compared to fallow at all soil depths. To sustain soil productivity, therefore, fallow should be replaced by continuous cropping and NT. Practicing NT for only 6 years resulted in significantly higher SOC at all soil depths than CTF for more than 24 years. Based on these results, it is recommended to intensify crop production and practice NT to sustain soil productivity.