Use of crop residues for biofuel production raises concerns on how removal will impact soil organic carbon (SOC). Information on the effects on SOC is limited and requires long-term experimentation. Fortunately, Pendleton long-term experiments (LTEs), dating to the 1930s, provide some answers. This study compared crop residue inputs and SOC balance in conventional tillage (CT) winter wheat (Triticum aestivum L.) - summer fallow (WW-SF) systems with annual rotation of WW and spring pea (Pisum sativum L.). The WW-SF consisted of Crop Residue (CR-LTE) (0-90 N ha-1 yr-1, 11.2 Mg ha-1 yr-1 of steer manure and 1.1 Mg ha-1 yr-1of pea vines additions, residue burning) and Tillage Fertility (TF-LTE) (tillage - plow, disc, sweep and N(0-180 kg ha-1)). Winter Wheat-Pea (WP-LTE) rotation treatments included Maxi-Till (MT-disc/chisel), Fall Plow (FP), Spring Plow (SP), and No-Till (NT). Soils were sampled (0-60 cm depth) at 10-yr intervals, and grain yield and residue data collected every year. In WW-SF systems, SOC was maintained only by manure addition and depleted at a rate of 0.22 to 0.42 Mg ha-1 yr-1 in other treatments. In WP-LTE, MT, FP, SP, and NT treatments increased SOC at the rate of 0.10, 0.11, 0.02, and 0.89 Mg ha-1yr-1, respectively. Minimum straw biomass to maintain SOC (MSB) in the CR-LTE, TF-LTE, and WP-LTE was 7.8, 5.8, and 5.2 Mg ha-1yr-1, respectively. WW-SF straw production was lower than MSB, therefore residue removal would exacerbate SOC decline. Harvesting straw residues under NT continuous cropping systems is possible when MSB and conservation requirements are exceeded.