A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia dasycapa) winter cover crops and fertilization regimes on soil organic matter (SOM) in an irrigated maize-based (Zea mays L.) conservation agriculture (CA) system following four years of continuous practice. Separate plots of oat and grazing vetch cover crops were grown in winter and then maize was planted in all plots in the following summer season. The four fertilization regimes used were: (i) fertilizer applied to the cover crops and the maize crop (F1), (ii) fertilizer applied to cover crops only (F2), (iii) fertilizer applied to the maize crop only (F3) and (iv) no fertilizer applied (F4). Control plots (weedy fallows) were included and the treatments were laid out in a randomized complete block design with three replications. Soil samples from 0-5, 5-20 and 20-50 cm depths were analyzed for total SOM, particulate organic matter (POM) fractions, hot water soluble C (HWC) and C-associated with water stable macro- and micro-aggregates (WSAC). While total SOM was more concentrated in the 0-5 cm soil depth across treatments, a lack of maize fertilization (F2 and F4 regimes) significantly (P
