Sustainable management of low fertile arid soils using carbon-rich organic amendments such as biochar and compost is of great concern from both agricultural and environmental points of view. The impact of pyrolysis, composting, and co-composting processes of different feedstocks on carbon loss and emissions, soil properties, and plant growth in arid soils with low organic matter content has not been sufficiently explored yet. Consequently, the aim of this work was to 1) investigate the effects of the pyrolysis, composting, and co-composting processes on the properties of the produced biochar, compost, and co-composted biochar from rice straw (RS) and sugarcane bagasse (SB), and 2) examine the impact of addition of RB biochar (RSB), SB biochar (SBB), RS compost (RSC), SB compost (SBC), co-composted RS biochar (RSCB), and co-composted SB biochar (SBCB) at an application dose of 10 ton/hectare on soil properties, carbon emission, and growth of zucchini (Cucurbita pepo) in a sandy arid soil. Carbon loss (kg C kg(-1) feedstock) was significantly (P < 0.05) lower during the preparation of the compost (90.36 in RSC, 220.00 in SBC) and co-composted-biochar (146.35 in RSCB, 125.20 in SBCB) than in biochar (176.5 in RSB, 305.6 in SBB). The C/N ratios of the compost and co-composted biochar (11-28.5) were narrower than the corresponding values of biochars (48-90). All amendments increased significantly soil organic carbon content (2.5 in RSC to 5.5 g kg(-1) in RSCB), as compared to the non-amended control (1.2 g kg(-1)). All amendments, particularly RSCB, increased significantly (P < 0.05) the zucchini seed vigor index, dry weight, total chlorophyll content, and root and shoot length, as compared to the control. Moreover, RSCB was the only amendment that showed a positive soil carbon balance. The modified integrated two-way ecological model data also indicated that the co-composted biochar, particularly RSCB, is a promising amendment to improve soil quality and plant growth in sandy arid soils. However, those data should be verified under field conditions.