Liquid agricultural compositions comprising pasteurized Chlorella cells, as well as methods of preparation and use thereof, are disclosed. The compositions are formulated for application to a plant, seed, seedling, or soil and are effective in enhancing at least one plant characteristic including, but not limited to: seed germination, seedling emergence, seedling size, plant fresh weight, plant dry weight, utilization, leaf production, leaf formation, thatch height, plant maturation, plant yield, plant growth, plant quality, plant health, plant resistance to salt stress, plant resistance to heat stress, plant resistance to heavy-metal stress, plant resistance to drought, maturation time, yield, root length, root mass, color, fruit production, fruit yield, fruit growth, and fruit quality.