Perennial crops are crops that – unlike annual crops – don't need to be replanted each year. After harvest, they automatically grow back. By eliminating replanting, perennial cropping can reduce topsoil losses due to erosion, increase biological carbon sequestration due to reduced soil-disturbing tillage, and greatly reduce waterway pollution through agricultural runoff due to less nitrogen input.
Mechanisms
Erosion control: Because plant materials can remain in place year-round, topsoil erosion due to wind and rainfall/irrigation is reduced
Water-use efficiency: Because these crops tend to be deeper and more fibrously-rooted than their annual counterparts, they are able to hold onto soil moisture more efficiently, while filtering pollutants traveling to groundwater sources.
Nutrient cycling efficiency: Because perennials more efficiently take up nutrients as a result of their extensive root systems, reduced amounts of nutrients need to be supplemented, lowering production costs while reducing possible excess sources of fertilizer runoff.
Light interception efficiency: Earlier canopy development and longer green leaf duration increase the seasonal light interception efficiency of perennials, an important factor in plant productivity.
Carbon sequestration: Because perennial grasses use a greater fraction of carbon to produce root systems, more carbon is integrated into soil organic matter, contributing to increases in soil organic carbon stocks.
Example crops
Miscanthus giganteus - a perennial crop with high yields and high GHG mitigation potential.
Perennial sunflower - a perennial oil and seedcrop developed through backcrossing genes with wild sunflower.
Perennial grain - more extensive root systems allow for more efficient water and nutrient uptake, while reducing erosion due to rain and wind year-round.
Perennial rice - currently in the development stage using similar methods to those used in producing the perennialized sunflower, perennial rice promises to reduce deforestation through increases in production efficiency by keeping cleared land out of the fallow stage for long periods of time.
