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Perennials Use in Agriculture for Improving Soil Health



I. Soil Physical Quality

i) Capacity to Accept, Hold, and Release Water	A soil’s capacity to accept, hold, and release water is ameliorated by perennial plant’s rooting system being permanently in place. By not being pulled out of the earth each season, this rooting system improves a soil’s physical structure over time. Roots tunnel the soil, which increases water’s rate of infiltration. Within the soil matrix, root tunneling provides channels for water to drain through the profile. This tunneling also improves soil structure, which further provides a network of channels for water to drain through. When these roots die, their decomposing roots increase soil organic matter. Organic matter has multiple benefits to the soil in terms of physical quality. The negative electromagnetic charge helps to create aggregates for better soil structure. Moreover, organic matter is able to retain water to be used by plants.	While plant roots of all kinds provide these beneficial aspects, what makes these soil improvements particularly beneficial is their development over time. With each passing year, these physical quality improvements are compounded. In addition, perennial crops require less management; as a result, overland machinery is not used to the same extent as seasonal crops. Hence, compaction and tillage are diminished. These practices damage soil structure, which would decrease the efficiency of drainage, infiltration, and soil structure development.

ii) Capacity to Facilitate Gas Exchange	This root tunneling network improves a soil’s relationship with air as well as water. Plant roots require oxygen in the soil in order for respiration.

iii) Capacity to Accept, Hold, and Release Nutrients	The accumulation of dead roots adds organic matter into the soil. This soil organic matter (SOM) is extremely fertile since it is made of decomposing organic tissue, which is built of nutrients necessary for plant growth. Hence, this SOM adds plant nutrients back into the soil like Nitrogen, Phosphorus, Potassium, Magnesium, and Calcium. Since perennials exists year-round in the soil, they are able to add much more SOM than annual plants.	SOM possesses a negative charge and has a high specific surface area. Chemical reactions occur on surfaces and this negative charge is able to attract positively charged plant nutrients. This phenomenon of how many cations can be held on a negative soil particle surface is called Cation-Exchange Capacity (CEC). This combination of more plant available nutrients, greater surface area, and a higher CEC improves a soil’s chemical quality and overall fertility for plant growth.

iv) Capacity to Resist Erosion	Erosion occurs due to the dislocation of soil particles by running water overland or high winds. When particle dislocation is resisted, erosion is less likely to occur.	With better soil structure, drainage, and infiltration, water is less likely to pool on the soil surface and runoff with soil particles. In the event of high winds, the rooting system anchors the soil in place and resists the wind’s force.	Perennial plant cover shelters the topsoil from the impact of high intensity rain. Foliage provides a barrier between the rain and the soil. Rather than rain hitting the soil with a high impact, it hits foliage first and diminishes its velocity. Rainfall directly onto soil can increase soil particle dislocation. Given a perennial protective barrier from plant cover, this dislocation is minimized.

v) Capacity to Sequester Carbon	Given the year-round nature of perennials, they are able to absorb more carbon dioxide out of the atmosphere and sequester carbon in the soil via their plant roots, which are constantly shedding. This accumulation of dead roots improves the soil fertility in turn as discussed above.

vi) Capacity to Optimize Soil Fauna Health	Perennial plant’s combination of improving physical and chemical quality in the soil provide a hospitable environment for soil fauna. Given good drainage, good aeration, and an abundance of SOM, soil fauna have adequate water, oxygen, and nutrients to thrive.	Perennials also tend to outcompete weeds and help with pest control, which reduces the usage of herbicides and pesticides. These synthetic chemical inputs damage soil chemical and biological quality; their absence is thus a benefit. Perennials control weed populations because once they are established they are able to outcompete weeds easily. Pests are controlled by toxins and chemicals produced by perennials (Lewis et al., 1997).

References: - Lewis, W. J., J. C. Van Lenteren, Phatak, S. C., & Tumlinson, J. H. (1997). A total system approach to sustainable pest management. Proceedings of the National Academy of Sciences of the United States of America, 94, 12243-12248.