Soil is composed of minerals, soil organic material (SOM), water, and air, according to Ann McCauley, a soil scientist at Montana State University. The actual composition of these various components in the soil has a great influence on porosity; that is, composition influences the movement of water in and through the soil (McCauley, 2005), and the movement of water in and through the soil is absolutely necessary for productive crops and healthy ecosystems. The bond between soil particles is called “aggregation” and as water passes through the soil the aggregation, if it is healthy, will keep porosity and water movement slow and productive, which “improves fertility and sequestration of carbon in the soil” (avoiding erosion at the same time) (McCauley). McCauley explains that pores in the soil have a number of important functions. Coarse soil will have many pores and fine textured soils; because they are “more tightly arranged” they have smaller pores. When soil has been cultivated for a long time, its porosity decreases due to the decrease in soil organic material, McCauley continues. When there is a lot of crust on the soil surface and compaction, it decreases porosity and “inhibits the entry of water into the soil” (McCauley). And when there is crust and water cannot penetrate the soil, erosion and rapid water runoff are evident. On the other hand, in Montana, when the soil has good porosity, water can pass through the surface layer and fill the pores until they are saturated. Some of that water will “drain freely from the soil by gravity,” and some will be held in “micropores” (called capillary forces), to be removed by plant roots that absorb it (“absorption”) or evaporate. .... middle of paper ... interact in ways that support both soil and crops or other vegetation, regardless of where on the planet this interaction might occur. In Montana, understanding the importance of soil porosity can help prevent farmers from over-farming; and in Brazil, where tree canopy ecosystems are being burned in favor of grassy savanna, understanding these dynamics helps agricultural professionals and farmers in their efforts to maintain balanced and productive soils. Works Cited McCauley, Ann, and Jacobsen, Jeff. Fundamental properties of soil. Retrieved June 10, 2011, from http://landresources.montana.edu/swm/PDF/Final_proof_SW1.pdf. (2005). Oliveira, R.S., Bezerra, L., Davidson, E.A., Pinto, F., Klink, C.A., Nepstad, D.C., and Moreira, A. “Function of Deep Roots in Soil Water Dynamics in Central Brazilian Cerrado Savannas . Functional Ecology, vol. 19 (2005): 574-581.