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Dirt, Soil, and Compost


This past Easter, the temperatures were warm and wonderful. Many gardeners took advantage of the weather to pick up their soil, which is not the same as dirt and not the same as compost. 


Geomorphologist and University of Washington professor of earth and space sciences David R. Montgomery informs us that "good soil is not just dirt." It is a "biological orgy recycling the dead back into new life" (David R. Montgomery. Dirt: The Erosion of Civilizations. Berkeley: University of California Press, 2007 p. 1). 



Dirt may contain organic matter and earth materials of various sizes. When we look at particle sizes, coarse sand is the largest, followed by fine sand, silt, and clay. Clay's actual particle size is not visible because it is too small to be seen with the naked eye. 



According to Soil Taxonomy, second edition, soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment. In short, soil is alive and dirt is not.



Compost is the end product of a controlled, aerobic (oxygen-required) process that converts organic materials into a nutrient-rich, biologically-stable soil amendment or mulch through natural decomposition. Compost does not replace fertilizer and the nutrients available in compost vary.


Aged manure is composted animal waste. Manure provides nutrients that vary depending on the type of manure used.


Both compost and manure are good products; however, more is not necessarily better.

Compost enhances soil structure by increasing aggregation, aeration, and drainage, especially in compacted or sandy soils. Compost improves root penetration and allows better water infiltration, reducing runoff and erosion. While compost is a valuable source of nutrients, its nutrient content may not match plants' specific needs. Some plants may require supplemental fertilization with specific nutrients not adequately provided by compost alone.


Manure is rich in essential nutrients such as nitrogen, phosphorus, and potassium, which are crucial for plant growth. However, improper manure application can lead to nutrient imbalances in the soil, potentially causing nutrient runoff into waterways and contributing to pollution.


Overall, while compost and manure offer several benefits as natural fertilizers and soil amendments, they require careful management to mitigate potential drawbacks such as nutrient imbalances. Proper application practices are essential to maximize their benefits while minimizing risks to the environment.

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