Decomposition rates soil particle size

In Figure 2.2, the relationship between soil particle size and mineralogy is illustrated qualitatively, demonstrating the prevalence of secondary minerals in the clay fraction. The primary minerals, which originally formed under conditions of high temperature and pressure, are unstable in the soil environment. Consequently, primary minerals, when they are reduced to small particle size by physical weathering, tend to chemically decompose (weather) rapidly. Nevertheless, clay-sized quartz particles persist in soils because of the resistance of the quartz structure to chemical decomposition, as will be discussed later in this chapter, but even this mineral eventually dissolves as silica is leached from the soil. Thus we see that reaction rates... 

CDU in pure form is a white powder. It is made slowly available to the soil solution by nature of its limited solubihty in water. Once in the soil solution, nitrogen from CDU is made available to the plant through a combination of hydrolysis and microbial decomposition. As with any CRE which is dependent on microbial action, the mineralization of CDU is temperature dependent. Product particle size has a significant effect on CDU nitrogen release rate. Smaller particles mineralize more rapidly because of the larger surface contact with the soil solution and the microbial environment. The rate of nitrogen release is also affected by pH because CDU degrades more rapidly in acidic soils. 

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