Published online 6 January 2006
Published in Soil Sci Soc Am J 70:306 (2006)
DOI: 10.2136/sssaj2005.0290l
© 2006 Soil Science Society of America
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Comments & Letters to the Editor
Letter to the Editor on "Rank Stability or Temporal Stability"
You-jun Chen
Inner Mongolia Agricultural University, 1328 Mailbox, Huhhot 010018, Inner Mongolia, China
chenyoujun{at}mail.china.com
Because soils are heterogeneous, the effect of scale must be understood to model and predict the behavior of soil properties (Western et al., 2002). The value of a soil property varies spatially and is related within a certain distance. Vachaud et al. (1985) observed the approximate spatial ranking of soil moisture measured at different times. They concluded that "there is a high probability that if a location is the most wet at a given time, it will remain the most wet at other times because it has the highest clay content." The implication is that the order of soil water content of different points will not change with time at a certain probability. This was confirmed by Kachanoski and de Jong (1988), Gomez-Plaza et al. (2000), Van Pelt and Wierenga (2001), Jacobs et al. (2004), Starr (2005), and many other researchers. Pachepsky et al. (2005) and Zhou and Jun (2003) have found that the rank order of soil moisture has some persistence in three-dimensional space. Farahani and Buchleiter (2004) came to a similar conclusion about soil electrical conductivity. Most studies have attributed such order to soil composition and structure.
This means there is a "temporal persistence of a spatial pattern" (Kachanoski and de Jong, 1988), which qualifies as "rank stability" or "order stability." Vachaud et al. (1985) describe this as "the time stability of the rank of individual observations in the probability distribution function of the whole population," and use the term "temporal stability" in the same context. Other authors (Van Pelt and Wierenga, 2001; Farahani and Buchleiter, 2004; Starr, 2005) have used the term "temporal stability" or "temporal persistence," but such usage is unfortunate for the following reasons:
- Stability means that something does not vary temporally or spatially, and in most case "stability" means that "something does not vary temporally."
- The term, "temporal stability," is very ambiguous. Clearly, the meaning is not that time is stable, but something is stable. When we say "the temporal stability of soil water," do we mean that the soil water content does not change with time, or that the rank of soil water content does not change? "Temporal stability" is too broad a term for an accurate meaning.
- Most soil properties are spatially and temporally highly variable; that is, soil moisture content or penetration resistance. Such variability contradicts the term, "temporal stability." The stability is the order or rank of a soil property at different spatial points that does not change at some probability.
The foregoing difficulties are avoided with the terms, "rank stability" or "order stability," which are thus a much better alternative to "temporal stability" in referring to the heterogeneity of soil properties.
REFERENCES
- Farahani, H.J., and G.W. Buchleiter. 2004. Temporal stability of soil electrical conductivity in an irrigated sand field in Colorado. Trans. ASAE 47:79–91.
- Gomez-Plaza, A., J. Alvarez-Rogel, J. Albaladejo, and V.M. Castillo. 2000. Spatial patterns and temporal stability of soil moisture across a range of scales in a semi-arid environment. Hydrol. Processes 14:1261–1277.[CrossRef]
- Jacobs, J.M., B.P. Mohanty, P. Binayak, and E.-C. Hsu. 2004. SMEX02: Field scale variability, time stability and similarity of soil moisture. Remote Sens. Environ. 92:436–446.[CrossRef]
- Kachanoski, R.G., and E. de Jong. 1988. Scale dependence and the temporal persistence of spatial patterns of soil water storage. Water Resour. Res. 24:85–91.[CrossRef]
- Pachepsky, Y.A., A.K. Guber, and D. Jacques. 2005. Temporal persistence in vertical distributions of soil moisture contents. Soil Sci. Soc. Am. J. 69:347–352.[Abstract/Free Full Text]
- Starr, G.C. 2005. Assessing temporal stability and spatial variability of soil water patterns with implications for precision water management. Agric. Water Man. 72:223–244.[CrossRef]
- Vachaud, G., A.P. De Silans, P. Balabanis, and M. Vauclin. 1985. Temporal stability of spatially measured soil water probability density function. Soil Sci. Soc. Am. J. 49:822–828.[Abstract/Free Full Text]
- Van Pelt, R.S., and P.J. Wierenga. 2001. Temporal stability of spatially measured soil matric potential probability density function. Soil Sci. Soc. Am. J. 65:668–677.[Abstract/Free Full Text]
- Western, A.W., R.B. Grayson, and G. Bloschl. 2002. Scaling of soil moisture: A hydrologic perspective. Ann. Rev. Earth Planet. Sci. 30:149–180.[CrossRef]
- Zhou, Q.Y., and S. Jun. 2003. Temporal stability of the spatial distribution pattern of soil water. Acta Pedol. Sin. 40:683–690.
