Measurements of water retention and pore‐size distribution for a soil are time consuming and affected by changes in aggregate‐size distribution. A method of compared distribution curves was used to relate distributions of pore size (PO), particle size (PA), aggregate size (AG), and pore size from water retention (WR). Seven surface soils varying in texture and aggregation were tested. After normalization to 100% volume, the pore‐, particle‐, and aggregate‐size distribution, as well as water‐retention (converted to pore diameter) curves were each fitted to a linearly transformed logistic function to evaluate their interrelations using R(m/n), a coefficient for the ratio of the diameters of component m to component n. Identical distribution curves have an R(m/n) value of 1. The R(PO/PA) and R(WR/PA) for the seven soils ranged from 0.25 to 2.26 and from 0.18 to 1.34, respectively, indicating that the theoretical packing parameters of 0.225 to 0.414 do not hold for PA distribution. The R(PO/AG) ranged from 0.06 to 0.23 and R(WR/AG) from 0.04 to 0.16. Both ranges of R values smaller than the theoretical packing parameters suggests interactions may occur between large and small aggregates. However, R(PO/AG) and R(WR/AG) values were more consistent and were significantly related to aggregation level and bulk density, suggesting that AG distribution should be used as a parameter to predict PO distribution and water retention. Comparisons between water retention curves and PO distributions from Hg intrusion gave R(PO/WR) ranging from 0.78 to 2.59, showing that equivalent PO for a given soil is not the same when different measuring methods are used.

The purpose of this study was to determine the rate of dissolution and migration of phosphorus from granular superphosphate under different soil conditions. The effect of variation in soil type, soil moisture, compaction, and soluble phosphorus level in soils was considered. Laboratory studies were conducted in which fertilizer granules and tablets were placed in soils for varying time periods, after which the remaining phosphorus in the recovered granule and in the soil was measured by chemical or radioactive isotope techniques. Rapid dissolution of phosphorus from fertilizer granules in contact with moist soil was experimentally verified. At field capacity moisture contents, 50 to 80% of water soluble phosphorus moved out of the granules in 24 hours. Even in soils as low as 2 to 4% moisture, approximately 20 to 50% of the phosphorus moved from the granule into the soil in a one day period. It was found that both commercial and experimental superphosphate 4–8 mesh granules had a strong tendency to absorb moisture when placed in a saturated atmosphere. In relatively dry soils, moisture is drawn from the soil mass toward the granule, thereby forming a moist shell. The degree of soil compaction around the granule affects the rate of fertilizer dissolution. However, differences in compaction were found to have less effect than variations in soil moisture. Placing radioactive fertilizer granules in soils with extremely high available phosphorus contents or in contact with non‐radioactive superphosphate did not markedly reduce the rate of dissolution of granular phosphorus. Migration studies showed that phosphorus moved very little under the conditions studied. Maximum movement of about one inch occurred at soil moistures approximating field capacity on three soils. Most of this movement took place in the first week of a 4‐week period. Compacting soil tended to increase both dissolution and migration of fertilizer phosphorus. The larger the superphosphate granule, the more extensive was phosphorus migration.

Perched water tables on hillsides located on the western border of the Willamette Valley in Oregon in some cases have the potential to transport pollutants from either domestic or agricultural sources downslope to streams, ponds, or reservoirs, resulting in the deterioration of the quality of these waters. In this paper, some factors responsible for the development and longevity of these potentially problem‐causing perched water tables on three hillsides were examined. Analyses of hydraulic conductivity data and the relationships between rainfall, soil water pressure potential, and time suggest that permeable rock below 110 cm rather than clayey B horizons is mainly responsible for the development of perched water tables on upper convex slope positions on two of these hillsides. The data also suggest that subsurface flow from the upper convex regions contributed significant amounts of water to the lower convex slope positions. Further, perched water tables developed more rapidly, to a greater extent, and lasted longer in upper horizons of a lower concave region of slope where a shallow perched water table was already present at the onset of rainfall. Finally, perched water tables did not develop in the upper horizons on a third hillside that had no impermeable regions in the soil or upper rock mantle.

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