This article is written in ordinary English, rather than mathematical, technical and scientific terms. It does not go into the electrostatic behaviour of clay particles. Nor does it cover the degree drying out when wilting occurs, reducing transpiration), and remaining soil moisture serves to maintain plants in drought mode. That period of semi-dryness so important for bulbs lasts longer in small particle soils than in granular, when soils are drying out and bulbs are 'dormant' http://noble.org/ag/soils/… On 15 May 2015 at 16:49, penstemon <penstemon@q.com> wrote: > > > >By observation, as well as my understanding however, clay does retain more > moisture, and for longer, than sand does, when wet and in a drying > environment. > > "The curve shift from sand to clay, causing [the soil water modifier] to > fall earlier in clay, but not as rapidly as in the sand, reflects the > differences in the hydraulic characteristics of soils with different > proportions of clay. At a given soil water content the water potential of > clay is significantly lower than in sandier soils ...." > This describes drying clay as being too dry for plants to continue growing. There is some (unavailable) moisture locked in the clay, but none in the sand which dries faster. > In arid and semi-arid climates, evaporation exceeds percolation in clay > soils. Deep penetration of water in clay is caused by gravity: the weight > of water on top of more water. So a couple of cm of rain falling on clay > doesn’t go much of anywhere unless it is followed by more rain. > "So, in a habitat where the soil is clay, a bulb would only get water from repeated “infiltration events” over a relatively short period of time. When the rain or snow melt stops, the soil dries out to the consistency of concrete." Agreed, bulbs sealed in the dry clay are protected from both dessication and flooding. In sand they can both dessicate, and flood with light rain which does not penetrate the clay. Peter (UK) <http://pacificbulbsociety.org/pbswiki/> _______________________________________________ pbs mailing list pbs@lists.ibiblio.org http://pacificbulbsociety.org/list.php http://pacificbulbsociety.org/pbswiki/