APUtL 30, 1908. 



The Weekly Florists' Review* 



^i^'^'^yy^"^ ■^ -^ ' 



"^->^ ^-^V-^ <» *«^>--x^'^'v^*-^«^-^».'^^^- 



i 

 S 



I 



SOIL AND 

 THE FLORIST 



Proper Drainage* 



The discussion of the composition, 

 structure and availability of plant foods 

 in soils (see page 13 of the Review for 

 December 26) brings me to consider a 

 principle underlying proper land drain- 

 age. It is very important that when 

 rain falls upon a field the excess water 

 remain only just long enough on its way 

 through the open water passage to sat- 

 urate the soil; anything longer than this 

 provides time and opportunity for the 

 most valuable plant food materials car- 

 ried in the water films about the soil 

 grains to diffuse out into the moving 

 water and so become lost in the drainage. 

 Thus we have an explanation of a seem- 

 ing paradox — namely, properly drained 

 fields lose less of their soluble plant 

 food by under-drainage than do those 

 poorly drained. 



Next in importance to the internal 

 soil surface, among the physical factors 

 which determine the productive capacity 

 of soils, is the segregation of their soil 

 particles into granules, crumbs or ker- 

 nels. Without it, all but the extremely 

 sandy soils must be sterile, even though 

 they carry an abundance of plant food. 

 Without segregation we have the pud- 

 dled clay, but with segregation highly 

 developed we have the light, deep, trac- 

 table, mellow, fertile loams so congenial 

 to the widest range of crops. 



Lack of Available Moisture. 



The low-producing power or absolute 

 sterility, so invariably associated with 

 puddled soils and with those too close in 

 texture, we believe to be due primarily 

 to a lack of available moisture, not- 

 withstanding the seeming paradox that 

 they are carrying an excess of it. It is 

 a familiar fact that crops wilt and cease 

 to grow in close-textured, clayey soil 

 still carrying eight to twelve per cent 

 of water, while they may grow luxuri- 

 antly in a coarse sandy soil possessing 

 but one to three per cent. So, too, we 

 often find desert types of vegetation 

 growing in humid climates on extremely 

 close-grained clayey soils and, more 

 strangely still, in peat swamps where 

 the water content is excessively high. To 

 understand thQpe facts it must be re- 

 membered that there is a certain thick- 

 ness of water film which is held so firm- 

 ly to soil grain surfaces as to be wholly 

 unavailable to the crop. Portions of 

 this layer cannot be driven off complete- 

 ly, even at the temperature of boiling 

 water. When all of the facts shall have 

 been worked out and demonstrated, we 

 believe it will be found, that ^the thick- 

 ness of the unavailable layer of water 

 about the surface of soil grains is es- 

 sentially the same whether these be 

 large, as in the coarse sandy types, or 

 yery small, as in the finest clays; and 

 if this is the case the absolute amount 

 of unavailable water must increase as 

 the internal surface of the soil becomes 



A paper by Prof. F. H. King, of Madison. 

 yi 18., read before the Congress of the National 

 <-ouncll of Horticulture. 



greater and as the diameter of the soil 

 particles decreases. 



Sandy and Clay Soils G>ntrasted. 



The coarse sandy soils, with their rela- 

 tively small internal surface, carry a 

 correspondingly small amount of unavail- 

 able water and hence in them small rain- 

 falls in dry times have a relatively high 

 eflBciency. So, too, must soluble plant 

 food and fertilizers, when applied to 

 them, and for the same reason, have a 

 relatively high eflSciency. But in the 

 finest clay soils, especially if they are 

 not strongly granulated, the amount of 

 unavailable water is very large and hence 

 it is that heavier rainfall during drought 

 periods and more liberal applications of 

 fertilizers are required to produce the 

 same relative increase, but it is possible 

 to have the finest clay soU so complete- 

 ly puddled, or separated into its ulti- 

 mate grains, and the effective soil sur- 

 face thereby so enormously increased by 

 the minuteness of the particles, that 

 nearly the whole of the water, even when 

 the soil is saturated, becomes unavail- 

 able to plants and for the simple reason 

 that the water films are too thin and 

 therefore too strongly held to be re- 

 moved. From the standpoint of plant 

 function we have the paradoxical condi- 

 tion of a sandy soil containing perhaps 

 one per cent of water being effectively 

 more moist than a puddled clay soil con- 

 taining twenty to thirty per cent, or 

 than a peaty soil containing perhaps for- 

 ty or fifty per cent. 



But when the finest clay soils are put 

 in a highly granular condition, with 

 the kernels having the order of coarse- 

 ness of the sandy soils, these compounu 

 grains may themselves become invested 

 with water films which are thick and 

 therefore available to crops. By such a 

 change in structure, therefore, the clay 



soils not only retain their enormous sur- 

 faces to carry water in which plant food 

 may develop and accumulate, but by the 

 bunching of the fine particles there has 

 been superadded to the already enor- 

 mous surface an additional large area 

 which now is able to retain much water 

 in available form and so fortunately 

 placed that the plant food from the 

 moisture within the soil kernels can dif- 

 fuse out into the available film and thus 

 also become available to the crop. 



Openness of Structtire* 



Tilth, or the physical condition of 

 the soil, then, must be of very great im- 

 portance in determining the productive 

 capacity of fields, first of all because it 

 limits the availability of the soil mois- 

 ture and through this, at the same time, 

 the availability of plant food itself. 

 Without the coarse-grained texture and 

 openness of structure there must be im- 

 perfect drainage, inadequate soil ven- 

 tilation and a lack of freedom for move- 

 ment and of room for the proper devel- 

 opment of either the roots of crops or the 

 multitude of soil organisms whose activ- 

 ity is so indispensable to the mainte- 

 nance of soil fertility. The full sig- 

 nificance of this openness of structure 

 may be better appreciated when it is 

 stated that exact measurement has shown 

 that when soils of the coarse sandy, 

 loamy and the finest clay types are re- 

 duced to their single grain condition 

 the rates of air and water movement 

 through them become as 900 to thirty- 

 six to one ; the flow being 900 times more 

 rapid through the coarse sandy soil than 

 through the finest clay type, rut in 

 another way, if 2.5 hours are required to 

 remove an excess of rainfall from a 

 coarse sandy soU, then four months 

 would be insuflBcient to effect the same 

 result in a field of the finest clay type 

 when in the condition of its single grain 

 structure, while some four days would be 

 required for the loamy soils, and this is 

 longer than the average interval between 

 rains in humid climates. More than this, 

 in the properly open soil there are but 

 2.5 hours between rainfalls during which 

 diffusion can carry the soluble plant 

 food into the water draining away, while 

 in the other conditions this loss by 

 drainage is continuous. 



(To be continued.) 





Gunpanula Glomerata Dahurica* 



