113. 



|?0/ of pore spRce per cubic foot gives 30,.; of i , The opti- 

 mum content lies between 4Q/..' and o(X of filling up, equivalent to at. oat 

 2 l j/' of the volume or l^",/ w.^-ter. Ordinnry noil has IQ-l^ ,-r per cu- 

 bic foot. 



1 cu.ft solid dirt -^0/f water 



1 M H water 60| (or 62.^,i : , more precisely) 



1 cu.ft.ciirt (porous) 75# wr.ter. 



In etrting the ^ci stare content of soils five different methods 

 r e been used. "rose ni 



1) in terr.s of Vnscd on the dry wtd^it of the soil. 



2) In t - on th ' " . 1. 



3) In trrms of ' of volume on the tot?.! volume 

 occupied by the soil. 



4} In cubic inches por efcbic foot, or cuhic centimeters per 

 liter or '">or cui i. c 



^) In inches in depth o:'. 3r over the surface of soil. 



140. 



'"or a dl ion of the- .hods see Lyon & Fipp^n, pages 138- 



re readily xilled by inundation, or too much water, es- 



pecially wont fa] nts. It Is a Eia-tcr of general experience that for 

 for most f.^TT/i crovs the saturated condition of th . soil is unfavorable 

 to the bc~t development. , of course, many plants whicli are 



r.ted to 'ionr,, as for ux?aiaple the swamp type of vegetation. 



About the c enltiYnted crops of sort arc rice ^.icl cranberries; 



, r oak, . , - . j.ress arid the syca-Tiorc c,^ also stand 

 . Other plants and trees will be killed in one season if flooded, 



building of a darn, no happened at Ann Arbor a couple of decad- 

 es = {o, on the Huron River. 



Practically -11 of the cormnon cultivated crops, from vegetables 

 to fruit t: 3,re p:i' ; r;tc:d to ;> rov,ing in soil froi;i *;jich the gravita- 

 tional moistur." hso b en removed. The gra.yitatioaal water is directly 

 injuri; growth of Dies: plants, and its practical removal from 

 the soil constitutes the practice of a^ricul Laral drainage, which may 



as a phsse of ?oil nianage^ent. It may therefore be stated 

 th-'t grp.vit-'tion-l -- -t--r in the root zone is injurious to most farm 

 crops, and consequently it is in n sense unavailable. It is the film 

 or cs.pillp.ry r which supports plants. 



Gravitational water nny be defined as that portion in excess of 

 the hygroscopic and cn.pillary cppacity of a soil. It is not reta/ined 

 by the s^me forces, and is, therefore, free to move under the influence 

 of gravity, in so f'-r ae the condition nnd tlie character of the soil will 

 permit. Vhe amount of grc.vi tio]i--;l \v- ter depends on the total pore space 

 of the soil on one hn.nd, ana on the total hygroscopic n/iu capillary ca- 



e on the other hand. It is the difference between trie tots! c 



city of tb-? roil for water, and thai hold in the other tv;o forms. It s 

 .ed by Lhn r, amount v#hic}i will flow from a soil havi/,, 11 ito pores 



ir,h vnter. Under such conditions the soil is said to be satura- 

 ted. Tho.t pln,ne in the soil to vhich level all of the pores are filled 

 with v, f -. ter--r> ^ed--is kno\ s /n HS the water-table, 'ill is region of sa- 

 tur-"j~.ion is rone Times kn ; the t4 giound-v/ater2. 



Cjr.vit'''; io 

 en it exists 



-.l ; ter is directly injurious to upland crops, but 

 depth o-f 4-6 feet below the surface, it may serve 



