'i'lir rcsiilts obtained \Yere as iollows : ' Y < j t n lbroiiiiiie :thsorptioti.
Dry, ordiiiary conditioti. ........... I 1 0 . 2 I O cc. x t t e r , ordinary temperature.. 10S.6 I O cc. water, cooletl ................ 109,s I O cc. water, heated ................ I 12.2
13runiiiie Broiiiiiie addition. wbstitutioii. l0j.S 2.7
104.0
2.3 2.9
10.3 .0
j.O
104.0
It is noteworthy that the results appear to be but slightl!.
:iffcctcd by the variations introduced and particularly that thc 1)restvicc of \rater seems to be i\-itliout serious effect.
FIXATION OF PHOSPHORIC ACID IN THE SOIL. B Y J . 'I C K A \ \ I , I > Y .
11% has been lilio~\-Iifor a long time that when soluble phos1)liatc.c arc applied to the .soil. the!- Imoiiie fixed 1)y the bases, linic, iron. ctc.. ant1 arc iiot Icachetl from the soil to any very cci:isitlerable extent by rain or irrigation waters. T:y this process \vater-solul)le phosphoric acitl is "rcvcrted" or chaiige'l to a combiiiatioii not soluble in Ivater. This is akin to the fisation of potash a n d ammonia. which arc cliaiigcztl into insoluble combinations i n the soil. This is a \vise provision u i nattirc aiicl prcwiits salts and bases in the soil which have been rentlcrctl soluble b!. \\-eatliering atit1 other agencies from being nashed out and lost from the soil : aiidit enables the agriculturalist to apply certain forms of s o l ~ b l e fertilizers to grojyiiig crops ivithout fear of losing them in thc tlrainage ivaters. 1:ut \\.hat liecomes o f the \\-ater-soluble pllosphoric acitl applietl as a fertilizcr : is it fixed near the surface, or is it well distributetl throughoiit tlic soil where tlic roots of plants can get it ? T h e following investigation {vas imclertalien for the purpose of (leterniiniiig to what extent \vater-soluble phosphoric acid is tlistributetl through the soil before it becomes fisetl. In certain sections o f these islands the cane grows by irrigation : in other scctioiis the rainfall is ample. \\'here irrigation is practiced the so1ul)le fertilizer is scattered along tlic cane rmv. in some cases covered, in other cases iiot. ant1 foilon-et1 1111 within a day or two 1 ) ~ .in-igatioii. Three or four iiiches of ivater ~voidtlreprcsent an
FIXATION O F P H O S P H O R I C ACID I N T H E SOIL.
II
I5
average irrigation. Usually the water disappears in the soil within twenty o r thirty minutes of application. \\'here rainfall is depended upon, fertilizers are covered up. APPARATUS A N D METHODS.
T h e most conclusive and determinate method would be to apply phosphoric acid in watcr solution to the soil, antl then, by making analyses of the soil, find where it has been fixed. This, however, is not practical since o u r chemical methods are not sufficiently delicate to detect slight differences in the amouiit of this acid, and \\ere a soil analyzed before and after the application of a n ordinary dose of phosphoric acid, this amouiit \\-ouItl not be detected. The I!.simeter methotl is the nest liest ; a given iveight of phosphoric acid is applied to the soil, followed by an excess of water, the drainage water caught antl analyzed. T h e difference between the amount of acid applied antl that found in the drainage is the amount abstracted and held by the soil. Ey varying the depth of soil in this espcriment we find the depth at which the phosphoric acid is held. Boxes, 9 in. cube, were made, several holes bored in the bottom for the purpose of allowing the drainage water to ebcape, ant1 varying depths of soil placed in them. Ten grams of double superphosphate were applied in each casq, which is as large an amount as is applied in the cane roivs to a space 9 inches by 9 inches. In each case 4800 cc. of water jvere atltled, this amount being probably an average irrigation. S o t e s \\ere macle of the time necessary for the water to percolate through the soil, ancT the total time of draining. RKSUL'I'S.
1. Experiments with dark-colored soil from lrakiki. This soil contains more phosphoric acid soluble in weak 1-egetable acid wlutions than any other Hawaiian soil thus far examined. ( I ) S i x inches of soil; water began percolating through the liottom of the soil at end of six minutes, and 1 7 9 cc. of water \\ere recovered within one-half hour, when drainage was practically completed. T h e 1 7 9 cc. of water containetl 0.023 gram P2()., or 0.j 7 per cent. of total applied. ( 2 ) Six inches of soil ; the phosphate \vas coveretl up in the moist soil antl allowed to stand over night. I\-ater began tlrain-
1x16
J . T . CR.iIVLET
ing \\-ithin t n o minutes. and 3300 cc. \\-ere drained in forty minutes, containing Ilut a trace of phosphoric acid.
11. Typical red soil from tlie Honolulu plantation. Six inches of soil ; Ivater began draining in t\vo minutes, ( I ant1 finished draining in fort!. minutes. Recovered 2072 cc. ivater containing 0.1113 grain P,@, or 2.78 per cent. of total applied. ( 2 ) S i s inches of soil containing 20.72 per cent. moisture: phosphate covered up and allon-ed to stand over night ; began draining in three minutes ; finished draining in fifty minutes. 2320 cc. of water were recovered, containing 0.0134 gram P,O, or 0.34 per cent. of total applied. ( 3 j Three inches of soil: began draining in one minute; finished draining in thirty minutes. Recovered 3130 cc. of water containing 0.3j gram P,O, or 8.75 per cent. of total applied. ( 4 ) Three inches moist soil ; phosphate covered up and allowed to stand aver night. 2886 cc. of \ v a t u n'ere recovered, containing 0.0408 gram P,O, o r 1.02 per cent. of total applied. T h e soil and phosphate were allowed to stand two days. T w o liters of ivater ivere poured over it, of which 1700 cc., containing 0.0048 g-ram P,C), or 1-7 per cent. of total applied. lvere recovercd. After standing tn-o days this was subjected to a further leaching. tlie drainage containing hut a trace of phosphoric acid. ( 5 ~) (-)ne inch of soil : began draining in ten secoiltls : finished draining in nine minutes. Reco.i.erztl 4260 cc. u x t e r containing 1.866 gram5 or 46.65per cent. of total applied. ( 6 ( )ne inch of soil : phosphate covered up ailti allo\\-ed to stand four hours before irrigation. Drainage \vater contained 0.274 grain of P,O, o r 6.8j per cent. of total applied. (7) O n e inch of soil : phospliate covered up and allowed to stand over night. Drainage contained 0.2928 gram P,O, o r 7 . 3 2 per cent. of total. Same after standing two days and washing with two liters of water, yield 0.033 gram P,O, or 0.82 per cent of total. Putting these results in tabulated form \ve have :
FIXATIOS
TABLEI.-sHOWING
I I 17
OF PHOSPHORIC A C I D I N THE SOIL. THE AMOUNTO F PHOSPHORIC ACID
HELD BY
THE
SOIL. Depth of soil. Black soil, Inches. when irrigated.
6 6 6 6 3 3 3 I I
I
Immediately After fifteen hours
P.05
retained. Per cent.
Red soil when irrigated.
99.43
....
... . . ..
....
....
100.00
.... .. . .... . . .. .. ..
pop5 retained. Per cent.
Immediately After fifteen hours Immediately After fifteen hours Same after two days Immediately After four hours After fifteen hours Same after two days
97-22 99.66 91.2j 98.98 99.SS 53.35 92.68 99.18
....
From this we see that when the application of the fertilizer is followed immediately by irrigation, ( I ) more than one-half the phosphoric acid remains in the first inch of soil, more than ninetenths in three inches, and practically the whole within six inches of the surface; ( 2 ) when an interval of fifteen hours intervenes between the application and the irrigation, more than nine-tenths of the phosphoric acid is retained by the first inch of soil and practically the whole by the first three inches. These conclusions are rather startling, inasmuch as it has been heretofore believed that water-soluble phosphoric acid, when applied to the soil, becomes pretty well distributed throughout the first eighteen inches or two feet of the soil when it is easily accessible to the roots of the plants. This bears on the question of the relative value of water-soluble and so-called citrate-soluble or "available" phosphoric acid. At the various experiment stations in the United States the same or very nearly the same valuation is put upon the two forms. Where there is a difference it is rarely more than I cent. per pound in favor of the water-soIuble. Certainly on Hawaiian soils where the phosphoric acid becomes reverted at the surface, or very near the surface, the two forms have very nearly the same value, for even under the most favorable circumstances the water-soluble phosphates are disseminated throughout the soil but sparingly. On the other hand, in cases where fertilizers are applied and covered up a few hours before irrigation practically all of the phosphoric acid becomes reverted and remains near the surface. Also on plantations depending on rainfall where the fertilizers are applied and covered up, water-soluble and reverted
phosphoric acid have practically the same value, as the ivatersol~iblebecoiiies rcvertctl a i i t l subseqiieiit rains caiiiiot \vnsli i t clo\vii to the roots of the I)laiits, nor tlisscininate it tlirouglioiit tlir soil. This is a possible esp1:uiation of a fact ivhich I have w t forth in former papers : namely. that phosphates have not slio\vii as gontl rcssults 011 Ihxvaiiaii soils as the other fertilizer itigredicnts --nitrogcii a i d potash. Tt takes considerable cultivation t o (lisseminate thcs phosphates throughout the soil, aiitl although the!. ilia!. 1~ tleficicnt, yet ai1 application is not followctl by the imnictliate results that the planter expects. Slciiig tliat tlic \\.ntcr-solul)lc~~iliospl~oric acitl is talicii 1111 s n readily, a furtlicr csl)criiiiciit \\.as niatlc t ( J clctcriiiiiie the tottrl cnptrcitj. of the soil t o fix pbosl)h(iric acitl. So0 grains c i f ret1 soil aiitl 50 grains ot’ t1oul)le sul)~~rI)lit)sl)liatc~ coiitaiiiing io.jS graiiis uxter-solitblt~ phosphoric acitl \yere tlioro~iglil!~iiiisetl t o ~ e t l i c r . This mixture \\.as kcyt moist t c i promote. tlic chemical action, a i i t l samples \ v e x withdra\vii from tinie to time to estimate the watersoluble acitl. \larch zGth, 800 grams soil and 50 grams double superpliosphate niisctl : 1Iarch 27th) 41.6 per cent. of E’?( ): hat1 become fisctl : l l a r c h q t h . 57.7 per cciit. of I.):( ): hat1 bccnmc fisctl : .\I)ril 31’11. /’3.0 per cent. of l):( ):, hat1 I1ecomc fisc11 : .\pril 17th. 85.6: 1)er cciit. nf I’:( ); hat1 1)ecoiiie fisetl. ( )I-% ta1;iiig 3.5~0.000I)ouii(ls a s tlic \\.eight ( i f o n c ~;icrc’ o f snil tn tlic tleiitli of I foot. \\‘e tint1 tliat this soil a1)sorlictl : .ifter oiic day 35,235 pouxitls I‘2(-)-,per acre to tleptli ( i f 1 foot : after three days 48,872 pounds P,O, per acre to tlcpth of I foot: after eight days 61.431 poiiiirls P,( ) z per acre to tlcpth of T foot : after t\\,ciit!--two t l a ! ~72,543 l)otiiitls P2OZlier acre to c!cl)tli of I foot. This latter figtire \voultl rcprcsent all the ~ ~ l i o s p l i ( i racitl ic iii I S I t o w of acitl phosphate. 'These astotiisliiiig figures lead to a consitlcratioii t)i t h c iiatiirc o f the soils experimented with, and the reason for t h i s rapid ant1 grcat fixation of phosphoric acid by Hawaiian soils. ( h i 1’. cy). ,-t . s l ~ t ~ of ,, llaswell’s ”1,avas ant1 Soils of tlic J-Ta\vaiiau lslantls” lvill lie foiiiitl a comparison o f I-Tawaiiati ;\iitl Amcricaii soils. in ivhicli it is sho\vii that T-Ta\\.aiian s o i l s arc vcry iiiiich i i i t i r c b l):i.(ic rhan .-liiicric;ui soils.
F I X A T I O S O F P H O S P H O R I C -4CIJ) I?; T H E SOII..
I I I9
TABI.~:11. Soils,
Hawaiian ;\inericaii
......................... .........................
Basic cotistitileiits. Per ceiit.
Acid co~istituei~ts Per ceiit.
63. 7 I 7
36.458 81.014
I 8.9So
\\-hereas the American soils from which these figures were drawn contain but 13.2j o per cent. iron ant1 alumiiiiim oxides, the Hawaiian soils contain 59.24 per cent. -411 Hawaiian soils are very basic, and these bases are probably in a condition to seize at once the phosphoric acid and hold it. The American soils being much older than Hawaiian soils the soluble bases ‘have been washed out, the soils are less basic in character, ant1 will prolnbly hold very much less phosphoric acid than the Hawaiian soils. Following is an average of a number of analyses of dark red soils, and the soil from the Honoltilu plantation would not differ very materially from these figures. TABLEIII.-DARK RED S O I J , ~ .
......................... ................................ ...................... .................................... so, ..................................... co, ..................................... CaO ..................................... 31go .................................... Fe,O,,................................... A1,0,. .................................. Mn,O,................................... x,o..................................... Sa,O .................................... Itisoluble matter Moisture Combustible matter TiO, .................................... P,O,
Per ceiit.
37.20 6.16
11.33 2.59
0.19 0.31 0.1s
0.34 0.44 22.94
16.84 0.42
0.39 0.75 100.08
With soils of this general composition it would be straiige if their absorptive power of phosphoric acid were not great. HOSOLULK. H. I.
