STUDIES ON PHYSICO-CHEMICAL RELATIONS OF SOIL AND WATER

Transcription

1 STUDIES ON PHYSICO-CHEMICAL RELATIONS OF SOIL AND WATER I. Water Retentive Frce f Sil as influenced by Chemical Fertilisers BY ]3. ~. SINGH AND ~r L. MEHTA (Frm the Instit~de f Agricultural Research. Ben~res Hi~4~e Uni~,ersity) Received Nvember 22, 193~ Intrductin SOIL misture is a prime factr in successful plant grwth. In p'revius cmmunicatins 6.9 frm this Experiment Statin published in this very peridical, the dminating influence f a prper supply and availability f water t crps has been emphasized. After having gained an insight int the relatins f sil misture t plant grwth, attentin has been further directed t studying sme f tile mst fundamental physic-chemical relatins f the water and sil, an aspect f cnsiderable imprtance in the study f water relatins f plants. The nrmal functining f a plant depends primarily n the cnstancy and the abundance f water supply thrugh it. The enrmus lss f water sustained by the plants in the prcess f transpiratin necessitates a crrespndingly energetic absrptin f water frm the sil. Cnsequently the prper develpment and health f plants depend primarily upn the capacity f the sil t deliver water t the plants. But as the misture cntent decreases, the sil particles develp a ' frce ' r ' back pull' by virtue f which they tend t retain their water. The measurement f this frce gives an estimate f the water retaining capacity f sils. Since the time Camern 2 emphasized the imprtance f sil frces, the general status f ur knwledge f the subject has been appreciably raised by the investigatins f Shull and Livingstn and his cwrkers. 5,~.4 Shull 5 frm his investigatins n the subsil f Osweg silt lam cncludes that as the sil becmes drier, the frces retaining water becme greater, until at the apprach f air-dry cnditins a very small change in misture cntent results in a huge change in the frces invlved. Livingstn and his c-wrkers 3,4 wrked with 12 types and mixtures f sils and cncluded that as the sil mass dries ut, its water supplying pwer decreases B2 F 133

2 134 B.N. Singh and M. L. Mehta and these changes ccur mst rapidly in the immediate vicinity f plant rts and near the sil surfaces. The investigatins f Stlull and Livingstn shw that the capacity f the sil t deliver water t rts is ne f the mst imprtant factrs influencing the intake f water by plants. It is imperative that fr successful crp prductin thse cnditins which rdinarily tend t reduce the water retentive frce f the sil t the minimum, need be given. The main aim f the present investigatin is t find ut the effect f the cmmn practice f adding artificial fertilisers t sil, n the water-retaining frce f sils at different misture percentage, i.e., hw the different fertilisers affect the water-retaining frce as the sil dries ut. Experimentatin Fr the determinatin f the water retentive pwer f the sil the smtic slutin methd develped by Shull 5 has been fllwed with minr mdificatins. The methd cnsists in determining the amunt f wa[er that air-dry seeds with semipermeable cats extract, frm the sils and frm salt slutins f varying mlar strengths. The smtic pressure f the salt slutin in which the water intake by seeds crrespnds t the water intake frm the sil represents the water retentive frce f the sil. The seeds used in the experiment came frm a pure line stck f Suttn's Peas " Earliest f all " which were tested and fund t have semipermeable cats. The fertilisers were added in the fllwing prprtins: Ammnium sulphate (N) 2 per cent.,* ptassium sulphate (K) 1 per cent. and duble super phsphate (P) 0.5 per cent. The fllwing misture percentages besides the air-dry (2.5 per cent.) sil, were maintained by adding that much vlume f water t 100 gin. f air-dry sil : 25 per cent., 20 per cent., 15 per cent., 10 per cent., 5 per cent. and the wilting cefficient. The wilting cefficient f each f the sils was fund ut by experimentally ascertaining the hygrscpic cefficient and dividing it by These agreed fairly with the values fund ut by direct methds fr all fertiliser effects and ther field experiments ging n at this Experiment Statin. 100 gin. f sil f each f the types mentined abve were placed in 500 c.c. screw-tpped bttles having a rubber band at the neck fr tight fitting. After keeping 100 sterilised and weighed seeds f as unifrm a size as pssible in the sil the bttles were tightly stppered and kept agitated * Weight f fertiliser per 100 gin. f sil. This prprtin f fertilisers has been fund t be mre r less ptimum [r the grwth f crps frm separate investigatins ~t t,his place.

3 Studies I~ Physic-Chemical Rela/ilzs /" Sil a~zct iva/er~/ 135 in a water-bath maintained at a temperature f 25 ~ ~ C. After a series f trials fur days time was fund t be sufficient fr the attainment f misture equilibrium between seeds and sils. I, nger duratins f time intrduced fungal infectins in higher misture cntents. At the end f the experiment the seeds were carefully remved ut f the sil, any adhering sil brushed ut, the misture cntent f bth seeds and sils determined and the intake f water by the seeds calculated. Anther series f air-dry seeds were placed in NaC1 slutins f varying mlar strengths and the percentage misture they imbibed under these cnditins determined. Tw days time was fund sufficient fr the attainment f misture equilibrium in salt slutins. The intake f water in the different salt slutins is prtrayed in Fig. 1 and that in different sils detailed in Table I. Fr the values f water intake 50 4a = 20 10: ~-.d~ :....~-'",1; ".~.~5....~".i~.;. #'t OL AR CONCEN TRA TI ON FIG. l.mlmbibitin f water by seeds frm the varius cncentratins f sdium chlride slutin in different sils the crrespnding strength f salt slutin is lked frm the graph (Fig. 1) and frm the latter the pressure in atmsphere ascertained

4 136 B. N. Singh and M. L. Mehta TABLe I Intake f water by Pisum seeds at varius misture percentages N. Trea!- men t Water absrbed at misture percenlage i Cntrl 13, , K 22, P :.4 N KP ,6 24, PN , KN , KPN 20 " , frm physical tables. f sils. These values are expressed as water retentive frces Experimental Findings Fig. 2 depicts the effect f decreasing misture cntent n the water retentive frce f sils. Cnsidering the cntrl it is nted that as the sil gradually dries frm 25 t 2.5 per cent. misture, tile water retentive frce becmes greater and greater. At higher misture cntents the changes brught abut in the frce are steady but belw 10 per cent. misture, large changes in the frces are invlved. All the treatments shw mre r less similar relatinships between the misture cntent and water retentive frce. At the higher misture ranges like 25 and 15 per cent., K has practically n effect, differing as it is, very little frm the cntrl. At the level f the wilting cefficient and belw, K exerts the greatest influence bringing the water retentive frce t a value higher ttlan the cntrl itself. Amng the ther single treatments P brings abut steady changes and keeps the frce at tile wilting cefficient, at the lwest level. In the duble cmbinatins nly Plg shws a steady change in this frce, the enhancing effect f K n the water retentive frce being again apparent in cmbinatins KN and KP. The triple

5 S/udies ~ Physic-Chemi~a/ Relalilzs f Sil and l/ualer~i 137 i GO~ I~ P -----I~ tb ~-.--Ktl r~ ~t0 ', '\ 8 "~-... -m I 0,, t'0 I is ~ ~s MlsruR~ e~.s~,r,~ FIG. 2.--Water ret.ent.ive fprce f variusly fertilised sils at different mistut'e cntents. Pints marked V~" represent the wilting cefficient cmbinatin KPN shws the mst level curse, the effect f K in increasing the water retentive frce presumably being checked by the ppsite effects f P and N. A survey f the curves thus demnstrates that as the sil dries the water-retaining pwer f the sils als increases a result agreeing with the findings f Shull 5 and Livingstn?,4 Duble superphsphate (P) appears t have the best effect in checking the increasing water retaining frces with decreasing misture cntents and ptassium sulphate (K) the least effect. Under the cnditins f excessive misture, K has n influence in checking the supply f water frm sils t plants which wuld naturally result in a wastage f water by plants and in cnditins f insufficiency f misture the K treatment excessively increases the retentive frce making it difficult fr the plant t get a prper supply f water.

6 138 B.N. Singh and M. L. Mehta TABLE II Increase in gradient f water retentive frce frm 25 per cent. misture t wilting cefficient Treatment Retentive Retentive frce at O/ wilting frce at 25/ misture cefficient Gradient f increase in the frce Cntrl K P H KP PH KIq KP Fig. 3 and Table III give the relatinship between the wilting cefficient and water retentive frce in variusly fertilised sils. It is bserved that TABLE III Water-retaining frce at wilting cesficient f the fertiiised sils Treatment Hygrscpic cefficient Wilting cefficient Water-retaining frce at wilting cefficient Cntrl K P 4.' H KP PH KS KPH

7 Sludies n g/~ysic-c/zernica! Relatiizs ff Sil auct l~vater~! 139 bth are greatly influenced b y the additin f fertilisers. With increasing values f wilting cefficient frm 3.85 (in case f K) t 6.2 (in case f P) there is a decrease in water retentive frce frm 12.5 t 6.8 atmspheres with the exceptin f KP, where althugh the wilting cefficient is higher t~z t.t..= U t~,t ~9.5 ~ ,5 W/L T/NG C OEFr Fig. 3.--~Vater retentiv frce f variusly fert,ilised sils as related t the wilting cefficient. than KN, Plg and K P N the frce is nt decreased but is higher than thse. K thus tends t decrease the wilting cefficient and increase the water retentive frce f the sil while P tends t increase the wilting cefficient and

8 140 B.N. Singh and M. L. Mehta decrease the water retentive frce. N has a balancing effect f these tw ppsing influences as evidenced by the intermediate value f KPN. Table II represents the gradient f increase in water retentive frce frm 25 per cent. misture t the wilting cefficient level in different treatments. The gradient is highest in the case f K treatment and least in KPX. The effectiveness f P is again evident as seen frm the lw gradient f increase in P and PN fertilised sils. It is well knwn that fr the prper intake f water by plants the rt cells have the capacity t adjust their smtic relatins in accrdance with the ppsing frces in the sil. This capacity f rts has certainly a lirfiitatin and t high a frce in the sil wuld demand a crrespnding high change in the smtic relatins f the plant cell which ften the plant may nt be able t cpe with. This wuld result in an upsetting f the water relatin f the plant and its metablism ultimately. Frm the data presented in Table II it is evident that the changes in the frce brught abut in the sil by the depletin f water t the stage f wilting cefficient is very high in K treated sils. Hence, in these sils, the plant has t make cnsiderable changes in the smtic relatins f the rt ceils when the misture cntent is reduced t lw values. The small changes in the smtic relatins f th.e rts f plants that will be required in the N and P treated sils naturally emphasise their usefulness all the mre. The results presented in this paper n the effect f artificial fertilisers as an imprtant factr influencing the water relatins f plants, may be said t be in cnfrmity with ther independent investigatins n their effect n the water requirements and yield f crps under Indian cnditins. T mentin but a few, in an yield trial experiment n ptates 8 the treatments KP and PN and N yielded 9.46, 9.63 and 8.79 tns per acre while K resulted in an yield (6.03 tns) less than that f the cntrl itself (6.07), and the treatment Plg in an investigatin n wheat 7 decreased the water requirement and increased the yield ver the KP and KIg treatments indicating thereby the effectiveness f Plg additins t the sil n the yield and water requirement. Summary and Cnclusins The paper deals with effects f ammnium sulphate (lg), ptassium sulphate (K) and duble superphsphate (P), singly and in cmbinatins (ttal 8 treatments) n the water retentive frce f the sil at different misture cntents. As the misture cntent f the sil decreases the water retentive frce f the sil increases. The changes in this frce are less at higher misture percentages while large changes are nted at lwer misture cntents.

9 Sludies n Physic.Chemical Relatins f Sil a~zcl [/Va/er--I 141 K has the least effect in reducing the water retentive frce as sil is being depleted f its misture, and P bth singly and in cmbinatins has the best effect in as far as it tends t keep the frces steady. The fertilisers influence bth the wilting cefficient and water retentive frce f sils (Table III). In general the fertilisers bringing abut increase. in wilting cefficient ats bring abut a crrespnding decrease in water retentive frce. The gradient f increase in water retentive frce f sils frm high t lw misture cntent is higher in K treated sils and lw in P treated sils (P, PN and KPbY). This necessarily calls fr drastic changes in the smtic relatins f the rt cells f plants in K treated sils if the plants have t maintain a prper water balance. It is cncluded that a cmbinatin f P and N is the best treatment as far as water relatins f plants are cncerned fr the prper grwth and yield f crps under Indian cnditins. 1. Briggs, L. J., and Shantz, ti. L. 2. Camern, F.K Livingstn, B. E., and Kketsu, R and Nrem, L.W. 5. Shull, C.A Singh. B. N., and Singh, B.R and Mehta, B. K and Mehta, M.L Singh. R. B., and Singh, K. LITERATURE CITED Bt. Gaz., 1912, 53, The Sil Slutin, Sil Science, 1920, 9~ Ibid., 1937, 43, Bt. Gaz., 1916, 62, Prc. Ind. Acad. Sei., 1936, r Amer. Jar. Affrn., 1938, 39j Die Ernahrunff Der "Pflanze (in press). Pre. Ind. Acad. Sci., 1935, 1, ]~2 a