SNOWNELT INFILTRATION INTO COMPLETELY-FROZEN. SUBSOILED SOILS by Dii. Gray. R.J. Granger and W. Nicholaichul? ABSTRACT Altering the macropore content of a ‘completely-frozen” soil - a soil whose frozen profile does not thaw to appreciable depth during snowcover ablation -greatly improves its ability to absorb meltwater. Infiltration into soil cracks and rips averaged 3.8 and 5.8 times the amounts into the same soils in uncracked or undisturbed condition. A model for estimating the depth of infiltration into subsoiled fields using line spacing. snowcover water and soil moisture (ice) content is presented. Subsoiling to depths between 400 and 500 mm on spacings between 0.9 and 1.3 m should enhance the infiltration capacities of frozen soils in the semi—arid prairie region so that they are capable of absorbing most of the snow water accumulated by stubble management practices in a normal snow year. Over a 4-yr period, increases in the annual yield of spring wheat from subsoiled areas over those from undisturbed plots of continuous stubble averaged 1033 kg/ha on plots with snow management and 240 kg/ha on plots without snow management. The useful life of the treatment effect is estimated of the order of 4 or 5 years. KEY WORDS: Snowmelt Infiltration: Frozen Soils: Subsoiling: Model: Yield (wheat) I Respectiveiy: Chairman and Research Officer. Division of Hydrology. College of Engineering. University of Saskatchewan. Saskatoon. Saskatchewan. Canada, S7N OWO: Chief. Hydrology Division. National Hydrology Research Centre. II Innovation Boulevard. Saskatoon. Saskatchewan. Canada. S7N 305.
Transcript
SNOWNELT INFILTRATION INTO COMPLETELY-FROZEN. SUBSOILED SOILS
by
Dii. Gray. R.J. Granger and W. Nicholaichul?
ABSTRACT
Altering the macropore content of a ‘completely-frozen” soil - a soilwhose frozen profile does not thaw to appreciable depth during snowcover ablation-greatly improves its ability to absorb meltwater. Infiltration into soil cracksand rips averaged 3.8 and 5.8 times the amounts into the same soils in uncrackedor undisturbed condition. A model for estimating the depth of infiltration intosubsoiled fields using line spacing. snowcover water and soil moisture (ice)content is presented. Subsoiling to depths between 400 and 500 mm on spacingsbetween 0.9 and 1.3 m should enhance the infiltration capacities of frozen soilsin the semi—arid prairie region so that they are capable of absorbing most ofthe snow water accumulated by stubble management practices in a normal snow year.
Over a 4-yr period, increases in the annual yield of spring wheat fromsubsoiled areas over those from undisturbed plots of continuous stubble averaged1033 kg/ha on plots with snow management and 240 kg/ha on plots without snowmanagement. The useful life of the treatment effect is estimated of the orderof 4 or 5 years.
I Respectiveiy: Chairman and Research Officer. Division of Hydrology. Collegeof Engineering. University of Saskatchewan. Saskatoon. Saskatchewan. Canada,S7N OWO: Chief. Hydrology Division. National Hydrology Research Centre. IIInnovation Boulevard. Saskatoon. Saskatchewan. Canada. S7N 305.
SNUWMELT INFILTRATION INTo COMPLETELY-FRoZEN. SLEsul CCL SoiLS
DV
D.M. Gray, R.J. Oranger and W. Nicholaichuk
Throughout the most part. of the semi-arid prairie region or central Canada annual
snowfall. whicn ranges in depth between 90 and 130 mm water equivalent. comprises on averageanout 3O of the annual precipitation and. excluding large-scale water development projects.
constitutes the most amenabie source of fresh water supply available for management.
Meltwater from the shallow snowcovers serves many beneficial purposes as wildlife habitat.
as a local SUPP1V for domestic ann livestock use. and for recharging groundwater supplies.
soil water reserves and lakes.
igriculture is the primary industry of the region with cereal grains, pulse and oil
seeds the principal crops. The importance of water to the production of cereal grains under
dryland farming is well-recognized. For example, the Saskatchewan Council on Soils and
Agronomy U9821 recommends that root-zone water reserves of 125 mm and 100 mm are needed at
-the time of seeding to achieve average yields in the Brown and Dark Brown soil zones.
respectively. This recommendation is based on the expectation of normal ralniall in the
growing season. Staple and Lehane U952. 1954) and Staple et al. 1960) reported that each
25—mm addition of soil water to a moisture reserve in the range between 262 mm and near 412
mm may increase the yield of spring wheat by 230 400 kg1ha. Corroborating data are given
by de Jong and Rennje (1969) wno reported increases in the range of 200 - 275 kgha for eacn
additional 25 mm of soii water above the long-term normal growing season precipitation for
the relatively-numid, east—central part of Saskatchewan.
in recent years on the Prairies there has been renewed interest on the potential of
‘managing’ snow to increase soil water reserves, Because of the type of crops and the nature
of the farming operatIons, stubble management practices employing non-competitive vegetative
barriers (“tall stubble. ‘alternate—height stubble. trap’ strips to trap snow are
commonly-used. Vegetative barriers also reduce the distance of snow transport, thereby
reducing the amount of snow water lost by sublimation during blowing snow events. This loss
may not oe insignificant. A recent study by Gray et al.: 1989) using the Prairie Blowing
Snow Model developed by Pomeroy (1988) and five years (1970—1976) of meteorological data
recorded at stations throughout the Prairie Provinces shows average annual sublimation losses
from 1000-rn fetches, expressed as a percentage of annual snowfall, ranging between 21 and
55 on stubble and 34 and 55 % on fallow in areas where snowcovecs are continuous.
Evidence show!ng that snow management practices can be successfully applied in a prairie
environment to increase snowcover depth is indisputable (for example see Nicholaichuk et al.
1986L However, an increase in depth of snowcover does not assure a proportional increase
in meitwater infiltration. The problem ar.ises because the period of snowcover ablation is
short and infiitrat.ion takes place into compieteiy—frozen soilsH he rein defined as those
solis whose frozen profile does not thaw to appreciable Oepth durIng snoweover ablation.
“ “d s.c’- c”oze” so “- es “e crp en”p’’o’ -‘ a ae ‘“-‘-
uranger e aL (10541 and urav et al. (198ba1 suggest that for practica. purposescemplr’tely-trozen soils may be grouped into toree broad classes in respect to their
meltwater jntLtraton potenta
1. Restricted intiltration is impeded by an ice lens on the surface or at shallowdepth. The amount of meitwater infiltrating the soil is negligible and most ofthe snow water goes to direct runort and evaporation.
. Limited infiltration is governed primarily by the snowcover water equivalentand the frozen water content or the 0aUU mm soil layer. The average depthinfiltrating meitwater penetrates “Lmited soils is about 260 mm and the limitof saturation of the wetted depth L an be approximated as: L -- U S - 0.3. inwhich L and 5. the average ice.water content of the wetted deptfl. are expressedas a degree or saturation in mm’s mm2. These findings demonstrate me capacity otZimited’ soils to absorb meltwater. For example, a soil with a porosity of 50%
at an initial moisture content of 20% by volume (dry to medium wetness) wouldlikely infiltrate on average less than about 37 mm of meitwater [0.5(0.5U.3O.4) - 0.2] 250 - 46.8L or the water equivalent of a normal snowcover w:tha depth in the range of 15-20 cm
.i. Unlimited soils containing a high percentage of large, air filled macroporeswhich are capable of inFiltrating most or all or the meitwater.
The material above suggests that snow management practices ror augmenting soil waterreserves from meltwater infiltration in completely frozen soils are likely to prove mostsuccessful in those soils which naturally crack on drying Non cracking, medium and fine-textured soils must have their structure significantly altered to increase their macroporecontent n order to have the same potential. This paper reports on studies conducted inSaskatchewan on meltwater infiltration into naturally-cracked soils and the effects orsubsoiling of non-cracking soils on infiltration enhancement and the yield of spring wheat.
FIELD EXPERIMENTS AND PROCEDURES
During the past nine years, snow and soil moisture monitoring programs have beenconducted on cracked and subsoiled soils within the Brown and Dark Brown soil zones of theProvince of Saskatchewan. The majority of the cracked sites are located in heavy, lacustrineclays (primarily Sceptre clay. 55% clay on fiat to gently undulating land under cultivationof cereal grains by dryland farming. The subsoiled sites, located near the vIllage ofRerrobert, 5K, are in glacial till wnose principal texture is clay loam, although heavy claysdominate the lower slope positions, The general topography varies from flat to moderatelyrolling. On the rolling land the variations 10 soii texture and topographic OSitlOfl causelarge gradients in yield over a field.
ln the fall of 1983 a small area (0.5 ha) was ripped with a single shank Kiileferplow to a depth of 600 mm on a spacing of 1 85 m. the wheel spacing of the power unit fl’sreatment was repeated on dirrerent p’ots or ani In the fail or i’54. n lUst and 19.otner smaL areas were saosoiled w;th an Ebson piow (depth 400 mm spa tiE ‘1.75 a. apea kello-b t p ow deptr 6u mm epac ngs c and 1,4 j. n I 87, two. 7 p1 S* r rip d w th a ub s s e a d p t 5 is re with a pa g
h wtl a spa :nt of U a Whe possible ‘ta I s ubb ap rr’p ir rat etcohtLe managemee: prac: res were usa mr sr,w “‘apIng 0501 P. on re ursc; lcd
areas were ringed w:h snow fences o enscre .arge acram’c.atiors .1 snc.w
ha pes in soi m istore were m r tIred w’rh ‘i tw rr ga’nrn dr S y ‘a t ‘r ost rcluring and immediately following snowcover abla n This system prov:des nnn destructivesampling of a cube of SOil approxImately Su mm woe. 5u mm iong and aU tam :h:cs, Witn toemethod, 50—mm diameter piastic access tunes spaced 05 mm apart are ins:aed vertically intothe sii, A raoica tive source is ‘nserted in ne tube and detect ‘ a” “I’e same cieptIc ther ard seas r s taker f n rumtcr of phI r t ik I e cie to ii
minute. ae densirs or he a .:a”ec Snr.wIng the r,teos y of t”o s’,: dada:ter.,a’crI ‘oerr,e:s cower at.a’r c” s’ and wa”cr B’; ,ics’u g “ebetween “‘he t’jbe or s ressi’;e ‘eu;’er’n a’ e’io’”’s •‘oosa t.Ot st “‘1 x
it or t It tt at a
attributed to changes in the mass of water contained in the volume. (Note: it is pertinentto mention that openIngs in frozen soils remain relatively stable until water is imbibed bythe surrounding soil. causing it to thaw and to sweil. The equivalent moisture change iscalculated from the readings assuming a denstv of water equal to 1000 kg m’s. Measurementsare taken at 0-inim increments of depth to 4u0 mm and at 40-mm increments between 400 mm andthe bottom at the access tubes. The equipment was extensively tested and calibrated tooperate reliably to temperatures of -20°C. Measurements were taken with a crack’ or “ripcentred between the access tubes. with the access tubes aligned perpendicular to a crack’or “rip on centres of 150 mm and 45u mm from the opening, and in tubes placed in uncrackedor undisturbed soIl.
The depth of snowcover was measured routinely and the snowcover water equivalentobtained either from nuclear or gravimetric density measurements. Some locations wereequipped with a Nipher precipitation gauge and these measurements were used to update thesnowcover data. Several sites were also equipped to monitor the ambient air temperature andsoil temperatures at different depths.
Yield samples were taken from the different treatments each year. The size of samplesvaried from I - m to field size. Small plots were harvested by hand, the larger units byswathing or straight combining.
RESULTS AND DISCUSSION
Infiltration into undisturbed (uncracked). cracked and subsoiled soils
Figures 1 and 2 show changes in soil-moisture distribution patterns in undisturbed.cracked and subsoiled soils due to meitwater infiltration. ifl Figs. lb and lb the changesare calculated from measurements taken with the crack and ‘rip located between the sourceand detector of the twin probe system; Figs. ic and 2c are changes measured perpendicularto the fractures at a distance between 150 and 450 mm. The subsoiling treatment was a“Killefer” plow and the measurements were made on a plot which was located in an upperslope position and protected against flow along the lines (rips) by plastic liners insertedto a depth of about 1 m. The data in Figs. 1 and 2 substantiate comments made in theINTRODUCTION, namely:
1. Undisturbed soil: The amount of Infiltration into undisturbed soIl is limited.both sites (Figs. Ia and la) show approximately 27 mm of meltwater infiltratingthe undisturbed soils to depths of 375 and 185 mm. The snowcover water equivalentsat the sites were 78 mm and 194 mm. respectively,
2. Cracks and Rips: Infiltration into cracks’ and ‘rips’ is substantially greaterthan to undisturbed soil. The increases xn SOil moisture in the fractures were94 non and 173 mm respectively Note the amount of infiltration to the ‘crack’(94 mm) is substantially greater than the snowcover water equivalent of 78 mm.This is attributed to interf law in inter—connecting cracks and surface runoff fromthe undisturbed soil between the fractures entering the opening directly. Thesubsoiled soil, which was ripped” to a depth of 600 mm, shows large amounts ofsoil water recharge to a depth of I m (Fig. 2b1.
Adacent to Craci<s and Rtps. The amount or infitraticn into tOe blocc ci soilmmediateiv adlacent to a crack or rip 15 less than that into the aperture. hutgr ater than the amount into undisturbed riul . Univ :3-6 mm of water anti itratedthe soil adjacent to the cracK IFig. id. a small increase over the amount ohser’vedat the “uncracked” site. However, a significant increase in moisture (>78 mm),which exten.ds bel.ow the depth of measurement, occurred adjacent to the “rip”. Thisis attributed to an increase in hydraulic conduct.ivity caused by rupture andfracture of the soil during installation of the lines and to the rip acting as asource of water for lateral movement, the vertical iv--elongated pattern s theresult of increasing hydraulic head and soil temperature with berth. At thebeginninc ci snawelt the frost depth was between OU and IJOC tm
E
1I
lc) Lh,cr-ockd Cb) Crocked c) Adjcrtto Cr-oak
Figure 1 soi moisture changes due to snowmeit infiltration in completely-frozen. uncrackedand cracked heavy ciay
Figure 2. Soii moisture changes due to snowmelt infiltration in completely-frozen.undisturbed and subsoiled clay loam. Rip was installed to a depth of 600 mm bya Killefer plow.
Table 1 summarizes the findings of the soil moisture monitoring program as averageamounts of snowmelt infiltration into undisturbed uncracked soils, cracks, and rips fordifferent ranges of snowcover water equivalent, These data show infiltration increasingwith snowcover water equivalent in both cracks and rips with a trend for rips to infiltratemore water than cracks However, the ratio of the amount or infiltration into an openingto toe amount infiltrating undisturbed soil varies only slightluwlrn death of snow waterOn cracked soi is toe ratio—values vary between 34 and 43 with a mean of 3.8 and on rrppedsoil between 54 and $5 with a mean of 58.
Analyses of soil moisture proriies toilowing meitwater nfitraron into undisturbed.cracRed and suesoiled completeiv-trozen soils show a strong relationship betweeninfiltration 1SF) and the depth of penetration of the wetting front d; Gray et ai.1986b. The curve enveiopng these variables can be approximated as 1SF O.2d. n which1SF and d are in mm. However, unless a snowcover is unusuaily deep hO cm: OWE ISv mm)d is less than I a (average 630 mm. Based on this finding and a review of profiles ofsoil moisture changes monitored at numerous s ubsoiied sites and assuming a root z•one of 1m, it is suggested that lines be installed at depths in the range of 400 - 500 mm forefficient moisture conservation.
50 -50 0 50
Soil Moitur- CHng (%-Vol)
Table 1. Average amounts of snowmelt infiltration into uncrackediundisturbed soits.cracks and rips tor different ranges or snowcover water equivalent SWE:.
4*INFILTRATIUN INFILTRATIONSWE Uncracked Crack Ratio Undisturbed Rips Ratio
Values for uncracked and cracked soils from all sites within Brown and Dark Brown soilzones of the Province in which soil cracking was observed. The major textural groupsare heavy clay and clay loam.
* Values for subsoiled and undisturbed SOIl are for Kerrobert where the prncipa1 soilis a glacial clay loam. The subsoiling treatments included: (a) Killeter plow —depth= 600 mm, spacing = 1.9 m: (b> Ebson plow - depth = 400 mm, spacing = 0.75 m: (C) Echohilt plow - depth = 600 mm. spacings 0.70 and 1.4 m: (d( Hubee subsoiler —depth 500mm. spacings = 0.70 and 0.90 m.Numbers in parentheses refer to the number of samplesEstimated values.
Areal infiltration and line spcing
Figure 3 shows group mean values of soil water changes due to snowmeit infiltration inrips, cracks, adjacent to rips and undisturbed stubble plotted agaInst snowcover waterequivalent. Expressing these relationships in equational form gives:
Cracks INFC = 8.48SWE0’°3> . [1)
INFR = 16.86SWE0’432
to Ri s
For SWE < 80 mm INFA = l.651NF 8.25(1 - OSWE°’584 and [3a)
For SWE a 100 mm TNFA -27.5 0.89SWE. [3b]
Undisturbed Soils
1NF 5,0:1 -
where: INFO = infiltration into a crack )mm). •INFR = infiltration into a rip (ma). INFAinfiltration into the column of soil lying 150 to 450 mm adjacent to a rip (mm.). INFinfjltration Into undssturoeo soii cam). SWE snowcover water eguivalent cam:, and- 8.a crane 5reTe Sc cc =“ .e -“p c ep=ssa e a g-eof saturation )mm>/mm).
Equations . 3 and 4 are used to develop a slmple. conceptual model oesc-r;ong theaverage depth of snowmeic infIltration over a subsoiled field iNEcareal: as a function ofSWE and line spacing :sc. Consider a soil which has been subsoiied with minimum disturbanceof structure to the narrow block of soil adjacent to a rip. The system can be representedby three individual soil blocks (rip, adjacent to rip, and undisturbed )see insert in Fig.4: . each having its own infiltration characterstcs. Taking toe widths of toe - rip andad acenr olock equal to toe width of reasuremen: of soil mois:ore mange a lOu mm - the
water balance equation can be written as:
Table 1. Average amounts at snowmelt infiltration into uncracked/undisturbed soijs,cracks and rips for different ranges at snowcover water equivalent (EWE),
*INFILTRATION INFILTRATION
EWE Uncracked Crack Ratio Undisturbed Rips Ratiommmm
* Values f or uncracked and cracked soils from all sites within Brown and Dark Brown soilzones of the Province in which soil cracking was observed, The major textural groupsare heavy clay and clay loam.
** Values f or subsoiled and undisturbed soil are f or Kerrobert where the principal soilis a glacial clay loam. The subsoiling treatments included: (a) Killefer plow —depth= 600 mm. spacing = 1.9 m: (b) Ebson plow depth = 400 mm, spacing = 0.75 a: (C) Kellobut plow — depth = 600 mm. spacings = 0.70 and 1.4 m: (dl Hubee subsoiler -depth = 500mm. spacings = 0.70 and 0.90 m.Numbers in parentheses refer to the number of samplesEstimated values.
infiltrationand1inesacin
Figure 3 shows group mean values of soil water changes due to snowmelt infiltration inrips. cracks. adjacent to rips and undisturbed stubble plotted against snowcover waterequivalent. Expressing these relationships in equational form gives:
Cracks INFC =8.4BSWEOSS0. [1]
INFR = 16.86SWE0’432 . [2]
nttoRis
For EWE < 80 mm INFA = 1.65INF = 8.25(1 O)SWE°’584 and [3aJ
For SWE > 100 mm INFA = -27.5 + 0.89SWE. [3b]
Undisturbed Soils
INE = 5.0(1 - 8p)SWE0°84.
where: INFC infiltration into a crack (mm). INFR = Infiltration into a rip (mm). INPA =
infiltration into the column of soil lying 150 to 450 mm adjacent to a rip (mm). 1NF =
infiltration into undisturbed soil (mm). EWE = snowcover water equivalent (mm). andaverage premeit. spil water (ice) content of the 0-300 mm SOIl layer expressed as a degreeof saturation (mmimm(,
Equations 2.. 3 and 4 are used to develop a simple, conceptual model describing theaverage depth of snowmeit infiltration over a subsoiled field (INFareal>( as a function ofEWE and line spacing (51. Consider a soil which has been subsoiled with minimum disturbanceof structure to the narrow block of soil adjacent to a rip. The system can be representedby three individual soil blocks (rip, adjacent to rip, and undisturbed (see insert In Fig.4.). each having its own infiltration characteristics. Taking the widths of the “rip” and“adjacent” block equal to the width of measuremen.t of soil moisture change ( 300 mm), thewater baiance equation can be written, as:
0 —
___ __
30 80 SC 120 150 180
.4EAN SNOW WkER EQU1VA,.EN 1.,
Figure . uroup mean values at snowmelt infiltration into undisturbed stub1e, adiacent torips, cracKs and rips as a tunction of mean snoweover water equva1ent tmmL
1NFR(areaH s INFE 0.3 - INF\ 0.6 INF s 0.ui, [5
in which the spacing or the rips i5 in metres. substituting the expressions tar INFR, IiFAand INE given by Eqs. 1 4 into Eq. 5 and solving gives:
For s 0.9 and SWE 70 mm
INHareali 5.ubSWE°’42 s - 0.09)[5l e)5WE°’4J)s [6a1
and for s 0. and SWE 100 mm
INF(areaI 5,0bSWE0’43 lb.5 0.5J45WE - s U.rJ)[5U e)SWE°’54]} s [bbj
‘l1 S0i. O9.R€, 8, — -
CD 120 1 180
W AiEE I A N
ieo OCCC1 I:r-a:ao iDe Cjoo •oo . : wat:00CPT1’ 10D s-s ‘‘D voao ba aoci :i
12C
I20 -
87—
2
21
OJ, 515
For snowcovers with 70 mm 5WE 100 mm. the lesser amount of INFareaIand 6b is used.
lear—
S :tE -j. S _-7
7 — —
HI
—
—- --
_< —- —--
given by Eqs. 6a
cqua’ions ha and ho are plotted top a ‘premelt’ soIl moisture. 0.4 dry to meduwetnessi and a range of sE values In tg. 4. also plotted is .SHareal ror rips spaceaat U 7 m and ror undisturbed soil To demonstrate the use or the curves assume averageannual snowfall water equivalents of Uu and 130 mm (range in snowfall over a large part ofsassat.hewan( and snow management trapping erriclencies 01 00 and 75 of annual snowta,l.Ising these values the lImrs n avarlab:e SE would be 54 to 00 mm and the spacing of linesrequired to inrltrate all he snow water by Fig. 4 would be 13 and u.7 m, respectivelysimilar caiculatons with u. wet soii gives spacings or u. and su.7 m. The resultsor the ca,cuiat ions suggest tnat rnrouOhour the semi arid Fraires lines spaced between o 7m and l.a m, depending on soil moisture conditrons. will liKely absorb one water Iron’snowcovers producea by normal snowrai. A spacing or 0.7 m iS considered very conservative,‘Field observations nave snown tnar musT commercial subsoilers, when operated on spacingsof 0.7 m or tess. rupture and tracture the mass of soil between the rips to sum an extentthat. at least in toe first year. it will have the capacity to infiltrate most of tne snowwater which is likely to be accumulated by a stubble management practice, independent of thesoil moisture content It can be expected that the infiltration characteristic.s ofsubsoiled soils will decrease naturally in time due to settiement and packing. However.field observations suggest that the beneficial effects of subsoiling on meitwater enhancementmay be longer lasting in fields ripped at wide spacings (to some maximum due to thenatural cracKs which develop between the lines in response to the strong gradients in soilmoisture established during crop growth. There is an upper limit to the spacing of lineshowever. Visual observations of crop growth on lines spaced at 1.3 m or wider shownonuniform stand, the plants directiv over the lines are taller and mature more slowly.
In summarizing the material above, it is suggested that subsoiling most glacial tillsoils of the Province to a depth between 4u0 500 mm on a line spacing between u.9 and l.am will allow efricient meitwater augmentation under normal snowfall and soil moistureconditions. For slightly solenetzic soils the spacings should be decreased slightly.
Areal infiltration of cracked soils
Measurements of the physical dimensions or cracks in heavy lacustrine clays showed amean length:area ratio of 1.75 m.ma ‘uray and uranger. 1986i. Assuming toe width of the soilcolumn sampled by a twin probe equal to 3u0 mm. a point measurement or infiltration into acrack is representative or a surrace area of 0.53 Combining the snowmelt infiltrationequations mr a crack (Eq. 1) and an undisturbed soil (Eq. 3 and weighting each accordingto their respective surtace area gives an expression for areal infiltration into a cracKedsoil as’
INFC - 4.535WE0 - a.aa[i SWE°
The application of Eq 7 will change as the length.area ratio for cracks varies from theassumed value of 1 75 m
Effects on yleda, in wheat
icirocighour :tiP study at subsoed pio”s were n ontnuous stubble ana no Supplementalferti1,zer was appirea ‘ieid samples tOiPOtCO lo thP yr berIng snowed that eachaaai±jna: mm of water to i nax:r’ir Ihu ‘tn’ 00000 p0 or ,jveraae arir...a; increase ‘ci
v’eo cit oing wneat ci ISo kg ,hs a e 7 3 K’ tie Is to ster,* Wi” ritesreporcd topic a ar I ru de d ceo
TabI a ists a crags visl4 dita rrr sobs irig it atments w th it sr w managemEnt.Be aus ‘re e lata are a gev basec on samples from a ots wri I’ t r ‘he subs itreatments were centred over a rip cv sciould be treated as ndic’es of potonrial increasethat may be expected ii fields will ci tiav been subsoiled at narrow spatlngs. The data showa oecreas in treatment erfec: on ved with time. in the first own years 10_lowIngsubsoiling he aecrease s small: in he first year mere rs an average difierence or 4135kg ha cotipa ng o roe v,.ed cram cing:s”nruea stoon Ic 3i increase . wniie on the second yeara di frerenc of 377 g. cia .o’i’s lcicr’-ase s observed. in toe r 0,1000 ‘ear the dirtpr’ence has
g ha :c.Iv 1.t incr”e cccii L::erene :r one “ci V€’ar IS005 ‘ 3di ‘0 ci( ‘W Ott .i1 0’ prccIrI:o 500W 0.11 ‘0 oe’eic t. lOot. ‘ UnIv
‘ear wi” ctn yea a . ,,cc’ Oar i’ or r i or a:’ or. en
mucn iower than norma er mean Mav_Augus: ra:nra —uU
. Errect or suDsoIng on the ved ox spring wheat without snow management.
:. 00 useann ge SWE Rain” Yieid kg na Rangeat Rips mm J1trerenceRatlO lii
Faiow’’4’ 110 bid l.q4 1.05 1.71
1st year 52 110 •‘435 .1.34 1.18 1.60Znn year 50 122 377 1.30 1.18 1.523rd year 42 122 132 1.11 106 1.154th year 26 100 20 1.01 1.01
Mean snowcover water equivalent.
Average growing season rainfall.Difference in yield from that on undisturbed sires at continuous stubbleRatio of mean yield on treatment to that on stubble.4-yr average yield from fallow without snow management was 1896 kgrha.
Table 3 summarizes the effects on the yield of spring wheat of combinea snowmanagement and subsoiling oractices relative to the yield tram undisturbed plots ofcontinuous stubble. As with Table 2 these data should ne used as indices of potentialincreases necause of the sampling procedures and because the depths of snowcover water areconsIderably higher than wouid naturally cover a field. During the four - year period theaverage snowcover water equivalent on undisturbed stubble was 39 mm. The data in Table aexnibit a trend similar to that reported aoove. namely a decrease in the average yield withage of treatment. If the tests for the tourth year 1987:. the iOW snow year are exciudea.the decrease is independent of available snow water. Regardless, the average increase of1033 kg na on the snowmanaged. subsoiled plots is higher than the increase of bib kg.nameasured on fallow.
Table 3. Effect of snow management and subsoiling on the yield of spring wheat.
Age of SWE Rain** yield kg/hal RangeTreatment mm mm Difference*** Ratio**** in Ratio
dirference in yield rrorn unoisturbea sites of cont.nuous s:ubbe.“ Ratito at mean vlea or treatment to that on stuoDe.
Toe average. 4-yr vie.d increases un spring wneat over roar monitored on unnlsturbea.continuous stubble of: a lOda sg ha on suosolea. snow-managec plots. :n;523sgna ons’s 9a’agd .190 s roed o ts ard : 4o g ha it s osit it 0 c’s xi thoit snow ra”agneclearly demonstrate the value of comhining subsoi.ling ann snow management practices. Itis reasonable to assume that larger increases would have been achieved with the addition atsupplemental tertilizer.
S [MM4fV
the results of a field monitoring program conducted wthin the Brown and Dark BrownSOIl zones in the Province of Saskatchewan on the meitwater infiltration cnaracter/stics orompleteiv-frozen’ uncracked. undisturbed. cracked and subsoiled SOilS are presented, Acompletely—frozen soil is one wnose frozen profile does not thaw to appreciable depth duringsnowcover ablation. The importance of the macropore content of these soils to theinfiltration process is emuhasized.
Meltwater znfiltration into soil cracks and rips’ averaged 3.8 and 5.8 times theamounts to the same soils in uncracked and undisturbed condition, independent ot availablesnow water. Based on the field observations a practical model as developed which gives theaverage depth of infiltration over a field subsoiled to a depth between 400 and 500 mm asa function of line spacing. snowcover water equivalent and soil moisture icel content.Using this model with long--term snowfall statistics and reported catcu efficiencies ofstubble management practices. it is suggested that subsoiling on spacings between 0.9 and1Dm should enhance the infiltration properties of frozen soils within the semi—arid Prairieregion so they are capable of absorbing most of the snow water accumulated by stubblemanagement practices in a normal snow year.
The annual yields of spring wheat over a 4—yr period on subsoiled plots with snowmanagement averaged 1033 kg/ha higher than the yields from plots of continuous, undisturbedstubble. This difference is in contrast to an average ancrease on subsoiled plots withoutsnow management of only 230 kg/na and emphasizes the neeo to combine the practices formaximum return. An average yield increase in the range of 7.3 kg/ha for each additional mmof available water found in the study corresponds closely with tOe values reported ov soilscientists, The difference between tOe annual yields from subsoiled areas and piots ofundisturbed stubble decreases substantially following toe second year of treatment. thistrend coupled with field observations of changes in the infiltration properties of rips withtime suggests a useful life for the treatment effects of the order 01 4 to 5 years.
ACKNOWLEDGEMENTS
The writers wish to acknowledge the technical support provided the project by Mr. Dellbavne and the tinanciai support of tOe Strategic Grants Program. Food and Agriculture,Natural Sciences and Engineering Research Council of Canada and the Agriculture DevelopmentFund. Province of Saskatchewan under the project “Snow Management and Meitwater Enhancement,ERDA Project 3.2.3
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