J. Agronomy & Crop Science 161, 145—147 (1988)© 1988 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Agricultural Engineering DepartmentIndian Institute of Technology, Kharagpur, India

Soil Water Flux Below the Root Zone of a Peanut Crop

A. R. KHAN

Author's address: Dr. A. R. KHAN, Agricultural Engineering Department, Indian Institute of Technology,Kharagpur-721 302, India.

Witb 3 figures

Received November 5, 1987; accepted December 29, 1987

Abstract

This paper reports the result of field experiments conducted in Agricultural Engineering Department Farm,Indian Institute of Technology, Kharagpur, India to estimate changes in water flux below the root zone of apeanut crop with varying irrigation levels in a lateritic sandy loam soil. The magnitude and direction ofmoisture flux around the root zone were considerably influenced by levels of irrigation and time.

Introduction

The availability of water to plant roots and thetransport of soluble salts and biocides in thesoil is directly related to the movement anddistribution of water in the soil profile. Soilwater flux measures the net amount of watermoving through the soil profile, if a favourablecontrol of both water and solutes is to beachieved m relation to the crop production.Earlier upward flow has generally beenthought possible only where a water table waspresent close to the surface. However, ROSE

and STERN (1967), LA RUE et al. (1968) and VAN

BAVEL et al. (1968) reported upward watermovement into the root zone even when noshallow water table exists, depending on theroot proliferation, soil profile characteristicsand water management practices followed. Theobjective of this study was to assess the netwater flux below the root zone of a peanutcrop in lateritic sandy loam as influenced byvarying irrigation depths.

Materials and Methods

The experiment wa.s conducted at the AgriculturalEngineering Department Farm, Indian Institute ofTechnology, Kharagpur, India. The experimental

soil is a leteritic sandy loam (ultisol, pH 5.8), resultsof analysis of organic carbon, total nitrogen, avail-able P, exchangeable K are 0.38, 0.054, 0̂ .̂0005 and0.101 per cent, respectively. The CEC is 6.5 m.e.100 g"' and electrical conductivity is 84.9 x10"^ mmohs/cm.

The peanut (Arachis Hypogaea) cultivar SB XIwas sown after normal tillage operations and fer-tilizer application. The plot .irea (4 m X 3 m) wassurrounded by a border to facilitate ponding and ameasured quantity of water was applied throughwater meter. The irrigation treatments consisted of2, 4 and 6 cm amounts of water. Mercury-manome-ter tensiometers were installed in each cropped plotat depth of 10, 20, 30, 40, 50 cm in rows and in interrows area. Data were obtained from all the tensiome-ters at each depth within the centre 1 m x 1 m areaof the plot. Soil water content at each depth wasestimated using soil water pressure data from thetensiometers and a soil water characteristic curve(desorption curve). The desorption curve for eachsoil depth was obtained using undisturbed cores.The hydraulic gradients were calculated using thehydraulic potential readings and a knowledge oftensiometer depth. Hydraulic gradients for the vari-ous depth intervals and hydraulic conductivity datawere used to calculate the average flux of waterbelow the root zone of the peanut crop. The hyd-raulic conductivity functions for various depths weredetermined using the instantaneous moisture profilemethod (HILLEL et al. 1972).

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146 KHAN

0.20010

Soil moisture flux

- 0 * 0.100 0.200

cm day

0.300 O.iOO

CL

20

z 30

0.500 0.600

—o—Before irrigation—•— 2i hours after irrigation—*—i8 hours after irrigation

— 72 hours after irrigation— 96 hours after irrigotion

Fig. L Soil moisture flux as a function of soil depth at 2 cm irrigation depth with 0.75 IW/CPE ratio

-1

-0

Soil moisture f lux , cm day

0.100 0.200 0.300 O.iOO 0.500 0.600 0.700

'— Before irrigation—•—2i hours after irrigation—'—i8 hours after irrigation—^— 72 hours after irrigation—o— 96 hours after irrigation

Fig. 2. Soil moisture flux as a function of soil depth at 4 cm irrigation depth with 0.75 IW/CPE ratio

Results and Discussion

Soil water flux measured across the 40 cmdepth during the growing period for differenttimes after irrigation under varying irrigationfrequency has been presented in Figures 1through 3. In the figures, a positive flux indi-cates that water moved upward towards thesoil surface and a negative flux means down-ward flow.

During the period of irrigation, high soilwater content prevails. Just after irrigation, thedownward flux was set in and continued until24 hours as shown in the figures. In responseto the rains even after 48 hours time lapsedownward flux was observed. Some down-ward flux occurred below 30 cm which is at-tributed to gravitational and matric potentialgradients. The average pattern of the figures

indicates that there is predominantly upwardflux in response to evapotranspiration demand.Soil water potential continued to decreasemonotonically just before irrigation which ischaracterized as the most rapid decrease in the

Soil moisture flux, cm day"0.300 -0+ 0,300 0.600 asoo

10

^- 20

Q.

XI

•5 30

Before irrigation2A hours afler irrigationA8 hours after irrigation72 hours after irrigation96 hours after irrigation

Fig. 3. Soil moisture flux as a function of soil depth

at 6 cm irrigation depth with 0.75 IW/CPE ratio

Soil Water Flux Below the Root Zone of a Peanut Crop 147

soil water potential. STONE et al. (1978) re-ported that slight changes in moisture contentand minimal water movement in lower depthsindicated little root activity in this zone. Theextensive net of roots of peanut plants is most-ly concentrated in the shallow depth of10—25 cm (ARNON 1972). The amount of wa-ter moving across the lower boundary of a rootzone can be substantial (ROSE and STERN 1967,LA RUE et al. 1968 and GUPTA and JAGGI 1978),which depends on the root proliferation, soilprofile characteristics and water managementpractices followed.

Zusammenfassung

Bodenwasser-Fluf^ unterhalb der Wurzelzo-ne eines Erdnufibestandes

Die Arbeit berichtet uber Ergebnisse in Feld-experimenten, die am Agricultural EngineeringDepartment Farm, Indian Institute of Techno-logy, Kharagpur, Indien, durchgefuhrt wur-den, um Anderungen im Wasserfluf^ unterhalbder Wurzelzone eines Erdnu£bestandes mitunterschiedlichen Bewasserungshohen in ei-nem lateritischen sandigen Lehmboden zu be-richten. Die Gr6f?e und die Richtung desFeuchtigkeitsflusses um die Wurzelzone wur-

den erheblich durch die unrerschiedlichen Be-wasserungen in ihrer Menge und Zeit beein-flui^t.

References

ARNON, L, 1972: Crop production in dry regions.Vol. 2 Systematic treatment of the principal crops.Barnes and Noble Books Inc. New York.

GUPTA, R. K., and I. K. JAGGI, 1978: Seasonal waterflux below the root zone of wheat as influenced byfrequency of irrigation. Indian J. Agric. Sci. 48,34—37.

HiLLEL, D., V. D. KRENTOS, and Y. STY'LIANAU,

1972; Procedure and test of an internal drainagemethod for measuring soil hydraulic characteristicsin situ. Soil Sci. 114, 395—+00.

LA RUE, M . E., D . R. NIELSEN, and R. M. HAGAN,

1968; Soil water flux below a rye grass root zone.Agron. J. 60, 625—629.

ROSE, G. W. , and W. R. STERN, 1967: Determina-tion of withdrawl of water from soil by crop rootsas a function of depth and time. Aust. J. Soil Res. 5,11—19.

STONE, L. R., R. J. RANEY, E . T . KANEMASU, and

W. L. POWERS, 1978; Irrigation water movementbelow the corn root zone in crete silt loam. J. Soiland Water Cons. 33, 294—299.

VAN BAVEL, C . H . M., K. J. BRUST, and G. B.

STIRK, 1968: Hydraulic properties of a clay loamsoil and the field measurement of water uptake byroots: 11. The water balance of the root zone. SoilSci. Soc. of Amer. Proc. 32, 317—321.