Root zone soil moisture redistribution in maize (<i>Zea mays</i> L.) under different water application regimes

doi:10.4236/as.2013.410070

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Vol.4, No.10, 521-528 (2013) Agricultural Sciences

http://dx.doi.org/10.4236/as.2013.410070

Root zone soil moisture redistribution in maize (Zea

mays L.) under different water application regimes

John Mthandi1*, Fedrick C. Kahimba1, Andrew K. P. R. Tarimo1, Baandah A. Salim1,

Maxon W. Lowole2

1Department of Agricultural Engineering and Land Planning, Sokoine University of Agriculture, Morogoro, Tanzania;

*Corresponding Author: [email protected]

2Department of Crop Science, Bunda College of Agriculture, Lilongwe, Malawi

Received 26 June 2013; revised 26 July 2013; accepted 1 August 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Soil moisture availability to plant roots is very

important for crop growth. When soil moisture

is not available in the root zone, plants wilt and

yield is reduced. Adequate knowledge of the

distribution of soil moisture within crop’s root

zone and its linkage to the amount of water ap-

plied is very important as it assist s in optimising

the efficient use of water and reducing yield loss-

es. The study aimed at evaluating the spatial

re dis tribution of soil moisture within maize roots

zone under different irrigation water application

regimes. The study was conducted during two

irrigat ation season s of 20 12 at Nkango Irrigation

Scheme, Malawi. The trials consisted of fa ctori al

arrangement in a Randomised Complete Block

Design (RCBD). The factors were water and ni-

troge n and both were at four levels. The Triscan

Sensor was used to measure volumetric soil mo-

isture contents at different vertical and lateral

points. The st udy inferred tha t th e de g ree of soil

moisture loss depends on the amount of water

present in the soil. The rate of soil moisture loss

in 100% of full water requirement regime (100%

FWRR) treatment was higher than that in 40%

FWRR treatment. This was particularly noticed

when maize leaves were dry. In 100% FWRR

treatment, the attraction between water and the

surfaces of soil particles was not tight and as

such “free” water was lost through evaporation

and deep percolation, while in 40% FWRR, water

was strongly attracted to and held on the soil

particles surfaces and as such its potential of

losing water was reduced.

Keywords: Soil Moisture Content; Full Crop Water

Requirement Regime; Maize Root Zon e

1. INTRODUCTION

Water use efficiency and water productivity are im-

portant agricultural performance indicators that are used

in assessing the impact of water management practices

that are used to produce more crops with less water [1].

It is vital to specify the water use components when de-

riving water use efficiency and productivity to avoid the

confusion over the two, since these terms are related, but

are not essentially the same [2].

In irrigation engineering terms water use efficiency is

defined as the ratio between amount of water required to

grow a crop (i.e. evapotranspiration, percolation and see-

page, leaching for salinity control, and land preparation),

and the total amount of water applied in irrigation sink

or within a spatial domain of interest [2]. Water use effi-

ciency (WUE) as an agronomic term means the ratio be-

tween marketable crop yield and amount of water stored

in the root zone that is only up-taken and transpired by

the crop [3]. Under agronomic definition of water use

efficiency, amount of water stored within the crop root

zone but lost through evaporation is not accounted for

[4]. Irrigation engineering and agronomic water use ef-

ficiencies may be related to each other but under nor-

mal circumstances increase in irrigation engineering wa-

ter use efficiency does not result in an increase in agrono-

mic water use efficiency. For example, in Irrigation engi-

neering water use efficiency is directly correlated with de-

crease in applied water. But this does not mean that re-

duced amount of water will result in an increase in crop

yield. This is because less amount of applied water may

not have the ability to flush out salts or may not be enough

to meet the demand of the crops hence low yield may oc-

cur meaning that agronomic water use efficiency is low.

The ambiguity in the definitions and interpretation of wa-

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528

522

ter use efficiency has resulted in the introduction of water

productivity replacing agronomic water use efficiency [5].

Water Productivity (WP) is defined as a ratio of unit

of yield produced to unit volume of water used to pro-

duce the yield [6]. When water is in short supply, the WP

is substantially increased through deficit irrigation. [7,8]

reported that in several situations, the 50% depletion level

of available soil moisture is the critical point of many

soils beyond which yields were reduced. On the other

hand, the 50% - 60% replacement of total crop water re-

quirements was found as the critical range in which WP

realises acceptable yields under deficit irrigation [9,10].

Agronomically the 50% - 60% depletion of readily avai-

lable water corresponds to the threshold for leaf expan-

sion [11]. Soil moisture availability to plant roots is very

important for crop growth. When soil moisture is not

available in the root zone, plants wilt and yield is re-

duced. [12] reported that status, availability and distri-

bution of soil moisture within a root zone of crop affect

the growth and yield of crops. When crop roots are using

less energy to extract water from the soil, the saved ener-

gy is converted into yield and this increases water pro-

ductivity [13]. When crop roots are having difficulties in

extracting water from the soil, the plant is stressed and

this is manifested through decrease in leaf area growth

which limits the ability of leaves to absorb sunlight and

transpire water resulting in less crop yield.

Adequate knowledge of the distribution of soil mois-

ture within crop’s root zone and its linkage to the amount

of water applied is very important as it will optimise the

efficient use of water and reduce yield losses. The aim of

this study was to evaluate the spatial redistribution of

soil moisture within maize roots zone under different ir-

rigation water application regimes.

2. MATERIALS AND METHODS

2.1. Site Description

The research study was done at Nkango Irrigation

Scheme in Kasungu district. Data were taken in two

irrigation growing seasons from 1st June to 8th September,

2012 during the first season,and from 10th September to

5th December, 2012 during the second season. Nkango

Irrigation Scheme is an informal scheme which is owned

and managed by the local communities and is situated at

Latitude 12˚35’ South and Longitudes 33˚31’ East and is

at 1186 m above mean sea level. The study area has a

unimodal type of rainfall with rains between December

and April. The mean annual rainfall is about 800 mm.

The site lies within maize production zone of Malawi

and has dominant soil type of coarse sandy loam. Small-

holder farmers in the area practise irrigation and are

conversant with water application regimes.

The soil of the plots is sandy loam with a low soil

organic matter and nutrient concentration as described in

Table 1. Characteristics of the top soil (0 - 20 cm) of at the

research site in Nkango, Malawi.

Soil properties Values

Clay (%) 13

Silt (%) 17

Sand (%) 70

Carbon (%) 0.599

C/N ratio 13.011

OM (%) 1.0773

Total nitrogen (%) 0.046

Total phosphorus (ppm) 33.206

Total potassium (µeq·K·g−1) 1.2153

Exchangeable calcium (µeq·K·g−1) 19.254

Exchangeable magnesium (µeq·K·g−1) 28.964

Moisture content (%) 4.163

Field capacity (%) 20

Wilting capacity (%) 10

Bulk density (g/cm3) 1.59

pH 5.2

Ta ble 1. The Cation Exchange Capacity is low (50.00 -

80.00 µeq·g−1), and the pH decreased from acidic (5.2)

to strongly acidic (4.7). The salinity of the soil was very

low (1.7 mmhos/cm).

2.2. Experimental Design

The plot size was 5 m by 5 m and ridges were spaced

at 75 cm. The plots were separated from one another by

a 2-metre boundary to avoid “sharing” of responses, wa-

ter and nitrogen (edge effects). Three maize seeds of hy-

brid maize (SC 407) were planted per hole at plantspac-

ing of 25 cm and row spacing of 75 cm. They were later on

thinned to one seed per station 7 days after germination.

The trials consisted of factorial arrangement in a Ran-

domised Complete Block Design (RCBD). The factors

were water and nitrogen, and both were at four levels.

Water had four application regimes and these were as

follows: farmers’ practice regime (contol); full (100%)

water requirement regime (FWRR) of maize plant; 60%

of FWRR; and 40% of FWRR. A full maize water re-

quirement was determined by using the procudure des-

cribed in [14]. Nitrogen had four application regimes

and these were as follows: The Typical Nitrogen Appli-

cation Rate in the area (TNPRA) of 92 kg N/ha was used

as a basis (control) to determine other dosage levels in

the study [15]. The nitrogen dosage levels were as fol-

lows: TNPRA, 92 kg N/ha; 125% of TNPRA, 115 kg

N/ha; 75% of TNPRA, 69 kg N/ha; and 50% of TNPRA,

46 kg N/ha.

2.3. Data Collection

The Triscan Sensor (EnviroScan, Sentek Pty Ltd.,

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528 523

Stepney, Australia), which has ability to sensor volu-

metric soil moisture at the instant time of inserting the

monitoring probe in the soil, was used to measure soil

moisture content at different points (defined by lateral

and vertical distances) within maize root zone depth.

The lateral distances were at interval of 5 cm as shown

in Figure 1. The measured points were: at point of ferti-

lizer application (represented by 0 cm, which is 10 cm

from the plant), at 5 cm away from the plant (represent-

ed by −5 cm), at 5 cm towards the plant, 10 cm towards

the plant (this point was maize planting station), and 15

cm (this point was 5 cm after planting station) as shown

in Figure 1. The lateral distances were taken based on

spreading and elongation pattern of lateral roots of maize

plants. The lateral readings of nitrogen were respectively

taken at five soil depths of 20, 40, 60, 80, and 100 cm

from the soil surface,and were selected based on maize

roots growth habits, which extend down to 100 cm [16].

2.4. Data Analysis

The data presented in this paper were from treatment

combinations of 100% of FWRR and 92 N Kg/Ha and

40% of FWRR and 92 N Kg/Ha. This is because statis-

tically treatment combination of 100% of FWRR and 92

N Kg/Ha gave the highest nitrogen use efficiency and

40% of FWRR and 92 N Kg/Hagave the highest water

Figure 1. Showing measurement points.

productivities. The data are presented in graphical form

to indicate comparative redistribution of soil moisture

content in both treatment combinations.

3. RESULTS AND DISCUSSIONS

Figures 2 and 3 indicate the spatial distribution of soil

moisture on 10th July in maize plots of 100% FWRR and

40% FWRR respectively. The figures indicate that at

point where maize was planted, the soil moisture was

high at 20 cm in 40% than in 100%, while at 40 cm deep

Figure 2. Soil moisture content distribution in 100% FWRR on

10 July.

Figure 3. Soil moisture content distribution in 40% FWRR on

10 July.

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528

524

soil moisture content was high in 100% FWRR than in

40% FWRR treatments. At 60 cm, the soil moisture was

very high in 100% FWRR and was about 27% while in

40% FWRR, the soil moisture was about 18%. At 100

cm below, the soil moisture contents were relatively the

same in both plots of 100% FWRR and 40% FWRR.

The general observations indicate that at 20 cm below,

there was negligible difference of soil moisture contents

in both treatments.Higher soil moisture contents were

observed from 40 cm, 60 cm to 80 cm. At 100 cm neg-

ligible differences were again observed in both treat-

ments. The reason to this observation is that at shallow

soil depths soil water loss through evaporation is propor-

tional to the degree of soil wetness, i.e. moist surface

loose high amount of water than less moist surfaces due

latent heat which is absorbed by soil water and hence

subjecting the surface to more water loss. Over the period,

the surface will relatively have the same moisture con-

tents. On 10th July, maize plants were almost 40 days

after planting and the leaves were not fully developed to

completely shade the land surface, as such during this

period water loss through evaporation was high.

Between 20 and 80 cm deep the differences in soil

moisture content may be due to uptake by maize roots.

In 40% FWRR, the plants roots are stressed and have

less ability to attract water from the surrounding areas.

In 100% FWRR, the surrounding soil has high moisture

contents due to applied water but also due to ability of

plant roots to attract water from the surrounding areas.

At the depth of 100 cm, the soil moisture contents may

entirely be due to not being uptaken by maize roots.

Several studies have shown that soil moisture increases

with depth. It is unlikely that on 20th July, water through

deep percolation may have greatly attributed to the

changes of soil moisture at 100 cm in both treatments.

Figures 4 and 5 show that spatial distribution of soil

moisture contents at 20 cm deep in both treatments had

similar pattern and they all spread with 15% to 25% soil

moisture contents. Big differences of spreading patterns

were observed in at 40 cm below. At 60 cm below the

distribution had similar pattern with the lowest figures at

lateral distance of 10 cm and highest at 0 cm. At 100 cm

below, soil moisture though similar distribution pattern

in both treatments, but the figures in 100% FWRR treat-

ment were much higher than those in 40% treatment.

The high differences at 60 cm may be due to absorption

of water by maize roots and this can be substantiated by

a low figure at lateral distance of 10 cm which was at the

point of maize seeds plantation. Many studies on maize

roots behaviour suggests that maize roots tend to grow to

100 cm, but during flowering stages, maize roots are

more active at depth between 50 to 70 cm below and this

study suggest that rate of water absorption was very high

within this soil depths. At 100 cm below soil moisture

increase in 100% FWRR treatment may be due to deep

percolation of water from the applied water. On 20th July

the maize plant had reached 50 days after planting. The

plant leaves had fully developed with leaf area index at

its highest, and during this period land surface is wholly

covered by leaves resulting in less evaporation and high

downward movement of water as there is less competing

force.

Figures 6 and 7 indicate the spatial distribution of soil

moisture on 30th July when the maize was 60 days after

planting old. The behaviour of soil moisture contents at

Figure 4. Soil moisture content distribution in 100% FWRR on

20 July.

Figure 5. Soil moisture content distribution in 40% FWRR on

20 July.

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528 525

Figure 6. Soil moisture content distribution in 100% FWRR on

30 July.

Figure 7. Soil moisture content distribution in 40% FWRR on

30 July.

20 cm in both treatments suggests increase in all plants

as compared to previous points i.e. the measured points

at 20 cm have more soil moisture contents than those

measured before. At 40 cm, huge differences are noted in

40% FWRR treatment where at lateral distance of −5 cm,

the content of soil moisture was lowest followed by at 10

cm. This period due to development of leaves there are

less evaporation losses but transpiration losses have in-

creased meaning that the ability of maize roots to absorb

soil water has increased, hence the negative gradient of

water has been created around maize roots.

The stressed roots tend to grow towards the regions

where there is water. This situation has made water to

move from surrounding areas to the areas next to plant

roots. The decrease in losses through evaporation has

made the surface soil to have high moisture content than

before.

On 9th August, when the maize plant was 70 days old,

Figures 8 and 9 indicate the high variations in the spatial

distribution of soil moisture. At 20 cm below, the dis-

tribution of moisture is in both treatments spread out

within 20 to 25%, at 40 cm below there is high variation

Figure 8. Soil moisture content distribution in 100% FWRR on

9 August.

Figure 9. Soil moisture content distribution in 40% FWRR on

9 August.

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528

526

of moisture distribution i.e. spread out from 22 at 15 cm

to 32% at −5 cm in 100% FWRR treatment while in

40% FWRR treatment the distribution is spread within

25 at −5 cm to 27% at 0 cm, the small difference at 40

cm in 40% FWRR shows that there was less water ab-

sorption activity which would have resulted in some

points having less moisture content due to absorption

than other points. In 100% FWRR treatment, the high

variations of soil moisture contents indicates that some

points were being absorbed than other points for example

at the lateral distances of 15 cm, 5 cm, and 0 cm more

water was being absorbed than at 5 cm away from the

plants (−5 cm) which had high value of 32%. At 60 cm

below, in 40% FWRR treatment we are now start to see-

ing an increase in variations of soil moisture distribu-

tions which ranged from 24% at 0 cm to 28% at 10 cm,

and the increase in variations of soil moisture has con-

tinued to increase at 80 cm from 26% at 10 cm to 31% at

15 cm, and at 100 cm the variations has further increased

from 24% at 10 cm to 31% at 0 cm. The general trend of

spatial soil moisture distribution in 40% FWRR treat-

ment is that is declining while in 100% treatment the

trend of spatial moisture distribution is increasing but the

variations of moisture distribution from 60 cm in de-

creasing. The differences may be attributed to the fact

that maize roots in 40% FWRR treatment have grown

longer and are able to tap soil water at lower depth of 60

cm to 100 cm while the maize roots in 100% FWRR have

not developed progressively to actively tap water at low-

er depths. The roots develop in respond to degree of wa-

ter availability, when soil water is scarce the plant roots

develop surviving strategy of long roots so that it can tap

water at lower depths but when soil moisture is available

plant roots will convert the energy saved into yield and

roots do not grow longer.

Figures 10 and 11 show that the general trend of mo-

isture contents at all points in both treatments is de-

creasing when compared with the trend of Figures 8 and

9 on 9 August. Specific observations indicate that the

variations of moisture contents in 40% FWRR treat-

ment started at 60 cm than in 100% FWRR treatment.

On 19 August, the maize plant was 80 days old and dur-

ing this late stage most of the lower leaves of maize

plants have dried exposing ground surface to evapora-

tion which has increased due to high temperature. The

evaporation made the soils to loss more water. However,

the maize is still absorbing water because plant is still lo-

sing water through transpiration stream and this is crea-

ting demand of more water in the plants.

Figures 12 and 13, on 29th August, the maize plant

was 90 days old and all the leaves in both treatments

have dried and are no longer losing water through trans-

piration. The dying of leaves though has exposed the soil

surface and water is being lost through evaporation.

Figure 10. Soil moisture content distribution in 100% FWRR

on 19 August.

However, of interest is the rate of soil water loss, if

compared with figures of 10 and 11 it shows that Figure

12 of 100% FWRR treatment has lost more water within

the same period than that of 40% FWRR treatment. For

example, at 100 cm below of Figure 11 (100% FWRR),

at point 15 cm has lost moisture from 37% on 19 August

to 28% on 29 August, yet during the same period of 10

days and the same depth 100 cm in 40% FWRR treat-

ment, the similar point (15 cm) has moisture from 24%

on 19th August to 21%. This shows that the soil that has

high moisture content loses more water than soil that has

less moisture content. One of the reason is that there is

loose water that is freely moving within soil pores and

therefore less energy from the sun is required to eva-

porate them but in soil that have less water, water is held

tightly together and more energy is required to evaporate

them.

On 8th September, the maize plant was 100 days old

and the maize including the cobs have completely dried.

The maize was harvested on this day. The spatial mois-

ture content distribution in Figures 14 and 15 indicated

shows that there is huge decline of soil moisture content

at the shallow depth of 20 cm in both treatments as com-

pared to lower depths.

4. CONCLUSION

In this study, we infer that the degree of soil moisture

loss depends on the amount of water present in the soil.

The rate of soil moisture loss in 100% FWRR treatment

was higher than that in 40% FWRR treatment. This was

particularly noticed when maize leaves were dry. In

100% FWRR treatment, the attraction between water

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528 527

Figure 11. Soil moisture content distribution in 40% FWRR on

19 August.

Figure 12. Soil moisture content distribution in 100% FWRR

on 29 August.

and the surfaces of soil particles was not tight and as

such “free” water was lost through evaporation and deep

percolation, while in 40% FWRR, water was strongly

attracted to and held on the soil particles surfaces and as

such its potential of losing water was reduced.

The soil moisture redistribution in the root zone is di-

rectly related to the amount of applied irrigation water

and spatial distribution of soil moisture content was pri-

marily influenced by roots water uptake and evaporation.

Evaporation was critical especially before leaves were

fully developed and after the leaves have dried.

Figure 13. Soil moisture content distribution in 40% FWRR on

29 August.

Figure 14. Soil moisture content distribution in 100% FWRR

on 8 September.

Soil loss through deep percolation was high in 100%

FWRR. When the soil moisture content is optimal for plant

growth, the water in the large- and intermediate-sized

pores can easily move about in the soil which can result

in a deep percolation.

The redistribution patterns of soil moisture in both

treatments were similar. However in 100% FWRR, the

measured points had higher soil moisture contents than

that in 40% FWRR treatment and soil water has fluxed

to deeper layers, while in 40% FWRR, soil moisture was

only concentrated in the top layers of the soil and this re-

stricted water uptake by plants roots in deeper layers.

J. Mthandi et al. / Agricultural Sciences 4 (2013) 52 1-528

528

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Figure 15. Soil moisture content distribution in 40% FWRR on

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Less water uptake and high evaporation resulted in wilt-

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5. ACKNOWLEDGEMENTS [11] Steduto, P., Raes, D.T., Hsiao, C., Fereres, E., Heng, L.,

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