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IV. Efficient Utilization of Rainwater

IV. Efficient Utilization of Rainwater

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EFFICIENT UTILIZATION OF RAINWATER BY RICE



0



93



=0.982



A = 0.972

A ~0.982



=0.908



I



0



I



2



I



4



I



6



8



1



Puddling depth (cm)



0



Figure 3 Effect of depth of puddling on water flux through soils of different texture (Is, loamy

sand; 1, loam; sil, silt loam; cl, clay loam) (Sharma and Bhagat, 1993).



nates most macropores, which transmit water. The remaining macropores are

partially filled by dispersed fine particles (Sharma and De Datta, 1986; Adachi,

1990). Consequently, there is a drastic reduction in percolation losses of water

and nutrients (Sharma and De Datta, 1985, 1986; Sharma etal., 1988). Sharma

and Bhagat (1993) reported a nonlinear reduction in water flux through soils with

an increase in puddling depth (Fig. 3). This benefits the rice plant by increasing

grain yields and decreasing water requirements, thus, improving water-use efficiency. In a study at IRRI on a clay soil (Alfisol), rice grown on puddled soil

used half as much water as rice grown on nonpuddled soil (Fig. 4). Rice production on puddled soil was 2.5 times more efficient in water use than rice grown

on nonpuddled soil because of decreased water percolation losses and greater

soil moisture retention in puddled soil (De Datta and Kerim, 1974). In a clay

loam soil (Typic Argiudoll), the average daily water use for transplanted rice

during a 90-day irrigation period was 501 mm day-' with zero tillage, 263 mm



94



PRADEEP K. SHARMA AND SURJIT K. DE DA'TTA

Cumulative amount of water (mm)

1200

NONPUDDLED SOIL



A



lo00



800

600



400

200

0



20



40



60



20

80 1( 0

Day8 after planting



40



60



80



1( 0



Figure 4 Comparison of cumulative water applied, evapotranspiration, and percolation loss in

puddled and nonpuddled soils continually flooded at 5 cm (De Datta and Kerim, 1974).



day-' with minimum tillage, and 164 mm day-' with puddling (Sharma et al.,

1988). Puddling increased water-use efficiency by 5 and 1.7 times over zero and

minimum tillage (Table IV). In another experiment, puddling significantly deTable IV

Tillage Effects on Rice Grain Yield, Total Water Use, and WaterUse Efficiency in a Clay Loam Soil '



Tillage

Zero'

Minimum"

Puddling'

CD (5%)f



Grain

yield

(Mg h a - ' )



Total water

use (mm)b



Water-use

efficiency

(kg grains

ha-' mm-l)



2.6

4.3

4.5



45,090

23,670

14,760



0.06

0.18

0.30



0.9



-



-



"Adapted from Sharma el a/. (1988).

'Computed for a 90-day period.

"One spray with paraquat (at I kg a.i. ha I ) followed by a 3-day

submergence before transplanting.

'One rotovation followed by a 3-day submergence before transplanting.

eTwo animal-drawn moldboard plowings followed by three harrowings.

'CD. Critical difference.

~



95



EFFICIENT UTILIZATION OF RAINWATER BY RICE

Table V



Tillage Effects on Leaching Losses (Computed for 77-Day Period) and Nutrient Uptake of

Rice in a Clay Loam Soil“

Nutrient loss

(kg h a - ’ )

Treatment

Nonpuddled

Puddled

CD(I%)’



Nutrient uptake

(kg ha - )







NH4+



P



K



N



P



K



8.67

I .57



1.62

0.33



0.86

0.21



71

14



74

110



15

25



138

209



2.61



0.34



0.19



30



20



6



36



NO,-



“Adapted from Sharma and De Datta (1985).

bCD, Critical difference.



creased leaching losses of major nutrients, i.e., N, P, and K, and increased their

uptake by rice plants (Table V).

Puddling increases soil water retention, usually below -0.01 MPa water potential (Sharma and De Datta, 1986). Evaporation losses from puddled soils are

also low because of the increased soil microporosity. The high water retention

capacity of puddled soil may increase the energy required to evaporate the same

quantity of water, compared to an upland soil. The higher unsaturated hydraulic

conductivity of puddled soils (because of the increased microporosity) may

also help in keeping the surface soil moist longer by transporting more profile

water upward to the soil surface. Studies have shown that puddled soils maintain higher water potentials than do nonpuddled soils under conditions of moderate moisture stress (Fig. 5). Thus, puddling is a preferred technique of land

preparation in areas experiencing low to moderate drought situations (De Datta

and Kerim, 1974; De Datta, 1981; Sharma et al., 1987; Mambani et al., 1990).

But under conditions of severe moisture stress, puddled soils shrink, there is

an increase in the mechanical resistance to growing roots, cracking occurs,

and consequently rice roots are damaged. In a rain-fed lowland field study,

Thangaraj et al. (1990) found that soil mechanical impedance as low as 0.01

MPa inhibited root growth and values greater than 0.3-0.5 MPa decreased root

growth and extension by 75%. In this case rice may perform better on granulated

than on puddled soil (Sanchez, 1973; Mambani et al., 1990). However, more

research is needed to substantiate these effects in relation to soil type and rainfall

pattern.

Rice responses to tillage vary with soil texture and climatic water balance. In

one study (Sharma et al., 1987), the grain yield of rain-fed lowland rice was

significantly affected by tillage in a sandy loam but not in a clay loam soil with

a shallow water table (Table VI). Studies have shown that intensive tillage is



PRADEEP K. SHARMA AND SURJIT K. DE DATTA



96



Matric suction (kPa)



-



B



Nonpuddled

Puddled ----



50 -



I



20



40



60



80

100

40

60

Days after transplanting



80



100



Figure 5 Matric suctions in puddled and nonpuddled (A) clay loam soil at 200 mm depth (De

Datta and Kerim. 1974) and (B)sandy loam soil at 150 mm depth (Sharma er uf.. 1987) under rainfed conditions.



required for rain-fed lowland rice in highly permeable, coarse to mediumtextured soils under drought-prone environments, but not in low-permeability

soils under adequate climatic water balance (Sharma and De Datta, 1985;

Sharma etal., 1987, 1988; Mambani et al., 1989, 1990).

Krishnamoorty (1979) discussed four types of contingencies based on the

amount and reliability of rainfall received:

1. Rainfall during the vegetative and reproductive phases is adequate and assured. It is the ideal system. Puddling would probably be the best tillage system.

2. Rains during the vegetative phase are inadequate and unreliable, but rains

Table V1

Tillage Effects on Grain Yield of Rain-Fed Lowland

Rice in Relation to Soil Texture"



'



Grain yield (Mg ha - )

Treatment



Sandy loam



Clay loam



Puddling

Dry seeding

CD ( 5 % ) b



4.0

2.8

0.6



5.3

4.8

Not significant



"Adapted from Sharma et al. (1987).

*CD, Critical difference.



EFFICIENT UTILIZATION OF RAINWATER BY RICE



97



during the reproductive phase are adequate and reliable. In this case there are

two alternatives. First, dry tilling of rice followed by conversion into wetland

later in the season; second, puddling of the field when rains are sufficient and

transplanting photoperiod-sensitive varieties.

3. Rains are adequate and reliable during the vegetative phase but inadequate

and unreliable in the reproductive phase. Again, two alternatives are available.

First, transplanting rice in the puddled field and providing supplemental irrigation by storing runoff from the early rains; second, by selection of short-duration

varieties.

4. Rainfall is inadequate and uncertain during both vegetative and reproductive phases. Under this situation rice is an extremely risky crop. Other crops

having low water requirements should be planted.



2. Soil Compaction

The physical properties of medium to coarse-textured soils, low in active clay,

change little with puddling (Lal, 1985a,b; Sharma and De Datta, 1986). For such

soils, Ghildyal (1969) suggested soil compaction as an alternative to puddling.

Compaction refers to the increase in soil bulk density caused by a static or transient load applied normal to the soil surface. During compaction soil particles

become more closely in contact. Bulk density increases, total porosity decreases,

but water retention and residual pores (pores <50 pm) increase at the expense

of water transmission pores. Consequently there is a reduction in infiltration and

in percolation losses of water and nutrients (Agrawal, 1991), and there is an

increase in the water-holding capacity of soil (Gulati et al., 1985). Abo-Abda

and Hussain (1990) obtained a 13-42% reduction in infiltration of a sandy soil

due to surface compaction. The saturated hydraulic conductivity and water fluxes

through soils are log-linear and inversely related to the bulk density (Gardner

and Chong, 1990; Sharma and Bhagat, 1993). The relationship between water

flux and degree of compaction in some soils is shown in Fig. 6 . Compacted soil

layers also have relatively low evaporation losses, especially when the soil water

content is below field capacity (El-Kommos, 1989), probably due to increased

microporosity.

Soil compaction may occur at surface or subsurface levels. It involves dry

plowing of land followed by compaction, using farm machinery such as tractors

or tractor-driven or manually operated rollers, etc., at approximately Proctor soil

moisture content. The compacted soil may be dry seeded by dibbling or by opening a furrow line for dry seeding, tilled shallow before dry seeding, or shallow

puddled for transplanting.

Many studies have shown that moderate soil compaction increases rice yield

(Varade and Ghildyal, 1967; Ghildyal and Satyanarayana, 1969; Kumar et al.,

1971; Mahajan et al., 1971; Varade and Patil, 1971; Gupta and Kathavate, 1972,



98



PRADEEP K. SHARh4A AND SURJIT K. DE DATTA

10-~



- 10-5 .

-E

In

X



c

8

c

10-S



-



,



values

o



0.970



0.968

A 0.991

A 0.940

D 0.972



16’ 1

1.0



I



1.1



I



I



I



I



1.2

1.3

1.4

1.5

Bulk density (Mg m3)



I



1.6



Figure 6 Effect of degree of compaction on the water flux through soils of different textures (Is,

sandy loam; I, loam; sil, silt loam; cl, clay loam) (Sharma and Bhagat, 1993).



1974; Bhan and Padwal, 1976; Kar et al., 1976; Patel and Singh, 1979, 1986;

Reddy and Hukkeri, 1979, 1983; Singh et al., 1980; Bhadoria, 1986). It may

result, among other factors, from better root-soil contact (Varade and Ghildyal,

1967). Ogunremi et al. (1986) reported a 20% increase in rice yield with soil

compaction over puddling in a sandy loam soil. Mathan and Natesan (1990)

obtained an 18% increase in rice grain yield by compacting a Vertisol from I . 1 1

to 1.33 Mg m-3. Bhadoria and Dutta (1984) found a 50-60% increase in the

yield of upland rice by compacting a laterite soil. Some data are given in

Table VII.

Two observations emerge from these studies. First, most of the compaction

studies have been made on irrigated rice; studies on rain-fed lowland rice are

almost nonexistent. Although the purpose of soil compaction in irrigated and

rain-fed situations is essentially the same, i.e., reduction in percolation losses,

under rain-fed situations the depth to the compacted layer below the soil surface

is an important consideration. The compact layers at relatively shallow depths

may have adverse effects on rice under prolonged dry spells. Second, there have

been few investigations on optimum compaction levels for rice, and conclusions

are diverse. According to some workers, a bulk density as high as 1.80 Mg m - 3

does not adversely affect rice growth and yield in loamy sand to sandy loam soils

(Ghildyal, 1969; Singh et al., 1980; Patel and Singh, 1986). Contrary to this,

Varade and Ghildyal (1967) obtained a reduction in rice yield when the bulk



EFFICIENT UTILIZATION OF RAINWATER BY RICE



99



density of a sandy loam soil increased above 1S O Mg m-3. Our studies show a

bulk density of 1.70 Mg m-3 as critical for root growth and grain yield of rainfed rice in a loamy sand soil. At this bulk density, the saturated hydraulic conductivity of the soil was 2.8 X

m sec-! (P. K. Sharma and S . K. De Datta,

unpublished data). In a silty clay loam soil, the critical bulk density limit was

observed to be 1.63 Mg m-3 (Ghildyal and Satyanarayana, 1969). Such variations in results emphasize the need for more research to determine critical limits

of soil compaction for optimum rice growth in relation to soil type and hydrological situations. Strong interactions exist among soil type, water content, bulk

density, and root growth. According to Ogunremi (1991), the optimum bulk

density for dry matter production, 100-grain weight, panicle length and panicle

weight per hill, root density, and grain yield was 1.5 Mg m-3 under nonflooded

conditions and 1.6 Mg m-3 under flooded conditions. Excessive soil compaction

led to a reduction in rice yield (Ogunremi et al., 1985).

Subsurface soil compaction may be achieved either by using heavy machinery,

such as road rollers, pneumatic tire rollers, tamping rollers, and bulldozers, at

the soil surface and then recultivating the surface soil layer (Yamazaki, 1988),

or by directly compacting the subsoil after removing the top soil layer (Mallick

et al., 1977; Somani and Kumawat, 1986; Yadav and Somani, 1990). The effec-



Table VI1

Effect of Different Land Management Practices on Grain Yield and Water-Use Efficiency of

Irrigated Rice



Soil

texture

Loamy

sand

Sandy

loam

Sandy

clay

loam



Water-use

Bulk

efficiency

density Grain yield (kg ha (Mg I I - ~ )(Mg h a - ’ ) m m - ’ )







Tillage

Puddling

Compaction

CD ( 5 % )

Dry seeding

Compaction

CD (5%)

Dry Seeding

Puddling

Compaction

CD (5%)

Dry seeding

Puddling

Compaction

CD ( 5 % )



1.75

-



1.42

I .63

I .so

1.45



1.62

-



8.42

8.82

0.39

1.80

2.75

0.19

1 .so

2.70

2.90

0.30

4.65

5.03

5.18

0.39



3.40

4.08

0.24

-



0.60

1.06

1.41

4.36

5.70

6.03



Ref

Patel and Singh (1986)



Bhadoria (1986)



Reddy and Hukkeri (1983)



Bhan and Padwal (1976)



100



PRADEEP K. SHARMA AND SURJIT K. DE DATTA



tive depth of soil compaction varies with the soil type, machine type, soil moisture content, and the extent of soil manipulation before compaction. Four to six

passes with a 6-ton road roller at Proctor moisture content may compact soil up

to a 30- to 35-cm depth (Yamazaki, 1988). The latter technique is in use in Japan.

Mallick et al. (1977) obtained a 25-44% saving in irrigation water, without any

adverse effect on rice yield, by compacting the 20- to 40-cm soil layer to as high

as 1.75 Mg m-’ bulk density.

Some information is available on the longevity of subsoil compaction effects.

McKibben (197 1) observed that deep frost conditions reduce compaction effects

over a period of time. But Gaultney et al. (1982) and Voorhees (1983) reported

limited effects of natural forces, such as wet-dry and freeze-thaw cycles, on

compacted soil layers. Voorhees et al. (1986) observed subsoil compaction effects after four seasons of freezing and thawing, whereas Blake et al. (1976)

observed such effects even after 10 seasons. Hakansson et al. (1987) and Lowery

and Schuler (1991) concluded that, depending on clay content, the compaction

effects may persist for 5 years or more. Mathan and Natesan (1990) observed

residual effects of compaction on rice in a Vertisol over five growing seasons.

According to Logsdon et al. (1992), compaction persisted for 7 years in the 35to 60-cm zone of a clay loam soil.

The choice between surface and subsurface compaction would depend on the

type of cropping systems being followed. In a rice-rice cropping system subsurface compaction has an advantage over surface compaction in that (1) it is not

repeated every season and (2) if below the root zone, it does not affect the rice

root system. Surface compaction above the critical limit would adversely affect

the rice roots. In a rice-upland crop cropping system, however, subsurface compaction may interfere with the roots of upland crops following rice growth.



3. Fallow Land Management

A considerable amount of soil moisture is lost through evaporation and transpiration by weeds if the land remains fallow for a few weeks during the dry

season before the onset of monsoons. If this moisture is conserved in situ, it will

help in the early establishment of rain-fed rice and reduce the chances of the crop

suffering from considerable drought damage.

Studies conducted at IRRI in the Philippines suggest that soil mulches created

by shallow (10 cm) or deep (20 cm) tillage, residue mulch, and chemical weed

control during the fallow period are effective in conserving soil moisture (Bolton

and De Datta, 1979; Hundal and De Datta, 1982). Weed-free plots lost no more

than 5 cm of water from a 1.05-m soil profile, whereas the loss was 25 cm in

conventional weedy-fallow plots (Fig. 7). According to Bolton and De Datta

(1979), tillage at the end of a previous wet season conserved so much soil mois-



EFFICIENT UTILIZATION OF RAINWATER BY RICE



y



101



soil water content (cm3/cm3



1.25 a50 0.7



1.25 0.W 0.7!



Rototillrd



Plowed and

rototilled



Straw-mulched



Bore soil



Weedy control



Figure 7 Soil water depletion in 6 weeks (3 April-15 May) under various dry season soil

management systems (Hundal and De Datta, 1982).



ture that it enabled crop establishment 3 weeks earlier than if the soil was prepared at the beginning of the following wet season.



4. Organic Amendments

The water-holding capacity (WHC) of soils depends principally on (1) the

number and size distribution of soil pores and (2) the specific surface area of

soils. Pore size distribution affects the WHC mainly at higher water potentials,

such as those at field capacity, where the WHC is a function of soil structure. At

lower water potentials, close to the permanent wilting point, the WHC is a function of soil texture, and it also depends on the specific surface area of soil particles. Organic matter affects both soil properties. It increases soil pores favorable

for water retention and the specific surface area of soils. The water-holding capacity of organic matter is very high, although much of the water is retained at

potentials below the permanent wilting point (Feustal and Byers, 1936; Jamison,

1953). Thus, when added to soil, organic matter dilutes material of low water

retention with that of high retention.



102



PRADEEP K. SHARMA AND SURJIT K. DE DATTA



Organic matter increases aggregation and decreases the bulk density of soils

(Biswas et al., 1971; Khaleel et al., 1981; De Datta and Hundal, 1984; Sharma

and Aggarwal, 1984; MacRae and Mehuys, 1985; Clapp et al., 1986). This

results in increased total porosity and the alteration of the pore-size distribution;

the relative number of water retention pores increases. This is especially true in

coarse-textured soils (Volk and Ullery, 1973). An increase in the WHC at lower

water potentials due to an increase in the specific surface area of soils on addition

of organic matter has also been reported by various workers (Volk and Ullery,

1973; Gupta et al., 1977; Rajput and Sastry, 1988a). Niskanen and Mantylahti

(1987), using data from 60 soils, obtained the following relationship (rz = 0.84)

between the specific surface area (m2g-I), clay (%), and organic carbon content

(OC) (96)of soils:

Specific surface area = 2.69



+



1.23 clay



+ 8.69



OC



(1)



Equation (1) shows that the effect of organic carbon on the specific surface area

is about 7 times that of the clay content.

Khaleel et al. (1 98 1) concluded that about 80% of the observed variations in

percentage increase in water retention may be explained by soil texture and increases in organic carbon. Coarse-textured soils, in general, show the greatest

increase in water retention at both field capacity and wilting point due to additions of organic matter (Clapp et al., 1986).

Unlike the WHC, the plant-available water capacity (PAWC), i.e., the water

retained between field capacity and wilting point, is affected little or not at all by

organic matter. This is due to organic matter raising the water retention of soils

at both lower and higher tensions, and decreasing their bulk density. The decreased bulk density tends to counterbalance any increase in the PAWC on a

mass basis. Therefore, when moisture content is computed on a volume basis,

increases in the PAWC may not be as dramatic or may be nonexistent (Khaleel

et al., 1981; MacRae and Mehuys, 1985; Clapp etal., 1986). Most of the studies

that show positive correlation between the PAWC and the soil organic matter

have computed water retention on a mass basis (Biswas and Ali, 1969; Epstein

et a f . , 1976; Gupta and Larson, 1979; Lal, 1979; De Kimpe et al., 1982). In

order to evaluate the real effects of organic matter on the PAWC, the moisture

content should be determined on a volume basis.

Diverse opinions have emerged regarding the effect of organic matter on the

PAWC in relation to soil texture. According to one group of workers, organic

matter benefits the PAWC in coarse-textured soils only. Jamison (1953), using

the data of Peele et al. (1948), concluded that organic matter increased the

PAWC of sandy soils having < 15% clay. As soil texture became finer, organic

matter had less effect on the PAWC; factors other than organic matter dominated

in determining the PAWC. In another study, Jamison and Kroth (1958) found

that organic matter influenced the PAWC only in soils of medium to low clay



EFFICIENT UTILIZATION OF RAINWATER BY RICE



103



content (13-20%). Earlier, Coile (1938) had also concluded that organic matter

increased the moisture equivalent of coarse-textured soils more than their permanent wilting point (PWP), and the effect on water retention in general decreased with textural fineness. Several other studies have reported increases in

the PAWC (on a volume basis) with increases in organic matter content of sandy

soils (Salter et af., 1965; Biswas et af., 1971; Kumar et af., 1984; Bhadoria,

1987; MacRae and Mehuys, 1987; Ramunni et af., 1987; Rajput and Sastry,

1988a,b; Tester, 1990). But contrary to this, many researchers did not find any

improvement in the PAWC of sandy soils due to addition of organic matter

(Petersen et af., 1968; Hartmann and De Boodt, 1974; Singh et af., 1976; Gupta

et al., 1977; Kladivko and Nelson, 1979).

According to another school of thought, it is the fine-textured soils that benefit

most in their PAWC from organic matter additions (Khaleel et al., 1981; Clapp

et af., 1986). These reviews conclude that in fine-textured soils increases in

water retention due to increases in organic matter are greater at field capacity

than at wilting point. This effect is probably the result of increased aggregation,

producing a greater number of larger size pores that cannot drain under gravity.

In coarse-textured soils, on the other hand, organic matter produced a larger

increase in water retention at the PWP than at field capacity, perhaps due to an

increase in the number of smaller pores not draining at - 1500 kPa. Consequently, the PAWC increased in fine-textured and not in coarse-textured soils due

to organic matter buildup. Russel et al. (1952) reported about a 0.012 cm3 cm-j

increase in the PAWC of a silt loam soil due to addition of 40 Mg ha-' manure.

However, Petersen et af. (1968), Morachan et af. (1972), Epstein (1975) and

Weil and Kroontje (1979) did not find any improvement in the PAWC due to

organic matter additions in silt loam to clay loam soils. Sommerfeldt and Chang

(1986) observed a decline in the PAWC with an increase in organic matter content of a clay loam soil.

Many researchers have reported improvements in the PAWC due to organic

matter, irrespective of soil texture. Unger (1975) observed an increase in the

PAWC by about 1.8% (volume basis) for each per cent increase in organic matter

for soils ranging in texture from sandy to clay. Mbagwu (1989) also obtained an

increased PAWC with manure additions (2-10%) in sandy loam, sandy clay

loam, and clay soils; the effect, however, decreased with textural fineness. Studies reveal that the influence of organic matter on the WHC is comparatively more

at lower rather than at higher tensions, irrespective of soil texture (Salter and

Williams, 1963; Biswas and Ali, 1969; Biswas et af., 1971; Sharma and Nath,

1979; Joe, 1990). On the basis of data from 144 rice soils, Joe (1990) concluded

that every 1% increase in organic matter increased field capacity and the PWP

by 2.21 and 1.01%, respectively (Table VIII). Water retention at the PWP is

largely affected by the clay content of soils (Biswas and Ali, 1967).

Such diversities in conclusions may arise due to the varied nature of soil or-



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