irrigation requirements of rice under shallow water table conditions

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Agricultural Water Management, 12 (1986) 127-136 127 Elsevier Science Publishers B.V., Amsterdam-- Printed in The Netherlands Irrigation Requirements of Rice Under Shallow Water Table Conditions* R.P. TRIPATHI, H.S. KUSHWAHA and R.K. MISHRA Department of Soil Science, G.B. Pant University of Agriculture and Technology, Pantnagar- 263 145, Distr. Nainital (India) (Accepted 17 July 1986) ABSTRACT Tripathi, R.P., Kushwaha, H.S. and Mishra, R.K., 1986. Irrigationrequirements of riceunder shallow water tableconditions. Agric. Water Manage., 12: 127-136. Irrigationexperiments with wetland rice (Oryza sativa L.) paddies for 2 years under shallow water table conditions showed that intermittentsubmergence 3 days afterwater vanished from the surfaceofthe soil produced grainyieldssimilar to continuous submergence. Whereas irrigation was necessary every 3 days in clay loam ($I) and silty clay loam ($2), and every 2 days in loam (Sa) under continuous submergence of 5 ___ 2.5 cm, itwas necessaryonly every 7 days in $I and $2, and every 6 days in Ss,under intermittentsubmergence of 7.5 cm 3 days afterwater vanished from the softsurface.The intermittentsubmergence led to a 34-43% saving of irrigation water. Per- colationlosses were reduced by 36, 31 and 25% in $I, $2 and $3,respectively, as compared to those under continuous submergence. Average percolationratewas 6.1-6.4rnm day-i in $I and $2,and 10.1 mm day -I in $3. Yields were higher in the betterdrained $3 than in the poorly drained S~ and $2. Average ET ranged from 7.4 to 9.2 rnm day-1 under continuous submergence and from 6.1 to 7.1 mm day- ~under intermittentsubmergence. The intermittentsubmergence produced 7.2-14.7 kg more grain per cm of ET than continuous submergence. Regression of seasonalwater require- ment (WR) on percolation(Pc) and ET, and grain yieldon WR and ET was highly significant. Yield was bettercorrelated with ET (r=0.92) than with WR (r=0.86). INTRODUCTION Knowledge of the various components of the water balance of wetland rice ( Oryza sativa L. ) together with its production function are necessary for devel- oping an efficient and economic irrigation schedule. Depending upon texture and structure of the soil, depth of water table, depth of field submergence and *This researchhas been financedin part by a grant madeby ARS, U.S. Department of Agriculture authorizedby Public Law-480. Research Paper No. 3836. 0378-3774/86/$03.50 © 1986 Elsevier Science Publishers B.V.

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Page 1: Irrigation requirements of rice under shallow water table conditions

Agricultural Water Management, 12 (1986) 127-136 127 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

Irrigation Requirements of Rice Under Shallow Water Table Conditions*

R.P. TRIPATHI, H.S. KUSHWAHA and R.K. MISHRA

Department of Soil Science, G.B. Pant University of Agriculture and Technology, Pantnagar- 263 145, Distr. Nainital (India)

(Accepted 17 July 1986)

ABSTRACT

Tripathi, R.P., Kushwaha, H.S. and Mishra, R.K., 1986. Irrigation requirements of rice under shallow water table conditions. Agric. Water Manage., 12: 127-136.

Irrigation experiments with wetland rice (Oryza sativa L.) paddies for 2 years under shallow water table conditions showed that intermittent submergence 3 days after water vanished from the surface of the soil produced grain yields similar to continuous submergence. Whereas irrigation was necessary every 3 days in clay loam ($I) and silty clay loam ($2), and every 2 days in loam (Sa) under continuous submergence of 5 ___ 2.5 cm, it was necessary only every 7 days in $I and $2, and every 6 days in Ss, under intermittent submergence of 7.5 cm 3 days after water vanished from the soft surface. The intermittent submergence led to a 34-43% saving of irrigation water. Per- colation losses were reduced by 36, 31 and 25% in $I, $2 and $3, respectively, as compared to those under continuous submergence. Average percolation rate was 6.1-6.4 rnm day-i in $I and $2, and 10.1 mm day -I in $3. Yields were higher in the better drained $3 than in the poorly drained S~ and $2.

Average ET ranged from 7.4 to 9.2 rnm day-1 under continuous submergence and from 6.1 to 7.1 mm day- ~ under intermittent submergence. The intermittent submergence produced 7.2-14.7 kg more grain per cm of ET than continuous submergence. Regression of seasonal water require- ment (WR) on percolation (Pc) and ET, and grain yield on WR and ET was highly significant. Yield was better correlated with ET (r=0.92) than with WR (r=0.86).

INTRODUCTION

Knowledge of the various components of the water balance of wetland rice ( Oryza sativa L. ) together with its production function are necessary for devel- oping an efficient and economic irrigation schedule. Depending upon texture and structure of the soil, depth of water table, depth of field submergence and

*This research has been financed in part by a grant made by ARS, U.S. Department of Agriculture authorized by Public Law-480. Research Paper No. 3836.

0378-3774/86/$03.50 © 1986 Elsevier Science Publishers B.V.

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intensity of puddling, a considerable amount of water in flooded rice is lost as percolation. Kung et al. (1965) reported that water requirement of rice in Thailand ranged from 520 to 2549 mm out of which 273-1275 mm was perco- lation. Water requirement values of 750-2500 mm were reported by Dastane et al. (1970) for India from which about 60% was lost as percolation (Ray and Pande, 1969). Kotter (1968) reports an average water requirement of rice in Laos of 12.4 mm day-1 out of which 7.3 mm day-1 was percolation. In general, percolation rates may range from 1 mm day- 1 in well-puddled heavy soils to 20 mm day-1 or more in light textured soils (Kung et al., 1965; Talsma and Van der Lelij, 1976; Wickham and Singh, 1978).

Submergence of 3-10 cm has been found better tbr rice by IRRI (1965), Oelke and Mueller (1969), Bhatia and Dastane (1971), Pandey and Mitra (1971), Jha et al. (1981) and Batchelor and Roberts (1983). Greater depth of field submergence was recommended for weed control (Davis, 1950). Because continuous submergence leads to greater percolation, intermittent submer- gence has been proposed by Hukkeri and Sharma (1980) and Jha et al. (1981). The objective of this investigation was to determine the effect of intermittent submergence and drying on rice yields, water requirement and water losses under shallow water table conditions.

MATERIALS AND METHODS

Field and lysimeter experiments were conducted during the monsoon season of 1981 and 1982 in the three principal soil series of the area, viz. Phoolbagh clay loam (Sx), Beni silty clay loam ($2) and Haldi loam ($3). The area lies at the foothills of the Himalayan mountains on a southward, gently sloping outwash plain. The soils are developed from silty alluvium sediments under the influence of non-saline (EC < 0.4 dS/m ) shallow water tables and tall grass vegetation (Deshpande et al., 1971 ). Table 1 gives the textural analysis of the three soil types. The increasing sand content below the B-horizon shows that the deeper layers allow rapid percolation. Depth of the water table ranged from 0.2 to 0.5 m in $1, from 0.35 to 0.65 m in $2 and from 1.2 to 1.6 m in $3 during the rice crop season. The climate is sub-humid tropic. About 90% of the aver- age annual precipitation of 140 cm falls between mid-June and September.

The field experiment was done with O. sativa var. Prasad in a randomized block design with six treatments in four replications. The treatments were: rainfed (To) ; continuous submergence of 5 + 2.5 cm (T1) ; 7.5 cm submergence 1 day after drying (T2); 7.5 cm submergence 3 days after drying (T~); 7.5 cm submergence 5 days after drying (T4); 7.5 cm submergence 7 days after drying ( T5 ). The field was puddled with a tractor-driven rotary puddler. The plot size was 6 m × 5 m separated by a 3.5 m-wide space for irrigation and drainage channels in the alternate rows of plots and a 3-m-wide passage on the side.

Rice seedlings of 24-29 days were transplanted in the period 16-21 July in

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TABLE 1

Particle-size distribution ( < 2 mm fraction) and bulk density of the soil

Horizon Depth Sand Silt Clay Bulk (m) (%) (%) (%) density

(gcm -3)

Series I, Phoolbagh clay loam Ap 0-0.15 23.6 46.8 29.6 1.39 A1 0.15-0.38 26.3 45.6 28.1 1.48 Big 0.38-0.53 30.1 45.6 24.3 1.55 B2g 0.53-0.66 38.5 43.2 18.2 1.52 Clg 0.66-0.94 49.0 37.9 13.1 1.58 C2g 0.94-1.35 49.1 39.7 11.1 1.55 Series II, Beni silty clay loam Ap 0-0.20 15.1 55.2 29.7 1.38 A1 0.20-0.41 22.6 43.4 34.0 1.40 B1 0.41-0.51 22.3 44.6 33.1 1.53 B2 0.51-0.66 19.6 45.4 35.0 1.45 B3 0.66-0.76 22.6 47.1 30.3 1.50 C1 0.76-0.96 40.5 40.8 18.7 1.58 C2 0.96-1.32 44.7 40.7 15.3 1.53 Series III, Haldi loam A, 0-0.20 33.2 49.0 17.7 1.39 A1 0.20-0.33 34.4 44.6 21.0 1.46 A2 0.33-0.46 35.0 44.2 20.3 1.47 B21 0.46-0.71 34.0 43.2 22.9 1.53 B22 0.71-0.89 33.7 45.6 20.5 1.57 B3 0.89-1.04 46.4 28.0 15.6 1.61 llC1 1.04-1.14 61.9 27.8 10.6 1.65 11C2 1.14-1.35 83.4 10.9 5.6 1.69

1981 and 23-28 July in 1982 at a spacing of 23 × 10 cm. A total of 120 kg N2, 60 kg P205 and 40 kg K20 per ha was applied as urea, single super phosphate and muriate of potash, respectively. One-third of the nitrogen and all P205 and K20 were applied immediately after puddling. The remaining nitrogen was top dressed in two parts 20 and 40 days after transplanting. To regulate the depth of submergence, a brick was installed on the bund as an overflow so tha t the water in excess of 7.5 cm flowed into the drainage channel. The amount of irrigation water applied was measured through a Parshall flume. In the rainfed plots, the brick was installed to allow submergence up to 20 cm. A ponding depth of 7.5 cm in the irrigated plots was decided upon considering weed growth, tillering, percolation and water application efficiency (Evatt , 1958; Yamada, 1965; Dastane et al., 1970; Pandey and Mitra, 1971; De Datta, 1981; Jha et al., 1981).

The total input of water was the sum of irrigation water (I) and precipita-

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tion (P) . The loss included seepage and percolation (Pc), runoff (Ro) and evapotranspiration (ET):

P + I=ET + Ro+ Pc (1)

Seepage and percolation losses were taken together as Pc because they are difficult to separate. Groundwater contribution and profile moisture depletion have also been considered under rainfed conditions.

All irrigations were given in the forenoon. Daily rainfall exceeding the capac- ity of the plot was considered as runoff. Preliminary observations showed that 5 cm of water disappeared in $3 in 2 days and in $1 and $2 in about 3 days. Therefore, during continuous rains for 3 days, total rainfall minus 10 cm for plots in $3, and rains in 4 days minus 10 cm for plots in $1 and $2, were consid- ered as runoff from T1. As per schedule, 7.5 cm irrigation was required each time in T2-Ts. Therefore, runoff from T2-T5 was calculated as total rainfall during 3 days minus 7.5 cm, when the ponded water vanished prior to rainfall, or actual deficit in 7.5 cm depth of ponding prior to rainfall, plus 5 cm con- sumed in 2 days in $3 and 3 days in S 1 and $2. A proportionate deduction was made for heavy rains of shorter duration but exceeding one day.

Daily measurement of the depth of submergence was also made each morn- ing in one of the representative plots of each treatment to account for the runoff due to rainfall.

In 1982, ET was determined in eighteen lysimeters with rain shelter, installed in three rows of six each at a spacing of 15 m within the row and 30 m between the rows ( Tripathi et al., 1986) in a rice field of 1 ha. Each row of lysimeters represented the soil series Phoolbagh ($1), Beni ($2) and Haldi (Sa) respec- tively, with horizons of the same thickness as in the original profile, and asso- ciated water table fluctuations of the field. Surface dimension of the lysimeters was 1.5 m × 1.5 m with depths of 1.9 m, 2.5 m and 2.7 m for $1, $2 and $3, respectively. In lysimeters the puddling was done manually with the help of a spade. Irrigation treatments and other operations were the same as in the field plots.

When the crop was ripe, soil moisture in rainfed lysimeters and field plots was measured down to the water table with a neutron probe to determine the profile moisture depletion.

Using lysimeter ET, measured irrigation, rainfall and runoff, the percolation (Pc) in 1982 was determined from equation (1). For determining Pc in 1981, the assumption was made that the ratio of percolation to the seasonal water requirement was the same as in 1982. This also enabled the estimation of ET in 1981 from equation (1). The crop was ripe in 88 days after transplanting in $3 and in 93 days in $1 and $2.

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TABLE 2

Effect of irrigation schedules on the grain yield of rice

Grain yield (kg ha-l)

Irrigation $1 $2 Ss Treatments

1981 1982 1981 1982 1981 1982

To (rainfed) 3000 2990 2820 3060 2090 2250 T~ (continuous 5850 6160 5950 6250 6050 6570

submergence ) T2 (7.5 cm submergence 5620 6090 5790 6030 5970 6440

I day after drying) T 3 (7.5 cm submergence 5390 5670 5510 5740 5570 6040

3 days after drying) T4 (7.5 cm submergence 4900 5120 4950 4910 4070 5270

5 days after drying) T5 (7.5 cm submergence 4550 4890 4690 4620 4470 4930

7 days after drying)

S. Error+ 160 180 170 270 180 210 C.D. at 5% 480 540 510 810 540 630

RESULTS AND DISCUSSION

Grain yield and irrigation schedules

Results (Table 2) show that both in 1981 and 1982, grain yield was maxi- mum under continuous submergence (T1) but there was no significant differ- ence between yields of T2 and T3. Yields of T4 and Ts were statistically equal but significantly lower than those ofT1, T2 and T3. As per schedule, irrigations in T1 were necessary every 3 days in $1 and $2 and every 2 days in Ss. Irrigations in T3 were necessary every 7 days in S1 and $2 and every 6 days in $3.

Under rainfed condition, yield in Phoolbagh clay loam (S1) and Beni silty clay loam ($2) were 1.4-1.5 times greater than those in Haldi loam ($3), pos- sibly due to proximity of the water table to the root zone in $1 and $2. Under irrigated conditions, yields in general were higher in $3 than in S1 and $2 (Table 2). This shows that the better-drained medium-textured $3 would be more suitable for rice production under irrigated conditions but a poorly drained, finer-textured S1 and $2 would produce better than $3 under rainfed or subop- timal irrigation conditions. Poorly drained, finer-textured soils are reported to be strongly reduced compared to lighter-textured, better-drained soils which retain an oxidizing root zone for longer periods (Ponnamperuma, 1972 ).

As shown in Table 2, yields in 1982 were higher than in 1981. This may be due to rainfall which was about 1.7 times greater in 1982 (81.9 cm) than in

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TABLE 3

Seasonal water requirement and amount of irrigation water ( rainfall = 47.8 cm in 1981 and 81.9 cm in 1982 )

S~ $2 S:,

T~ T:~ T~ TI T:, T.~ 'I'~ T~ T4

1981 Water requirement (cm) 160.5 115.9 93.4 162.1 120.2 99.7 198.4 146.0 123.5 Irrigation (cm) 115.0 67.5 45.0 125.0 82.5 60.0 160.0 105.0 82.5 Runoff (cm) 9.7 6.8 6.8 6.4 3.8 3.8 6.4 3.8 3.8 1982 Water requirement (crn) 156.1 111,9 96.9 159.4 123.9 101.4 200.7 158.6 128.6 Irrigation (cm) 110.0 60.0 45.0 115.0 75.0 52.5 140.0 90.0 60,0 Runoff (cm) 31.8 26.1 26.1 31.8 26.1 26.1 32.2 24.2 24.2 Average of 1981 and 1982

WR (cm) 158.3 113.9 95.1 160.2 122.0 100.5 199.5 152.3 126.0

1981 (47.8 cm) during the crop season. However, this difference in rainfall caused differences in irrigation requirements of only 5-7.5 cm in $1 and 10-20 cm in $2 and $3 because a major portion (90-96%) of the rain fell during July and August and was largely removed as runoff.

Water requirement

The water requirement of the rice was about 1.3 times greater in $3 than in $1 (Table 3). Two years' average seasonal water requirement was 158.3 cm in

22oF

,! WR= 3.1Z..ET - 59.6 ~ ~,/ / 1901C., r" =0 .96 , N= 36 \ , / / -

13or- • oo

°//... ~ 70~

4op- I i

10i I _ _ l l __ } l ] 0 20 ~0 60 80 100 120 SEASONAL E]" AND Pc (¢rn)

Fig. I. Regression of WR on ET and Pc in rice culture.

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133

8000[ /

7000 Y : 0.90 E r - ~'857 / r'= 0.92 / ~ ~/ e

,ooo } • O®

5000 i~ ~ ' / ®

3000 ~ e

/ ' 7 2000 / , " o o

100010 Io 710 II0 130 160 190 • 220 SEASONAL ET AND WR (¢m)

Fig. 2. Regression of rice yield on seasonal evapotranspiration (ET) and water requirement (WR).

S,, 160.2 cm in $2 and 199.5 cm in $3 under continuous submergence (T~) and 113.9 cm in S~, 122.0 cm in $2 and 152.3 cm in $3 under 7.5 cm submergence 3 days after drying (T3) for statistically similar yields (Table 2 ). Seasonal water requirements were reduced by about 17% in T4 and 27.5% in T5 from those in T3 (Table 3 ) but yields also were significantly reduced from those in T~, T2 or T3 (Table 2). Therefore, a comparison of results from T~ with T3 only are important. Results from all the t reatments have been presented in Figs. I and 2.

To meet the above water requirements in T,, in 1981 and 1982, 115 and 110 cm irrigation was given in S~, 125 and 115 cm in $2, and 160 and 140 cm in $3, respectively, which, for similar yields in T3, reduced to 67.5 and 60 cm in S,, 82.5 and 75.0 cm in $2 and 105 and 90 cm in $3. This led to a 34-43% saving of irrigation water for T3 without significant yield losses.

Percolation

Percolation loss was maximum in $3 and minimum in S, (Table 4). On an average, it was 89.3 cm in S,, 87.0 cm in $2 and 118.7 cm in Ss in T, and 56.9 cm in S,, 59.9 cm in $2 and 89.3 cm in $3 in T3 during the 2 years. Thus a water regime with 7.5 cm submergence 3 days after water vanished from the soil surface (T3) led to 36, 31 and 25% reduction in the percolation loss in S~, $2 and $3, respectively, from those under continuous submergence (T~). The per- colation loss in T4 was reduced by 42-52% from that in T, but the grain yield

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TABLE 4

Seasonal percolation (Pc) and evapotranspiration (ET)

S~ $2 S:~

To T~ T~ T, To T, T3 T4 T~, T~ T~ T4

1981 Po (cm) 23.5 90.5 57.9 42.0 20.7 85.8 59.0 47.0 24.6 116.8 85.1 67.5 ET (cm) 41.1 70.0 58.0 51.4 37.4 76.3 61.2 52.7 30.4 81.6 60.9 56.0 1982 Po (cm) 34.2 88.1 56.0 43.6 34.7 88.2 60.8 47.9 48.9 120.7 93.6 70.4 ET (cm) 45.9 68.0 55.9 53.3 43.2 70.2 63.1 53.5 38.0 80.0 65.0 58.2 Aversge of 1981 and 1982 Pc (cm) 28.8 89.3 56.9 42.8 27.7 87.0 59.9 47.4 36.7 118.7 89.3 68.9 ET (cm) 43.5 69.0 56.9 52.3 40.3 73.2 62.1 53.1 34.2 80.8 62.5 57.1

was also significantly lower. On a daily basis, the average percolation rate in T3 was 6.1 mm day-1 in $1, 6.4 mm day -1 in $2 and 10.1 mm day -~ in $3 for opt imum yields. Under continuous submergence it was between 9.3 and 9.6 mm day-1 in $1 and $2 and 13.5 mm day-1 in $3.

Evapotranspiration and functional relationships

Seasonal ET was closely related with yield. It was maximum in $3 and min- imum in S~ under irrigated conditions (Table 4). Differences in seasonal ET between $1 and $3 were maximum in T1 (11.6 -12.0 cm) and narrowed down to 4.6-4.9 cm in T3. Under rainfed conditions, a relatively higher ET in $1 (41.1-45.9 cm) and lower in $3 (30.4-38.0 cm) was due to groundwater con- tribution and resultant increase in yield. Under irrigated conditions, the two years' average seasonal ET was 69.0, 73.2 and 80.8 cm in T1 and 56.9, 62.1 and 62.5 cm in Ts in S1, $2 and $3, respectively. This shows a reduction in ET of 11.1 to 12.1 cm in S1 and $2 and 18.3 cm in $3 for t reatment T3 without signif- icant loss of yield. Higher ET under continuous submergence may be due to lower root and leaf resistance (Reddy, 1979). The seasonal average ET in T~ was 7.4, 7.9 and 9.2 mm day -1 in S1, $2 and $3, respectively, which reduced to 6.1, 6.7 and 7.1 mm day -1 in T3. In T3, both the percolation and the ET were of the same order in $1 and $2 (Table 4).

Regression of seasonal water requirement (WR) on percolation (Pc) and ET ( Fig. 1 ) for the average of the replications of each t reatment in the three soils was highly significant. At Pc-- 0, the WR was 31.8 cm. There was a greater increase in Pc than ET with the amount of irrigation and rainfall.

Water use efficiency

Although the true crop water requirement is the depth of water needed to meet ET (Doorenbos and Pruitt, 1977), a considerable amount of water is

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required due to inevitable percolation losses in rice culture. Therefore, water use efficiency (WUE) of rice has often been calculated as the ratio of grain yield to ET plus Pc losses. The average water use efficiencies so obtained were 37.9, 38.1 and 31.6 kg ha -I cm -I in T~; 40.7, 40.6 and 34.6 kg ha -~ cm -~ in T2; and 47.9, 45.7 and 38.1 kg ha -~ cm -I in T3 in S~, $2 and Ss, respectively. These differences show that 7.5 cm submergence 3 days after water vanished from the soil surface for wetland rice culture produced 6.5 - 10 kg more grain per cm of water added than continuous submergence. The WUE values calculated as grain yield ET were 86.9, 83.3 and 78.1 kg ha -~ cm -~ in T~; 89.5, 89.7 and 86.1 kg ha -I cm -~ in T2; and 95.9, 90.5 and 92.8 kg ha -~ cm -~ in T3 of S~, $2 and $3, respectively.

Regression of grain yield on seasonal water requirement (WR) and ET (Fig. 2) showed that yield was better correlated with seasonal ET (r--0.92) than with seasonal WR (r = 0.86). Of course r was highly significant in both cases.

ACKNOWLEDGEMENT

The authors are grateful to Dr. Paul R. Nixon and Dr. L.N. Namken, Coop- erating Scientists, U.S. Department of Agriculture, Weslaco, TX, for their technical assistance in carrying out this work. The authors are also grateful to Dr. J. Wesseling for his valuable suggestions and technical editing of the manuscript.

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