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Percolation losses of water in relation to pre-puddling tillage and puddling intensity in a puddled sandy loam rice (Oryza sativa L.) field
Soil & Tillage Research 78 (2004) 1–8
Percolation losses of water in relation to pre-puddling tillage and puddling intensity in a puddled sandy loam rice (Oryza sativa L.) field S.S. Kukal∗ , A.S. Sidhu Department of Soils, Punjab Agricultural University, Ludhiana, Punjab 141004, India Received 21 April 2003; received in revised form 24 November 2003; accepted 15 December 2003
Abstract Effects of puddling in rice (Oryza sativa L.), especially the water loss, depend upon the extent of initial manipulation by pre-puddling tillage. The interactive effects of pre-puddling tillage and puddling intensity were studied for 3 years (2000–2002) in a field experiment at Punjab Agricultural University, Ludhiana, India, on a sandy loam soil (coarse loamy, calcareous, mixed, hyperthermic Typic Ustochrept). Treatments included three levels of pre-puddling tillage-one discing followed by a tine cultivation and planking, one discing followed by two tine cultivations and plankings and one discing followed by four tine cultivations and plankings; and three levels of puddling-one, two and four cultivations in ponded water each followed by planking. Increasing pre-puddling tillage intensity to four operations decreased percolation rate of water by 22–40% from that with one operation. Four puddling operations decreased percolation rate of soils by 30% from that with one puddling operation. This led to decrease in irrigation water used by 22–27% when pre-puddling tillage intensity increased from one to four operations. During an irrigation cycle, the percolation rate of soils decreased with time (days 1–4 after irrigation), the extent of decrease being same at all the levels of pre-puddling tillage. Higher levels of puddling increased the clay content of 0–1, 1–2 and 2–3 cm soil layers, the increase being more pronounced at higher levels of pre-puddling tillage. Puddling index, ratio of initial to final volume of settled sediments, was not affected by pre-puddling tillage intensity. It, however, increased with increasing levels of puddling intensity. Puddling index was also not a function of clay content of the surface soil layers (0–3 cm). © 2004 Elsevier B.V. All rights reserved. Keywords: Pre-puddling tillage; Puddling intensity; Rice; Percolation rate; Puddling index
1. Introduction Rice (Oryza sativa L.) has been known to be less water efficient than other crops. The amount of water consumed in the field to produce 1 kg of rice is significantly greater than for other important cereal crops (Bhuiyan, 1992). In Asia, irrigated agriculture ∗ Corresponding author. Fax: +91-161-2400945. E-mail address: [email protected] (S.S. Kukal).
accounts for 90% of total diverted fresh water and more than 50% of this is used to irrigate rice. Because of depleting ground water resources, global water crisis threatens the sustainability of irrigated rice production. Therefore, a need is being felt for decreasing water use and improving water use efficiency of lowland rice. Large reductions in water inputs can be potentially realized by reducing the unproductive percolation + seepage losses during crop growth (Bouman and Tuong, 2001). Percolation is
0167-1987/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2003.12.010
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the vertical movement of water beyond the root zone to the water table, whereas, seepage is the lateral movement of subsurface water and the two are often inseparable (Wickham and Singh, 1978). Percolation losses have been reported to vary from 0.1 to several hundred millimeter per day (Sharma and De Datta, 1985; Hardjoamidjojo, 1992; Humphreys et al., 1992; Aggarwal et al., 1995; Kukal and Aggarwal, 2002). These can be reduced by increasing the resistance to water flow in the soil and decreasing the hydrostatic pressure of the ponded water (Anbumozhi et al., 1998; Kukal and Aggarwal, 2002). The hydrostatic water pressure governing percolation flow is determined by the depth of ponded water and the distance from the soil surface to the ground water table. The resistance to percolation flow is governed by different soil factors. Bouman et al. (1994) and Wopereis et al. (1994) showed that, for most puddled lowland situations, percolation rates are fairly stable during a cropping season and little affected by ground water table depths. The resistance of water flow can be increased by changing the soil physical properties through puddling (Humphreys et al., 1992). In a sandy loam soil percolation rate of water into the soil decreased from 30.1 mm day−1 in unpuddled soil to 13.2 mm day−1 with medium puddling and 11.9 mm day−1 with high puddling (Kukal and Aggarwal, 2002). Increased puddling intensity decreased hydraulic conductivity of the puddled layer, whereas hydraulic gradient between puddled and unpuddled layers increased with increase in puddling intensity. The process of puddling actually consists of primary (pre-puddling) and secondary (puddling) tillage. The pre-puddling tillage is mainly aimed at mixing/burying stubbles, leveling the land and reducing the weed growth. The effect of puddling (wet tillage) on puddle quality and percolation rate depends on initial soil conditions created by pre-puddling (dry) tillage. Studies (Gajri et al., 1999) have reported a decrease in weed biomass with increase in pre-puddling tillage intensity in sandy loam soils in addition to decrease in percolation losses during rice. Differences in the effectiveness of puddling, apart from other factors, may also arise from the intensity of pre-puddling tillage at which the puddling was conducted. In the major rice growing area in northwest Indo-Gangetic plains, 67% of the farmers apply 4–8 pre-puddling tillage operations including harrowings and discings
(Chatha et al., 1994) in the absence of any recommendation. It is done simply to bury the wheat stubble and reduce weed growth in addition to create favorable soil tilth for puddling. There is thus, need to decide on the appropriate number of pre-puddling tillage operations in relation to percolation losses of water in rice soils. Also, the studies on the interactive effect of pre-puddling tillage and puddling on the process of percolation losses of water in rice are lacking in the literature. The present study was thus, aimed to observe the process of percolation losses in rice in relation to pre-puddling tillage intensity and puddling intensity in a sandy loam rice field.
2. Materials and methods A field experiment was conducted for 3 years (2000–2002) at Punjab Agricultural University, Ludhiana, India (30◦ 56 N, 75◦ 52 E and 247 m above mean sea level). The area is characterized by a sub-tropical and semi-arid climate with dry summers (March–June) and severe winters (December–January). The area experiences an average rainfall of about 700 mm of which 80% is received during July–September coinciding with the rice season, whereas the remaining 20% is received during rabi (November–April) season. Maximum air temperature during three rice seasons ranged between 34.3 ± 1.1 ◦ C (July) and 32.8 ± 1.6 ◦ C (October) and minimum air temperatures were between 27.2±0.5 ◦ C (July) and 18.1±1.3 ◦ C (October). Mean relative humidity during these seasons varied between 83 ± 4.3% (July) and 63 ± 4.1% (October). The soil was deep alluvial sandy loam soil (USDA: Typic Ustochrept; FAO: Dystric Cambisol). The physico-chemical characteristics of the experimental soil are given in Table 1. The soil was low in organic carbon (3.3 g kg−1 ), low in KMnO4 -extractable N (152 kg ha−1 ), medium in 0.5 N NaHCO3 -extractable P (13.7 kg ha−1 ) and medium in available K (145 kg ha−1 ). The experiment was initiated in June 2000 with rice crop after the harvest of wheat (Triticum aestivum). The treatments included three intensities of pre-puddling tillage (dry) in main plots and three intensities of puddling (wet tillage) in sub-plots in a split plot design with three replications each. Each sub-plot measured 14 m × 5.8 m. The pre-puddling treatments
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8
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Table 1 Physico-chemical properties of the study soil Soil depth
0–15 15–30 30–60 60–90 90–120 120–150 150–180
Percent
pH
Sand
Silt
Clay
78 76 68 68 70 68 74
13 14 18 18 18 20 17
9 10 14 14 12 12 9
8.0 8.1 7.9 7.9 8.0 8.0 8.1
EC (dS/cm)
0.28 0.20 0.18 0.17 0.18 0.18 0.18
were (i) one discing 1 week after harvest of wheat crop + one harrowing with a tine cultivator and a planking (PP1 ); (ii) one discing 1 week after wheat crop harvest + two harrowing operations with a tine cultivator at weekly intervals after discing, each followed by planking (PP2 ); (iii) one discing 1 week after wheat crop harvest + four harrowing operations with a tine cultivator, each followed by planking (PP4 ). The planking refers to one run of post-tillage packing and leveling of soil with a wooden plank. The discing operation was done 4–5 days after the field had been irrigated immediately after the wheat crop was harvested, with a tractor-mounted disc harrow. The harrowing operations were carried out using a tractor-mounted tine cultivator which is most commonly used by the farmers of the region for these operations. Puddling was done by harrowing with the same tine cultivator as used for pre-puddling tillage, once (P1 ), twice (P2 ) and four times (P4 ) in 8–10 cm ponding water followed by one planking operation. All the cultivation tools were operated with a 45 bhp tractor. The pre-puddling tillage and puddling operations were carried out in the same plots during all the 3 years of study in the same experimental design. Basal doses of zinc sulfate, superphosphate and one-third of total N fertilizer were applied in two equal installments at 3 and 6 weeks after transplanting. Four week old seedlings of rice, cultivar PR 113, were transplanted in 0.2 m wide rows with a distance of 0.15 m between the plants (33 plants m−1 ) between 10 and 23 June during 2000–2002 immediately after puddling. All the plots were kept flooded for the first 15 days to ensure 5 cm submergence. Afterwards, all the irrigations (each of 7.5 cm amount) were applied 2 days after complete infiltration of ponded
Bulk density (g/cm3 )
1.50 1.52 1.54 1.57 1.53 1.55 1.57
Water content, w (%) 0.3 bar
15 bar
10.7 10.2 14.4 14.4 13.5 14.4 15.0
6.2 6.8 8.6 8.7 7.8 7.8 7.4
water (Sandhu et al., 1980). Weeds were controlled by broadcasting 3 l ha−1 Butachlor 50 EW (water flowable emulsion) mixed with sand in standing water for 3 days after transplanting (DAT) and by manual weeding at 35 DAT. The crop was well protected against pests through two sprays, one each of Endosulfan 35 EC (emulsifiable concentrate) and Deltamethrin 28 EC. The percolation rate of water was recorded periodically, especially when plots were irrigated, by measuring depth of the ponded water in the whole plots between 24 h periods starting at 0800 h. Depth of water was recorded with a hook gauge from three leveled and fixed platform sites in each plot to get an average value for each plot. Percolation rates (PR) were determined from data on water levels and evaporation from open pan located in the irrigated area surrounded by rice paddies. Percolation loss was also measured simultaneously in iron rings installed in the center of each plot, while maintaining different depths of water in the rings, during the years 2000 and 2001. This was done to maintain different depths of ponded water. After the harvest of rice crop during the year 2002, soil samples were taken at depths of 0–1, 1–2, 2–3, 3–5 and 5–10 cm from each plot and the amount of clay determined in each sample using International pipette method. Samples of soil–water suspension immediately after puddling were collected in 2 l PVC containers and immediately transferred to 1 l cylinders in the laboratory. The volume of settled sediments at zero (initial) and after 48 h (final) of settling was recorded for each treatment to calculate puddling index as ratio of initial to final volume of suspended sediments. Statistical significance of the treatment effects on different parameters was inferred from the least
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significant difference using analysis of variance for a split-plot design (Steel and Torrie, 1960).
3. Results and discussion 3.1. Percolation rate and irrigation water used Both pre-puddling tillage and puddling affected the percolation rate of water into the soil during all the 3 years of study (Table 2). The percolation rate decreased significantly by 25 and 40% when pre-puddling tillage intensity increased from one to two and four operations, respectively, during the year 2000. The corresponding values during 2001 and 2002 were 14 and 30% and 14 and 22%, respectively. Increasing puddling intensity from one to two and four reduced percolation rate of water, respectively, by 15 and 25% during the year 2000, 14 and 28% during 2001 and 18 and 30% during 2002. Puddling has been reported to decrease hydraulic conductivity of puddled layer (0–10 cm) of sandy loam soil from 0.064 cm h−1 in unpuddled to 0.015 cm h−1 with medium puddling and 0.009 cm h−1 with high puddling (Kukal and Aggarwal, 2002). However, the percolation rates Table 2 Average percolation rate in rice (mm day−1 ) in relation to pre-puddling tillage and puddling intensity during 2000–2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
Year 2000 P1 P2 P4 Mean LSD (0.05), P = 1.2
40.5 36.5 31.8 36.3 PP = 1.0
32.0 26.4 22.8 27.1
25.4 20.5 18.8 21.6
32.6 27.8 24.5
Year 2001 P1 P2 P4 Mean LSD (0.05), P = 1.6
37.9 33.8 27.5 33.1 PP = 1.3
33.3 28.5 23.7 28.5
26.3 21.8 19.0 22.4
32.5 28.0 23.4
Year 2002 P1 P2 P4 Mean LSD (0.05), P = 2.6
44.1 38.0 32.2 38.1 PP = 1.4
40.1 31.2 26.3 32.6
35.6 29.2 24.8 29.9
39.9 32.8 27.8
reported by Kukal and Aggarwal (2002) in similar soil were lower compared to those obtained in the present study. This could be due to higher mean maximum air temperature during 2000–2002 throughout the crop season except for the first 4 weeks after transplanting, than that during 1994–1996. In addition, lower levels of the pre-puddling tillage treatments in the present study might have resulted in higher percolation in these plots. The percolation rates were maximum at PP1 level of pre-puddling tillage and minimum at PP4 level. In Kukal and Aggarwal (2002), the pre-puddling tillage intensity was PP4 in all the puddling treatments. Pre-puddling tillage and puddling did not interact to affect the percolation rate of water. The amount of irrigation water was affected by both pre-puddling tillage and puddling (Table 3). However, pre-puddling tillage intensity was more instrumental in reducing the amount of irrigation water used compared to puddling intensity. During the year 2001, the amount of irrigation water used decreased by 22 and 27% when pre-puddling tillage increased from PP1 to PP2 and PP4 , respectively. The corresponding values during the year 2002 were 19 and 22%, respectively. On the other hand, increase in puddling intensity from P1 to P2 and P4 decreased the amount of irrigation water by 4 and 7% in 2001 and 7 and 10% in 2002. The dominance of pre-puddling tillage in reducing the amount of irrigation water could be due to increased amount of clay content of surface 3 cm layers at higher levels of pre-puddling tillage. Table 3 Amount of irrigation water used (mm) in rice in relation to pre-puddling tillage and puddling intensity during 2000–2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
Year 2001 P1 P2 P4 Mean LSD (0.05), P = 8.70
179 168 165 171 PP = 4.70
139 133 130 134
131 128 117 125
149 143 138
Year 2002 P1 P2 P4 Mean LSD (0.05), P = 4.27
192 175 171 179 PP = 3.73
153 144 139 145
147 141 132 140
164 153 147
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8 PP1
PP2
5 PP4
4 Percolation rate (cm)
3.5 3 2.5 2 1.5 1 0.5 0 0
1
2
3
4
5
Days after irrigation
Fig. 1. Variation of percolation rate of water during an irrigation cycle as affected by pre-puddling tillage intensity.
3.2. Percolation losses during an irrigation cycle
3.3. Clay content of the puddled surface layers
Percolation rate of water decreased with time during an irrigation cycle at all the levels of pre-puddling tillage. (Fig. 1), the decrease being more pronounced at lower levels of pre-puddling tillage. At PP1 level of pre-puddling tillage, the percolation rate decreased by 23% from day 1 to 4, 24% at PP2 and 22% at PP4 levels. At PP1 level the percolation rate of water on day 1 after irrigation, was 3.5 cm day−1 and it decreased to 2.7 cm day−1 on day 4. Same was the trend at PP2 and PP4 levels. However, unlike puddling intensity (Kukal and Aggarwal, 2002), the extent of decrease was same at all the levels of pre-puddling tillage. The decrease in percolation losses of water with decrease in PWD was, thus, not a function of pre-puddling tillage intensity as was the case in puddling, where the decrease was more at lower levels. Kukal and Aggarwal (2002) observed decreasing percolation rates with time during an irrigation cycle at all the levels of puddling intensity and puddling depth in similar type of soils. The decrease in PR with time during an irrigation cycle could be due to the decreasing ponding water depth (PWD) as the percolation of water into the soil progressed (Kukal and Aggarwal, 2002). Shallow PWD reduces the wetted area of inter-plot bunds and limits the amount of water infiltrating laterally into the bunds. Furthermore, if the PWD is kept very low or if the field is maintained at saturation point, the water loss is greatly reduced because the unevenness of the soil surface prevents water movement to the bunds and subsequent loss through under-bunds (Tabbal et al., 1992).
The clay content of 0–1, 1–2, 2–3 and 3–5 cm puddled soil layers in relation to pre-puddling tillage and puddling is depicted in Fig. 2. Puddling increased clay content of 0–1, 1–2 and 2–3 cm soil layers, whereas in 3–5 cm soil layers, no significant difference in clay content was observed. Higher level of puddling intensity resulted in higher clay content in 0–1 cm soil layer at all the levels of pre-puddling tillage, but the differences in clay contents due to puddling intensity were more at higher level of pre-puddling tillage. At PP1 , the clay content of 0–1 cm soil layer was higher with P4 , but the difference was not significant (Fig. 2a). At PP2 level of pre-puddling tillage, the clay content was maximum with P4 and minimum with P1 (Fig. 2b) and this difference between P2 and P4 further increased at PP4 level of pre-puddling tillage (Fig. 2c). At PP1 level the clay content of 1–2 cm soil layer decreased at all the levels of puddling, whereas in 2–3 and 3–5 cm soil layers the clay content resembled to that in 0–1 cm soil layer. At PP2 level clay content of 3–5 cm soil layer was less at all the levels of puddling except P1 where it was similar to that in 0–1 cm soil layer, indicating that the aggregates of this layer could not be destroyed at P1 level of puddling. In PP4 level, the clay content of lower layers decreased at all the levels of puddling intensity except at P2 , where it was slightly higher even from that in 0–1 cm soil layer. This difference could be due to higher clay content of 3–5 cm soil layer even before puddling. The clay content of lower layers (1–2 and 2–3 cm) was not different for different puddling
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16
17
18
Percent clay 19
20
21
Soil depth (cm)
0 1 2
P1 3
P2 4
P4
(a) 5
16
17
Percent clay 18 19
20
21
Soil depth (cm)
0 1 2
P1 3
P2 4
P4
(b) 5 Percent clay 16
17
18
19
20
21
Soil depth (cm)
0 1 2 P1
3
P2
4
P4
(c) 5
Fig. 2. Effect of puddling intensity on the clay content of 0–5 cm soil layers with (a) PP1 ; (b) PP2 ; (c) PP4 levels of pre-puddling tillage.
intensities at PP1 level of pre-puddling tillage, but at PP2 and PP4 levels, the differences increased in lower layers as well. This signifies that pre-puddling tillage has a role to play in preparing the soil for an efficient puddling, bringing finer soil particles into suspension. These particles then settle according to their size with the coarsest particles settling first and finest in the last. Graded sediment layer with coarsest particles on the bottom and the finest particles on top gives more seepage control than even a uniform compact layer (Bouwer et al., 2001). Thus, pre-puddling tillage
intensity is responsible for determining the extent of amount of clay particles brought into suspension by puddling and their settling on the surface layer of soil and reducing the percolation rate of soils. 3.4. Puddling index of soil The puddling index was not affected by pre-puddling tillage intensity (Table 4). However, puddling intensity helped increase puddling index of soils significantly. It was higher by 48% with two puddling operations
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8 Table 4 Puddling index of soils in relation to pre-puddling tillage and puddling intensity during the year 2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
P1 P2 P4 Mean LSD (0.05)
0.015 0.028 0.043 0.029 PP = NS, P = 0.002
0.017 0.033 0.046 0.032
0.016 0.033 0.051 0.033
0.016 0.031 0.047
and 66% with four operations than that with one puddling operation. More churning action with higher level of puddling resulted in more dispersion of soil particles and ultimately the high puddling index. Puddling index, however, was not a function of clay content of the puddled surface layers. Thus, the clay content of the surface layer and puddling index are two separate indices of puddling especially in sandy loam soils and are independent of each other. Thus, in coarse-textured soils the clay content of surface layer may be used as an index of puddling. In such soils even four pre-puddling tillage operations could help in better controlling the percolation losses at the lower level of puddling intensity as intensive puddling in such soils results in development of sub-surface compaction (Kukal and Aggarwal, 2003).
4. Conclusions Pre-puddling tillage plays a significant role in decreasing the percolation losses of water in rice fields by manipulating the initial soil conditions especially the soil particle detachment so as to be able to be brought into suspension by the puddling operations. The clay content in the surface 3 cm soil layers increased with increase in puddling intensity but the increase was more pronounced at higher levels of pre-puddling tillage. Thus, the clay content of the surface layers is the most controlling factor for percolation rate of soils in the sandy loam soils. The percolation rate decreased with time during an irrigation cycle, the decrease being more at higher levels of pre-puddling tillage. Puddling index was not a function of clay content of surface soil layers.
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Acknowledgements The authors are grateful to Indian Council of Agricultural Research, New Delhi, for providing the financial assistance for carrying out this study under NATP Project (PSR mode). References Aggarwal, G.C., Sidhu, A.S., Sekhon, N.K., Sandhu, K.S., Sur, H.S., 1995. Puddling and N management effects on crop response in a rice–wheat cropping system. Soil Tillage Res. 36, 129–139. Anbumozhi, V., Yamaji, E., Tabuchi, T., 1998. Rice crop and yield as influenced by changes in ponding water depth, water regime and fertigation level. Agric. Water Manage. 37, 241– 253. Bhuiyan, S.I., 1992. Water management in relation to crop production: case study on rice. Outlook Agric. 21, 293–299. Bouman, B.A.M., Tuong, T.P., 2001. Field water management to save water and increase its productivity in irrigated rice. Agric. Water Manage. 49, 11–30. Bouman, B.A.M., Wopereis, M.C.S., Kropff, M.J., tan Berge, H.F.M., Tuong, T.P., 1994. Water use efficiency of flooded rice fields. II. Percolation and seepage losses. Agric. Water Manage. 26, 291–304. Bouwer, H., Ludke, J., Rice, R.C., 2001. Sealing pond bottoms with muddy water. J. Ecol. Eng. 18, 233–238. Chatha, I.S., Singh, J., Grewal, S.S., 1994. A Study on Adoption of Rice Technology in Punjab. Technical Bulletin. Department of Economics and Sociology, Punjab Agricultural University, Ludhiana, India, pp. 39. Gajri, P.R., Gill, K.S., Singh, R., Gill, B.S., 1999. Effect of pre-planting tillage on crop yields and weed biomass in a rice–wheat system on a sandy loam soil in Punjab. Soil Tillage Res. 52, 83–89. Hardjoamidjojo, S., 1992. The effect of flooding and method of water application on water requirements and yield of wetland paddy. In: Murty, V.V.N., Koga, K. (Eds.), Proceedings of the International Workshop on Soil and Water Engineering for Paddy Field Management, Bangkok, Thailand, 28–30 January 1992. Asian Institute of Technology, Bangkok, pp. 63– 71. Humphreys, L., Muirhead, W., Fawcett, B.J., Tounsend, J., 1992. Minimizing deep percolation from rice. Farmers Newslett. 172, 41–43 (Griffith, NSW, Australia). Kukal, S.S., Aggarwal, G.C., 2002. Percolation losses of water in relation to puddling intensity and depth in a sandy loam rice (Oryza sativa) field. Agric. Water Manage. 57, 49–59. Kukal, S.S., Aggarwal, G.C., 2003. Puddling depth and intensity effects in rice–wheat system on a sandy laom soil. I. Development of subsurface compaction. Soil Tillage Res. 72, 1–8. Sandhu, B.S., Khera, K.L., Prihar, S.S., Singh, B., 1980. Irrigation needs and yield of rice on a sandy loam soil as affected by
8
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continuous and intermittent submergence. Indian J. Agric. Sci. 50, 492–496. Sharma, P.K., De Datta, S.K., 1985. Effects of puddling on soil physical properties and processes. Soil Physics and Rice. IRRI, Los Banos, Philippines, pp. 217–234. Steel, R.G.D., Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York, pp. 232–251. Tabbal, D.F., Lampayan, R.M., Bhuiyan, S.I., 1992. Water efficient irrigation technique for rice. In: Proceedings of the International Workshop on Soil and Water Engineering for Paddy Field
Management. Asian Institute of Technology, Bangkok, 28–30 January 1992, pp. 146–159. Wickham, T.H., Singh, V.P., 1978. Water movement through wet soils. Soils and rice. IRRI, Los Banos, Philippines, pp. 337– 357. Wopereis, M.C.S., Bouman, B.A.M., Kropff, M.J., tenBerge, H.F.M., Maligaya, A.R., 1994. Understanding the water use efficiency of flooded rice fields. I. Validation of the soil–water model SAWAH. Agric. Water Manage. 26, 277–289 (Amsterdam).
Percolation losses of water in relation to pre-puddling tillage and puddling intensity in a puddled sandy loam rice (Oryza sativa L.) field S.S. Kukal∗ , A.S. Sidhu Department of Soils, Punjab Agricultural University, Ludhiana, Punjab 141004, India Received 21 April 2003; received in revised form 24 November 2003; accepted 15 December 2003
Abstract Effects of puddling in rice (Oryza sativa L.), especially the water loss, depend upon the extent of initial manipulation by pre-puddling tillage. The interactive effects of pre-puddling tillage and puddling intensity were studied for 3 years (2000–2002) in a field experiment at Punjab Agricultural University, Ludhiana, India, on a sandy loam soil (coarse loamy, calcareous, mixed, hyperthermic Typic Ustochrept). Treatments included three levels of pre-puddling tillage-one discing followed by a tine cultivation and planking, one discing followed by two tine cultivations and plankings and one discing followed by four tine cultivations and plankings; and three levels of puddling-one, two and four cultivations in ponded water each followed by planking. Increasing pre-puddling tillage intensity to four operations decreased percolation rate of water by 22–40% from that with one operation. Four puddling operations decreased percolation rate of soils by 30% from that with one puddling operation. This led to decrease in irrigation water used by 22–27% when pre-puddling tillage intensity increased from one to four operations. During an irrigation cycle, the percolation rate of soils decreased with time (days 1–4 after irrigation), the extent of decrease being same at all the levels of pre-puddling tillage. Higher levels of puddling increased the clay content of 0–1, 1–2 and 2–3 cm soil layers, the increase being more pronounced at higher levels of pre-puddling tillage. Puddling index, ratio of initial to final volume of settled sediments, was not affected by pre-puddling tillage intensity. It, however, increased with increasing levels of puddling intensity. Puddling index was also not a function of clay content of the surface soil layers (0–3 cm). © 2004 Elsevier B.V. All rights reserved. Keywords: Pre-puddling tillage; Puddling intensity; Rice; Percolation rate; Puddling index
1. Introduction Rice (Oryza sativa L.) has been known to be less water efficient than other crops. The amount of water consumed in the field to produce 1 kg of rice is significantly greater than for other important cereal crops (Bhuiyan, 1992). In Asia, irrigated agriculture ∗ Corresponding author. Fax: +91-161-2400945. E-mail address: [email protected] (S.S. Kukal).
accounts for 90% of total diverted fresh water and more than 50% of this is used to irrigate rice. Because of depleting ground water resources, global water crisis threatens the sustainability of irrigated rice production. Therefore, a need is being felt for decreasing water use and improving water use efficiency of lowland rice. Large reductions in water inputs can be potentially realized by reducing the unproductive percolation + seepage losses during crop growth (Bouman and Tuong, 2001). Percolation is
0167-1987/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2003.12.010
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the vertical movement of water beyond the root zone to the water table, whereas, seepage is the lateral movement of subsurface water and the two are often inseparable (Wickham and Singh, 1978). Percolation losses have been reported to vary from 0.1 to several hundred millimeter per day (Sharma and De Datta, 1985; Hardjoamidjojo, 1992; Humphreys et al., 1992; Aggarwal et al., 1995; Kukal and Aggarwal, 2002). These can be reduced by increasing the resistance to water flow in the soil and decreasing the hydrostatic pressure of the ponded water (Anbumozhi et al., 1998; Kukal and Aggarwal, 2002). The hydrostatic water pressure governing percolation flow is determined by the depth of ponded water and the distance from the soil surface to the ground water table. The resistance to percolation flow is governed by different soil factors. Bouman et al. (1994) and Wopereis et al. (1994) showed that, for most puddled lowland situations, percolation rates are fairly stable during a cropping season and little affected by ground water table depths. The resistance of water flow can be increased by changing the soil physical properties through puddling (Humphreys et al., 1992). In a sandy loam soil percolation rate of water into the soil decreased from 30.1 mm day−1 in unpuddled soil to 13.2 mm day−1 with medium puddling and 11.9 mm day−1 with high puddling (Kukal and Aggarwal, 2002). Increased puddling intensity decreased hydraulic conductivity of the puddled layer, whereas hydraulic gradient between puddled and unpuddled layers increased with increase in puddling intensity. The process of puddling actually consists of primary (pre-puddling) and secondary (puddling) tillage. The pre-puddling tillage is mainly aimed at mixing/burying stubbles, leveling the land and reducing the weed growth. The effect of puddling (wet tillage) on puddle quality and percolation rate depends on initial soil conditions created by pre-puddling (dry) tillage. Studies (Gajri et al., 1999) have reported a decrease in weed biomass with increase in pre-puddling tillage intensity in sandy loam soils in addition to decrease in percolation losses during rice. Differences in the effectiveness of puddling, apart from other factors, may also arise from the intensity of pre-puddling tillage at which the puddling was conducted. In the major rice growing area in northwest Indo-Gangetic plains, 67% of the farmers apply 4–8 pre-puddling tillage operations including harrowings and discings
(Chatha et al., 1994) in the absence of any recommendation. It is done simply to bury the wheat stubble and reduce weed growth in addition to create favorable soil tilth for puddling. There is thus, need to decide on the appropriate number of pre-puddling tillage operations in relation to percolation losses of water in rice soils. Also, the studies on the interactive effect of pre-puddling tillage and puddling on the process of percolation losses of water in rice are lacking in the literature. The present study was thus, aimed to observe the process of percolation losses in rice in relation to pre-puddling tillage intensity and puddling intensity in a sandy loam rice field.
2. Materials and methods A field experiment was conducted for 3 years (2000–2002) at Punjab Agricultural University, Ludhiana, India (30◦ 56 N, 75◦ 52 E and 247 m above mean sea level). The area is characterized by a sub-tropical and semi-arid climate with dry summers (March–June) and severe winters (December–January). The area experiences an average rainfall of about 700 mm of which 80% is received during July–September coinciding with the rice season, whereas the remaining 20% is received during rabi (November–April) season. Maximum air temperature during three rice seasons ranged between 34.3 ± 1.1 ◦ C (July) and 32.8 ± 1.6 ◦ C (October) and minimum air temperatures were between 27.2±0.5 ◦ C (July) and 18.1±1.3 ◦ C (October). Mean relative humidity during these seasons varied between 83 ± 4.3% (July) and 63 ± 4.1% (October). The soil was deep alluvial sandy loam soil (USDA: Typic Ustochrept; FAO: Dystric Cambisol). The physico-chemical characteristics of the experimental soil are given in Table 1. The soil was low in organic carbon (3.3 g kg−1 ), low in KMnO4 -extractable N (152 kg ha−1 ), medium in 0.5 N NaHCO3 -extractable P (13.7 kg ha−1 ) and medium in available K (145 kg ha−1 ). The experiment was initiated in June 2000 with rice crop after the harvest of wheat (Triticum aestivum). The treatments included three intensities of pre-puddling tillage (dry) in main plots and three intensities of puddling (wet tillage) in sub-plots in a split plot design with three replications each. Each sub-plot measured 14 m × 5.8 m. The pre-puddling treatments
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8
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Table 1 Physico-chemical properties of the study soil Soil depth
0–15 15–30 30–60 60–90 90–120 120–150 150–180
Percent
pH
Sand
Silt
Clay
78 76 68 68 70 68 74
13 14 18 18 18 20 17
9 10 14 14 12 12 9
8.0 8.1 7.9 7.9 8.0 8.0 8.1
EC (dS/cm)
0.28 0.20 0.18 0.17 0.18 0.18 0.18
were (i) one discing 1 week after harvest of wheat crop + one harrowing with a tine cultivator and a planking (PP1 ); (ii) one discing 1 week after wheat crop harvest + two harrowing operations with a tine cultivator at weekly intervals after discing, each followed by planking (PP2 ); (iii) one discing 1 week after wheat crop harvest + four harrowing operations with a tine cultivator, each followed by planking (PP4 ). The planking refers to one run of post-tillage packing and leveling of soil with a wooden plank. The discing operation was done 4–5 days after the field had been irrigated immediately after the wheat crop was harvested, with a tractor-mounted disc harrow. The harrowing operations were carried out using a tractor-mounted tine cultivator which is most commonly used by the farmers of the region for these operations. Puddling was done by harrowing with the same tine cultivator as used for pre-puddling tillage, once (P1 ), twice (P2 ) and four times (P4 ) in 8–10 cm ponding water followed by one planking operation. All the cultivation tools were operated with a 45 bhp tractor. The pre-puddling tillage and puddling operations were carried out in the same plots during all the 3 years of study in the same experimental design. Basal doses of zinc sulfate, superphosphate and one-third of total N fertilizer were applied in two equal installments at 3 and 6 weeks after transplanting. Four week old seedlings of rice, cultivar PR 113, were transplanted in 0.2 m wide rows with a distance of 0.15 m between the plants (33 plants m−1 ) between 10 and 23 June during 2000–2002 immediately after puddling. All the plots were kept flooded for the first 15 days to ensure 5 cm submergence. Afterwards, all the irrigations (each of 7.5 cm amount) were applied 2 days after complete infiltration of ponded
Bulk density (g/cm3 )
1.50 1.52 1.54 1.57 1.53 1.55 1.57
Water content, w (%) 0.3 bar
15 bar
10.7 10.2 14.4 14.4 13.5 14.4 15.0
6.2 6.8 8.6 8.7 7.8 7.8 7.4
water (Sandhu et al., 1980). Weeds were controlled by broadcasting 3 l ha−1 Butachlor 50 EW (water flowable emulsion) mixed with sand in standing water for 3 days after transplanting (DAT) and by manual weeding at 35 DAT. The crop was well protected against pests through two sprays, one each of Endosulfan 35 EC (emulsifiable concentrate) and Deltamethrin 28 EC. The percolation rate of water was recorded periodically, especially when plots were irrigated, by measuring depth of the ponded water in the whole plots between 24 h periods starting at 0800 h. Depth of water was recorded with a hook gauge from three leveled and fixed platform sites in each plot to get an average value for each plot. Percolation rates (PR) were determined from data on water levels and evaporation from open pan located in the irrigated area surrounded by rice paddies. Percolation loss was also measured simultaneously in iron rings installed in the center of each plot, while maintaining different depths of water in the rings, during the years 2000 and 2001. This was done to maintain different depths of ponded water. After the harvest of rice crop during the year 2002, soil samples were taken at depths of 0–1, 1–2, 2–3, 3–5 and 5–10 cm from each plot and the amount of clay determined in each sample using International pipette method. Samples of soil–water suspension immediately after puddling were collected in 2 l PVC containers and immediately transferred to 1 l cylinders in the laboratory. The volume of settled sediments at zero (initial) and after 48 h (final) of settling was recorded for each treatment to calculate puddling index as ratio of initial to final volume of suspended sediments. Statistical significance of the treatment effects on different parameters was inferred from the least
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significant difference using analysis of variance for a split-plot design (Steel and Torrie, 1960).
3. Results and discussion 3.1. Percolation rate and irrigation water used Both pre-puddling tillage and puddling affected the percolation rate of water into the soil during all the 3 years of study (Table 2). The percolation rate decreased significantly by 25 and 40% when pre-puddling tillage intensity increased from one to two and four operations, respectively, during the year 2000. The corresponding values during 2001 and 2002 were 14 and 30% and 14 and 22%, respectively. Increasing puddling intensity from one to two and four reduced percolation rate of water, respectively, by 15 and 25% during the year 2000, 14 and 28% during 2001 and 18 and 30% during 2002. Puddling has been reported to decrease hydraulic conductivity of puddled layer (0–10 cm) of sandy loam soil from 0.064 cm h−1 in unpuddled to 0.015 cm h−1 with medium puddling and 0.009 cm h−1 with high puddling (Kukal and Aggarwal, 2002). However, the percolation rates Table 2 Average percolation rate in rice (mm day−1 ) in relation to pre-puddling tillage and puddling intensity during 2000–2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
Year 2000 P1 P2 P4 Mean LSD (0.05), P = 1.2
40.5 36.5 31.8 36.3 PP = 1.0
32.0 26.4 22.8 27.1
25.4 20.5 18.8 21.6
32.6 27.8 24.5
Year 2001 P1 P2 P4 Mean LSD (0.05), P = 1.6
37.9 33.8 27.5 33.1 PP = 1.3
33.3 28.5 23.7 28.5
26.3 21.8 19.0 22.4
32.5 28.0 23.4
Year 2002 P1 P2 P4 Mean LSD (0.05), P = 2.6
44.1 38.0 32.2 38.1 PP = 1.4
40.1 31.2 26.3 32.6
35.6 29.2 24.8 29.9
39.9 32.8 27.8
reported by Kukal and Aggarwal (2002) in similar soil were lower compared to those obtained in the present study. This could be due to higher mean maximum air temperature during 2000–2002 throughout the crop season except for the first 4 weeks after transplanting, than that during 1994–1996. In addition, lower levels of the pre-puddling tillage treatments in the present study might have resulted in higher percolation in these plots. The percolation rates were maximum at PP1 level of pre-puddling tillage and minimum at PP4 level. In Kukal and Aggarwal (2002), the pre-puddling tillage intensity was PP4 in all the puddling treatments. Pre-puddling tillage and puddling did not interact to affect the percolation rate of water. The amount of irrigation water was affected by both pre-puddling tillage and puddling (Table 3). However, pre-puddling tillage intensity was more instrumental in reducing the amount of irrigation water used compared to puddling intensity. During the year 2001, the amount of irrigation water used decreased by 22 and 27% when pre-puddling tillage increased from PP1 to PP2 and PP4 , respectively. The corresponding values during the year 2002 were 19 and 22%, respectively. On the other hand, increase in puddling intensity from P1 to P2 and P4 decreased the amount of irrigation water by 4 and 7% in 2001 and 7 and 10% in 2002. The dominance of pre-puddling tillage in reducing the amount of irrigation water could be due to increased amount of clay content of surface 3 cm layers at higher levels of pre-puddling tillage. Table 3 Amount of irrigation water used (mm) in rice in relation to pre-puddling tillage and puddling intensity during 2000–2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
Year 2001 P1 P2 P4 Mean LSD (0.05), P = 8.70
179 168 165 171 PP = 4.70
139 133 130 134
131 128 117 125
149 143 138
Year 2002 P1 P2 P4 Mean LSD (0.05), P = 4.27
192 175 171 179 PP = 3.73
153 144 139 145
147 141 132 140
164 153 147
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8 PP1
PP2
5 PP4
4 Percolation rate (cm)
3.5 3 2.5 2 1.5 1 0.5 0 0
1
2
3
4
5
Days after irrigation
Fig. 1. Variation of percolation rate of water during an irrigation cycle as affected by pre-puddling tillage intensity.
3.2. Percolation losses during an irrigation cycle
3.3. Clay content of the puddled surface layers
Percolation rate of water decreased with time during an irrigation cycle at all the levels of pre-puddling tillage. (Fig. 1), the decrease being more pronounced at lower levels of pre-puddling tillage. At PP1 level of pre-puddling tillage, the percolation rate decreased by 23% from day 1 to 4, 24% at PP2 and 22% at PP4 levels. At PP1 level the percolation rate of water on day 1 after irrigation, was 3.5 cm day−1 and it decreased to 2.7 cm day−1 on day 4. Same was the trend at PP2 and PP4 levels. However, unlike puddling intensity (Kukal and Aggarwal, 2002), the extent of decrease was same at all the levels of pre-puddling tillage. The decrease in percolation losses of water with decrease in PWD was, thus, not a function of pre-puddling tillage intensity as was the case in puddling, where the decrease was more at lower levels. Kukal and Aggarwal (2002) observed decreasing percolation rates with time during an irrigation cycle at all the levels of puddling intensity and puddling depth in similar type of soils. The decrease in PR with time during an irrigation cycle could be due to the decreasing ponding water depth (PWD) as the percolation of water into the soil progressed (Kukal and Aggarwal, 2002). Shallow PWD reduces the wetted area of inter-plot bunds and limits the amount of water infiltrating laterally into the bunds. Furthermore, if the PWD is kept very low or if the field is maintained at saturation point, the water loss is greatly reduced because the unevenness of the soil surface prevents water movement to the bunds and subsequent loss through under-bunds (Tabbal et al., 1992).
The clay content of 0–1, 1–2, 2–3 and 3–5 cm puddled soil layers in relation to pre-puddling tillage and puddling is depicted in Fig. 2. Puddling increased clay content of 0–1, 1–2 and 2–3 cm soil layers, whereas in 3–5 cm soil layers, no significant difference in clay content was observed. Higher level of puddling intensity resulted in higher clay content in 0–1 cm soil layer at all the levels of pre-puddling tillage, but the differences in clay contents due to puddling intensity were more at higher level of pre-puddling tillage. At PP1 , the clay content of 0–1 cm soil layer was higher with P4 , but the difference was not significant (Fig. 2a). At PP2 level of pre-puddling tillage, the clay content was maximum with P4 and minimum with P1 (Fig. 2b) and this difference between P2 and P4 further increased at PP4 level of pre-puddling tillage (Fig. 2c). At PP1 level the clay content of 1–2 cm soil layer decreased at all the levels of puddling, whereas in 2–3 and 3–5 cm soil layers the clay content resembled to that in 0–1 cm soil layer. At PP2 level clay content of 3–5 cm soil layer was less at all the levels of puddling except P1 where it was similar to that in 0–1 cm soil layer, indicating that the aggregates of this layer could not be destroyed at P1 level of puddling. In PP4 level, the clay content of lower layers decreased at all the levels of puddling intensity except at P2 , where it was slightly higher even from that in 0–1 cm soil layer. This difference could be due to higher clay content of 3–5 cm soil layer even before puddling. The clay content of lower layers (1–2 and 2–3 cm) was not different for different puddling
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16
17
18
Percent clay 19
20
21
Soil depth (cm)
0 1 2
P1 3
P2 4
P4
(a) 5
16
17
Percent clay 18 19
20
21
Soil depth (cm)
0 1 2
P1 3
P2 4
P4
(b) 5 Percent clay 16
17
18
19
20
21
Soil depth (cm)
0 1 2 P1
3
P2
4
P4
(c) 5
Fig. 2. Effect of puddling intensity on the clay content of 0–5 cm soil layers with (a) PP1 ; (b) PP2 ; (c) PP4 levels of pre-puddling tillage.
intensities at PP1 level of pre-puddling tillage, but at PP2 and PP4 levels, the differences increased in lower layers as well. This signifies that pre-puddling tillage has a role to play in preparing the soil for an efficient puddling, bringing finer soil particles into suspension. These particles then settle according to their size with the coarsest particles settling first and finest in the last. Graded sediment layer with coarsest particles on the bottom and the finest particles on top gives more seepage control than even a uniform compact layer (Bouwer et al., 2001). Thus, pre-puddling tillage
intensity is responsible for determining the extent of amount of clay particles brought into suspension by puddling and their settling on the surface layer of soil and reducing the percolation rate of soils. 3.4. Puddling index of soil The puddling index was not affected by pre-puddling tillage intensity (Table 4). However, puddling intensity helped increase puddling index of soils significantly. It was higher by 48% with two puddling operations
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8 Table 4 Puddling index of soils in relation to pre-puddling tillage and puddling intensity during the year 2002 Puddling intensity
Pre-puddling tillage intensity PP1
PP2
PP4
Mean
P1 P2 P4 Mean LSD (0.05)
0.015 0.028 0.043 0.029 PP = NS, P = 0.002
0.017 0.033 0.046 0.032
0.016 0.033 0.051 0.033
0.016 0.031 0.047
and 66% with four operations than that with one puddling operation. More churning action with higher level of puddling resulted in more dispersion of soil particles and ultimately the high puddling index. Puddling index, however, was not a function of clay content of the puddled surface layers. Thus, the clay content of the surface layer and puddling index are two separate indices of puddling especially in sandy loam soils and are independent of each other. Thus, in coarse-textured soils the clay content of surface layer may be used as an index of puddling. In such soils even four pre-puddling tillage operations could help in better controlling the percolation losses at the lower level of puddling intensity as intensive puddling in such soils results in development of sub-surface compaction (Kukal and Aggarwal, 2003).
4. Conclusions Pre-puddling tillage plays a significant role in decreasing the percolation losses of water in rice fields by manipulating the initial soil conditions especially the soil particle detachment so as to be able to be brought into suspension by the puddling operations. The clay content in the surface 3 cm soil layers increased with increase in puddling intensity but the increase was more pronounced at higher levels of pre-puddling tillage. Thus, the clay content of the surface layers is the most controlling factor for percolation rate of soils in the sandy loam soils. The percolation rate decreased with time during an irrigation cycle, the decrease being more at higher levels of pre-puddling tillage. Puddling index was not a function of clay content of surface soil layers.
7
Acknowledgements The authors are grateful to Indian Council of Agricultural Research, New Delhi, for providing the financial assistance for carrying out this study under NATP Project (PSR mode). References Aggarwal, G.C., Sidhu, A.S., Sekhon, N.K., Sandhu, K.S., Sur, H.S., 1995. Puddling and N management effects on crop response in a rice–wheat cropping system. Soil Tillage Res. 36, 129–139. Anbumozhi, V., Yamaji, E., Tabuchi, T., 1998. Rice crop and yield as influenced by changes in ponding water depth, water regime and fertigation level. Agric. Water Manage. 37, 241– 253. Bhuiyan, S.I., 1992. Water management in relation to crop production: case study on rice. Outlook Agric. 21, 293–299. Bouman, B.A.M., Tuong, T.P., 2001. Field water management to save water and increase its productivity in irrigated rice. Agric. Water Manage. 49, 11–30. Bouman, B.A.M., Wopereis, M.C.S., Kropff, M.J., tan Berge, H.F.M., Tuong, T.P., 1994. Water use efficiency of flooded rice fields. II. Percolation and seepage losses. Agric. Water Manage. 26, 291–304. Bouwer, H., Ludke, J., Rice, R.C., 2001. Sealing pond bottoms with muddy water. J. Ecol. Eng. 18, 233–238. Chatha, I.S., Singh, J., Grewal, S.S., 1994. A Study on Adoption of Rice Technology in Punjab. Technical Bulletin. Department of Economics and Sociology, Punjab Agricultural University, Ludhiana, India, pp. 39. Gajri, P.R., Gill, K.S., Singh, R., Gill, B.S., 1999. Effect of pre-planting tillage on crop yields and weed biomass in a rice–wheat system on a sandy loam soil in Punjab. Soil Tillage Res. 52, 83–89. Hardjoamidjojo, S., 1992. The effect of flooding and method of water application on water requirements and yield of wetland paddy. In: Murty, V.V.N., Koga, K. (Eds.), Proceedings of the International Workshop on Soil and Water Engineering for Paddy Field Management, Bangkok, Thailand, 28–30 January 1992. Asian Institute of Technology, Bangkok, pp. 63– 71. Humphreys, L., Muirhead, W., Fawcett, B.J., Tounsend, J., 1992. Minimizing deep percolation from rice. Farmers Newslett. 172, 41–43 (Griffith, NSW, Australia). Kukal, S.S., Aggarwal, G.C., 2002. Percolation losses of water in relation to puddling intensity and depth in a sandy loam rice (Oryza sativa) field. Agric. Water Manage. 57, 49–59. Kukal, S.S., Aggarwal, G.C., 2003. Puddling depth and intensity effects in rice–wheat system on a sandy laom soil. I. Development of subsurface compaction. Soil Tillage Res. 72, 1–8. Sandhu, B.S., Khera, K.L., Prihar, S.S., Singh, B., 1980. Irrigation needs and yield of rice on a sandy loam soil as affected by
8
S.S. Kukal, A.S. Sidhu / Soil & Tillage Research 78 (2004) 1–8
continuous and intermittent submergence. Indian J. Agric. Sci. 50, 492–496. Sharma, P.K., De Datta, S.K., 1985. Effects of puddling on soil physical properties and processes. Soil Physics and Rice. IRRI, Los Banos, Philippines, pp. 217–234. Steel, R.G.D., Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York, pp. 232–251. Tabbal, D.F., Lampayan, R.M., Bhuiyan, S.I., 1992. Water efficient irrigation technique for rice. In: Proceedings of the International Workshop on Soil and Water Engineering for Paddy Field
Management. Asian Institute of Technology, Bangkok, 28–30 January 1992, pp. 146–159. Wickham, T.H., Singh, V.P., 1978. Water movement through wet soils. Soils and rice. IRRI, Los Banos, Philippines, pp. 337– 357. Wopereis, M.C.S., Bouman, B.A.M., Kropff, M.J., tenBerge, H.F.M., Maligaya, A.R., 1994. Understanding the water use efficiency of flooded rice fields. I. Validation of the soil–water model SAWAH. Agric. Water Manage. 26, 277–289 (Amsterdam).