Impact on soil salinity and crop yield under conventional and controlled subsurface drainage system in saline Vertisols of TBP irrigation command

Introduction

Tungabhadra Project (TBP) reservoir on Tungabhadra river, a tributary of river Krishna, was commissioned in 1953 (Anonymous, 2013) to provide protective irrigation to the drought prone areas of Northern Karnataka (3,63,000 ha) and Andhra Pradesh (1,60,000 ha). Based on soil characteristics, topographical and drainage conditions of the command area, it was proposed to allocate nearly 8 and 4 per cent of command area under paddy and sugarcane, respectively, to avoid development of waterlogged and soil salinity (Karegoudar et al., 2022) [4] . Presently deviation in the cropping pattern, farmers in downstream areas is not only facing shortage of canal water supply for paddy crop but also the problem of secondary salinization and thus reduction in the yield levels of different crops drastically. To reclaim these lands TBP-CADA (Tungabhadra Project-Command Area Development Authority) has taken up surface and subsurface drainage (SSD) works especially in the downstream area of the command. However, there are issues related to operation of SSD systems. The farmers in downstream area stop/ block the SSD system due to fear of water shortage during critical stages of paddy crop coupled with leaching loss of nitrate nitrogen (N). However, earlier results by the blockage of outlets increased soil salinity from 2.22 to 4.1 dSm -1 during rabi and from 2.22 to 2.68 dSm -1 during Kharif within two years after adoption of blockage practice. It means that blockage of the system undo benefits of SSD system. This experience suggested that SSD system should work but in controlled way. This controlled system is known to reduce the drainage discharge while maintaining the necessary function of the drainage system. Ghannam et al., (2016) [2] reported that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity due to rising of water table but carefully monitored and managed the system. In view of the above, a study the effect of controlled drainage on soil salinity and crop yield in different spacing under saline vertisols of TBP Command area was planned.

Materials and Methods

The study was carried out in a 9.42 ha area at Agricultural Research Station, Gangavathi during the year of 2021-22.The treatments consisted of conventional and controlled SSD spacing viz., 40 (2.62 ha), 50 (2.8 ha) and 60 m (4.0 ha) each with a lateral depth of 1.0 m. These three experimental lands were divided into two equal plots to establish conventional and controlled sub surface drainage systems and each was served by three lateral drains. In both the systems, the collector drains (100 mm diameter PVC corrugated plastic pipe) were installed perpendicular to surface drain (nala) at 1.10 m depth and all lateral drains (PVC corrugated pipe covered by synthetic envelope materials) were installed at a depth of 1.0 m with an average spacing of about 50 m between the laterals. The slope of lateral drain was 0.1 to 0.2% and connected to the collector drains whose slope was 0.2 to 0.3% which directly drains into nala through man hole. In controlled drainage system the water table control device was made up of PVC pipe consisting of three parts (Fig. 1). The first is a horizontal PVC pipe 80 mm diameter fitted onto the end of lateral drain inside the man hole and closed at the end by a PVC closing device (Karegoudar et al., 2019) [3] The second part is a riser with the provision of variable height depending on the minimum water table depth required and connected with the first part. In this study controlled drainage was applied at 30 cm water table depth from the soil surface at the outlet of lateral drain during both kharif and rabi seasons of paddy. The third part is another horizontal PVC pipe (80 mm dia) connected with the riser as a lateral drain at the desired minimum water table depth. This control device was designed in such a way to restrict the drain flow by blocking the actual drain outlet as is the case in conventional SSD system.

Plan

Fig 1:

A view of indigenously developed water table control device installed in manhole (Adopted from: M.A.S. Wahba et.al, 2001) [6] Rice was transplanted in Kharif -21 (BPT 5204) season in these experimental sites. The paddy crop was transplanted in August and January and harvested in December season. Except the control device, agronomic practices followed for paddy were similar in both the systems. The soil samples were collected to a depth of 90 cm with 15 cm increment were taken from both conventional and controlled plots in zigzag position using GPS and analyzed for initial soil pH and soil salinity (EC, dSm -1 ) on a 1:2.5 soil water suspension and the EC so obtained was converted to ECe (dSm -1 ) i.e., EC of saturation paste extract by multiplying EC with a conversion factor 2.66 which was worked out for these soils at ARS, Gangavathi (USSL, 1954). Soil samples to a depth of 90 cm were also collected at the end of each cropping season and analyzed for soil salinity appraisal.

Results and Discussion

Soil salinity: The mean soil salinity under 40 m spacing under conventional SSD during Kharif-21 reduced from 8.05 to 2.44 at 0-15cm, from 8.66 to 3.35 at 15-30 cm, from 9.70 to 4.17 at 30-60 cm and from 9.94 to 4.30 dSm -1 at 60-90 cm, respectively (Table .1). In case of controlled drainage system, the average soil salinity reduced from 7.34 to 1.20 dSm -1 at 0-15 cm, from 8.15 to 3.15 dSm -1 at 15-30 cm and salinity increased from 8.63 to 4.34 dSm -1 at 30-60 cm and from 9.18 to 3.90 dSm -1 at 60-90 cm, respectively. The mean soil salinity under 50 m spacing under conventional SSD during Kharif-21 reduced from 4.30 to 1.34 at 0-15cm, from 5.09 to 1.22 at 15-30 cm, from 5.91 to 1.73 at 30-60 cm and from 5.26 to 2.71 dSm -1 at 60-90 cm, respectively. In case of controlled drainage system, the average soil salinity reduced from 6.30 to 1.50 dSm -1 at 0-15 cm, from 8.29 to 3.44 dSm -1 at 15-30 cm, from 12.0 to 3.75 dSm -1 at 30-60 cm and from 13.85 to 4.57 dSm -1 at 60-90 cm, respectively. The mean soil salinity under 60 m spacing under conventional SSD during Kharif-21 reduced from 3.06 to 1.87 at 0-15cm, from 3.83 to 2.66 at 15-30 cm, from 7.21 to 4.52 at 30-60 cm and from 8.79 to 4.50 dSm -1 at 60-90 cm, respectively. In case of controlled drainage system, the average soil salinity reduced from 5.99 to 2.24 dSm -1 at 0-15 cm, from 6.29 to 3.26 dSm -1 at 15-30 cm, from 6.42 to 3.33 dSm -1 at 30-60 cm and from 6.11 to 5.20 dSm -1 at 60-90 cm, respectively. Results of the study indicated that, irrespective of the spacing, with continuous flow of drain water removal of dissolved salts through drainage effluent was faster as well as from deeper depth in conventional drainage than controlled drainage system (Karegoudar et al., 2019) [3] .

Conclusion

The rate of reclamation of waterlogged saline land was faster under conventional drainage as compared to controlled drainage. The continuous flow of drain water removal of dissolved salts through drainage effluent was faster as well as from deeper depth in conventional drainage than controlled drainage system. Hence, mean soil salinity (ECe) in all the spacing under both conventional and controlled drainage system was reduced. The paddy grain yield improvement was slightly higher (from 30 to 36%) for conventional as compared to controlled drainage conditions (from 20 to 30%) at 40 to 60 m spacing respectively.

References

1. Anonymous. Annual report. Command Area Development Authority (CADA), Tungabhadra Project. Munirabad, Karnataka, India; 2013. p. 1-30.
2. Ghannam EMK, Waly ME, Gaheen SA, Karajeh FF, Gendy AA. Controlled drainage effects on nitrate leaching, salinity buildup and sugar beet production in Egypt. Merit Research Journal of Agricultural Science and Soil Sciences. 2016;4(2):23-32.
3. Karegoudar AV, Vishwanath J, Anand SR, Rajkumar RH, Ambast SK, Kaledhonkar MJ. Feasibility of controlled drainage in saline vertisols of Tungabhadra Project command area of Karnataka, India. Irrigation and Drainage. 2019;68:969-978.
4. Karegoudar AV, Viswanath J, Rajkumar RH, Anand SR, Polisgowdar BS, Ayyanagowdar MS, Nemichandrappa M, Kaledhonkar MJ. Economic feasibility of subsurface drainage to control waterlogging and soil salinity under different scenarios in Tungabhadra Project command, Karnataka. International Journal of Irrigation and Drainage. 2022;71:1063-1076.
5. United States Salinity Laboratory. Diagnosis and improvement of saline and alkali soils. In: Richards LA, editor. USDA handbook. Washington (DC): United States Department of Agriculture; 1954. p. 1-60.
6. Wahba MAS, El-Ganainy M, Abdel-Dayem MS, Gobran A, Kandil. Controlled drainage effects on water quality under semi-arid conditions in the western delta of Egypt. Journal of Irrigation and Drainage. 2001;50:295-308.