CHARACTERIZATION, CLASSIFICATION AND EVALUATION OF SOIL AND WATER RESOURCES ACROSS THE TOPOSEQUENCES OF SOUTHERN SAURASHTRA
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Date
2005-02
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Abstract
Sixty three soil samples from sixteen representative pedons of four toposequences viz., Hiran, Shingoda, Machhundri and Rayadi in southern Saurashtra across the five land forms viz., hill slopes, upper piedmont, lower piedmont, piedmont plain and coastal plain were collected during 2002-03 to study the morphological, mineralogical, physical, hydrological and chemical characteristics, taxonomic classification of soils, underground water quality and soil-water and climatic conditions with the aim to evaluate soil-site suitability and water resources for different crops.
The results reveal that the soils of different toposequences across the land forms of southern Saurashtra have developed from basaltic and Gaj bed milliolitic lime stone parent materials from hill slope to lower piedmont and alluvium in piedmont plain and coastal plain. The soils have clay loam to clayey texture, moderate to strong sub angular blocky structure and very dark grayish (10YR 3/1M) to brown (10YR 5/3M) colour. Smectite was the dominant clay mineral, while plagioclase and quartz were dominant in silt and sand fractions. The total sand, silt and clay content varied from 20.56 to
51.87, 20.20 to 43.98 and 16.40 to 49.45 per cent with the mean of 34.12, 33.57 and 32.31 per cent, respectively. The proportion of silt content in soil separate increased with the decrease in elevation. The bulk density varied from 1.28 to 1.57 Mg m-3 with the mean of 1.41 Mg m-3. Higher bulk density was recorded from lower piedmont and coastal plain. The soils of upper piedmont were highly expandable as compared to other land slopes. The maximum water holding capacity (MWHC), saturated hydraulic conductivity and infiltration rate of soils decreased with the decrease in elevation from hill slope to coastal plain. The total plant available water capacity (PAWC) and water storage capacity (WSC) of the soils varied from 0.063 to 0.767 and 0.179 to 1.539 m ha-1 with mean of 0.229 and 0.537 m ha-1, respectively which were found in the order of piedmont plain > coastal plain > lower piedmont > upper piedmont > hill slope. The PAWC/ WSC ratio ranged from 0.346 to 0.498 with the mean of 0.407 indicating 41 per cent available water for plant out of total water storage capacity of the soils of 0.537 m ha-1.
In general, the pH, EC, O.C. and CaCO3 ranged from 7.70 to 8.59, 0.18 to 1.06 dSm-1, 0.12 to 0.93 per cent and 1.96 to 47.05 per cent with the mean of 8.13, 0.36 dSm-1, 0.49 per cent and 17.24 per cent, respectively indicating that the soils were moderately alkaline in reaction, low in EC and O.C. status and highly calcareous in nature.
The values of pH and EC increased gradually along the elevation gradient from hill slope to coastal plain. While traversing from hill slopes to coastal plain, a gradual decrease in the content of organic carbon was observed. The CaCO3 content increased down the slope and it was maximum (22.42 per cent) in coastal plain. The CEC varied from 16.11 to 28.80 cmol (p+) kg-1 with the mean of 24.39 cmol (p+) kg-1. However, no definite trend in distribution of CEC from hill slope to coastal plain was observable. The proportion of exchangeable cations were observed in order of Ca2+ > Mg2+ > Na+ > K+. The BSP and ESP ranged from 90.15 to 93.50 and 6.38 to 14.90 with the mean of
92.47 and 9.67, respectively. The ESP > 10.0 in lower piedmont to coastal plain and has the potential of achieving alarming proportions, if neglected.
The pHs and ECe ranged from 7.79 to 8.16 and 0.75 to 3.66 dSm-1 with mean of 7.96 and 1.32 dSm-1, respectively indicating that the soils were non-sodic and non saline except some part of coastal plain. The pHs and ECe increased with decrease in elevation from hill slope to piedmont plain and hill slope to coastal plain, respectively, The proportion of water soluble Na+ was dominant followed by Mg2+, Ca2+ and K+. The distribution of total water soluble cations increased with decreasing topography. The CO32- was absent in water soluble anions in saturation extract, while Cl- was dominant followed by HCO3-. The HCO3-, Cl- and SAR increased gradually with decreasing topography.
The soils were low in available N and P2O5 and medium in available K2O. The available N decreased with decrease in elevation, while reverse trend was observed in case of available P2O5. The soils were high in available Fe, Mn, Zn and Cu micronutrient cations.
The soils were classified as Lithic Ustorthents, Typic Ustorthents, Vertic Ustochrepts, Typic Ustochrepts, Typic Ustropepts, Fluventic Ustropepts, Fluventic Calciustepts and Calcic Ustropepts at sub groups level. Now Ustochrepts are named as Haplustepts as per Soil Survey Staff (2003).
The pH and EC of underground water increased with decreasing elevation. The pH and SAR of underground water increased with increase in EC. As per the limits proposed by Richards (1954), the underground water for irrigation over hill slope, upper piedmont and lower piedmont, was placed under safe class of C2S1 and C3S1 while the piedmont plain and coastal plain were in the doubtful class of C4S2 and C4S3. In general, the irrigation water of whole southern Saurashtra was placed under C3S1 water quality class except that of the coastal plain. The guidelines for its suitability and management strategy are discussed in detail in the text.
The climatic condition of southern Saurashtra was recorded. The natural soil, water and climatic constraints were also identified in the study area. The soils of pedon P1 were in sustainable class S2, while the pedons P2 to P8, P10 to P13 and P15 were in sustainable with high input (S3) class. However, the soils of pedons P9, P14 and P16 were under class S4, i.e. sustainable with alternate land use. The mean score of weight factors of four toposequences were found in order of Hiran (26) < Shingoda (27) < Machhundri (28) < Rayadi (29) indicating that the soils constraints / limitations increased from west to east direction in southern Saurashtra. The soils of hill slope and piedmont plain area were facing overall relatively less soil constraints as compared to upper piedmont, lower piedmont and coastal plain areas. The remedial measures were discussed to overcome the soil and water constraints in different land slopes for soil sustainability.
The reserve water and water balance varied from 0.136 to 0.518 and -0.203 to +0.653 m ha-1 with the mean of 0.308 and +0.253 m ha-1, respectively. The negative water balance in piedmont plain (-0.323 m ha-1) and coastal plain (-0.203 m ha-1) lead to ground water depletion every year and ultimately resulted in the ingress of seawater.
Alternate land use plans for various land forms under study have been suggested for their better management. Thus, rabi sorghum is most suitable in Borvav (P2) and sugarcane, mustard and sorghum in Devali (P7) village were found to be highly suitable (S1) crops. Whereas, soils in Jamwala (P5), Maljinjava (P3), Kareda (P6), Judavadali (P10), Chotara (P15), Devali (P7) and Chauhani Khan (P8) villages were suited for soybean, while in soils of Maljinjava (P3), Chotara (P15), Devali (P7), Chauhani Khan (P8) and Rampara (P12) villages, sunflower can be introduced as these soils have been moderately suitable (S2).
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CHARACTERIZATION, CLASSIFICATION