1. SOIL SUITABILITY AND MANAGEMENT FOR RICE PRODUCTION
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2. Abstract
Rice is an aquatic or semi-aquatic plant, loves water for its growth, grown in all types of soils.
However, soils with better water holding capacity like heavy neutral soils (clayey, clay loamy and loamy) are preferred compared to light textured soils.
Rice is the typical crop which requires different soil environment which vary with other arable and submerged crops.
Since the rice is under submergence, many of soil constraints are alleviated.
Majority of rice grown in problem soils and its nature of cultivation makes suitable in these soils.
Learning objectives:
To learn the best suitable soil environment for rice cultivation
To learn the possibility of raising rice under problem soils and their suitable management strategies.
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3. Introduction
The wide range of agro climatic conditions suggests an equally wide variety of soils suitability for rice crop.
Rice is an aquatic plant, mainly grown in heavy neutral soils (clayey, clay loamy and loamy) and also grown in light textured soils.
Rice is grown on loamy sands in Punjab to heavy Vertisols in Andhra Pradesh of India.
Important group of soils for successful rice cultivation are alluvial soils, red soils, laterite or lateritic soils and black soils.
Rice prefers slightly acidic pH, but, can grow in 5-8 pH range.
Because of its better adaptation, it is grown under extreme soil conditions such as acid peaty soils of Kerala (pH 3) and highly alkaline soils (pH 10) of Punjab, Haryana and Uttar Pradesh in India.
With the exception of coastal saline soils, occurs in high rainfall, saline or alkaline soils adversely affect growth and productivity of rice.
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4. Long back, Moorman (1978) observed that the most important soil sub-orders on which rice is grown are
Aquents,
Aquepts,
Orchepts,
Tropepts,
Aqualfs and
Aquults (Table 1).
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5. Major rice growing soils
Orders
Alfisols
Aqualfs, Ustalfsa
Udalfs
Xeralfs
Aridisols -
Orthids2, Argids2
Entisols
Aquents
Fluvents
Orthents, Psamments
Histosols
Hemists, Saprists
Inceptisols
Aquepts, Orchepts, Tropepts
Audepts
Mollisols
Aquolls
Udolls
Oxisols
Orthox, Ustox
Spodosols
Aquods
Ultisols
Aquults, Udults
Humults
Ustults
Vertisols
Uderts, Usterts
Torrerts, Xererts2
Sub-Orders
Of major importance
Of local importance
Of minor importance
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6. Rice Growing Ecosystems
Rice is mainly grown in irrigated lowland, rain fed lowland, upland and flood prone ecosystems, covers 55, 25, 13 and 7% of world’s rice area and accounts 76, 17, 4 and 3% production, respectively.
By considering these, irrigated ecosystem is the major one and mainly grown under submerged puddled condition.
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7. Special features of submerged soil
In any case, one important characteristic of rice soils is that they must remain submerged at least for some time during the growth period of the crop.
The submergence leads to gradual depletion of oxygen and causes reduction of a number of ions such as nitrates, sulphates, iron, manganese etc. in the soil.
The following chemical reactions happen in soil under submergence which affects rice plant growth.
Under acid soils, pH increases and reduction of pH occurs in sodic soils .
Reduction in redox potential .
Reduction of nitrates to N2O or N2 (denitrification)
Reduction of sulphate to sulfide resulting in sulfide toxicity, reported from highly reduced soils in Japan.
Reduction of Mn4+ to Mn2+ and Fe3+ to Fe2+ resulting in Mn and Fe toxicity in rice.
Increased availability of native soil P due to release of occluded P.
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8. Problem soils and management for rice
Problem soil is one where one can’t grow crop(s), but, has to adopt some specific and economical management practices to alleviate the soil related constraints to some extent and simultaneously choose crops best suited for the situation.
Rice is the typical crop which requires different soil environment to grow.
Since the rice is under submergence, the constraints of the soil are partly alleviated.
Majority of rice grown in problematic in nature and its nature of cultivation makes suitable in these soils.
Hence, major problem soils under which rice is grown are briefed with their management (Cont)..
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9. Problem rice soils include:
Sodic soils
Saline soils (includes inland and coastal saline soils)
Saline-sodic soils
Acid, red and lateritic soils
Acid sulphate soils
Peat soils
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10. Sodic soils
Soils with sufficient amount of exchangeable sodium to interfere with the growth of crops and with less quantity of soluble salts are referred as sodic or alkali soils.
There are about 65 million hectares of these soils in Asia, where rice is grown.
Rice is the most suitable crop to be grown on these soils because submergence or flooding leads to lowering of soil pH and also helps in lowering of salt concentration.
Rice in sodic soils
(Cont)..
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11. Soil management for rice cultivation
Application of gypsum is the handiest method to reclaim sodic soils when the pH is more than 10.
Shallow rooted rice crop may require t ha-1 depending on the soil texture and sodic status.
Application of organic amendments such as FYM, compost and green manure incorporation, releases abundant Co2, organic acids, lowers pH and releases
Using resistant varieties, increased seedling hill-1, use of aged seedlings (30-40 days), split application of nitrogen, use of slow release nitrogenous fertilizers (sulphur coated urea, urea super granules), leaching in summer season and raising green manure crops are some of the crop management strategies for better production of rice in sodic soils.
Gypsum application in rice fields
(Source:
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12. Saline soils
Saline soils are those soils contains sufficient soluble salts to interfere with crop growth.
Saline soils remain flocculated and the hydraulic conductivity is more or equal to non saline soils.
Soil pH is < 8.5, electrical conductivity is > 4.0 dSm-1 at 25oC and Exchangeable sodium percentage is < 15 Cmol(P+) kg-1.
These soils are with low physiologically available water due to high osmotic potential, poor aeration and toxic effect of sodium carbonate, sodium chloride and sodium sulphate.
Though rice crop is considered as salt tolerant crop, no rice variety can withstand the adverse effect of high salinity throughout its life cycle. Due to submergence in most of rice soils, imparts tolerance to salinity.
Rice in saline soils
(Source:
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13. Soil management for rice cultivation
Maintenance of submergence throughout life cycle of rice are suggested to better rice crop under saline soil conditions
Selection of salt tolerant rice varieties based on salinity levels and water depths.
Deep ploughing before submergence, heavy pre-sowing irrigation, high seed rate, closer spacing, green manuring with Dhaincha (Sesbania aculiata), use of organic amendments, placement of N fertilizer below soil surface, split application of N,
Green manure incorporated rice field
(Source:
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14. Saline-sodic soils
These soils contain both high amount of exchangeable sodium and soluble salts to cause crop growth.
The pH values are > 8.5 (but vary with salts proportion and exchangeable sodium), Electrical conductivity of saturated extract is > 4.0 dSm-1 at 25oC and Exchangeable sodium percentage is > 15 Cmol(P+) kg-1.
These soils generally occur in low-lying areas with obstruction of drainage and occasional water logging.
These soils not only cause due to high salt content but also, poor internal drainage due to the presence of hard pan.
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15. Soil management for rice cultivation
Gypsum application (5-7.5 t ha-1) followed by leaching with good quality water is essential.
Gypsum application along with green manure incorporation enhances better yield of rice.
Leaching after transplanting and leaching under intermittent submergence decreases salinity and sodicity.
Cultural management is similar to saline or sodic soils.
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16. Acid, red and lateritic soils
These soils are
Shallow to medium deep,
Low water retentively,
Dominant of oxides of Fe and Al,
Low CEC,
Dominant of kaolinite and
Illite clay minerals etc.
Higher fixation of P and K, poor N status, crust formation on the surface, susceptibility to erosion due to light texture in nature and slope etc are some of the characteristics of these soils.
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17. Soil management for rice cultivation
Artificial compaction to reduce to deep percolation is needed.
To correct soil acidity, lime or other basic materials such as calcium silicate are to be applied.
Addition of organic matter, FYM, compost, green leaf manures application to satisfy the organic matter requirement in soils.
Due to high fixation of P, powdered rock phosphate, partial acidulated rock phosphate is better than water soluble P fertilizers.
Bronzing of rice may occur in these soils can be corrected by lime application, drainage, foliar application of urea etc.
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18. Acid sulphate soils
As the name indicates these soils are acid and have pH values below 3.5 ( Entisols) or 4.0 (Inceptisols) in the upper 50 cm.
There are about 5 million hectares under these soils in Asia.
These soils are generally found in tidal swamp areas.
Fe-toxicity is a major problem in acid sulfate soils.
This can be managed by soil drainage, liming and by adding green manure or compost.
However, amounts of liming material needed in some of these soils are too large and soil drainage is difficult to provide, because it is to be done on an area basis and an individual farmer cannot do it.
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19. Peat soils
Peat soils have organic matter content of at least 65% in the upper 50 cm, are characterized by high water table and are found mostly low-lying coastal areas.
Chemical toxicities including organics such as phenols etc. are common.
Sterility of rice
Copper deficiency or non-availability may be responsible for this sterility.
Clearing of trees and vegetation and providing drainage can reclaim and improve these soils.
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20. Summary
The major rice growing soil orders are Alfisols, Entisols, Inceptisols and Ultisols.
The most important characteristic of rice soil is that submergence for at least a part of the growth period.
Submergence leads to changes in soils pH, which tends to reach neutrality both in acid as well as sodic / calcareous soils. Submergence increases the availability of Fe, Mn and P but leads to loss of N by denitrification and reduced nitrogen use efficiency.
Major problem soil under which rice is grown are sodic soils, saline soils (includes inland and coastal saline soils), saline-sodic soils, acid, red and lateritic soils, acid sulphate soils and peat soils.
Application of gypsum is important for sodic soils and selection of tolerant varieties with organic amendments are important for better growth of rice under saline soils.
Lime application play greater role to reclaim acid soils. Ground rock phospahete is better alternative to water soluble P fertilizers in acid sulphate soils.
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21. Assessment
Rice is an aquatic or semi-aquatic plant prefers to grow under submergence (True/False)
Rice grow well under light textured soils (True/False)
Submergence of soils generally neutralizes the soil (True/False)
Most suitable amendment to reclaim the sodic soil is gypsum (True/False)
Green manures and manures application can improve the saline soils and makes suitable for rice cultivation (True/False)
Gypsum application followed by leaching with good quality water makes the saline-sodic soils suitable for rice (True/False)
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22. References
Biswas, C.R. and A.K. Bandyopathyay Agronomy of rice in coastal saline soils – a review. Journal of Indian Society of Coastal Agricultural Research, 5:
Hand book of Agriculture, Indian Council of Agricultural Research, New Delhi.
Gupta, R.K. and I.P. Abrol Salt affected soils: Their reclamation and management for crop production. Advances in Soil Science. 11:
Moorman, F.M Morphology and classification of soils on which rice is grown. In: Soils and rice. IRRI, Philippines.
Rajendra Prasad, A text book of Rice Agronomy. Jain Brothers, New Delhi.
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