Soil aeration

SOIL AERATION BY MEENAKSHI ATTRI

1. Sher-e-Kashmir University of Agricultural Sciences & Technology of Jammu Division of Agronomy Chatha Campus, Jammu - 180009 Incharge : Dr. Peeyush Sharma Presented by: Meenakshi Attri J -19-D-363-A Ph.D. Agronomy SOIL PHYSICS SOIL AERATION

2. Soil Aeration Soil aeration may be defined as the exchange of carbon dioxide and oxygen gases between the soil pore space and the aerial atmosphere.

3. Definition of Soil Aeration: Soil aeration is phenomenon of rapid exchange of oxygen and carbon dioxide between the soil pore space and the atmosphere, in order to prevent the deficiency of oxygen and/or toxicity of carbon dioxide in the soil air. The well aerated soil contains enough oxygen for respiration of roots and aerobic microbes and for oxidation reaction to proceed at optimum rate. The rate of exchange of gases between soil air and outer atmosphere {soil aeration}

4. Process of Air Aeration

5. Composition of average soil

6. Gaseous Exchange The more rapidly roots and microbes use up oxygen and release carbon dioxide, the greater is the need for exchange of gases b/w the soil and the atmosphere. Gaseous exchange between respiring sites (plant roots , microbes etc,) and outer atmosphere takes place in 2 steps 1. Outer atmosphere and air filled soil pores (gaseous phase) 2. Air filled soil pores and the respiring sites (water film) Exchange of gases between soil and atmosphere is achieved through two Mass flow- gas exchange is due to fluctuations in water content of soil that force air in and out. Diffusion – gas exchange is by partial pressure. Soil aeration process is achieved by gaseous exchange

7. 1. Mass flow: The mass flow occurs due to total pressure gradient of gas. The pressure gradient causes movement of entire mass of air from a zone of high pressure to that of low pressure. Such a flow of air occurs within the soil or from atmospheric air to soil air or vice-versa. When the soil temperature is higher than the atmospheric temperature during mid-day then the soil gases will expand and move out of the pore space into the atmosphere. When the soil is cooler than the atmosphere during night, then the atmospheric gases enter the soil. When the atmospheric pressure is high, the atmospheric gases will enter in to the soil. 2. Diffusion: The gaseous interchange between the soil and atmosphere takes place by diffusion. The partial pressure of O 2  is higher in the atmospheres than in soil pore space and the partial pressure of CO 2  is higher in the soil pore space than the atmosphere. However, total pressure both in the soil and the atmosphere may be the same. Thus O 2  will move into the soil and the CO 2  will move out of the soil. The renewal of gases by mass flow is less important than the diffusion in determining the total exchange that occurs between soil and the atmosphere.

8. Characterization of Soil Aeration: : There are various parameters that can be used for characterizing soil aeration. The volume percentage of soil air or air capacity is that part of the pore space which is filled with air. This is generally determined by applying the tension equivalent to a water column of 50 cm to a saturated soil on a tension table. Gaseous composition. The oxygen diffusion rate (ODR). It is determined by using the platinum microelectrode technique where the diffusing oxygen is allowed to reduce at the platinum electrode at a given electric potential. The rate of diffusion of oxygen to the platinum electrode is used as an index of the rate of diffusion of oxygen through the water film to the roots. Oxidation-reduction potential, indicating the oxidized or reduced condition of the soil. Composition of the soil for its reduced components.

9. Factors Affecting Soil Aeration 1. Amount of air space: The top soil contains much more pore spaces than the sub-soil, thus the opportunity for gaseous exchange is more in the top soil than in sub-soil. Hence the oxygen content of the top soil is greater that the sub-soil. The soil properties such as  soiltexture , bulk density and aggregation affect the amount of pore space and hence the soil aeration. 2. Soil organic matter: When organic matter is added to the soil it is readily decomposed by the micro-organisms to liberate the CO 2  in soil air. Thus the concentration of both O 2  and CO 2  are affected by microbial decomposition of the organic residues. Besides, the respiration of higher plants and the micro-organisms around the roots is also a significant process affecting the soil aeration. 3. Soil moisture: The macro-pores are filled up with water immediately after heavy rain or irrigation and level of oxygen content falls to zero. When the soil is artificially drained again, the macro-pores are filled up with air and the oxygen content of the soil increases. 4. Seasonal differences: There is a considerable seasonal variation in the composition of soil air. In the spring time in temperate-humid regions the soils are wet and cold and the gaseous exchange is poor. In summer months, when the soils are dry, the gaseous exchange will increase. This will result in relatively high content of O 2  and low CO 2 .

10. Composition of Soil Air: The soil air contains a number of gases of which nitrogen, oxygen carbon dioxide and water vapour are the most important. Soil air constantly move from the soil pores into the atmosphere and form the atmosphere into the pore space. Although soil air and atmospheric air differ in the compositions, soil air contains a much greater proportion of carbon dioxide and a lesser amount of oxygen than atmospheric air. At the same time, soil air contains a far greater amount of water vapour than atmospheric air. The amount of nitrogen in soil air is almost the same as in the atmosphere

11. Factors affecting Composition of soil air Season Soil fertilty Soil water content Soil texture Soil aggregation Soil depth

12. Factors Affecting the Composition of Soil Air: The composition of soil air is influenced by a number of factors such as nature of soil, soil condition, type of crop, microbial activity, season etc. Oxygen: The quantity of oxygen in soil air is less than that in atmospheric air. Plant roots and various microorganism require oxygen which they take from the soil air, thus, depleting the concentration of oxygen in the soil air. The amount of oxygen also depends upon the soil depth . The oxygen content of the air in lower layer is usually less than that of the surface soil. This is possibly due to the more readily diffusion of oxygen from the atmosphere into the surface soil than in the sub-soil. The quantity of oxygen is usually higher in dry season than during the monsoon. Because soils are normally drier during the summer months, opportunity for gaseous exchange is greater during this period. This results in relatively high O 2  and low CO 2  levels. Light texture soil i.e., sandy soil contains much higher oxygen percentage than heavy soil.

13. Carbon dioxide: Decomposition of organic matter produces CO 2 . Hence, soils rich in organic matter contain higher percentage of carbon dioxide . Production of CO 2  is associated with microbial activity, CO 2  increases with the increasing number and activity of microorganism. High temperature during summer season encourages microorganism activity which results in higher production of CO 2 . The concentration of CO 2  is usually greater in sub-soil probably due to more sluggish aeration in lower layer than in the surface soil. Water vapour : Soil air, however, contains much more water vapour than atmospheric air. Capillary water in the soil is used to saturate the soil air with vapour . During crop growing period, when soil remains moist, the amount of water vapour in the soil air would be more.

14. Aeration Status of Soils: It can be determined in the three ways i . e: ( i ) Percentage oxygen and carbon dioxide content of the soil, (ii) Oxygen diffusion rate, and (iii) The oxidation reduction potential ( Redox potential).

15. ( i ) Percentage composition of soil air: Well aggregated soils contain enough macrospores to keep the soil aerated for proper growth and functioning of roots and micro-organisms. After a heavy rain, the macrospores are filled up with water but the soil may still contain some quantity of air dissolved in water. So micro-organisms can grow for a short time only, after which the soil must be drained so that the macrospores are re-filled with air.

16. ii) Oxygen Diffusion Rate (ODR): It determines the rate at which the oxygen should be supplied to the soil when it is being continuously used for the respiration of roots and soil micro-organisms. The growth of roots of most crops ceases when the oxygen diffusion rate decreases to about 20 x 10 -8  gm./sq. cm/min . It should be above 40 x 10 -8  gm./sq.cm/min . for good growth of most crops. (iii) Oxidation-reduction potential of soil. The oxidation potential of chemical systems including soil is a measure of the tendency of the oxidation reaction to occur in that system, including soils. Highly reduced soils have a high oxidation potential of +0.50 volts. So a highly reduced soil which has a tendency to be oxidized has a Reduction Potential or Redox Potential Eh of- 0.50 volts. Well drained and aerated soils which are highly oxidized usually have a redox potential of +0.50 volts. The value of the Redox Potential increases when the oxygen content of soils decreases.

17. Redox reaction sequence of reductions that take place when well aerated soil becomes saturated with water Once oxygen is gone, the only active microorganisms are those that can use substances other than oxygen as electron acceptors ( anaerobic ) E h drops Shows E h levels at which these reactions take place Poorly aerated soil contain partially oxidized products: Ethylene gas, methane, alcohols, organic acids organic substrate oxidized (decomposed) by various electron acceptors: O 2 NO 3 - Mn +4 Fe +3 SO 4 -2 rates of decomposition are most rapid in presence of oxygen

18. Oxidized form Reduced form Eh (v) O 2 H 2 O .38 - .32 NO 3 -1 N 2 .28 - .22 Mn +4 Mn +2 .22 - .18 Fe +3 Fe +2 .11 - .08 SO 4 -2 S -2 -.14 - -.17 CO 2 CH 4 -.2 - -.28

19. Oxygen requirements of plants Plant require some minimum amount of oxygen for their optimum growth and yield and the requirement varies with the plant species. Foroptimum plant growth and yield soil aertaion must be adequate The critical aeration below which plant growth is adversely affected is atleast 10% air filled porosity or 10% oxygen concentration of soil air or 30×10-8 g/cm2-min oxygen diffusion rate in the root zone.

20. Importance of soil air It is used for the respiration by the root Decomposition of the organic matter by the microorganisms.

21. Importance of Soil Aeration: Soil aeration affects the availability of some nutrients elements to plant roots. Manganese and iron occurs in the well aerated soil in their higher valent forms ( Mn ++++ , Mn +++ , Fe +++ ) and in poorly aerated soils in their lower valent forms ( Mn ++ , Fe ++ ). They are available to plants only in their lower valent forms. Ferric phosphate would be reduced to ferrous phosphate. Carbon dioxide produced from the decomposition of organic matter reacts with water to form carbonic acid which slowly dissolves insoluble phosphate. So the availability of phosphates (would be increased to the plant roots. Sulphur occurs as sulphate in well aerated soil. Plant roots assimilate sulphate . Sulphate is reduced to sulphide in poorly aerated (water logged) soils. Hydrogen sulphide is toxic to plant a root which suffers from it in water logged soil. Organic matter is decomposed by aerobic bacteria in well aerated soil when complex organic nitrogen and phosphorus compounds are decomposed to their respective simple inorganic compounds which plant roots readily assimilate symbiotic and non-symbiotic nitrogen fixation takes place only in well aerated soils.

22. Nutrient absorption is an energy consuming process. Energy is available from respiration is expended in absorbing nutrient ions from the soil. Hence nutrient absorption is retarded in poorly aerated soils. If an excessive amount of readily decomposable organic matter has been added to the soil, then it would decompose to evolve high amounts of carbon dioxide to the soil. Consequently root growth and germination of seeds would be adversely affected. Some crops become infested with pathogens in poorly aerated soils. The incidence of will disease caused by the fungus ( Fusarium sp) has been attributed to poor aeration. Citrus and suffers from die-back in poorly aerated soils have also reviewed the works of some investigators who have observed that poorly aerated soils (waterlogged soils) has an effect on the pathogenicity of root infesting fungi. Nitrates are reduced to oxides of nitrogen and nitrogen gases in poorly aerated soils. These gases escape to the atmosphere, long light coloured roots develop in well aerated soils. Root hairs develop best under well aerated condition.

23. Some conclusions about aeration: Forms/mobility Roots Decomposition 1. Forms and Mobility Soil aeration determines which forms of chemicals are present and how mobile they are Redox colors in Poorly and Well-Aerated Soil Nutrient elements A) Poorly aerated soils reduced forms of iron and manganese Fe +2 , Mn +2 Reduced iron is soluble; moves through soil, removing red, leaving gray, low chroma colors ( redox depletions) B) Well-aerated soils: Oxidized forms of iron and manganese Fe +3 Mn +4 Fe precipitates as Fe +3 in aerobic zones or during dry periods Reddish brown to orange ( redox concentrations)

24. C. Nutrient Elements Plants can use oxidized forms of nitrogen and sulfur Reduced iron, manganese Soluble/”good” in alkaline soils More soluble in acid soils; can reach toxic levels 2 . Root respiration Good aeration promotes root respiration Poor aeration: water-filled pores block oxygen diffusion into soil to replace what is used up in respiration 3. Decomposition In aerated soils, aerobic organisms rapidly oxidize organic material and decomposition is rapid In poor aeration, anaerobic decomposers take over and decomposition is slower

25. Soil Air in Relation to Soil and the Crop Management: Soil Management: The maintenance of a stable soil structure is an important means of augmenting good aeration. . Maintenance of organic matter by addition of Farm yard Manure and crop residues and by growth of legumes is perhaps the most practical means of encouraging aggregate . Stability, which, in turn, encourages good drainage and better aeration. In heavy textured (clay) soil, it is very difficult to maintain optimum aeration. Aeration in the soil can be added by controlling weeds and tilling the heavy soil. Consequently, no tillage ( zero tillage ) or minimum tillage practices, which the quite satisfactory on well-drained soils, have limitations on poorly drained soils. Crop management: Selection of crop is important criteria for adaption of crop in the soil. Alfalfa, fruits and forest trees and other deep-rooted plants require deep, well- aerated soils, such plants are sensitive to a deficiency of oxygen, even in the lower soil horizon. In contrast, shallow-rooted plants, such as grasses, clovers etc . do well on soils that tend to be poorly aerated, especially in the subsoil. The rice plant flourishes even when the soil is submerged in water.

26. Ghildayal , B.P.1972.Effect of physical environment of plant growth.In : Advanced Soil Physics. Indian Council of Agricultural Research ,New Delhi, India.159-178 Lemon ,E.R. and Erickson A.E.1952. The measurement of oxygen diffusion in the soil with a platinum electrode, Soil Science Society. Am. Proceeding . 16:160-163 . Russell, E.J and Appleyard , A.1915. The atmosphere of the soil . its composoition and cause of variation. Journal of Agricultural Sciences ,7:1-48 . Verma , S and Sharma, P.K, 2008.Long term effects of organics, fertllizers and cropping systems on soil physical productivity evaluated using a single value index. Soil and Tillage Research, 98:1-10 A Textbook of Soil P hysics by Dr. PK Sharma A Textbook of Soil Physics by Dr. AK Saha and Dr. Anuradha saha References

27. Steudle , E. Water uptake by plant roots: An integration of views. Plant Soil 2000, 226, 45–56. Armstrong , W. Aeration in higher plants. In Advances in Botanical Research; Elsevier: Hull, UK, 1980; Volume 7, pp. 225–332. Brady, N.C.; Weil, R.R. Soil Aeration and Temperature. In The Nature and Properties of Soil, 12th ed.; Prentice Hall: New York, NY, USA, 1999; pp. 265–306 . Vartapetian , B.B.; Jackson, M.B. Plant adaptations to anaerobic stress. Ann. Bot. 1997, 79, 3–20. [ Bhushan , L.; Ladha , J.K.; Gupta, R.K.; Singh, S.; Tirol-Padre, A.; Saharawat , Y.S.; Gathala , M.; Pathak , H. Saving of water and labor in a rice–wheat system with no-tillage and direct seeding technologies. Agronomy 2007, 99, 1288–1296 . www.google wikipedia.com References

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