1. Course Title : Master Seminar Course No : SOILS - 591

3. Atomic Number Atomic Number. ► The number of protons in the nucleus of an atom is called the Atomic Number. Mass number ► The number of protons + neutrons in a nucleus of an atom is referred to as the mass number. ► A particular element can have differing numbers of neutrons and therefore have a different mass number.

4. » Atoms with the same number of protons and electrons but differing numbers of neutrons. Stable Isotopes Radioactive Isotopes

5. *Image Source: Introduction to Chemistry, General, Organic, and Biological v. 1.0 by David W. Ball, John W. Hill, Rhonda J. Scott

6. ► Isotopes of the same element will have different masses. ► Examples of isotopes with the same atomic number (subscript) but with different mass number (superscript) are 1 1 H, 2 1 H, 3 1 H 31 15 P, 32 15 P, 33 15 P ► Another way of expressing a particular isotope is to list the mass number after the element name, like carbon-12 or hydrogen-3.

7. ► A nucleus contains protons, which are positively charged so they should repel. The presence of neutrons, however, keeps the protons together and so stabilises the nucleus. Stability depends upon the neutrons : protons (n:p) ratio. ► For light elements, the number of neutrons greatly exceeds the number of protons for stability. For heavier elements more neutrons than protons are necessary for stability. ► When the ratio of neutrons to protons is outside a particular number, which varies with each atom, the nucleus becomes unstable and spontaneously emits particles and/or electromagnetic radiation and such a substance is called radioactive.

8. ► Three types of particles can be emitted from an unstable nucleus. ( α ) » Alpha particle ( α ) ( β ) » Beta particle ( β ) ( γ ) » Gamma particle ( γ ) ► Alpha, beta, and gamma emissions have different abilities to penetrate matter. » Alpha particle are heavy, slow-moving, have low energy and are easily stopped by a sheet of paper or a few cm of air. » Beta particle can travel further than an alpha particle and, a few meters of air or a sheet of aluminium is needed to stop them. » Gamma rays can penetrate deeply into matter and can impart a large amount of energy into the surrounding matter.

9. ► The half-life of a radioactive isotope is the amount of time it takes for one-half of the radioactive isotope to decay. ► The amount of radioactivity from a radioisotope is measured as a rate i.e. number of disintegrations per unit time.

10. ► There are 90 naturally occurring elements with roughly 250 stable isotopes, and over 3200 unstable or radioactive isotopes. ► Different isotopes of the same element often have completely different properties. ► While discovered less than 100 years ago, Isotopes are now used in a wide variety of scientific applications.

11. ► These include: » Radiopharmaceuticals used for medical imaging in the diagnosis of a wide range of ailments, from pneumonia to heart problems for cancer treatment and other therapeutic applications. » Smoke detectors used in home and offices. » Batteries that power NASA satellites in the far reaches of our solar system. » Control rods that prevent nuclear power reactors from melting down. » To calibrate detectors used to keep our shipping ports safe from nuclear terrorism » Many other applications in energy production, industrial diagnostic methods, archeology, geology, ecology, astronomy and physics.

12. How Isotopes can be used in Soil Science?  Many researchers have Worked with isotopes and have found them quite helpful in soil fertility management for quantification of biological nitrogen fixation, availability of nutrients in the soil, fertilizer use efficiency, residual effect of applied amendments, salinity of soil and Water, methods of fertilizer application and relative efficiency of applied organic manures.

13.  Total evapo-transpiration and its partitioning into contributing components in many ecosystems have been successfully quantified through this technique.  The suitability of plants to drought or salinity conditions Was also evaluated using radiotracers.  15 N isotopic dilution techniques are also finding favour in ground Water monitoring, soil Water recharge, soil and Water pollution assessments.  Play an important role in soil erosion, soil formation and clay mineralogical studies.

14.  The only direct means of measuring nutrient uptake from the applied fertilizer is through the use of isotopes.  Extensive work has been conducted using N-fertilizers labelled with the (Stable isotope) 15 N and P-fertilisers labelled with the (Radioactive isotope)s 32 P or 33 P.  The principle tracer isotopes used in soil-plant relationships studies are shown in the Table.

16. Element Tracer isotope Typical Applications Potassium 40 K(Radioactive isotope) Exchangeable K in soils 42 K(Radioactive isotope) Ion uptake mechanisms. Limited use because of short half-life Calcium 45 Ca(Radioactiv e isotope) Soil Ca (ion uptake, exchangeable Ca) and plant Ca movement (root autoradiography) Strontium 85 Sr(Radioactiv e isotope) Cation exchange capacity of soil, ion uptake mechanisms Magnesium 28 Mg(Radioactiv e isotope) Movement in plants Sulfur 35S(Radioactiv e isotope) Uptake from atmosphere (SO 2 ), S- cycling studies, availability from soil

17. Element Tracer isotope Typical Applications MICRONUTRIENTS Iron 59 Fe(Radioactive isotope) Erosion studies, soil and plant movement, availability from soil Copper 63 Cu(Radioactive isotope) Complexing in soil solution, soil and plant movement Manganese 54 Mn(Radioactive isotope) Complexing in soil solution, availability from soil, soil and plant movement Zinc 65 Zn(Radioactive isotope) Complexing in soil solution. Availability from soil and fertilizer. Soil and plant movement. Boron 10 B(Stable isotope) Foliar absorption, soil moisture studies Molybdenum 99 Mo(Radioactive isotope) Plant nutrition

18. Element Tracer isotope Typical Applications OTHER ELEMENTS Hydrogen 2 H(Stable isotope), 3 H(Radioactive isotope) Water movement, metabolism, leaching Carbon 13 C(Stable isotope), 14 C(Radioactive isotope) Photosynthesis and C translocation,Soil organic matter studies Oxygen 18 O(Stable isotope) Photosynthesis, respiration, soil organic matter studies Chlorine 36 Cl(Radioactive isotope) Solute movement in soils. Cesium 134 Cs, 137 Cs(Radioactive isotope) Soil erosion and sedimentation *SOURCE : Use of Isotope and Radiation methods in soil and water management and crop nutrition, current science, vol. 98, NO.11,IAEA,Vienna,2001

19.  Isotopes have identical chemical properties but some slightly different physical properties.  Detection methods use one of these properties such as mass, emission spectrum, IR absorption.  The most common and most precise method to measure stable isotopes is mass spectrometry.

20.  In Isotopic-aided fertilizer experiments, a labeled fertilizer is added to the soil and the amount of fertilizer nutrient that a plant has taken up is determined.  In this way different fertilizer practices (placement, timing, sources, etc.) can be studied.  The first parameter to be determined when studying the fertilizer uptake by a crop by means of the isotope techniques is the fraction of the nutrient in the plant derived from the (labelled) fertilizer.

21.  15 N labeled fertilizers such as urea and ammonical fertilizers are applied in the plant- soil-water system and 15 N tracer technique determines the fate of applied N in the system.  The use of 15 N a tracer is the most powerful tool to distinguish between the fates of a particular N source and background soil N.

22.  There are six main variations in the use of 15 N labelled substrates: » The 15 N isotope dilution method (ID) » The A-value method (AV) » The single treatment method (ST) » Yield dependent model, yield independent method and » The natural abundance method

23. Use of 15 N Enriched Fertilizers or Substrates

24.  It is generally accepted that the 15 N dilution method is a most reliable estimation for evaluating total amount of Ndfa (total N in plant derived from atmosphere).  By this method, total N in plant derived from fertilizer (%Ndff),soil (%Ndfs) can be also calculated at the same time.  The procedure followed in the calculation of this fraction and other derived parameters for nitrogen using 15 N labelled materials is as follow.

25.  For all field and greenhouse experiments with 15 N (or any other stable isotope) labelled materials, the following basic primary data need to be recorded for each plot: » Dry matter (D.M.) yield for the whole plant or sub-divided into plant parts. » Total N concentration (% N in dry matter) of the whole plant or plant parts. This is done by chemical methods, e.g. Kjeldahl or by combustion (Dumas). » Plant % 15 N abundance, which is analyzed by emission or mass spectrometry. » Fertilizer % 15 N abundance. » 15 N labelled fertiliser(s) used and N rate(s) of application. For Experiments with 15 N

26.  The method involves the growth of plants in soil fertilized with 15 N enriched inorganic or organic fertilizers.  Urea, ammonium nitrate or ammonium sulphate fertilizer can be applied in a solid or liquid form (fertilizer dissolved in at least 500 ml water/m ).  Precaution should be taken not to apply the fertilizer when the soil temperature is very high due to direct ammonia volatilization.

27.  At the time of harvesting, the plots of reference crop should always be harvested at the same time as the plots with fixing crops.  These parts are then weighed and subsampled after chopping into small fragments.  Subsamples should be ground after drying at 70°C. These samples can then be analyzed for total N by the Kjeldahl procedure.  The N 15 abundance can be analyzed by either emission or mass spectrometer

28.  After the analyses of % N abundance in the plant and fertilizer samples, % 15 N atom excess calculated as the difference between the 15 N atom % in plants/fertilizer and its natural abundance in the atmosphere (0.3663%).  The % 15 N atom excess values are used for all the following calculations. For Experiments with 15 N

29.  N derived from fertilizer(Ndff) » N derived from fertilizer was calculated according to FAO/IEAE manual (2001).  15 N recovery calculation

30.  In the NF crop the source of N available to the plants are from fertilizer and soil N.  For the N fixing crop (F), there is a third source of N available to the plants i.e., N 2 from the atmosphere.  The total N in plant can therefore were derived from fertilizer (%Ndff),soil (%Ndfs) and atmosphere (%Ndfa) through biological nitrogen fixation represented by the following equation:

31. *SOURCE : ACIAR publication, Measuring plant-associated nitrogen fixation in agricultural systems, pg-157,The Australian Centre for International Agricultural Research (ACIAR)

32. *SOURCE : ACIAR publication, Measuring plant-associated nitrogen fixation in agricultural systems, pg-157,The Australian Centre for International Agricultural Research (ACIAR)

33.  It is assumed that both non-fixing and fixing crops take up N from soil and fertilizer in the same ratio.  %Ndfa, as quantified by the 15 N isotope dilution method, is usually calculated by the following equation:  Amount of N 2 fixed can be calculated according to:

34.  Often, it is necessary to apply different doses of N to fixing and non-fixing plants.  As high levels of inorganic N can depress N 2 fixation it is necessary to apply low amounts of labelled N fertilizer to the fixing crop in order to estimate N 2 fixed.  However, such amounts may be too low to support the proper growth of the reference plants, especially in soils of low fertility.  For these reasons it is practical to give a reasonable dose of N 15 labelled fertilizer to the reference crop, while the fixing crop receives a low quantity.

35.  When different fertilizer rate is applied to the F and NF crops n is the relative amount of fertilizer applied i.e. » n = amount of fertilizer applied to the F crop divided by the amount of fertilizer applied to the NF crop.

37.  Often, it is necessary to apply different doses of N to fixing and non- fixing plants.  As high levels of inorganic N can depress N 2 fixation it is necessary to apply low amounts of labelled N fertilizer to the fixing crop in order to estimate N 2 fixed.  However, such amounts may be too low to support the proper growth of the reference plants, especially in soils of low fertility.  For these reasons it is practical to give a reasonable dose of N 15 labelled fertilizer to the reference crop, while the fixing crop receives a low quantity.  The A-value method is similar to 15 N dilution method except that the reference non-fixing plants receive higher rate of N fertilizer to obtain satisfactory growth (Hardarson et al 1991). However, it was criticized that this method has no advantage over the 15N dilution method.

38.  This method as originally presented used the following A-value concept of Fried and Broeshart (1975):  where A f is the amount of fertilizer applied, whereas A s and A a are nitrogen available from soil and air, respectively, as expressed in fertilizer units.

39. ST

40.  In the "single treatment" experiment all treatments are the same as far as the plant and soil are concerned but only one fertilizer application in each treatment combination has been labelled with isotopes.  By this approach, time of application of fertilizer, fertilizer source, and placements at the same time as N fixation can be evaluated.  The calculations for this type of experiments are similar to the ones for previous Methods where different amounts of labelled fertilizer are applied to the fixing and the non-fixing crops.

41.  By labelling the soil with 15 N-labelled nitrate or urea it is possible to trace the fate of fertiliser derived nitrate down the soil profile.  This can be achieved by taking sequential soil cores or by using suction cups, tensionic samplers, mini lysimeters and other techniques to sample the nitrate in the soil water.

43.  Ghoneim (2008) reviewed fertilizer use efficiency in rice using the N 15 isotope techniques in Egypt. » N 15 labeled biogas slurry (digested anaerobic organic residues - DAOR) and chemical fertilizer (CF) were applied to soil with low fertility cropped with rice. » The 15N dilution method was used to estimate the N uptake and recovery

44. » DW = dry matter, » Ndfa-N derived from applied CF or DAOR; » Ndfs- N derived from soil. » Numbers in parentheses are N uptake % derived from CF, DAOR and soil. » # Means in a column followed by the same letter were not significantly different

45.  He observed that fertilizer use efficiency calculated by the 15 N dilution method tended to be higher for CF (Chemical Fertilizer) than DAOR (digested anaerobic organic residues).

46.  Application effects of sewage sludge (SS) on growth indices, yield, and nutrient uptake in Komatsuna (Brassica campestris var. perviridis) grown in a low fertility soil were investigated and compared with those of chemical fertilizer (CF) and no-fertilizer (NF) treatments. » The N-use efficiencies of CF and SS were 19.7% and 12.1%, respectively, of the applied N. Therefore, the relative efficiency of the sewage sludge to chemical fertilizer was 61.5%. (Asagi et al. 2008)

47.  Widory et al. (2005) tracked the sources of nitrate pollution in groundwater pollution through mineral fertilizers, wastewater and animal manure.  Jagadeeswaran et al. (2004) studied on NUE in turmeric at coimbatore and observed recovery of N in turmeric was in favour of 4 splits at 180 days growth stage (19.46%) as well as harvest (30.76%).  Bronson and Fillery (1998) conducted a study on fate of nitrogen-15-labelled urea applied to wheat on a waterlogged texture-contrast soil, recorded that denitrification was the largest loss mechanism identified during waterlogging.

48.  Ko-H-J (2003) investigated that the nitrate contamination sources in different agricultural system in Korea Republic, by using nitrogen isotope ratios. » The nitrate concentrations of groundwater in livestock farming area were higher than those in conventional and organic farming area and exceeded the national drinking water standard of 10 mg N/litre.

49. » Obvious advantage is inherent non-radioactivity. » Stability in environment is not limited by time i.e. there is no isotope decay with time and can be used for long time experiment. » Their use doesn’t pose any health hazards or any disposal problem on biological system. » No permission is needed to carry out experiment using 15 N tracer technique without any licensing and radioactivity monitoring. » Less need of background information of the experimental plot where the tracer will be introduced.

50. » High cost and unavailability of 15 N labelled fertilizer. » Difficulty in N isotope ratio analysis. It requires highly skilled technicians and operational procedures. » Ndff equation doesn’t give the route taken by the nitrogen in going from pool A to pool B. » It is possible to recovery of soil N in the plant by subtracting that recovered from the added label from the total N content of the plant.

51. » 15 N tracer technique is a valuable approach for obtaining basic information about soil N transformations. Gains and losses of Nitrogen may be evaluated accurately. » 15 N tagging in fertilizer enables a direct and accurate evaluation of the fertilizer contribution to the crops. » 15 N study also provides precise information on the fate of fertilizer nitrogen in soil plant system under field conditions for calculating a balance sheet for N. » Such knowledge will be indispensible in the long run for improving empirical methods of managing fertilizer N as well as biologically fixed N.