Interpreting Soil Tests

Transcription

1 Interpreting Soil Tests 1. What analytes 2. What do they mean 3. Value of them, cost, etc. 4. How frequent do I test? 5. Sampling procedure. aora

2 developed in 1869 aora

3 Essentiality 1. Element is essential for plant to complete its life-cycle. 2. Role of the element must be unique. 3. Essentiality is universal among plants.

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5 Inputs Outputs Fertiliser Water Natural weathering Atmospheric fixation Crop residues Carbon Leaching Run-off Crop removal Residue removal Burning Carbon

6 Essential Nutrients 16 mineral nutrients known to be essential for plant growth (17 including Si for cane) Major nutrients» (macronutrients primary & secondary) Minor nutrients» (micronutrients or trace elements) aora

7 Dynamic Equilibria occurring in soils Nutrient Uptake by Plants Organic matter and microorganisms Soil solution Exchange and surface adsorption Crystalline minerals and properties

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9 Analyte Result Depth (cm) Organic Carbon % 1.1 Colour Texture med. Clay med. Clay med. Clay ph (water) ph (CaCl) Nitrate nitrogen mg/kg Sulfate sulfur mg/kg Phosphorus (colwell) mg/kg Potassium meq/100g Calcium meg/100g Magnesium meq/100g Sodium meq/100g Chloride mg/kg Copper mg/kg Zinc mg/kg < 0.1 < Manganese mg/kg Iron mg/kg Cation Exchange Capacity (CEC) meq/100g Calcium/Magnesium Ratio Electrical Conductivity (Sat. Extract) Sodium % Cations

10 Soil ph and nutrient availability aora

11 Soil ph ph is measured on a logarithmic scale A one-unit decrease or increase in ph is a tenfold change in acidity or alkalinity ph water 7 is neutral ph 6 is 10 times more acidic than ph 7 ph 5 is 100 times more acidic than ph 7 ph 4 is 1000 times more acidic than ph 7 this does not mean a log increase in lime rates

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13 Analyte Result Depth (cm) Organic Carbon % 1.1 Colour Texture med. Clay med. Clay med. Clay ph (water) ph (CaCl) Nitrate nitrogen mg/kg Sulfate sulfur mg/kg Phosphorus (colwell) mg/kg Potassium meq/100g Calcium meg/100g Magnesium meq/100g Sodium meq/100g Chloride mg/kg Copper mg/kg Zinc mg/kg < 0.1 < Manganese mg/kg Iron mg/kg Cation Exchange Capacity (CEC) meq/100g Calcium/Magnesium Ratio Electrical Conductivity (Sat. Extract) Sodium % Cations

14 Exchangeable Cations, and Cation Exchange Capacity aora

15 What is Cation Exchange Capacity - CEC? ion = atom with charge (+ or -) ion -ve charge = anion e.g. NO 3 - SO 4 2- Cl - H 2 PO 4- MoO 4 2- ion +ve charge = cation e.g. K + Na + Ca ++ Mg ++ Al +++ NH ++++ Mn ++ Fe ++ Cu ++ Zn ++ Fe +++ aora

16 Cation Exchange Capacity Cations are attracted to negatively charged soil particles and OM Mg ++ K + Ca ++ Na + Mg ++ K + Ca ++ Mg ++ Al +++ Ca ++ Na + K + Ca ++ Mg ++ Ca - ve - ve ++ - ve - ve K - ve - ve - ve + Mg ++ Al +++ Na + - ve - ve K + Mg ++ Ca ++ - ve - ve Soil Colloid - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve - ve Ca ++ Ca ++ - ve - ve Ca ++ Mg ++ Ca ++ Mg ++ Na + Al +++ K + Na + Al +++ Ca ++ Mg ++ K + Ca ++ K + Ca++ Mg ++ Ca ++

17 Calculating exchangeable % Cation Value (cmol(+)/kg) % of Effective CEC or meg/100gms Calcium (Ca 2+ ) * Magnesium (Mg 2+ ) Potassium (K + ) Sodium (Na + ) Aluminium (Al 3+ ) 0 0 Total ( Effective CEC ) 25.9 Calcium (% of CEC) = 16.3/25.9 x 100 = aora

18 Converting Ex Cations: mg/kg to cmol(+)/kg Aluminium: 20mg/kg divided by 90 = 0.22 cmol(+)/kg Calcium: 3200mg/kg divided by 200 = 16.0 cmol(+)/kg and visa versa: to convert cmol(+)/kg to mg/kg, multiple by figures in table mg/kg = cmol(+)/kg x Eq. wt. x 10 E.g. Potassium: 117 mg/kg = 0.3 cmol(+)/kg x 39.1 x10

19 Analyte Result Depth (cm) Organic Carbon % 1.1 Colour Texture med. Clay med. Clay med. Clay ph (water) ph (CaCl) Nitrate nitrogen mg/kg Sulfate sulfur mg/kg Phosphorus (colwell) mg/kg Potassium meq/100g Calcium meg/100g Magnesium meq/100g Sodium meq/100g Chloride mg/kg Copper mg/kg Zinc mg/kg < 0.1 < Manganese mg/kg Iron mg/kg Cation Exchange Capacity (CEC) meq/100g Calcium/Magnesium Ratio Electrical Conductivity (Sat. Extract) Sodium % Cations

20 The Nitrogen Cycle Urea It is Nitrogen in the organic form Can add 3 days to the process before it becomes plant available Is NOT plant available Requires microbial action to convert to Ammonia aora

21 Nitrogen Pathway Urea This step can add an extra 3 days for your nitrogen to become plant Ammonia NH 3 Ammonium NH 4 : quite stable, is fixed onto the soil clays Nitrite: NO 2 an intermediate step and easily lost in wet soil, toxic if allowed to accumulate in the plant. Nitrate: NO 3 plant available form, also very soluble and therefore subject to leaching available Converted by natural soil bacteria

22 Nitrogen Balance Sheet aora

23 Analyte Result Depth (cm) Organic Carbon % 1.1 Colour Texture med. Clay med. Clay med. Clay ph (water) ph (CaCl) Nitrate nitrogen mg/kg Sulfate sulfur mg/kg Phosphorus (colwell) mg/kg Potassium meq/100g Calcium meg/100g Magnesium meq/100g Sodium meq/100g Chloride mg/kg Copper mg/kg Zinc mg/kg < 0.1 < Manganese mg/kg Iron mg/kg Cation Exchange Capacity (CEC) meq/100g Calcium/Magnesium Ratio Electrical Conductivity (Sat. Extract) Sodium % Cations

24 Fertilisers and acid soils Fertiliser selection and management play an important role in arresting acidification Nitrogen fertilisers can be acidifying As NH 4+ is converted to NO 3-, H + is produced Ammonium (NH 4+ ) + Oxygen Nitrate (NO 3- ) + 2 H + Nitrifying bacteria CO 2 + S + O 2 + 2H 2 O CH 2 O + SO H + Thiobacillus

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28 Soil Phosphorus Fractions aora

29 Phosphorus Buffering Index Amount of P fertiliser required to raise soil P by one mg/kg, 6-12 months after application, according to its P buffer index (PBI) PBI PBI Class kg P to raise Olsen P 1mg/kg kg P to raise Colwell P 1mg/kg < 36 Very Very Low Very Low Low Moderate High > 840 Very High aora

30 Predicted critical Colwell P soil test values for Standard PBI categories. < >840 PBI category Extremely low Very very low Very low Low Moderate High Very High Critical value for mid point PBI category (range) 23 (20-24) 26 (24-27) 29 (27-31) 34 (31-36) 40 (36-44) 55 (44-64) na Source: Better Fertiliser Decisions for Grazed Pastures aora

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32 35 Phosphorus (Colwell) mg/kg Phosphorus (Colwell) Lower Upper aora

33 Electrical Conductivity EC Definition: a measure of the conductivity of electricity through water. The value reflects the amount of soluble salts in an extract and therefore provide an indication of soil salinity. Electrical Conductivity ds/m Electrical Conductivity (saturated extract) aora

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35 Saline soils Salinity is the presence of soluble salts in the plant root zone or on the soil surface at a concentration high enough to impact plant growth In Australia, soil salinity is predominantly due to salts of sodium: NaCl, Na 2 CO 3 & NaHCO 3

36 What is a salt? By the combination of an acid and a base, the hydrogen of the acid is replaced by the metal of the base, and the result is the formation of a salt. HCI + NaOH = NaCI + H 2 O Acid base salt water aora

37 developed in 1869 aora

38 Measuring soil salinity Soil salinity is commonly measured as the electrical conductivity (EC) of soil water EC is often given in units of deci-siemens per metre (ds/m) and is measured in soil using two methods: Saturated paste extract (ECse) most accurate, or 1:5 soil:water extract (EC1:5) most commonly used It s important to know which measurement is taken, as the different methods give different results aora

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40 No. 1 No. 2 Medium Clay Soil % Change Sandy Clay Soil % Change NUTRIENT Sulfate Sulphur 0-10cm , , cm , , cm cm cm Calcium 0-10cm cm cm cm cm Magnesium 0-10cm cm cm cm cm Sodium 0-10cm cm cm cm cm Chloride 0-10cm , , cm , , cm cm cm aora

41 No. 1 No. 2 Medium Clay Soil % Change Sandy Clay Soil % Change NUTRIENT C.E.C. (Cation Exchange Capacity) 0-10cm cm cm cm cm Ca:Mg 0-10cm cm cm cm cm E.S.P % (Exchangeable Sodium Percentage) 0-10cm cm cm cm cm E.C.ds/m (Electrical Conductivity) 0-10cm , cm cm cm cm aora

42 Natural soil variability with depth aora

43 Sampling method Zig-zag B A C Zone Transect Cluster Grid

44 SAMPLING; most errors occur here in practice aora

45 Soil Nitrate - Number of Cores Confidence Level Number of cores needed for Medium accuracy Nitrate N+/- 20% of mean Water +/- 2% 66% % % 8 5 Higher level Nitrate N +/- 10% of mean Water +/- 1% 66% % % 29 20

46 Analyte Result Depth (cm) Organic Carbon % 1.1 Colour Texture med. Clay med. Clay med. Clay ph (water) ph (CaCl) Nitrate nitrogen mg/kg Sulfate sulfur mg/kg Phosphorus (colwell) mg/kg Potassium meq/100g Calcium meg/100g Magnesium meq/100g Sodium meq/100g Chloride mg/kg Copper mg/kg Zinc mg/kg < 0.1 < Manganese mg/kg Iron mg/kg Cation Exchange Capacity (CEC) meq/100g Calcium/Magnesium Ratio Electrical Conductivity (Sat. Extract) Sodium % Cations

47 And we can save 700 Lira by not taking Soil Tests. aora

48 Any Questions????? aora

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51 The Function of Organic Material in 1. Organic Matter Soils. 2. Organic carbon, nitrogen, phosphorus and sulphur, etc. 3. How does the process work? 4. Efficiency of process 5. Process drivers aora

52 Organic matter Usually < 5% of the soil mass Strongly influences the physical and chemical properties of soils Decomposition is more rapid in warmer wetter climates. aora

53 Functions of organic matter Stabilising agent soil porosity Decreases erosion Reduces the effects of sodicity Improves water infiltration and holding capacity Supplies plant nutrients Moderates extreme soil temperatures Buffers against rapid changes in salinity, sodicity, and ph Energy and nutrient for micro-organisms Adds to CEC of soil aora

54 Decomposition of Organic Matter Influenced by: Type of material fragile or not Composition C:N ratio, chemicals, animal or plant Age and moisture content Soil oxygen status aerobic or anaerobic Crop rotations legumes Tillage options cultivation levels Soil type soil ph Soil temperature and moisture aora

55 Carbon Cycle +3.3 Gt/year Decay losses

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57 5 major soil carbon pools. Living organisms and roots (labile) <5% 2. Soluble - fresh residues (labile) <10% 3. Particulate organic C -decomposing (labile) 10-50% 4. Humus (decadal) 33-50% 5. Charcoal/Resistant (inert) 1-30% *Adapted from Skjemstad & Baldock

58 Composition of soil organic carbon Crop residues on the soil surface (SPR) Buried crop residues (>2 mm) (BPR) Particulate organic matter (2 mm 0.05 mm) (POC) Humus (<0.05 mm) (Hum C) Resistant organic matter (ROC) Extent of decomposition increases Rate of decomposition decreases C/N/P ratio decreases (become nutrient rich) Dominated by charcoal with variable properties aora

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60 Nitrogen Losses Leaching Denitrification Immobilisation Volatilisation Run-off

61 Good news bad news story Immobilisation Mineralisation Immobilisation Mineralisation Immobilisation Mineralisation

62 Nitrogen Pathway Urea This step can add an extra 3 days for your nitrogen to become plant Ammonia NH 3 Ammonium NH 4 : quite stable, is fixed onto the soil clays Nitrite: NO 2 an intermediate step and easily lost in wet soil, toxic if allowed to accumulate in the plant. Nitrate: NO 3 plant available form, also very soluble and therefore subject to leaching available Converted by natural soil bacteria

63 Nitrifying bacteria Nitrosomonas Nitrobacter

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68 Any Questions????? aora

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