Soil Fertility Exam #3 Review

what are the forms of sulfate that is absorbed?

almost exclusively as sulfate (SO42-) (elemental sulfur must undergo oxidation to sulfate before uptake)

Thiosulfate

(S2O3-2) - can also be adsorbed by roots

less energy required by plant in conversion to cysteine and S2-

what is the function of S in plants?

• required for synthesis of amino acids (cystine, cysteine, methionine)

• formation of disulfid bonds between polypeptide chains

  • catalytic and structural properties of proteins

• synthesis of coenzyme A

  • fatty acids, amino acid synthesis, citric acid cycle

• synthesis of chlorophyll

what are sulfur deficiency symptoms?

• uniformly chlorotic plants or interveinal chlorosis on younger leaves

• stunted growth

• can appear similar to N deficiency but on younger leaves

  • not as easily transported as plant N

• reddish color on undersides of cruciferous plants

  • canola, cabbage

what are the characteristics of solution SO42-

• transported easily by diffusion and mass flow

• can be easily leached

• most soils contain 5-20 ppm SO42-

what are the characteristics of adsorbed SO42-?

• + charges on the edges of clay minerals and Al/Fe oxides

• more abundant in highly weathered soils

what are the forms of S in solutions?

solution SO4-2

adsorbed SO42-

what are factors that affect SO4-2 adsorption/desorption?

• clay minerals

  • hydrous Al/Fe oxides

  • 1:1 > 2:1 clays

• organic matter

  • OM increases with sulfate adsorption potential

• Depth

  • SO4-2 adsorption typically greater in subsoils

• pH

  • as pH increases, So4-2 decreases (negligible above pH = 6)

• competing anions

what happens when the C:S ratio is < 200?

mineralization

what happens when the C:S ratio is 200-400?

no change

what happens when the C:S ratio is > 400?

immobilization

what are the factors that affect the mineralization or immobilization of S?

• S content of OM

• Soil temp, moisture, and pH

  • warm, moist soil with near neutral pH favors mineralization

• Presence of plants

what are sulfur sources?

• atmospheric S

  • released as SO2 oxidized and deposited as SO4-2

  • contributes to acid rain

• Irrigation water

• organic S (animal and municipal wastes)

• fertilizers

what are sulfur fertilizers?

• elemental sulfur (100% S)

• Ammonium sulfate (24% S) (NH4)2SO4

• Ammonium thiosulfate (26% S) (NH4)2S2O3

• Potassium Sulfate

• Potassium-magnesium sulfate

• calcium sulfate (gypsum)

what are the forms that calcium is taken up by plants?

Ca2+

what is the function calcium in a plant?

• essential to cell wall structure and permeability

• regulation of cation uptake

  • in absence of Ca2+, K+ uptake = Na+ uptake

• cell elongation/division

• translocation of carbohydrates and nutrients

what are calcium deficiency symptoms?

• deficiencies are typically in areas of rapid growth (meristematic regions - buds, blossoms, root tips, leaf tips)

• poor nodulation in legumes

• end rot in fruit and vegetable crops

what are factors that affect Ca2+

• total Ca supply

• soil pH

• CEC

• Ca2+ saturation on CEC

• Clay type (2:1 clays require greater Ca2+ saturation than 1:1 clays)

• ration of Ca2+ to other cations

what are the other calcium sources?

• natural (Ca minerals: anorthite, calcite, dolomite, gypsum)

• liming materials

• gypsum

• triple and single superphosphate

• calcium nitrate

• calcium chelates

• animal and municipal wastes

• papermill sludge

what are the forms of magnesium taken up?

absorbed as Mg2+

what is the function of magnesium?

• structural component of ribosomes - protein synthesis

• phosphate transfer from ATP

• primary constituents of chlorophylls

• readily transported in plant tissues

what are Mg deficiency symptoms?

• appear first on lower (older leaves)

• interveinal chlorosis or under severe deficiency, uniformly chlorotic or necrotic

• some plants develop reddish purple color in older leaves (cotton)

what is grass tetany?

• caused by low Mg in forages, resulting in Mg deficiency in livestock

• high rates of NH4+ or K+ can suppress uptake of Mg by forage crops

• typically happens in spring when NH4+ and K+ availability are the highest

what are things that affect Mg availability?

• total Mg supply

• CEC

• pH

• clay type (vermiculite has high Mg content)

• amount of exchangable K+ and NH4+

• Recommended K:Mg ratios

what are the recommended K:Mg ratios?

5:1 or less for field crops

3:1 or less for vegs and sugar beets

2:1 or less for fruit crops

what are natural Mg sources?

Natural:

• minerals: biotite, dolomite, hornblende, olivene, serpentine

• clay minerals: chlorite, illite, montmorrilonite, and vermiculite

Dolomitic limestone

Potassium sulfate - magnesium sulfate (sulpomag) in dry fertilizer formulations

Epsom salts (MgSO4)

Animal and municipal wastes

what are the frequently used foliar sprays?

• most commonly used to correct deficiencies in citrus crops

  • MgSO4

  • MgCl2

  • Mg(NO3)2

  • Synthetic and natural chelates

iron

is the fourth most abundant element is earths crust behind O, Si, and Al

what percentage is iron usually in the soil?

usually 1-5 % iron but can be up to 55%

typically in the silicate minerals (olivine and pyroxenes), iron oxides, and iron hydroxides

iron gives rise to reddish and yellowish colors in soil from oxide and hydroxide coatings on clay minerals

what does a Georgia red clay consist of?

dark red = iron oxides

old and highly weathered soils

typically, in hot climates with high rainfall

parent material consists of granite and gneiss

what is the function of iron in plants?

• the availability of iron to exist as both Fe2+ and Fe3+ allow it to act as an electron donor or acceptor

  • iron is important for many enzymatic reactions in plants including chlorophyll synthesis

• also a structural component of cytochromes, heme, hematin, ferrichrome, and leghemoglobin

• chlorosis in young leaves is common

how does the concentration of Fe change based on the pH?

• for each unit pH decreases, Fe3+ increases 1000X

• for each unit pH decreases, Fe2+ increases 100X

what are the characteristics of iron in the soil?

• solution Fe2+/Fe3+ concentration is typically very low in well aerated, neutral pH soils

• solubility of Fe2+ increases as soils become reduced in anaerobic conditions

• over normal soil pH range total solution Fe is not sufficient to meet plant requirements

what are chelate dynamics?

• numerous natural and synthetic compounds are able to complex or chelate Fe3+ (and other metal micronutrients)

• it functions to keep them soluble and mobile by preventing reaction with OH-

• moves to plant roots via diffusion

• at the root surfaces Fe3+ dissociates from the chelate through interaction between cell wall compounds and the chelate

what are common synthetic chelates used in agriculture?

EDTA, DTPA, and EDDHA

what are soil conditions that decrease the availability of Fe?

• high pH

• low OM

• wet, cool soil conditions

• high concentrations of other metal cations

how does iron interact with other nutrients?

• other metal cations compete with Fe and can cause deficiency

  • Cu, Mn, Zn, Mo

• Fe-P interactions have been observed through insoluble Fe-phosphates

• Plants receiving NO3- more likely to have Fe deficiency than those that are receiving NH4+ (rhizosphere pH effects)

what are the organic sources of Fe?

• manures, biosolids

• enhances chelation effects through the addition of OM

what are the inorganic sources of Fe?

• synthetic chelates (NaFeEDTA)

• soil application of inorganic Fe fertilizers (ferric and ferrous sulfates) are not effective at high pH

• can correct deficiencies with foliar applications

what are the symptoms of iron deficiency?

• small necrotic spots at first

• spots combine to cover whole leaf area

what is iron deficiency caused by?

• low pH

• high iron relative to manganese (induced Mn deficiency)

• applying large amounts of Fe fertilizers and/or foliar sprays

how abundant is zinc and where is it found/mined?

• it is the fourth most widely used metal (following iron, aluminum, and copper)

• zinc is mined mostly in Canada, Australia, Mexico, and the US

• Specifically, Tennessee, New York, Missouri in the US

• Zinc is one of the big three micros in WI

what are the functions of zinc in plants?

• involved in many enzymatic activities, but not known precisely if it acts in functional or structural roles

• involved in the production of growth hormones such as IAA (indole-3-acetic acid)

• involved in chlorophyll synthesis, activation of certain enzymes, and cell membrane integrity

what are the zinc deficiency symptoms?

• interveinal chlorosis leading to eventual necrosis

• shortening of stem/stalk internodes

• small thickened leaves

• premature leaf drop

• fruit malformation

what concentrations is zinc found in the soil?

• soil solution concentrations range from 2-70 ppb Zn2+

• more than half is typically complexed with OM

• reacts similarly in soils to Fe

  • solubility decreases as pH increases

  • chelated Zn diffuses more readily to roots than unchelated Zn2+

what are factors affecting Zn availability?

• soil pH

  • most Zn deficiencies observed in neutral and calcareous soils

• held tightly at surfaces of oxide minerals

• adsorbed strongly to MgCO3, CaMg(CO3)2, and CaCO3

• waterlogged soil conditions (precipitation and Zn containing minerals)

• interactions with other nutrients

Zn interactions with other nutrients

• competition with other metal cations (Cu, Mn, Fe)

• low Zn availability and high P availability

  • can cause toxic accumulation of P

  • excess P in plants restrict Zn mobility

• conversely, high Zn can induce P deficiencies due to inhibition of root growth

  • (sometimes observed in soils affected by high Zn tailings in SW WI)

what are the organic Zn sources?

• manure, biosolids (some manure can cause excess Zn accumulation)

what are the inorganic Zn sources?

-zinc sulfate (ZnSO4)

-Zinc oxides, carbonates, phosphates

-Zinc chelates (Na₂ZnEDTA)

how do we manage zinc?

• rates up to 10 lbs/ac zinc fertilizers and 0.5 lbs/ac Zn chelates usually sufficient for most field crops (3-5 yrs)

  • incorporation or banding recommended

• preplant applications 20-100lbs/ac for perennial crops

• foliar applications for turfgrass, fruit trees

• seed treatment, root dips

how is Zn managed in WI?

• soil test - 0.1N phosphoric acid is used in WI

• other common tests are DTPA and Mehlich 3

  • results can’t be interpreted with WI guidelines

• more of a problem on soils with

  • high pH (>6.5)

  • eroded/scalped knolls

  • sands, sandy loams, some organic soils because they contain low total Zn level

what are the WI Zn recommendations?

• based on soil test and relative crop need

• Zn deficiency can be corrected with band (2-4 lb Zn/a) or broadcast (4-8 lb Zn/a) applications if in the sulfate form

information about copper

• mainly taken up in plants as Cu2+

• has similar relationships with the soil like Fe and Zn

what is the function of copper in plants?

• photosynthesis and respiration

  • component of enzymes involved in energy transfer

• lignin formation

  • enzymes involved in lignin formation

    • plant standability and disease resistance

• carbohydrate and lipid metabolism

  • CHO accumulation during reproductive stages

  • cold tolerance and other environmental stresses

what are copper deficiency symptoms?

• chlorosis in young leaves

• corn and small grains: yellow and stunted leaves, advanced stage in necrosis along leaf edges and tips (resembles K deficiency)

• increased disease incidence and lodging

• deficiency is not common, except in some organic soil (mucks)

what is copper toxicity?

• reduces Fe uptake (Fe deficiency symptoms)

• thickened, shortened roots

• areas with history of orchard, potato, or snapbean production

  • Bordeaux fungicide mixture

• some manures (swine and dairy) and biosolids can contain high amounts of copper