Soil fertility and fertilzers

What percentage of plant biomass comes from mineral nutrients?

About 4%; most plant biomass comes from C, H, and O.

What is Liebig’s Law of the Minimum?

Yield is limited by the essential factor in shortest supply relative to crop need.

What are the nutrient concentration ranges?

Deficient → critical → sufficient → excessive/toxic.

What happens when nutrient is added in the deficient range?

Yield responds strongly.

What is the Steenburg effect as described in the study guide?

Nutrient concentration may decrease as yield increases in the deficient range because of dilution.

What is the most widely used method to assess soil fertility status?

Soil testing.

How can plant tissue analysis help diagnose nutrient problems?

It complements soil testing and can verify visual symptoms.

How should normal and abnormal plant tissue be compared when diagnosing a deficiency?

Collect and compare properly sampled normal and abnormal tissue, rather than sampling only abnormal plants.

What does NDVI stand for?

Normalized Difference Vegetation Index.

What information does NDVI require?

Reflectance in red and near-infrared wavelengths.

What does a SPAD meter estimate?

Relative chlorophyll concentration in leaf tissue; it can indicate crop N status.

What is the corn stalk nitrate test used for?

End-of-season diagnosis of N management; it does not adjust the current season’s N rate.

What is chlorosis?

Yellowing of plant tissue.

What is necrosis?

Dead plant tissue.

What are the essential macronutrients listed in the study guide?

N, P, K, Ca, Mg, and S.

What are the essential micronutrients listed in the study guide?

B, Cl, Cu, Fe, Mn, Mo, Ni, and Zn.

What does macro vs. micro refer to in nutrient classification?

The quantity required by plants, not the nutrient’s importance.

What does CEC stand for, and what is a common unit?

Cation exchange capacity; meq/100 g, numerically equivalent to cmolc/kg.

What mainly creates permanent negative charge in clay minerals?

Isomorphic substitution within clay mineral structures.

Where does pH-dependent charge develop?

On broken clay edges and organic functional groups; its magnitude and sign vary with pH.

What is the layer arrangement of 2:1 clays?

A 2:1 clay has two tetrahedral sheets surrounding one octahedral sheet

How does kaolinite rank in CEC?

Low CEC.

How does mica/illite rank in CEC?

Intermediate CEC.

How do smectite (montmorillonite) and vermiculite rank in CEC?

High CEC.

How does organic matter compare in CEC?

Organic matter can have very high CEC.

Which soils generally has greater CEC?

Soils high in clay and especially organic matter generally have greater total CEC than light-colored sands.

Which generally has lower root CEC, grass roots or broadleaf crop roots?

Grass roots generally have a lower CEC

How does base saturation generally change as soil pH increases?

Base saturation generally increases.

What is nutrient intensity?

Nutrient concentration or activity in the soil solution.

What is nutrient quantity?

Nutrient held on exchange or solid phases that can replenish the soil solution.

What is soil buffer capacity?

How strongly soil resists a change in solution concentration.

How can greater soil buffering affect nutrient diffusion toward roots?

It can slow diffusion by reducing the concentration-gradient response toward roots.

What is humus?

The slowly decomposable, stable fraction of soil organic matter.

What approximate share of soil organic matter does humus comprise according to the study guide?

Roughly 50–85%.

What is mineralization?

Conversion of nutrients from organic forms into plant-available inorganic forms.

What is immobilization?

Conversion or uptake of inorganic nutrients into microbial or organic forms, temporarily reducing plant availability.

What controls N and S availability closely?

Soil organic matter content and decomposition rate.

How do mycorrhizae help plants acquire nutrients?

They extend the effective soil volume explored by roots and are especially important for relatively immobile nutrients such as P.

What is mass flow?

Nutrients move with water flowing toward roots.

Which nutrient is mainly supplied to roots by mass flow?

Nitrate-N.

What is diffusion?

Nutrients move down a concentration gradient toward depleted soil near roots.

Which nutrients commonly move to roots by diffusion?

K and often P.

What is root interception?

Growing roots physically contact nutrients on exchange surfaces, it usually contributes less than other mechanisms.

What conditions increase diffusion?

Greater soil water content, higher temperature, and a greater diffusion coefficient.

Why is nitrate more mobile in soil than phosphate?

Nitrate is weakly retained by most negatively charged soil surfaces, while phosphate is strongly sorbed or precipitated.

What does a Brønsted acid do?

Donates H⁺.

What does a Brønsted base do?

Accepts H⁺.

What is the primary natural contributor to acidity in unpolluted rainfall?

Carbonic acid formed from CO₂ and H₂O.

What is a major source of acidity and acid buffering in mineral soils?

Aluminum hydrolysis.

How does greater NO₃⁻ uptake than NH₄⁺ uptake tend to affect rhizosphere pH?

It tends to increase rhizosphere pH.

How does greater NH₄⁺ uptake tend to affect rhizosphere pH?

It tends to acidify the rhizosphere.

How can nitrate leaching acidify soil?

NO₃⁻ can leach with base cations, decreasing base saturation.

What happens to most ammonium-based N fertilizers after nitrification?

They acidify soil.

Which fertilizer has the greatest lime requirement per equal amount of N among the choices emphasized in the guide?

Ammonium sulfate.

What does soil-water pH measure?

Active acidity, not potential or reserve acidity.

What is the liming reaction to memorize?

CaCO₃ + 2H⁺ → Ca²⁺ + CO₂ + H₂O.

How does dolomite’s acid-neutralizing capacity per unit mass compare with pure calcite?

The study guide states dolomite, CaMg(CO₃)₂, has greater acid-neutralizing capacity per unit mass than pure calcite, CaCO₃.

How does Ca(OH)₂ affect pH?

Liming material; it neutralizes acidity.

How does CaCl₂ affect pH?

Neutral salt; no major liming effect.

How does CaCO₃ affect pH?

Liming material.

How does gypsum (CaSO₄·H₂O) affect pH?

Neutral/no major liming effect; it supplies Ca but is not a liming material.

How does Al₂(SO₄)₃ affect pH?

Acidifying; aluminum hydrolysis generates acidity.

How does H₂SO₄ affect pH?

Acidifying; it is a strong acid.

How does CaSiO₃ affect pH?

Liming; silicate can consume acidity.

How does CaO affect pH?

Liming; it is a strongly basic oxide.

What does ECe/ECse indicate?

Soluble salt concentration.

What does ESP indicate?

The percentage of cation exchange sites occupied by Na.

What is the general pattern of a saline soil?

High soluble salts; ESP is not high.

What is the main plant problem in saline soil?

Low osmotic potential makes water uptake difficult.

What is the general pattern of a sodic soil?

High ESP; soluble salts may be lower.

What problems can sodic soils have?

Clay dispersion, poor aggregation, crusting, and low infiltration.

What defines a saline-sodic soil?

Both soluble salts and ESP are high.

What are the classic threshold values for saline and sodic soils?

Saline

How would you classify soil with ECe = 7 dS/m and ESP = 22?

Saline-sodic.

What is physiological drought?

Salts make soil-water osmotic potential more negative, so plants can be water-stressed even when soil contains water.

Why does sodium cause clay dispersion?

Na-saturated clays repel one another, degrading soil aggregation and structure.

What amendment is commonly used before leaching to reclaim sodic soil?

Gypsum (CaSO₄·2H₂O); Ca replaces exchangeable Na.

How can furrow irrigation affect salt distribution?

Evaporation can concentrate salts in certain areas; bed shape and wetting patterns affect salt accumulation near the seed row.

What historical decline is associated with salinization from poor irrigation management?

Ancient Mesopotamia.

What is the ESP formula?

ESP = exchangeable Na ÷ CEC × 100.

What is a common unit for electrical conductivity (EC)?

dS/m; historically, mmho/cm.

What is the conversion between dS/m and mmho/cm?

1 dS/m = 1 mmho/cm.

For medium-textured Wisconsin soils, how much P₂O₅ raises the soil test by 1 ppm?

18 lb/ac P₂O₅.

For medium-textured Wisconsin soils, how much K₂O raises the soil test by 1 ppm?

7 lb/ac K₂O.

How many square feet are in one acre?

43,560 ft².

Under the conventional acre-furrow-slice assumption of about 2,000,000 lb soil, what does 1 ppm equal?

About 2 lb nutrient/acre, when that soil-mass assumption is intended.

Who is associated with the essential nutrient criteria

Haber and Bosch, or Arnon and Stout?

Does standard NDVI require near-infrared data?

Yes. It uses red and near-infrared reflectance.

Which has lower CEC; kaolinite or vermiculite?

Kaolinite.

Is it true that all productive soils are fertile, but not all fertile soils are productive?

True, as worded in the study guide. Fertile soils are not necessarily productive under their environment and management.

Which deficiency is classically associated with chlorosis on older leaves

N or P

Why does ammonium sulfate acidify soil?

Nitrification of ammonium generates H⁺; sulfate does not neutralize that acidity.

How do you calculate neutralizing index (NI) from CCE and fineness factor?

NI (%) = CCE (%) × fineness factor (%) ÷ 100.

What is NI when CCE = 90% and fineness factor = 80%?

72%. Calculation

How do you classify soil with EC = 6 dS/m and ESP = 12% using the guide’s thresholds?

Saline

Which of these are macronutrients…B, Ca, Cl, Cu, Fe, K, Mg, Mn, Mo, N, Ni, P, S, Zn?

Ca, K, Mg, N, P, and S.