Soil Fertility and Fertilizers Exam #1 Review

what are the criteria for essential plant nutrients according to Arnon and Stout?

1.) Must be required for completion of life cycle for plant

2.) Must not be replaceable by another element

3.) Must be directly involved in plant metabolism

what is soil fertility?

the quality of the soil that enables it to provide nutrients in adequate amounts and in proper balance for the growth of specified plants or crops (can be crop specific)

what is soil productivity?

it is the ability of a soil to produce an adequate amount of plant growth with optimum management

• includes all other factors that influence plant growth (like water)

what did Sir Francis Bacon contribute to understanding of soil plant-soil systems?

postulated that water is the only need nutrients for plants

what did Jethro Tull contribute to understanding of soil plant-soil systems?

he thought the roots ingested tiny soil particles, he wrote horse hoeing husbandry, developed horse hoe and seed drill

what did Justis Von Liebig contribute to understanding of soil plant-soil systems?

he is considered the father of modern soil fertility, stressed the value of mineral elements, discovered carbon in plants comes from CO2, H and O come from water, derived source and function of several nutrients , first to document the “law of minimum”

what did Haber and Bosch contribute to understanding of soil plant-soil systems?

• Haber first documented the process of synthetic N fixation

• Bosch industrialized these processes

• importance of this is that it made nitrogen fertilizers cheap, revolutionized agricultural production and made the “green Revolution” possible

What other criteria should be added to Arnon and Stouts definition of essentials nutrients?

it should also be substantial for a number of plant species

What are the 17 essential nutrients?

Nitrogen, Phosphorus, Potassium, Sulfur, Calcium, Iron, Magnesium, Boron, Manganese, Copper, Zinc, Molybdenum, Chlorine, Nickel, Carbon, Hydrogen, and Oxygen

what are considered the non-mineral nutrients (not derived from the soil)

C, H, O

what is a beneficial element?

promotes plant growth in many plant species but are not absolutely necessary for completion of the life cycle

what are examples of beneficial elements?

Na, Co, Si, Se, (Cr, V, Ti)

what is a primary nutrient?

a most often limiting from a crop production standpoint (N, P, K)

what is a secondary nutrient?

less limiting and less often added to soils as fertilizer (S, Mg, Ca)

what observations can be made regarding the forms of nutrients taken up by plants?

1.) Plants take up and use nutrients almost exclusively in INORGANIC forms

2.) Almost all elements are taken up as ions with charges of -2, -1, +1, or +2

3.) Plants can take up N in both anionic (NO3-) or cationic (NH4+) forms

4.) Forms of P (and some extent of B) taken up depends on the soil pH

what are the common -2 anions macronutrients in elemental forms?

HPO4^2- and SO4^2-

what are the common -2 anions micronutrients in elemental forms?

MoO4^2-

what are the common -1 anions macronutrients in elemental forms?

NO3-, H2PO4-

what are the common -1 anions micronutrients in elemental forms?

Cl-, H2BO3-

what are the common +1 cations macronutrients in elemental forms?

K+, NH4+

what are the common +2 cations macronutrients in elemental forms?

Ca2+, Mg2+

what are the common +2 cations micronutrients in elemental forms?

Fe2+, Mn2+, Ni2+, Zn2+, Cu2+

what is the most common micronutrient form neutral charge?

H₃BO₃

what tools do plant and soil scientists have at their disposal to diagnose nutrients sufficiency/deficiency levels?

• visual deficiency symptoms

• yield response

• plant tissue tests

• soil tests

• others: spectral absorbance/reflectance (chlorophyll meters)

deficient

concentration is low enough to cause decreased yield and visual deficiency symptoms

critical range

concentration is below the level at which yield response to added nutrients occurs - no deficiency symptoms

sufficient

concentration range in which added nutrients do not increase yield

excessive or toxic

concentration is high enough to reduce plant growth of yield

what is luxury consumption of nutrients?

when the nutrient concentration is above the optimal level and plants are taking up more nutrients than they need

what is the Steenburg effect?

why must caution be used when diagnosing nutrient deficiencies?

• many nutrient deficiency symptoms look very similar

• some diseases/pests also cause symptoms that look like nutrient deficiency

• typical symptoms may not occur if there are other stresses present

• not effective for managing soil fertility problems because yield losses are already likely once symptoms are observed

phosphorus deficiency

dark green foliage, lower leaves sometimes yellow between veins, purplish color on leaves of petioles

nitrogen deficiency

leaves are small and light green, lower (older) leaves light than upper ones, nut much leaf drop, small, weak stalks

molybdenum deficiency

older leaves die at the tip, along margins, and between veins, looks like N deficiency because it is involved in N fixation (legumes) and nitrate conversion in all plants

magnesium deficiency

lower leaves are yellow between veins (veins remain green), leaf margins may curl up or down or leaves may pucker, leaves die in later stages

potassium deficiency

lower leaves may be mottled, dead areas near tips and margins of leaves, yellowing at leaf margins continuing toward center

boron deficiency

tip of the shoot dies, stems and petioles are brittle, can be toxic in high amounts

calcium deficiency

tip of the shoot dies, tips of young leaves die, corn: tips of leaves are hooked-shaped

sulfur deficiency

tip of the shoot stays alive, light green upper leaves, leaf veins lighter than surrounding areas

iron deficiency

tip of the shoot stays alive, new upper leaves turn yellow between veins (large veins remain green), edges and tips of leaves may die

manganese deficiency

tip of the shoot stays alive, new upper leaves have dead spots over surface, leaf may appear netted because of small veins remaining green, can look similar to iron deficiency

zinc deficiency

interveinal light striping beginning at base of younger leaves

why might tissue testing not be feasible for correcting a nutrient deficiency?

• tissue testing may have already caused yield loss

• the crop may not respond to the applied nutrient at the specific growth stage tested

• the crop may be too large to apply nutrients

• climatic conditions may be unfavorable for fertilization

why is it recommended to take samples from both healthy (normal) areas and unhealthy areas when taking tissue samples?

mostly this is done for comparison to see how the nutrients level differs between the areas, it can also help with diagnosis of the issue

how are tissue tests for total nutrient analysis are conducted in a lab?

• performed on specific plant parts (petioles, stems, and leaves) in lab after tissue is dried down

• nutrient content determined after wet digestion with acids or dry ashing in a furnace

• samples should be clean and dried or refrigerated immediately after sampling

• part of plant selected is important

how is a cell sap test performed?

• estimated of nutrient concentration in tissues can be made in the field using cell sap extracted from the plant

• typically done on conductive tissues (petioles most used for vegetable crops)

• time of day, variety, and location can affect concentrations

what is the critical nutrient concentration?

part of the nutrient concentration curve where nutrient concentration changes from deficient to adequate

what is the critical nutrient range?

the range above which nutrients additions are not likely to increase yields, and below which nutrient additions are likely to increase yield

what are some commonly used sensors used in evaluating tissue nutrient content?

• chlorophyll meters

• remote sensing

• NDVI

what is a N sufficiency index and how is it calculated from chlorophyll meters?

chlorophyll is highly correlated with the %N in leaf tissue over the range of yield response

N sufficiency index (SI) = average meter reading from unknown area/average meter reading from reference area x 100

what types of electromagnetic radiation are used most commonly in assessing crop nutrient status?

Images collected by platforms like handheld, toolbar devices, UAVs, airplanes, or satellites

this is done because chlorophyll absorbs blue and red wavelengths and reflects green and infrared wavelengths

the contrast in light reflectance and absorption monitored by optical sensors (cameras) enables assessment of both the quantity and quality of vegetation

what is NDVI?

Normalized Difference Vegetation Index - common index used to evaluate vegetation cover that uses visible red light (RED) and near infrared (NIR) reflectance data

how is NDVI calculated?

NDVI = NIR - RED/NIR + RED

• Healthy vegetation will reflect more near infrared and absorbs more visible red light

• generates a number between -1 and +1

• highly correlated with plant N status - some crops better than others (wheat)

• eliminated some of the variation observed in imagery with changing angle of the sun

what are some NDVI common sensors used for handheld and toolbar-based measurements?

Crop Circle - Holland Scientific

Greenseeker - Trimble

Cropspec - Topcon

why is calibration needed for remote-sensed data?

why are most standard drone cameras not capable of generating a “true” NDVI image?

most standard UAV cameras do not have NIR - capable sensors (some use software to calculate a “false” NDVI)

what are the two types of postmortem tissue testing that can be used in developing N management strategies?

1. Corn Stalk Nitrate Tests

   • 8” stalk section (6” above soil surface) collect 1-3 weeks after physiological maturity

2. Grain testing

   • grain protein can be used to indicate if additional N required for optimum yield

what is the primary disadvantage of post-mortem tests?

they often require multiple years of data to accurately estimate N requirements

what is the basic process of soil testing?

chemical extraction of soil sample to estimate nutrient availability, extracts part of the total nutrient content that is related but not equal to, the quantity of available plant nutrient

why is soil testing the widely used tool in assessing soil fertility status?

• provides an index of nutrient availability

• predicts probability of profitable response to fertilizer or lime

• provide basis for development of fertilizer and lime recommendations

what are factors that will influence the concentration of nutrients in soil solution?

nutrient uptake, surface (ion) exchange, solid minerals, rainfall/evaporation/drainage, soil OM, soil air

what is the ion exchange?

reversible process by which cation or anion adsorbed on the soil surface is exchanged with another cation or anion in the liquid phase

what is more important in soils CEC or AEC?

CEC

where in the soil does ion exchange occur?

1. Mineral surfaces (aluminosilicate clay minerals)

2. Organic matter surfaces

3. Root surfaces

what are the two types of layers make up the silicate clay minerals and list the ionic forms of elements that comprise each layer?

Tetrahedra: Si⁴⁺

Octahedra: Al³⁺

what is isomorphic substitution?

• it gives rise to permanent charge on surfaces on clay minerals

• caused by substitution of ions with lower charge for Si4+ and or Al3+

what effect does charge have on the CEC associated with these minerals?

the negative charge will be distributed evenly over the clay mineral surface

what are the two major sources of pH-dependent charge in soils and what gives rise to the pH-dependent charge in them?

1. Broken Clay Minerals

   • Broken edges of minerals

   • Happens at a low pH (high H+ concentration) where the H+ associates with Al-OH and Si-OH giving them a more positive charge

   • At high pH some of the H+ is neutralized and the negative charge increases

2. Organic Matter

   • involved disassociation of H+ from carboxylic or phenolic functional groups

what percentage of total charge is pH dependent on 2:1 mineral?

5-10%

what percentage of total charge is pH dependent on 1:1 minerals?

50%

what are the standard units used to express cation and anion exchange?

meq/100g or cmol/kg of dry soil

*represents the total number of cationic (+) or anionic (-) charges absorbed to the CEC or the AEC respectively

what is the CEC of Kaolinite?

1-10 meq/100g

what is the CEC of Mica?

20-40 meq/100 g

what is the CEC of vermiculite?

120-150 meq/100g

what is the CEC for montmorillonite?

80-120 meq/100g

what is the CEC for organic matter?

100-300 meq/100g

what is a lyotropic series?

it is the strength of cation adsorption for most mineral surfaces

Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+

what is base saturation?

the percentage of total CEC occupied by Ca2+, Mg2+, K+, and Na+

where in soils are anions typically adsorbed?

adsorbed to positive charges on mineral edges

*usually in soils that are predominately 1:1 clay minerals

list the common soil anions in order of decreasing adsorption strength

H2PO4- > > SO42- > NO3- > Cl-

what is the most important things about the buffer capacity?

the ability of the soil to maintain the concentration

what is soil buffer capacity?

the soil’s ability to resupply an ion to the soil solution

are monocots or dicots more likely to have a higher root CEC?

Legumes or broadleaf dicots

what is primarily responsible for root cation exchange capacity?

carboxyl groups (COOH) - attribute to 70-90% of the root CEC

what is mineral solubility?

the concentration of elements or ions in solution supported or maintained by a specific mineral

what is the Ksp constant and how is it used to define mineral solubility in pure water systems?

it is quantitatively defined as the solubility product constant and can be used to predict whether a mineral will dissolve or precipitate in a solution

what is ksp?

the product of the concentration of the ions when the mineral is dissolved in pure water at standard temperature and pressure

what role does mineral solubility play in the buffering of solutions?

if the concentration of one ion decreases such that the ion product falls below the Ksp, the mineral will dissolve and resupply the ion

what affect does pH have on the solubility of common soil minerals like Al(OH)3, Fe(OH)3, and CaHPO?

Fe and Al minerals are more soluble at low pH

Ca minerals are more soluble at high pH

what is mineralization?

what is immobilization?

what percent of organic matter is composed of decomposable organic residues?

10-20%

what percent of organic matter is composed of heterotrophic biomass?

1-8%

what percent of organic matter is composed of humus?

50-85%

what are the three ways that nutrient ions reach the root surface?

• root interception

• mass flow

• diffusion

what determines the amount of nutrients reaching the roots via mass flow?

determined by the rate of water flow to plant roots and average nutrient concentration

which of the three macronutrients is diffusion the is primary method of nutrients transport to root?

Phosphorus

what are examples of mobile nutrients?

nitrate, sulfate, chloride, boric acid

what are examples of immobile nutrients?

ammonium, phosphate, potassium, calcium, magnesium, zinc, iron, molybdate

what are the four basic steps to nutrient uptake?

1. Water and ions enter root free space via capillary action and osmosis

2. Once in cortical cells, is actively taken up across the cell membrane

3. Nutrient is then transported to the xylem vessel by mass flow, diffusion, or active uptake

4. Nutrient in xylem is transported by mass flow