CRSS 4590 final exam

What are the techniques to access nutrient status?

Nutrient deficiency symptoms, plant analysis and biological tests

what is biological tests to access nutrient status?

growing plants with or without the nutrient and see how they respond by decreasing or increasing levels

Visual deficiency symptoms may be caused by:

-more than one nutrient

-toxicity of another nutrient

-similar to damage caused by abiotic or biotic factors

-apparent after economic damage has occurred

what is the best way to analyze nutrients?

plant analysis

what are the goals of plant analysis?

-detect deficiencies before symptoms develop

-confirm deficiency

-determine whether the soil supplies adequate nutrients

-relationship between nutrient status and crop performance

what is the tissue test?

when you collect fresh tissue in the field and then squeeze sap out and use a meter to measure nutrient

what is the issue with tissue tests in the field?

the portable instruments are not extremely accurate

plant sap analysis

when you squeeze sap from plants and perform a range of tests

what is the most common way of looking at plant nutrient levels?

total analysis

what is total analysis?

when you collect tissues and send it to a lab to perform tests

which tissues should you sample?

recently full grown leaves from upper canopy and from 1-15 different plants

which tissues should you not sample?

tissues with disease or other stress related symptoms

what range do you want nutrient levels to be in?

critical nutrient range

limitations of plant analysis

-it may be too late to prevent problems

-crop may not respond to a specific nutrient during a specific growth stage

what are other methods of plant analysis besides tissue and sap tests?

chlorophyll meter and remote sensing

what can chlorophyll meters measure?

can be used to estimate N,K, and S

issue with chlorophyll meters

does not tell you specifically which nutrient is responsible for low chlorophyll content

what is the most common source of error in soil test results?

sampling error

what is the goal of soil sampling?

to obtain a representative sample

what should you collect soil samples in?

clean, plastic container

soil sampling precautions

-banded fertilizer

-avoid band

-sample band proportionally

-if location of band is unknown then sample randomly and take more cores

-do not sample near fences, trails, troughs

what are the soil sampling approaches?

field average sampling, zone sampling, site specific sampling

field average sampling

zig zag, several samples, composite, obtain average value for field

zone sampling

sample select zones

site-specific sampling

soil analysis results are assigned to entire cell of grid

what is soil analysis?

used to estimate the availability of soil nutrients to plants and from that to make nutrient application recommendations

what is soil test interpretation

determines the probability of response to nutrient application

do high or low sites have a higher probability of response?

low sites

nutrient recommendations can be based on what two different approaches for P and K?

fertilize the soil and fertilize the crop

what is the difference between fertilize the soil and fertilize the crop?

fertilizing the soil is building and maintaining the soil for the long term while fertilizing the crop is applying fertilizer needed to obtain optimum yield

nutrient recommendations can be based on what two approaches for N?

yield goal and response curve

what is main problem with leaching?

nitrate

pathways for phosphorus loss

erosion, surface runoff and leaching

how to reduce surface runoff

conservation tillage, vegetated buffers and pasture aeration

explain how permanent charges are generated in clay minerals

permanent charges are generated in clay minerals due to isomorphic substitution

explain how ph-dependent charges are generated in clay minerals

ph-dependent charges are generated in clay minerals due to the broken edges in clays

explain why increasing the pH of a soil increases the CEC associated with the organic matter in that soil

increasing the ph of a soil increases the CEC associated with the organic matter in that soil. this is because the organic matter enhances nutrient retention due to the negatively charged sites in the soil so they can attract and hold more nutrients so therefore the CEC is increased.

as soil ph increases, the CEC of a soil with 2:! clay minerals (lime montmorillonite) increases due to ph dependent charges in the soil organic matter and in the 2:1 caly. indicate which ph-dependents (organic matter or clay) are more responsive to a ph increase.

organic matter is more responsive to a ph increase

list two soil factors that affect the rate at which a nutrient diffuses to roots and for each factor describe whether an increase in that factor increases or decreases the rate of nutrient diffusion

Temperature: increasing temperature increases the rate of nutrient diffusion because ions move faster in warmer conditions

Water content: increasing water content increases nutrient diffusion because more water creates better pathway for ions to move toward roots

describe the mechanism of mass flow for nutrient movement to roots

mass flow is the product of the concentration of nutrients and amount of water. the greater the inputs the greater mass flow is. mass flow moves nutrients to the roots for uptake.

define soil ph buffering capacity and list the main mechanisms or reactions through which soils can buffer soil ph

soil ph buffering capacity is the resistance of the soil to a change in ph. soils can buffer soil ph by by broken edges of clays and organic matter releasing hydrogen ions.

explain why the lime buffering capacity (LBC) determined by the UGA soil testing lab can be used to estimate the amount of lime needed to increase soil pH or the amount of acid needed to decrease soil ph

because the ph buffering capacity of a soil is constant between ph 5 and 7

what measurements would you need to take in a soil to determine if the soil is saline and/or sodic?

you would need to take EC for saline soil and ESP for sodic soil

what is the reason why sodic soils have low water infiltration rates?

sodic soils have low water infiltration rates due to the higher level of sodium in the soil. porosity is decreased due to clay dispersion.

explain the main fates of an essential plant nutrient in relation to the plant. hint: from a plant perspective what all can happen to an essential nutrient near its root

an essential nutrient can be acquired, translocated, immobilized, sequestered, and stored

explain how root architecture influences nutrient acquisition. explain two potential modifications of root architecture that plants employ to increase nutrient acquisition

the root architecture influences nutrient acquisition because the root architecture can affect nutrients being taken up into the root. one potential modification is to increase root surface area which can increase root hairs. another modification is increasing ATP by increasing respiration

what are the main routes an essential plant nutrient can take from the soil solution to the root vascular system? explain the role of the endodermis in regulating these route

Nutrients can move through the apoplastic route, traveling around cells through the outer spaces until they reach the endodermis, but the Casparian strip (made of lignin and suberin) blocks this path. Because of this barrier, most nutrients must take the symplastic route, entering the cells through the plasma membrane and moving cell-to-cell until they reach the xylem.

explain the two main methods for nutrient transport across plant membranes

the two main methods for nutrient transport across plant membranes are passive and active transport. passive transport is when nutrients move with a concentration or electrical gradient. the nutrients move from areas of high to low concentrations and require no energy during passive transport. active transport requires energy usually in the form of ATP and nutrients can move against the electrochemical gradientd. during active transport nutrients move from areas of low to high concentrations

a farmer asks you which animal manure he should use to obtain a high percentage of N mineralization so he can apply less manure to supply sufficient N to his crop. which animal manure would you recommend and why?

poultry litter because of its high N content

list the N fertilizer most commonly used worldwide and the N fertilizer most commonly used in the US. explain the reasons for their respective popularities

the N fertilizer most commonly used worldwide is urea and the N fertilizer most commonly used in the US is UAN

describe the process of industrial N fixation to manufacture fertilizers and list feedstocks used.

industrial N fixation is the process of converting nitrogen from the air into ammonia so it can be used by plants

define critical relative humidity (CRH) for a fertilizer, list a fertilizer that has very low CRH and the associated potential problems.

critical relative humidity for a fertilizer is the rate at which it dissolves and fertilizers with a very low CRH can be potnetial problems when stored such as ammonium nitrate

application of urea on the soil surface can lead to gaseous ammonia losses in acidic soils. explain how this is possible and list two management practices that can minimizes losses

the application of urea an the soil surface can lead to gaseous ammonia losses in acidic soils because urea hydrolysis increases soil ph. to minimize losses you can wait to put out fertilizers when it is not windy and when it is not rainy or humid.

explain why the acidity generated by a nitrogen fertilizer depends on whether the N is taken up by a plant or not

the acidity generated by a nitrogen fertilizer depends on whether N is taken up by a plant or not because when taken up by a plant you have to subtract 1.8 from the number that correlates to that fertilizer. if it not uptaken you do not have to subtract

explain why inorganic P in solution has to be replenished several times per day for plants to take up sufficient P

inorganic P has to be replenished several times per day for plants to take up sufficient P because P is adsorbed by clays

describe why P availability decreases with time after P fertilization to an acidic soil and a neutral or alkaline soil

P availability decreases with time after P fertilizer application due to adsorption and precipitation. in acidic soils, P precipitates as Fe/Al to phosphorus secondary minerals such as variscite and strengite. and P is adsorbed to Fe/Al oxides and clays. In neutral or alkaline soils p precipitates as Ca to P secondary minerals such as fluorapatite and hydroxyapatie. phosphorus is adsorbed to CaCO3 and clays.

explain why it is difficult to measure P mineralization and describe potential approaches to measure P mineralization

it is difficult to measure P mineralization because of the P sorption to clays. potential approaches to measure P mineralization are using sandy soils without clays because without clays there would be no adsorption and to use P isotopic dilution to estimate how P was released.

list three factors that affect P fixation in soil and for each factor describe how it affects P fixation

-high clay content because phosphorus is adsorbed more with a higher clay content

-soil ph because when soil ph is at the optimum level of 6.5 this is when P fixation is at its lowest and when soils are below or above this ph this is when precipitation and adsorption occur

-organic matter content because it can lower P fixation

explain why the use of animal manures as fertilizers may cause environmental problems related to phosphorus

because the N:P ratio of manure is 2:1 but plants uptake nitrogen and phosphorus at an 8:1 ratio so therefore plants uptake manure as fertilizers at an 8:1 ratio and some phosphorus gets left behind because of this. this causes a buildup of P and can cause environmental issues such as leaching

describe how available P is determined in inorganic fertilizers

available P is determined in inorganic fertilizers by the sum of both water soluble phosphorus and citrate soluble phosphorus

list primary minerals that are mostly responsible for releasing K through weathering

the primary minerals that are mostly responsible for releasing K through weathering are micas and feldspars. micas release K faster though weathering than feldspar. the order in which they release K are biotite, muscovite, and feldspar. with biotite releasing K the fastest and feldspar being the slowest.

describe non-exchangeable and exchangeable K in soil

non-exchangeable K in the soil is K that is not readily available for uptake by the plant. non-exchangeable K is fixed in 2:1 clays and is trapped between platelets. exchangeable K in the soil is K that is in the CEC and ready to be taken up by the plant

explain why K is easily leached from manures and crop residues

K is easily leached from manures and crop residues because of its weak affinity to particles meaning it does not attach to particles making K easily leachable

what is biological N fixation? which is the most common group of organisms involved in symbiotic biological fixation with plants?

biological N fixation is when bacteria take N2 from the atmosphere and convert it to a useable form such as NH3. the most common group of organisms involved in symbiotic biological fixation with plants are rhizobium

name the enzyme involved in biological N fixation? which other element is essential for the function of this enzyme?

the enzyme involved in biological N fixation is nitrogenase. molybdenum is essential for the function of this enzyme

many plants use nitrate as an inorganic source of N. explain how nitrate is reduced before it is used in plant metabolism. where within the plant does most of this reduction generally occur? why?

nitrate has to underho nitrate reduction before it is used in plant metabolism. nitrate reduction is a two step process. first nitrate is converted into nitrite and then nitrite is converted into ammonium to be used in plant metabolism. most of this reduction occurs in the cytoplasm due to the light dependency from photosynthesis

explain how ammonium is assimilate in plants. in which part of the plant does this occur if ammonium is taken in by the plant from the soil? why?

ammonium assimilation occurs in the GS-GOGAT pathway. fist ammonium binds with glutamate to get glutamine by using 1 ATP. then the NH2 from the glutamine reacts with 2-oxyglutarate to make 2 glutamates. one glutamate goes back to the beginning of the process to start it over and the other glutamate goes to nitrogen transfer. ammonium assimilation occurs in the mesophyll of the cell because this is where a majority of photosynthesis takes place and the products from photosynthesis are needed for ammonium assimilation

explain three mechanisms by which plants respond/adapt to P deficiency

the three mechanisms by which plants responds/adapt to P deficiencies are signaling to mycorrhizae fungi for symbiotic relationships, altering their root hair density to expand search for P, and exudation carboxylic acids and phosphates

explain the role of K in regulating stomatal opening in plants

K regulates stomatal opening in plants by controlling water potential in the guard cell. when the stomata open K+ diffuses into the guard cell and when the stomate closes K+ diffuses out of the guard cell

explain mechanisms by which K can enter plant cells: when available K is low, and when available K is high

K enters plant cells as K+. the uptake is a result of an electrochemical gradient. when available K is low a high affinity transport system is used and when available K is high a low affinity transport system is used