R2102 3.1 – 3.3 Plant Nutrition

Question 1

Role of iron and signs of deficiency?

Answer 1

Involved with chlorophyll production

Symptoms:

Yellowing of leaves – younger ones first

Failure to flower and fruit

Question 2

What is the standard way to reduce pH?

Answer 2

Sulphur, aluminum sulphate or sulphuric acid are fastest

Question 3

What are the advantages of liming?

Answer 3

Raises pH and can make other nutrients available

Provides calcium

Encourages worm and bacteria population

Discourages some diseases such as clubroot in brassicas

Makes clay soils workable by flocculation (improved aeration, drainage)

Question 4

Name 3 plants that prefer acid soils (calcifuges).

Answer 4

• Rhododendron*
• Camelia japonica*
• Pieris japonica*

Question 5

Name 3 plants for neutral soils.

Answer 5

• Malus*
• Cucumis*
• Daucus*

Question 6

Name 3 plants for alkaline soils (calcicoles).

Answer 6

• Clematis montana*
• Agapanthus africanus*
• Fagus sylvatica*

Question 7

Which nutrient is most likely leached form soil and therefore needed to be replaced?

Answer 7

Nitrogen

Question 8

What is meant by soluble fertiliser?

Give an example.

Answer 8

Dissolves immediately with water

Ammonium sulphate

Potassium chloride

Ammonium nitrate

Superphosphate

Triple superphosphate

Question 9

What is meant by slow-release fertiliser?

Give an example.

Answer 9

• Doesn’t dissolve immediately with water but provides nutrients in soluble form over a long period of time
• Degrade slowly, usually under the influence of soil micro-organisms to release their nutrients
• Dependant on soil temperature
• Usually organic and include hoof & horn and bone meal

Question 10

What is meant by a straight fertiliser?

Give an example.

Answer 10

• Supply one major nutrient.
• Usually used to provide different nutrients at different times of the year, or to correct particular nutrient deficiencies.
• Usually inorganic.

Ammonium nitrate (33-35% N)

Superphosphate (21% P)

Question 11

What is meant by a compound fertiliser?

Give an example.

Answer 11

• They may be organic or inorganic, or contain both
• Supply two or more nutrients of N, P and K (N:P:K), e.g. 20-10-10
• Potassium nitrate (46%K, 14%N) supplied both K and N
• Growmore 7-7-7 supplies 7%N, 7%P, 7%K.
• K: potassium sulphate (50%K)

Question 12

What is meant by a controlled-release fertiliser?

Give an example.

Answer 12

• Granules of inorganic fertilisers coated with a porous material, such as sulphur or synthetic resin, so release at right time for plant
• Water enters the granule and the fertilisers leach out into the surrounding soil. The warmer the soil, the faster the leaching; this corresponds to plant growth which is faster in warm weather. By varying the thickness of the coating granules can be designed to feed plants for different periods of time.

Osmocote

Question 13

What is meant by base dressing and when would you apply it?

Answer 13

Fertiliser incorporated into soil

Dug in before sowing/planting

Question 14

What is meant by top dressing and when would you apply it?

Answer 14

Added to surface of soil

When nutrients are needed after plants are established e.g lawns in autumn

Question 15

What is meant by liquid feed and when would you apply it?

Answer 15

• Fertilisers dissolved and watered onto soils
• Applied to the soil or growing media, directed to the roots of plants
• A liquid feed of a compound fertiliser (e.g. Tomorite) may be applied to tomato plants growing in pots in a greenhouse, hanging baskets and pot plants

Question 16

What is meant by foliar feed and when would you apply it?

Answer 16

• Application of fertiliser in a diluted form to the foliage of the plant
• Generally restricted to application of trace elements
• Works relatively quickly and can be used to correct nutrient deficiencies
• It is a wasteful method, as a lower percentage of the nutrients supplied actually enter the plant
• E.g. a foliar feed of Epsom salts may be applied to correct magnesium deficiency in the foliage of apple trees

Question 17

Comparison of organic matter to fertilisers

Answer 17

OM bulky, F concentrated

OM low-nutrient content, F high

OM imprecise control, F precise control

OM slow effect, F quick effect except slow release

OM effective over long period, F effect may be quickly lost

OM improves soil structure, F no impact on soil structure

OM will contain pests and diseases, F no pests and diseases

Question 18

Describe the construction of a compost heap.

Answer 18

(i) Accessibility of the site: positioned in a sheltered area away from wind, orientated away from heat e.g. south and west.
ii) Mixture of soft green (25–50%) and brown (woody) material
(iii) Avoid perennial weeds/seeds /diseased/cooked material
(iv) Material to be shredded to increase surface area
(v) Suitable materials include vegetable peelings, shredded prunings, herbaceous material etc.
vi) Constructed on bare soil, wooden sides, cover to keep excessive rain off, compost heap to be minimum size of 1m³, material to be layered inside the compost heap.
vii) Ensure that the compost heap does not dry out, water when required, turn the compost heap regularly by turning the outer edges into the centre to ensure that all the material can become hot

Question 19

Name 2 organic fertilisers.

Answer 19

Fish, blood and bone

Bonemeal

Question 20

Name 2 inorganic fertilisers.

Answer 20

Growmore:

Growmore has a ratio of 7:7:7 for these materials, but is actually 7% nitrogen, 3.1% phosphorus and 5.8% potassium, or 7:3.1:5.8. Therefore it is a high-nitrogen feed, rather than the ‘balanced’ fertiliser commonly assumed.

Ammonium sulphate:

For alkaline soils. The ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil, while contributing essential nitrogen for plant growth

Question 21

What is meant by the term pH?

Answer 21

Expresses the amount of acidity or alkalinity in the soil in terms of hydrogen ions concentration. The more hydrogen ions the more acidic.

Question 22

Why do plants need nitrogen?

Answer 22

• Vigorous vegetative growth and roots
• The dark green colour of plants (i.e. chlorophyll)
• Increases the plumpness of grains, the protein component of seeds and foliage and the succulence of crops such as lettuce
• Needed for proteins (make up the structural materials of all living matters) and enzymes (facilitate the vast array of biochemical reactions)

Question 23

What are mobile nutrients?

Name them.

Answer 23

the transportability of substances within the plant

• nitrogen (N) in the form of nitrate
• phosphorus (P) in the form of phosphate
• potassium (K)
• magnesium (Mg)
• chlorine (Cl)
• zinc (Zn)
• molybdenum (Mo)

Question 24

What are immobile nutrients?

Answer 24

not easily transportable within the plant

• calcium (Ca)
• sulphur (S)
• iron (Fe)
• boron (B)
• copper (Cu)

Question 25

What are the symptoms of nitrogen deficiency?

Answer 25

• Chlorosis on older leaves first, generally beginning at the tip of the leaf progressing to the middle of the leaf
• Stunted appearance and thin, spindly stems

Question 26

What are symptoms of too much nitrogen?

Answer 26

• ‘lodging’ with heavy rain and wind, where plants fall over due to excessive vegetative growth.
• May also delay plant maturity and cause plants to become more susceptible to disease and pests.
• Reduced flowers in ornamentals.

Question 27

Why do plants need phosphorus?

Answer 27

• Plays a vital role in virtually every plant process that involves energy transfer. Essential to photosynthesis, nitrogen fixation, flowering, fruiting and maturation.
• Needed in meristematic tissue
• Root growth, esp at seedling stage
• Essential to seed formation and germination, this mineral is often found in large quantities in seed and fruit
• For creating ATP

Question 28

What affects phosphorus availability?

Answer 28

• can be lost from the soil through erosion of soil particles and organic matter, and loss of soluble P in runoff from soils
• most soil phosphorous occurs as relatively insoluble minerals and organic matter in the soil
• the availability of these forms is very sensitive to soil pH

Question 29

What are the symptoms of phosphorus deficiency?

Answer 29

• Stunted new growth

• Weak, poor root development

• Purple colouring, particularly in young plants; oldest leaves are affected first

Question 30

Why do plants need potassium?

Answer 30

• Controls physiological processes: from photosynthesis, nitrogen fixation, starch formation, sugar translocation
• Osmotic regulator – critical in reducing water loss from leaf stomata and increasing uptake of water via the roots; controls water uptake and helps plants cope with environmental stresses such as drought, hardiness and disease
• Promotes flowering, fruiting and general hardiness

Question 31

What are the symptoms of potassium deficiency?

Answer 31

• Yellow or purple (caused by a buildup of carbohydrates) leaf-tints with browning at the leaf edge
• Older leaves become scorched and curl before younger leaves
• Reduced shoot growth
• Poor flowering or fruiting, yields
• Shortages are more likely on light, sandy or chalky soils where potassium is easily washed away. Clay soils, by contrast, hold potassium within their structure.

Question 32

What are main reasons why N, P and K needed?

Answer 32

Nitrogen:

• Healthy foliage
• Chlorophyll and ATP production
• Vegetative growth

Phosphorous:

• Development of flowers
• DNA/RNA synthesis
• Strong roots

Potassium:

• Hearty growth
• Synthesize proteins and carbohydrates

Question 33

Why do plants need calcium?

Answer 33

• Integral part of plant cell walls – holds cell wall together after cell division
• Promotes proper plant-cell elongation and division (meristems) especially in root tips
• Protects cells against toxicities of other elements and diseases

Immobile

Question 34

What are the symptoms of calcium deficiency?

Answer 34

• Localised tissue necrosis leads to stunted growth, die backorburns on leaves, curling of leaveswhich leads todeath of terminal buds and root tips

Immobile – so appears in growing parts/younger tissues –blossom end rot in melons & tomatoes (inadequate Ca for the cell walls of expanding fruits)

Question 35

Why do plants need magnesium?

Symptoms of deficiency?

Answer 35

• Key component of chlorophyll, plays a critical role in photosynthesis
• Critical role in protein synthesis and activation of enzymes in energy metabolism
• For healthy leaves

Symptoms:

• Interveinal chlorosis on older leaves first
• Early leaf fall
• Common in tomatoes, apples, grape vines, raspberries, roses and rhododendrons

Question 36

Why is pH 6.5 the most suitable pH for a wide range of plants in the UK?

Answer 36

Availability of nutrients is at its highest and soil organism activity is at its optimum at pH 6.5 to 6.8

E.g. Solanum tuberosum tolerates down to pH 4. 9 but celery needs to be above pH 6.3.

Vaccinium corybosum needs higher than pH 5.5. Ditto Rhododendron spp.

Question 37

Why is pH important?

Answer 37

• Availability of nutrients to plants: at neutral pH nutrients can be exchanged between soil particles and soil water at a regular rate – making nutrients available to most plants; at higher or lower pH, nutrients can be ‘locked-up’ in soil particles, held in toxic amounts in the soil water or made so soluble that they are washed away. Each of these conditions will affect nutrient availability to plants and affect growth.

As a soil becomes progressively more alkaline, phosphorus and boron become insoluble; Fe, Zn, Cu and Mn become less available.

In acidic soils nutrients such as Ca, K, Mg and Cu become more soluble and are easily washed away. P and Mo become deficient, too, because they become insoluble. Al, Mn, Fe, Zn and H reach toxic levels.

• Activity of soil organisms: in acidic soils they become less active, slowing the rotting of organic matter resulting in fewer nutrients being released
• Soil structure: soils that have high CECs (clay) tend to have high concentrations of colloidal particles and a neutral to high pH

Question 38

How does particle type affect CEC?

Answer 38

• Cat-ion Exchange Capacity affected by the amount of clay particles (-vely charged, hold on to nutrients tightly) vs sand (not so tightly bonded)
• Soils that have high CECs tend to have high concentrations of colloidal particles and a neutral to high pH

Question 39

What is lime-induced chlorosis? How can you treat it?

Answer 39

• Occurs when ericaceous plants (calcifuges), such as camellias are grown in alkaline soil conditions
• Plants have difficulty absorbing iron and manganese from the soil if growing in an alkaline soil
• Symptoms appear as a yellowing of the leaves due to an iron and manganese deficiencies as a result of too much alkalinity

Treatment:

• Add chelated or sequestered fertilisers, which are organic compounds supplying iron and manganese in a form that the plant is able to take up

Question 40

Benefits and limitations of lime?

Answer 40

Benefits:

• Raises pH and promotes the release of phosphorus and other nutrients needed for photosynthesis
• Promotes the activity of earthworms and nitrogen-fixing bacteria as well as the breakdown of organic material that releases N, P, sulphur
• Liming prevents the build-up of aluminum and manganese to toxic levels and corrects calcium and magnesium deficiencies
• Improves soil structure and less susceptible to compaction
• Can help reduce the acidity of run off which enters watercourses

Limitations:

• Can reduce the availability of Zn, Fe and boron if overused
• Requires regular applications
• Needs soil moisture to become active so timing of application is very important
• Liming products often unpleasant and difficult to handle

Question 41

Benefits and limitations of sulphur?

Answer 41

Benefits:

• Will lower pH, eventually
• Can help reduce sodium levels
• Used by bacteria (as a source of energy) in the sulphur cycle. These bacteria make elemental sulphur available to plants as sulphates

Limitations:

• Takes many weeks/months to take effect
• Large quantities can affect phosphorous levels and repeated applications can lead to build up of aluminum
• Requires correct timing of application (not in winter and not when very wet) and when soil-moisture levels are adequate
• Sulphates can acidify soil water and this can run off into watercourses

Question 42

Benefits and limitations of organic manure on pH?

Answer 42

• Most sources of organic matter are pH 6.5 to slightly alkaline and can help combat soil acidification (through buffering)
• Some organic matter can cause acidification such as composted needles, ericaceous compost
• FYM can mitigate against soil acidification

Question 43

Examples of calcifuges?

Answer 43

• Camellia japonica*
• Rhododendron luteum*
• Vaccinium myrtillus*
• Erica tetralix*
• Pieris japonica*
• Hamamelis x intermedia*

Question 44

Examples of alkaline plants?

Answer 44

• Buddleja davidii*
• Brassica oleracea*
• Dianthus barbatus*
• Acanthus mollis*
• Potentilla fruticosa*
• Scabiosa caucasia*
• Euonymus europaeus*
• Viburnum lantana*

Question 45

Examples of neutral plants?

Answer 45

• Campanula trachelium*
• Potentilla fruticosa*
• Acanthus mollis*

Question 46

How is nutrient availability affected by pH in soils?

Answer 46

pH of 6.5 needed for big 3 to all be available

Acidic soils:

• Al and Mn can become more available and more toxic to plants
• Ca, P and Mg are less available

Alkaline soils:

• Fe, Mn, P and most micronutrients become less available

Question 47

State whether effect of these materials acid, neutral or alkaline?

Peat, Coir, Green manure, Composted bracken, Wood ash, Ammonium sulphate

Answer 47

Peat – Acidic

Coir – Neutral

Green manure – Acid

Composted bracken – Neutral

Wood ash – Alkaline

Ammonium sulphate – Acid

Question 48

Example of base dressing?

Answer 48

Organic:

Hoof and horn (nutrient release slower than with blood, so good for organic crops) 70–270g/m²

Growmore

Bone meal

• 70–200g/m² for long-standing and perennial plants
• Fairly slow acting and need to apply well in advance of planting
• Provides about 5% of N, 20–25% of P

Inorganic:

Ammonium sulphate

Question 49

Example of a top dressing?

Answer 49

Organic:

Hoof and horn (nutrient release slower than with blood, so good for organic crops) – depends on how coarse; provides 7–15% of nitrogen (N) and lesser amounts of phosphorus (P) and other elements.

Dried blood 17–34g/m² – faster acting (nutrients are released in the soil by bacterial action within 7–10 days); provides about 7–14% of N and lesser amounts of P.

Inorganic:

• Ammonium sulphate used as a top dressing at the rate of 17–34g/m²
• Superphophate (also as base dressing)
• Triple superphosphate (also base)

Question 50

Benefits and limitations of organic fertilisers?

Answer 50

Benefits:

• Generally safe to use.
• An overdose does not generally cause a too highly concentrated soil solution.
• Provide a steady supply of nutrients of over a long period so provide long-standing and perennial crops with a supply of available plant foods throughout their period of growth.
• They do not react so readily with other other fertilisers.

Limitations:

• Some are slow acting and need to be applied well in advance of planting so that decomposition can occur and nutrients are available to plants.
• The amounts of nutrients may vary considerably.

Question 51

What are the advantages of top dressing?

Answer 51

Helps reduce the need for frequent fertilizing

• Helps soil become richer in terms of organic matter
• Helps soil stay airy and light, fighting the natural tendency of soil to grow heavier over the years
• Enhances soil structure; soil that is well structured has superior water-retention properties and is a more fertile environment for plants
• When you add soil mix or compost, the ground grows more porous; this maximizes local gaseous exchanges that promote proper root growth

Question 52

Examples of inorganic fertilisers?

Answer 52

Growmore

Miracle-Gro

Phostrogen

Sulphate of ammonia

Sulphate of potash

Superphosphate

Tomorite

Question 53

What are the benefits and limitations of inorganic fertilisers?

Answer 53

Benefits:

• Precise amounts of nutrients can be supplied.
• As they are often more concentrated only small amounts need to be stored and supplied.

Limitations:

• Many react with other fertilisers so care requiring if combining them.
• The application of one inorganic fertiliser may cause a deficiency in another.
• Obvious environmental concerns so as run-off into watercourses of nitrates, sulphates and phosphates.
• Care required as N may be lost by volatilization if left on the soil surface.

Question 54

Environmental issues?

Answer 54

• Excess fertilisers can be leached out from the soil by rainwater. This can then enter watercourses and cause algal blooms.
• The breakdown of the algae by microorganisms causes oxygen to be used up in the water and this causes aquatic species to die. Known as eutrophication and results in a decrease in biodiversity.
• Environmentally sensitive periods for application, e.g. , if a slow-release organic fertilizer is applied in late spring or early summer, a leguminous cover crop would need to be sown in the autumn to absorb excess nitrate being released