presentaties_wiki_teeltmaatregelen-groen_kennisnet_473051.pptx

Chapter 5a: Impact of fertilizers soil and
organic farming on nutritional value of plants
Sander van Delden
Horticulture and Product Physiology, WUR

 The dilution effect
 The effects of plant fertilizers on the nutritional value of plants for
humans per element:
● Calcium
● Potassium
● Iron
● Zinc
● Selenium
● Iodine
 Effect of soil health on the nutritional value of plants for humans
 Effect of Organic farming on the nutritional value of plants for
humans
2
Presentation Structure

Linking all the info
Organic
Matter
Structure
Drainage
Pathogens
Justus von
Liebig
“Yield is proportional to the amount of the
most limiting nutrient”
“Yield is proportional to the most limiting
growth factor”

 If all factors are optimal:
● Light
● Temperature
● Water and Nutrients
● Soil and Substrate
● Relative Humidity and Gas Exchange
● Phytohormones and plant volatiles
 There is optimal growth.
4
Dilution effect

5
Building blocks (elements) of
Production machinery
Vertical farming repairs the
barrel on all fronts
Vertical
farm
Optimal
CO2
H2O
Light
Minerals
Jarrell WM, Beverly RB. 1981. The Dilution Effect in Plant
Nutrition Studies In: Advances in agronomy. New York, 197–
224. DOI: 10.1016/S0065-2113(08)60887-1
The dilution Effect
High growth Lower mineral concentration
Also holds for many phytochemical

6
Example dilution effect: Increased CO2

Function and Facts on Calcium:
 Cell signalling
 Formation and stability of cell walls
 Membrane structure and permeability (turgor loss)
 Activation of some enzymes
 Big element 0.412 nm (hydrated)
7
Fertilizers and nutritional value: Calcium
Ca
Atom mass: 40 u
Atom no: 20
Plant uptake:
Ca2+

 Ca
2+
(± 0.5% of dry matter)
 Distribution via xylem (transpiration driven)
 Phloem seems to be unable to relocate Ca
8

Calcium excess can be toxic:
● Ca2+ neutralises excess of: Mg, K, P, Mn, Fe, B & Zn
● If low uptake of other elements is prevented Ca levels in
plant can increase without being toxic (upto 10 % of
DM).
High Mg, K, N  low uptake of Ca
 There is an interaction with nitrogen and calcium - though not
direct. When nitrogen is over applied to soil it will tend to bind
with calcium to form calcium nitrate and will leach calcium out.
In the plant high nitrogen pushes growth, but too quickly for
calcium to catch up and calcium deficiencies in the growing tip
are often the result.
9

10
Busse JS, Palta JP. 2006. Investigating
the in vivo calcium transport path to
developing potato tuber using 45Ca:
a new concept in potato tuber
calcium nutrition. Physiologia
Plantarum 128: 313–323. DOI:
10.1111/j.1399-3054.2006.00741.x.

 Plant calcium concentrations for optimal growth are e.g.:
● 2.5 μM monocot ryegrass
● 100 μM dicot tomato.
 40 fold difference caused by a different Ca demand, i.e.
● ryegrass needs 0.7 mg g kg-1
● tomato 12.9 g kg-1
 In general differences in Ca requirements between
species are explained by Ca2+-binding sites in the cell
walls, i.e. the cation-exchange capacity CEC (White and
Broadley 2003)
 Dayod et al. 2010 give a nice overview between plant
species
11
Dayod M, Tyerman SD, Leigh RA, Gilliham M. 2010.
Calcium storage in plants and the implications for calcium
biofortification. Protoplasma 247: 215–231. DOI:
10.1007/s00709-010-0182-0.

12

 Uptake is highly selective
 Very mobile in the plant
 Important in water relations
● And plant movement like leaf orientation
13
Fertilizers and nutritional value: Potassium
K
Atom mass: 39 u
Atom no: 19
Plant uptake:
K+

14
K
+
(± 1.0% of dry weight)
Key in plant water balances
Functioning of stomata
Cofactor in protein synthesis
Mobile

 Optimal plant growth is in the range of:
● 20–50 g K kg-1
dry mass
 Simply put:
● Low potassium, low overall nutritional status and
post-harvest quality.
● Especially fleshy fruits and tubers
 If growers want to increase plant organ K concentration this is simply
done by increasing K fertilization rate.
 Unfortunately, higher K fertilizer dose does not influence grain and
seeds K concentration this seems to be fixed on +/- 3 g kg-1.
 At high K supply rates ‘luxury consumption’ occurs, this deserves
attention as it can induce Mg and Ca deficiency symptoms.
15

Fertilizers and nutritional value: Iron
 Physiological function of iron:
● Iron is a component of cytochromes (mitochondrion, ATP
metabolism); activation of some enzymes
● Required for chlorophyll production and immobile
● hence lighter (white) young leaves
 Iron deficiency very common in lettuce and leafy greens in
general
 Availability issues by e.g.: high pH, broken chelates (UV),
unbalanced nutrient solutions
Fe
Atom mass: 55.8 u
Atom no: 26
Plant uptake:
Fe2+ & 3+

 Iron can be applied as ferrous sulfate or in a chelated form.
 Ferrous sulfate (FeSO4) contains about 20% iron.
● is inexpensive, mainly used for foliar spraying.
● Often ineffective in soils
 Iron chelates: Chelates stabilize metal ions and protect against
oxidation and precipitation.
 Iron chelates consist of three components:
● Fe3+ ions
● A complex, such as EDTA, DTPA, EDDHA, amino acids, humic-
fluivic acids, citrate.
● Sodium (Na+) or ammonium (NH4
+) ions

17

 Different chelates hold iron ions in different strengths at different pH levels.
They also defer in their susceptibility to iron replacement by competitive ions.
For example, at high concentrations, calcium or magnesium ions may replace
the chelated metal ion.
18

 Iron solubilization is required for plant uptake.
 Even in hydroculture where pH can be controlled,
aeration can lead to Fe oxidation, making it unavailable
for plant uptake.
 Chelates are organic molecules that help solubilize iron
19

 Uptake in the form of Zn2+
● And at high pH ZnOH+
 Important in enzyme functioning and present in all six enzyme
classes: oxidoreductases, transferases, hydrolases, lyases,
isomerases and ligases.
● Hence Zn deficiency affects many aspects of plant
functioning. (Also photosynthesis)
 The critical deficiency concentrations <15–20 μg Zn g-1 dw
20
Fertilizers and nutritional value: Zinc
Zn
Atom mass: 65.3 u
Atom no: 30
Plant uptake:
Zn2+

 Zinc deficiency occurs in Overall low Zn level is:
● Low stress tolerance
● Low Pollen fertility => Low seed yield
● Low sugar content
● Lower phosphate as Zn is essential for P uptake
 Not mobile in plants
21

 Zn is essential for humans:
● 2800 proteins in the human proteome require Zn
 Strong binding of Zn to phytic acid =>
● Phytates reduce bioavailability of Zn
● Higher phytate concentration lower the
bioavailability of Zn and Fe
22

 Selenium is present in soil in small amounts:
● 0.01 to 2 mg kg⁻¹
 Chemically selenium (Se) has
commonalities with sulphur (S)
● Upregulated expression of sulphate transporters
leads to increase in selenate uptake
● Brassicaceae species accumulate more selenium
because they have a greater ability to accumulate
Sulphur
23
Fertilizers and nutritional value: Selenium
Se
Atom mass: 79 u
Atom no: 34
Plant uptake:
(H)SeOx
x-

24
Species Se concentration (mg kg-1 dw)
Astragalus pectinalus 4000 Accumulator
Stanleya pinnnata 330 Accumulator
Gutierrezia fremontii 70
Zea mays 10 Non Accumulator
Helianthus annuus 2 Non Accumulator
Selenium concentrations in shoots of accumulator and non-accumulator species
growing on a soil with 2–4 mg Se kg-1 (Copied from Marschner 2012)
Based on uptake plants are classified into Se-accumulators and
non-accumulators:
 Most agricultural and horticultural plant species are non-
accumulators

 White et al. (2007) found that Se non-accumulators had
a strong relationship between leaf S and leaf Se
concentration
 Transporter(s) of non-accumulators have a higher affinity
for sulphate than for selenate.
 Visa versa Se accumulators have a higher selectivity for
selenate than for sulphate.
25
Copied from Marschner 2012

 The high variation in Se soil content results in variation
of Se in the human diet.
 The minimum Se concentration for animals and humans
is about 50–100 μg Se kg-1 dw in fodder/food (Gissel-
Nielsen et al. 1984).
 Currently there are two strategies to increase human
intake of Se:
● using Se fertilizers: Agronomic biofortification
● Genetic biofortification by improvement in crop
Se accumulation.
26

 Agronomic biofortification
 Relatively easy to increase Se concentrations in food
crops by fertilization
● selenate is highly bioavailable to plants and is
readily transported from roots to shoots
● Se non accumulators can experience toxicity at high
Se fertilization
27

 Biofortification through classical breeding is hard:
● Requires genetic variation within the species
● In many species this no variation is found in Se uptake/assimilation
 Inter species variation is much bigger, as illustrated by the Se accumulators
(Table previous slide).
● Increase in Se uptake by transgenic plants overexpressing various
genes involved in S/Se assimilation.
● This was aimed to enhance Se uptake in Se-contaminated soils
(extremely high Se concentration)
● Unknown if these transgenic plants can accumulate more Se from soils
with low Se availability
28
Genetic Selenium biofortification

 Iodine is essential in human nutrition NOT for higher
plant species.
● billions of people have insufficient iodine intake
● lower plant species, including marine algae require
iodine as an essential element
 Iodine is not part of standard nutrient solutions in
horticulture nor of fertilization schemes in open field
agriculture
29
Fertilizers and nutritional value: Iodine
I
Atom mass: 127 u
Atom no: 53
Plant uptake:
I- and IO3
-
Best uptake

 Biofortification of vegetables with iodine can be used
to increase human iodine intake.
 Fertilization is a promising strategy for Iodine
biofortification concentration in edible plant parts
● Many studies found a significant increase upon
Iodine fertilization.
● Plant do not seem to be affected by additional
iodine in the nutrient solution. Growth is
comparable to “untreated” plants.
30
Fertilizers and nutritional value: Iodine

 All minerals we ingest originate from soils or substrates
and reach our bodies via the process of plants mineral
uptake (sometimes via animals).
 Not much research on the relation between soil health
and human health has been done.
31
Relation between soil health and the
nutritional value of plants for humans

 It is hard to isolate separate soil components in open
field agriculture.
● That is pot experiments and studies in artificial
environments can help, but effect are often
different from the reality in the field.
● In the field there are many confounding factors:
seasonal, location, soil condition, cultivar choice,
pest, disease, quality of sown seed
● all these factors can interact and together will
influence the outcome of the management
factors (treatment) applied
32
Scientific difficulties in relating soil health and
human health

 How does the factor organic matter influence nutritional value?
 Higher levels of organic matter increase:
● soil rooting capabilities,
● nutrient holding capacity,
● nutrient supply,
● aeration,
● water relations,
● self-cleaning capacity (i.e. breakdown of pesticides and
other toxic chemicals).
● reduces soil borne diseases by improving the resilience
and ecosystem complexity
 That seems good ! But is it too good?
33
Example of complexity: soil organic matter

 It can be that additional organic matter increases growth
so much that plant nutrient concentration is diluted.
 Too much organic matter can lead to slemping and
diseases. Or mineral toxicities.
 Effects of organic matter on poor sandy soil will be much
higher than on clay soils.
34
Example of complexity: soil organic matter
• The story of the
effects of tilling
on organic
matter content

 Three ways that soil health can impact human health:
i. Direct toxic effects such as radioactive or chemical contamination,
either naturally occurring or man-made
● E.g. high Cadmium levels in cheap P fertilizer
ii. Nutrient deficiencies or excesses
● Many ions can be supplied in excess to biofortify crops: e.g.
Zn, Fe, I, Se
● Soils can also contain low levels of these nutrients leading to
low content in the crop
iii. A general positive effect of soil health itself on plant and animal
health?
35
Relation between soil health and the

 Organic farming is not a clear cut “treatment” with a clearly
defined control “conventional farming”
● There is a lot of variability (soil, crops, management)
 On a policy level organic practices and regulations do not differ
substantially between countries
● Policy steers to organic as “chemical-free” farming
 Unfortunate as originally organic farming was conceived as a
holistic farming system aimed primarily at improving soil
health, and secondarily would lead to long term improvements
in animal, human, and societal health.
• (William A. Albrecht (1888–1974)
36
Organic farming and the nutritional value of
plants for humans

 Does the nutritional value of crops from organic farming differ
in nutritional value from conventional crops?
 NO: meta-analyses articles Dangour et al. (2009), Smith-
Spangler et al. (2012), Hoefkens et al. (2009)
● All show there are no significant composition differences
between organic and conventional crops.
 YES: meta-analyses articles Brandt and Mølgaard 2001;
Worthington 2001; Smith-Spangler et al. 2012; Barański et al.
2014
● Higher antioxidant/(poly)phenolics
● lower toxins like pesticides and cadmium
● lower concentrations of proteins, amino acids and fibre in
organic crops/crop-based compound foods
37
Ambiguity among research

 Organic farming has on average 20% lower yields and
higher yield fluctuation
 The higher stress resilience, higher antioxidants of
organic crops have benefits in post harvest
 Increase postharvest performance:
● potatoes with 17.7%, carrots 18.0%, turnips
15.7% and beets 29.4%.
 Thus, although the yield at harvest of organically grown
crops is lower, lower storage loss can compensate for
these losses.
39
Post harvest effect: Organic farming and the

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