Avner SILBER Institute of Soil, Water and...
Transcript of Avner SILBER Institute of Soil, Water and...
High frequency irrigations as means for reduction of pollution hazards to soil and
water resources and enhancement of nutrients uptake by plants
Avner SILBER Institute of Soil, Water and Environmental
Sciences, Agricultural Research Organization, Volcani Centre, P.O. Box 6, Bet Dagan 50250,
Israel
Plant adaptation to low nutrient availability: different physiological mechanisms
Increasing acquisition efficiency through
modification of
Proteoid roots
Root hair
Root Shoot ratio Allocation roots
to shallow soil horizons
Rhizosphere modification with:
organic acids, protons and enzymes
Mycorrhizal symbioses
Regulation the transcript of nutrient transporters
In our world nothing is gratis; you have to pay
for goodies you get
Benefits: Improved nutrient
acquisition
Costs: Photosynthesis
products (up to 50%)
Photosynthesis improvement
Mechanisms of plant adaptation to nutrient deficiency
Enhancement of biomass production
Carbon Carbon
Carbohydrates allocated to: roots, fungus, root exudation, etc.
Lynch and Ho, 2004. Rhizoeconomics: Carbon costs of phosphorus acquisition
Alternative approach: optimising nutrient application:
Location: Nutrients are applied
in the vicinity of the roots
Plant demand: Amount and concentration of nutrient can be adjusted to crop requirements
Teaspoon feeding
Schematic presentation of the depletion zone
Water and nutrients acquisition by roots leads to differences in water and nutrients concentration between the rhizosphere and the bulk soil.
Rhizosphere Bulk soil
The depletion zone
Depletion zone
Bulk soil
Nutrient transport from the soil solution to the root surface takes place by two simultaneous processes:
Convection in the water flow (mass flow)
Diffusion along the concentration
gradient Soil-grown plant Soilless-grown plant
The grower’s dilemma: irrigation scheduling
High irrigation frequency was defined in the 1980s and the 1990s to be less than seven days intervals (Martin et al., 1990).
Nowadays?
Background
Daily cycle of plant activity in semi-arid climates is 10-14 hours
Daily transpiration is usually 5-10 mm (Shalhevet et al., 1981)
Daily cycle of irrigation is usually (using standard device) 1-3 hours
Dynamic of nutrient concentration in the root zone
Plant demand
Chemical equilibrium
Excessive rate
Deficiency rate
Irrigation Fast surface reaction
(adsorption)
Slow chemical reaction
Time
Nut
rien
t con
cent
ratio
n
Dynamic of nutrient availabilty in the root zone
Fast (hours) time-dependent processes governs nutrient concentration in the
media • Electrostatic surface reactions:
Adsorption/desorption • Precipitation\dissolution of insoluble
compounds • Microbial activity
The effect of time on solution-Zn concentration in perlite suspensions
Step I Step II
Step I: Adsorption on external surfaces Step II: Solid-state diffusion to internal binding sites
The effect of time on solution-P concentration in soil suspensions
Step I: Adsorption on external surfaces Step II: precipitation
The effect of time on solution Mn
concentrations in perlite media
pH 7.2-7.5; media height: 15-20 cm, high irrigation frequency Solution flow through the medium: 10-15 min
Biotic oxidation of Mn(II): effect of time on solution Mn(II) concentration in used perlite
suspensions
µ
Step I: Mn(II) adsorption onto the external surfaces of the bacteria
Step I Step II
Step II Extracellular Mn((II) oxidation
How to prevent nutrient deficiency in the rhizosphere during the day ?
raising nutrient concentrations
Not recommended
Environmental problems
Increases of excessive rate
Formation of insoluble compounds
dS/dt=k(Ct-Ce) (Enfield et al., 1981)
Alternative I: Force
Alternative II
• Supplying water and nutrients at a similar rate of plant uptake throughout the potential transpiration cycle.
Reducing discharge rate of emitter
Increasing the frequency of irrigation
Plant demand
Chemical equilibrium
Excessive rate
Deficiency rate
Time
Irrigation N
utri
ent c
once
ntra
tion
High irrigation frequency may affect the uptake of nutrients by plants through:
• Increased temporal water content (θ):
• Increased nutrient availability:
Enhanced the convection flow
Frequent replenishment of nutrients in the depletion zone
Enhanced the diffusive movement
Diffusion coefficient of nutrient ion in water (Di) and order of magnitude in soil (De; cm2 s-1) (from Barber, 1995)
NO3-
K+ H2PO4
-
Di (250 C)
1.9x10-5
2.0x10-5
0.9x10-5
De (soil)
10-6-10-7
10-7-10-8
10-8-10-11
Diffusive movement (cm/day)
1.3
0.13
0.004
θ=moisture content De = Diθf(dCi/dCs) f=tortuosity f (θ)
Increased temporal water content (θ)
Decreased water suction (ψ)
Increased hydraulic conductivity (K)
Enhanced transport of nutrients by convection (mass flow)
Measured
Calculated
Ψ
Irrigation
Bulk soil
Depletion zone
Replenishment of nutrients
After irrigation: formation of depletion zone induced by
water and nutrients acquisition by roots
Hypothesis
Continuous application of water and nutrients at a similar rate as plant uptake throughout the potential transpiration cycle may reduce fertilizer quantities needed to achieve optimum yield
Results: • Increasing irrigation frequency improved time-
averaged water availability • The effect of irrigation frequency on water
uptake (per unit of leaf area) or on leaf conductance was meager
• Increasing irrigation frequency improved yield • The main effect of irrigation frequencies was on
the uptake of nutrients • Differences in leaf-P concentration between
treatments were accounted for the majority of variations in DW production
Results: • Adjustment of the NH4/NO3 ratio under
high irrigation frequency is necessary • Irrigation frequency significantly affected
the rhizosphere pH • Irrigation frequency significantly affected
root system and the root/shoot ratio • Irrigation frequency may have a negative
role on diseases incidence
Results:
• Increasing irrigation frequency improved time-averaged water availability
• The main effect of irrigation frequencies was on the uptake of nutrients
• Differences in leaf-P concentration between treatments were accounted for the majority of variations in DW production
• Irrigation frequency significantly affected root system and the root/shoot ratio
Soilless-grown bell pepper: effect of irrigation frequency on daily variations of water tension
Soil-grown bell pepper: effect of irrigation frequency on daily variations
of matric potential in soil (0-20 cm)
Irrigation
Irrigation
Water stress Water uptake under non-stress condition
Soilless-grown bell pepper: effect of irrigation frequency on water uptake
(rate per leaf unit area)
Water uptake (per unit of leaf area) was not affected by irrigation frequency
Soilless-grown bell pepper: effect of irrigation frequency on
leaf conductance
Effect of irrigation frequency on leaf area (m2/plant)
Soilless-grown bell pepper: effect of irrigation frequency on water uptake
(rate per plant)
The increases of water uptake resulted from higher DW production
Soilless-grown lettuce: effect of irrigation frequency and P concentration on yield
General • As long as water availability did not
limit plant growth, yield improvement can be primary attributed to enhances availability of nutrients
• Effect of irrigation frequency on nutrient concentration in plant followed the order: P>K>N
Soilless-grown bell pepper: effect of irrigation frequency on leaf-P
concentration
Soilless-grown bell pepper: effect of irrigation frequency on fruit-Mn
concentration
µ
Relationship between fruit-Mn content and blossom-end rot incidence?
Multiple stepwise regression analysis: pot-grown lettuce
Multiple stepwise regression analysis: soilless-grown bell pepper
Relationships between DW production and leaf-P concentrations, as
determined by irrigation frequency
Combination of high irrigation frequency and NH4
+ nutrition
Negative outcome Increase the hazards
of NH4 toxicity
High transient NH4 concentrations in the rhizosphere
Bell pepper: effects of irrigation frequency and irrigation-NH4-N concentration on the
vegetative growth
Bell pepper: effects of irrigation frequency and irrigation-NH4-N concentration on the
yield
The effects of irrigation frequency on rhizosphere-pH of wax flower plants
Mechanism
Nitrification decreases the temporal concentrations of NH4 between consecutive fertigation
NH4++2O2 NO3
-+H2O+2H+
Increasing irrigation frequency
Increasing temporal concentration of NH4
+
Mechanism
NH4+ NO3
- H+ OH-
Increasing NH4+
concentration Increasing irrigation frequency
Reducing soil pH
Effect of N source on pH in the vicinity of roots (rape plant)
Based on Gahoonia and Nielsen, (1992a)
Unplanted
soil
Possible effects of irrigation frequency on root system
Increased irrigation frequency
Enhancing P uptake by plant
Decreasing root/shoot ratio
Changing wetting patterns and water distribution in soil volume Shallower root system
Indirect effect Direct effect
Soil-grown bell pepper: root distribution
Soilless grown bell pepper: integrated effect of irrigation frequency and P level
on root/shoot ratio
The effect of leaf-P concentration on root/shoot ratio
Soil-grown melon: negative effect of irrigation frequency
The increases of θ value which is beneficial for the uptake of water and nutrients, may have a negative role on diseases incidence, especially on soilborne pathogens.
Based on Pivonia et al. (2004)
Conclusions • High-frequency irrigation regimes enhance
the time-averaged moisture content in the root region.
• The main beneficial effect of high fertigation frequency may be related to an improvement of P, K and micronutrients mobilisation and uptake.
Conclusions
• An increase in fertigation frequency enables the concentrations of immobile elements in irrigation water to be reduced, so reducing environmental pollution.
• Frequent irrigation, in combination with NH4 nutrition, may be very effective for modifying the pH and, consequently, nutrients availability in the rhizosphere.
Caution
• High irrigation frequency may cause severe damage to crops as a result of soilborne pathogens.
• Adjustment of fertilisation regime, especially that of NH4 concentration is recommended.
Thank you
Integrated effect of irrigation frequency and P level on leaf-starch concentrations
µ
Under normal P condition the product of photosynthesis process (carbon) is converted to hexose-P. Under P deficiency starch is accumulated.