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 Allocation roots to shallow soil horizons Root hair Proteoid roots In our world nothing is Increasing acquisition efficiency through modification of gratis; you have to pay for goodies you get Mycorrhizal symbioses Root Shoot ratio Rhizosphere modification with: organic acids, protons and enzymes Regulation the transcript of nutrient transporters
Lynch and Ho, 2004. Rhizoeconomics: Carbon costs of phosphorus acquisition Mechanisms of plant adaptation to nutrient deficiency Costs: Photosynthesis products (up to 50%) Benefits: Improved nutrient acquisition Carbohydrates allocated to: roots, fungus, root exudation, etc. Carbon Photosynthesis improvement Enhancement of biomass production Carbon
Alternative approach: optimising Location: Nutrients are applied in the vicinity of the roots nutrient application: Teaspoon feeding Plant demand: Amount and concentration of nutrient can be adjusted to crop requirements
Schematic presentation of the depletion zone Rhizosphere Bulk soil The depletion zone Water and nutrients acquisition by roots leads to differences in water and nutrients concentration between the rhizosphere and the bulk soil.
Bulk soil Depletion zone Nutrient transport from the soil solution to the root surface takes place by two simultaneous processes: Convection in the water flow (mass flow) Soilless-grown plant Diffusion along the concentration gradient Soil-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 Irrigation Nutrient concentration Fast surface reaction (adsorption) Time Plant demand Slow chemical reaction Chemical equilibrium Excessive rate Deficiency rate
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 Step I Step II µ Step I: Mn(II) adsorption onto the external surfaces of the bacteria Step II Extracellular Mn((II) oxidation
How to prevent nutrient deficiency in the rhizosphere during the day? Alternative I: raising nutrient concentrations Force Not recommended Increases of excessive rate Formation of insoluble compounds Environmental problems ds/dt=k(c t -C e ) (Enfield et al., 1981)
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
Nutrient concentration Irrigation Time Plant demand Chemical equilibrium Excessive rate Deficiency rate
High irrigation frequency may affect the uptake of nutrients by plants through: Increased temporal water content (θ): Enhanced the diffusive movement Enhanced the convection flow Increased nutrient availability: Frequent replenishment of nutrients in the depletion zone
Diffusion coefficient of nutrient ion in water (D i ) and order of magnitude in soil (D e ; cm 2 s -1 ) (from Barber, 1995) NO 3 - K + H 2 PO 4 - D i (25 0 C) 1.9x10-5 2.0x10-5 0.9x10-5 D e (soil) 10-6 -10-7 10-7 -10-8 10-8 -10-11 Diffusive movement (cm/day) 1.3 0.13 0.004 De = Diθf(dCi/dCs) f=tortuosity θ=moisture content f (θ)
Increased temporal water content (θ) Decreased water suction (ψ) Increased hydraulic conductivity (K) Measured Calculated Enhanced transport of nutrients by convection (mass flow) Ψ
Irrigation After irrigation: formation of depletion zone induced by water and nutrients acquisition by roots Bulk soil Depletion zone Replenishment of nutrients
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 timeaveraged 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 NH 4 /NO 3 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 timeaveraged 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)
Water stress Irrigation Water uptake under non-stress condition Irrigation
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 (m 2 /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 Relationship between fruit-mn content and blossom-end rot incidence? µ
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 NH 4 + nutrition High transient NH 4 concentrations in the rhizosphere Negative outcome Increase the hazards of NH 4 toxicity
Bell pepper: effects of irrigation frequency and irrigation-nh 4 -N concentration on the vegetative growth
Bell pepper: effects of irrigation frequency and irrigation-nh 4 -N concentration on the yield
The effects of irrigation frequency on rhizosphere-ph of wax flower plants
Mechanism Nitrification decreases the temporal concentrations of NH between 4 consecutive fertigation NH 4+ +2O 2 NO 3- +H 2 O+2H + Increasing irrigation frequency Increasing temporal concentration of NH 4 +
Mechanism NH 4 + NO 3 - Increasing irrigation frequency H + OH - Increasing NH 4 + concentration 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 Direct effect Indirect effect Changing wetting patterns and water distribution in soil volume Shallower root system Enhancing P uptake by plant Decreasing root/shoot ratio
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 NH 4 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 NH 4 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.