High frequency irrigations as means for reduction of pollution hazards to soil and water resources and enhancement of nutrients uptake by plants

Transcription

1 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

2 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

3 Lynch and Ho, 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

4 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

5 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.

6 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

7 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?

8 Background Daily cycle of plant activity in semi-arid climates is hours Daily transpiration is usually 5-10 mm (Shalhevet et al., 1981) Daily cycle of irrigation is usually (using standard device) 1-3 hours

9 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

10 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

11 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

12 The effect of time on solution-p concentration in soil suspensions Step I: Adsorption on external surfaces Step II: precipitation

13 The effect of time on solution Mn concentrations in perlite media ph ; media height: cm, high irrigation frequency Solution flow through the medium: min

14 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

15 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)

16 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

17 Nutrient concentration Irrigation Time Plant demand Chemical equilibrium Excessive rate Deficiency rate

18 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

19 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) 1.9x x x10-5 D e (soil) Diffusive movement (cm/day) De = Diθf(dCi/dCs) f=tortuosity θ=moisture content f (θ)

20 Increased temporal water content (θ) Decreased water suction (ψ) Increased hydraulic conductivity (K) Measured Calculated Enhanced transport of nutrients by convection (mass flow) Ψ

21 Irrigation After irrigation: formation of depletion zone induced by water and nutrients acquisition by roots Bulk soil Depletion zone Replenishment of nutrients

22 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

23 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

24 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

25 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

26 Soilless-grown bell pepper: effect of irrigation frequency on daily variations of water tension

27 Soil-grown bell pepper: effect of irrigation frequency on daily variations of matric potential in soil (0-20 cm)

28 Water stress Irrigation Water uptake under non-stress condition Irrigation

29 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

30 Soilless-grown bell pepper: effect of irrigation frequency on leaf conductance

31 Effect of irrigation frequency on leaf area (m 2 /plant)

32 Soilless-grown bell pepper: effect of irrigation frequency on water uptake (rate per plant) The increases of water uptake resulted from higher DW production

33 Soilless-grown lettuce: effect of irrigation frequency and P concentration on yield

34 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

35 Soilless-grown bell pepper: effect of irrigation frequency on leaf-p concentration

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37 Soilless-grown bell pepper: effect of irrigation frequency on fruit-mn concentration Relationship between fruit-mn content and blossom-end rot incidence? µ

38 Multiple stepwise regression analysis: pot-grown lettuce

39 Multiple stepwise regression analysis: soilless-grown bell pepper

40 Relationships between DW production and leaf-p concentrations, as determined by irrigation frequency

41 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

42 Bell pepper: effects of irrigation frequency and irrigation-nh 4 -N concentration on the vegetative growth

43 Bell pepper: effects of irrigation frequency and irrigation-nh 4 -N concentration on the yield

44 The effects of irrigation frequency on rhizosphere-ph of wax flower plants

45 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 +

46 Mechanism NH 4 + NO 3 - Increasing irrigation frequency H + OH - Increasing NH 4 + concentration Reducing soil ph

47 Effect of N source on ph in the vicinity of roots (rape plant) Based on Gahoonia and Nielsen, (1992a) Unplanted soil

48 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

49 Soil-grown bell pepper: root distribution

50 Soilless grown bell pepper: integrated effect of irrigation frequency and P level on root/shoot ratio

51 The effect of leaf-p concentration on root/shoot ratio

52 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)

53 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.

54 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.

55 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.

56 Thank you

57 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.