8.2.3 Liquid
The application of fertilizer in liquid form (with the exception of foliar fertilization and localized fertilizer application) is always carried out in conjunction with an irrigation measure. Simple (sprinklers) or more advanced irrigation systems can be used for this. The difference lies in the precision of applying the water and nutrient amounts.
For defining (narrowing) the concentration range of the nutrient solution, the concentration concept has proven effective
Soil - Field
Main Application Methods (Field Use):
Fertigation (Application via Irrigation Systems):
  • Drip/Trickle Irrigation: Precise, localized placement of nutrients in the root zone. Maximizes efficiency and minimizes losses (leaching, volatilization). Common in high-value crops (vegetables, orchards, vineyards).
  • Center Pivot/Sprinkler Systems: Broadcast application over large areas. Good for top-dressing, but less efficient than drip due to potential foliar interception, evaporation, and runoff.
  • Broadcast Spraying (Top-Dressing): Spraying liquid fertilizer (often UAN or liquid NPK blends) directly onto the soil surface or the crop canopy. Most common for nitrogen side-dressing in cereals (e.g., wheat, corn). Risk of nitrogen loss through volatilization if not incorporated.

Common Liquid Fertilizers for Field Use:
  • UAN (Urea Ammonium Nitrate Solution): A 28% or 32% nitrogen solution. The most widely used liquid N fertilizer in field crops. Can be knifed-in, banded, or applied via fertigation.
  • Liquid Urea: Less common than UAN, highly susceptible to volatilization losses if surface- applied without incorporation or inhibitors.
  • Ammonia Solutions: Aqua ammonia or ammonium hydroxide. Must be injected to prevent massive nitrogen loss.
  • Liquid NPK (Suspension or Clear Liquid Blends): Custom blends of N, P, K, and sometimes S or micronutrients. Often used in starter fertilizers or in fertigation programs for high-value crops.
  • Liquid Potassium (e.g., Potassium Thiosulfate - KTS): Used in fertigation, especially where chloride sensitivity is a concern.

Advantages for Field Use
  • Uniformity & Precision: Easier to achieve even distribution compared to dry spreaders, especially with injection or fertigation.
  • Timeliness & Speed: Can be applied quickly over large areas. Ideal for in-season top-dressing when timing is critical.
  • Flexibility: Easy to blend and adjust formulations. Well-suited for variable rate application (VRA) using GPS and soil/plant sensor data.
  • Starter Fertilizer: Excellent for placing a small amount of nutrients (especially P) close to the seed at planting to boost early growth.
  • Integration with Crop Protection: Can sometimes be tank-mixed with certain herbicides or pesticides (requires strict compatibility checks).

Disadvantages / Considerations:
  • Logistics & Cost: Requires specialized equipment (tanks, pumps, injectors, sprayers), higher energy for transport (mostly water), and often higher cost per unit of nutrient.
  • Volatilization Risk: Surface-applied urea-based liquids (UAN, urea) can lose significant nitrogen as ammonia gas if not incorporated by rain, irrigation, or injection.
  • Leaf Burn (Phytotoxicity): Risk of foliar damage if sprayed directly on plants, especially in hot, sunny conditions or with high salt-index fertilizers.
  • Corrosion & Safety: Some liquids (e.g., UAN) are corrosive to equipment and require careful handling and storage.
  • Limited Soil Incorporation: Broadcast applications rely on rainfall for incorporation, which can be unpredictable.

Key Trends (Precision Agriculture Integration):
  • Variable Rate Application (VRA): Applying different rates across a field based on soil maps, yield maps, or real- time sensor data (e.g., optical crop sensors). Liquid systems are highly adaptable to this.
  • Y-Drop or 2x2 Placement: Precise placement of liquid fertilizer 2 inches to the side and 2 inches below the seed (or beside the row) to maximize nutrient availability while avoiding salt damage to seedlings.
  • Use of Stabilizers: Adding urease or nitrification inhibitors (e.g., NBPT, DCD) to liquid urea or UAN to reduce nitrogen losses from volatilization and leaching.
In summary, liquid fertilizers are a versatile and efficient tool in modern field crop production, particularly valued for their suitability for precise, timely applications and integration into high-tech, precision farming systems.
Substrate - Greenhouse
In greenhouse cultivation, production occurs either in soil (enhanced with additives like compost, manure, etc.) or in substrates. Depending on the system used, the available substrate volume per plant—and consequently the storage capacity for nutrients and water—varies greatly. This primarily influences:
  • The frequency of irrigation cycles, and
  • The operational reliability/risk of production disruption.
This is because: with low storage capacity, the failure of an irrigation pump is more problematic than with high storage capacity.
Produktion Systems
Produktionssysteme mit (inertem) Substrat

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Beetanbau
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Sack und Damm
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Steinwolle

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Hydroponics
Hydroponic systems are characterized by the fact that the substrate, as the site for plant anchorage and root nutrient uptake, is largely replaced by water. In German vegetable production, hydroponic methods have so far been of minor importance. However, in other countries (e.g., the Netherlands), they are among the most efficient production methods in terms of marketable yield per unit of greenhouse area.
Due to their low storage capacity for water and the nutrients contained within, these systems place high demands on:
  • Technical operational reliability,
  • Technical and horticultural know-how, and
  • Hygiene within the operation, because of the rapid movement of water through the entire system.
Given access to suitable water, hydroponic systems can also be operated as closed systems, i.e., without discharging water from the operation.
Production Systems
Production Systems

Pot-Hydroponics
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Flooding/Drainage in a gravel bed

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Tank system

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Nutrient Film Technique
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Nutrient solution spray system / Mist system. (aeroponic system)
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Open vs Closed Systems
Closed systems, i.e., systems with recirculating nutrient solution, are only feasible if the source water quality allows for the preparation of a nutrient solution with a low total concentration (osmotic potential, salt content, electrical conductivity).


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Leaf Application (Foliar Fertilizers)
The efficiency of foliar fertilization depends on:
  • The penetration of the ion through the cuticle,
  • Its transport across membranes into the leaf cell, and
  • The transport of the ion in the phloem and xylem.
First, here are some images (radiograms) showing the distribution of nutrient ions applied to the leaf of a faba bean (Dr. Hüve, ZALF). Each case shows faba bean (Vicia faba); the distribution within the two leaves was recorded after 2 hours, and within the plants after 24 hours.
Important: All percentages are calculated with: absorbed tracer = 100%. Estimating what percentage of the applied tracer was actually absorbed is difficult, as distinguishing between tracer residue at the application site and absorbed tracer is challenging.

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