Fertigation
Fertigation
Fertigation is an advanced agricultural technique that integrates the use of fertilizers into the irrigation water supply. This methodology offers significant potential to boost crop yields and reduce environmental pollution by optimizing fertilizer efficiency, lowering the application rates, and enhancing return on investment. With fertigation, it's easy to regulate the timing, quantity, and concentration of fertilizers administered to crops.
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A variety of fertilizers, both in solid and liquid forms, can be used in fertigation depending on their physicochemical properties. For extensive field operations, solid fertilizers are often a more cost-effective choice when compared to liquid formulations. However, the solubility of these fertilizers can vary significantly. Ensuring sufficient water is added to the stock solution can help prevent issues when using solid fertilizers in nurse tanks.
When selecting fertilizers for fertigation, consider these four key factors:
- Type of crop and stage of growth
- Soil characteristics
- Water quality
- Fertilizer accessibility and cost.
The ideal fertilizer for fertigation should be of high quality, highly soluble, and pure. It should have low salt content, an acceptable pH level, and must align with the farm's management program.
Benefits of Implementing Fertigation
-
- Both nutrients and water are supplied close to the active root zone, facilitating better absorption by crops.
- Uniform distribution of water and fertilizer through fertigation can potentially increase yield by 25-50%.
Example of water saving and yield improvement in various crops under drip and drip + fertigation systems
- Fertilizer use efficiency via fertigation ranges from 80-90%, which helps save at least 25% of nutrients.
Nutrient Efficiency (%): Soil application vs Fertigation
Nitrogen: 30-50% vs 95%
Phosphorous: 20% vs 45%
Potassium: 50% vs 80%Comparison of fertilizer efficiencies for different application methods
- This technique not only saves water and fertilizer but also reduces time, labor, and energy consumption.
Optimal Fertilizers for Fertigation
Urea, potash, and highly water-soluble fertilizers are ideal for fertigation. Urea is particularly favorable for micro-irrigation systems as it dissolves easily without reacting with other substances in the water. It doesn't cause precipitation issues either. Conversely, super phosphorus is not suitable for fertigation due to phosphate salt precipitation; phosphoric acid is a preferable liquid alternative.
Specialized fertilizers such as mono ammonium phosphate (nitrogen and phosphorus), Poly feed (nitrogen, phosphorus, and potassium), Multi K (Nitrogen and Potassium), and Potassium sulphate (potassium and sulphur) are extremely beneficial for fertigation owing to their high water solubility. Additionally, trace elements such as Fe, Mn, Zn, Cu, B, and Mo are also supplied.
| Fertilizer | N-P2O5-K2O Content | Solubility (g/l at 20°C) |
|---|---|---|
| Ammonium nitrate | 34-0-0 | 1830 |
| Ammonium sulphate | 21-0-0 | 760 |
| Urea | 46-0-0 | 1100 |
| Monoammonium phosphate | 12-61-0 | 282 |
| Diammonium phosphate | 18-46-0 | 575 |
| Potassium chloride | 0-0-60 | 347 |
| Potassium nitrate | 13-0-44 | 316 |
| Potassium sulphate | 0-0-50 | 110 |
| Monopotassium phosphate | 0-52-34 | 230 |
| Phosphoric acid | 0-52-0 | 457 |
A selection of fertilizers frequently used in fertigation
The global water shortage for agricultural use, coupled with increased urbanization, has relocated agricultural development to regions less suited for traditional irrigation methods like flooding or canals, thus driving the advancement of fertigation. This method was initially developed for field and horticultural crops and later extended to tree plantations. Eventually, small gardens and potted plants also adopted fertigation, leveraging automatic irrigation scheduling for urban and domestic gardens.
Nowadays, fertigation is utilized in various agricultural systems, both small and large scale, across the globe. Monitoring activities across all fields and farming operations is also essential in fertigation. Using tools like AGRIVI, farmers can log every irrigation, fertilization, and crop protection action, allowing them to track the usage of water, fertilizers, and pesticides per field and analyze the data daily.
Fertigation for Vegetables: A Practical Guide for Small Fields
Fertigation for Vegetables: A Practical Guide for Small Fields
Introduction
With the increasing trend of farmers cultivating fruits and vegetables on small plots for specialized local markets, fertigation has become an invaluable practice. These production areas, ranging from 1/10 to 1 acre in size, often rely on drip irrigation systems to provide both water and soluble fertilizer for fertigation. The term "fertigation" refers to the process of mixing and delivering fertilizer through irrigation water (Figure 1). Farmers commonly grow multiple crops at varying growth stages simultaneously to ensure a steady supply of produce for customers. Thus, they must strategically schedule plantings and calculate diverse fertilization requirements. Grouping crops with similar nutrient needs can further enhance production and irrigation efficiency. Both water and nutrient demands vary according to the crop and its growth stage. This guide aims to help growers accurately interpret fertilizer recommendations and calculate precise amounts for fertigation events based on crop nutrient requirements.
Figure 1.
Credit: UF/IFAS
Figure 2.
Credit: UF/IFAS
Step 1. Conduct a Soil Test
Begin with a soil test 1-2 months before planting to adjust liming requirements well ahead of time. A soil test will also evaluate levels of available phosphorus, potassium, magnesium, sulfur, calcium, and micronutrients. Recommendations are typically expressed in elemental or oxide forms per planted acre.
Example: 50 lbs N/acre, 30 lbs P2O5/acre, or 50 K2O/acre
Step 2. Calculate Planted Acreage
The University of Florida Vegetable Production Handbook provides crop-specific nutrient requirements and growth stages. Utilize the guide for specific weekly nutrient requirements, as needs vary by crop. These requirements are based on standard bed or row spacing (e.g., 8 ft for watermelon; 5 ft for tomato, pepper, cucumber, squash, and cantaloupe; 4 ft for strawberry).
Field surface area in acres = [Distance between bed centers in ft x bed length in ft x number of beds] / 43,560
Example: A strawberry field with eight 250 ft long beds on 4 ft centers results in:
(4 x 250 x 8) / 43,560 = 0.184 acres
Step 3. Choose the Right Fertilizer
Fertilizers come in three forms: granular, dry soluble, or liquid. For drip irrigation, either dry soluble or liquid forms are appropriate. Granular fertilizers are typically used for soil applications before or after bed formation and drip tape installation. This preplant application should cover the entire crop demand for phosphorus and micronutrients and up to 50% of nitrogen (N) and potassium (K2O). The remaining N and K2O should be injected during the growing season as per the plant's needs. In certain cases, all N and K2O may be supplied via fertigation. This guide assumes a scenario where all phosphorus, micronutrients, and a portion of N and K2O are applied preplant, with additional N and K2O supplied during the season. If fertigation plans require unequal N and K2O injections, utilize a liquid fertilizer analysis or individual dry ingredients to match the recommended amounts.
Step 4. Calculate the Necessary Fertilizer Amounts
University of Florida researchers have documented fertilizer requirements for most vegetable crops, usually based on N, P2O5, or K2O per acre for the entire crop cycle.
Example: For strawberries, a typical soil test may recommend 150 lbs N, P2O5, and K2O per acre for the full season. Preplant, apply 40 lbs N, 150 lbs P2O5, and 40 lbs K2O per acre. Inject the remaining 110 lbs of N and K2O weekly at 0.3-0.75 lbs/A/day, varying by plant growth stage. Applying nutrients in small increments prevents leaching during heavy rain and avoids unnecessary costs from nutrient loss.
Example: For strawberries needing 0.75 lbs N and K2O per acre per day, multiply by 7 to convert to weekly amounts (0.75 lbs/day x 7 days = 5.25 lbs/week).
Step 5. Determine Fertilizer Needs Per Planted Acre
Not all fertilizers are the same as they contain varying proportions of N and K fixed to the type of fertilizer. This guide covers common formulations used in small drip irrigation systems in Florida.
Liquid formulations often have equal amounts of N and K2O, simplifying calculations if equal amounts are needed. Potassium nitrate supplies potassium, while both potassium nitrate and ammonium nitrate provide nitrogen.
Example: For a strawberry crop requiring 0.75 lbs N and K2O per day, convert to weekly amounts (5.25 lbs/week) and then per acre (5.25 lbs/acre x 0.184 acres = 0.97 lbs). Consult Tables 1 and 2; for instance, 2 lbs of 13.5-0-46 potassium nitrate provides 0.9 lbs K and 0.3 lbs N. Supplement with about 2 lbs of ammonium nitrate.
Step 6. Define Water Needs for Fertilizer Solubility
Small acreage fertigation events may require minimal water for highly soluble fertilizers like ammonium nitrate and potassium nitrate. Ensure fertilizers dissolve fully, avoiding field-grade materials. Hot water can aid solubility, requiring less volume. Minimize water use to reduce injection duration. Some fertilizers, like those containing calcium and phosphorus, may precipitate in concentrated solutions, so always test mixtures first. Common compatible mixtures include ammonium nitrate plus potassium nitrate, or calcium nitrate plus potassium nitrate.
Step 7. Time Fertilizer Injection
Ensure proper fertilizer application during irrigation to target the crop root zone. Follow backflow prevention requirements (Figure 3). Allow irrigation systems to pressurize fully (8-12 psi) before fertigation, typically 15 minutes or less. Time injection to avoid leaching, limiting irrigation duration to 1-1.5 hours for sandy soils. Continue running water post-injection to distribute fertilizer evenly. Flush the system afterwards to clear particles that could clog emitters.
- Example: 10 minutes for water to reach farthest emitters and stabilize at full pressure +
- 30 minutes to inject the solution +
- 15 minutes for final fertilizer to reach farthest emitter +
- 5 minutes to flush the system =
- Total time of 60 minutes
Regular flushing keeps drip lines free of clogs. If a single weekly fertigation event exceeds 1-1.5 hours, inject smaller amounts more frequently to prevent leaching. To check for leaching, examine a cross section of the bed after irrigation (Figure 4). Adjust run times for optimal root zone delivery.
Figure 3
Credit: UF/IFAS
Figure 4
Credit: UF/IFAS
Table 1.Amount (rounded to the nearest tenth of a lb) of N and K20 supplied in various amounts of potassium nitrate (13.5-0-46). z
Potassium nitrate (13.5-0-46)
(lbs)
N
(lbs)
K2O
(lbs)
1
0.135
0.46
2
0.3
0.9
5
0.7
2.3
10
1.3
4.6
15
2
6.9
20
2.6
9.2
25
3.3
11.5
30
3.9
13.8
35
4.6
16.1
40
5.2
18.4
45
5.8
20.7
50
6.5
23.0
z For amounts not included in column 1, take the amount of the first row (0.135 for N and 0.46 for K2O) and multiply it by the number of pounds of potassium nitrate needed.
Table 2.Amount (rounded to the nearest tenth of a lb) of N supplied from various amounts of ammonium nitrate. z
Ammonium nitrate (34-0-0)
(lbs)
N
(lbs)
1
0.34
2
0.7
5
1.7
10
3.3
15
5.0
20
6.7
25
8.3
30
10.0
35
11.7
40
13.3
45
15.0
z For amounts not included in column 1, take the amount of the first row (0.34) and multiply it by the number of pounds of ammonium nitrate needed.
Table 3.Amount (rounded to the nearest tenth of a lb) of N supplied from various amounts of calcium nitrate. z
Calcium nitrate (15.5-0-0)
(lbs)
N
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