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newSchoolWorks.com › VoTechWorks › Agriculture, Environment & Public Service › Agriculture / Horticulture / Landscaping › Crop Production: Principles and Field Practices › Lesson 4
AGR-HORT49-03 · Lesson 4 · 12 clock hours · lab

Crop Nutrition and Fertilizer Application

Objective. Students will read a soil test report, identify nutrient deficiencies, and calculate fertilizer type and rate needed to meet crop requirements without exceeding recommended application levels.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Crop Nutrition and Fertilizer Application

Plants require a steady supply of nutrients to grow, produce, and resist stress. As a horticulture or landscaping professional, you must be able to read a soil test, spot deficiencies, and select the right fertilizer at the right rate. Guessing wastes money, damages plants, and can harm the environment. This lab puts all three skills together.

Why Soil Testing Matters

A soil test report tells you what nutrients are already present, the soil pH, and the percentage of organic matter. pH controls nutrient availability: most crops do best between 6.0 and 7.0. Outside that range, even nutrients that are physically present in the soil can be locked up and unavailable to roots. Organic matter feeds soil microbes and holds moisture and nutrients. The test results guide every decision you make about amendments and fertilizer.

Cooperative Extension offices in every state publish crop-specific nutrient requirement tables. These tables list how much nitrogen (N), phosphorus (expressed as P₂O₅), and potassium (expressed as K₂O) a crop needs per 1,000 square feet or per acre. Comparing those requirements against what your soil already holds gives you the nutrient gap — the amount you must supply.

Reading the N-P-K Numbers

Fertilizer bags display a guaranteed analysis as three numbers: N – P₂O₅ – K₂O. A bag labeled 10-6-4 contains 10% nitrogen, 6% phosphate, and 4% potash by weight. Every other ingredient is filler or carrier material. To find how much actual nutrient is in a bag, multiply the bag weight by the percentage:

When you calculate how much fertilizer to apply, you work from the nutrient gap back to the product weight, not the other way around.

Identifying Deficiencies

Soil test reports flag values as Low, Medium, Optimum, or High. Common deficiency signs you may also see in the field include:

A soil test can reveal hidden deficiencies before symptoms appear, which is why testing before planting is standard practice.

Calculating Fertilizer Rate

The calculation follows three steps:

1. Find the nutrient gap — subtract the soil's current level from the crop requirement.

2. Determine product amount — divide the gap by the nutrient percentage in the fertilizer (as a decimal).

3. Scale to your area — adjust from the per-1,000-square-foot rate to the actual plot size.

Always apply at or below the label rate. Applying more than the label directs is illegal under federal law (FIFRA) and wastes inputs. It can also cause fertilizer burn, groundwater contamination through nitrate leaching, and excess phosphorus runoff into waterways.

Fertilizer Forms: Choosing the Right Product

Quick-release (water-soluble) synthetics — nutrients are immediately available. Good for correcting acute deficiencies or feeding fast-growing annuals, but they carry a higher burn risk and leach more readily.

Slow-release (controlled-release) synthetics — coated or polymer-encapsulated granules release nutrients over weeks to months. Lower burn risk, more efficient, better for turf and woody plants.

Organic amendments (compost, feather meal, bone meal, kelp) — release nutrients slowly as microbes break down organic matter. They also improve soil structure. Nutrient percentages are lower, so larger volumes are needed.

Product selection depends on the crop, timing, budget, and environmental sensitivity of the site.

Record-Keeping and Regulatory Connection

State Pesticide Applicator licenses require detailed application records: product name, EPA registration number, rate applied, date, site, and applicator information. Fertilizer application records are separate from pesticide records legally, but many commercial operations track them in the same system. Good records protect you legally, help you spot patterns over seasons, and are required for many certification audits. Get in the habit of filling out records completely every time — it is a professional standard, not optional paperwork.

Safety in the Lab

Fertilizer dust irritates eyes, nose, and lungs. Some granular products are skin irritants.

Sweep up any spills immediately. Fertilizer left on hard surfaces can wash into drains and cause nutrient pollution.

Key terms8

Nutrient gapThe difference between the amount of a nutrient a crop requires and the amount already available in the soil, representing what must be supplied through fertilizer or amendments.
Guaranteed analysisThe three-number N-P₂O₅-K₂O label on a fertilizer bag expressing the minimum percentage by weight of each primary nutrient the product must contain.
Soil test reportA laboratory document showing measured levels of soil pH, organic matter, macro- and micronutrients, used to guide fertilizer and amendment decisions.
Slow-release fertilizerA fertilizer formulated to release nutrients gradually over an extended period, reducing leaching risk and the potential for fertilizer burn.
Interveinal chlorosisYellowing of leaf tissue between the veins while the veins remain green; a symptom commonly associated with iron or magnesium deficiency.
LeachingThe downward movement of soluble nutrients, especially nitrates, through the soil profile and potentially into groundwater when water moves through faster than plants can absorb nutrients.
Organic amendmentA material of biological origin (such as compost, manure, or feather meal) added to soil to supply nutrients slowly and improve soil physical properties.
Application rateThe amount of a fertilizer or amendment applied per unit area (e.g., pounds per 1,000 square feet), which must not exceed the product label direction.

Worked examples4

1. A soil test shows potassium is Low. The Extension table says the crop needs 2.0 lb K₂O per 1,000 sq ft; the soil currently supplies 0.5 lb K₂O per 1,000 sq ft. You plan to use a 0-0-50 fertilizer (muriate of potash). How many pounds of fertilizer do you need per 1,000 sq ft?
  1. Step 1 — Find the nutrient gap: 2.0 lb needed − 0.5 lb present = 1.5 lb K₂O gap per 1,000 sq ft.
  2. Step 2 — Convert the percentage to a decimal: 50% K₂O = 0.50.
  3. Step 3 — Divide the gap by the decimal: 1.5 ÷ 0.50 = 3.0 lb of 0-0-50 per 1,000 sq ft.
Answer: 3.0 lb of 0-0-50 fertilizer per 1,000 sq ft.
2. You need to apply 3.0 lb of a granular fertilizer per 1,000 sq ft to a simulated bed that is 500 sq ft. How many ounces do you weigh out?
  1. Step 1 — Scale the rate to 500 sq ft: 3.0 lb × (500 ÷ 1,000) = 3.0 × 0.5 = 1.5 lb.
  2. Step 2 — Convert pounds to ounces: 1.5 lb × 16 oz/lb = 24 oz.
Answer: 24 oz of fertilizer for the 500-sq-ft bed.
3. A soil test shows nitrogen is Low. The crop requires 4.0 lb N per 1,000 sq ft; available N in the soil is 1.0 lb per 1,000 sq ft. You have a 20-5-10 fertilizer. How many pounds of this fertilizer are needed per 1,000 sq ft to meet the nitrogen requirement?
  1. Step 1 — Find the nitrogen gap: 4.0 lb − 1.0 lb = 3.0 lb N needed per 1,000 sq ft.
  2. Step 2 — Convert the N percentage to a decimal: 20% = 0.20.
  3. Step 3 — Divide the gap by the decimal: 3.0 ÷ 0.20 = 15.0 lb of 20-5-10 per 1,000 sq ft.
Answer: 15.0 lb of 20-5-10 fertilizer per 1,000 sq ft.
4. Using the same 20-5-10 applied at 15.0 lb per 1,000 sq ft, how many pounds of P₂O₅ and K₂O will also be delivered per 1,000 sq ft?
  1. Step 1 — Calculate P₂O₅ delivered: 15.0 lb × 0.05 = 0.75 lb P₂O₅.
  2. Step 2 — Calculate K₂O delivered: 15.0 lb × 0.10 = 1.5 lb K₂O.
  3. Step 3 — Note that these amounts are byproduct of meeting the N requirement and must be compared to crop P and K needs to avoid over-application.
Answer: 0.75 lb P₂O₅ and 1.5 lb K₂O per 1,000 sq ft will be delivered.

The math in this lesson1

Learners divide a 1.5 lb K₂O gap by 50% potash to find fertilizer per 1,000 sq ft, then scale to 500 sq ft.
7.RP.3
Brush up in the math halls at newSchoolWorks.com:
In class: Lab station: each student receives a real or realistic soil test printout (pH, N-P-K, organic matter, micronutrients) and a crop nutrient requirement table; students complete a fertilizer prescription worksheet, showing N-P-K gap calculation and product selection. · Hands-on mixing and weighing: students weigh out a calculated amount of granular fertilizer (using a scale) into labeled bags for a simulated 500-square-foot bed, converting bulk recommendations to small-plot quantities. · Group discussion on slow-release vs. quick-release forms, organic amendments vs. synthetic, and how fertilizer records connect to State Pesticide Applicator record-keeping requirements — instructor facilitates using label examples.
Materials: Sample soil test reports, nutrient requirement reference tables (Cooperative Extension publications), granular fertilizer samples (labeled containers), digital scale, measuring cups, safety gloves, dust mask, fertilizer prescription worksheets
Check: Fertilizer prescription worksheet scored by instructor: correct identification of at least two deficiencies, correct rate calculation within 10% of key, and correct product selected; all PPE worn during weighing — 80% overall to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Crop and Soil Management
1. A soil test report shows phosphorus rated 'Low' and potassium rated 'Optimum.' Which action is most appropriate?
Crop and Soil Management
2. A bag of fertilizer is labeled 10-4-8. What percentage of that bag's weight is potassium (K₂O)?
Crop and Soil Management
3. Uniform yellowing of the older, lower leaves on a vegetable crop most strongly suggests deficiency of which nutrient?
State Pesticide Applicator — Laws and Regulations
4. Why is it illegal to apply a fertilizer or pesticide at a rate higher than the product label directs?
Crop and Soil Management
5. A crop requires 1.0 lb N per 1,000 sq ft. The soil already supplies 0.25 lb N per 1,000 sq ft. Using a 25-0-0 fertilizer, how many pounds of fertilizer are needed per 1,000 sq ft?
Workplace Safety
6. Which PPE combination is required when weighing granular fertilizer at the lab station?
State Pesticide Applicator — Record-Keeping
7. A commercial landscaper applies fertilizer to a client's site. Which record-keeping practice best aligns with professional standards and State Pesticide Applicator requirements?
NALP Landscape Industry Certified — Horticulture/Plant Management
8. Compared to a quick-release synthetic fertilizer, a slow-release fertilizer is generally preferred for established turf because it:
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