What are the best free extension-style agronomy sites for learning fertilizer basics by crop and soil type?

Here are some of the best free, extension-style agronomy resources for learning fertilizer basics by crop and soil type. I’m focusing on sites that are practical, research-based, and written in an extension/land-grant style rather than commercial marketing.

Best overall extension-style sites

1. University Extension crop fertility guides

These are often the best starting point because they’re crop-specific and soil-test focused.

Good places to search:

• Iowa State University Extension
• University of Minnesota Extension
• Penn State Extension
• University of Illinois Extension
• Kansas State Research and Extension
• Nebraska Extension
• Purdue Extension
• Ohio State Extension
• North Dakota State Extension
• South Dakota State Extension

Why they’re useful:

• Fertilizer recommendations by crop
• Soil test interpretation
• Nitrogen, phosphorus, potassium basics
• Manure and micronutrient guidance
• Region-specific soil considerations

What to search for on these sites:

• “crop fertilizer recommendations”
• “soil fertility”
• “soil test interpretation”
• “corn nitrogen management”
• “soybean fertility”
• “wheat phosphorus potassium”
• “fertility by soil type”

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2. NRCS / USDA soil and nutrient basics

Not crop-fertilizer guides in the same sense as extension sites, but very useful for understanding soil types, texture, drainage, and nutrient behavior.

Useful resources:

• USDA NRCS Web Soil Survey
• USDA NRCS soil health materials
• USDA extension/education resources on soil properties

Why it helps:

• Understand how sandy, loamy, clay, and organic soils differ
• See how drainage and cation exchange capacity affect fertilizer use
• Match fertilizer strategy to soil limitations

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3. Land-grant university nutrient management handbooks

These are often the most practical “how much fertilizer and when” references.

Examples:

• Tri-State Fertilizer Recommendations
  Common in the Midwest; very practical for many crops.
• Northeast / Mid-Atlantic nutrient management guides
• Southeast crop nutrient management guides
• Great Plains crop fertility publications

These often cover:

• Yield goal vs. soil test approaches
• Fertilizer placement
• Timing
• Starter fertilizer
• Split nitrogen applications
• Liming and pH correction

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Best crop-focused free resources

Corn

• University of Illinois N-Watch / corn fertility resources
• Iowa State corn nitrogen and phosphorus guides
• Nebraska corn fertility publications
• Purdue corn fertilizer guides

Look for:

• N rate calculators or algorithms
• corn N timing
• P and K removal rates
• soil type effects on N loss risk

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Soybeans

• University of Minnesota soybean fertility guides
• Iowa State soybean fertility publications
• Ohio State / Purdue soybean nutrient resources

Look for:

• Whether soybeans usually need fertilizer
• P and K maintenance
• micronutrient exceptions
• nodulation and biological N fixation basics

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Wheat

• Kansas State wheat fertility
• Oklahoma State wheat nutrient management
• Oregon State / Washington State wheat fertility resources if in the Pacific Northwest

Look for:

• Split N applications
• sulfur needs
• early-season fertility
• soil pH and zinc or other micronutrients

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Alfalfa and forage crops

• Penn State forage fertility
• University of Wisconsin forage fertility
• Minnesota forage nutrient management
• Ohio State forage guides

Look for:

• potassium management
• sulfur and boron
• pH and lime requirements
• cutting schedule effects on fertility

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Vegetables and specialty crops

• Cornell Cooperative Extension
• University of Minnesota Extension
• University of California Agriculture and Natural Resources
• Rutgers NJAES
• NC State Extension
• UF/IFAS Extension

These are especially useful because vegetable fertility depends heavily on:

• crop species
• soil organic matter
• texture
• irrigation
• planting method
• high-value production systems

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Best sites for soil-type-specific learning

1. Extension soil fertility bulletins

Search extension sites for:

• sandy soils and nitrogen leaching
• clay soils and phosphorus fixation
• low pH soils and liming
• calcareous soils and micronutrient availability
• organic soils and nitrogen mineralization

2. Web Soil Survey + extension interpretation guides

Use:

• USDA NRCS Web Soil Survey
• then pair it with your state extension fertilizer guide

That combination helps you understand:

• whether your soil is prone to leaching
• whether it needs more split N
• whether pH or drainage will limit nutrient uptake

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Very useful “general agronomy” extension-style sites

1. Cornell Agronomy Fact Sheets

Great for practical, research-backed basics.

2. UC ANR (University of California Agriculture and Natural Resources)

Excellent for nutrient management, especially for horticulture, orchards, vineyards, and vegetables.

3. North Carolina State Extension

Strong in soil fertility and nutrient management basics.

4. Oklahoma State / Kansas State / Nebraska Extension

Good for crop fertility in different soil environments, especially Great Plains systems.

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Best free tools to pair with these sites

• USDA Web Soil Survey
• State soil testing lab recommendation sheets
• Nutrient removal charts
• Extension fertilizer rate calculators if available
• Soil pH and lime requirement guides

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If you want the shortest “starter list”

If you only want 5 places to begin, I’d pick:

1. Iowa State Extension
2. University of Minnesota Extension
3. Kansas State Extension
4. Penn State Extension
5. USDA NRCS Web Soil Survey

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Practical tip

The best way to learn fertilizer basics is to combine:

1. your crop
2. your soil test results
3. your soil type
4. your state extension guide

That’s much more useful than generic fertilizer articles.

If you want, I can also make you a ranked list by crop — for example:

• best free sites for corn
• best free sites for soybeans
• best free sites for vegetables
• best free sites for orchards/vineyards