John Sawyer

Dr. John Sawyer is a professor of agronomy and extension specialist in soil fertility and nutrient management at Iowa State University. His extension program involves soil fertility management, efficient crop nutrient utilization, and environmentally sound fertilizer and manure systems. Dr. Sawyer's educational efforts focus on helping producers, agronomists, and industry leaders better understand soil-nutrient interactions with water quality. His research includes fertilizer and limestone needs of agronomic crops, manure nutrient utilization, site-specific systems, and impact of soil management and nutrient application on water quality.

Dr. Sawyer is an ARCPACS Certified Professional Agronomist, ARCPACS Certified Professional Soil Scientist, and Certified Crop Adviser.

John Sawyer photo
March 27, 2017 11:33 AM

The regional Corn Nitrogen Rate Calculator (CNRC) website was recently updated with a revised Iowa N response trial database that includes data through the 2016 crop year. Last year the CNRC website was revised and the url changed to (...

Soil Fertility
January 19, 2017 3:14 PM

Making sound soil fertility management decisions is an important part of successful crop production, on both an economic and environmental level. Iowa State University Extension and Outreach will be offering a two-day short course focusing on principles of soils, soil fertility and nutrient...

Soil Fertility
June 15, 2016 1:05 PM

The Using Manure Nutrients for Crop Production publication (PMR 1003) has recently been updated with revised beef cattle and dairy manure nitrogen (N) and phosphorus (P) crop...

Crop Production, Soil Fertility
June 6, 2016 6:01 PM

Most of Iowa has not received high precipitation amounts this spring, however, some regions have–most notably western Iowa (see maps). Wet springtime conditions typically raise the question about the status of applied nitrogen (N).

Soil Fertility
May 3, 2016 9:45 AM

You should visit the newly formatted and revised Corn Nitrogen Rate Calculator (CNRC) website. The site has a new url ( http://cnrc.agron.iastate.edu/ ). For Iowa, there are now two regions, the Main Iowa area and a Southeast Iowa area (SEIA) – see...

Soil Fertility
April 14, 2016 10:05 AM

It seems that anhydrous ammonia (AA) applications and planting may fall very close together on the timeline of events this spring. This could be concerning with drying soils and lack of significant rainfall chances in the near future.

Important notes to remember:

1) Application...

Crop Production, Soils, Soil Fertility