Northwest Iowa Crops Page
Soil Moisture
by Todd Vagts
ISU Extension Crops Specialist
Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.

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Subsoil moisture survey

Each spring and fall, I pull soil samples in one foot increments (to a depth of five feet) to determine the status of soil moisture that is available for plant uptake and use.  The samples are collected at the same locations in farmer fields each year.  This information can be useful when determining tillage, fertility and cropping sequences in the geographic area. 

The maximum amount of plant available water (PAW) in the top five feet of soil is around eleven inches for most northwest Iowa soils. The subsoil moisture samples are taken to a depth of five feet in one-foot increments. Five feet is the normal depth that corn, soybeans and alfalfa can extract moisture. On average, a corn and soybean crop requires 26 inches of water to produce a normal yield. Timeliness and intensity of the rain events greatly effects water infiltration into the soil and the plant's ability to utilize the moisture. Keep in mind that rainfall is variable across the region and the samples capture only a snapshot of time and location of actual subsoil moisture status.

Soil Moisture - Fall 2005 | Soil Moisture - Spring 2005

Soil Moisture - Fall 2004 | Soil Moisture - Spring 2004

Soil Moisture - Fall 2003 | Soil Moisture - Spring 2003

Soil Moisture - Fall 2002 | Soil Moisture - Spring 2002

Soil Moisture - Fall 2001 | Soil Moisture - Spring 2001

For questions or comments please respond to vagts@iastate.edu

This page last updated on 11/10/05

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