Soil Moisture Levels Improving for 2013 Crop Production
Iowa State University has completed their spring survey of subsoil moisture in northwest Iowa. Subsoil moisture levels are surveyed in pre-determined areas each spring and fall, says Joel DeJong, Iowa State University Extension Field Agronomist.
The April rains have contributed greatly to subsoil moisture levels. Subsoil moisture levels in the NW corner of Iowa have increased an average of 5.0 inches since these sites were sampled last fall. The level of subsoil moisture at the soil moisture sites in Lyon, Osceola, Sioux, O’Brien, Plymouth, Cherokee, Woodbury, Ida and Monona counties range from 4.8 inches near Akron to 9.8 inches of plant available moisture south of Marcus (table 1) as of the end of April.
The amount of moisture in the subsoil is now at or above normal in several locations. The exceptions are west of Sibley, along with northern Plymouth and southern Sioux county sites. Sites in O’Brien, Cherokee, Ida and Woodbury counties are approaching field capacity at this time, if early May precipitation is included.
Typical soils in northwest Iowa have the potential to hold from 10.0 to 11.0 inches of moisture in the top five feet of soil. The dry conditions last summer and last fall left the soil moisture reserve very low. Soil moisture readings from sites ranged from 1.2” in Monona County to 7.8” in eastern Cherokee County last fall. (table 1).
The drought conditions that began in mid-July 2011 greatly depleted soil moisture reserves. However, this subsoil moisture survey information indicates that the rainfall that occurred during April recharged the soil moisture a great deal. Additional precipitation in early May 2013 has helped even more, but is not included in this data.
The subsoil moisture recharge season begins when last year’s crop reaches maturity, which was September 1, 2012 in many locations. In much of NW Iowa there has been about eight or more inches of rainfall since the 2012 crop reached maturity. Spring moisture levels in 2013 are greater than they were at this time in 2012 in all but the Sioux and Osceola county sites.
The 2012 crop likely accessed soil moisture that is below the typical five foot soil profile and maybe as deep as six to seven feet deep in the soil. This survey does not measure soil moisture below five feet deep. However, the sites in Cherokee and Ida counties show that the fifth foot of soil from the surface is getting close to capacity, which could mean that excess water found there is migrating down into the sixth and seventh foot. Data from Monona, Woodbury, Sioux, Plymouth, Lyon, and Osceola counties look to have a lot of storage left in the fifth foot of subsurface soil at this time, meaning deeper recharge has not yet occurred.
The soil moisture situation therefore is not the concern that it has been even as recently as early April. The corn and soybean crop needs about 20 inches of moisture to produce a normal crop yield. The recent April rains have done a lot to replenish the soil moisture reserves. However, adequate and timely summer rainfall will still be needed to produce normal corn and soybean crops. Sioux City “normal” rainfall for May 1 through August 30, the typical growing season of most Iowa crops, totals 14.3 inches, with probably 80% of that available for the crop to use.
Table 1. Subsoil moisture levels, fall 2012 and spring 2013.
Location County 2012 crop 11/1/12 4/26/13
----------Inches plant available moisture----------
Doon Lyon corn 3.0 7.3
Sibley Osceola corn 2.2 6.2
Ireton Sioux soybean 4.5 6.8
Melvin O’Brien corn 4.5 8.4
Sutherland O’Brien corn 5.1 9.4
Akron Plymouth corn 1.8 4.8
Le Mars Plymouth corn 2.2 8.2
Hinton Plymouth soybean 2.0 7.2
Marcus Cherokee corn 4.7 9.8
Lawton Woodbury corn 1.6 8.9
Anthon Woodbury corn 2.6 9.3
Battle Creek Ida soybean 2.8 9.4
Castana Monona corn 1.2 7.6
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