UNL CropWatch Nov. 12, 2010: Monitor Soil Moisture for 2011 Cropping Season

UNL CropWatch Nov. 12, 2010: Monitor Soil Moisture for 2011 Cropping Season

Nov. 12, 2010

Prcipitation Amounts


Departure from normal precipitation

What a difference a year makes in regard to harvest activity. Last year, Nebraska producers struggled to harvest crops during October due to a combination of poor weather conditions, late maturing crops, and high moisture grain. This year, virtually all of the harvest activity was completed by the end of October, outside of isolated areas of western and northern Nebraska.

The lack of significant moisture across much of eastern Nebraska during October yielded optimum harvest weather, but didn’t help to build soil moisture reserves for the 2011 production season. Much of eastern Nebraska has accumulated precipitation deficits of one to three inches since October 1, with the greatest departures in south central, east central, and southeastern Nebraska (Figures 1 and 2).

With all of the moisture that fell on the 2010 crops through mid-July, assessing current soil moisture conditions is fraught with uncertainty. Harvest reports consistently indicated below normal yields on bottom land, while above normal to exceptional yields on side slopes. In a typical year, we would expect bottom land yields to outpace side slope areas.

Some of the bottom land areas were flooded repeatedly during the heavy rains from late May through June. We suspect that shallow rooting was a problem this year and roots may not have efficiently used stored moisture below the three-foot depth. Side slope areas likely had excellent roots that were able to penetrate deep into the profile and effectively use moisture stored in top 5-6 feet.

The degree of yield variability within individual fields presents a problem in trying to assess prospects for next year’s crop. Moisture in dryland fields across the eastern third of Nebraska primarily resulted from moisture carried over from the 2010 production season and is not a result of precipitation since October 1.

Under normal October precipitation conditions, dryland farmers across eastern Nebraska would have seen an average of two inches of soil moisture recharge, with most of this moisture confined to the top 12-18 inches of the soil profile. On average, less than two inches of available soil moisture would have carried over from the previous cropping season. Normally, soil profiles at the end of October should hold 3-4 inches of available moisture. By the end of April, normally there should be 8-10 inches of available moisture in the top 5-6 feet of the soil profile.

Based on precipitation deficits from October 1, climatological statistics indicate there is only a 40%-45% chance that these deficits will be completely negated by May 1. Although it’s probably too early to decide about crop insurance for 2011, serious attention should be placed on understanding where soil moisture exists within fields and how much available water is in the top 5-6 feet.

How Much Soil Water do You Have?

Bottom land fields currently may have more soil moisture than rainfall statistics indicate, especially if shallow root syndrome developed due to the early season soil profiles that were nearly saturated, promoting inadequate root development. Hilly ground may have less soil moisture carryover from this past growing season as roots may have gone deeper into the soil profile in search of stored moisture.

If you are an eastern Nebraska dryland farmer, you typically expect to receive 11 inches of moisture between October 1 and April 30. About 70% of this total (about 8 inches) will become available for plant growth in the upper 5-6 feet of the profile. For every inch short of the 11-inch mark, coupled with normal precipitation during the growing season, dryland corn yields will drop an average of 2.5% from baseline yields.

In making cropping plans for next year, it’s good to understand how much available moisture your fields currently contain. At a bare minimum, eastern Nebraska producers should now have at least three inches of available moisture in the top 5-6 foot of the soil profile, preferably in the top 18 inches of the profile. Even though October precipitation departures of 2-3 inches are common across eastern Nebraska, 2010 growing season soil moisture carryover may have completely offset these large precipitation deficits.

By the end of February, dryland producers should have received a minimum of 5 inches of recharge in the top 3 feet of the soil profile. By the end of March soil moisture recharge should approach 6.5 inches, with 8 inches of recharge normal by end of April.

To get a good estimate of your soil moisture next spring, determine your current soil moisture and use that as a base. Then take any moisture received from now on this fall and winter, multiply it by 0.70, then add it to current moisture level to get a rough estimate of soil moisture.

Al Dutcher
Extension State Climatologist