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Climate Observations: More precipitation boosts soil moisture recharge.

Mark Seeley

March 3, 2017

2 Min Read
SOIL SOAKER: University of Minnesota research shows that in years of surplus April precipitation, an average of 1.5 inches of additional moisture is stored in the corn root zone.

Examining trends in the Minnesota climate record reveals that in five of the past six years, April has brought above-normal precipitation to most parts of the state where corn is grown. The exception was 2015, which was marginally drier than normal.

Despite this trend, Minnesota farmers have done a remarkable job in planting the corn crop in a timely manner. Later-than-normal planting was evident only in 2011 and 2013, when much of the corn crop went into the ground in mid-May or later. In both of those years, climate observers not only reported above-normal precipitation in April, but also reported that 20 of the 30 days in the month were wet, a much higher than normal frequency.

Certainly tile drainage, combined with better and higher-capacity machinery, as well as very long field-working days (sometimes into the night, with running lights on), have enhanced the ability to plant corn faster than ever before. So the ability to maximize fewer field-working opportunities afforded by the weather during April has fully been in evidence.

According to the USDA National Agricultural Statistics Service, in both 2012 and 2016, Minnesota farmers had planted half of the corn acreage — approximately 3.5 million acres — by the end of April, and sometimes at a pace of more than 2 million acres per week. This is a phenomenal testament to the deployment of new technology and hard work.

Moisture insurance policy
Perhaps an underappreciated benefit of the trend towards wetter than normal Aprils is the additional moisture recharge placed in the soil profile for use by the crop later in the growing season. Measurements of soil moisture recharge from the University of Minnesota Southern Research and Outreach Center in Waseca, and from the Southwest Research and Outreach Center in Lamberton, show that in years of surplus April precipitation, an average of 1.5 inches of additional moisture is stored in the crop root zone.

In some individual years, the soil moisture recharge from surplus April precipitation has been as high as 3 inches, enough to carry a healthy stand of corn for three weeks without any rainfall during the growing season. This is like a moisture insurance policy, or money in the bank, to see the corn crop through any dry periods.

Overall, the average increase in April precipitation from this trend analysis shows a net change of 1.10 to 1.30 inches across many parts of southern Minnesota. Smaller increases in April precipitation have been measured in western counties, but still range up to a net change of half an inch or so. In addition, the net change in frequency of daily precipitation has jumped by four to five days. Some areas now measure precipitation on average about half the days of the month.

Do not be surprised if April 2017 follows this trend and delivers above-normal precipitation to your area.

Seeley is an Extension climatologist with the University of Minnesota.

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