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Crop Water Use Comparison Study

Water use efficiency (or crop water productivity) is important in crop production. The seed Industry has invested scientific efforts and financial resources into developing hybrids and varieties that can better tolerate environmental stresses such as water stress.

Rainfed corn has increased in acres, replacing sorghum year after year.  This trend may be partly due to the basis price, herbicide options, and newer corn hybrids bred with root systems to better withstand water stress.  In 2009 the question was posed, “Is sorghum still the most crop-water-use-efficient crop, given newer corn hybrids in rainfed fields are providing decent yields and more herbicide options?” To answer the question the Nebraska Grain Sorghum Board funded a project in south-central Nebraska.

On-farm research was conducted for three years in rainfed production fields near Lawrence with the most adapted and high-yielding corn, sorghum, and soybean hybrids and varieties for that area. The research was conducted in no-till fields where the previous crop had been sorghum. A randomized complete block design with three replications was used.

Corn and soybean were planted between May 5 and May 7; sorghum planting ranged from May 19 to May 28. Corn was planted at 20,000 seeds/acre, soybean at 135,000, and sorghum at 65,000.  Rainfall in this area varied greatly from 2009 to 2011: 2009 was dry with only 10 inches of rain during the growing season; 2010 had 16 inches, and 2011 had 20.5 inches from May 1 to October 15.

To monitor soil moisture, Watermark sensors were placed at 1-, 2-, 3-, and 4-foot depths in each plot and the readings were recorded hourly throughout the growing season via Watermark dataloggers. Data were compiled and analyzed to determine crop water use efficiency (CWUE) values. The CWUE values were determined from the Watermark soil moisture data, actual crop water use (evapotranspiration), and grain yield for each crop.

Results:  Table 1 shows actual crop evapotranspiration (ET) in inches, grain yield, and crop water use efficiency for each crop in each year. Corn was the most water use efficient of the three in 2009. Sorghum results in 2009 might have been different if rainfall had occurred to activate the sorghum herbicide as grass pressure was heavy in the sorghum plots that dry year. In 2010-2011, sorghum yielded the most, had good weed control, and had the best crop water use efficiency value.

Table 1.  Crop water use efficiencies in on-farm field trials conducted near Lawrence, Nebraska, 2009-2011.
2011
ET (in)
2011
Yield
(bu/ac)
2011
CWUE
(bu/in)
 2010
ET (in)
2010
Yield
(bu/ac)
 2010
CWUE
(bu/in)
2009
ET (in)
2009
Yield
(bu/ac)
2009
CWUE
(bu/in)
 Corn  22.0  127.2  5.8  23.3  101.2 4.3  14.5  97.5  6.7
 Soybean  21.3  61.3  2.9  22.0  44.0  2.0  14  33.4  2.4
 Sorghum  17.3  138.9  8.0  21.3  118.0  5.5  13.7  77.4  5.6

Overall in this study, sorghum had a crop water use efficiency of at least 5.5 bu/inch; corn, at least 4.3 bu/inch, and soybean, at least 2.0 bu/inch. These results show sorghum’s continued value as a crop that efficiently uses water. Sorghum produced more grain per unit of water used than corn or soybean, an important benefit in water-limited environments. On a three-year average, sorghum resulted in 1.2 bu/inch and 3.5 bu/inch more grain production per inch of water used than corn and soybean, respectively. This study did not compare sorghum or soybean with new “drought-tolerant” corn hybrids.  Graphs, charts, and production information can be found here.

Acknowledgements:  Special thanks to John Dolnicek of Lawrence, Nebraska for allowing this research to be conducted on his farm and for all his help and efforts to make it a successful study and to the Nebraska Grain Sorghum Board for funding this study.

Crazy?

Crazy?  Perhaps!  Which according to one of my farmer friends is a little typical of me when I put my mind to figuring out something.  So I had been analyzing my crop water use data from my dryland corn, sorghum, soybean crop water use comparison study.  It’s the one where we had coon problems this year and ended up trapping a skunk!  I noticed how much the soil moisture profile had been depleted and knowing we’ve received minimal precip during fall and winter, I wondered what our soil moisture profile would be for dryland fields by planting.  During a meeting yesterday I thought it would be good to install some watermark sensors to determine soil moisture profile recharge with the pending storm.  Problem was I was at a meeting over 100 miles from my equipment and the pending storm was starting today.  But I was still determined to get them in the ground as early as possible in order to measure the soil moisture status.  So I woke up at 4:00 a.m. to heavy rain.  Great!  It was such a gorgeous day yesterday, and the past week…past month…  The first thing my colleagues had asked me when I told them my idea was “Why didn’t you think of this sooner?”  Answer:  “Guess I needed a precipitation event!”  

So I drive to the field in the rain, get the gear together and start installing the sensors.  First foot went in easy with the rain that had soaked in.  Then it seemed like I tried for 20 minutes (although probably not near that long) putting all my weight on the soil probe to get the 2nd foot in.  Wind-driven rain soaked my jeans since I didn’t have rainpants on…fingers were numb from the cold.  I kept telling myself this will still hopefully be worth it!  On the research data from this field, the second foot was driest of all the crops (was depleted well above plant available water).  I got the third foot in and John, the man who farmed the field appeared.
While he thought it was crazy he graciously volunteered to help as he always does.  He put in the rest of the sensors while I
hooked everything up.  

The last several years we have been blessed to have a fully charged profile going into planting.  Even with this rain/snow event, I’m not sure we will have that in dryland fields in this area of Nebraska.  So I thought it would be interesting to know where we stood before planting and figured the farmers may want to know that as well.  Perhaps a little crazy regarding installing the sensors on such a bad weather day but hoping the data in the end will benefit our farmers and be worth it!

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