Knowing when to begin irrigating corn, when to stop, and how much water to apply are questions that many farmers have asked for years. Surveys have found that typically irrigation begins too late and ends too soon during the growing season. Irrigated corn yields tend to average 150 bu/acre when they should be averaging in the 200 bu/acre range. A study was done at the Agronomy Research Center near Columbia, MO in 2001 to compare two methods of irrigation: the Woodruff Charts and the Arkansas Scheduler.
The Woodruff Chart developed by Dr. C.M. Woodruff at the University of Missouri is based upon the water use of a corn crop during a growing season. It is an easy way for the farmer to keep track of when to start irrigating, how much water to apply, and when to stop. All the farmer needs to do is to record daily rainfall or irrigation on a chart. The Arkansas Scheduler, a computer based program, was developed at the University of Arkansas also uses water use of the corn crop but in addition utilizes actual daily high temperatures. Both methods allow the farmer to predict several days in advance when to irrigate and are available free of charge on the WEB. They only ask basic information concerning emergence date, soil type, county, and relative maturity.
Woodruff Chart:
http://agebb.missouri.edu/irrigate/index.htm
Arkansas Scheduler:
http://www.aragriculture.org:80/computer/schedule/default.asp
Pioneer 33G26 hybrid corn was planted on a Mexico silt loam soil on May 1 at a seeding rate of 29,500 kernels per acre in 30 inch rows with a final population of 26,500 plants/acre. Nitrogen, as ammonium nitrate, was applied before planting at a rate of 160 lb/acre. A stationary overhead sprinkler irrigation system was laid out to develop three treatments based on the Woodruff Chart, the Arkansas Scheduler, and a control receiving no water. Each of the three treatments was replicated three times. When corn reached the V6 stage an additional 100 lb N/acre was applied to half of each plot.
Irrigation began on June 22 for the Arkansas Scheduler and on June 25 for the Woodruff Chart. Throughout the growing season corn was irrigated 9 times using the Arkansas Scheduler and 7 times using the Woodruff Chart. The main difference was that the Arkansas Scheduler called for irrigation two more times early in the growing season than the Woodruff Chart. Typically, each schedule was within 3 days of one another.
Corn yield (averaged over both nitrogen treatments) for the control plots was approximately 142 bu/acre compared to 171 bu/acre with the Arkansas Scheduler and 192 bu/acre for the Woodruff Chart (Table 1). Only with the Arkansas Scheduler was there a difference in corn yield due to nitrogen treatment. This response to nitrogen with the Arkansas Scheduler is probably a result of heavy rains that occurred 24 hours after water was applied in late June and early July resulting in a loss of nitrogen. This would explain the lower yield without supplemental nitrogen with the Arkansas Scheduler. Regardless of nitrogen treatment, irrigation scheduling resulted in a 30 to 50 bushel per acre increase over control.
A question arises as to what component of corn yield was affected. Recent studies have indicated that with irrigation there are more rows of kernels on the ear and more kernels per row. In our data there was only a slight increase in these two yield components (Table 2). The large increase in corn yield was mainly attributed to an increase in the weight of each kernel (Table 2). There was approximately a 27% increase in kernel size from the Woodruff Chart as compared to the control, and a 35% increase in overall yield.
This study indicates that corn yield approaching 200 bu/acre can be achieved when irrigation is based upon a schedule. Research will continue in 2002 and beyond to look at other factors that can interact with irrigation management.
Table 1. Corn yield from the irrigation study at the Agronomy Research Center, near Columbia MO in 2001.
| Treatment | N | Yield |
| lb/acre | bu/acre | |
| Control | 160 260 | 144 138 |
| Arkansas | 160 260 | 155 186 |
| Woodruff | 160 260 | 189 195 |
| LSD (0.05) | 24 | |
Table 2. Corn yield components from the irrigation study at the Agronomy Research Center, near Columbia MO in 2001.
| Treatment | N | Rows/ ear | Kernels/ Row | wt/ kernel |
| lb/acre | # | # | g | |
| Control | 160 260 | 17.1 17.7 | 32.9 35.5 | 0.210 0.228 |
| Arkansas | 160 260 | 17.6 17.3 | 35.1 36.8 | 0.256 0.274 |
| Woodruff | 160 260 | 18.1 17.2 | 35.2 38.5 | 0.268 0.290 |
| LSD (0.05) | 0.5 | 8.2 | 0.036 | |