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30” Versus 60”
Polypipe irrigation in an Arkansas soybean field.
U of A System Department of Agriculture file photo
Trials Show Bed Size, Soil Types Play Role In Irrigation Efficiency
BETTY VALLE GEGG-NAEGER
MidAmerica Farmer Grower
MEMPHIS, TENN.
In a team-talk presentation at the 21st Annual National Conservation Systems Cotton and Rice Conference, Dave Freeze, University of Arkansas County Agent, and Joey Massey, Green County, Ark., soybean farmer, delivered the results of a two-year irrigation trial.
The goal was to compare water use efficiency and yields for soybeans grown on 30-inch versus 60-inch beds. The trials were conducted in 2015 in Light, Ark., on Foley-Bonn and Wiville fine sandy loam soils, and in 2016 at Walcott, Ark., on Foley-Bonn complex (silt loam) soils.
Each year 80,000 acres of soybeans are grown in Greene County Arkansas with over half these acres grown on 60-inch beds. The beds are prepared with a bedder-roller, a popular implement for local producers.
“Using wide beds, producers may not be able to thoroughly saturate the soil profile when they irrigate which could result in lower yields,” Freeze explained. To investigate this, the tests utilized flow meters, surge valves, and soil moisture sensors to help improve irrigation efficiency, and to monitor irrigation water use and soil moisture status.
“We wanted to learn when and where we should use the 30-inch or 60-inch beds,” said Massey.
2015 Results
In the 2015 test, 60-inch beds were established on the north half of the test field and 30-inch beds on the south half. Pioneer 48T53 soybeans were planted on 30-inch row spacing on June 2. The plants emerged to a good stand of 115,000 plants/acre on the wide and narrow beds.
An electric well was located on the southeast corner of the project field. Considering slope, the fall from east to west was 1/10th foot. The polypipe pad also had about a foot of total rise from the well to the end of the polypipe tubing. The 60-inch beds were irrigated as one set with the north riser and the 30-inch beds as another set with the south riser.
The test field was harvested Oct. 15, and a three bushel advantage was seen for soybeans grown on the 60-inch beds compared to the 30-inch beds. Soil texture for the project field was variable, with about half the field being sandy and the rest a mix of silt loam and silty clay loam. Sandy areas likely allowed good percolation of irrigation water across the 60 inch beds.
Massey speculates the yield difference may be due to better root functioning on the wide beds early in the season during a long period of excessive rainfall. He also indicated that irrigation water jumped across some beds on the 30-inch rows which may have left some rows in that part of the field inadequately watered. One final factor that may have contributed to this yield difference is the extra irrigation received for soybeans on the 60-inch beds. The second irrigation on the 60-inch beds was completed Aug. 17. Heavy rain in the forecast spurred a halt in watering soybeans on the 30-inch rows.
Results & Discussion-Water Use
For the growing season, the project field received 20.8 inches of rainfall. Surge valves were used to improve irrigation throughout the soil profile.
Irrigation water use was tracked using flow meters. The 30-inch beds received a total of 6.0 acre inches (AI) for the season, averaging 2.0 AI per irrigation. Meter reading data from the 60-inch beds show them receiving a total of 6.4 AI for the season, averaging 1.6 AI per irrigation. These data show that soybeans on narrow beds were able to receive an extra 25 percent more water with each irrigation compared to those on 60-inch beds.
Results & Discussion-Moisture Sensors
Watermark soil moisture sensors were set at 6, 12, 18, and 30 inch depths, in the soybean row, on a 30-inch bed, at one site in the field. Dr. Chris Henry determined irrigation should to be triggered when sensors reached the 45-70 centibar (cb) zone.
Reviewing data for sensors on the 30-inch bed, soil moisture readings averaged 37 and 19 centibars across all irrigations, for the 6- and 12-inch settings respectively. Adequate top soil moisture was maintained for this site.
Considering subsoil moisture on the 30-inch bed site, soil moisture readings averaged 6- and 0-centibars across all irrigations, for the 18- and 30-inch settings respectively. These data show subsoil moisture was good through mid-September.
Sensors were also set at 6, 12, 18, and 30-inch depths, in the soybean row, on a 60-inch bed, at one site in the field. Another set of sensors was placed next to these, a few inches away, in the center of the bed. Sensor readings averaged across all irrigations for the season were 34, 18, 27 and 8 centibars for 6, 12, 18, and 30 inch sensor depths respectively in the soybean row site for 60-inch beds. Sensors in the center of the bed had similar readings of 42, 24, 12, and 4, for 6, 12, 18, and 30-inch sensor depths. These data suggest irrigation water was able to wick all the way across beds at this site.
Sensors on the 60-inch beds show a similar trend in readings regarding adequate top soil moisture through mid-September, with subsoil moisture available to finish the crop off heading into maturity.
2016 Results
This test was conducted at Walcott, Ark., on Foley-Bonn complex (silt loam) soils. Again, a bedder-roller was used in 2016 to establish 60-inch beds on the south half of the test field and 30-inch beds on the north half. Pioneer soybeans were planted on the 30-inch rows on May 18. They emerged to a good stand (127,000 plants/acre) on the 30” and 60” beds.
An electric well (one riser for 30” beds, one riser for 60” beds) was used on the project field. Considering slope, the fall from top to bottom was 1/10th of a foot for the field. The polypipe pad had less than a foot total fall from the well to the north field border.
Results & Discussion-Yield
The test field was harvested Oct. 15. A four-bushel yield advantage was recorded for soybeans grown on the 30-inch beds compared to the 60-inch beds. This is just the opposite of what happened in 2015. Massey thinks the higher yield for the 30-inch rows may be due to drainage not being as good on the bottom of the field on the side with 60-inch beds.
“We also observed that more irrigation water was applied per irrigation on the 30-inch beds which may have improved yields on them compared to the wide rows,” Freeze explained.
Results & Discussion-Water Use
Rainfall data show 11 inches was received from mid-June through mid-September. Most, 7 inches of it, came during a 10-day monsoon period in mid- to late-August.
Surge valves were used again this year at each riser. Most furrows watered out fairly uniformly. Some shoveling was required at the top of the furrows at the beginning of the first irrigation where water was skipping across beds due to erosion from heavy early season rainfall.
Flow meters captured irrigation water use. The 30-inch beds received three irrigations, using a total of 2.53 acre inches (AI). The 60-inch beds got four irrigations, totaling 2.7 AIs. Per irrigation, the 30-inch beds averaged .84 AIs. compared to .68 for the 60 inch beds for 24 percent more water per irrigation.
“These data are similar to what we saw in 2015,” Freeze said. “The slight yield advantage with narrow beds this year may be due to better rewetting of the root zone on them compared to wide beds.”
Results & Discussion-Moisture Sensors
Watermark soil moisture sensors were used again in 2016 at the same soil depths as in 2015 for both the wide and narrow beds. Henry determined irrigation should be triggered when soil moisture sensors at the 6- and 12-inch depths reached the 100 centibar (cb) zone. Overall, the sensors worked well and the field was irrigated as the crop reached the trigger zone.
Summary
Yield response and irrigation water use varied for the 30- versus 60-inch beds each of the two project years. One of the major reasons is the different soil type at each test site.
The 2015 project field had variable soil texture, but was sandy in over half the field. This helps explain the slightly higher yield response (3 bushels) seen on the wide beds. Moisture sensors indicated that irrigation water was able to wick completely across the beds for each irrigation. Massey also believes the wide beds promoted better drainage and seedling soybean root development during a period of heavy early season rainfall.
A more consistent silt loam soil texture seen on the 2016 project field likely provided an edge for the 30-inch beds over the 60-inch beds at this site. Irrigation water may not have soaked into the soil profile as good on the wide beds compared to the 30-inch beds.
Regarding water use, each year of the study, flow meter readings show that 25 percent more irrigation water could be applied per irrigation using 30-inch beds compared to the 60-inch beds. The extra irrigation water allowed by using narrow rows would provide a significant advantage during dry years.
“Finally, flow meter data show that we were able to apply more acre inches (AI) per irrigation at the sandy location (1.5- 2.0 AI) compared to the silt loam site (.7 - .9 AI). On a crusting silt loam, a more frequent irrigation schedule is likely needed to keep up with the water demands of the crop,” Freeze concluded. ∆
BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
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