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An In-Depth Look at the Influence of Soil Temperature and Moisture in Southern Illinois - Part 1

Published on Wednesday, February 01, 2017

In 2016, the most common question we received at the Southern Illinois (SIL) Practical Farm Research (PFR)® site was “Is tile effective on farms in southern Illinois?” The most popular opinion is that tile does not work in southern IL due to less than ideal soil types throughout the area, such as tight clay. But what if we could make tiling effective? How would that change management practices throughout the southern half of the state?

We have experienced extremely wet conditions the past few springs which has made it difficult to plant before mid-May. However, Beck’s SIL PFR planting date studies have revealed that the optimum corn and soybean planting dates are before mid-May. Could tile help solve this problem? Also, what about irrigation? If an investment is made into tile, can the tile do more than just drainage? In 2016, a section of the SIL PFR site was devoted to a water management study to evaluate just that. 

Study Design

This water management study evaluated three different components: tile spacing and depth, drip-irrigation, and sub-irrigation. The tile spacing portion evaluated widths of 15, 30 and 60 ft., all of which were all evaluated at both 24 and 30 in. depths. In addition to spacing and depth, this study also looked at sub-irrigation and what would happen if we pumped water back into the contour lines when the soils became dry throughout the season. The drip-irrigation portion compared drip-irrigated (alone and with tile) as well as 30 ft. tile (alone). This study was conducted in collaboration with AGREM, LLC., CropX Inc., 360 Water Solutions, Netafim™, and Nutra Drip. The study was disk-ripped in the fall of 2015 to help remove any compaction or hard pans.

Figure 1. Aerial view of tile spacing.​

Sub Irrigation 2
Figure 2. Aerial view of the contour tile lines used in the sub-irrigation.

Growing Season
Finding the perfect window to plant in southern IL proved to be challenging in 2016. Luckily the soils in this study dried out much more quickly than other areas of the farm. Thanks to the tile, water management was one of only three corn studies that we were able to plant in April. Planting conditions in the 60 ft. tile were better than the control, but the 15 ft. and 30 ft. tile areas had the best seed beds. One thing that did stand out in the tile spacing portion of this study was plant development. Visual height differences were noticeable when comparing the 15 ft. tile to the 30 ft. tile vs 60 ft. tile, with the 15 ft. tile having a substantial height advantage.

Figure 3. Plant height difference between 15 ft., 30 ft., and 60 ft. tile.

In the drip-irrigation portion of the study, treatments without tile had spotty stands, especially in corn (Figure 4A). The drip-irrigation was able to replenish the moisture that was lost in June when we hit a dry spell. CropX Inc. sensors (Figure 4B) were used in the sensor-based sub-irrigation to ensure plants had adequate soil moisture throughout the growing season. With irrigation there was plant available moisture throughout all stages of development. We did observe a differences in plant growth between the drip-irrigation with 30 ft. tile versus drip-irrigation without tile or the control.  

Figure 4A. Spotty stands were found in the control.

Figure 4B. CropX Inc. soil moisture and temperature sensor.

Soil Moisture During the Growing Season
On June 20, the water was turned on in the sub-irrigation and drip-irrigation portion of this study. CropX LLC. sensors were installed to measure soil moisture (percent volumetric water content) and temperature (°F) at both 8 in. and 16 in. depths. The information gathered was utilized in the sub-irrigation, sensor-based portion of the study to measure moisture levels to ensure adequate moisture was available to the plants. The sensors were also placed in other portions of the study to determine the influence of other water management practices on soil moisture and temperature. The following tile spacing and irrigation averages and comparasions were all made after June 20, 2016.

At the 8 in. depth, the influence of irrigation was substantional for both the drip-irrigation and sub-irrigation portions of this study (Figure 5). By the end of June, the soil water was recharged which resulted in substantial differences between treatments. At this depth, manual sub-irrigation had the highest soil moisture throughout the majority of the season and never fell below 35% volumetric water content (VWC) after July 5. The sensor-based sub-irrigation and drip-irrigation portions also had soil moistures greater than 35% VWC at an 8 in. depth after July 5. The sensor, manual sub-irrigated, and drip-irrigated (with or without tile) systems all resulted in less variablilty in soil moisture compared to the controlled water table at an 8 in. depth. Areas without irrigation were dependent on rainfall to replenish the water table which resulted in a delayed response. Therefore, in June and July, the controlled water table was lower compared to the sub-irrigated and drip-irrigated portions. Following heavy rains in July and August, however, the controlled water table at  8 in. moisture was comparable to some of the other irrigation treatments. The controlled soil moisture never fell below 30% VWC at an 8 in. depth. The 30 ft. tile saw a 5 to 13% VWC reduction in soil moisture at an 8 in. depth compared to the control during the growing season. The better surface drainage systems resulted in prime planting conditions compared to the control, which also resulted in better stands. With the help of sub-irrigation and drip-irrigation, adequate soil moisture was available during critical growth stages.

Figure 5. CropX LLC. 8 in. soil moisture (% volumetric water content) from the irrigation portion of Beck’s water management study.

For the tile spacing portion of the study, the greatest soil moisture reduction with the 8 in. depth was directly over the tile lines (Figure 6). At this spacing, planting over the tile resulted in a 21% VWC reduction in soil moisture compared to planting between the tile lines. The greatest reduction in soil moisture over the tile occurred in the 15 ft. spacing. The greatest difference between the 15 ft. and 60 ft. soil moistures at the 8 in. depth occurred directly over the tile. Even during July and August, when rainfall was substantial, the 15 ft. tile soil moisture over the tile was less than 16% VWC. Between tile lines, the 15 ft. tile resulted in the best drainage at 8 in. depth. Between tile lines, the 15 ft. tile averaged a 3% VWC reduction in soil moisture compared to the 60 ft. tile. This reduction in soil moisture explains why the soils dried out quicker and resulted in a better seed bed compared to the 60 ft. or the control. However, even with a reduction in soil moisture at an 8 in. depth, the corn placed over the 15 ft. tile had greater plant height compared to the 30 ft. and 60 ft. tile. This could simply be a result of the soil conditions at planting as the soil surface over the 15 ft. tile was drier, allowing for a better seed bed. Another influence could have been the rains we experienced mid-summer. The 15 ft. tile was more efficient at removing excess water in the root zone, reducing the chance of anaerobic conditions. 

Figure 6. CropX LLC. 8 in. soil moisture (percent volumetric water content) from the tile spacing portion of Beck’s water management study.

Soil moisture was also recorded at 16 in. depth with the CropX LLC. sensor in both the irrigation and tile spacing portions of the study. At the 16 in. depth, soil moisture was greater in the irrigated portion of the study compared to an 8 in. depth (Figure 7). The drip-irrigated portion with 30 ft. tile had the greatest soil moisture for the majority the season and never fell below 40% VWC after July 5. The drip-irrigated portion without tile had the least amount of variation in soil moisture at a 16 in. depth and ranged from 33 to 35% VWC. In the drip irrigated system, areas with no tile were 9% drier than the areas with tile. 

One theory why this occurred was that the water remained in the upper soil surface in the drip-irrigated portion when no tile was used. With the tile, water infiltrated deeper into the soil profile. How? When the tile is placed in the soil, it improves soil aggregation around the tile line, acting like an in-line ripper breaking hard pans and allowing better water infiltration. As a result of gravity, water moves down which creates deeper infiltration. This allows adequate moisture for deeper-rooted plants such as corn. The manual sub-irrigation, which had the greatest soil moisture at the 8 in. depth, was more variable compared to sensor based sub-irrigation. Irrigation was reduced in the manual sub-irrigation compared to the sensor-based system. In the manual sub-irrigation there was no sensor to tell us when to water and because of the high upper surface moisture, the water was not turned on as frequently compared to the sensor based sub-irrigation. This resulted in up to a 7% VWC reduction in soil moisture compared to drip-irrigated with tile. The controlled water table had the lowest soil moisture at the 16 in. depth and had up to 15% VWC reduction at the 16 in. depth compared to the drip-irrigated with tile. The water table was rainfall dependent, resulting in greater soil moisture differences between the irrigated treatments of the study. 

Figure 7. CropX LLC. 16 in. soil moisture (percent volumetric water content) from the irrigation portion of Beck’s water management study.

In the tile spacing portion of the study, we saw the greatest soil moisture at the 16 in. depth over the tile (Figure 8). Just like in the irrigation study, moisture had deeper infiltration into the soil profile where tile was in place. The closer to the tile, the greater the infiltration and increase in soil moisture. The greatest infiltration occurred directly over the tile line at the 16 in. depth. Therefore, over the tile had the greater soil moisture versus between tile lines. In the 15 ft. and 60 ft. spacing, the soil moisture was increased by 7 to 12% VWC between the lines vs. over the tile lines, respectively. This showcases one of the hidden benefits of tile – that it is not only able to help reduce surface moisture but also increase moisture in the subsurface, allowing more moisture for deeper rooted plants such as corn.

Figure 8. CropX LLC. 16 in. soil moisture from the tile spacing portion of Beck’s water management study.​

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Author: Joe Bolte

Categories: PFR, PFR Reports


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