The specter of water regulations always hovers over Southeastern farmers, especially during drought years when agriculture demands more of the precious resource.
When and if regulations are ever imposed, one option for reducing water requirements will be conservation-tillage, according to research conducted in the past several years.
The impetus for the conservation-tillage research was the various water issues that have confronted Georgia farmers in recent years, says David Bosch of the USDA Agricultural Research Service. Bosch, who specializes in hydrology, presented his findings during the recent Conservation-Tillage Workshop and Field Tour held in Tifton, Ga.
“Most of us are familiar with the ‘Water Wars’ that have been going on since the early 1990s, primarily between Georgia, Alabama and Florida concerning water that flows along the borders and down into Florida,” says Bosch. “That generated a lot of controversy as far as who owns the water rights — how much belongs to Atlanta and how much belongs to the other states.”
The discussion expanded, he says, into an issue involving urban versus rural areas and irrigation use in the rural areas. Now, he adds, federal regulations are being discussed.
“During this discussion, studies were conducted on irrigation use along the Flint River basin and how much water was being delivered to farms. As a result, the Georgia General Assembly came up with the Lower Flint River Drought Protection Act which was intended to allow a buyback of groundwater during designated dry years. They try to forecast when a dry year occurs and how much water could be gained from reducing irrigation. Then, they send out bids to the farmers in the area,” says Bosch.
In 2001, the Georgia Environmental Protection Division accepted offers from 194 farms to hold out 33,000 acres of irrigation throughout the year. The accepted bids ranged from about $30 to $200 per acre, with an average of about $135.
“This impacted farmers directly in terms of their inability to irrigate and ultimately in terms of the yields they were getting from their farms. The overall change was that farmers had to manage their land and reduce irrigation — they had to do a better job of planning. It certainly changed how people were looking at irrigation because they had to more closely regulate what their crop needed, and they had to justify that back to the state in terms of withdrawals,” says Bosch.
The plan, he says, affected the yield and profit farmers received from their land, and it made farming more complicated in terms of water withdrawal.
It was during this time, says Bosch, that researchers from the various universities and agencies began to look at conservation-tillage systems in terms of their environmental impact in the Coastal Plains Region.
“It already had been fairly well documented that conservation-tillage had significant water quality benefits in terms of reducing erosion and reducing runoff from the land. So we set up a controlled study where we could collect numbers that then would be used as guidance for farmers on using conservation tillage,” he says.
Bosch’s area of interest in the study was the impact of conservation tillage on runoff from the land, how much water is going into the soil, and how much is available to the plant. “More importantly, can conservation-tillage lead to a water or cost saving and to increased crop growth on farms in our region?”
The conservation-tillage study began in 1998 on a four and a half acre area that was divided into six separate tracts to compare conventional-tillage with conservation-tillage, he says. “We captured the surface runoffs, took water quality samples, and measured the amount of flow. We also had a subsurface tile system that captured the shallow flow within the profile, and then we characterized how much was leaving the plot in subsurface flow. We also measured the flow from the tile system.”
Three plots of strip-tillage and three plots of conventional-tillage were established in 1998, he says. Cotton was planted for three years, from 1999 to 2001. Then, a peanut/cotton rotation was begun due to problems with nematodes and continued from 2002 to 2006.
Looking at precipitation patterns, Bosch says the first four years of the study were drought years in Georgia, with lower-than-normal rainfall. Then, conditions began returning to normal in 2002, and the region received above-average rainfall from 2003 to 2005.
Researchers captured all surface runoff from the site, he says, and measured the volume and characteristics in terms of daily, seasonal and annual runoff. “As is expected, the conventional system generates more runoff than do the strip-tillage systems. In a strip-till system, you increase your infiltration into the soil. That translates into how much sediment is being carried with the surface runoff, and how much of the pesticides are being carried off with the sediment.”
On the average, says Bosch, surface runoff was about 60 percent more in conventional-tillage plots. “If you receive 50 inches of rainfall in a year, 30 inches of that is running off the surface. If you get more surface runoff from the conventional than from the strip-till, this translates into increasingly more water going into the soil profile of the strip-tillage system.”
Researchers also looked at a tile system where they measured the subsurface flow, he says. This measures how much is running off from the shallow portion of the soil, he explains.
“In strip-tillage, we’re putting more water into the soil, so naturally more of it is flowing into this tile system. We saw about 68 percent more subsurface runoff in the strip-till plots than in the conventional systems. It’s a bit of a trade-off. You’re losing more in the subsurface flow because you’re putting more into the profile.”
The next step in the study, says Bosch, is comparing the net gain between conventional and conservation-tillage — in terms of inches of water and the number of times farmers will have to irrigate.
“In the dry years, we get considerable gain from the strip-till system. We saw a significant gain in 2000 and 2001. In 2004, we were actually losing more water from the strip-till system. We had more water going into the profile that was running off into the tile flow. But on average for the seven years, we gained about 1 inch of water with conservation-tillage. This translates into one irrigation during the season.”
More important, he says, are the seasonal differences seen when comparing the two systems. “In this region, we tend to get high precipitation in January, February and March, reduced amounts in April and May, and then we have fronts from hurricanes and such during the summer, and we get very intense rainfall and high precipitation again in June, July and August. We get reduced precipitation in September and October, and then it kicks up again in December. This means that during the season we have very high ET where the water goes into the soil and the plants use it. There’s not a lot of runoff because of the dry conditions, despite the rainfall.”
During the winter, says Bosch, ET rates are low as water hits the soil and goes into the profile and into the groundwater. December to March, he says, is when surface runoff is high.
“The bottom line is that we can improve or at least get equivalent crop yields from strip-tillage. The general observation we see in terms of hydrology is that strip-till reduces the surface runoff which translates into more water that should be available to the plant. It also increases infiltration. We’re getting more residue on the surface, leading to more water going into the plant.
Conversely, strip-till does increase the subsurface flow from the plant. This certainly is a management issue. If you have water-soluble chemicals, you have to be more careful about putting more water through the profile.”
The biggest advantage to conservation-tillage has been seen in dry years, says Bosch. “If you have a dry year and get a rainfall event, you get all the moisture going into the soil. This translates into improved yields. If you have a wet year, and you have a saturated profile, you’ll get surface runoff in both systems.”
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