The intent of this study was to determine the feasibility of using minimum tillage on high-salinity ground rather than traditional tillage. Salts in the soil impede nutrient uptake and water movement to plants, reducing crop yield and quality. In the South Platte Valley of northeast Colorado, it is estimated that 119,000 acres are affected by moderate salinity, and another 22,100 acres are severely affected, causing a loss in corn production of $3.43 million.
The study site on the farm of Randy and Lisa Honstein covers 200 acres. Of that, 130 are irrigated by center pivot sprinkler with low-pressure drop nozzles and 70 are irrigated by open ditch and siphon tubes. Water is supplied to both areas from well water pulled from a river basin aquifer at about 60 feet. The area south of the pivot was plowed by traditional moldboard plow in April 2001. North of the pivot, a Schlagel machine was run at manufacturer recommendations, although it required continual adjustment in the wet ground. Experience with the machine helped to overcome the difficulties.
Soil and plant characteristics varied from one site to the other during the growing season, but no differences were found in the grain yield or quality.
Given the few differences in the results, and because of higher weed pressure in the minimum tillage plot that required greater expense to manage, the project team concluded that changing to minimum tillage would not be economically feasible at this time.
The study area was planted to corn on May 6, 2001. Emergence in the minimum tillage portion was rated good to excellent, and the traditionally plowed portion was rated excellent.
At cultivation, the minimum till surface was dry and hard, and the leaves and stalks from the previous year were visible, having been slow to decompose. In addition, weeds flourished in the minimum tillage area, requiring spraying several times to control field bindweed, Canada thistle and lambs quarter.
The plants in the minimum till portion were light green to yellow at 1½-feet high, while plants in the traditionally plowed portion were dark green. The discoloration may have been related to a soil deficiency, but was more apparent in the minimum tillage portion and in areas where salt concentrations were high.
Tensiometers, provided by the North Colorado Water Conservation District, were placed at 12, 18 and 36 inches to monitor water availability and indicate irrigation needs for optimal plant growth. The well water was tested to assess salinity level to see if the salts in the water contribute to the problem or whether the salts come mainly from the soil, which comprises the marine seabed of ancient salty inland seas. Indeed, the well water was found to be a major source of salts, with an electro-conductivity rating of 3.18 in well No. 1 and 2.47 in well No. 2. A rating of 2.6 is considered a severe problem.
Soils tests conducted in November 2001 showed sodium levels of 341 parts per million on the portion under minimum tillage and 376 parts per million where the ground had been plowed. This may indicate that the salts leach easier in the minimum till ground. The minimum tillage portion that is flood irrigated soaked well despite surface residue. However, the water infiltrated faster in the plowed portion than in the minimum till portion two out of three times, both in the furrows and on the ridges.
For now, the Honsteins say that changing tillage equipment is not feasible based on cost alone. As yields averaged the same on both areas of the study, it would not be advisable at this time, they said. In addition, the weed pressure was greater in the minimum tillage area, creating an additional expense in chemicals for control and creating more compaction during spraying.
Studies such as this are needed to find appropriate methods of irrigating high-salinity soils with the least impact on crop performance.
“I believe this project alerted some people to a very real problem that is not going to go away soon without assistance,” writes Randy Honstein in the project’s final report. “We made some wonderful contacts and received a lot of useful information along the way. The feedback we received has been positive and encouraging.”
FARMER ADOPTION AND DIRECT IMPACT
Given that the project found no immediate reason to change tillage practices, there have been no results that other producers can adopt. However, the study has raised awareness in the area of the need to address the persistent salinity problems.
FUTURE RECOMMENDATIONS OR NEW HYPOTHESES
With one year of study, the differences in the two tillage systems were nominal. However, project members suggest that greater differences would likely be found if such a study were to be conducted over five years in conjunction with a study of the river level, water table levels and precipitation.
“As we have determined that the well water contributes a significant amount of salts to the soil, leaching those salts through the soil becomes a major factor to consider,” says the project’s final report. “With high water tables and significant river flow this leaching is inhibited. There is much more to be learned about salts and the soil.
Another consideration in future studies is weed pressure. Apparently, increased weed pressure and the reduced effectiveness of chemical controls were attributable to a waxy film the plant produces naturally from the salts in the soil and in the root system.
“This is an issue that should be addressed if further studies of this nature are to be conducted.”
DISSEMINATION OF FINDINGS
The Honstein farm served as the launching pad and end-of-tour barbecue site for a salinity tour June 14, 2001, conducted with the Sterling, Colo., field office of the Natural Resources Conservation Service and attended by farmers, scientists, legislators and producers.
Joan Waldoch, editor of the Colorado Farmer-Stockman, attended the tour, interviewed the Honsteins and wrote a cover story for the August 2001 issue of the magazine. In addition, congressional aides on the tour took extensive notes and have since requested input on how to direct funds to be most useful.
In June 2002, the Colorado Foundation for Agriculture hosted a summer institute for teachers to educate them and give them direct contact with producers. The teachers visited the Honstein farm, where they were shown the saline soils and the maps and equipment used to process data. One teacher from Denver returned to spend a day on the farm, and she is now incorporating what she learned into her lessons.
Given the thousands of acres affected by high salinity, many producers in the area have been interested in the project, including Randy Jenik and Rob McClary, both of whom discussed their problems with salts in their soils and water.