Keeping soil, yields and income healthy
OKOBOJI — Since the 1800s, Iowa has lost between 30 and 70 percent of its original soil organic matter.
That’s according to Mahdi Al-Kaisi, Iowa State University professor of agronomy and ISU Extension soil and water specialist, who spoke at the Okoboji Crop Advantage conference recently.
Al-Kaisi said that statistic should make producers think.
“(Soil) carbon is money,” said Al-Kaisi, adding that Okoboji soil, found abundantly in northwest Iowa — naturally contains the most organic matter content because of the soil’s formation. “If your soil doesn’t have a good CSR, your (land) is worth less.”
He added regional soil and climate conditions have a big effect on soil organic matter and, in turn, the economic return of corn and soybeans, even using various methods of tillage and crop rotations.
Various tillage systems affect corn and soybean yields because different tillage practices produce changes in soil organic carbon and soil water availability.
According to Al-Kaisi, a long-term study by ISU measured yield, economic return of corn and soybeans, and soil carbon changes between 2002 and 2013, using no-till, strip-till, chisel plowing, deep ripping and moldboard plowing.
The three kinds of crop rotations used included a corn and soybean rotation, corn on corn to soybean rotation, and continuous corn.
Across all forms of tillage practices, Al-Kaisi said the corn-soybean rotation showed the greatest advantage for yield and economic return.
“Corn yield and economic return penalties with no-till were greater than conventional tillage, especially in the northern locations with poorly-drained soils, as compared to the southern locations with well-drained soils,” said Al-Kaisi.
Corn yield penalties associated with continuous corn were “location-specific,” he added, and varied from 11 to 28 percent across the state. Corn input costs were greater for conventional tillage systems (chisel plowing, deep ripping and moldboard plowing) compared to no-till (7.5 percent) and strip-till (5.7 percent).
“Soybean yields showed no significant response to different tillage systems at different locations, and the economic return with no-till of $509/acre exceeded that with conventional tillage at $502/acre,” said Al-Kaisi, who added soybean input using no-till was lower at $187/acre than with conventional tillage at $207/acre.
He went on to say that a corn-corn-soybean rotation resulted in greater soybean yields (9 percent) and economic returns (11 percent) than tests using the corn-soybean rotation in five of the seven testing locations across Iowa.
“(Crop) rotation effect on soybean yield was greater than the effect of tillage … where differences in soybean yields were not significant,” said Al-Kaisi.
Al-Kaisi called soil organic matter the “savior” of productivity and the heart of soil health. The physical, chemical and biological soil properties are all affected by the soil’s organic matter.
Testing done on fields in Sutherland (northwest Iowa), Kanawha (north central Iowa) and Crawfordsville (southeast Iowa) showed across the board that soil organic matter increased with no-till and strip-tillage practices with all three crop rotations (0.26 and 0.20 tons/acre/year at Sutherland; 0.20 and 0.15 tons/acre/year at Kanawha, and 0.24 and 0.16 tons/acre/year at Crawfordsville, respectively).
Soil organic matter in northwest Iowa decreased with chisel plowing, deep ripping and moldboard plowing, with the greatest loss stemming from the practice of moldboard plowing on corn-soybean rotations, followed closely by chisel plowing on corn-corn-soybean rotations.
Testing in north central Iowa showed the most soil carbon decreases with moldboard plowing in all three kinds of crop rotations. Following closely behind was the practice of chisel plowing — nearly the same results with all three kinds of crop rotations, and deep ripping resulted in significantly less soil organic carbon losses on all three crop rotations.
“Generally, the average gain in soil organic carbon with no-till and strip-till across all crop rotations and sites over 14 years was 0.23 and 0.17 tons/acre/year, respectively,” said Al-Kaisi.
He added the average soil organic carbon loss with chisel plow, deep rip and moldboard plow across the same rotations and sites was -0.28, -0.21 and -0.31 tons/acre/year, respectively. This shows that soil organic carbon gain or loss is highly affected by tillage intensity.
Spacial variability is also a contributing factor to yield variability (including hydrology, soil type and climate), and Al-Kaisi said that strip-till is highly competitive with conventional tillage systems in the areas of yield, fuel and labor.
Additionally, he said there was almost no difference in soybean yields among all tillage systems and that a decline in continuous-corn yield ranged from 11-28 percent compared to a corn-soybean rotation.
Al-Kaisi said major measurements for evaluating soil health include soil organic matter, microbial biomass, soil bulk density, water infiltration, aggregate stability and traditional N, P and K and pH tests.
Overall, he said tillage (especially intensive tillage) is hard on all of those factors, creating areas of surface run-off, decreasing soil organic matter and reducing aggregate stability.