Submitted to: Proceedings of the Soil Science Society of America
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2006
Publication Date: 12/1/2005
Citation: Schepers, J.S., R.S. Tubbs, and J.L. Hatfield. 2005. Experiences with strip cropping soybeans into small grains in Nebraska. Proc. 2005 Indiana Certified Crop Advisor Conference. C.D. Dec. 13-14, 2005. Indianapolis, IN. Interpretive Summary: The situation in parts of Nebraska is that the shallow groundwater aquifer contains 20 to 30 ppm (mg/L) of nitrate-nitrogen or more. The safe drinking water standard in the U.S. is 10 ppm nitrate-nitrogen. An annual groundwater quality reporting system initiated in 1988 by the Central Platte Natural Resources District has documented increases in nitrate-nitrogen concentrations that are especially delineated by fields producing seed corn, popcorn, and potatoes and those receiving multiple applications of manure. Limitations already exist on when fertilizer can be applied and producers are required to use soil and water testing procedures to make better-informed nutrient and water management decisions. But, there are no restrictions on how much water, nitrogen fertilizer, or manure that can be applied. Beginning in 2001, wheat was planted as a scavenger crop in the fall after seed corn harvest to remove excess nitrate from soil so that it could not leach to groundwater. In late spring, a soybean crop was inter-seeded into the wheat that was heading. When the wheat was harvested in early July the soybean plants were 8 to 10 inches tall and quickly emerged into full sunlight. This study in now completing its fifth cycle with average wheat yields of 64 bu/acre and soybean yields of 51 bu/acre. These yields were ~20% lower than for monocrop production of either wheat or soybean. Environmentally, using wheat as a fall cover crop followed by soybean has been very effective at reducing soil residual nitrogen levels to a minimum because both crops can function as a scavenger. As with any more intensive production system, additional management skills are required to insure timely and appropriate practices. These extra efforts can be rewarded by extra profitability of $50 to $100/acre or more.
Technical Abstract: Seed corn is a high value crop and so yield is very important to producers. Input costs for nutrients and water are small relative to the return, especially when compared to commercial corn production. It doesn’t help that inbred plants used to produce hybrid seed are less vigorous than hybrids and so producers frequently tend to over-fertilize inbred fields. Residual nitrogen remaining in soil at the end of the growing season is subject to leaching resulting in ground water contamination. Using plants to extract excess nitrate from soil can be an effective way to protect against eutrophication of standing water, hypoxic conditions in lakes and oceans, or elevated nitrate concentrations in domestic water supplies. Wheat was planted in the fall after seed corn in 10-inch rows so that two rows could be positioned between recently harvested corn rows. This left an opening of 20 inches in the vicinity of the old corn row for inter-seeding soybean. A special track vehicle was used to plant the soybean crop in late May. Wheat was harvested in early July when the soybeans were 8 to 10 inches tall. Soybean matured in late September, thus completing the two-year cycle of three crops in two years. Environmentally, the combination of wheat and soybean after seed corn proved to be an excellent pair of scavenger crops by reducing residual soil N to low levels. Economically, wheat yields averaged 64 bu/acre over the four years of the study and soybean yields averaged 51 bu/acre. These yields were ~20% lower than for monocrop production of either wheat or soybean.