ARS | Publication request: Cover crop effects on nitrogen load in tile drainage from Walnut Creek Iowa using root zone water quality model (RZWQM)

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2011
Publication Date: July 21, 2011
Citation: Singer, J.W., Malone, R.W., Jaynes, D.B., Ma, L. 2011. Cover crop effects on nitrogen load in tile drainage from Walnut Creek, Iowa, using root zone water quality model (RZWQM). Agricultural Water Management. 98(10):1622-1628.

Interpretive Summary: Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify effect of winter cover crops on nitrogen loads from tile drains in a subbasin of the Walnut Creek, Iowa (Story County) watershed using the agricultural system model Root Zone Water Quality Model (RZWQM) for corn-soybean and corn-corn-soybean rotations from 1981 to 2005. The results indicate that using a winter annual cover crop can reduce annual N loads from tile drains 24% in a corn-soybean rotation and 19% in a corn-corn-soybean rotation at the watershed subbasin scale over a long-term period. This research provides producers, land managers, and other agency personnel information that quantifies one of several benefits from using winter cover crops as a conservation practice.

Technical Abstract: Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from tile drains in a subbasin of the Walnut Creek, Iowa (Story Co.) watershed using the hybrid RZWQM-DSSAT model for a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] and corn-corn-soybean rotations in all phases with and without a winter wheat (Triticum aestivum L.) cover crop during a 25-yr period from 1981 to 2005. Simulated spring cover crop dry matter (DM) and N uptake averaged 1854 and 36 kg ha-1 in the corn-soybean phase of the 2-yr rotation and 1895 and 36 kg ha-1 in the soybean-corn phase during 1981-2005. In the 3-yr rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha-1 in the corn-corn-soybean phase, 2039 and 43 kg ha-1 in the soybean-corn-corn phase, and 1963 and 43 kg ha-1 in the corn-soybean-corn phase during the same period. Annual N loads to tile drains averaged 28.5 kg ha-1 in the corn-soybean phase and 25 kg ha-1 in the soybean-corn phase compared to 21 and 19.5 kg ha-1 in the same phases with a cover crop. In the 3-yr rotation, annual N loads averaged 46, 43, and 43 kg ha-1 in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha-1 with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 24% in a corn-soybean rotation and 19% in a corn-corn-soybean rotation at the watershed subbasin scale over a long-term period.