RYE COVER CROP EFFECTS ON CORN YIELDS AND NITRATE LEACHING

REFERENCE 
Martinez-Feria R.A., R. Dietzel, M. Liebman, M.J. Helmers, S.V. Archontoulis (2016) Rye cover crop effects on maize: A system-level analysis, Field Crops Research. doi: 10.1016/j.fcr.2016.06.016.
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HYPOTHESIS
The effect of rye cover crop on corn yield, water and nitrate leaching in subsurface drainage is proportional to the amount of rye biomass produced at termination.  

METHODOLOGY
We tested the hypothesis by synthesizing experimental, literature and APSIM model results to perform a comprehensive systems level analysis and shed light into the underlying mechanisms by which rye affects corn-based systems in Iowa (Fig. 1). We considered six years of data on soil moisture, soil temperature, water and nitrogen leaching, rye above and below ground biomass and its carbon and nitrogen concentration, corn yields and N uptake at harvest. We supplement these data with 30-yr APSIM model simulations and literature data to develop robust relationships to support deeper understanding and decision making. ​

Figure 1. Framework of the the abiotic mechanisms by which rye cover crop can affect corn yield and N losses

KEY FINDINGS​

1. Experimentally, rye cover crop reduced drainage by 12% and NO3-N losses by 20% (or 31% per unit of N applied), and corn yields by 6%.
2. We also found minimal effects on soil temperature, water deficits that reduced yields only during drought years (2012 and 2013), and lower NO3-N losses that were related to reduced NO3-N concentrations in drainage.
3. APSIM model scenario analysis (4 termination dates × 30 years) indicated that rye cover crop decreases NO3-N losses (-25.5 ± 26%) but does not always reduce drainage water (-3.9 ± 13%) or grain yields (-1.84 ± 6%), which is consistent with experimental and literature results. However, analysis of the synthesized measured and simulated dataset do not support a strong relationship between these variables and rye biomass (Fig. 2).

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Figure 2. Simulated relative treatment differences in corn yield, annual tile drainage and annual NO3-N losses versus rye biomass production (top panes) compared to relative differences from values reported in studies conducted in the US Midwest (bottom panes)