Nitrogen Fertilizer Replacement Value of Soybean for Corn
2007
Swink, Sheryl N. | Ketterings, Quirine M. | Cox, William J.
Soybean (Glycine max. (L) Merrill) is often grown in rotation with corn (Zea mays L.) and, in response to increasing N fertilizer prices, growers ask about possible N fertilizer savings for first year corn after soybean. A literature review was conducted to evaluate potential causes for site and year differences in soybean N fertilizer replacement values (NFRVs) and predictability of N fertilizer rate adjustments for corn after soybeans. Two types of rotation effects were identified, those that can be compensated for with fertilizer N application (N rotation effects), and ones for which fertilizer N application does not compensate (non-N rotation effects). The latter included interruption of pest cycles, improved soil physical properties, moisture availability, and changes in mycorrhizal fungi communities. Soybean NFRVs reported in the literature ranged from 0 to 188 lb of N per acre. Soybean yield was not a reliable predictor of NFRV and adjustments in N rates should only be applied for one year after soybeans. We conclude a NFRV of 20 to 30 lb of N per acre can be applied for first year corn after soybean with minimal risk of a negative impact on yield. Additional research is needed to quantify impacts of management and environment (rotation, tillage, soil type, weather) on NFRV of soybean for corn.
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