Title:

Can starter fertilizers improve plant nitrogen uptake by cycling through microbial and mineral pools?

Over 50% of the crop nitrogen (N) originates from the soil organic matter pool (SOM-N) while the contribution of applied N fertilizers to this pool is unknown. We conducted i. a laboratory incubation experiment with two different soils (from New Hampshire and Nebraska, USA; NH and NE) in mesocosms (no plants) over 6 weeks and ii. a subsequent field microplot experiment with corn at NH and NE to show how the rate, form, and placement of starter fertilizers influence internal N cycling. The starter fertilizers were InFurrow, a proprietary biostimulant nutrient solution (AgSpectrum, Iowa, USA), and 28% urea ammonium nitrate (UAN) injected in mesocosms alone, and in combination, at concentrations equivalent to 1x and 2x the rate of typical field application. In the field, at planting, InFurrow was applied in crop row while UAN was banded 4-6 inches from crop row. These fertilizers were labeled at 10 at% with 15N. Destructive soil samples (in mesocosms at days 14 and 48) and plant samples at V3 and V6 stage (field) were collected and separated into several N pools for analysis: whole soil, mineral-associated OM (MAOM), total dissolved N (TDN), and microbial biomass N (MBN), roots, and shoots. Out of the total fertilizer applied, we recovered about 47-66% in the TDN, 5-30% in the MAOM, and 5-17% in the MBN at day 14 and day 48 of incubation. In the field, small applications of InFurrow fertilizer had similar or greater recovery in shoots as well as in MAOM than much higher rates of UAN fertilizer at the V3 stage. This study will help indicate how microbial processing of fertilizer N and mineral and organic storage of fertilizer N can inform best practices for optimizing NUE of starter fertilizer in agricultural soils.

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