| Abstrakt: |
Information on water absorption from the air by urea fertilizers and on NH3 loss when applied to grasslands is limited. Urea application to grassland is typically broadcast (Bcast), whereas urea‐ammonium nitrate (UAN) is applied either Bcast or in bands (dribble). This work was conducted to (1) evaluate water absorption from the air by Bcast granular urea, Bcast UAN, and dribble UAN under laboratory conditions, and (2) compare NH3 losses from Bcast urea, Bcast UAN, and dribble UAN when applied to a grassland. Six field studies were conducted from 2017 to 2019. In the laboratory, Bcast UAN exposed to 100% relative humidity absorbed water from air at a faster rate than dribble UAN and Bcast urea. In the field, all three fertilizers lost similar amounts of NH3 when applied to relatively wet soil (> −0.1 MPa). In contrast, when the fertilizers were applied to dry soil (≤ −1.2 MPa), Bcast UAN lost the most NH3 (17.3% and 19.8%) likely because of its capacity to absorb water from the air. Also, at −1.2 MPa, dribble UAN lost more NH3 than Bcast urea (15.3 vs. 10.7%, p < 0.05), probably because the low osmotic potential of UAN (−55 MPa) allowed it to absorb water from the soil at a faster rate than urea could absorb water from the air. In contrast, when the soil water potential was −5.7 MPa, dribble UAN lost less NH3 than Bcast urea (4.4 vs. 17.3%, p < 0.05), likely because the low soil water potential reduced its water absorption. Core Ideas: Water absorption from air was faster for broadcast (Bcast) urea‐ammonium nitrate (UAN) than from banded UAN or granular urea.Urea concentration in solution decreased faster below 6 mol L−1 in Bcast and banded UAN than in granular urea.Bcast UAN lost more NH3 than banded UAN or granular urea when soil water content was low (< −1.2 MPa).UAN (Bcast or banded) and granular urea lost similar amounts of ammonia when soil water content was high (> −0.1 MPa). Plain Language Summary: Granular urea or nitrogen solutions containing urea can be broadcast (Bcast) or applied in bands to grasslands, where they absorb water from the air or from the soil to release nitrogen to the forage. In grasslands, a significant portion of the applied fertilizer falls on leaves and therefore absorbs water from the air. This work was conducted to evaluate absorption of water from the air for Bcast and banded nitrogen solution and from Bcast granular urea. Bcast nitrogen solution absorbed water from the air at a faster rate than banded nitrogen solution or granular urea. This study also evaluated gaseous losses of ammonia from Bcast and banded nitrogen solution and from Bcast granular urea when applied to a grassland. Ammonia losses were similar for all three fertilizers when the soil water content was high, but when the water content was low, Bcast nitrogen solution lost more ammonia than banded nitrogen solution or Bcast granular urea. [ABSTRACT FROM AUTHOR] |
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