Estimates of residual dairy manure nitrogen availability using various techniques

Area of Science:

• Agricultural Science
• Soil Science
• Agronomy

Background:

• Repeated dairy manure application is common practice.
• Accurate assessment of plant-available nutrients necessitates accounting for residual soil nutrients from prior manure applications.
• Understanding residual nutrient dynamics is crucial for sustainable agricultural management and nutrient use efficiency.

Purpose of the Study:

• To quantify the residual nitrogen (N) availability from semisolid dairy manure in the second and third years after application.
• To compare different methods for estimating residual manure N availability, including fertilizer N equivalence, difference, and relative effectiveness methods, alongside 15N-labeled manure recovery.
• To provide reliable estimates of residual N availability for improved nutrient management planning.

Main Methods:

• A field experiment was conducted on a Plano silt loam soil from 1998 to 2003.
• Plots received semisolid dairy manure at two rates, applied annually, every 2 years, or every 3 years.
• Residual N availability was assessed using fertilizer N equivalence, difference, and relative effectiveness methods, and by measuring the recovery of 15N-labeled manure.

Main Results:

• Second-year residual N availability estimates varied by method: 12% (fertilizer equivalence), 8% (difference), and 4% (relative effectiveness).
• Third-year residual N availability estimates were 3% (fertilizer equivalence), 1% (difference), and 5% (relative effectiveness).
• Recovery of 15N-labeled manure showed 6% and 2% availability in the second and third years, respectively, with substantially reduced year-to-year variability compared to other methods.

Conclusions:

• Methods like fertilizer N equivalence, difference, and relative effectiveness exhibited significant year-to-year variability in estimating residual N availability.
• The use of 15N-labeled manure significantly reduced variability, enhancing confidence in residual N availability estimates.
• Recommended second- and third-year residual N availability from single semisolid dairy manure applications are 9-12% and 3-5% of the original application, respectively.