Addressing Pre-Sidedress Nitrogen Testing in Fields Injected with Dairy Slurry.

Addressing Pre-Sidedress Nitrogen Testing in Fields Injected with Dairy Slurry

Andrew M. Bierer¹, Rory O. Maguire¹, Michael Strickland², Wade Thomason¹, and Ryan Stewart¹

¹Department of Crop and Soil Environmental Sciences, Virginia Polytechnic and State University, Blacksburg, VA

²Department of Biological Sciences, Virginia Polytechnic and State University, Blacksburg, VA

Manure has traditionally been surface applied, but injection in strips under the soil surface is becoming more common as it increases nitrogen capture and decreases odors. However, difficulty has been encountered in taking a representative soil sample in fields utilizing manure injection equipment compared to surface applications of manure. Pre-sidedress nitrate testing (PSNT) is a soil test designed to guide sidedress applications of in-organic nitrogen. Standardizing a method for PSNT sampling fields injected with manure will provide increased accuracy of fertilizer recommendations while also providing a method for extension services to recommend farms utilizing injection. A field study was conducted in 2016 and 2017 testing two different soil sampling techniques for PSNT. Soil nitrate was compared seasonally between plots treated with a surface application of dairy slurry and injection of dairy slurry. Further, corn yield and forage quality were compared between manure applications. Results from 2016 indicate that taking equally spaced soil cores across the injection slit results in lower sample variance than the area based samples taken directly across the slit and between slits. Manure application method did not affect corn yield significantly, although it appears that nitrogen may not have been yield limiting. Additionally, forage analyses did not differ between methods of manure application. Providing a standardized method for PSNT sampling injected fields will increase the accuracy of fertilizer recommendations as well as improve comparisons between injection studies using soil nitrate sampling.