Manure injection effects on soil nitrate, carbon mineralization, and POXC dynamics and spatial distribution under corn silage

Abstract

Manure injection is an alternative manure application method that can alter the spatial distribution of manure relative to surface application. Eight study sites were established to assess how manure injection versus surface broadcasting affects corn (Zea mays L.) silage growth, soil nutrient dynamics, and spatial distribution. Specifically, corn silage yield, nitrogen (N) uptake, soil nitrate (NO₃-N), carbon mineralization (C-min), and permanganate oxidizable carbon (POXC) were measured. Soil samples were taken to represent whole plot soil means for both treatments, while in-band (IB) and between-band (BB) soil samples were taken in injected plots to assess nutrient spatial distribution after injection. Corn silage yield and N uptake did not differ between injection and broadcast treatments at 7 of 8 sites but was greater under injection in the one site that did not receive a sidedress N application. No consistent differences in soil NO₃-N were seen between treatments; however, a clear alteration in soil NO₃-N spatial distribution was observed with IB > BB = surface. Manure injection did not result in any consistent differences (p > 0.05) in POXC or C-min compared to broadcast plots, nor did it result in an alteration in their spatial distribution. This study shows manure injection alters the spatial distribution of soil NO₃-N, specifically elevating it in the injection band, but this was difficult to pick up when using the equi-spaced method to represent the whole injection application area. The inability of POXC and C-min to detect changes related to spatial variation under injection casts doubt on their utility as short-term indicators for changes in C in manured systems.