Fertilizer placement and tillage effects on phosphorus leaching in fine-textured soils

Authors: Williams, Mark; King, Kevin; Duncan, Emily; Pease, Lindsay; Penn, Chad

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2017
Publication Date: 1/10/2018
Citation: Williams, M.R., King, K.W., Duncan, E.W., Pease, L.A., Penn, C.J. 2018. Fertilizer placement and tillage effects on phosphorus leaching in fine-textured soils. Soil and Tillage Research. 178:130-138.

Interpretive Summary: No-tilled fields with clayey soils may be more susceptible to dissolved phosphorus (P) losses in tile drainage due to the greater potential for vertical stratification of P in the soil profile, formation of preferential flow pathways, and broadcast fertilizer application. In this study, we examine the effect of tillage and fertilizer application practices on P leaching. We tested three treatments during a rainfall simulation study on four fields in northwestern Ohio: 1) Broadcast (surface-applied fertilizer); 2) Till (surface-applied fertilizer incorporated with tillage 3 to 4 inches); and 3) Inject (fertilizer placed in slits 3 to 4 inches deep that were spaced 30 inches apart). Results showed that both till and inject treatments decreased dissolved P concentrations by approximately 70%. This suggests that injecting fertilizer into the subsurface may be a compromise between no-tillage and tillage, whereby injection not only minimizes soil disturbance and erosion, but also decreases dissolved P leaching.

Technical Abstract: Adoption of no-tillage in agricultural watersheds has resulted in substantial reductions in sediment and particulate phosphorus (P) delivery to surface waters. No-tillage, however, may result in increased losses of dissolved P in tile-drained landscapes due to the accumulation of P in surface soil layers and prevalence of preferential flow pathways. The objective of this study was to examine the effect of fertilizer placement and tillage on P leaching in fine-textured soils following fertilizer application. Rainfall simulations were conducted on plots with pan lysimeters (0.6 m depth) in four agricultural fields located in northwestern Ohio, USA. Three fertilizer placement treatments that covered a range of soil disturbance and soil-fertilizer mixing (broadcasted, injected, and tilled) were replicated on each field. Stable water isotopes were used to separate leachate into preferential and matrix flow components. Results showed that leachate dissolved P concentration was significantly greater when fertilizer was surface broadcast on no-tilled plots (43.7 mg L-1) compared to when the fertilizer was either injected (14.9 mg L-1) or tilled (11.0 mg L-1) into the soil. Event water comprised between 6 and 46% (mean = 22%) of lysimeter leachate and did not vary among treatments. Similar event water contributions among treatments suggest that the disruption of the macropore network was not likely the main mechanism responsible for decreased P leaching, but rather increased soil-fertilizer contact and decreased interaction between the highly soluble fertilizer and surface runoff were responsible for decreased P concentrations observed for the injected and tilled treatments compared to the broadcasted treatment. Findings indicate that subsurface injection of fertilizer has the potential to limit dissolved P leaching compared to surface broadcast applications and also minimize soil disturbance relative to tillage; thus, it should be considered a promising conservation practice to help meet water quality goals in tile-drained landscapes.