Effect of Broadcast versus Banded Phosphorus Application on Fate of Applied P in Soil and in Snowmelt Water Flow

Phosphorus moves very slowly in soil and is often called immobile. In soils that are somewhat deficient in P, it is important to place the P so that the roots of the crops grow into the area where the P fertilizer is placed. The objective of this study is to compare various placements of P fertilizer in relation to the seed row. These placement treatments included pre-plant banding below the seed row, seed row placement during the planting operation, pre-plant broadcast and incorporation, and pre-plant broadcast without incorporation. The study has been conducted for two years, soybean in 2014, and wheat in 2015. It is planned for canola in 2016. There were seven P treatments including a zero P control, with the four placement methods described above, all at 20 kg P₂O₅/ha, then two more broadcast without incorporation treatments at rates of 40 and 80 kg/ha. All treatments were replicated four times for a total of 28 plots, using a randomized complete block design.

Analysis of the 2015 wheat crop samples and soil samples is currently underway. The soybean yields were greater by placing the P fertilizer in the soil, either in the seed row, in a pre-plant band, or broadcast followed by incorporation, compared to any of the broadcast methods that were not incorporated. In the fall after harvest, each plot was sampled to assess soil-available P and other nutrients in the soil profile. A significant part of the research included a simulated snow melt study, that consisted of taking intact slabs (0 to 15 cm) of surface soil from selected treatment plots at the research site in the fall of 2014 and freezing them. The frozen slabs were placed in insulated boxes and snow placed on the surface followed by a simulated spring thaw. Water from the simulated snowmelt was collected and analyzed for soluble reactive P and particulate P. Fertilizer P application method and rate was found to have a statistically significant effect on total dissolved P (TDP). Broadcast application of fertilizer P at 20 kg P₂O₅/ha resulted in greater TDP export compared to the control treatment or when fertilizer P was placed in the soil (incorporated, seed row, or deep banded). The research results from the three crop years of research will be analyzed and a final report completed after the 2016 crop year.