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

Phosphorus (P) moves very slowly in the soil and is often called immobile. In soils that are 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 P fertilizer placement methods in relation to the seed row. These 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 was conducted in the field for three years, specifically soybean in 2014, wheat in 2015, and canola in 2016. In 2017 further laboratory analyses have been conducted to improve the understanding of the fate of applied P in the fertilizer treatments. There were seven P treatments including a zero-P control, with the four placement methods described above, all at 20 kg P₂O₅/ha, and 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.

Measurements have been completed on plant and soil samples taken during the three years of field research. These measurements included: grain and straw yield, P uptake and removal, post-harvest soil and residue P amounts, forms and distribution - extraction, PRS, sequential, x-ray absorption near edge structure (XANES), P-31 nuclear magnetic resonance (NMR) spectroscopy identification of soil P forms, and run-off water P forms and amounts - chemical speciation and P-31 NMR. The work conducted to date in this project supports the implementation of several agricultural methods that fit within the 4R Nutrient Stewardship framework, specifically regarding the right place and the right rate of fertilizer application. The findings so far suggest that in-soil placement of fertilizer P, especially in a band, may be considered as an effective method to achieve the greatest yield response, as well as limit the potential off-site transport of applied P. In general, placement of fertilizer P in a band below the seed row caused a greater proportion of applied P to be absorbed into the plant as available inorganic orthophosphate. These findings are in line with our previous results that band placement resulted in greater uptake and recovery of applied fertilizer P. Ongoing work will further evaluate the effectiveness of the P speciation techniques to reveal the nature of P residual in the soils and in the runoff water. A final report from this project will be added to the IPNI Research Database when completed.