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 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 has been conducted for three years, specifically soybean in 2014, wheat in 2015, and 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.

The 4R Nutrient Stewardship has been proposed as an effective framework for the application of fertilizers. As a part of this framework, an agricultural producer should consider the right source, right rate, right time, and right place when making decisions about fertilization. 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 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 remain in the plant available inorganic orthophosphate form compared to broadcast application, regardless of incorporation. This finding is in line with our previous results that band placement resulted in greater uptake and recovery of applied fertilizer P. Ongoing work will evaluate the effectiveness of the P speciation techniques to reveal the nature of P in the run-off water, from samples taken during the study.