Seed-placed phosphate outperforms foliar applications

In this study, foliar phosphorus (P) application was unable to substitute for seed-placed P. Overall, foliar P had a marginal effect on grain yield, P uptake and seed nutritional value.

Generally, little research has been conducted in western Canada to assess the potential of foliar-applied phosphorus (P) in small grain crops. The objective of this study was to determine the effect of different proportions of soil- versus foliar-applied P on canola, hard red spring wheat, and green field pea.

The research was conducted on two adjacent fields, one used for the 2016 season and one for the 2017 season, in the Black soil zone near Pilger, Saskatchewan. The soil at the sites was classified as an Orthic Black Chernozem loam. The two fields had similar crop rotations over the previous decade, with little to no P fertilizer applied, and both were deficient in P at less than 7 PPM modified Kelowna extractable P.

The five treatments were: (C) control with no added P; 17.8 lbs. P2O5 /ac (20 kg/ha) seed-placed (SP); 13.4 lbs./ac (15 kg/ha) seed placed and 4.5 lbs./ac (5 kg/ha) foliar applied (F25); 9 lbs./ac (10 kg/ha) seed placed and 9 lbs./ac (10 kg/ha) foliar applied (F50); and all 17.8 lbs./ac (20 kg/ha) foliar applied (F100).

The seed-placed P was MAP (11–52–0) fertilizer. The foliar P source used was monopotassium phosphate (KH2PO4) dissolved in water, with dimethicone (Xiameter) adjuvant added to promote foliar absorption.

Foliar application to canola was at the 5–8 leaf stage prior to bolting (BBCH 15–18), and prior to flag leaf emergence (BBCH 43) for the wheat. The foliar P treatments were applied to peas at the 6–9 node stage (BBCH 36–39).

Seed-placed MAP generally yielded the highest

Overall, yield response decreased as the proportion applied as seed-placed MAP decreased. Of the three crops, canola was the most responsive to P fertilization in terms of yield and P uptake response, followed by wheat and pea.

Seed-placed MAP produced significantly higher canola yield in 2016 at 88 bu/ac (4.966 t/ha) compared to foliar P yields around 39 bu/ac (2.18 t/ha). In 2017, canola yields were not significantly different between P applications, likely due to low yields around 30 bu/ac (1.7t/ha). The 100% foliar-applied P treatment in canola was able to maintain significantly higher yield than the unfertilized control in the absence of seed-placed MAP, indicating some uptake and response.

Pea yield with seed-placed MAP (27 bu/ac) was significantly higher than foliar P (about 20 bu/ac) in 2017, but was not significantly different in 2016.

Overall, wheat yield and P uptake were not significantly affected by treatment in both years with yields ranging from 21 to 28 bu/ac (1.417 to 1.909 t/ha).

Source: Froese et al. 2019

The results of this study suggest that the overall uptake of foliar P fertilizer applied to plant leaves at canopy closure was not high enough to have a major impact on the P uptake, yield and quality. However, there was some indication of foliar P uptake. As a result, more research is needed to evaluate the potential of different foliar P fertilizer compounds, adjuvants, fertilizer nutrient blends, and application timing on different crops. There may be greater potential for foliar P to be used as a supplement fertilizer treatment to be added on top of seed-placed P as opposed to splitting the application of a fixed recommended rate.

This study was funded by the Agriculture Development Fund, Sask Canola, Sask Wheat, and Sask Pulse Growers.

S.Froese, J.T.Wiens, T.Warkentin, and J.J.Schoenau. Response of canola, wheat, and pea to foliar phosphorus fertilization at a phosphorus-deficient site in eastern Saskatchewan. Canadian Journal of Plant Science. 100(6): 642-652.

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