Research Objective
To determine the crop response to foliar applied phosphorus (P) fertilizer, applied alone and in combination with soil applied P; to determine the efficiency of the added P fertilizer in recovery by the crop and increasing the yield.
This study evaluated the response (agronomic, nutritional, and environmental) to foliar mono-potassium phosphate (KH2PO4) fertilization of canola, peas, and wheat grown in Brown, Dark Brown, and Black soils in Saskatchewan. In a randomized complete block design (RCBD), each phosphorus (P) fertilization treatment plot received equivalent P fertilizer rates of 20 kg P2O5 ha-1, with varying proportion of P applied as seed-placed mono-ammonium phosphate (MAP) versus foliar KH2PO4.
The treatments were:
1) control with no added P;
2) 20 kg P2O5 ha-1 seed-placed MAP;
3) 15 kg P2O5 ha-1 seed-placed and 5 kg P2O5 ha-1 foliar applied;
4) 10 kg P2O5 ha-1 and 10 kg P2O5 ha-1 as seed-placed and foliar applied P;
5) No seed-placed MAP with all 20 kg P2O5 ha-1 as foliar applied P.
Foliar treatments were made prior to anthesis in controlled environment studies conducted with two soils (Echo and Krydor associations), and field studies with four soils (Echo, Krydor, Sutherland, and Weyburn associations) in 2016 and 2017.
Of the three crops, canola was the most responsive to foliar P fertilization in terms of yield and P uptake response, followed by wheat, and peas. Peas showed little response to P fertilization in general, attributed to its ability to effectively scavenge soil reserves of P. Evidence of P uptake through canola and pea leaf material was observed, but foliar P application did not effectively balance off the yield lost by reduced rates of seed-placed MAP fertilizer. Foliar P fertilization at the rates applied in this study had limited effect on human nutritional value of the grain, as assessed through effect on grain zinc (Zn), iron (Fe), and phytate concentrations. Furthermore, there were no large discernible impacts of proportion of P applied in foliar versus soil-applied on the dissolved reactive inorganic P (DRP) measured in simulated snowmelt runoff from post-harvest soils in controlled environment and field studies. It is concluded that midseason foliar P applications would be most suitable for a top up of P nutrition, applied in small amounts under conditions of soil P deficiency, rather than a substitution for seed-row applied P fertilizer. It may be most suitable for canola where P demands are high and amounts applied at seeding in the seed-row may be limited
by seed-row safety concerns.