Seed-placed phosphorus and sulphur fertilizers: effect on canola plant stand and yield
Hybrid canola has a high requirement for phosphorus (P) and sulphur (S). Conventional P and S fertilizers differ in their risk of ammonia and salt toxicity and can significantly reduce canola plant stands if applied in the seed-row above recommended safe rates. Enhanced efficiency fertilizers such as polymer coated monoammonium phosphate (cMAP), Vitasul, or Microessentials S15 (MES15) could be more seed-safe than conventional sources. Field studies were conducted to determine the effect of various sources and rates of seed-placed P and S fertilizers on plant stand and yield of canola. Soil properties may also affect the toxicity of the fertilizer. The risk of ammonia toxicity from ammonium sulphate (AS) may be especially severe on soils with a high calcium carbonate (CaCO3) content, which can frequently occur on eroded knolls in Canadian Prairie landscapes. A growth room experiment was conducted to determine the effect of soils from different landscape positions on the toxicity of seed-placed AS and monoammonium phosphate (MAP) with canola. Under controlled environment conditions, canola emergence was reduced and delayed by conventional sources of seed-placed P and S fertilizers due to salt and ammonia toxicity. Ammonium sulphate, in particular, has a high salt index and risk of ammonia toxicity, especially on calcareous soils; therefore, AS has a greater potential to reduce plant stands than MAP. Under field conditions, the highly available sources of P and S may increase the risk and severity of seedling toxicity, but they also increase the frequency and size of yield response in situations where these nutrients are deficient. Enhanced efficiency fertilizers (cMAP, MES15 and Vitasul) were effective in decreasing seedling damage, but may not be as effective as conventional sources in providing sufficient available nutrients to reach yield potential.
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