OPTIMIZING SOIL BASE SATURATION FOR ENHANCED CANOLA (Brassica napus) PRODUCTION

Bishal Lamsal

Soil acidification is a growing concern for farmers in the inland Pacific Northwest (iPNW) for canola (Brassica napus) production. The problem arises from the use of ammonium (NH₄⁺)-based nitrogen (N) fertilizers, in which NH₄⁺ undergoes nitrification, producing hydrogen (H⁺), which causes soil acidification. Acidic soil leads to the reduction of soil base saturation (BS%) and induces aluminum (Al) toxicity, which can restrict canola growth and development. Assessing the soil and canola response to liming is crucial for proper amelioration of soil acidity. Therefore, this study aimed to (i) quantify the effect of increasing lime rates (LR) on key soil chemical attributes and plant mineral nutrients, (ii) determine the thresholds and relationships among the soil acidity indicators and their linkage to canola yield and productivity, and (iii) identify the optimal BS% and LR targets for maximizing canola productivity and effective correction of soil acidity. A greenhouse experiment (GE) and a field experiment (FE) were conducted, and in both experiments, liming significantly increased BS%, soil pH, and exchangeable calcium (Ca), while significantly reducing potassium chloride-extractable aluminum (KCl-Al) and soil acidity (AC). KCl-Al declined exponentially in response to liming and dropped to non-phytotoxic levels within the pH range of 5.5–5.6, the BS% range of 81%–86%, and the AC range of 2.1–2.7 cmolc kg⁻¹ across both experiments. Similarly, canola seed yield, biomass, root development, and reproductive traits showed nonlinear responses to liming and were strongly associated with soil chemical attributes. Plant productivity was consistently optimal at BS% in the 82–89% range and declined with increasing KCl-Al, approaching near-zero productivity at approximately 30–40 mg Al kg⁻¹ soil in GE and 20 mg Al kg⁻¹ soil in FE. Similarly, with an approximate threshold of 2.0 cmolc kg⁻¹, AC outlined functional and toxic zones for canola development. Overall, BS% acted as a reliable indicator of both soil chemistry and canola productivity. To develop a practical framework for optimizing BS% and correcting soil acidity to achieve the functional elimination of Al toxicity and improve soil fertility, our study suggests a target of 85% BS% in acidic soils of eastern Washington.

OPTIMIZING SOIL BASE SATURATION FOR ENHANCED CANOLA (Brassica napus) PRODUCTION

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