The most important nutrient for oil production is

Nitrogen (N) is the most important nutrient for oil production in oilseed crops because it plays a fundamental role in plant metabolism, growth, and seed development.

Why is nitrogen essential for oil production?
Protein and enzyme synthesis: Nitrogen is a key component of amino acids, which form proteins. These proteins regulate metabolic pathways involved in oil biosynthesis.
Chlorophyll formation: Nitrogen is essential for chlorophyll production, which supports photosynthesis—the process that provides energy for oil accumulation.
Enhanced seed development: Oilseeds such as soybeans, canola, and sunflower require high nitrogen availability to maximize oil content in seeds.

How does nitrogen impact oilseed crops?
In soybeans and canola, nitrogen increases seed oil content by improving lipid metabolism.
In sunflower crops, nitrogen improves both seed yield and oil percentage by supporting the synthesis of fatty acids.
Adequate nitrogen supply ensures better seed filling, which directly influences oil quantity and quality.

Comparison with other nutrients:
Sulfur (S) is important for certain enzyme functions but is not the primary driver of oil synthesis.
Magnesium (Mg) supports photosynthesis but has an indirect role in oil production.
Zinc (Zn) helps enzyme activation but does not directly influence oil yield.

Conclusion:
Nitrogen has the most significant impact on oilseed crops because it directly influences the metabolic processes required for oil formation.
A proper nitrogen supply enhances oil yield, seed quality, and overall crop productivity.