Nitrogen is an essential nutrient for plant growth, but it must be available in a form plants can use.They can use ammonia (NH₃), but not atmospheric nitrogen gas (N₂).Legumes such as peas and beans have nodules on their roots that contain Rhizobium, a nitrogen-fixing bacterium that can trap N₂ and transform it into NH₃.Suppose two similar fields are planted, one with corn alone, and one with corn and soybeans combined.How would the growth of corn alone be likely to compare with the growth of corn combined with soybeans? A) Corn alone would be nitrogen limited and show less growth. B) Corn alone would prevent nitrogen limitation by finding a way to use N₂. C) Corn alone would grow better because it would not be competing with soybeans. D) Corn alone would attract Rhizobium and develop root nodules to fix atmospheric N₂. E) Corn alone would grow at approximately the same rate with or without soybeans.

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Corn alone would likely be nitrogen limited and show less growth because it cannot use atmospheric nitrogen gas (N₂) and may not have access to enough ammonia (NH₃) in the soil. However, when combined with soybeans, the nitrogen-fixing ability of the soybean plants can provide nitrogen for both crops, leading to better growth for both corn and soybeans.

Nitrogen Is an Essential Nutrient for Plant Growth, but It