What issue can arise from using certain organic soil additives like straw and sawdust?

Using organic soil additives like straw and sawdust can lead to a nitrogen deficiency in the soil, which is why the correct answer is that it requires additional nitrogen. These materials are rich in carbon but relatively low in nitrogen. When they decompose, the microorganisms that break down these organic materials consume nitrogen from the soil in the process. This can result in reduced nitrogen availability for plants, leading to poor growth and nutrient deficiencies, particularly in nitrogen-sensitive crops.

In practice, this means that when these carbon-rich materials are added to the soil, it is often necessary to supplement the nitrogen levels, either by adding nitrogen-rich fertilizers or by incorporating other organic materials that contain higher amounts of nitrogen, such as manure. Understanding this relationship is crucial for effective soil management, particularly in organic farming systems.

The other options do not accurately reflect the primary issue associated with straw and sawdust. For example, while these additives can affect soil acidity and pH, the predominant concern during decomposition is their interaction with nitrogen levels in the soil, which stems from their high carbon content. Thus, managing the nitrogen input is essential when using these organic amendments.