What type of nitrogen form in manure analysis is readily plant available?

The correct answer is ammonium-N. This form of nitrogen is readily available to plants because it can be directly taken up by plant roots without any further transformation. Ammonium (NH4+) is a positively charged ion that plants can absorb directly, making it an efficient source of nitrogen for plant growth.

In manure, nitrogen content can be present in various forms, some of which require conversion before plants can utilize them. Ammonium-N is distinct in that it does not require mineralization or nitrification processes to become available. As such, it contributes to the immediate nitrogen supply upon application to the soil.

Total-N includes all forms of nitrogen present in the sample, but it does not indicate availability. Organic-N represents nitrogen that is part of organic matter and requires microbial activity to be converted into plant-usable forms, making it less immediately available. Nitrite-N, while technically a form of nitrogen, is typically found in very small quantities and is considered a temporary state in the nitrogen cycle, as it quickly nitrifies to nitrate, which is also plant-available but not as immediate as ammonium. Thus, ammonium-N is the most readily plant-available form of nitrogen found in manure analysis.