1. Excess moisture must be removed from food grains before storage. 2. After harvesting, crops are threshed and winnowed to obtain the grain. 3. Decomposition is the process in the nitrogen cycle where dead plants and animals are converted into ammonium. 4. Microorganisms significantly facilitate changes in nitrogen states in the soil.

1. Excess moisture must be removed from food grains before storage to prevent the growth of mold, fungi, and bacteria. When food grains contain too much moisture, they provide an ideal environment for these organisms to thrive. This can lead to spoilage, loss of nutritional value, and the production of toxins, such as aflatoxins, which can be harmful to both humans and animals. Furthermore, excess moisture can also encourage the proliferation of insects and pests that may infest the grains. To ensure long-term preservation and maintain quality, food grains are typically dried to a safe moisture level before being stored.

2. After harvesting, crops are indeed threshed and winnowed. Threshing is the process of separating grains or seeds from the stalks and husks. This can be done by beating the harvested crop to break the bonds holding the grains to the plant. Meanwhile, winnowing is a subsequent step where the grain is separated from the chaff (the lighter husks) typically using a wind or a fan. This is often done by tossing the mixture into the air so that the chaff is carried away by the wind while the heavier grains fall straight down.

3. Decomposition is an essential process in the nitrogen cycle where microorganisms, including bacteria and fungi, break down dead plants, animals, and other organic matter. During decomposition, complex organic compounds are converted into simpler substances, and in the case of nitrogen-containing compounds, they are often converted into ammonium (NH4+). This ammonium can then be used by plants or further processed by microorganisms in the soil to be converted into other forms of nitrogen, such as nitrates.

4. Microorganisms play a critical role in facilitating changes in nitrogen states within the soil. They are involved in processes such as nitrogen fixation, nitrification, and denitrification. Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into forms that plants can use, such as ammonia (NH3) or nitrates (NO3-). Other bacteria are responsible for nitrification, which is the conversion of ammonia to nitrites (NO2-) and then to nitrates. On the other hand, denitrifying bacteria can convert nitrates back to N2 gas, releasing it into the atmosphere and completing the nitrogen cycle.