Describe how waterlogging of soil affects the availability of nitrates to plants.

An organic farmer cultivates alfalfa (a leguminous crop) in a crop rotation system. Before sowing a crop of wheat, the alfalfa is chopped and tilled directly into the soil. Suggest how this agricultural practice leads to an increased wheat yield.

Explain why only about 10% of the energy stored in the biomass of the wheat is transferred to the primary consumers (herbivores) that feed on it.