Submitted to: Beltsville Agricultural Research Center Symposium
Publication Type: Abstract Only
Publication Acceptance Date: May 4, 1992
Publication Date: N/A
Technical Abstract: Nitrates produced in the soil following the killing of alfalfa can be leached towards and finally into groundwater if not absorbed by subsequent crops. A series of replicated field experiments were conducted over a six year period to determine the amount of nitrate that is formed in the soil following the killing of alfalfa, factors that control the rate at which it is formed, and if the amount is sufficient to provide the nitrogen needs of cereal grains and corn. Results showed that tillage enhanced decomposition processes so that nitrate formed in the soil about two weeks earlier following alfalfa killing than when no tillage was done. Sufficient nitrate becomes available from alfalfa roots and nodules to supply to needs for corn and cereal grains but the alfalfa must be killed in late summer or early fall to provide sufficient mineralization time to provide adequately for cereal grains whereas it can be killed in the spring or provide adequately for corn. the best crop to grow following alfalfa the first year is corn. In plots where alfalfa was killed April 7, the top 61 cm of soil contained 280 kg nitrate-N ha-1 where small corn plants were growing and 331 kg nitrate-N ha-1 where there was no corn on July 5. By September 13, after the corn had matured, the top 152 cm of soil contained only 116 kg nitrate-N ha-1 but where no corn was grown to remove the nitrate, it had concentrated to 625 kg nitrate-N ha-1. Nitrate continues to form in the soil after corn matures, and seeding winter cereal soon after corn harvest is a good practice to capture that nitrate into a crop and reduce the potential for winter leaching.