Relationships of soil nitrogen level to yield and nitrogen content in corn

Yield data for this investigation were collected from corn plots that were located on a Sequatchie loam soil with added fertilizer nitrogen levels of 0, 60, 120 and 180 pounds of N per acre. Soil samples were collected from each plot at depths of 0-6 and 6-12 inches when plants were approximately two feet high, during the ear leaf stage of growth and at maturity. Leaf tissue samples were collected during the ear leaf stage of growth. Percent nitrogen in leaf tissue along with NO₃-N and total NH₄-N in soil samples were determined on the Technicon AutoAnalyzer. Nitrate nitrogen in leaf tissue was determined with the Orion 701 digital pH meter equipped with a nitrate electrode. Soil samples were also analyzed for NH₄-N by two procedures that were modifica-tions of the total NH₄-N procedure. Correlation coefficients were determined between various plant and soil nitrogen measurements taken during three different stages of plant growth and each of these measure-ments were also correlated with yield data. During the two feet high stage of growth, total soil nitrogen and soil NO₃-N were both found to be poor indicators of the nitrogen status of soils for com production. However, yield was significantly correlated with the amount of NH₄-N in the upper six inches of the soil profile using the extraction procedure that was proposed and used in this study. The nitrogen extracted by the partial digestion procedure used in this study was significantly correlated with yield during this stage of growth at both depths to which soil samples were collected. Soil organic matter and total NH4₃-N in the 0-6 and 6-12 inch layer of the soil profile were both significantly correlated with corn yield during the ear leaf stage of growth. Soil organic matter at a depth of 6-12 inches was highly significantly correlated with yield during this stage of growth. Airanonium-N determined by the partial digestion procedure in the upper six inches of the soil profile during the ear leaf stage of growth was highly significantly correlated with yield. Neither soil NO₃-N nor NH₄-N determined by the extraction procedure were found to be significantly correlated with corn yield during the ear leaf stage of growth. The amount of NO₃-N in the soil at a depth of 0-6 inches was significantly correlated with the percent N in ear leaf tissue but the percent N in ear leaf tissue was not significantly correlated with yield. The amount of NH₄-N determined by the extraction procedure in the upper six inches of the soil profile was highly significantly correlated with the percent NO₃-N in ear leaf tissue but the percent NO₃-N in ear leaf tissue was not significantly correlated with yield. No other soil nitrogen measurements were found to be significantly correlated with the amount of nitrogen in the plant.