Calibration of Nitrogen Content of Soil with Sweet Corn

It was found that quantitative and qualitative indices of the sweet corn yield correlate with the nitrate nitrogen content of the upper soil layer (0-30 cm). As no correlation was established between the nitrate nitrogen content of the lower layers and the sweet corn, the conclusion was drawn that the quantity of sweet corn yield is determined even before its roots reach deeper down than 30 cm and the nitrogen content of the lower layers could affect the sweet corn. Depending on the NO ₃ -N content of the soil before fertilization the maximal corn ear mass achievable with fertilization may vary. In the study the same yield could not be accomplished in the case of the lowest soil nitrogen concentration (2.9 mg NO ₃ -N/kg) with the highest fertilizer rate (200 kg N/ha) - but probably irrespective of any amount of fertilizer - as on the soil of 4.6 mg NO ₃ -N/kg. In the case of the poorly supplied soil the fertilization curve becomes flat sooner or turns negative. The phenomenon that, regarding various soils, the maximal yield achievable on soils with good production features with fertilization is higher than in the case of soils having worse features, is well-known. That this fact is also valid in the case of the same soils was expected after calibration experiments carried out with winter oilseed rape and beet root, but it has not been proven for sweet corn as yet. The results also showed that the grain dry matter production of sweet corn per hectare can still be enhanced with the increase in the soil's nitrogen supply, even if the corn ear does not grow. The presented calibration curves show - in the range of 2.9-4.6 mg NO ₃ -N/kg soil - how much corn ear and grain dry matter produce are expected on soils with differing nitrogen supply, distributing 0-200 kg nitrogen fertilizer in spring.