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Nitrogen Concentration of Young Corn Plants as an Indicator of Nitrogen Availability

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

M. E. Cerrato

Dep. of Soil Sci., Univ. of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2

^* Corresponding author.

Soil tests for evaluating the N status of cornfields in late spring show promise as a tool for improving N management during corn production. An alternative tool for evaluating N status is tissue testing, which offers the potential advantages of easier sampling and better integration of factors that influence N availability. Here we evaluate total N concentrations of whole corn (Zea mays L.) plants in late spring as an indicator of N availability in cornfields. Studies were conducted at 14 site-years in Iowa during 1986, 1987, 1988, and 1989. Whole plant samples were taken when corn was 15 to 30 cm tall. Total N concentrations in these plants were determined. Relationships between concentrations of N in young plants and fertilizer N applied were not consistent across the 14 site-years. The concentrations of N in young plants were poor predictors of soil NO₃ concentrations in situations where good relationships between soil NO₃ concentrations and grain yields occurred. The tissue test could not detect excessive amounts of NO₃ in soils. Concentrations of N in young plants were greatly influenced by factors having relatively little effect on final yields. Overall, the results show that a tissue test based on the concentrations of N in young plants would not be a reliable indicator of the N availability in cornfields.

Received for publication May 10, 1991.