Correlations between Soil Nitrate Concentrations in Late Spring and Corn Yields in Iowa

Abstract

A soil test for improving N management is greatly needed in much of the Corn Belt. Relationships between yields of corn (Zea mays L.) grain and concentrations of nitrate in the surface l‐ft layer of soils when corn plants were 6 to 12 in. tall were studied across a total of 756 plots at several locations during 1985 and 1986 to evaluate the late‐spring soil test for nitrate. The time of sampling for this soil test represents a compromise between the need to sample late enough to reflect the effects of spring weather conditions on N availability but early enough so that supplemental N can be applied as a sidedressing if needed. A linear‐response‐and‐plateau (LRP) model showed that nitrate concentrations could explain 82% of the variability in relative yields (yields expressed as percentages of the highest yields observed within rotation‐site‐years) across all data collected. Although this model indicates that 21 ppm nitrate‐N in the surface l‐ft layer of soil is adequate to attain maximum yields, we suggest that a range of 20 to 25 ppm should be considered optimal. These findings indicate that this soil test offers great potential for improving N management in the Corn Belt. Amid mounting concerns that many farmers are applying more fertilizer than is desirable for environmental and (or) economic reasons, the most important use of the soil test may be to reduce excessive applications of fertilizer by showing when additional N is not needed.

Influence of varying nitrogen levels on growth, yield and nitrogen use efficiency of hybrid maize (Zea mays)

“…Among the various major nutrients required for proper plants, Nitrogen has a key role and particularly it has been proven for maize by various experiments (Subramanian et al, 2006;Carpici et al, 2010). The nitrogen requirement of maize is depend on weather conditions, soil type and crop rotation pattern (Blackmer, et al, 2009;Bundy, et al, 2011).…”

Nitrogen management for corn after corn and corn after soybean

“…Critical concentrations generally were lower than those observed by Binford et al (1992a) and Blackmer et al (1989). The mean critical levels for NO'g to 30 cm, for example, were 19 mg N kg'^ in the present study, 29 mg N kg"^ in the study reported by Binford et al (1992a), and 25 mg N kg'^ in the study reported by Blackmer et al (1989).…”

“…1 and 2, this method of identifying critical levels has two major shortcomings. The first, as noted by Blackmer et al (1989), is that the determined value for critical concentration varies with the model used. The second, as noted …”

“…Analysis of variance (Table 11) suggests that a soil test based on these concentrations can be used to adjust N fertilization rates toward optimal on a site-specific basis. (Magdoff et al, 1984(Magdoff et al, , 1990Blackmer et al, 1989;Fox et al, 1989;Binford et al, 1992a;Meisinger, et al, 1992;Roth et al, 1992).…”

Effects of crop rotation and nitrogen fertilization on soil nitrate concentration and corn yield

“…The late spring nitrate test (LSNT) is based on the measurement of nitrate-N concentration in the 30 cm surface layer of soil when the plants are 15-30 cm tall. This test has shown reasonably good correlations with yield response to N fertilization (Magdoff et al, 1984 andBlackmer et al, 1989;Fox et al, 1989;Binford et al, 1992;Bundy et al, 1999). Use of the LSNT also has been a useful tool to reduce nitrate loss to water resources.…”