Illinois
Fertilizer Conference Proceedings
January 29-31, 1996
| Main Index | 1996 Index | Search |
| Main Index | 1996 Index | Search |
F.E. Below, P.S. Brandau, and J.A. Yockey1
Because soils cannot supply enough nitrogen (N) to meet the optimal needs of corn, applications of fertilizer N are almost always necessary for maximum crop growth and productivity. Since N deficiency can result in serious yield reductions, and because fertilizer is relatively inexpensive, growers can easily apply more N than is needed. However, excess fertilizer is economically wasteful and can become a contaminant if lost from the rooting zone. Although many factors involved in N loss are beyond the growers control, they are nonetheless under increasing pressure to more effectively manage their applications of fertilizer N.
Nitrogen management is further complicated by the complex cycle of nitrogen in the environment. Corn plants can utilize N as either NO3 or NH4, however, only NO3 is susceptible to N losses such as leaching or denitrification. In addition, NH4 in the soil is rapidly converted to NO3 through nitrification. This process can be blocked by the application of nitrification inhibitors (such as N-Serve), which increase the proportion of soil N as NH4. The use of nitrification inhibitors can help reduce fertilizer N loss, and may allow the predominant form of N in the soil to be altered (Huffman, 1989).
Increasing the amount of NH4 in soils has been shown to enhance plant performance through increased N absorption and more rapid growth (Barber et al, 1992; Smiciklas and Below, 1992). Yield increases of 6 to 11% have been reported when corn plants were supplied with a mixture of NO3 and NH4, compared to situations that provided predominately NO3 (Barber et al, 1992; Smiciklas and Below, 1992). In addition, experiments involving mixed N nutrition in fieldhydroponics have shown consistent yield increases averaging 12% across a wide range of environments and genotypes (Below and Gentry, 1987 and 1992; Gentry and Below, 1993). Currently, producers have the ability to alter the NO3 and NH4 ratio in the soil through the use of different fertilizer N sources as well as nitrification inhibitors. However, information is limited concerning the ideal ratio which leads to optimum productivity, especially under varied tillage conditions and soil types.
Therefore, the objective of this project is to characterize the effects of
varying the ratio of NO3 to NH4 in the soil on N use efficiency
and productivity of maize. Our specific objectives are to evaluate: 1) the effect
of varying this ratio in the soil by using different N sources and through inhibiting
nitrification; 2) the cultural and/or environmental conditions where altering
this ratio will affect productivity; and, 3) the relationship between NO3/NH4
ratio and the level of applied N.
Experiments which examined nitrogen use and productivity of corn as a function of N source, N rate, and nitrification inhibitor treatment were conducted at four diverse locations in Illinois over three years (1993, 1994, 1995). These locations include: 1) the Agronomy-Plant Pathology South Farm at the University of Illinois, Urbana-Champaign, which is devoted to agricultural research and has irrigation capabilities; 2) a grain farm in Geneseo with conventional tillage and continuous corn; 3) a grain farm in Geneseo with a sandy soil type, conventional tillage, and a corn/soybean rotation, and 4) another grain farm in Geneseo which is under no-till and a corn/soybean rotation. Further descriptions of each individual location and some of their cultural and soil characteristics are presented in Table 1. At all locations, the single-cross hybrid LH132 x LH212 was overplanted and after emergence thinned to a stand density of 26,000 plants per acre.
Five sources of fertilizer N designed to allow variation in the NO3/NH4 ratio of the soil (calcium nitrate, ammonium nitrate, urea, urea-ammonium nitrate, and ammonium sulfate) were applied at four rates (0, 60, 120, 1801bs of N per acre) and evaluated at each location. All N treatments were applied either with or without the nitrification inhibitor N-Serve, which was intended to maintain soil-applied N as NH4. At all locations, the experiment was arranged in a split-split plot design with four replications with N rates as main plots, N sources as subplots, and the nitrification inhibitor treatment as the sub-sub plot. An experimental unit consisted of five rows 20 feet long spaced 30 inches apart, with the center three rows receiving the N treatment.
N treatments were established just after seedling emergence at approximately
the V2 growth stage by hand applying the proper amounts of solid fertilizer
down the center of each row. For plots receiving the nitrification inhibitor
treatment, the inhibitor was mixed with water and an antifoaming agent and sprayed
onto the fertilizer band immediately after application. At the sites which received
tillage, the fertilizer was spread in a band approximately 10 inches wide and
incorporated with a field cultivator to a depth of 2 to 3 inches. At the no-till
site, a narrow furrow approximately 2 inches wide and 5 inches deep was made
down the center of each row with the passage of a 2inch straight chisel point.
The fertilizer was poured into this opening and the furrow covered with soil
by hand hoeing. At the Champaign site, plots received approximately 1.0 inches
of irrigation water immediately following N application. Ammonium sulfate was
included as an N source at two locations in 1994 and at all locations in 1995,
but was not used in 1993. Because this limited data tended to skew the average
response to ammonium sulfate downward, the yield and soil N data with ammonium
sulfate as the N source is not included in the individual location summaries.
Despite relatively large differences in the seasonal growing conditions, the treatment effects at each site were remarkably similar over the three years (data not shown), and there were few instances of significant year by N-treatment interactions. For this reason, and for ease of data presentation, the data for each location is averaged over the three years (Figs. 1, 2, and 3). We also averaged the data over the four locations and the three years (Fig. 4) to visualize the overall response to the treatments.
At all locations, and for all N sources, increasing the rate of applied N resulted in corresponding increases in the level of available N in the soil (Fig. 1). Differences in total soil N attributed to N source were most apparent at the higher levels of applied N (120 and 1801bs N/acre). In general, fertilizer sources containing high levels of N as NO3, such as calcium nitrate or ammonium nitrate, had the highest levels of total soil N, while urea-containing sources had the lowest levels. Except for a slight decrease with urea as the N source, inclusion of the nitrification inhibitor had no affect on the availability of soil N (Fig. 1). For the most part, the environmental conditions at all site/years were not conducive to NO3 losses (e.g. leaching or denitrification), which could explain the high soil N levels obtained from fertilization with NO3 sources of N. Alternatively, microbial immobilization may have been lower when the bulk of the available soil N was present as NO3.
In addition to affecting the soil N level, the source of fertilizer N also
altered the predominant form of N in the soil (Fig.
2). At all locations, soils fertilized with calcium nitrate displayed the
highest proportion of total soil N as NO3; especially at the higher
N rates. Conversely, when the N source was urea or ammonium sulfate most of
the available soil N was present as NH4. Fertilizing with either
mixed N source (ammonium nitrate or UAN) resulted in approximately equal mixtures
of NO3 and NH4 in the soil. For all N sources except calcium
nitrate, the NO3 to NH4 ratio remained relatively constant
over the different N rates (Fig. 2). For
calcium nitrate, this ratio increased with increasing rates of fertilizer N.
Regardless of the fertilizer N source, including the nitrification inhibitor
tended to decrease the NO3 to NH4 ratio in the soil; indicative
of more N in the NH4 form.
Grain yield was increased by addition of fertilizer N at all locations in each
year (Fig. 3). The N sources differed
in the yield they produced without the nitrification inhibitor, while inclusion
of the inhibitor tended to minimize differences between the N souces. At all
locations, the yield obtained with the all (calcium nitrate), or high (ammonium
nitrate) NO3 N sources was surprisingly high; which may be related
to the high levels of total available soil N observed with these sources (Fig.
1).
The grain yield and the soil parameters averaged over the four locations and
three years are presented in Figure 4.
Similar to the individual locations, this summary shows that the amount of total
N available and the ratio of nitrate to ammonium in the soil can be altered
by adjusting the source of fertilizer N used, and in some cases by including
the nitrification inhibitor. Grain yield was higher than expected for the high
NO3 sources, and enhanced by nitrification inhibition for the urea
source (Fig. 4).
The overall goal of our research is to find strategies that growers and fertilizer dealers can use to improve the efficiency of N use while safeguarding the environment and maintaining profitability. In this project, we examined the effects of maintaining a mixture of NO3 and NH4 in the soil on N use and productivity of corn. Our findings showed that the predominant form of soil N can be readily altered by adjusting the source of fertilizer N used, and in some cases by including a nitrification inhibitor. In general, high NO3-containing N sources resulted in the highest levels of total available soil N, and urea containing fertilizers the lowest. Nitrogen sources also altered the nitrate to ammonium ratio, with calcium nitrate giving the highest ratio and ammonium sulfate the lowest. Inclusion of the nitrification inhibitor always lowered this ratio. Differences in yield attributable to N source (or form) were relatively small, and were minimized by addition of the nitrification inhibitor. The basic response to these treatments was similar at each of the four locations, and over each of the three years. Although additional work is needed, these findings suggest improvements in N management can be obtained by altering the source of N used, and the form of N available in the soil.
The authors wish to express their gratitude to Gary Johnson and Edward Kiefer
for their help at the Geneseo locations. Financial support from the Fertilizer
Research and Education Council, DowElanco, and AlliedSignal is also greatly
appreciated.
1Associate Professor of Plant Physiology, Research Specialist in Agriculture, and Graduate Research Assistant, Dept. of Agronomy, Univ. of II. at Urbana-Champaign.
Barber, K.L., L.D. Maddux, D.E. Kissel, G.M. Pierzynski, and B.R. Bock. 1992. Corn responses to ammonium-and nitrate-nitrogen fertilization. Soil Sci. Soc. Am. J. 56:1116-1121.
Below, F.E., and L.E. Gentry. 1987. Effect of mixed N nutrition on nutrient accumulation, partitioning, and productivity of corn. J. Fert. Issues 4:79-85.
Below, F.E., and L.E. Gentry. 1992. Maize productivity as influenced by mixed nitrogen supplied before or after anthesis. Crop Sci. 32:163-168.
Gentry, L.E., and F.E. Below. 1993. Maize productivity as influenced by form and availability of nitrogen. Crop Sci. 33:491-497.
Huffman, J.R. 1989. Effects of enhanced ammonium nitrogen availability for corn. J. Agron. Educ. 18:93-97.
Smiciklas, K.D. and F.E. Below. 1992. Role of nitrogen form in determining yield of fieldgrown maize. Crop Sci. 32:1220-1225.
