Abstract

Research on corn-soybean strip-cropping has demonstrated higher yields on the edge rows of corn and reduced yield on the edge rows of soybeans. Nitrogen application to the strip-cropped corn is often applied uniformly on each row of corn. The objective of this study was to evaluate if ESN, a 44% polymer coated controlled release nitrogen, would improve corn yield in a narrow (6-row) strip cropping system.

ESN was applied with a centrifugal spreader in a double pass procedure. Excessive June and July rainfall in 2004 resulted in denitrification or leaching losses of the 28% (UAN) Urea starter treatment and the controlled release nitrogen ESN starter treatment improved efficiency with a nearly 20% increase in yield. Corn edge rows yielded 10% higher than the 4 middle rows for ESN and 11% higher for the UAN & Urea treatment.

GENERAL INFORMATION

In 2004, we started a two year agronomy field trial to evaluate Agrium ESN nitrogen fertilizer on zone till corn verses urea in the starter fertilizer. Six rows of corn in 30 inch spacing were alternated with 6 rows of soybeans in 30 inch spacing narrow strip cropping corn soybean rotation. Four or more side by side replications in field length plots were compared using Urea fertilizer for corn verses ESN as a substitute for urea in the starter fertilizer.

ESN is a polymer coated urea that is time released into the soil based on soil temperature and moisture conditions. It has a guaranteed analysis of 44% nitrogen. It is sized similar to other blend fertilizer sources and has a unique light green color. Water moves through the polymer coating until the urea inside is dissolved into solution inside the polymer coated granule. N moves out by diffusion through the granule via soil temperature controlled diffusion into the soil solution where the biological transformation of urea occurs to make it available for plant uptake. Below is a summary of our observations and results of the 2004 and 2005 field trials.

The objective of this study was to determine if corn yield in strip cropping is improved by using ESN polymer coated urea compared to urea as a nitrogen source in surface banded starter fertilizer in zone tilled corn. Research in Minnesota on narrow strip cropping in a corn soybean rotation with 6 rows by 30 inch corn next to a 6 rows by 30 inch soybeans has demonstrated a 11% higher corn yields on the edge rows of corn and reduced yield on the edge row of soybeans (Iragavarapu and Randall, 1996).

Methods in the Field

In 2004 corn and soybeans were planted in N – S oriented strips in a two crop rotation. The field trial was Strip tilled with 3 coulters on April 10, 2004 to layout 6 row strips. Roundup Ready Pioneer 38A81 corn was planted at 30,000 seeds per acre on April 23, 2004. Pioneer 92M91 Roundup Ready soybeans were planted between the corn strips on April 29, 2004. Nitrogen starter was applied as dry commercial fertilizer surface banded (placed 1-4 inches beside the row and 0-4 inches deep) in a zone beside the seed. An equal blend starter fertilizer of Urea (46-0-0), Di-ammonium Phosphate (DAP) (18-46-0) and Ammonium Sulfate (AMS) (21-0-0) verses ESN urea, DAP and AMS each at 237 lbs/ac at planting was compared. UAN or 28% nitrogen solution was broadcast with a double application at 20 gals/ac or 120 lbs/ac of nitrogen after planting on the urea starter. UAN 28% liquid fertilizer was broadcast applied before the crop emerged to prevent leaf burn on the corn. ESN was broadcast over 6 rows of corn after corn emergence (2 leaf stage) with a double application using a centrifugal spreader at 150 lbs/ac or132 lbs N/ac. Excessive June and July rainfall in 2004 (total of 17 inches verses the normal historical rainfall average of 7 inches for that time period) resulted in de-nitrification and leaching losses of the traditional UAN and urea starter treatment.

In 2005, the same planting and fertilization procedure was followed as in 2004. Six by 30-inch row Roundup Ready Pioneer 38H86 corn was planted at 32,000 on April 14, 2005 in soybean residue. Six by 30-ich rows of Pioneer 92M91 Roundup Ready soybeans were strip till planted between the corn strips on corn residue. Timely rains in April of ½ inch or more after planting incorporated the fertilizer in both treatments. Below normal rainfall in May and June followed by normal rainfall in July and August was ideal for retaining Nitrogen from all sources.

A dry blend starter fertilizer with equal Urea, DAP and AMS verses ESN, DAP and AMS at a rate of 237 lbs/ac at planting was compared to the broadcast placement of 28% or ESN broadcast after planting plus the starter fertilizer. The goal was to get as close to 200 lbs/ac N with the equipment we were using. (See table 2). The 2004 and 2005 fertilizer treatments and comparisons were the same. In 2005, the only management variables were corn hybrid, earlier planting date and higher planting rate compared to 2004. In 2005, spring rainfall total for May and June was much less than 2004 and the timing was different.

Four control plots were added to the trial in 2005 to compare the use of starter nitrogen zone banded at planting or one half of the recommended N rate to achieve a 200 bushel per acre yield goal. The control plots with (84 lbs N total) 66 lbs of starter N from ESN or Urea plus 18 lbs of nitrogen from DAP broadcast in April before planting. There were 2 replications of each control comparison.

Results

Corn grain was hand harvested and shelled by NRCS Crops 101 students using 1/1000 acre point samples opposite each other at 200 foot intervals across the field. Four replications of each treatment and four point samples each 1/1000 acre in length (17.5 feet in 30 inch rows) directly E-W of each other were hand harvested and the corn yield was estimated for each row. The outside corn edge rows yielded 10% higher than the 4 middle rows in this 6 row x 30 inch strip cropping system with ESN and 11 % higher with 28% UAN. This is comparable to similar finding by (Iragavarapu and Randall, 1996) that reported corn yields in the outside two rows 25% greater in north south rows compared to nonborder rows in a 2 crop system. In the 2004 field trial randomly selected, hand harvested sections of all rows estimated yield an average of 30% higher than machine harvest yield. (Kaufman, 2007)

In 2004, the ESN controlled released starter and broadcast ESN treatment proved superior over the urea starter and UAN treatment in efficiency that resulted in a 20% increase in corn yield. However, in 2005, a dry spring, there was similar edge effect of higher yield on the edge rows with both treatments, but no additional yield increase was attributed to ESN as the N source. In 2005, we evaluated corn yield using starter N zone banded at half the land grant university recommended N rate for a 200 bu/ac yield goal in the control plots. Unlike 2004 we observed less N loss via denitrification or leaching in 2005. However, in 2005, the results were similar with ESN or Urea zone banded at planting with the starter fertilizer. There was no advantage to using ESN in a dry spring.

2005 Stalk Nitrate Tests and PSNT results were used to evaluate the efficiency of N in the 200 lb/ac N fertilized ESN and Urea plots. Soil nitrogen available was evaluated with PSNT in the starter only control plots. PSNT results of starter N only (84 lbs/ac) plots suggest we could apply less N to a long term (20 + years) no-till corn field and still achieve the desired 200 bu/ac yield goal. (See table 3) In our control plots, Nitrogen starter at 84 lbs/ac had a 197 bu/ac average yield. The ESN starter and ESN broadcast plot at 216 lbs/ac total nitrogen rate had a yield averaging 209 bu/ac. The Urea starter and UAN broadcast plot at 205 lbs/ac total nitrogen rate had a yield averaging 214 bu/ac.

A crop budget analysis of the 200 lb/ac N rate for the 209 bu/ac from ESN and 215 bu/ac from Urea/28% indicates we lost money compared to the control N rate of 84 lbs/ac. corn at $2.20 per bushel and nitrogen at 35 cents per pound. Here is breakeven analysis: to yield 215 bu/ac required adding115 lbs/ac nitrogen at 0.35 cents per pound or $40.25 per acre. Therefore, adding115 lbs/ac additional nitrogen increased the corn yield 18 bu/ac above the 197 bu/ac control yield. At 18 bu/ac and $2.20 /bu the additional profit was $39.60/ac. At these prices there was more corn to sell but no additional profit from using additional Nitrogen to achieve the higher yield. Economists would say the maximum economic yield was at 197 bu/ac and 85 lbs N/ac to break even at 2.20/bu of corn in 2005.

However, ESN appeared to provide insurance against N loss by de-nitrification in a wet year. Using a reduced N rate with Urea or 28% UAN without ESN at planting may cause significant yield loss after the fertilizer is applied. 2004 was a very wet spring with 10 inches of rain above normal in May and June. ESN appears to provide insurance against de-nitrification losses in a wet year and thus is good insurance for maintaining yield in a wet year.

Tissue tests, stalk nitrate tests and PSNT analysis are recommended when growers try to fine tune their N needs to achieve the desired corn yield goal especially in above normal rainfall growing seasons. The results of these tests for 2004 and 2005 are presented in tables 1-4.

At 1286 ppm, the End-of-Season Corn Stalk Nitrate Test of the 2005 field trial indicates that the ESN treatment provided sufficient Nitrogen throughout the growing season. However, the 446 ppm results of the End-of –Season Corn Stalk Nitrate Test indicated that the Urea fertilizer treatment resulted in minimal amount of nitrogen needed for adequate nitrogen to the corn crop. However, with the urea starter the final corn grain yield 214 bu/ac was five bushel per acre more than the 209 bu/ac with the ESN. (See table 2).

“The End of the Season Cornstalk Test, developed at Iowa State University (Blackmer & Mallarino, 1996) allows growers to conduct a “post-morten” evaluation of the adequacy of their nitrogen fertilizer program for the current growing season. The test is described as “post-morten” because stalk samples are taken after the grain is physiologically mature. Given that this is a very late season test, the interpretation of the results offers no assistance in the fine-tuning nitrogen (N) management for the current production year, but rather provides insight into N management options for coming years.”

Four Control plots were added with Urea starter and DAP broadcast for a total of 84 lbs of nitrogen. Our PSNT results of the four plots recommended additional nitrogen was needed to achieve our 200 bu/ac yield goal. However, in 2005 our control treatment average yield was 3 bu/ac less than the 200 bu per acre yield goal without the additional nitrogen recommended by MSU.

A 200 bu/ac corn crop removes about 0.9 lb Nitrogen per bushel of grain or 180 lbs/ac N for 200 bushel/ac corn. (E2904) The 2005 corn crop was able to obtain about 120 lbs of Nitrogen from other sources (air and soil) to produce the 197 bushel per acre yield. This field was no-tilled or zone tilled for 20 years prior to this field trial. Long term no till farmers claim they can achieve their corn grain yield goal with 0.5 lb of nitrogen for every bushel of corn. In 2005, our control (Total N applied 84 lbs/ac) nitrogen efficiency was 0.42 lbs of N for every bushel of corn. This supports the observations of veteran no till farmers that belong to the Great Lakes No Till Discussion Group. In Table 5 and 6 is a summary of our hand harvested data by row and machine harvest data for 2004 and 2005.