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Crop and Soil Environmental News, May 2000

Greg Evanylo, Extension Specialist and Associate Professor
Department of Crop and Soil Environmental Sciences, Virginia Tech

May 96 Use PSNT For Corn Following Biosolids Application

The results of a corn (Zea mays L.) trial in 1999 on land that had previously received biosolids at Rapidan River Plantation demonstrates the value in using the pre-sidedress soil nitrate test (PSNT) for determining the need for supplemental fertilizer N. The biosolids demonstration was employed as a tour stop at the 1999 Virginia Ag-Expo at the Orange County farm.

In 1998, a lime-stabilized biosolids was applied to a Rapidan silt loam having a pH of 6.2 and testing "high" in P and "very high" in K, according to soil testing analyses conducted by A&L Eastern Agricultural Laboratories, Inc. in Richmond. The soil had an initial organic matter concentration of 2.7% and a cation exchange capacity of 6.3 cmol (+)/kg [me/100 g]. The recommended amounts of N, P, K and limestone from biosolids for the 1998 corn crop were 150 lbs N, 0 lbs P, 0 lbs K, and 2 tons limestone per acre. The agronomic N rate provided 142 lbs N, 155 lbs P, 25 lbs K, and 1.32 lbs lime per acre for 1998. Expected amounts of residual N to be carried over in year 2 and 3 were 71 and 36 lbs N/acre, respectively. Excessively droughty conditions during the 1998 growing season severely reduced corn yields, and increased the potential for unused N to be carried into the 1999 growing season.

The soil was cultivated in March, 1999 and Pioneer 32K61 was planted in 30-inch rows at a population of 28,000 on April 14. No starter fertilizer was applied at or prior to corn planting. Routine Virginia Cooperative Extension recommended weed and insect control measures were implemented. The corn seedlings had germinated, and emergence was greater than 95% on May 3. The results of Virginia Cooperative Extension Soil Testing Lab routine soil analysis from samples taken at this time showed: pH=6.8, P=151 lbs/ac (VH), K>314 lbs/ac (VH), Ca=2082 lbs/ac (H), and Mg=89 lbs/ac (M).

Soil samples were collected to a depth of 12 inches when corn plants were 10-12 inches tall (June 2) and analyzed for soil nitrate-N with the Hawk Creek Lab Pre-sidedress Soil Nitrate Quick Test. The corn plots were divided into 16 plots (4 plots x 4 rows) and four sidedress N rate treatments were established (0, 50, 100, and 150 lbs N/acre) by applying 30% urea ammonium nitrate solution with a backpack sprayer. Each N rate treatment was replicated four times in a randomized complete block design.

Seaonal rainfall was below average and amounted to 9.9 inches between April 10 and July 24, 1999, a period of time during which the corn crop accumulated most of its dry matter. Soil nitrate-N concentration with the quick test was 25 ppm, which indicates that enough N should be present in the soil to allow maximum corn yield potential to be attained (Evanylo and Alley, 1996). The soil N results were supported by the corn grain yields, which were not increased by any rate of sidedressed N. Grain yields at 15.5% moisture averaged 131 bu/acre for all treatments. The amount of N carried over from the droughty 1998 season plus the second year mineralizable N provided enough plant available N to maximize corn yield potential under the climatic conditions of 1999.

Reference: Evanylo, G.K. and M.M. Alley. 1996. Nitrogen soil testing for corn in Virginia. Virginia Cooperative Extension Publ. No. 418-016.

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