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Nutrient Management & Soil & Plant Analysis

Soil Conductivity as a Measure of Soil and Crop Status—A Four-Year Summary

^a USDA-ARS, U.S. Meat Animal Research Center, P.O. Box 166, Clay Center, NE 68933
^b Univ. of Nebraska, Lincoln, NE

^* Corresponding author (eigenberg{at}email.marc.usda.gov)

Animal manure can be an important resource providing soil available N for plant needs, but determining the nutrient availability resulting from such amendments is difficult. A study was conducted to examine changes in electromagnetic induction (EMI) soil conductivity and available N levels during four growing seasons in relation to manure or compost application and use of a green winter cover crop. With simultaneous soil samples, a series of soil conductivity maps of a research cornfield were generated using a global positioning system (GPS) and EMI methods. The Clay Center, NE, site was treated during a 10-yr period with a winter wheat (Secale cereale L.) winter cover crop (+CC) and no-cover crop (–CC). The site was split for subtreatments of manure and compost at rates matching either the P or the N requirements of silage corn (Zea mays L.). Differences between the +CC and –CC treatments for values of NO₃–N and water-filled pore space (WFPS), as estimated by apparent electrical conductivity (EC_a), were compared for each year. Differences in profile weighted soil conductivity explained 79.5, 98.0, 93.4, and 98.4% of the variability due to NO₃–N differences, and only 20.5, 2.0, 6.6, and 1.6% of the variability due to WFPS differences for years 2000, 2001, 2002, and 2003, respectively. Sequential measurement of profile-weighted soil electrical conductivity (EC_a) was effective in identifying the dynamic changes in plant-available soil N, as affected by animal manure and anhydrous ammonia fertilizer treatments during four corn growing seasons.

Abbreviations: ATV, all terrain vehicle • +CC, cover crop treatment • –CC, no-cover crop treatment • CN, compost applied to meet nitrogen requirements of crop • CP, compost applied to meet phosphorus requirements of crop • DOY, day of year • EMI, electromagnetic induction • EC_a, apparent electrical conductivity • GPS, global positioning system • MN, manure applied to meet nitrogen requirements of crop • MP, manure applied to meet phosphorus requirements of crop • NCK, commercial fertilizer treatment • WFPS, water-filled pore space