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

Abstract

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 (ECa), 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 (ECa) 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.