Recovery of fertilizer nitrogen from continuous corn soils under contrasting tillage management
2003
Martens, D.A. | Dick, W.
Tillage systems influence soil properties and may influence the availability of applied and mineralized soil N. This laboratory study (20°C) compared N cycling in two soils, a Wooster (fine, loamy Typic Fragiudalf) and a Hoytville (fine, illitic Mollic Epiaqualf) under continuous corn (Zea mays) production since at least 1963 with no-tillage (NT), minimum (CT) and plow tillage (PT) management. Fertilizer was added at the rate of 100 mg 15N kg-1-1 soil as 99.9% 15N as NH4Cl or Ca(NO3)2 and the soils were incubated in leaching columns for 1 week at 34 kPa before being leached periodically with 0.05 M CaCl2 for 26 weeks. As expected, the majority of the 15NO3- additions were removed from both soils with the first leaching. The majority of applied 15NH4+ additions were recovered as 15NO3- by week 5, with the NT soils demonstrating faster nitrification rates compared with soils under other tillage practices. For the remaining 22 weeks, only low levels of 15NO3- were leached from the soils regardless of tillage management. In the coarser textured Wooster soils (150 g clay kg-1), mineralization of native soil N in the fertilized soils was related to the total N content (r2 >or= 0.99) and amino acid N (r2 >or= 0.99), but N mineralization in the finer textured Hoytville (400 g clay kg-1) was constant across tillage treatments and not significantly related to soil total N or amino acid N content. The release of native soil N was enhanced by NH4+ or NO3- addition compared to the values released by the unfertilized control and exceeded possible pool substitution. The results question the use of incubation N mineralization tests conducted with unfertilized soils as a means for predicting soil N availability for crop N needs.
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