Monday, November 13, 2006

Cropping System Management Effects on Soil N Mineralization Dynamics.

Ana B. Wingeyer1, Daniel Walters2, Ken Cassman1, and Achim Dobermann3. (1) University of Nebraska, 245 Keim Hall, Lincoln, NE 68583-0915, (2) Univ.of NE-Dept. of Agron & Hort., "PO Box 830915,261 Plt Sci Bldg", "PO Box 830915,261 Plt Sci Bldg", Lincoln, NE 68583-0915, United States of America, (3) University of Nebraska-Lincoln, University of Nebraska-Lincoln, PO Box 830915 253 Keim, Lincoln, NE 68583-0915

High yield crop management systems (high yield = high residue return) can enhance soil organic matter and increase the indigenous soil N pool. However, achieving high yield production without increasing nitrogen (N) losses requires improved synchrony between crop N demand and the N supply from indigenous soil and applied N throughout the growing season. Therefore, reliable soil N supply prediction is a key factor in determining the amount and time of N fertilizer applications. We studied the impact of high yielding continuous corn (CC) and corn-soybean (CS) systems that lead to greater soil organic matter (SOM) content on soil N supply. Previous work on these high yield systems demonstrated the importance of light fraction (LF) and mobile humic acid (MHA) pools in the carbon (C) and N cycle dynamics over relatively short time periods. Based on this work, we hypothesize that intensive management practices that enhance primary productivity and C input to soil results in an increase of the size of soil indigenous N pool. The study includes two field experiments with two crop rotation mainplot treatments: CC, CS, two nutrient management regime subplot treatments (intensive-M2 versus current recommendations-M1, where the intensive treatment attempts to produce yields that are about 95% of the yield potential), and two plant populations: P1 and P2 (30000 and 40000 pl/a). N exclusion subsubplots where created within the M1-P1 and M2-P2. Soil samples were collected in spring 2006 and incubated at 25º C and 60% WFPS to measure net N mineralization by periodic leaching Field measurements involved periodic plant N uptake and soil inorganic N. Monitoring the rate and quantities of N transfer from indigenous N pools to the crop will help to elucidate the impact of high yield crop management systems on the size and dynamics.