Tillage, Crop Rotation, and Cultural Practice Effects On Dryland Soil Nitrogen Dynamics.

Management practices may influence dryland soil N dynamics. We evaluated the effects of tillage, crop rotation, and cultural practice on dryland crop biomass (stems + leaves) N from 2004 to 2007 and surface residue and soil N fractions at the 0-20 cm depth in a Williams loam from autumn 2007 to spring 2008 in eastern Montana, USA. Treatments were two tillage practices (no-till [NT] and conventional till [CT]), two crop rotations (continuous spring wheat [CW] and spring wheat-barley hay-corn-pea [W-B-C-P]), and two cultural practices (regular [conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height] and ecological [variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height]). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH₄-N and NO₃-N. Crop biomass N was greater in CW than in W-B-C-P in 2005 and 2006. Surface residue N was greater in NT with regular and ecological than in CT with regular practice. The STN, PON, and MBN at 10-20 and 0-20 cm were greater in NT or CW with regular practice than in CT or CW with ecological practice. The PNM at 5-10 cm was greater in regular than in ecological practice. The NH₄-N and NO₃-N contents at 10-20 and 0-20 cm were greater in CT with W-B-C-P and regular practice than with most other treatments in 2007. Surface residue and soil N fractions declined from 2007 to 2008. No-till with regular cultural practice increased surface residue and soil N storage but conventional till with diversified crop rotation and regular practice increased soil N mineralization and availability. Reduction in N input reduced surface residue and soil N storage and N mineralization from autumn to the following spring.