Tillage system effects on 15-year carbon-based and simulated N budgets in a tile-drained Iowa field

Abstract

Tillage influences N fate and transport by changing soil structure, aeration, macropore continuity, plantresidue placement, and organic-matter mineralization rates. Our objective was to use 15-year N budgets to compare four primary tillage treatments for continuous corn (Zea mays L.) production on tile-drained Aquic Hapludolls (FAO: Haplic Phaeozems) in northeastern Iowa, USA. A carbon-based N budget used annual grain yield, grain-N concentrations measured in 1992, changes in surface-soil C content between 1977 and 1988 or 1992, surface-soil C : N ratios, and measurements of NO 3 -N lost in tile-drainage water. It accounted for 98, 104, 99, and 99% of the fertilizer N applied to moldboard-, chisel-, ridge-, and no-tillage-treatments, respectively. Averaged for 1977 through 1992, increased soil organic matter, harvested grain, and tile drainage accounted for ≈42, 45, and 13% of the N budget, respectively. Simulated N budgets were computed using version 3.25 of the root-zone water quality model (RZWQM). The best grain-yield predictions for 13 of the 15 years were 9% higher than the measured values, and if extreme outliers were eliminated, the predicted values were correlated (r 2 =0.75) with the average measured yield for the four tillage treatments. Simulations for 1988 and 1989 failed completely because RZWQM could not accurately describe hydrology associated with low rainfall seasons. Predicted total N accumulation was much higher than measured in 1990, 1991, or 1992. Estimates of profile NO 3 -N, mineralization, seepage loss, and denitrification were not satisfactory, presumably because the model failed to simulate an accurate hydrology for the different tillage practices. We conclude that the simulation results were not suitable for predicting the fate of fertilizer N. However, both approaches for computing N budgets suggested that adopting ridge tillage, without changing N rates and other management practices related to N application technology and crop sequencing, will not reduce the potential for off-site water quality degradation. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. AbstractTillage in¯uences N fate and transport by changing soil structure, aeration, macropore continuity, plant-residue placement, and organic-matter mineralization rates. Our objective was to use 15-year N budgets to compare four primary tillage treatments for continuous corn (Zea mays L.) production on tile-drained Aquic Hapludolls (FAO: Haplic Phaeozems) in northeastern Iowa, USA. A carbon-based N budget used annual grain yield, grain-N concentrations measured in 1992, changes in surface-soil C content between 1977 and 1988 or 1992, surface-soil C : N ratios, and measurements of NO 3 ±N lost in tile-drainage water. It accounted for 98, 104, 99, and 99% of the fertilizer N applied to moldboard-, chisel-, ridge-, and no-tillage-treatments, respectively. Averaged for 1977 through 1992, increased...

RZWQM simulated effects of crop rotation, tillage, and controlled drainage on crop yield and nitrate-N loss in drain flow

“…Simulated N fixation for soybean was highest under MP, followed by CP and NT (Table 4) due to higher N uptake demand and higher soybean biomass. Increase in soil organic N was slightly higher with CS compared to CC, which is in agreement with experimental observations (Karlen et al, 1991(Karlen et al, , 1998. The slightly higher soil organic N increase under MP for CS was due to higher soybean yield simulated under MP.…”

“…The seasonal water table fluctuates from 20 to 160 cm and subsurface drainage tubes/pipes (10 cm in diameter) were installed in the fall of 1979 at 120 cm depth and 29 m apart. A trenchless drain plow was used to install the center drain in each plot and a chain trencher was used to install the drains between the plots (Karlen et al, 1991(Karlen et al, , 1998.…”

“…In RZWQM, tillage practice only affects the soil hydraulic properties and mixes surface crop residue. It may be necessary to increase mineralization of organic N under MP or CP as suggested by McGechan et al (2005) to simulate lower organic N under MP compared to NT (Karlen et al, 1998). Higher residual soil nitrate-N was simulated under CC than under CS during the 24 years of simulation.…”

RZWQM simulation of long-term crop production, water and nitrogen balances in Northeast Iowa

“…Lksat for these two layers were optimized and listed in Table 2 (Ma et al, 2007b-this issue). Soil carbon pools were calibrated based on measured data assuming all the carbon was in the slow humus pool since the site had very low fertility when the experiments were started in 1978 (Karlen et al, 1991(Karlen et al, , 1998. Microbial population was initialized by running the model using current management practices for Plot #25 and weather data for a course of 26 years.…”

Integrating soil and crop research with system models in the midwest USA: Purpose and overview of the Special Issue

“…The results of these studies have been reported in many publications (Bjorneberg et al, 1998;Karlen et al, 1991;Weed et al, 1995;Singh and Kanwar, 1995;Weed and Kanwar, 1996;Singh et al, 1996;Kanwar et al, 1997;Azevedo et al, 1997;Karlen et al, 1998;Kumar et al, 1998a,b;Kanwar et al, 1999;Kumar et al, 1999;Bakhsh et al, 1999Bakhsh et al, , 2000aBakhsh et al, , 2002Karlen et al, 2004;Bakhsh and Kanwar, 2004;Kanwar et al, 2005;. The publications seniorauthored by Singh, Azevedeo, Kumar, and Bakhsh involved the use of models.…”