SOIL CARBON AND NITROGEN CHANGES ON INITIATION OF NO-TILL CROPPING SYSTEMS

Previous research indicates that increased cropping intensity (crops/time) under no-till may increase soil organic C and N contents and reduce risk for NO3-N leaching, compared with tilled and frequent-fallow systems. This study was conducted to determine the effect of cropping intensity on changes in soil organic C and N and NO3-N after 4 yr (1985-1989) of no-till and perennial grassland management. The effects were examined over three toposequences in the west-central Great Plains that had been previously under tilled and frequent-fallow systems for > 50 yr. Production systems included wheat (Triticum aestivum L.)-fallow (WF), wheat-corn (Zea mays L.) or sorghum (Sorghum bicolor [L.] Moench)-millet (Panicum miliaceum L.)-fallow (WCMF), and perennial grass (CG). Organic C and N accumulated, was maintained, and declined in 0- to 2.5-, 2.5- to 5-, and 5- to 10-cm soil layers, respectively, for all systems in the relatively short study period (4 yr). More intense systems (WCMF and CG) had greater contents of soil organic C and N in the aggregate 0- to 10-cm layer than WF after 4 yr. Smaller profile (0-180 cm) NO3-N contents occurred under WCMF (60 kg ha-1) and CG (10 kg ha-1) than WF (120 kg ha-1) systems, and showed promise for reducing NO3-N leaching risk with increased cropping intensity. This study indicates that rapid changes in C and N occur with initiation of no-till in soils previously managed under tilled and frequent-fallow systems and that increased cropping intensity will promote higher equilibrium levels of organic C and N, but lower levels of NO3-N.