Mikha, Maysoon (USDA-ARS, 40335, County Road, GGAkron, CO, 80720; Phone: 970-345-2259; Fax: 970-345-2088; Email: maysoon.mikha@ars.usda.gov)


Soil Carbon and Nitrogen in Dryland Cropping Systems


M.M. Mikha *, M.F. Vigil


The predominant cropping system in the Central Great Plains winter wheat summer fallow (W-F) is not sustainable.  Losses of soil organic matter (SOM) in the Great Plains are associated with tillage and summer fallow management.  Intensive cropping systems with reduced tillage and fallow frequency are management practices that provide more residues and may increase soil C and N content.  This study investigated the effect of five different crop rotations on soil total C (TC), total N (TN), and yield. Various cropping intensities comprised of winter wheat (Triticum aestivum L.), corn (Zea mays L.), proso millet (Panicum miliaceum L.), seed pea (Profi Pea), and fallow were evaluated and to compared to W-F.  The experiment was established in 1990 on a Weld loam (fine, smectitic, mesic aridic Paleustolls).  In 2004, soil samples were collected (0- to 5 and 0 to 15 cm depths) from the field treatments and evaluated for soil C and N.  Fourteen years of continuous cropping improved soil TC compared with NT and CT W-F rotation at 0- to 15 depth.  Soil TC and TN significantly (p less than 0.05) increased with NT W-F compared to CT W-F especially at 0- to 5 cm depth.  Continuous cropping such as W-C-M significantly (p less than 0.1) increased soil TC (0-to 5 cm) compared with NT W-F and W-C-F cropping systems.  There was a trend for increased TC for W-C-M-F and W-C-M-P compared with W-F but the increase was not statically significant (p less than 0.1).  More than 40% of  TC and TN was associated with 0- to 5 cm depth except for CT W-F were TC and TN represent 35 and 33% of 0- 15 cm, respectively.  Wheat grain yield was significantly affected by rotations.  Grain yields were significantly greater in NT W-F, W-C-F, and W-C-M-F than in CT W-F and W-C-M.  Generally, NT and continuous cropping with reduced fallow improved soil TC at the soil surface (0-5 cm).