Monday, November 13, 2006

Deep Tillage Effects on Crop Productivity and Soil Properties 30 Years After Treatment.

R. Louis Baumhardt1, Ordie R. Jones2, and Robert C. Schwartz1. (1) USDA-ARS Conservation and Production Res. Lab., PO Drawer 10, 2300 Experiment Station Rd., Bushland, TX 79012, (2) Texas Cooperative Extension, 6500 Amarillo Blvd. West, Amarillo, TX 79106

Limited plant available soil water decreases dryland crop yields on the southern Great Plains. Deep tillage to disrupt dense subsoil layers may increase rooting and infiltration for greater soil water availability, but the duration of treatment efficacy may not offset costs. Objectives were to quantify soil density, penetration resistance, ponded infiltration and crop yield on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) 30 years after deep tillage at the USDA-ARS, Conservation and Production Res. Lab., Bushland, TX (35° 11’ N, 102° 5’ W). In 1971, paired 24 x 460 m level conservation bench terrace plots were moldboard plowed to 0.7 m or stubblemulch tilled and cropped with grain sorghum [Sorghum bicolor (L.) Moench] thru 2004 for yield comparisons. Ponded infiltration, bulk density, and penetration resistance were measured during the summer of 2002. Deep inversion tillage decreased initial soil profile bulk density and penetrometer resistance, but were not significantly different after 30 years. Ponded infiltration after 30 years, however, increased with deep tillage. Longterm mean annual grain yield increased ~ 10% with deep tillage compared with stubblemulch tillage because of increased infiltration and, possibly, rooting depth. Increased yield with deep tillage for two of the 14 paired crops accounted for > 50% of the cumulative yield benefit and was attributed to improved drainage of rain flooded plots. Deep inversion tillage effects measured after > 30 years show that flow limiting subsoil layers did not redevelop, which extended the period to recoup the 1971 plowing costs of $160 per ha. For a Pullman soil, deep inversion plowing may be an economical soil profile modification treatment.