Long term effects of profile-modifying deep plowing on soil properties and crop yield

Authors: Baumhardt, Roland - Louis; JONES, O. REGGIE - TX COOP EXT; ARS-RETIRED; Schwartz, Robert

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2007
Publication Date: 5/1/2008
Citation: Baumhardt, R.L., Jones, O., Schwartz, R.C. 2008. Long term effects of profile-modifying deep plowing on soil properties and crop yield. Soil Science Society of America Journal. 72:677-682.

Interpretive Summary: Insufficient plant-available soil water limits dryland crop yields on the semiarid Southern Great Plains. Deep plowing to break up dense subsoil may increase available soil water by increasing infiltration and rooting, but the duration of plowing effects must be long to pay plowing costs. Our objective was to quantify the long-term effects of deep plowing a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) on soil bulk density, penetration resistance, ponded infiltration, and crop yield. In fall 1971, paired 80 x 1500 ft. level conservation bench terrace plots at the USDA-ARS, Conservation and Production Research Laboratory, Bushland, Texas, were moldboard plowed to 27 inches or untreated and, subsequently, maintained with sweep tillage. Grain sorghum was grown intermittently during the next 34 years for 15 paired yield comparisons. Compared with the control, deep plowing significantly decreased bulk density (BD) and penetration resistance (PR) and increased water infiltration in 2002. Long-term mean annual grain yield of 2800 lbs/acre with deep plowing was significantly (p < 0.05) greater than the 2550 lbs/acre yield in control plots; however, four of the 15 paired sorghum crops accounted for about 85% of the total yield benefit with deep plowing. We attributed this yield benefit to improved internal drainage that prevented crop injury due to rain flooded plots. Thirty years after soil profile modifying deep plowing, our measurements show improved water intake and that flow limiting subsoil layers did not redevelop. The sustained deep plowing benefit extended the period to recoup 1971 deep plowing costs of $65 per acre.

Technical Abstract: Insufficient plant available soil water limits dryland crop yields on the semiarid Southern Great Plains. Deep plowing to eliminate dense subsoil layers may increase soil water by increased infiltration and rooting, but the duration of treatment effects must be sufficiently long to recoup plowing costs. Our objective was to quantify the long-term effects of deep plowing a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) on soil bulk density, penetration resistance, ponded infiltration, and crop yield. In fall 1971, paired 24 x 460 m level conservation bench terrace plots at the USDA-ARS, Conservation and Production Research Laboratory, Bushland, Texas (35 degrees 11' N, 102 degrees 5' W) were moldboard plowed to 0.7 m or untreated and, subsequently, maintained with sweep tillage. Grain sorghum [Sorghum bicolor (L.) Moench] was grown during the next 34 years for 15 paired yield comparisons. Compared with the control, deep plowing decreased bulk density (BD) and penetration resistance (PR) and increased water infiltration in 2002. Long-term mean annual grain yield of 2.87 Mg ha-1 with deep plowing was greater (p < 0.05) than the 2.61 Mg ha-1 yield in control plots; however, four of the 15 paired sorghum crops accounted for ~ 85 percent of the cumulative yield benefit with deep plowing. We attributed this yield benefit to improved internal drainage that prevented crop injury due to rain flooded plots. Thirty years after soil profile modifying deep plowing, our measurements show improved water intake and that flow limiting subsoil layers did not redevelop. The sustained deep plowing benefit extended the period to recoup 1971 deep plowing costs of $160 ha-1.