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Fall Plow vs Disk-Ripper after Wheat in a W. Wheat-Sp. Barley-Fallow Rotation: Year 2

Kevin Scholz, Colfax, WA
with Roger Veseth, WSU Cooperative Extension; Lavaine Logan, St. John Hardware, Fairfield;
and Dennis Roe, USDA-NRCS, Colfax

Objective

Test the concept that reducing tillage intensity on more erodible, water-short portions of field landscapes could improve soil erosion protection, precipitation storage efficiency and crop yield potential.

Location: Colfax, WA
Average annual precipitation: 17 inches
Soil series: Calouse silt loam
Landscape position: 25-30% slope with south-southeast exposure
Previous crop: Winter wheat, approximately 85 bu/A yield in the trial area
Crop rotation: Winter wheat, spring barley, fallow

Treatments (Fall primary tillage only in winter wheat stubble in October, 1993)

1. Moldboard plow without trashboards to a depth of 7 inches and furrow turned uphill
2. Disk-subsoil with a Sunflower disk-ripper with 20-inch front tandem disk at a 3-inch depth and 7-shank straight-point rippers on 2-ft spacings at about 12-inch depth

Comments

This study was established in the fall of 1993 to compare the effects of fall uphill plowing versus disk-subsoiling after winter wheat on spring barley production in 1994 and on soil erosion protection during the 1995-96 winter wheat crop on fallow following spring barley. The disk-ripper resulted in similar tillage impacts on residue and roughness as with disking after harvest and late-fall chiseling, a common sequence of operations in the intermediate precipitation zone.

Plots were arranged end-to-end along the contour in the top 80 feet of a divided-slope field division. Plot lengths ranged from 300 to 450 feet. Plow treatments were established first, with the plow being pulled out to cross disk-ripper plots. The disk-ripper plots were then established using a back-and-forth pattern, turning on the edge of the adjourning plowed plots with the turning margins excluded from data collection. Spring field operations on all plots in 1994 included: harrowing, field cultivation, shank fertilizer application, rod weeding, and seeding spring barley.

Summer fallow operations in 1995 included spring chiseling, 3 rodweedings, field cultivation (following a heavy August rainstorm), shank fertilizer application, rodweeding and seeding winter wheat in late September with double disc drills.

Surface residue levels have been determined in 1994 before spring tillage for spring barley and after barley seeding, and in 1995 after winter wheat seeding on summer fallow to help evaluate the effect of these 1993 primary tillage operations after wheat on water erosion potential in the rotation.

Highlights of trial results from 1994 PNW On-Farm Test Results publication -- The spring pre-tillage disk-ripper treatment plots contained 2.8 times more surface residue than the plow plots (3326 vs 1187 lb/A). Surface residue percent cover remaining after seeding spring barley was also significantly higher (67 vs 47%).

The disk-ripper significantly increased overwinter soil water storage (.64 inches) in the top 3 feet of soil and resulted in a significant yield increase (320 lb/ac) over moldboard plowing.

Data

Conclusions and Comments

Although there was a trend towards higher surface residue levels in the disk-ripper treatments, the difference was not statistically significant at the 5% probability level due to the variability of residue levels between reps in disk-ripper plots. Surface residue levels were lower than normal after winter wheat seeding in this field and attributed partially to an intense August rainstorm and increased residue decomposition rate with moist conditions through the fallow season. Soil erosion will be monitored in the plots overwinter in the winter wheat crop.

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU