Soil Quality and Water Intake in Traditional‐Till vs. No‐Till Paired Farms in Washington's Palouse Region

Many farmers in the steeply sloped Palouse region of eastern Washington and northern Idaho practice no-till (NT) farming. Soil quality and water intake parameters were assessed in standing wheat (Triticum aestivum L.) stubble along summit, side, and toe-slope positions in a 2-yr study at three paired-farm sites using traditional tillage (TT) vs. NT management. Paired sites had similar south-facing aspect, slopes ranged from 29 to 45%, and NT fields had not been tilled from 2 to 20 yr. Soil aggregates .1000 mm were 5.4 to 9.8% higher in NT compared with TT. Soil organic carbon (SOC) in NTwas 30% greater than in TT at the toe-slope position. Dehydrogenase enzyme activity (DEA) was higher in TT, mainly due to the exposed CaCO3 layer at the side-slope position and higher pH of TT. Phospholipid fatty acid methyl ester (PLFA) analysis showed that fungal biomarkers were higher and Gram positive and Gram negative biomarkers were lower in NT compared with TT. There were no differences in over-winter soil water storage or ponded water infiltration rate in undisturbed standing wheat stubble between TT and NT, indicating soils that produce high wheat grain yield of 6 Mg ha or more have similar water intake regardless of tillage history as long as the stubble is left standing over winter. Results show long-term cumulative benefits of NT vs. TT on soil quality, but no differences in soil water intake when stubble is left standing over winter, possibly due to the high quantity of wheat root channels produced in both systems. MANY FARMERS in the Palouse region are adopting NT practices to reduce water erosion, enhance soil quality, increase water use efficiency, and improve farm economics. The Palouse region encompasses 750000 ha of cropland that is recognized for world record grain yields of dryland winter wheat that average 6.5 to 7 Mg ha. Tillage is generally intensive, with the moldboard plow historically used to completely invert the top 15 to 25 cm of soil to bury winter wheat stubble to prepare a seedbed. Water erosion rates following moldboard plowing used in past years averaged 45 Mg soil loss ha yr (USDA, 1978). Presently, more than 40% of Palouse cropland is under conservation tillage and water erosion rates are reduced from previous (USDA, 1978) levels, but still exceed the tolerable rate of 11 Mg ha yr in some areas (Renard et al., 1997). Approximately 5% of dryland crop hectares in the western USA are planted using NT (CTIC, 2002). The Palouse region receives an average of 420-to 600-mm annual precipitation with the majority occurring during the winter. Farming is performed on 8 to 45% slopes on deep loessial soils. The land was broken out of native prairie grassland for farming only 125 yr ago, but SOC has declined to half the original values of the native soil during that time (Papendick et al., 1985). Reduction or elimination of tillage will slow or halt the rate of SOC loss and is critical in the development of successful conservation tillage systems (Papendick and Parr, 1997). Research on conservation tillage and cropping systems is needed to improve soil quality, maximize overwinter soil water storage, and reduce water erosion. Potential for economic and environmental benefits is amajor driving force in the ongoing gradual shift by farmers to adopt reducedand no-till farming methods. Surface residue retention and the amount of soil disturbance are key factors in choosing management systems. Surface residue improves soil quality (Doran et al., 1996) by increasing SOC accumulation (Nyakatawa et al., 2001), fungal biomass, earthworm populations, and DEA (Holland and Coleman, 1987; Karlen et al., 1994). Changes in the soil ecology that occur with NT are dependent on many factors, such as landscape position, soil type and depth, precipitation, temperature, and residue management. Due to high residue levels and steep slopes, farmers in the Palouse region have lagged behind other areas of the USA and the world (i.e., Argentina, Brazil, and Canada) in adopting NT. The main collaborators for the study, John and Cory Aeschliman of Colfax, WA, have been leaders in the NT farming movement in the PNW for more than 20 yr (Mallory et al., 1999). The Aeschlimans have adopted NT on their family owned land and, in recent years, on land that they lease. Thus, parcels of the Aeschliman farm have been in continuous NT from 2 to 20 yr. These fields with various years into NT provided an avenue to study changes with NT compared with TT over time. In the PNW, residue burial with tillage during the fall reduces over-winter soil water storage compared with leaving stubble standing over the winter (Papendick and McCool, 1994). One of our goals was to measure the long-term cumulative effects of TT vs. NTon over-winter soil water storage and ponded water infiltration rate, thus tillage was conducted in the spring in this study. Our hypothesis for the experiment was that, as the time in NT A.C. Kennedy, USDA-ARS, 217 Johnson Hall, Washington State Univ., Pullman, WA 99164-6421; W.F. Schillinger, Dep. of Crop and Soil Sciences, Washington State Univ., Dryland Res. Stn., Lind, WA 99341. Mention of product and equipment names does not imply endorsement by the authors or by USDA-ARS and Washington State University. Received 23 May 2005. *Correspondingauthor(akennedy@