Eight years of annual no-till cropping in Washington's winter wheat-summer fallow region

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Abstract

The tillage-based winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) cropping system has dominated dryland farming in the Pacific Northwest USA for 125 years. We conducted a large-scale multidisciplinary 8-year study of annual (i.e., no summer fallow) no-till cropping systems as an alternative to WW-SF. Soft white and hard white classes of winter and spring wheat, spring barley (Hordeum vulgare L.), yellow mustard (Brassica hirta Moench), and safflower (Carthamus tinctorius L.) were grown in various rotation combinations. Annual precipitation was less than the long-term average of 301 mm in 7 out of 8 years. Rhizoctonia bare patch disease caused by the fungus Rhizoctonia solani AG-8 appeared in year 3 and continued through year 8 in all no-till plots. All crops were susceptible to rhizoctonia, but bare patch area in wheat was reduced, and grain yield increased, when wheat was grown in rotation with barley every other year. Remnant downy brome (Bromus tectorum L.) weed seeds remained dormant for 6 years and longer to heavily infest recrop winter wheat. There were few quantifiable changes in soil quality due to crop rotation, but soil organic carbon (SOC) increased in the surface 0–5 cm depth with no-till during the 8 years to approach that found in undisturbed native soil. Annual no-till crop rotations experienced lower average profitability and greater income variability compared to WW-SF. Yellow mustard and safflower were not economically viable. Continuous annual cropping using no-till provides excellent protection against wind erosion and shows potential to increase soil quality, but the practice involves high economic risk compared to WW-SF. This paper provides the first comprehensive multidisciplinary report of long-term alternative annual no-till cropping systems research in the low-precipitation region of the Pacific Northwest.

Introduction

An agroecosystem approach to dryland farming is needed in the low-precipitation (<340 mm annual) dryland cropping zone of the inland Pacific Northwest because the wide spread practice of growing only one crop every 2 years in a tillage-intensive WW-SF rotation has degraded soils and contributed to environmental problems. Blowing dust from excessively tilled soil is the major soil loss and agricultural environmental concern in the 1.5 million hectare WW-SF region.

Soils in the region are particularly vulnerable to wind erosion due to the dry environment, limited vegetation, high winds, intensive tillage, and because they contain substantial quantities of readily erodible and suspendible fine particulates (Papendick, 2004). Fine particulate emissions during dust storms are hazard to motorists due to lack of visibility and are a health concern when inhaled into lungs (Saxton et al., 2000). These soils have lost 50% of their original SOC in the surface 10 cm from topsoil erosion and oxidation since the onset of farming (Kennedy et al., 2004). Options for maintaining and improving soil quality are to increase the cropping intensity and reduce or eliminate tillage.

The WW-SF system is popular with farmers because it provides relatively stable grain yields and poses less economic risk compared to wheat or barley grown on an annual basis (i.e., one crop each year) (Young et al., 1999). Tillage practices for the WW-SF system frequently involving eight or more passes with various tillage implements during the 13-month fallow period. Conservation-till and no-till farming methods have become increasingly popular with farmers in many areas of the world, but adoption of such practices in the low-precipitation dryland zone in the Pacific Northwest has been limited (Schillinger et al., 2006).

The objective of our experiment was to evaluate the agronomic and economic feasibility of long-term no-till annual crop production in a typical WW-SF production region. A further objective was to document soil quality changes and benefits that may occur during the transition period from intensively tilled WW-SF to no-till annual cropping.

Section snippets

Treatments

An 8-year field study of no-till annual cropping systems was conducted from 1997 to 2004 at the Ronald Jirava farm near Ritzville, Washington. The soil at the experiment site is a Ritzville silt loam (coarse-silty, mixed, superactive, mesic Calcidic Haploxeroll) (US classification system), also known as a Haplic Kastanozems (FAO/UNESCO, 1990). Soil is more than 2 m deep with no rocks or restrictive layers and slope is less than 1%. The bulk density of native (i.e., never been farmed) soil is

Precipitation and soil water

Crop year (1 September–31 August) precipitation during the 8-year period ranged from 188 to 486 mm and averaged 262 mm (Table 1). Long-term (30-year) precipitation for the site averages 301 mm. Below average precipitation occurred in seven of the eight crop years.

Plant available soil water in late winter/early spring (measured just before planting) for the continuous annual soft white spring wheat treatment ranged from 81 to 257 mm and averaged 134 mm over the 8 years (Table 1). Wheat farmers in the

Summary and conclusions

  • 1.

    The oilseed crops safflower and yellow mustard used more soil water by harvest compared to cereals, resulting in significantly less available soil water for crops that followed in the rotation.

  • 2.

    Rhizoctonia bare patch caused by Rhizoctonia solani AG-8 infected all crops in all rotations beginning in year 3 and continued through year 8. The area with bare patches averaged over all crops during these years ranged from 7.5 to 11.7% of total plot area.

  • 3.

    Russian thistle was the most troublesome

Acknowledgements

The authors gratefully acknowledge the cooperation, technical guidance, and support of Ronald Jirava on whose farm the research was conducted. We thank Harry Schafer, Steven Schofstoll, and Tami Stubbs, Washington State University agricultural research technicians, and Jeremy Hansen USDA-ARS research technician for their excellent support. Funding for the study was provided by Washington State University, the USDA-ARS, the Columbia Plateau PM10 Project, and the Solutions to Economic and

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