Soil Quality Assessment of Long-Term Direct Seed to Optimize Production

Project Overview

Project Type: Research and Education
Funds awarded in 2012: $193,448.00
Projected End Date: 12/31/2015
Region: Western
State: Washington
Principal Investigator:
Ann Kennedy
Washington State University/ARS

Annual Reports


  • Agronomic: barley, canola, wheat, grass (misc. perennial), hay


  • Animal Production: feed/forage
  • Crop Production: conservation tillage
  • Education and Training: decision support system, demonstration, extension, farmer to farmer, mentoring, on-farm/ranch research, participatory research, workshop, youth education
  • Farm Business Management: agricultural finance, risk management
  • Natural Resources/Environment: carbon sequestration, biodiversity, indicators, soil stabilization
  • Production Systems: agroecosystems
  • Soil Management: organic matter, soil analysis, nutrient mineralization, soil microbiology, soil chemistry, soil physics, soil quality/health


    Producers in the Pacific Northwest of the United States and worldwide are adopting direct-seed practices to reduce soil erosion, improve soil quality, increase water infiltration, and reduce the number of passes with farm equipment. Direct-seed farming creates the physical conditions of surface-managed residues and undisturbed soil that leave soil less susceptible to erosion and keeps more soil on the land. Direct-seed producers are concerned about not reaching the yield and profit potentials that were anticipated with long-term direct seeding.

    To identify those soil characteristics that differ between farming practices and may play a part in limiting yield potential, soil from thirteen long-term direct-seed sites and three conservation-farmed sites was examined. Sites were selected to represent low, intermediate, and high rainfall zones of the dryland farming region of Eastern Washington and Northern Idaho. Soil from direct-seed, conservation-farmed, and undisturbed sites was collected from 2.5 cm (1 in) increments for the first 10 cm (4 in) and 5 cm (2 in) increments there-after to 20 cm (8 in) at three landscape positions. The physical, chemical, and biological parameters of soil quality were evaluated at each landscape position.  Unique soil stratification caused by the lack of soil disturbance inherent in direct seeding coupled with the continual application of fertilizers in the same soil depth has resulted in zones of low pH.  The pH values of these soils ranged from 4.49 to 7.5 with Al (KCl extractable) to as high as 180 mg/kg, and Mn as high as 239 mg/kg.  The pH values were lowest in the 5-7.5 cm (2-3 in) and 7.5-10 cm (3-4 in) depths.

    We found:

    1. Bulk soil sampling to 10 or 15 cm (4 or 6 in) could not identify low pH soil layers. Instead, sampling in 2.5 to 5 cm (1 or 2 inch) increments was needed to illustrate the low pH layers.
    2. Only 7 of the 16 sites had soil layers with significantly lower pH, higher Al, and higher Mn than the bulk soil.
    3. The sites with low pH, high Al, and high Mn layers were more frequent in the high rainfall zone (67%), but these layers were found in the other precipitation zones as well (Intermed. 33%; Low 25%).
    4. The layers of low pH soil were more prevalent in the top and mid landscape than the bottom.
    5. Two direct-seed sites (8, 13) received 1 or 2 additional tillage passes than other direct-seed sites each year and low pH layers were not evident.
    6. Broadcast lime increased the surface soil pH and partially increased pH  from 0 to 5 cm (0 to 2 in).
    7. Lime and tillage incorporated lime from 0 to 7.6 cm (0 to 3 in) but did not increase pH at the lower depths.
    8. Lime application to increase pH in these layers is not economically feasible when compared with tillage. Liming costs  7.5 times more than occasional tillage or subsoiling. Some sites were low in potassium, sulfur, zinc, nickel, or boron that may collectively contribute to lower yields.

    Our recommendations to producers are:

    1. Check soil pH by taking incremental 2.5 to 5 cm (1 to 2 in) field measurements with a handheld, flat surface pH meter. Bulk soil samples dilute the layer effects.
    2. Lime application to increase pH in these layers is not economically feasible when compared with tillage.
    3. Tillage (vertical cut) once every 4 years minimizes layers without costly lime. Additional tillage passes do not alter soil quality and soil organic matter benefits of direct-seed.
    4. One-time fertilizer additions may improve macronutrient and micronutrient availability.

    This project furthers our knowledge of soil quality in agricultural systems, points to the importance of incremental soil tests, and assists in refining profitable best management practices for direct-seed systems.

    Project objectives:

    We investigated soil quality characteristics of thirteen long-term direct-seed sites and three conservation tillage sites Table 1 Table 1 sites SW12-122 to identify those characteristics that may play a part in reducing system resiliency or limiting yield potential. Soil quality is critical for sustainable agriculture and one of our goals is to better understand and improve soil quality to improve sustainable agriculture. Net farm income is also critical for sustainable agriculture and economic feasibility of management systems is key. With these factors identified, management options can be investigated and strategies developed.

    Our objectives were to:

    1) Evaluate, incrementally with depth, soil quality of long-term direct-seed fields across landscape in relation to crop yield parameters;

    2) Evaluate management options to remedy the yield-limiting soil characteristics;

    3) Compute the effects on profitability of management remedies to sustain long-term direct-seed yields; and

    4) Inform producers, land managers, agri-business personnel and landlords about the agronomic and economic benefits of direct-seed cropping systems and also the management options to remedy soil quality and yield potential concerns.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.