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

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

Summary

Producers in the Pacific Northwest, United States, and worldwide are adopting direct seed farming to reduce soil erosion, improve soil quality, increase water infiltration, and reduce 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 wind and water erosion to keep more soil on the land. Direct seed producers are concerned about not reaching the yield and profit potential that was expected with long-term direct seed. One of the many factors contributing to this yield suppression is the unique soil stratification caused by lack of soil disturbance that makes nutrients unavailable for plant uptake due to pH, electrical conductivity (EC), or banding of nutrients; or nutrients present at high levels that inhibit plant growth. We are investigating the soil quality of thirteen long-term direct seed sites and three sites farmed with conservation tillage to identify those characteristics that play a part in limiting yield potential. Sites were selected to represent low, intermediate, and high rainfall zones of the dryland farming region of eastern Washington and northern Idaho. The bulk pH values of these soils range from 5.0 to 7.4, with the lowest pH values in the 2 to 4 inch depths. At some depths pH was as low as 4.49 and aluminum (Al) was as high as 180 mg/kg. Aluminum levels were highest in the 2-3 and 3-4 inch depths, and lowest at 6-8 inches. Averaged over all the farmed sites, pH was highest at the 6-8 inch depth and did not differ significantly from the 0-1 inch depth. A mail survey of the 16 producers had a 75% overall response rate, and 89% of those with high Al in some soil depths responded. Gradual lime application suffered a substantial economic disadvantage compared to the tillage-only practices. Cultivating once and twice every fourth year, and subsoiling every fourth year increased costs only 5.13, 10.27 and 9.99 $/ac/yr. Liming practices (0.5t/ac/yr) averaged 71.68 $/ac/yr, 7.47 times higher costs on average. This project is furthering our knowledge of soil quality in agricultural systems and is assisting in developing profitable best management practices for direct seed systems.

Objectives/Performance Targets

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

In the fall of 2015, soil samples were collected from each of the four sites to which lime was applied. Three sites in this study, after being identified as having potential pH and Al problems, were involved in liming studies associated with the individual producer’s county.  Those results are not included here. We sampled from fields that were previously monitored and limed in 2014 or 2015. The pre- and post- lime soil characteristics were compared. The sites used were in the winter wheat phase of the crop rotation.  At each site, three landscape positions were sampled as previously indicated: ridgetop, mid-slope, and bottomland.  Three replications were collected from each landscape position, with each replication the composite of five cores collected using a king tube (5 cm dia.).  The samples were collected at increments of 0-1 inch, 1-2 inch, 2-3 inch, 3-4 inch, 4-6 inch, and 6-8 inch  Soil samples were stored at 4^oC until analysis.  In addition to the pH, EC, Al, C (total and organic), NO₃-N, NH₄-N, K, Ca, Mg, P, S, CEC, Fe, Zn, B, Mn, Cd, Mo, Ni, Cu, β-glucosidase and dehydrogenase enzyme activity that have been performed, we are conducting phospholipid fatty acid analysis (PLFA) for soil microbial community analyses.

The goal of this objective was to investigate the soil quality parameters that may be contributing to direct seeders’ inability to reach yield potential and provide an outlet to disseminate new information, while allowing experienced producers to share the skills and understanding they have gained from years of direct seeding. Yields were not collected during soil sampling, but investigators elicited producers’ annual yields and annual precipitation for 2010-2014, plus other information in a mail survey during 2015.  We discuss these results under objective 3.

Objective 2: Evaluate management options to remedy the yield-limiting soil characteristics.

We sent mail questionnaires to all 16 producers in the study sample. Appendix I contains the 4-page questionnaire sent to seven and two producers with high and minor Al at several depths in their soils, respectively.  The 2-page questionnaire sent to the seven growers with no Al potential included questions 10, 11, 12, 13, and 14 from the questionnaire in Appendix I.  Al levels from soil testing categorized growers into high, minor, and no AL levels.  Among the 16 producers, three used conservation tillage and the other 13 direct seeded.

After several phone calls and emails by the investigators, survey response achieved 75% overall and 89 and 57 percent for the some (high and minor) Al group and no Al groups, respectively. We were pleased with the relatively high response rates among the key Al group.  Two of the three conservation producers responded.  As will be noted, not all respondents answered every section of the questionnaire.

The evaluation of management options to remedy the yield-limiting soil characteristics will be presented under Objective 3 which presents an economic comparison of these options. This section will present an overview of survey findings regarding dominant crop rotations, tillage sequences, and farm size of responding producers.

Table 1 shows that all seven of the responding producers from the high precipitation zone grew pulses or other broadleaves in their crop rotations, including peas, garbanzo beans, lentils, and canola. As expected, three of five of the low and intermediate precipitation zone producers included fallow in their rotation.  Somewhat surprisingly, two of the five used continuous cropping with spring wheat alone or alternated with winter wheat.

Conservation Tillage Producer-#5 and Conservation Tillage Producer-#7 in Table 1 reported using somewhat more aggressive tillage than the other direct seeders; Direct Seed Producer-#4 reported using vertical tillage, Producer-#8 disking, and Producer-#11 chiseling. Consequently, 3 of 10 or 30% of the direct seeders reported using some tillage.  Eleven responding producers reported a median farm size of 2,600 acres ranging from 320 to 7,000. This is typical of commercial farms in the region.

Objective 3: Compute the effects on profitability of management remedies to sustain long-term direct seed yields.

Soil scientists have lamented the serious absence of economic analysis of practices to remediate acidity in direct seeded or other fields (Schroeder and Pumphrey, 2013; Sullivan, Horneck and Wysocki, 2013). The only analyses found in the agricultural economics literature focused on Bangladesh (Shaheb, Nazrul and Rahman, 2014) results from 50-year-old experiments (Malhi, Mumey, Nyborg, Ukrainetz and Penney, 1994), and research based on Oklahoma soils ranging from pH of 4.1 to 5.2 (Lukin and Epplin, 2003).  In contrast, sites selected for this inland Pacific Northwest sites displayed pH values averaging 5.0 to 7.4.

This section reports two avenues for exploring economic consequences of different management remedies to sustain direct seeding. The first is to compute the added cost of different practices to ameliorate high aluminum levels in soil.  We also compute the associated breakeven winter wheat yield increases to pay for these practices.  Our computation of costs is compared to the surveyed producers’ perceived costs.  Secondly, we present the results of regression results to attempt to determine the effect of high Al, annual precipitation, and other factors on annual winter wheat yields.  The latter are a primary driver of gross economic returns.  Our methodology and sources for the added costs and breakeven wheat yield increases in Table 3 are described in the footnotes.

The breakeven yield increase to pay for a practice equals: added cost/price wheat. We use a five-year average price of wheat to remove transient spikes and depressions in wheat prices. Because the breakeven yield increase is measured in bu/ac/yr, a producer with a WW/fallow rotation would need to compare it to his annualized yield or crop year yield divided by two.

Table 2 presents the added costs and breakeven winter wheat yield increases for 11 practices for remediating the effects of high Al and potential Al toxicity. Practices #1-#8 correspond to the same-numbered practices on page 1 of the Al toxicity questionnaire in Appendix I.  Practice #0 is a benchmark “Do nothing” practice and practices #9 and #10 were recommended by a producer and investigator, respectively.  Practice #’s 1, 2, 8, 9 and 10 propose tilling without adding lime.  The rationale for tilling, reinforced by the soil testing data from this project, is that high Al, low pH, and potential other soil problems are banded heterogeneously at different depths.  Mixing the soil with tillage may improve the ability of crop roots to cope with these potentially toxic layers (Mahler, 1994; Ball, undated; Sullivan, Horneck and Wysocki, 2013).

All costs in Table 2 are annualized per the units listed in the text and table. This compares apples to apples.  For example one tillage pass every four years equals the cost of a pass in a single year divided by four.  As noted in the units of measurement, the liming treatments assume application of 0.5 t/ac of lime every year.  These costs include the cost of broadcasting the lime, if designated, and then the cost of tilling it in, plus the delivered cost of the lime.  The same consistent annualization applies to the breakeven winter wheat yield increases (bu/ac/yr).  Practices #3-#7 describe applying lime by various methods. Soil scientists recommend applying lime gradually and periodically to increase effectiveness and reduce annual cost (Sullivan, Horneck and Wysocki, 2013; Ball, undated).  Consequently lime application is limited to the modest rate of 0.5 t/ac/yr.  Even this rate is founded on little definitive research that lime application increases yields in the inland Pacific Northwest. Koenig (email communication, 12/13/2015) provided data from four unpublished studies in eastern Washington that failed to show statistically significant yield response to lime in winter wheat or peas.  Bezdicek, Beaver and Granatstein (2003) failed to detect a significant yield response to 1.2 t/ac of lime to peas in two of two trials and in one of two winter wheat trials. These conclusions were based on starting pH ranging from 4.36 to 5.33 which are relatively more acidic than the sites in this project.

In sharp contrast to the inconsistent evidence from the soil science literature of a yield response to lime in this region, the estimates in Table 2 show that gradual lime application suffers a definite economic disadvantage compared to the tillage-only practices #’s 1, 2, and 10. Cultivating once and twice every fourth year, and subsoiling every fourth year add only 5.13, 10.27 and 9.99 $/ac/yr.  Liming practices #3-#7 average 71.68 $/ac/yr, averaging 7.47 times higher costs.  And recall, there is inconsistent evidence that liming will boost yields. The three tillage practices require an average of only 1.39 bu/ac/yr more winter wheat to pay for them, compared to 11.79 bu/ac/yr to pay for the liming practices. Neither our research nor other findings in the literature documented yield increases from varying amounts of tillage on only moderately acidic soils.  However, the modest yield increases to justify a yield response should motivate both scientists and producers to document yield results with tillage. Questions 6-10 of the Al toxicity questionnaire probed for producers’ willingness to incorporate some tillage in their dominantly direct seeding systems.  The results, not summarized in a table, revealed that 38, 13, and 0 percent would permit one, two, and three tillage passes, respectively, “enthusiastically or with minor reluctance.”  Others were strong adherents to pure no-tillage.  Some 25, 38, and 75 percent would “absolutely refuse” to use one, two, or three tillage passes, respectively.

How do our estimates of the costs of practices to manage high Al compare to producers’ perceptions elicited in the survey? Table 3 presents producers perceptions for practices #’s 1-9 and the costs presented in Table 3.  Table 3 abbreviates the practices from the survey but they are essentially the same as the more precise practices in Table 2.  Rough consistency exists between producers’ and our estimates.  Three of seven producers perceived our inexpensive practices #’s 1 and 2 as least expensive and five of six producers evaluated our most expensive #’s 4 and 7 as most expensive.  Somewhat surprisingly only one producer preferred our inexpensive practices #’s 1 or 2.  Only two producers supplied answers to “a most difficult practice.”  An unexpected two of seven producers perceived the expensive liming practices (#’s 4 and 7) as least expensive.  We attribute this to little recognition of the high, $84/ton, price of delivered lime.  Broadcasting and tilling in lime also elevates the cost.

As a second avenue to estimate the effects of high Al, producer resistance to tillage, plus other factors on winter wheat yields, we estimated the following simple linear regression by ordinary least squares (regressit.com, 2015):

(1) AvwwYield_jt= B₀+B₁PPT_jt+B₂Fal_j+B₃High AL_j+B₄Outlier_j+B₅Till_j + Error Term

• AvwwYield_jt
  • Average whole farm winter wheat yield (bu/ac) of surveyed producer j in year t
• PPT_jt
  • Producer_j’s reported inches Sept.-Aug. crop year precipitation in year t
• Fal_j
  • =0 if dominant crop rotation does not include fallow for producer j
  • =1 if dominant crop rotation does include fallow for producer j
• High Al_j
  • = Highest KCL Al mg/kg across season year, landscape and soil depth for producer j based on project soil tests
  •  
• Outlier_j
  • =0 if not producer_j with statistically different yield pattern and management
  • = 1 if producer_j with statistically different yield pattern and management
• Till_j
  • =multiplicative index of producer j’s resistance to tillage based on answers to questions 6-9 of Al toxicity questionnaire. (Likert Scale) 
  • multiplicative index: ∑(No. tillage passes, 1-4)(Likert Scale)
  • Would absolutely refuse to till = 5
  • Strongly reluctant but might do so = 4
  • Would begrudgingly do so = 3
  • Would do so with minor resistance = 2
  • Would enthusiastically do so = 1

Example Index Calculation

Regression data summary:

Seven producers providing full information X 5 years (2010-2014) = 35 observations Lost degrees of freedom (B₀, …, B₅) = 6 Remaining degrees of freedom =  29

After extensive experimentation, the regression specification in equation (1) achieved the highest adjusted R².  Table 4 presents the final data we utilized to estimate the equation. Two producers from the low precipitation region provided the 10 annual observations for FAL = 1.  Annual winter wheat yields range from 12.6 to 64.3 bu/ac and annual precipitation from 8.1 to 14.2 in/yr for this group of semiarid region producers.  This group had relatively lower High Al ranging from 7 to 30 KCL Al mg/kg and the upper bound resistance to tillage of 50. Five high precipitation region producers, with FAL = 0, provided complete data for our regression.  Farm wide annual winter wheat yields range from 51.0 to 115.5 bu/ac and annual precipitation from 13.7 to 25.4 in/yr for this group of high moisture region producers. The lower yields were found on the outlier farm.  This group had relatively elevated High Al ranging from 17 to 84.  Their resistance to tillage was moderate at 33 to 50. Eleven of 50, or 22%, of the annual farm wide winter wheat yields from the high precipitation group exceeded 90 bu/ac.  This is evidence that high Al was not a barrier to excellent winter wheat production in favorable years.

Equation (2) lists our final estimated equation with p-values under the coefficients:

(2) AvwwYield = 67.66 + 2.46  PPT + -33.96 Fal + -0.12 High Al + -23.27 Outlier + -0.43 Till

                        0.034^**   0.003^**        0.000^***           0.338^ns                 0.005^***                  0.391^ns

NOTE: ^*** significant at <= 0.01, ^** significant at <= 0.05, ^ns not significant

Adj. R² = 0.811, Std. error of regression = 12.21

PPT, Fal, and Outlier display expected signs at statistically significant levels; however, our important High Al and Till variables fail statistical significance for this data set. The absence of a depressing yield influence for only moderately high Al coincides with the conclusions of most previous research in the region.  On the whole, we consider the regression result to be relatively weak because of the small number of observations, only five independent variables and data based on grower recall.

Two surveyed producers provided annual spring wheat (SW) yield data with annual precipitation. Our attempts to estimate yield regressions failed with this 10-observation data set.  The highest adjusted R² was 0.296 and none of the three coefficients were statistically significant.  We lacked sufficient complete data for pulses to attempt any yield regressions.

Objective 4: Inform producers, land managers, agribusiness 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.

Highlights of this study for growers

In sharp contrast to evidence from the soil science literature of an inconsistent yield response to lime in this region, our analysis showed that gradual lime application suffers a sharp economic disadvantage compared to tillage-only practices. Cultivating once and twice every fourth year, and subsoiling every fourth year, increased cost only 5.13, 10.27 and 9.99 $/ac/yr for an average of 8.46 $/ac/yr.  Liming practices averaged 71.68 $/ac/yr, 8.47 times higher.  The three tillage practices required an average of only 1.39 bu/ac/yr more winter wheat to pay for them, compared to 11.79 bu/ac/yr to pay for the liming practices.  Neither our research nor other findings in the literature have documented yield increases from varying amounts of tillage on only moderately acidic soils.  However, the modest yield increases we estimated to justify a yield response should motivate both scientists and producers to try and document the results of tillage.

Neither a review of the research literature from the region nor regressions of surveyed producers’ winter wheat yields on Al levels in the 2 to 4 inch depths showed a consistent negative yield effect from moderately acidic soils in the region.

Suggestions for further research relevant to growers

We considered only periodic tillage and lime application management practices for low pH soils. Other alternatives including planting acid tolerant varieties of wheat, crops like triticale that tolerate acidic soils, and better lime application procedures should be considered.  If data were available, economic analysis should consider longer run consequences of different management practices, including doing nothing.  Similarly, if data were available, managing for optimal pH might permit economizing on fertilizer or other inputs.

Outreach

Individual producers were contacted each winter and results were discussed with them for their land. These meetings and discussions were a critical part of this project so that the producers were made aware of the data collected as soon as possible and could make decisions based on the data collected. Other outreach efforts to producers, land managers agribusiness personnel and landlords are listed below.

2013: We were invited and presented fourteen seminars on Soil Quality in Cropland, Direct Seed Production or Rangeland Situations : (420 producers or landowners) Highlights; Columbia Basin Crop Consultants Association Seminar Moses Lake, WA; ‘Soil Quality’ to BLM Pesticide Certification Training 03/20/13, Boise ID; and 4/30/2013, Albuquerque NM

2014

Received Far West Award for Technology Transfer Oct 21, 2014:

We were invited and presented 14 seminars on Soil Quality in Cropland, Direct Seed Production or Rangeland Situations (>650 people): Highlights: dePaul University, Chicago, IL multiple talks (12/10); BLM pesticide certification classes Albuquerque, NM (2/26) and Boise ID (4/2); Worley, ID (7/14)

2015

We were invited and presented 38 seminars on Soil Quality in Cropland, Direct Seed Production or Rangeland Situations (1205 people) on Soil Quality: Webinar CA producers (10/10); Marsing ID, (10/27); Aberdeen Area Producers, Aberdeen, ID (10/29); Nampa Producers, Nampa, ID, (10/29); Colfax, WA (2/11); BLM, pesticide certification classes Albuquerque, NM (2/24) and Boise ID (3/24); SARE Stacie Clary visit seminar (5/11).

Public and K-12 activities.

Our soil quality group is committed to increasing the exposure of soils and soil quality and to educate the public about science. We work with K-12 teachers monthly to bring soil quality science experiments into the classroom as a means to encourage young students’ interest in science.  We routinely go into the classroom for science demonstrations, Career Days and Science Fairs.  Annually we bring several groups of students into the laboratory and the field to develop their interests in agricultural science.  The Soil Quality group was instrumental in bringing the Smithsonian Dig-It exhibit to the PNW and providing funding for travel and tickets for classroom students.  We led the hands-on-experiments that were provided to more than 9,000 student visitors to the exhibit. Our outreach efforts communicate with more than 750 producers and 600 students annually. Our activities further the education of students, so that they will recognize their abilities in thinking and problem solving to make the best choices for their future. As additional management data are collected, we will present the results at producer field days. Upon completion of the project, results will be published in industry publications as well as scientific journals.

• Table 1. Dominant crop rotations and tillage sequences for 12 responding producers
• Table 2. Added costs and breakeven winter wheat (WW) yield increases of selected practices
• Table 4. Regression data for five producers supplying complete information
• Appendix I Grower Questionnaire
• Table 3. Producers’ evaluations of surveyed management practices (number producers expressing

Accomplishments/Milestones

Soil quality analyses of direct seed and conventionally farmed fields:

The study sites represented low, intermediate, and high rainfall zones of the dryland farming region of eastern Washington and northern Idaho. Four sites were involved in the liming study.  For SARE Sites ”A”, “B”, and “C”, pH and KCl Al were determined from soils sampled in fall 2013, limed in 2015, and soil sampled in fall 2015 (Tables 5, 6, 7). For SARE Site “D”, pH and KCl Al were determined from soils sampled in fall 2013, limed in 2014, and soil sampled in fall 2015 (Table 8).  In each of the sites, liming increased pH in the top 3 inches for bottomland, middle, and the top; however, not all increases were statistically significant. Values for pH at the lower depths (4 to 8 inches) actually decreased in 2015 compared to 2013.  Aluminum levels decreased in the top 3 inch depths for all landscape positions; however, not all depths were significantly different.  Overall, liming increased pH and reduced Al in the 0 to 3 inch depths, but only reduced Al to near zero in some of the 0-2 depths. Often Al was still quite high in the 2 to 4 inch depths.  Increases in Al in the 3 to 4 inch depth need more study but could be related to the change in pH and Al in the upper layers.  The high Al values in the 2 to 6 inch depths are still of concern and additional management options are needed.

Economic Analyses:

Our economic analysis showed that gradual lime application incurred an economic disadvantage compared to tillage-only practices. Cultivation or subsoiling every fourth year cost from 5 to 10 $/ac/yr. Liming practices averaged about 72 $/ac/yr, 8.47 times higher than tillage on average.  The tillage practices required less than 1.4 bu winter wheat /ac/yr to pay for them, compared to 11.79 bu winter wheat/ac/yr to pay for the liming practices. Neither our research nor other findings in the literature have documented yield increases from varying amounts of tillage on only moderately acidic soils. However, the modest yield increases we estimated to justify a yield response should motivate both scientists and producers to document the results of occasional tillage.

Statistical regression analysis of surveyed producers’ winter wheat yields on Al levels showed no statistically significant yield effect from the moderately low pH soils in the region. Eleven of 50, or 22%, of reported high precipitation region annual winter wheat yields exceeded 90 bu/ac. This is evidence that high Al was not a barrier to excellent winter wheat production.

• Table 7.Comparison of pH and aluminum in samples from 2013, limed in 2014, and post -limed taken in 2015 at SARE Site C.
• Table 8. Comparison of pH and aluminum in samples from 2013 and post -limed samples taken in 2015at SARE Site D.
• Table 5. Comparison of pH and aluminum in samples from 2013, and post -limed samples taken in 2015 at SARE Site A.
• Table 6. Comparison of pH and aluminum in samples from 2013, and post -limed sampled taken in 2015 at SARE Site B.

Impacts and Contributions/Outcomes

From these analyses, and the management practices implemented, we are developing a greater understanding of the soil characteristics that influence plant growth to be included in management recommendations. Soil pH and micronutrients are deviating from the norm due to long-term zone application of nutrients.  These changes are now affecting resiliency in direct seed systems and management efforts are being studied to improve these factors.

Stratification of low pH and very high Al levels were found in seven of the sixteen sites and in both conservation and direct seed sites. The severity of this problem varied among the seven sites. Another two of the sites had minor issues with zones of low pH and occasion high Al generally in the 2 to 4 inch depths. The final seven sites had no problems with low pH and elevated Al levels at any depth.

Economic analysis of the costs associated with increasing pH and reducing Al levels showed that lime application was not economically competitive compared to the tillage-only practices. Lime application practices were 7.5 times more expensive than various tillage operations.  Tillage practices required 1.4 bu/ac/yr more winter wheat to pay for them, while liming needed 12 bu/ac/yr more winter wheat. There is a need to publicize the many benefits and negatives of direct seeding and continue to educate both producers and the general public, while addressing the obstacles to adoption and the difficulties of long-term direct seed that might limit farm profit.

To date, twelve student workers with interest in pursuing careers in agriculture have been employed to work on the soil analyses for this project and gain experience in their chosen field. We have presented hands-on soils experiments to local high school, middle school, and elementary school students. Meetings were held for the producer/cooperators on this project to present the results of the soil quality analyses and to solicit suggestions and feedback on the project and interest in slight changes in management to mitigate the decrease in pH in the 2 to 4 inch soil depth. This research will further our knowledge of soil quality and assist in developing profitable best management practices for direct seed systems.

• SW12-122 References

Collaborators: