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

Final Report for SW12-122

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

Abstract:

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.

Introduction:

Soil erosion from dry-farmed (i.e., non-irrigated) cropland in most regions of the United States exceeds the tolerable rate (NRCS, 2001). Adoption of conservation tillage and a continued movement toward direct-seeding is necessary to reduce soil erosion. Producers in the United States and worldwide are adopting direct-seed cropping to reduce soil erosion, improve soil quality, increase water infiltration, reduce number of passes with farm equipment over their fields, and to achieve economic benefits. Direct-seeding refers to the practice of planting a crop into a field where there has been no specific tillage operation to prepare a seedbed (Baker et al., 1996). Surface residue from the previous crop is maintained, swept into windrows, or removed by baling or burning (Schillinger et al., 2010). Within direct-seed systems there are many different management techniques and tillage implements that offer varying degrees of disturbance and yield different results.

Direct-seed cropping creates the physical conditions of surface-managed residues and undisturbed soil that leave soil less susceptible to wind and water erosion (Baker et al., 1996). Maintenance of surface residues often increases microbial populations and diversity. Soil organic matter (OM) levels increase with direct seeding, resulting in the sequestration and utilization of C that would otherwise be lost to the atmosphere as CO2. In spite of the advantages of direct-seed farming, making the transition from tillage-based cropping is not without challenges. With less soil disturbance, changes in soil nutrient status and plant-microorganism interactions within the soil environment takes place. As interest grows in developing sustainable cropping systems that mimic the processes driving the soil organic matter turnover of a native, undisturbed system, it is imperative to understand how changes in tillage affect the soil environment.

Adoption and implementation of a direct-seed cropping systems is often slow because of transition costs, lack of producer experience and expert knowledge with the direct-seed practice, producer resistance to change, uncertainties with crop yields, and risks of crop loss resulting from unpredictable agronomic factors. However, the potential long-term economic gain, resource conservation, and environmental benefits resulting from direct-seed systems provide incentives for a gradual, continuing shift to this technology.  As producers reduce soil disturbance, they may experience reduced crop yield due to interference with residue (Rasmussen et al., 1997), increased disease (Schroeder and Paulitz, 2006), reduced seedling emergence, nutrient immobilization (Elliott and Papendick, 1986), and increased weed pressure (Kettler et al., 2000). The changes observed in soil quality with direct seeding include increases in mineralized C and active microbial biomass (Alvarez and Alvarez, 2000), greater soil organic matter, improved aggregate stability, higher exchangeable Ca and extractable P, Mn, and Zn, and less extractable K, Fe, and Cu (Rhoton, 2000). Direct-seeding requires adjustments to traditional seeding rates, fertilization, and stratification of nutrients (Doran et al., 1980). Acidification of soil horizons, lack of key micronutrients in those horizons, compaction, and other factors may also play a role at suppressing yields. Understanding the changes in the soil with long-term direct seeding is key to effective management (Schillinger et al., 2010).

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, which are in line with other soils in the area.

With both producers and the general public favoring a transition to sustainable agricultural practices, there is a growing need for a better understanding of the ecology of the soil system and the economics of such transition to less tillage. The degree of soil disturbance, and the quantity, type, and quality of residue in a system add to the complexity of the system and result in the mixed results and conclusions found in the literature. Ecological investigations with individual producer fields will enhance the understanding of changes that occur with the adoption of reduced tillage and direct-seed cropping systems so that these systems become increasingly viable. Soil quality studies are critical to understanding changes with management and the impact of these changes on productivity as direct-seed systems are used continuously for longer periods. Producers also need accurate information of the costs and profitability of remedial management to sustain crop yields when direct seeding is utilized continuously for ten or more years. Indeed, as producers continue with direct seed for more than ten years, it is unclear as to what is really occurring in the soil, making quality studies critical to understanding changes with management and the impact of these changes on productivity. Investigations will enhance our understanding of the changes that are occurring with the adoption of minimum tillage or direct-seed systems so these practices become viable alternatives to high-disturbance practices. These studies will enhance the adoption of direct-seed systems by assisting in developing management options that improve productivity. In addition, advancing direct-seed options will assist in reducing farm fuel costs and lessen time-in-the tractor for producers. The educational materials and efforts on agriculture and the issues facing producers today inform the public about the importance of agriculture in their lives.

Cooperators

Click linked name(s) to expand
  • Aaron Esser
  • Dr. Douglas Young

Research

Materials and methods:

Thirteen producers who have been direct seeding in dryland wheat cropping systems for the past 4 to 15 years were interested in studying their soil more thoroughly (Table 1Table 1 sites SW12-122).Three conservation tillage producers were also interested in understanding the soil quality determinants of their soils. At each farm, soils were sampled annually from multiple direct-seed sites with varying cropping histories and lengths of time under direct-seed management in eastern Washington and northern Idaho. For comparisons, soil was also sampled from adjacent, conventionally tilled fields with winter wheat in rotation with similar slope and aspect. Soil was also sampled from undisturbed sites nearby. Soil samples were collected in the fall and spring.  Three landscape positions were sampled with five replications at each position. Each soil sample was a composite of seven cores taken using a king tube (5 cm dia.) to obtain incremental depths every 2.5 cm 1 in) for the first 10 cm (4 in), and 5 cm (2 in) thereafter to 20 cm. Climatic information was collected from weather stations at select sites.

We established field-size experiments to test treatments that may remediate the problems identified in Objective 1. Management options included, but were not limited to, vertical tillage, subsoiling, micronutrient applications, liming, etc. The field experiments were located on producers’ fields. Soil samples and grain yield were determined as indicated above. Treatments of nutrient additions consisted of three different nutrient amounts and a control, while a disturbance treatment may only have two treatments (ie., subsoiler or control). Data were analyzed as described above.

Select biological, chemical, and physical analyses were used in these studies, including soil nutrient levels (N, P, K, Ca, CaCO3, S, Mg), micronutrients (Cd, Co, Fe, Zn, Bo, Mn, Ni, Mo), cation exchange capacity, soil pH and EC (Smith and Doran, 1996). Carbon, nitrogen, and sulfur content was determined by oxidation (LECO, St. Joseph, MO). Nitrate and ammonia N was determined by colorimetric analysis (Latchat Autoanalyzer, Latchat Industries, Milwaukee, WI). Also analyzed were the physical soil traits of texture,  water holding capacity, and bulk density (Doran and Mielke, 1984). Biological analyses included soil biomass and microbial community structure by phospholipid fatty acid and enzyme analyses (Ibekwe and Kennedy, 1998). From these analyses we have developed a greater understanding of the soil characteristics that influence plant growth and should be included in management recommendations.

We sampled soil each year in spring and fall and we sampled crops that were harvested in the fall. Soils were stored at 4oC (40oF) until analysis, which typically occurred within 2 weeks after sampling. Analyses were completed within 3 months of sampling and data analyzed by the end of each year. Field studies with the selected treatments were conducted in years 2 and 3.  Only spring data are presented here.

Data were analyzed using a general linear model methodology including analysis of variance, analysis of covariance, regression, and correlation (SAS, 2016). In addition, structural equation modeling was used to examine relationships among sites, climate, landscape, management, crop growth, soil depth, and soil physical, chemical and biological variables wherever possible. Multivariate analysis of variance was applied to simultaneously determine the effects of experimental treatments on soil characteristics and grain yield. For each study, the impact of direct- seed management options on plant growth, the relationships among these data and the variables of location, soil characteristics, and climate were examined.

Research results and discussion:

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.  We sampled from the same locations, but different fields each year that were in the winter wheat phase of the crop rotation. At each site, three landscape positions were sampled: ridgetop, mid-slope, and bottomland.  The soil quality analyses completed are soil moisture, pH, electrical conductivity (EC), dehydrogenase enzyme assay, β-glucosidase assay, macro- and micronutrient analyses.  The mean values from spring, 2013 and spring 2014 for soil quality analyses (Table 2Table 2 Soil quality analysesSW12-122), macronutrients (Table 3Table 3 MacroNutSW12-122) and micronutrients (Table 4Table 4 Micro nutSW12-122) are listed for each site.  Values varied with year and site.  The spring 2014 enzyme activities were lower than those for spring 2013. The highest β-glucosidase level of 20.2 mg ρ-nitrophenol g-1 soil hr-1 was found at Site 8, Colfax, WA, and the lowest level of 9.7 mg ρ-nitrophenol g-1 soil hr-1 was found at Site 12, Bickleton, WA (Table 2).  Dehydrogenase enzyme activity was highest at Site 3, Wilbur, WA with 2.0 µg TPF g-1 soil hour-1, and lowest at Site 5, Pullman, WA at 0.5 µg TPF g-1 soil hour-1.  The pH values of these soils ranged from 5.2 at Site 5, Pullman, WA to 7.3 at the Site 15, Wilbur, WA.  Electrical conductivity ranged from 88 µs cm-3 at Site 1, Genesee, ID to 513 µs cm-3  at Site 14, also near Genesee, ID.  Cation exchange capacity ranged from a high of 22.2 meq at Site 1, Genesee, ID to a low value of 10.1 meq at Site 7, Ritzville, WA.

As in spring 2013, the Site 7, Ritzville, WA in spring 2014 had the lowest NO3-N (6.0 parts per million (ppm)), NH4-N (2.0 ppm) and Olsen P (P; 17.7 ppm) values (Table 3).  Highest NO3-N was found at the Site 2, Davenport, WA (43.4 ppm), highest NH4-N at the Site 8, Colfax, WA (8.8. ppm), and highest P at Site 4, Dayton, WA (46 ppm).  Highest K was found at Site 4, Dayton, WA) site (618 ppm), and lowest K at the Site 11 (313 ppm).  Sulfur ranged from 32 ppm at Site 5, Pullman, WA to 10 ppm at Site 6, Ritzville, WA.  Calcium was also highest at Site 14, Genesee, ID (15.2 ppm), but lowest at Site 6, Ritzville, WA (5.6 ppm).  Magnesium content ranged from 1.6 ppm at Site 3, Wilbur, WA to 3.6 ppm. The actual sites were different in 2014 from those in 2013 but the data were about the same.  The pH values and Al differed among the sites and years.

We found that bulk soil samples using 0-10 or 0-15.2 cm (0-4 or 0-6 in) deep cores were not able to illustrate the low pH levels that were seen with incremental sampling as well as taking 0-2.5 or 0-5 cm (0-1 or 0-2 in) sample.  Bulk samples dilute the low pH and high in layers.  Two and a half or 5 cm (1 in or 2 in) incremental samples are critical to determining if there is stratification occurring.  A simple hand held pH meter, a bottle of water and a 6 inch deep hole can easily and quickly tell producers if their soils have low pH stratification with depth. 

Of the 16 sites, only 7 had a major problem with stratified soil layers of low pH and high Al.  Four of the sites with zones of low pH were in the high rainfall zone and only one was in the low rainfall zone.  The other two then were in the intermediate rainfall zone.  These seven sites also showed high levels of Manganese (Mn) that is a problem in acids soils. The stratification, unfortunately, were not limited to only direct-seed producers, but conservation-tillage sites also showed low pH depths with depth (Table 5Table 5 Micro defSW12-122).

It is important to realize that while low pH layers may be a problem to some producers this effect with ammonia based fertilizers does not occur in all soils. These low pH layers are not universal and again pH measurements are needed to quickly and simply inform a producer if they have a problem or not.  One site had very high soil Al and Cd and it this thought that some contamination came from an application of an amendment in the past.  Three sites of the 16 sites were deficient in zinc, one had low potassium, and several sites were low in B, but few sites had other micronutrients that were low with depth.  Interestingly two sites in the intermediate rainfall zone did not show stratification and these direct-seed sites practice one or two more tillage passes than the other sites.  There extra tillage passes appear to have mixed the low pH soils layer in with  higher pH soil.  Illustrating the importance of one or two more tillage passes to mix the low pH layers with others or to deliver lime to the layer in which it is needed most. 

Zn were low in several of the low rainfall zones sites and Mn was high when the pH was low, but was not generally follow the layers. Alarming high. Sulfur and zinc were deficient in low and intermediate  conserve tillage. Cu was low in intermediate zones  and  B was low in lower depths  and on ridge tops. 

Two sites were direct seeded in the intermediate rainfall zone, but were involved in a multiple pass system.  These two sites sided not have the low pH at the 2 to 4 inch depth.  On the other hand, the site conservation till in the high rainfall had  severely pH low  and high Al.

The broadcast application of lime followed by tillage mixed the lime into the soil profile more effectively, but still did not increase the pH of the lower layers.  The addition of lime to these soils was found to not be economical as the cost of lime was high.  Tillage appears to be cost effective; however, not an option chose by any of the direct seeder.

Comparison of direct seed and conventionally farmed sites:

One conservation-tilled site was selected in each of the rainfall zones for comparison with a direct-seed site.  The result of this comparison with select soil quality analyses is shown in Table 6 (Table 6 ds.conservSW12-122.  In comparing the high rainfall sites near Colton and Pullman, WA, we found few differences in β-glucosidase, N, P or K between the direct seed and conservation-tilled soils.  In contrast to other data, β-glucosidase, dehydrogenase enzyme activity, CEC, N, P, K, and Cd were not different between the direct-seed site and the conservation-tillage site. pH was higher in the direct seed site. EC, S, and Al, were lower in the direct-seed site.  In the intermediate rainfall comparison of farms near Wilbur, WA, there were no differences in β-glucosidase, dehydrogenase, N, or Al between direct seed and conventional.  pH, EC, and CEC were higher in the conservation-tilled soils, while P, K, S, and Cd were higher in the direct-seed soils.  At the Ritzville, WA direct seed and conservation-tilled sites there were not different in β-glucosidase, pH, or NH4-N.  In the conservation-tilled, low rainfall site, dehydrogenase, EC, and CEC were higher, and all other means across depth and landscape were higher in the direct-seed soils. 

At twelve of the direct-seed locations, a native or undisturbed area was sampled for comparison.  At half or fewer of the locations there were no differences in β-glucosidase, CEC, NO3-N, K, S or Al between the direct seed and undisturbed soils (Table 7.Table 7 DS.ZUndisturbSW12-122). Comparison of select soil characteristics between direct seed and native/undisturbed sites, averaged across all depth increments. Different letters in the same grower’s section in the same column are significantly different at P<0.05. Comparison of select soil characteristics between direct seed and native/undisturbed sites, averaged across all depth increments. Different letters in the same grower’s section in the same column are significantly different at P<0.05).  At the majority of sites, dehydrogenase enzyme activity and pH were significantly higher in the undisturbed soils.  Electrical conductivity, NH4-N and P were higher in the undisturbed soils at ten of the twelve locations, although those differences were not always significant (Table 7).  Cadmium concentration was higher in the direct-seed soils than the undisturbed soils at eight of the locations.

Comparison of direct-seed and native/undisturbed soils:

Native or undisturbed areas were sampled for comparison with the agricultural soils.  At the majority of sites, dehydrogenase enzyme activity and pH were significantly higher in the undisturbed soils compared to the direct seed sites (Table 7).  At more than half of the sites, there were no differences in the mean across all landscape and depths the β-glucosidase, CEC, NO3-N, K, S or Al between the direct seed and undisturbed soils.  Electrical conductivity, NH4-N and P were higher in the undisturbed soils at ten of the twelve sites, although those differences were not always significant (Table 6).  Cadmium concentration was higher in the direct-seed soils than the undisturbed soils at eight of the sites.

Landscape position:

Averaged over all sites, year, and sampling depths (0 to 4 inch), the native/undisturbed soils had higher β-glucosidase and dehydrogenase enzyme activity, pH, EC, K, NO3-N, Ca, P, Zn, B, and NH4-N than the ridgetop, mid-slope or bottom soils (data not shown).  The undisturbed soils were lowest in Al, Na, Ni, Mn, Fe and Cu, although the differences were not significant in many cases (data not shown).  Bottom soils were higher in dehydrogenase, EC, K, NO3-N, P, S, Fe, Mn, and B than ridgetop and mid-slope soils.  Ridgetop soils had lower pH and B; and higher Al, Mg, CEC, Na, and Cu than either mid-slope or bottom soils.  There were no differences in concentration of the micronutrients Cd and Mo among any landscape position. 

Soil depth:

In spring 2013 soil samples, there were no differences in CEC, Mg, Ca, Cd, Mo, Ni, Fe or B with sampling depth when averaged across all sample sites and landscape positions (data not shown).  Levels of β-glucosidase and dehydrogenase enzyme activity, EC, K, NO3-N, NH4-N, P, S, Zn, and Mn were highest in the 0-1 in. samples and decreased with depth to 6-8 in.; however, the differences among depth increments were not significantly different in all cases (data not shown).  Aluminum levels were highest in the 5 to 7.6 cm and 7.6 to 10 cm (2-3 and 3-4 in.) depths, and lowest at 15 to  20 cm (6-8 in).  Averaged over all the farmed sites, pH was highest at the 15 to  20 cm (6-8 in) depth and did not differ significantly from the 0 to 2.5 cm (0-1 in.) depth.  The depth increments from 2-3 in. and 3-4 in. were significantly lower in pH than the 0 to 2.5 cm (0-1 in.) depth, but did not differ from the 5 to 7.6 cm (1-2 in.) and 10 to 15 cm (4-6) in. depths.  Aluminum levels were highest in the 5 to 7.6 cm (2-3 in.) and 7.6 to 10 cm (3-4 in.) depths, and lowest at 15 to 20 cm (6-8 in).  pH was lowest at the 15 to 20 cm (6-8 in)  depth and did not differ significantly among the other increments.  

In spring 2014 soil samples, there were no differences detected in levels of CEC, Mg, Ca, Cd, Mo, Ni, Fe or B with sampling depth when averaged across all sample sites and landscape positions (data not shown).  Levels of β-glucosidase and dehydrogenase enzyme activity, EC, K, NO3-N, NH4-N, P, S, Zn and Mn were highest in the 0-1 inch samples and decreased with depth to 6-8 inch; however, the differences among depth increments were not significantly different in all cases (data not shown).  Aluminum levels were highest in the 2-3 and 3-4 inch depths, and lowest at 15 to 20 cm (6-8 in) inch depths.  The depth increments from 5 to 7.6 cm (2-3 in) and 3-4 inch were significantly lower in pH than the 0-1 inch depth, but did not differ from the 5 to 7.6 cm (2-3 in) and 10 to 15 cm (4-6 in) depths.

LIMING

Four sites were involved in the liming study.  For SARE Sites 1, 10, and 11-13, 11-14, pH,  Al and Mn were studied from soils sampled in fall 2013, limed in 2015, and soil sampled in fall 2015 (Tables 8 Table 8 phlime s1SW12-122, 9Table 9 ph.lime SW12-122, 10 Table 10 pH Lime s10SW12-122, 11 Table 11 Ph.lime s11a SW12-122).  For SARE Site 11-13, pH and KCl Al were determined from soils sampled in fall 2013, limed in 2014 (11-14), and soil sampled in fall 2015 (Table 9).  In each of the sites, liming increased pH in the top 7.6 cm (3 in) for bottom, middle, and the top; however, not all increases were statistically significant. Values for pH at the lower depths 10 to 20 cm (4 to 8 in) actually decreased in 2015 compared to 2013. Aluminum levels decreased in the top 7.6 cm (3 in) depths for all landscape positions, however not all depths were significantly different. Overall, liming increased pH and reduced Al in the 0 to 7.6 cm (0 to 3 in) depths, but only reduced Al to near zero in some of the 0 to 5 cm ( 0-2 in) depths. Often Al was still quite high in the 5 to 10 cm (2 to 4 in) depths.  Increases in Al in the 7.6 to 10 cm (3 to 4 in) depths need more study, but could be related to the change in pH and Al in the upper layers.  The high Al values in the 5 to 15 cm (2 to 6 in) depths are still of concern and additional management options are needed.

In the 150 years of farming these sites nitrogen was added by anhydrous ammonium to the greatest extent.  The Ammonia form of N cases the increase in the soil pH.  With 20 plus years of farming, the direct-seed sites had  anhydrous ammonia added at the the 7.6 to 10 cm (3 to 4 in) every year which lowered the pH at that level.  The addition of lime to surface soil by broadcast increased the pH, but the greatest pH change was in the surface layers with less so increasing pH in the 7.6 to 10 cm (3 to 4 in) zone where it is needed (Table 12 Table 12 pH lime TILLED.SW12-122).  In addition, it appears that the lower depths saw and a further decrease in pH that was not present before the liming.  Lime and tillage to 10 cm (4 in) saw the greatest positive effect on the low pH and Al.  pH was increased in the 2 to 4 inch depths with time and tillage with no decrease in pH a with broadcast lime application.  The addition of lime to these soils was found to not be economical as the cost of lime was high.  Tillage appears to be cost effective; however, not an option chosen by many direct seeders.  The tillage without lime was not accepted by the producers as something they wanted to attempt within the time frame of this study. We tested number of tillage passes by comparing sites within the study. 

Research conclusions:

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, micronutrients, and some macronutrients 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, very high Al and sometimes high Mn levels was 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 the occasion high Al generally in the 2 to 4 inch depths.

Economic analysis of the costs associated with increasing pH and reducing Al levels showed that lime application is not an economically-feasible practice compared to the tillage-only practices.  Liming costs 7.5 times more than various tillage operations.  Occasional tillage practices required 1.4 bu/ac/yr more winter wheat to pay for them, while annual 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 limit net farm profit.

The final seven sites had no problems with low pH and elevated Al and Mn levels at any depth.  This information allowed the other nine sites to focus on other nutrient issues on their farm.  Several macronutrients and micronutrients were determined to be lacking in some soils and producers have initiated studies.

Making the transition from conservation-tilled cropping systems to direct seeding is risky and requires long-term commitment; however, change in direct seeding management is needed to resolve this decrease in pH.  Additionally, the specialized equipment required to farm the landscape of the inland Pacific Northwest is expensive with limited availability.  The benefits of direct seeding on stopping soil erosion and reducing fuel costs through fewer trips over the field are well-documented; however, soils in most areas of the inland Northwest continue to remain productive in spite of high input costs and erosion.  There seem to be few incentives for making the transition to direct seeding.  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 downfalls of long-term direct seed that limits net farm profit. 

Various management options were discussed with the producers to increase the pH of those low pH soil zones.  These management options were broadcast lime, lime applied with spoke wheel or shanked into the soil at the 5 to 10 cm (2 to 4 in) depth; surface tillage, wide-spaced shank tillage, and no action.  The majority of the producers experiencing low pH in the 5 to 7.6 cm (2 to 3 in) depths decided on applications of lime broadcast on the soil surface and some incorporated using their direct seed drill prior to seed drilling.  The least expensive practice to increase the pH of these seven sites would be one or two more tillage passes. While only one producer was willing to till their soil during this study, others have put in field studies this year to test our conclusions on their land.  Some of the items listed here will be practiced by producers in the coming years.

Each of the producers received a hand-held pH meter and calibration solution to test their pH with depth and to also test the neighbor’s soil pH.  These pH meters will allow the widespread testing of soil incrementally with depth.

To date, twelve student workers interested in careers in agriculture have been employed by the labs 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. Seminars and workshops on soil quality have been given to inform producers, land managers, and landlords.  This research along with their economic analyses will further our knowledge of soil quality and assist in developing profitable, sustainable, best management practices for direct seed systems and conservation tillage producers.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Outreach to Producers:  We met with individual producers and managers, or producer groups each winter to discuss results and solutions with them individually and in small local groups.  These meetings and discussions are 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.  Our educational objective was to inform target audiences about soil quality, microbiology, micronutrients, pH, compaction, and plant microbe interactions in agricultural systems. We developed and disseminated technical publications and fact sheets and presented seminars and posters. Other outreach efforts to producers, land managers agribusiness personnel, and landlords are listed below.  Results of this work are being fully incorporated into technical and outreach materials, coordinated field trips and/or workshops and presented present results at national and regional scientific conferences annually.

Outreach: The public and K-12 education:  Over the course of this study, we have contributed to the education of agricultural professionals and students at the university, high school, and elementary school level by 1) providing research opportunities, 2) delivering research seminars and lectures to these students, and 3) the development of undergraduate curricula. Students were exposed to field, greenhouse, and laboratory research using various standard practices and cutting-edge analytical techniques, and they were responsible for presentations using both seminar and poster format. We have presented the results from this study in seminars in colleges and universities across the west. Investigations from this research proposal have also been adapted for science curricula. We have been, and continue to, be active in outreach to involve students in hands-on science and agricultural education. Our outreach program covers Central and Eastern Washington and the Idaho Panhandle and reaches more than 600 students annually with semester-long, hands-on agricultural science. We expanded on our current experiments to include additional sessions on agriculture, where food comes from and information on soils and plant science. We developed exercises for K-12 students to expand their knowledge on the importance of agriculture, pH, and micronutrients in their lives. These activities align with the following National Science Education Standard: Content Standard C: Life Science – Populations and Ecosystems; Diversity and Adaptations of Organisms.

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. Seminars and workshops on soil quality have been given to inform producers, land managers, and landlords. This research will further our knowledge of soil quality and assist in developing profitable best management practices for direct-seed systems. Management efforts along with their economic analyses are being directed to improve these factors.

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 on soil pH and soil health (12/10); BLM pesticide certification classes Albuquerque, NM (2/26) and Boise ID (4/2); Worley, ID (7/14)

2015:  We 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).

 

From this research and extension collaboration we are developing several scientific publications.

1. We have a manuscript ready to submit to Agronomy Journal titled “Economics of Managing Acidic Soils in Eastern Washington and Northern Idaho”.

2. We have two manuscripts in preparation to submit to Soil Science Society of America Journal or Applied Soil Ecology with potential titles of:

a. Soil quality differences among long-term direct-seed fields in eastern Washington and northern Idaho and

b. Limiting factors in long-term direct seeding in Washington and Idaho: Correlation of select factors and yield using multivariate analysis. Each peer-reviewed manuscript will be used as the basis to contribute to an extension, technical and popular publication.

REFERENCES

Project Outcomes

Project outcomes:

Remedial management by producers to improve, maintain or restore soil quality will depend considerably upon their efficiency in carrying out field operations.  Past research has confirmed that some of the most efficient machinery managers in eastern Washington are found in the Horse Heaven Hills (HHH) in Benton County who grow winter wheat in the driest rainfed area of the world (Schillinger and Young, 2004).  One HHH producer with over 10,000 ac in direct seeded winter wheat, and known for efficient machinery management, recently shared his superb records with the project economist.  The costs in Table 13 Table 13 Econ costs SW12-122were computed from these records using machinery costs software (University of Idaho, 2013).  Table 13 presents 5-yr average variable and fixed costs by field operation.  Most of the direct-seed producer/cooperators in this study are located in the annual cropping area of the eastern Palouse.  However, the project economist has found it useful to compare field operation costs among producers and across regions.  The variable and fixed costs in Table 13 will serve as a useful efficiency benchmark for the farm cooperators in this study.

Costs are typically divided into variable and fixed categories.  The former vary by the number of acres cultivated.  These include labor, fertilizer, herbicides, seed, fuel, machine rental and machine repairs and maintenance.  Fixed costs include depreciation, interest, property taxes, housing and insurance on machinery.  Land is also traditionally included as a fixed cost.  Land cost equals the cash or share rent for land and property taxes.

In order to provide a forward perspective of the results for producers in the region, 2012, 2013, and 2014 prices were utilized for fertilizer, herbicides, seed, fuel and labor.  The HHH producer reported that he broke even with respect to crop insurance premiums and indemnities so no net charge was deducted for crop insurance. 

A mail survey (Appendix 1)APPENDIX I of the 16 producer cooperators elicited their history of crop yields by year, precipitation by year, crop rotation, personal resistance to tillage, preference for practices to manage acidic soils, and perceived costs of these practices. Extensive soil testing by this project determined the levels of Al  for each producer. Among the 16 producers, three used conservation tillage and the other 13 direct seeded. Survey response achieved 75% overall and 89 and 57 percent for the high Al and low Al groups, respectively. We were pleased with the relatively high response rates among the key Al toxicity group. Two of the three conservation producers responded. As will be noted, not all respondents answered every section of the questionnaire.

All seven of the responding producers from the high precipitation zone grew pulses or other broad leaves in their crop rotations, including peas, garbanzo beans, lentils, and canola (Table 1 , in Results and Discussion). 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.  Most producers in the low precipitation zone used winter wheat-fallow rotations, but two also grew spring wheat. All seven of the responding producers from the high precipitation zone grew pulses or other broadleaves in their crop rotations. Some 30% of the direct seeders reported using some tillage.  

Conservation tillage producers 5 and 7  (Table 1) reported using somewhat aggressive tillage; 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.  Annual winter wheat yields ranged from 12.6 to 64.3 bu/ac and annual precipitation from 8.1 to 14.2 in/yr for this group of low precipitation region producers. This group had relatively low Al levels, while still above the normal, ranging from 7 to 30  KCL AL mg/kg and the upper bound resistance to tillage of 50.  Unfortunately, no surveyed producers from the intermediate precipitation zone provided complete data for the regression analysis. Five high precipitation region producers provided data. 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. The lower yields were found on the outlier farm. This group had relatively elevated Al ranging from 17 to 84 . Their resistance to tillage was moderate at 33 to 50. Eleven of 25, or 44%, of the annual farm wide winter wheat yields from the high precipitation group exceeded 90 bu/ac. This is evidence that AL toxicity was not a barrier to exemplary winter wheat production in favorable years.

This next 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 break even 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 break even wheat yield increases in Table 14Table 14 Econ berakeven SW12-122are described in the footnotes.

The break even 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 break even 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.

The added costs and break even winter wheat yield increases for 11 practices for remediating the effects of high Al and potential Al toxicity are presented in Table 14  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, et al., 2013).

All costs in Table 15 Table 15 Econ eval SW12-122 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 break even 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 in this exercise was 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 et al. (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 14 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 15 presents producers perceptions for practices #’s 1-9 and the costs presented in Table 16.  Table 15 abbreviates the practices from the survey but they are essentially the same as the more precise practices in Table 15.  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) AvwwYieldjt= B0+B1PPTjt+B2Falj+B3High ALj+B4Outlierj+B5Tillj + Error Term

  • AvwwYieldjt
    • Average whole farm winter wheat yield (bu/ac) of surveyed producer j in year t
  • PPTjt
    • Producerj’s reported inches Sept.-Aug. crop year precipitation in year t
  • Falj
    • =0 if dominant crop rotation does not include fallow for producer j
    • =1 if dominant crop rotation does include fallow for producer j
  • High Alj
    • = Highest KCL Al mg/kg across season year, landscape and soil depth for producer j based on project soil tests
  • Outlierj
    • =0 if not producerj with statistically different yield pattern and management
    • = 1 if producerj with statistically different yield pattern and management
  • Tillj
    • =multiplicative index of producer j’s resistance to tillage based on answers to questions 6-9 of Al toxicity questionnaire.

multiplicative index: ∑(No. tillage passes, 1-4)(Likert Scale)

(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

No. tillage passes for example

Likert Scale for example

(Passes)(LS)

1

Enthusiastically=1

1

2

Minor resist=2

4

3

Absolutely=5

15

4

Absolutely=5

20

∑(No.passes)(LS)=Tillj

40

Regression data summary:

7 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 16 Table 16 Econ RegressSW12-122 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  + -.12 High Al + -23.27  Outlier + -0.43 Till

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

 

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 producer 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.

Farmer Adoption

The producers in this study will have their own, hand-held pH meter to test their soils with depth.  They have all been enthusiastic about wanting to test the pH of their own soils. Their neighbors have been interested as well.  They also have soil test data that is detailed information from two fields –  three landscapes in 1 to 2 inch increments to 8 inches.  They are using their pH meters to gain information about the soil on their land.  They are using the soil test data in their planning.  The producers have a greater appreciation for testing their pH and taking more soil samples.  Those producers at our talks and in conversations in the field should also be adopting a more thorough soil test strategy.  It starts first with testing pH with depth.

Even though these studies indicate that lime addition is not economically feasible, and broadcast application of lime does not get it to the layer which needs it the most,  field experiments using deep placement of lime and/or tillage may be successful at increasing pH in the layers to allow other improvements set up for collectively increasing yield.  Perhaps with addition of macro and micronutrients to soils that are identified as being deficient will be part of the solution to higher yields.  Even an increased appreciation of detailed soil tests will give producers more information about their individual soils. 

Tillage is a good option to increase pH in the subsurface layers; however, several direct-seed producers in this study were reluctant to till their fields.  Eventually more direct-seeder producers will adopt additional tillage passes, as some have done already.  The documents from this study will help producers weigh the benefits of ‘a bit more’ tillage in their direst-seed systems.  

The focus on soil factors that may be limiting yield (low pH zones, some macronutrients, micronutrients)  will add to producers’ toolbox and our study increased the knowledge base of these nutrients.  Hopefully this study provided more information to producers to work towards management of these limiting factors so they can practice long-term sustainable agriculture on their land and enjoy full benefits soil has to offer.

Recommendations:

Areas needing additional study

In our study, we were not able to convince producers early in the funding cycle to add more tillage passes to their direct seed systems.  Additional studies are needed to determine the influence of  one or two extra tillage passes ever year or so on layers, yield, etc.  Would those extra tillage passes destroy all the good microbes that have been built up in their direct-seed soils?   The concerns of the direct-seed producers need to be answered.

More studies are needed on lime using shanked or drilled methods of application along with tillage.  The same types of studies are needed on micronutrients in soils with low levels of the various micronutrients.  These is little information on liming western soils and how many equivalents are really needed.  In addition, lime is considered the answer to these layers of low pH; however, more studies are needed before too many producers spend too much on lime.

More information is needed from independent researchers, not from research funded by the companies selling the products.  This is especially important in the case of lime.  In addition, it is imperative that field studies include solid economic investigations as well.   For instance, the most economical method of micronutrient application is with using a salt, not a chelate.  In high iron soils, the chelate will bind to iron and drop the micronutrient, only to be sorbed back into the soil and made unavailable to the plant.  Chelated material is generally more expensive than the salt form, but results in very little micronutrient into the plant.  With that said, many micronutrient studies are conducted with the chelate form of the micronutrient. It may increase yields for one year, but not longer. Long-term studies are needed for lime, macronutrients, and micronutrients.

 

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.