Journal of the NACAA
ISSN 2158-9429
Volume 11, Issue 1 - June, 2018


Addressing Soil Acidity on Nez Perce Tribe Agricultural Lands

Finkelnburg, D.C., Area Extension Educator, University of Idaho
Schroeder, K.L., Cropping Systems Agronomist, University of Idaho


Increasing acidity in agricultural soils on Nez Perce Tribal lands threatens long-term productivity and may limit crop rotation options. A replicated demonstration trial evaluated soil and crop effects of a Nez Perce Tribe sourced agricultural lime applied to tribal land in northern Idaho. Lime application lowered uppermost topsoil acidity (0-3 inches) and reduced potentially toxic plant available aluminum quantities. Base saturation increased in this zone at 2 and 4.8 ton/acre lime rates. Winter wheat yields trended upward and grain protein was increased with increasing rates of lime. Protein increases were statistically significant, yields were not. Macronutrient concentrations in wheat flag leaves were unaffected by liming treatments while manganese levels declined with increasing lime. While deeper incorporation would have resulted in greater improvements in the 3 to 6 inch zone, this work demonstrates that surface applied lime with minimal incorporation in a direct seed system may help to alleviate topsoil acidity in northern Idaho.


Increasing topsoil acidity has been documented in northern Idaho agricultural fields since the 1980’s (Mahler et al., 1985). This is the result of several decades of applying high quantities of acidifying forms of fertilizer, typically ammonium-based nitrogen formulations. Soil acidity has been associated with less efficient nutrient cycling, reduced microbial activity, altered herbicide activity and persistence, increased disease pressure on wheat, and in extreme cases, metal-induced plant toxicity (Koenig et al., 2011). One method of mitigating soil acidity has been the application of agricultural lime. The effectiveness of agricultural lime is dependent on both the quantity and quality of lime material applied (amount of carbonate and fineness of material) and individual soil characteristics (soil pH and cation exchange capacity).

To determine the quantity of lime to be applied, a pH buffer test is often employed. This test measures the reserve acidity of a soil which is the concentration of hydrogen ions bound onto soil particles and organic matter which are not part of the soil solution. As opposed to direct measurements of soil pH which only record the hydrogen concentration in the soil solution. Higher clay content and organic matter will increase the reserve acidity and thereby the quantity of lime that needs to be applied to increase the soil pH to a target level.

While the use of ag-lime to lower soil acidity has been a common practice in agriculture in other areas of the United States, the practice has been slow to be adopted in northern Idaho. A key challenge to the adoption of liming is transportation costs due to limited availability of locally sourced liming materials and limited knowledge of the effectiveness of this practice on fields in north Idaho.

The Nez Perce Tribe owns a lime deposit that was previously mined for use in the bleaching process at a nearby paper mill but has been inactive for years. The deposit is centrally located within north Idaho agricultural lands and the Nez Perce Tribe was interested in reopening the site and exploring agricultural lime production as a potential economic development enterprise. This endeavor also would provide a beneficial soil amendment to achieve environmental and economic sustainability goals. University of Idaho Extension collaborated with the Nez Perce Tribe and a local tribal land lessee and direct-seed farmer to evaluate effects of lime sourced from the Nez Perce Tribe on soil and crop production. This article describes the benefits observed in a replicated field study following the application of this liming material.



Figure 1. Applying ground limestone with a “floater” dry product applicator.



A field with a silt-loam soil (Taney-Setters Complex Xerolls), representative of much of the local farmed ground, was identified. The topsoil acidity in this field was pH 5.1, a level known to limit crop performance and yield of small grains and grain-legumes, crops typical for this region of Idaho (Mahler and McDole, 1987). Lime sourced from the Nez Perce Tribe’s pit was processed at a local crushing facility into agricultural grade lime (Table 1). Lime was surface applied by a custom applicator to plots using a “floater” vehicle in the fall of 2013 (Figure 1). Lime was lightly incorporated with a disc to 3 inches in the fall of 2014. Plots were 60-ft wide by 300-ft long and arranged in a randomized, complete block design with four replications. Liming rates were: a no-lime check, 1-ton/acre, 2-tons/acre, and the lime requirement, determined by the Adams-Evans test, to raise the soil pH to 6.5 in the top 6 inches (4.8 tons/acre). Plots were sampled at depths of 0” to 3”, 3” to 6”, and 6” to 12”. Five sub-samples at each depth were collected per plot and homogenized in a plastic bucket before being placed on ice for transport to a refrigerated storage area. Soil samples were passed through a 2-mm sieve and air dried for 72 hr at 70°F before shipping to Best-Test Analytical Services (Moses Lake, WA) for analysis. Tissue samples were collected from approximately 100 flag leaves per plot at the late boot stage (Feekes 10). Plots were harvested in 2017 using the grower's combine and plot weights were taken by offloading grain into a bank-out wagon on truck scales. Grain sub-samples were collected for quality and test-weight analysis. All statistical analyses were performed using SAS statistical software (Version 9.4, SAS Institute, Cary, NC). Analysis of variance was performed with all data using the General Linear Model (GLM) procedure. Mean comparisons were made using Fisher’s least significant difference (LSD) test at P = 0.05.


Table 1. Lime particle size, calcium carbonate equivalent (CCE) and lime score.

Seive Size

Total % Pass
2.360 (#8) 100
2.000 (#10) 100
0.865 (#20) 85
0.425 (#40) 68
0.250 (#60) 59
0.075 (#200) 40
CCE = 102%
Lime Score = 79




Effects of applied lime to this soil were largely restricted to the top three inches, coinciding with the maximum depth of mechanical incorporation. Significant increases in soil pH in the top three inches were seen with the 4.8-tons/acre rate within a year and increases were observed at all rates 32 months after application (Table 2). Potassium chloride (KCl) extractable aluminum was present at all depths sampled with highest concentrations observed in the 3-6-inch depth. Quantities of aluminum were significantly lowered in the top three inches at the 4.8 ton/acre rate at 32 months after application, but lower depths were unaffected.


Table 2. Soil acidity and plant available aluminum. Means within a column with different letters are significantly different using Fisher’s LSD (P=0.05).

  12 Months Post Liming 32 Months Post Liming
 Soil Depth 0"-3" 3"-6" 6"-12" 0"-3" 3"-6" 6"-12"
 Check 5.3a 5.2a 6.1 5.3a 5.3 6.0
 1-ton 5.4a 5.1a 6.2 5.6b 5.2 6.0
 2-tons 5.5ab 5.3ab 6.2 5.9bc 5.1 6.0
 4.8-tons 5.7b 5.5b 6.2 6.1c 5.3 6.1
 LSD (0.05) 0.3 0.2 ns 0.3 ns ns
  12 Months Post Liming 32 Months Post Liming
  KCl Extractable Aluminum (ppm)
 Soil Depth 0"-3" 3"-6" 6"-12" 0"-3" 3"-6" 6"-12"
 Check 1.8 4.5 0.3 2.3a 7.8 0.5
 1-ton 1.0 4.5 0.5 1.0ab 6.8 0.8
 2-ton 0.8 3.8 0.3 0.5ab 7.3 0.3
 4.8 ton 0.5 0.8 0.0 0.0b 3.0 0.0
 LSD (0.05) ns ns ns 1.8 ns ns


Calcium in the 2 and 4.8 ton/A rates plots were not significantly higher than the no-lime check 12 months after liming (Table 3). There also was no significant increase in the soil’s base saturation at 12 months. However, by 32 months after liming significant increases were seen in both calcium quantities and base saturation at all rates. No change in potassium or magnesium quantities were observed at any rate of lime tested at either sampling interval.


Table 3. Base saturation changes in uppermost topsoil (0-3 inches). Means within a column with different letters are significantly different using Fisher’s LSD (P=0.05).

  12 Months Post Liming 32 Months Post Liming
% Base Ca K Na Mg Total Bases Ca K Na Mg Total Bases
 Check  46.8  6.0  0.1  6.5 59.4  45.3a  5.3  0.4  5.8 56.7a
 1-ton 48.5 5.5 0.1 6.2 60.3 49.8b 4.9 0.1 6.0 60.8ab
 2-tons 51.3 5.0 0.1 6.2 62.6 52.5b 5.4 0.1 5.5 63.5bc
 4.8-tons 51.3 6.0 0.1 6.7 64.1 56.8c 5.6 0.1 5.8 68.2c
 LSD (0.05) ns ns ns ns ns 3.9 ns ns ns 4.9


Winter wheat tissue tests showed no statistical macronutrient differences among limed or non-limed treatments (Table 4). Likewise, there were no differences between treatments for the micronutrients measured in this study with the exception of manganese concentrations which were significantly lower at the 2 and 4.8-ton/acre rates.


Table 4. Winter wheat tissue test macro- and micronutrients. Means within a row with different letters are significantly different using Fisher’s LSD (P=0.05).

  Check 1-ton 2-ton 4.8-ton LSD (0.05)
Nitrogen 2.8 2.6 2.7 2.9 ns
Phosphorus 0.3 0.3 0.3 0.3 ns
Potassium 0.9 1.2 0.9 1.2 ns
Calcium 0.5 0.5 0.5 0.5 ns
Magnesium 0.1 0.1 0.1 0.1 ns
Sulfur 0.3 0.3 0.3 0.3 ns
Iron 118 185 123 117 ns
Manganese 75a 72ab 65bc 58c 8
Zinc 17 19 18 17 ns
Copper 8 6 6 6 ns


Wheat yields trended upward with increased lime rate but these improvements were not statistically significant (Table 5). Complications with weigh-scales in-field resulted in the loss of data at the 2-ton treatment rate and is not reported. Grain test-weights were unaffected by lime rate, while grain protein content increased with higher lime rates.


Table 5. Winter wheat performance. Means within a column with different letters are significantly different using Fischer's LSD (P=0.05). 

 Treatment Yield Test Weight Protein
  bu/acre lbs/bu %
 Check 75 61.2 8.5a
 1-ton 80 61.2 8.6ab
 2-tons -- 61.0 8.7ab
 4.8-tons 82 61.1 8.9b
 LSD (0.05) ns ns 0.3
 CV (%) -- -- 2.1



This agricultural lime increased soil pH and base saturaion to the depth it was incorporated (3 inches). Despite not seeing a significant increase in yield, the yield of winter wheat did trend upward with increasing lime application. While winter wheat is the primary cash crop for rainfed northern Idaho, rotation crops such as pea, lentil and alfalfa also are important components of the cropping system. Previous work has demonstrated that these crops are even more sensitive than wheat and yield declines will be observed at a soil pH of 5.5 to 5.7 depending on the legume (Mahler & McDole, 1987). This is partially due to the sensitivity of the nitrogen fixing bacteria to low soil pH (Mahler & McDole, 1985). The soil pH in the surface layer of soil increased to approximately 6 with 2 or 4.8 ton/A application rates of lime. This increase in soil pH returned the soil to a state that should allow for improved nutrient availability as well as providing an environment conducive for symbiotic bacteria and growth of legume crops.

High applications of lime have been associated with concerns of displacement of key nutrients (Magdoff and van Es, 2009) but our results show no negative grain yields, kernel test-weights or tissue nutrient concentrations associated with lime application at any of the rates applied. Although plant tissue concentrations of manganese were reduced at the higher lime rates, they remained sufficient for wheat development (Schwab et al., 2007). The availability of manganese increases as the soil pH decreases and at very high concentrations this micronutrient can cause toxicity to plant shoots.

Fortunately, the acidification in northern Idaho is primarily restricted to the upper 6 inches of soil, coinciding with the proximity of nitrogen fertilizer application. Being localized to the topsoil layer should allow for effective management of acidity. However, 32 months after application, there was no evidence that lime influenced soluble aluminum concentrations below the zone of incorporation indicating greater soil disturbance will be necessary to better incorporate liming material. More thorough mixing of the soil will ensure that soil pH increases and the soluble aluminum is more effectively reduced in concentration where it is highest.

Results of these efforts will help inform Nez Perce Tribal land management and economic development planning efforts. It also will benefit producers considering lime application to mitigate soil acidity. Information on effective liming solutions in northern Idaho does not exist and this data will help to fill that knowledge gap.


Literature Cited

Magdoff F. R., and van Es H. M., (2009). Other fertility issues: Nutrients, CEC, acidity, and alkalinity. Building soils for better crops. 3rd Edition. (pp. 227-234). Sustainable Agriculture Research & Education USDA’s National Institute of Food and Agriculture, University of Maryland and University of Vermont

Mahler R. L., Halvorson A. R., and Koehler F. E. (1985). Long-term acidification of farmland in northern Idaho and eastern Washington. Communications in Soil Science and Plant Analysis 16(1): 83-95.

Mahler R. L., and McDole R. E. (1987). Effect of soil pH on crop yield in northern Idaho. Agronomy Journal 79(4):751-755.

Mahler R. L., and McDole R. E. (1985). The Influence of lime and phosphorus on crop production in northern Idaho. Communications in Soil Science and Plant Analysis 16(5):485-499.

Koenig R. T., Schroeder, K. L., Carter A. H., Pumphry M. O., Paulitz T. C., Campbell K. G., and Huggins D. R. (2011). Soil acidity & aluminum toxicity in the Palouse region of the Pacific Northwest. Washington State University Extension Fact Sheet. FSO5OE

Schwab G. J., Lee C. D., and Pearce R. (2007). Sampling plant tissue for nutrient analysis. University of Kentucky Cooperative Extension Service AGR-92.