Improved simple on-site soil quality testing for soils in the Intermountain West

View the project final report

Commodities

• Fruits: apples, apricots, cherries, peaches, pears, plums, general tree fruits

Practices

• Education and Training: demonstration, mentoring
• Soil Management: earthworms, soil analysis, soil quality/health

Simple on-site tests provide a possible avenue for farmers to improve their understanding of soil quality without the difficulty or cost associated with laboratory testing. Simple soil quality tests were compared with corresponding laboratory tests for their ability to distinguish between soils with known quality differences in an orchard setting. Despite overall weak correlations between simple tests and laboratory tests, several of the simple test results accurately differentiated the majority of orchard floor treatments based on soil quality. The best correlations between simple tests and laboratory findings were found between Solvita respiration and microbial biomass, the modified surface soil slake test and microbial biomass, Lamotte simple N test and laboratory measured N in the conventional orchard, and Mosser N and laboratory measured N. Modified slake tests and soil biodiversity/earthworm abundance counts consistently ranked as most preferred simple tests among growers in terms of user friendliness and cost.

Introduction

Maintaining soil quality is essential for the long-term prosperity of a farm or other land-based system (Wienhold et al., 2004). In the U.S., cropland loses an average of seven tons of soil per acre, per year  (Sullivan, 2004).  Maintaining soil quality can prevent loss in system productivity while also improving long-term financial outcome for farmers.  For example, growers in Iowa were able to increase yield by 3-12% and reduce costs from inputs by 41-79% (Liebman et al., 2003). Despite attempts, little progress has been made in increasing grower involvement in maintaining soil quality (Herrick, 2000). Even when growers are interested in learning more about soil quality, soil quality tests are not always available, affordable, reliable, or feasible. (Friedman et al., 2001).

A number of simple soil health tests have been developed over the years, in particular, soil health cards and test kits such as the NRCS soil quality test kit. Soil health cards can be useful for soil health professionals in discussing soil health with growers. However, evaluating soil health based on comparisons to pictures or descriptions on cards alone can be subjective. (Friedman et al., 2001). The NRCS test kit is one of the most comprehensive test kits available, yet many of the tests are time consuming and confusing for someone new to soil testing (Friedman et al., 2001). Submitting soil samples to an analytical laboratory is the most straightforward testing method for growers. However, most laboratories do not offer biological and physical tests, and when they do, it is often cost prohibitive to a grower.

Aggregate stability is the ability of primary soil particles to remain attached under disruptive forces. There are generally three different categories of aggregate stability tests: 1) ease of dispersion by turbidimetric techniques (Emerson, 1967), 2) evaluation of aggregate strength related to raindrop impact (Bruce-Okine and Lal, 1775), and 3) aggregate stability by wet sieving (Yoder 1936). All three categories of soil aggregate tests have on-site versions. As rainfall simulators are often bulky and complicated to build, the most effective on-site aggregate testing options for growers are turbidimetric tests or wet sieving/slake tests. The NRCS incorporated a modified version of a slake test developed by Herrick et al. (2001) into their field test kit. Herrick et al. (2001) developed a stability test kit that could be made inexpensively with simple tools. Aggregate stability tests are useful in addressing a soil’s potential for erosion, in particular, for comparing the same soil type among multiple management systems (Kemper and Koch, 1966; Kemper and Rosenau, 1986). 

Soil organisms are also important indicators of soil health as they may rapidly respond to shifts in management practices (Pankhurst et al., 1997). The most common simple biological test recommended is counting earthworms and or measuring soil respiration in a given volume of soil. However, earthworms are not native to all soils and soil respiration can be highly affected by weather (Friedman et al., 2001).  Other tests to measure soil biological health include those for soil arthropods. The Berlese funnel test is commonly used to measure abundance of soil athropods in a laboratory (Macfadyen, 1953; Macfadyen, 1961; Sabu and Shiju, 2010). Foldable or collapsible Berlese funnels have been constructed for lightweight transportation (Saunders, 1959; Northon and Kethley, 1988).  Hence, perhaps a Berlese funnel could be further modified as a convenient, affordable test for growers. 

Chemical tests, such as nitrogen, potassium, phosphorus, and pH tests, are the one type of soil quality assessment easily available in most laboratories. But questions remain on the accuracy of do-it -yourself chemical test kits commonly available, such as Rapidtest kit, Lamotte test kit, and Mosser test kit. Accurate on site tests might increase adoption of soil testing by growers.

The goal of this study was to increase adoption of soil quality testing by growers through assessing the effectiveness and use of a number of simple on-site chemical, biological, and physical soil quality indicator tests. Simple tests for measuring soil physical, biological, and chemical properties were correlated to comparable lab analysis for their ability to distinguish between soils of known soil quality characteristics. Physical simple tests measured aggregate stability and included the NRCS slake test and other modified slaking tests. The biological simple tests included in this study were the Solvita respiration test which measures CO₂ evolved in a given mass of soil over 24 hours, simplified Berlese funnel tests, earthworm abundance tests, and soil biodiversity tests measuring arthropods, earthworms, and organism diversity in soils respectively.  The chemical tests included, LaMotte, Mosser, and Rapid soil test kits to measure macronutrients and pH, and the Hana pH meter to measure only pH. Tests that compared favorably with corresponding lab analysis were taught to orchardists through demonstrations, and survey results were collected on their perceptions of these tests. Surveys on soil quality were also administered to Utah orchardists, to gain a better understanding of their current level of interest in and knowledge of soil quality.

1) Compare results of simple soil testing strategies to comparable standard lab tests.

2) Determine the most predictive soil quality tests by comparing results to an existing database collected from the Kaysville systems orchards.

3) Conduct onsite training sessions with growers to determine usefulness of the tests in a range of field settings.

4) Collect feedback from growers on ease of use and applicability.