SOIL QUALITY - UPLB SOIL TEST KIT

The condition of our soils ultimately determines human health by serving as a major medium for food and fibre production and a primary interface with the environment, influencing the quality of the air we breathe and water we drink. Thus, there is a clear linkage between soil quality and human and environmental health. As such, the health of our soil resources is a primary indicator of the sustainability of our land management practices. (Acton and Gregorich 1995)

Soil quality concise definition includes “fitness for use” and “the capacity of a soil to function. “ Combining these, soil quality is the ability of a soil to perform the functions necessary for its intended use. Soil functions include: sustaining biological diversity, activity, and productivity; regulating water solute flow; filtering, buffering, degrading organic and inorganic materials; storing and cycling nutrients and carbon; and providing physical stability and support. (USDA Soil Quality Indicator)

There are three main categories of soil indicators: chemical, physical and biological. Typical soil tests only look at chemical indicators. Soil quality attempts to integrate all three types of indicators. The categories do not neatly align with the various soil functions, so integration is necessary.

Organic matter, or more specifically soil carbon, transcends all three indicator categories and has the most widely recognized influence on soil quality. Organic matter is tied to all soil functions. It affects other indicators, such as aggregate stability (physical), nutrient retention and availability (chemical), and nutrient cycling (biological); and is itself an indicator of soil quality. (Doran and Parkin, 1996)

Chemical indicators can give you information about the equilibrium between soil solution (soil water and nutrients) and exchange sites (clay particles, organic matter); plant health; the nutritional requirements of plant and soil animal communities; and levels of soil contaminants and their availability for uptake by animals and plants. Indicators include measures of: Electrical conductivity, soil nitrate and soil reaction (pH). (Doran and Parkin, 1996)

One significant indicator measure under chemical is the soil pH as it influences the solubility of nutrients. It also affects the activity of micro-organisms responsible for breaking down organic matter and most chemical transformations in the soil. Soil pH thus affects the availability of several plant nutrients. A pH range of 6 to 7 is generally most favorable for plant growth because most plant nutrients are readily available in this range. However, some plants have soil pH requirements above or below this range.

Soil Sampling

The main objective of soil sampling is to collect a small amount of sil sample weighing about half kilogram that will represent the soil in a large area, e.g., one hectare furrow slice that weighs about 2 million kilograms. Since only a small amount of soil sample is used in chemical analysis and results are projected for a large quantity of soil, the accuracy of soil testing depends largely on proper soil sampling (UPLB Soil Test)

500g soil sample of three replicates were scooped and collected each from S1, S2 and S3. Replicates from collected samples from different stations were mixed in a bucket. 3 samples from each station were packed by 150g of soils each using aluminium foil. Samples were transported to the laboratory subjected for 24 hours oven incubation at 100^oC.

Test for Chemical Factors

Test for the chemical factors of soil: N, P, K, and pH using soil test kit. Analysis by the soil test kit is a quick method of evaluating the fertility status of a soil. It involves chemical analyses that measure the amount of nutrients in the soil that are available to the plant. Results are interpreted and used as basis in making a recommendation on the right kind and amount of fertilizer for a particular crop when grown in the soil being tested. 

Nitrogen (N)

For Nitrogen (N), fill the test tube with soil sample up to the scratch mark. Add 16 drops (1 ml) of solution B; mix well by gently swirling the test tube 30 times. Repeat swirling after 5 minutes and let the test tube stand for 30 minutes. Match the color of the resulting solution on top of the soil with the color chart. Take note if the soil is low, medium, or high in available nitrogen. 

Phosphorous (P)

For Phosphorous (P), fill the test tube with soil sample up to the scratch mark. Add 16 drops (or 1 ml) of solution C and 2 drops of solution C1; Mix well by gently swirling the tube for about 1 minute. Repeat swirling after about 3 minutes and let the test tube stand for 5 minutes. Take one foil or tin strip and wrap it firmly at one end of the plastic stick; without disturbing the soil, stir the solution slowly with the thin strip for one minute (repeat this step about 2 minutes). Match the blue color intensity of the solution with the color chart below and take note if the soil is low, medium or high in available phosphorous. 

Potassium (K)

For Potassium (K), fill the test tube with soil sample up to the scratch mark; add 16 drops (or 1 ml) of solution D and 4 drops of solution D1. Mix well by gently swirling the tube for about 1 minute. Repeat swirling after about 3 minutes and let stand for 5 minutes until the soil particles have settles at the bottom of the tube. 

Add solution E as follows: Slowly insert the dropper containing 0.6 ml of solution E inside the test tube so that its tip is about 2 cm above the solution. Slowly add drops of solution E one drop at a time. Do not mix or shake the solution. 

Let the solution stand for 2 minutes, then observe the appearance of a cloudy yellow layer on top of the orange solution. A distinct cloudy yellowish layer indicates that the soil has sufficient available potassium. If no distinct cloudy yellowish layer appears on top of the orange solution, the soil is deficient in available potassium.

Soil pH

To determine soil pH using soil kit, fill the test tube with soil sample up to the scratch mark. Add 7 drops of CPR pH indicator dye. Mix by gently swirling the test tube 20 times. Repeat swirling after about 2 minutes and let the test tube stand for 5 minutes. To get the pH of the soil, match the color of solution on top of the soil with the corresponding color chart of pH indicator dye used. If soil pH is equal to or greater than 6 repeat step 1 to 5 using BTB instead of CPR. However, if soil pH is less than or equal to 5 repeat steps 1 to 5 using BCG instead of CPR. 

Organic Matter

For organic matter, performed in the laboratory by weighing 10g of incubated soil samples; place the 10g of soil samples in a pre-weighed crucibles and place it in the furnace for 1700^oC for 4 hours. Weigh again the crucible and compute for organic matter in the soil by deducting the final weight from initial weight.