Articles
COMPARISON OF RHIZON SOIL MOISTURE SAMPLER, POUR-THROUGH, AND SATURATED MEDIA EXTRACT EXTRACTIONS OF CONTAINER ROOT SUBSTRATE
Article number
927_121
Pages
981 – 987
Language
English
Abstract
The Rhizon soil moisture sampler (RS) provides a non-destructive method for extracting soil solution.
The RS with a 2.5 mm outer diameter draws solution from a small area and raises the question whether it can represent the whole pot.
Also, when placed diagonally or vertically in a pot more solution would be expected to be collected from the base relative to the top of the pot due to lower water container capacity at the top.
When 5 RS samplers were placed horizontally at 1, 3, 5, 7, and 9 cm above the bottom of 16.5 cm diameter, 10 cm substrate depth, 1.8 L volume pots containing lettuce plants, the following average gradients from bottom to top of pot were found: EC 1.1-1.8 dSm-1, pH 6.3-5.6, and relative rate of solution extracted 1:0.32. When the solution from a Rhizon sampler oriented diagonally (D-RS) from top to bottom of the pot was compared to the five horizontally and equally spaced Rhizon samplers (H-RS), pH level in the D-RS extract was equivalent to that in the lower 20% of the substrate column (H-RS1). EC in the lower three H-RS and D-RS extracts were within standard error of each other.
A comparison of extracts from D-RS, pour-through (PT), and saturated media extract (SME) showed equivalent EC levels for the D-RS (1.21) and PT (1.26) but lower values for SME (0.69). The pH levels were significantly different for all three methods and were 6.6, 6.2, and 5.5 for the PT, D-RS, and SME methods, respectively.
Overall, separate EC and pH standards are required for interpreting SME results compared to the other two methods which is reasonable because SME alters the solution by dilution whereas the other two do not.
Similar EC standards can be used for PT and D-RS but pH levels can be lower in the D-RS procedure.
Data indicated that the D-RS drew solution primarily from its lower end, far in excess of the proportion suggested by the five H-RSs.
The RS with a 2.5 mm outer diameter draws solution from a small area and raises the question whether it can represent the whole pot.
Also, when placed diagonally or vertically in a pot more solution would be expected to be collected from the base relative to the top of the pot due to lower water container capacity at the top.
When 5 RS samplers were placed horizontally at 1, 3, 5, 7, and 9 cm above the bottom of 16.5 cm diameter, 10 cm substrate depth, 1.8 L volume pots containing lettuce plants, the following average gradients from bottom to top of pot were found: EC 1.1-1.8 dSm-1, pH 6.3-5.6, and relative rate of solution extracted 1:0.32. When the solution from a Rhizon sampler oriented diagonally (D-RS) from top to bottom of the pot was compared to the five horizontally and equally spaced Rhizon samplers (H-RS), pH level in the D-RS extract was equivalent to that in the lower 20% of the substrate column (H-RS1). EC in the lower three H-RS and D-RS extracts were within standard error of each other.
A comparison of extracts from D-RS, pour-through (PT), and saturated media extract (SME) showed equivalent EC levels for the D-RS (1.21) and PT (1.26) but lower values for SME (0.69). The pH levels were significantly different for all three methods and were 6.6, 6.2, and 5.5 for the PT, D-RS, and SME methods, respectively.
Overall, separate EC and pH standards are required for interpreting SME results compared to the other two methods which is reasonable because SME alters the solution by dilution whereas the other two do not.
Similar EC standards can be used for PT and D-RS but pH levels can be lower in the D-RS procedure.
Data indicated that the D-RS drew solution primarily from its lower end, far in excess of the proportion suggested by the five H-RSs.
Authors
K. Jeong, P.V. Nelson, J.M. Frantz
Keywords
substrate pH, substrate EC, soil testing
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