San flow analyzer

In addition to previous research^{6 (link)}, we determined the chemical composition of the pure chitin flakes and evaluated differences in peat substrate chemical composition due to chitin addition. Total N (Dumas method, ISO 16634-1, Thermo Scientific flash 4000 N analyzer, Massachusetts, United States), organic matter (OM, EN 13039) and P, Ca, K, Mg, Fe, Al and Mn (ashing and digestion with 7 N HNO₃⁻ (p.a. 65%) and measured with an Agilent 5110 ICP-OES, Santa Clara, USA) concentrations were determined.
Readily available nutrients, electrical conductivity (EC) (EN 13038) and pH in H₂O (EN 13037) in the pure chitin flakes and in the control and chitin amended peat were measured in a 1:5 soil to water (v/v) suspension. Water-extractable PO₄-P, Cl, SO₄ and NO₃-N were measured with a Dionex DX-3000 IC ion chromatograph (Dionex, Sunnyvale, CA). Water soluble NH₄-N was measured with a Skalar SAN++ flow analyzer (Skalar Analytical B.V, Breda, The Netherlands). Water-extractable C, Fe, Si, K, Ca, Mg and Na concentrations were measured with ICP-OES.

Root activity was determined using the triphenyl tetrazolium chloride method of Lindström and Nyström (1987 (link)). The activities of root enzymes involved in soil nitrogen cycling (e.g., nitrate reductase and urease) and metabolism in rice roots (e.g., nitrate reductase, glutamate synthetase, and glutamine synthetase) were determined spectrophotometrically. Enzyme activities were assayed within 1 week of sampling. Table S1 lists the conditions used in the enzymatic assays.
The dry matter mass of each part of rice plants was determined by weighing the dried plant materials. A SPAD-502 chlorophyll meter (Minolta, Osaka, Japan) was used to determine the chlorophyll status in rice. Soil and plant total nitrogen concentrations were determined by initially digesting the root samples with H₂SO₄–H₂O₂ at 60 ℃ and then measuring the concentrations using a San + + flow analyzer (Skalar, Breda, Netherlands).

The SRS1000 T soil carbon flux measurement system, connected to a LCI thermocouple temperature sensor and EC-5 soil moisture sensor, was used to measure soil temperature and moisture in the 0–5-cm soil layer. Soil chemistry indicators were referenced from Agricultural Chemical Analysis of Soil by Bao Shidan. Soil organic carbon (SOC) content was determined using the potassium dichromate oxidation-external heating method. Soil dissolved organic carbon (DOC) was evaluated using 0.5 mol/L potassium sulfate (with a 2:1 water-to-soil ratio). Soil total carbon (TC) content was determined using a total organic carbon analyzer (MultiN/C2 100, Germany). Soil total phosphorus (TP), total nitrogen (TN), and inorganic nitrogen (NH₄⁺-N and NO₃^–-N) content were determined using a SKALAR San +  + flow analyzer (The Netherlands). Soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were determined via chloroform fumigation and leaching.