Mastersizer 2000 particle analyzer

Soils were homogenized, air-dried immediately after sampling and passed through a 2-mm sieve with roots removed before analysis. Soil pH was measured at a soil:water ratio of 1:2.5 (w:v). SOC and total N contents were determined using the Walkley–Black modified acid-dichromate ferrous sulfate titration method and micro-Kjeldahl digestion method coupled with colorimetric determination⁶⁰ . Organic C and N contents of plant samples were measured by combustion using an elemental analyzer (Vario EL III, Elementar, Hanau, Germany). Reactive Fe, Al were extracted by the citrate-bicarbonate-dithionite method^{61 (link)} and measured on the inductive coupled plasma emission spectrometer (Thermo ICAP6300, USA). To measure soil texture, sieved soils (<2 mm) were treated repeatedly with 10 ml of hydrogen peroxide solution (30%) to remove organic matter until no bubbles were produced. The residues were boiled with 10 ml of hydrochloric acid (HCl; 10%) to remove lime, rinsed repeatedly with deionized water to pH 7 and then dispersed in 10 ml of sodium hexametaphosphate (0.5 M) by sonication (30 s). Particle size distribution was determined using Malvern Mastersizer 2000 particle analyzer^{62 (link)}. Clay is defined as particles smaller than 2 µm.

The particle size distributions of non-hydrated microcapsules were determined using a Mastersizer 2000 particle analyzer with Hydro μP dispersion unit (Malvern Instruments, Worcestershire, UK). Spray dried powders were dispersed in propan-2-ol and added to the dispersion unit according to manufacturer guidelines. A refractive index of 1.51 and an absorption index of 0.1 were assumed for the powder, and a general purpose spherical model was selected. Measurements were made while the dispersion unit pump was set to 2,500 rpm. Prior to each sample measurement, samples were sonicated in the dispersion unit at 50% intensity for 10 minutes to break up aggregates. Each sample was measured in triplicate (each replicate returned ten measurements), and Malvern software was used to calculate an average distribution from the 30 distributions. The reported size parameters are the average ± standard deviation for the three replicates.
In addition, particle size distributions were determined as powders hydrated and released PPFM. For this analysis, powders were suspended in water and added to the dispersion unit, with water as the dispersing fluid. Measurements were performed every 2 min as the particles circulated through the dispersion unit (no sonication).