Starter 2100 ph probe

Soil pH was measured in a 1:2.5 soil solution (0.01 M CaCl₂) with a Starter-2100 pH probe (Ohaus, Brooklyn, NY, USA). Soil organic C (SOC) and total N (TN) contents were determined by the K₂Cr₂O₇ digestion and Kjeldahl determination methods, respectively. Available P (AP) content was determined by NaHCO₃ extraction-colorimetry and available K (AK) content by CH₃COONH₄ extraction-flame photometry. Invertase activity (ITA) was analyzed using a 3,5-dinitrosalicylic acid method (Bandick and Dick, 1999 (link)). Urease activity (UEA) and alkine phosphatase activity (PTA) were quantified by measuring the breakdown rate of substrates urea and p-nitrophenyl-phosphate, respectively (Tabatabai, 1994 ).

A Starter-2100 pH probe was used to measure the soil pH (Ohaus, Brooklyn, NY, USA) in a soil-to-water ratio of 1:2.5 (wt/vol) soil solution (0.01 CaCl₂). After drying at 105°C for 24 h, the soil moisture content was calculated. Soil total nitrogen (TN) was determined using Kjeldahl digestion, distillation, and titration (73 (link)). Water and inorganic carbon were removed by reacting the sample with phosphoric acid (74 ), and the soil organic carbon (TOC) was determined using the dry combustion method using an NC analyzer (Sumigraph NC-900; Sumika Chemical Analysis Service, Tokyo, Japan). After perchloric acid digestion and ascorbic acid reduction, AP was determined using molybdic acid colorimetry (75 (link)), and AK was analyzed using a flame atomic absorption spectrophotometer (76 ). The soil was extracted with KCl, the contents of soil nitrate nitrogen (NO₃^–-N) and ammonium nitrogen (NH₄⁺-N) were determined, and an automatic flow analyzer (FIAstar 5000 analyzer; Foss Tecator, Hillerød, Denmark) was used for analysis (77 (link)).

A Starter-2100 pH probe was used to measure the soil pH (Ohaus, Brooklyn, NY, USA) in a soil-to-water ratio of 1:2.5 (wt/vol) soil solution (0.01 CaCl₂). After drying at 105°C for 24 h, the soil moisture content was calculated. Soil total nitrogen (TN) was determined using Kjeldahl digestion, distillation, and titration (73 (link)). Water and inorganic carbon were removed by reacting the sample with phosphoric acid (74 ), and the soil organic carbon (TOC) was determined using the dry combustion method using an NC analyzer (Sumigraph NC-900; Sumika Chemical Analysis Service, Tokyo, Japan). After perchloric acid digestion and ascorbic acid reduction, AP was determined using molybdic acid colorimetry (75 (link)), and AK was analyzed using a flame atomic absorption spectrophotometer (76 ). The soil was extracted with KCl, the contents of soil nitrate nitrogen (NO₃^–-N) and ammonium nitrogen (NH₄⁺-N) were determined, and an automatic flow analyzer (FIAstar 5000 analyzer; Foss Tecator, Hillerød, Denmark) was used for analysis (77 (link)).