Pe 10

Soil was collected from the top layer (0–20 cm) of a calcareous soil with a light loamy texture at the Soil Fertility and Fertilizer Efficiency Monitoring Network Station, Zhengzhou, Henan Province, China (34°47′02″ N, 113°39′25″ E). The soil samples were air-dried and ground to pass through a 2-mm sieve. Some of the soil characteristics are shown in Table 1. Soil pH was measured with a compound electrode (PE-10, Sartorius, Germany) using a soil to water ratio of 1:2.5. Soil EC was determined in 1:5 (w/v; g cm⁻³) soil-water mixtures. The contents of TOC and TN in soil were determined using a total organic C/total N analyzer (Multi N/C 3100/HT1300, Analytik Jena AG, Germany). Inorganic N (NH₄⁺-N and NO₃⁻-N) was extracted with 2M KCl and subjected to flow injection analysis (TRAACA-2000, Germany).

Soil analyses were performed by the soil-testing lab in Qiyang at the red soil experimental station of the Chinese Academy of Agricultural Sciences. Soil pH was measured with soil-water (1:2.5, w/v) slurry using a compound electrode (PE-10; Sartorious, Germany). Soil organic C (SOC) and total N (TN) were determined with an Elementar Vario EL III (Germany). Plant-available N was hydrolyzed with 1.0 mol l⁻¹ NaOH and measured according to the methods of Shi (1996 ). Total P was determined by perchloric acid digestion (Olsen and Sommers, 1982 ). Plant-available phosphorus (Olsen-P) was extracted with sodium bicarbonate and measured using the molybdenum-blue method (Watanabe and Olsen, 1965 (link)). Total and plant-available K were measured by flame photometry (Knudsen et al., 1982 ).

The concentrations of soil organic carbon (SOC) and total nitrogen (TN) were determined through dichromate oxidation (Kalembasa and Jenkinson, 1973 (link)) and Kjeldahl digestion (Bottomley et al., 2020 ), respectively. The concentration of soil inorganic N, specifically NO₃⁻N and NH₄⁺N, was determined by analyzing a 12 g fresh soil sample mixed with a 0.01 mol L^–1 CaCl₂ solution at a 1:10 ratio. The analysis was conducted using continuous flow analysis with the Foss FlAstar 5,000 instrument from Sweden. The pH of the soil was determined by employing a compound electrode (PE-10, Sartorius, Germany) and utilizing a soil-to-water ratio of 1:2.5. The fumigation extraction method using 0.5 M K₂SO₄ was employed to conduct the microbial biomass C (MBC) and microbial biomass N (MBN) analyses (Brookes et al., 1985 (link)), and the results were determined using a total organic C/N analyzer (Multi N/C 3100/HT1300, Analytik Jena AG).

Soil pH was determined with a compound electrode (PE 10, Sartorius, Goettingen, Germany) using a soil/water ratio of 1:2.5(w/v; g cm^-3). Electrical conductivity (EC) was measured at 25°C in 1:5 soil-water mixtures. Soil bulk density was measured using the cutting ring method after drying the soil cores at 105°C for 48 h. Soil organic carbon (SOC) and total nitrogen (TN) were determined by the heated dichromate/titration method [22 (link)] and the Semimicro-Kjeldahl method [23 ], respectively. Soil nitrate-N (NO₃⁻N) and ammonium-N (NH₄⁺-N) was extracted by 2 M potassium chloride (KCl; soil/KCl ratio of 1:5) and measured using a flow injection autoanalyzer (Smartchem 200, Alliance, France). Soil available phosphorus (P) was extracted by 0.5 M sodium bicarbonate (pH 8.5) and determined by the Olsen method [24 ]. Soil available potassium (K) was extracted by 1 M ammonium acetate, adjusted to pH 7.0, and then measured by atomic absorption spectrometry (NovAA300, Analytik Jena AG). Soil microbial biomass carbon/nitrogen (MBC/MBN) was measured by the chloroform fumigation-extraction method and determined by C/N analyzer (Multi N/C 3100/HT1300, Analytik Jena AG, Germany) [25 (link)]. Moreover, the values of MBC and SOC were used to calculate the microbial quotient (MQ, the ratio of MBC to SOC), which could be used as indicators of soil microbial activity [26 (link)].

Various parameters of each pepper, such as shoot length, shoot diameter, shoot dry weight, root dry weight and leaf area were measured during the vegetative period. Parameters of fruit quality, including concentrations of vitamin C (VC), soluble sugars, proteins and nitrate were determined. Soil physical and chemical properties were analyzed. Soil available phosphorus (AP) was extracted with 0.5 M NaHCO₃ and then determined using the ammonium molybdate ascorbic method. Soil organic C (SOC) and total N (TN) were determined using a TOC analyzer (Elementar, Langenselbold, Germany). Soil pH was assayed in a soil extraction solution (1:2.5, w/v) with a compound electrode (PE-10; Sartorious, Göttingen, Germany). Available potassium (AK) was extracted with 1 M ammonium acetate solution and then determined using a flame spectrophotometer (FP640: INASA, Shanghai, China). NO₃⁻-N and NH₄⁺-N were extracted with 0.01 M CaCl₂ and the contents were determined with a continuous flow analytic system (Santt System; Skalar, Holland).