*2.1. Collection, Preparation and Characterization of Soil*

Three soils varying in soil texture were collected from the following three geological regions of Schleswig-Holstein, Germany: (1) the sandy outwash region (Geest, the outwash region is dominated by Brunic Arenosols or Cambisols, Podzols and Gleysols, as well as Histosols), (2) the Weichselian glacial region in the east (Östliches Hügelland, the Weichselian glacial deposits contain very fertile Luvisols, Cambisols, Anthrosols derived from colluvic material, Gleysols and Rheic Histosols), and (3) the marshland with alluvial deposits in the west (Marsch, the marshland includes different types of Fluvic Gleysols and Histosols) [18]. The selected soils represent the major soil types or climatic zones of the state of Schleswig-Holstein. The soils belong to three different natural grasslands of the state.

Soils from the upper 20 cm soil horizon were collected. Visible plant residues and stones were removed by passing soil through a 2 mm sieve. A representative subsample of each soil was analyzed for salient characteristics, namely, particle size distribution (clay, sand and silt), pH, total carbon (C) and N, NH4 +-N and NO3 −-N following standard methods (Table 1).


**Table 1.** Salient characteristics of the experimental soils.

Values (mean ± SE, *n* = 4).

#### *2.2. Incubation Experiment*

Four NIs, namely, dicyandiamide (DCD), 3, 4-dimethylpyrazole phosphate (DMPP), nitrogenous mineral fertilizers containing the DMPP ammonium stabilizer (ENTEC) and PIADIN (active ingredients: 3.00–3.25% 1, 2, 4-triazole and 1.50–1.65% 3-methylpyrazole), were tested with the three different soil types (Marsch, Östliches Hügelland and Geest). For comparison, a control without the addition of NI was also included for each soil type. The soils were packed into cylindrical pots (15 cm diameter and 33 cm length, sealed at the bottom) to achieve a bulk density of 1.4 g cm−<sup>3</sup> with 20 cm depth. The experimental treatments, each having four replications, were arranged in a completely randomized design. All the pots were fertilized with 0.5g NH4 +-N kg−<sup>1</sup> soil using ammonium sulfate ((NH4)2SO4) salt in solution form. The NIs were applied at 5% of applied NH4 +-N (i.e., 25 mg kg−<sup>1</sup> soil in solution form). The control treatment involved the application of N fertilizer and deionized water only. Deionized water was added each day to maintain the moisture content equivalent to the water-holding capacity of the soils. Following treatment application, pots were incubated for a period of 57 days in a climatic chamber adjusted to a consistent temperature (15 ◦C), soil moisture (80% soil water-holding capacity) and air humidity (50%).
