## 2 Materials and Methods
### Field Demonstration 2021 and 2022  
Three field demonstrations were performed: maize 2021, grass 2021, and grass 2022. Each was prepared in the spring of the corresponding year on a clay soil (Table A1), and on a sandy soil in Wageningen, The Netherlands. Fertilization advice was determined by Eurofins Agro and mineral N was measured prior to the experiment. Each field had 6 plots: 3 blocks and 2 randomized fertilizer treatments per block. Fertilizer treatment 1, AS, consisted of the N-stripped product (6% N, 7% S), while treatment 2, CAN + S, consisted of a combination of a S containing CAN (Triferto, Doetinchem, The Netherlands; Novasul 23% N, 7% S), and gypsum (Triferto, The Netherlands (gypsum, 24% S)); a combination designed to make the total S dosage equal to the AS treatment. The AS used in 2022 was slightly more concentrated, with 7% N and 8% S (Table A2). The AS was applied using a low-emission technique from Slootomid (Borculo, The Netherlands): application of the liquid AS was carried out by its placement in shallow vertical slots about 5 cm deep, cut into soil by a disc, and each application unit consisted of two discs and injectors. The distance between the maize seeds (_Zea mays_ L., cv Ronaldinio) was 75 cm (100,000 seeds per ha), and the AS was injected at 7 cm from both sides of the maize seeds. The distance between the application units in grass was 25 cm and it was 75 cm in maize (Figure A2). In the 2022 grass demonstration, one additional control plot was added to both fields. Each plot was 10 m \(\times\) 9 m. Weed control was applied to all maize plots by standard methods. No irrigation was used as there was sufficient precipitation during the experiment. The soil used for the maize was tilted in the spring and was seeded with the guidance of GPS. The grasslands were existing grasslands used by farmers with swards dominated by _Lolium pereme_ L.  
Maize was harvested in September of 2021 using a forage harveseter (New Holland, Torino, Italy, 1770). The fresh yield was determined per two rows of maize, a random sample was taken for dry matter content and chemical analysis. After cutting the maize, all plots were sampled in November 2021 for soil mineral N, and soil density on the basis of soil organic matter, to calculate mineral N of the 0-90 cm soil layer per hectare. In 2021, the first grass cut was in early June using a Haldrup forage harveseter (Notec Engineering GmbH, Ilsenhofen, Germany), no second cut was harvested due to a mistake in the second fertilization (incorrect fertilization treatments). In 2022, there were two cuts (May and June), after which the experiment was stopped because sulfur was only added in the first two fertilizers to mimic agricultural practice. In NW Europe, ammonium- and sulfate-rich fertilizers are specifically used in spring when soil mineralization is relatively low. For each of these grass cuts, fresh grass matter was determined directly; a random subsample was taken to determine dry matter content. Chemical analysis of the grass and maize was performed on samples dried at 70 \({}^{\circ}\)C, including a determination of the water content (70 \({}^{\circ}\)C-105 \({}^{\circ}\)C). Total N and P were determined using SFA, after digestion with H\({}_{2}\)SO\({}_{4}\)/H\({}_{2}\)O\({}_{2}\)-Se, and total Ca, K, Mg, N, and S were determined using ICP-OES analysis after microwave digestion with HNO\({}_{3}\)-HCl-H\({}_{2}\)O\({}_{2}\)[16]. Soil mineral N was only measured following the conclusion of the field demonstrations, including plant available S (0.01 M CaCl\({}_{2}\) according to [20]) after the 2022 field demonstration. The N\({}_{2}\)O measurements during field demonstrations were only performed in 2022, and were similar to the measurements in the greenhouse. N\({}_{2}\)O emissions were measured repeatedly following the first fertilization using the Innova gas analyzer in the same manner as described for the greenhouse experiment, except that the PVC tube was pressed into the grass sod.