The Quantity and Quality of White Mustard (Sinapis alba L.) Seed Depending on Nitrogen Fertilization and Soil Enzyme Activity

The aim of this research was to determine the response of white mustard (Sinapis alba L.) cultivated in 2021–2022 in Lucim (53°23′06″ N 17°50′08″ E) in Poland to the soil nitrogen doses: N40—40 kg N·ha−1, N60—60 kg N·ha−1, N80—(40 + 40)-80 kg N·ha−1, as well as the method of its foliar application (0%—no foliar fertilization, 50%—half of the nitrogen dose and 75%—⅔ of the nitrogen dose). The effect of mustard cultivation on the activity of soil dehydrogenase, arylsulfatase, and rhodanese was examined. The highest white mustard seed yield was obtained after application of 80 kg N·ha−1 (1.577, 1.597 Mg·ha−1) and after application of Multi-N50% (1.490, 1.515 Mg·ha−1). Total nitrogen (50 g·kg−1) content was highest in seeds from treatments fertilized with 80 kg N·ha−1. Similar total nitrogen content in seeds was obtained using a 50% dose of foliar nitrogen. Increasing nitrogen doses resulted in a decrease in the crude fat yield in seeds. However, a significant increase in this nutrient content was observed after application of 50% foliar nitrogen. Soil nitrogen fertilization increased the enzymatic activity of dehydrogenases, particularly at the N80 dose. The activity of this enzyme was positively correlated with the obtained mustard seed yield, as well as with its quality measured by total phosphorus and crude fat content.