Accession to the Duchy and continuation of the patronage
After the death of his father on 4 June 1680 and the loss of the Archbishopric of Magdeburg, Johann Adolf dedicated his first efforts to finishing the still incomplete Schloss Neu-Augustusburg that was begun by his father in 1660; construction at the castle resumed on 18 August 1680. The consecration of the castle chapel took place on 1 November 1682 and the castle was finally paved in the year 1694. A large theatre had been built earlier that sponsored performances of opera in German beginning in 1685. At his estate, near the Guardhouses, Johann Adolf created the most important formal garden in central Germany of his time. In 1690 pipes were built to supply the castle complex with water from the Selauer Area. The city of Weissenfels prospered to the point where it became not only an administrative center, but also an economic center. Johann Adolf was a patron of the arts following the model of his father and other members of his family; as court Kapellmeister he appointed Johann Philipp Krieger, who had already served under the late duke. Johann Adolf also discovered the musical talent of the son of his court surgeon Georg Händel and encouraged him to let the young Georg Friedrich seek training in music. Like his father, Johann Adolf was accepted into the Fruitbearing Society.
When the county of Rosenburg fell to the Archbishopric of Magdeburg in 1659 after the extinction of the male line of the counts of Barby, Johann Adolf's father, duke August, continued to administer these areas in spite of the protests of the Electors of Brandenburg and Saxony, who desired those lands in accordance with the terms of the Peace of Westphalia. In 1666, the Elector of Saxony finally consented to give Barby and Rosenberg to duke August until the extinction of the Weissenfels line. After the death of the duke, Barby was inherited by one of his younger sons, Heinrich. Johann Adolf, who saw his inheritance reduced by his father, protested. After his father's death, Johann Adolf turned to the elector of Brandenburg to obtain a declaration of nullity for the sales contract that relinquished Rosenberg. In April 1681 it was sold for 60.000 Taler to the Elector Frederick of Brandenburg. Due to the debts accumulated by his father, Johann Adolf was forced in 1687 to sell Burg bei Magdeburg.
After the death of Elector Johann Georg II of Saxony in 1680, the will of his father Johann Georg I was disputed by the new Elector Johann Georg III with regard to the appanages of his younger sons; he refused to recognise the principalities and collateral lines of his cousins. This brought some difficulties to Johann Adolf after he recognised a threat from the Saxonian Electorate to his own territories. The conflict could only be settled with the Contract of Torgau and two other contracts signed in Dresden in 1682 and 1688; with these pacts, Johann Adolf secured his rule over Querfurt and his seat in the Upper-Saxonian Council. On his death, his three surviving sons, Johann Georg, Christian, and Johann Adolf II, successively assumed rulership over the duchy of Saxe-Weissenfels.
After the death of his wife in 1686, Johann Adolf married a second time in Querfurt on 3 February 1692 to Christiane Wilhelmine of Bünau. This marriage was morganatic and only made by contract; the completion of the marriage in the presence of a clergyman was left to his discretion. Johann Adolf give her 6,000 Taler as Morgengabe and an annual income of 3,000 Taler and the use of Schloss Dahme for her residence as dower. He admonished his sons to show her due respect, and should any children come from this marriage he would make further divisions over the family lands. After five years of marriage, Christiane Wilhelmine was created Imperial Countess in 1697 at the request of her husband. They had no children.
