Combination of an agricultural tractor and a sowing machine which is attached to the agricultural tractor and is suitable for direct sowing, wherein: the sowing machine has a crossmember, on which a plurality of sowing units are mounted laterally next to one another, the sowing units each comprise a framework which is prestressed downwards in relation to the crossmember by prestressing means comprising an actuator actuated by pressure medium, and on which a feed container, a furrow opener, a depth gauge wheel, a sowing coulter and a metering device are mounted, and the metering device is configured to remove successive seeds from the seed container and to feed the seeds to the sowing coulter which discharges the seeds into a furrow, which is produced by the furrow opener and the depth of which is predetermined by the depth gauge wheel, wherein the crossmember of the sowing machine is mounted on a three-point coupling of the agricultural tractor, and the three-point coupling comprises a lower link which can be adjusted in height by means of a double-action hydraulic cylinder, and, during the sowing mode, the pressing forces of the furrow openers (78, 80) are introduced via the sowing units, the framework, the prestressing means, the crossmember and the three-point coupling into the chassis of the agricultural tractor, while the sowing machine is supported on the ground only at the three-point coupling and the depth gauge wheels of the sowing units, characterized in that the three-point coupling is lockable per se in relation to the chassis of the agricultural tractor, for which purpose the hydraulic cylinder is blockable per se by a valve during the sowing mode, in that the actuators which are actuated by pressure medium are designed in the form of pneumatic cylinders which can be subjected to a predeterminable pressure, and in that the pressing force of the furrow opener, which is predetermined by the pneumatic actuator, can be varied by means of a pneumatic control device, which is controllable by an operator from a cab of the agricultural tractor via an interface and a bus line, or by an automatic mechanism for adaptation to the respective circumstances in the field. the sowing machine has a crossmember, on which a plurality of sowing units are mounted laterally next to one another, the sowing units each comprise a framework which is prestressed downwards in relation to the crossmember by prestressing means comprising an actuator actuated by pressure medium, and on which a feed container, a furrow opener, a depth gauge wheel, a sowing coulter and a metering device are mounted, and the metering device is configured to remove successive seeds from the seed container and to feed the seeds to the sowing coulter which discharges the seeds into a furrow, which is produced by the furrow opener and the depth of which is predetermined by the depth gauge wheel, wherein the crossmember of the sowing machine is mounted on a three-point coupling of the agricultural tractor, and the three-point coupling comprises a lower link which can be adjusted in height by means of a double-action hydraulic cylinder, and, during the sowing mode, the pressing forces of the furrow openers (78, 80) are introduced via the sowing units, the framework, the prestressing means, the crossmember and the three-point coupling into the chassis of the agricultural tractor, while the sowing machine is supported on the ground only at the three-point coupling and the depth gauge wheels of the sowing units, characterized in that the three-point coupling is lockable per se in relation to the chassis of the agricultural tractor, for which purpose the hydraulic cylinder is blockable per se by a valve during the sowing mode, in that the actuators which are actuated by pressure medium are designed in the form of pneumatic cylinders which can be subjected to a predeterminable pressure, and in that the pressing force of the furrow opener, which is predetermined by the pneumatic actuator, can be varied by means of a pneumatic control device, which is controllable by an operator from a cab of the agricultural tractor via an interface and a bus line, or by an automatic mechanism for adaptation to the respective circumstances in the field.