A method for applying a substance, such as a plant protection product, a pesticide, and/or a fertilizer, to cultures by means of a sprayer that is mounted to a mobile support and has a height-adjustable spray rodding to which a plurality of dosing facilities for the substance and at least four evenly spaced ultrasonic sensors are mounted, wherein during use of the mobile support sound pulses are cyclically delivered toward the culture by means of the ultrasonic sensors and the echoes reflected by the culture and the ground are detected, characterized in that the method comprises: (a) cyclically determining the distance between the ultrasonic sensors and the surface of the culture; and height adjustment of the spray rodding if the distance between the ultrasonic sensors and the surface of the culture deviates from a given value; and at the same time (b) cyclically determining the biomass to generate a biomass value that is a measure for the actual biomass on an area that is scanned by the ultrasonic sensors; calculating the rate of application of the substance to be applied to the culture of said area to generate at least one control signal for the dosing facilities; and adjusting the rate of application of the substance by means of the dosing facilities on the basis of the control signal(s); wherein - the cyclically determination of the distance between the ultrasonic sensors and the surface of the culture in step (a) is done based on the echoes that are received first in time by the ultrasonic sensors within a first cycle; - the cyclically determination of the biomass in a second cycle is done based on all of the echoes that are received by the ultrasonic sensors within a first cycle; and - for each ultrasonic sensor in each first cycle a value for the distance between the ultrasonic sensor and the culture surface and a value for the distance of the ultrasonic sensor from the ground is calculated. (a) cyclically determining the distance between the ultrasonic sensors and the surface of the culture; and height adjustment of the spray rodding if the distance between the ultrasonic sensors and the surface of the culture deviates from a given value; and at the same time (b) cyclically determining the biomass to generate a biomass value that is a measure for the actual biomass on an area that is scanned by the ultrasonic sensors; calculating the rate of application of the substance to be applied to the culture of said area to generate at least one control signal for the dosing facilities; and adjusting the rate of application of the substance by means of the dosing facilities on the basis of the control signal(s); wherein - the cyclically determination of the distance between the ultrasonic sensors and the surface of the culture in step (a) is done based on the echoes that are received first in time by the ultrasonic sensors within a first cycle; - the cyclically determination of the biomass in a second cycle is done based on all of the echoes that are received by the ultrasonic sensors within a first cycle; and - for each ultrasonic sensor in each first cycle a value for the distance between the ultrasonic sensor and the culture surface and a value for the distance of the ultrasonic sensor from the ground is calculated. - the cyclically determination of the distance between the ultrasonic sensors and the surface of the culture in step (a) is done based on the echoes that are received first in time by the ultrasonic sensors within a first cycle; - the cyclically determination of the biomass in a second cycle is done based on all of the echoes that are received by the ultrasonic sensors within a first cycle; and - for each ultrasonic sensor in each first cycle a value for the distance between the ultrasonic sensor and the culture surface and a value for the distance of the ultrasonic sensor from the ground is calculated.