Statistical models for observation the uniformity of the working depth of machine-tractor unit during disking and cultivation depending on soil moisture

The uniformity of operation of a machine-tractor unit, influenced by the current soil moisture has been studied, and regression models describing the relations between them were developed. The study was based on three years of field experience in an area of 32400 m
²
in central Bulgaria (42°08′04″N25°21′31″E). The following tillage system was applied: first agricultural year (FAY) – triple disking with cultivation; second agricultural year (SAY) – double disking with rolling; third agricultural year (TAY) – triple disking. The disking was conducted with a tractor with a power of 200 hp. and a six-meter mounted disc harrow, and the Cultivation with an eight-meter cultivator aggregated to a tractor with 240 hp. Data on the instantaneous soil moisture was taken with a soil moisture meter AM-128 SOIL. The working depths of the disking and cultivation operations were measured with a linear meter. During the harvest, the following average yields were obtained: FAY-628kg/da, SAY-603kg/da, and TAY-545kg/da. Calculated correlation coefficients show a very strong correlation between soil moisture in the three observed years and the depth of disking (r=0.769; 0.790; 0.937). A weak, negative correlation (r=-0.172) has been reported between soil moisture and depth of cultivation. Statistically significant differences between depths of disking for the three observed years were found. From all regression models compiled for the first and second agricultural years, the Quadratic model best describes the influence of soil moisture on the depth of disking (R
²
=0.903, 0.617), and for the third agricultural year - the Cubic model (R
²
=0.667). No statistically significant regression models describing the relation between instantaneous soil moisture and the depth of cultivation were found. Statistically significant differences between the mеan yield in the FAY and TAY, as well as between the SAY and TAY were reported. The depth of disking affects the productivity of wheat by 36.2%.