Dynamic performance of drill coulters in a soil bin

A laboratory experiment was conducted to examine the vertical movement of two different conventional drill coulters in a soil bin. The bin was filled with air-dried sand, and was configured without straw, and with a surface covering of straw of two different length distributions. The objective of the experiment was to compare the movement of a disc coulter and a hoe coulter depending on the straw cover of the surface, and to analyse the dynamics of the coulter-soil system. The penetration depth was not affected by the surface condition for the hoe coulter, but the disc coulter had a smaller penetration depth in the straw-covered soil than in the straw-free soil. Both coulters penetrated steeper in the straw-free soil than in the straw-covered soil. The penetration after passing a solid object in the soil also followed the same course, affecting the disc coulter more than the hoe coulter. Here, the disc coulter on the surface with short straw had the smallest penetration depth, and the penetration angle was least for the same coulter on the surface with short straw. The depth of the hoe coulter was unaffected by straw covered treatment on the surface. The depth of the disc coulter was reduced in the straw covered treatments compared to the non-covered treatment. Of the straw-covered treatments, the reduction in the depth of the disc coulter was greatest for surface with short pieces of straw. Frequency analysis of the depth signal varying over time showed that the frequencies below 1 Hz dominated the signal. Rescaled range analysis showed persistence in the data and indicated that the test distance of 3.9 m was not long enough to establish a stable coulter depth. The frequency analysis of coulter depth data was very sensitive to the coulter run distance, but proved less sensitive in detetecting the vertical coulter movement pattern. To eliminate the depth trends and duration effects of the tests, the depth fluctuations were calculated. Coulter depth fluctuations were almost non-existent for the hoe coulter, but the disc coulter was affected by the surface with short straw compared to the straw-free surface. The fluctuations were in the range 0.25-11 Hz for the disc coulter. Long pieces of straw damped the vertical oscillation of the coulter considerably compared to the straw-free surface and the surface with short pieces of straw. (C) 1999 Silsoe Research Institute.