MODELING AND CORRELATION OF SOIL CONE INDEX FOR BULK DENSITY, MOISTURE CONTENT AND PENETRATION DEPTH LEVELS IN A SANDY LOAM SOIL

            Soil cone index (CI) is as criteria for representing soil strength. Itis a useful tool to evaluate the impact of tillageprocess and predicting draft force of tillage implements. The current research investigated modeling and correlation of CIfor bulk density, moisture content and penetration depth levels in a sandy loam soil. CI datawere gathered and analysed. Regression models for correlatingCIwith independent parameters were developed and compared with the most promising models which selected from literature.Statistical analysis indicated that soil moisture content (MC), soil bulk density (BD) and penetration depth(PD) had significant effect (P=0.01) on CI. The all interactions among variables (BD, MC and PD) had alsosignificant effect (P=0.01) on CI. It is found that BD and PD are linearly and directly proportional to CI. However, MC is quadratic curve (second degree) and inversely proportional to CI. The results showed thatmaximum value of CI (5153 kPa) was recorded at BD (1.82 g/cm³), MC (4.6%) and PD (15 cm). But, minimum value of CI (346 kPa) was recorded at BD (1.36 g/cm³), MC (8.8%) and PD (5 cm).Two equations developed by regression analysis (linear and polynomial) for estimating of CI were obtained. The polynomial equation (R²=95.6%) was more precision compared with linear equation (R²=93.3%). The obtained two regression models (linear and polynomial) were compared with other regression models (exponential and power) from literature. It can be concluded that the linear and polynomial equations were exhibiting the closest match to measured CI. The polynomial equation was also the best matching equation for estimating of CI (highest R² of0.968 and lowestroot mean squared error of 127.2kPa).