Soil Drying Effects on Soil Strength and Depth of Hardpan Layers as Determined from Cone Index Data

Site-specific detection of a soil hardpan is an important step in precision farming. Different methods have been developed including the ASABE standard soil cone penetrometer to detect presence of hardpan layers. Most of the newly developed methods use results obtained by a soil cone penetrometer as a reference to validate their potential. Soil factors, mainly soil moisture and bulk density, may influence the cone index measurement and the prediction of the relative strength and depth of the hardpan layer. The effects of soil drying on hardpan characterizing attributes of peak cone index, depth to the peak cone index and depth to the top of the hardpan layer were studied for three compaction levels on a Norfolk sandy loam soil in a soil bin. The soil in the bin was wetted to near saturation and then subjected to four levels of soil drying. A multiple-probe soil cone penetrometer (MPSCP) was used to measure soil cone index. The results showed that soil drying had a significant effect on peak cone index for the single pass compaction (1.78 Mg m-3 within hardpan) and the double pass compaction (1.83 Mg m-3 within hardpan). The peak cone index increased two-fold and 1.3 times due to soil drying from ‘day-1’ to ‘day-4’ for the single pass compaction and for the double compaction, respectively. The depths to the top of the hardpan determined from the depth to the peak cone index and the depth to the top of the hardpan showed a statistically significant decreasing trend for the single pass compaction. The differences, however, were too small (< 2 cm) to justify varying prescription tillage depth due to soil drying

A modeling framework to quantify the effects of compaction on soil water retention and infiltration

The water retention curve (WRC) of arable soils from the southeastern United States at different levels of compaction (no compaction, and 10 and 20% increases in soil bulk density) was estimated using the van Genuchten-Mualem (VG) model. The VG water retention parameters of the noncompacted soils were obtained first by fitting measured soil hydraulic data. To construct the WRC of the compacted soils, gravimetric values of the permanent wilting point (theta(gw), 1,500 kPa) and the residual (theta(gr)) water content were assumed to remain unchanged with compaction. The VG parameter alpha and exponent eta after compaction were estimated using two approaches. In Approach 1, alpha and eta were estimated from saturation, the permanent wilting point, and the residual water content. In Approach 2, the value of eta was assumed to remain unchanged with compaction, which allowed alpha to be estimated immediately from the VG equation. Approach 2 was found to give slightly better agreement with measured data than Approach 1. The effect of compaction on the saturated hydraulic conductivity (K-s) was predicted using semitheoretical approaches and the VG-WRC function. HYDRUS-1D was further used to simulate vertical infiltration into a single-layered soil profile to determine the impact of compaction on the infiltration characteristics of the soils used in our analyses. Results showed that a 10-20% increase in soil bulk density, due to compaction, reduced cumulative infiltration (I-c) at time T = T-final (steady-state) by 55-82%, and the available water storage capacity by 3-49%, depending upon soil type

Investigating the Effects of Interaction of Single-Tine and Rotating-Tine Mechanisms with Soil on Weeding Performance Using Simulated Weeds

Mechanical weeding augmented with automation technology should result in highly effective weeding systems. However, the interaction between weeding mechanisms and soil is not well understood. Moreover, soil is highly variable, which makes studying this interaction challenging. The main objective of this research was to develop a method to investigate the effects of mechanical tool-soil interaction on weeding performance for different operating conditions in a controlled environment. Experiments were conducted in an indoor soil bin with loam soil, and the weeding performance was studied using small wooden cylinders as simulated weed plants. The investigations featured a single cylindrical tine and a rotating tine mechanism, vertically oriented and inserted into the soil. The total width of soil disturbance and potential weeding rate were evaluated for the single cylindrical tine at different levels of three operating parameters: tine diameter (6.35, 7.94, and 9.53 mm), working soil depth (25.4, 50.8, and 76.2 mm), and tine speed (0.23 and 0.45 m s-1). Potential weeding rate was examined for the rotating tine mechanism with two operating parameters: working soil depth (25.4 and 76.2 mm) and rotational speed (25, 50, and 100 rpm). Statistical analysis was performed using ANOVA at p < 0.05. A simulation of the rotating tine mechanism was developed that estimated the disturbed area. For the single tine, soil disturbance width was independent of tine speed; however, tine diameter and depth had significant effects, as the width increased with increased levels of these two parameters. All three parameters had significant effects on the potential weeding rate of the single tine, and the rates were observed to increase with higher levels of the parameters. For the rotating tine mechanism, both depth and rotational speed were significant. The potential weeding rate for the rotating tine mechanism was found to increase with higher levels of these parameters. The results showed that although the width of soil disturbance due to a cylindrical tine was affected by the tine diameter and working soil depth, operating parameters such as increased longitudinal and rotational speeds also affected plant disturbance. The percentage of disturbed soil area in the simulation followed similar patterns as the percentage of disturbed plants observed in the experiments

Thirteen‐year stover harvest and tillage effects on soil compaction in Iowa

Abstract Corn (Zea mays L.) stover is an abundant biomass source with multiple end‐uses including cellulosic biofuel production. However, stover removal may increase soil compaction by reducing organic matter inputs and increasing vehicle loads during harvest. While numerous studies have reported stover removal impacts on soil physical quality, few have assessed the role played by traffic compaction. Our objective was to quantify subsurface soil compaction after 13 years of chisel plow versus no‐till management and no, moderate (3.5 ± 1.1 Mg ha−1 year−1), or high (5.0 ± 1.7 Mg ha−1 year−1) stover harvest rates. Penetration resistance was measured in most‐ and least‐trafficked interrow spaces. Chisel plowed plots with moderate and high levels of stover removal had higher penetration resistance in trafficked areas relative to least‐trafficked areas, whereas there was no evidence of traffic compaction when stover was retained. Traffic compaction did not negatively impact yields, which were greater with high levels of stover removal compared to no removal. The no‐till practice led to very small increases in penetration resistance with wheel traffic and had no evidence of increased compaction with residue removal. This lack of traffic compaction indicated soils under no‐till practice have a higher load‐bearing capacity than soils under chisel plow practice. Overall, there were no yield‐limiting effects of tillage practice or stover removal, and no evidence of soil compaction below the plow layer, suggesting stover removal with both tillage practices can be effectively employed without detrimental effects on plant or soil health