Back to Contents6.2.5 Potential of Precision Tillage to Improve Cropland Productivity
Investigators: Larry Wells, Scott Shearer and Lloyd Murdock
The objectives of this portion of the proposed project are: 1) to measure the spatial distribution of soil bulk density and strength as indicated by cone penetrometer resistance for five disparate fields; 2) to apply precision tillage to those fields, i.e. to apply tillage only where penetrometer resistance exceeds 2.5 MPa; and 3) to determine the cost effectiveness of precision tillage as determined by tillage cost and potential increase in crop yield.
Five fields will be identified for which previous yield mapping and other observations indicate likely reduction owing to soil compaction by equipment. The fields will be chosen to represent a range of textural and topographic soil conditions. Soil penetrometer measurements will be made in these fields utilizing the same grid density (1 acre) as used for yield mapping and nutrient ssampling.
A special recording soil penetrometer system will be fabricated for use in this study. Four penetrometers, each consisting of a stainless steel shaft and cone mounted on the rod of a hydraulic cylinder, will be mounted 60 cm apart on a horizontal tool bar which will attach to a Category I hitch of a small utility tractor. Identical pressure-compensated flow control valves will be used to establish the specified penetration rate of 3 cm per during extension of the cylinders. The corresponding upstream pressure of the cylinders will be measured by pressure transducers and recorded electronically at intervals of 0.5 sec. The hydraulic cylinder will have a nominal stroke length of 90 cm (36 in.) and a bore diameter of 3.8 cm (1.5 in.). Readings will be taken to a depth of 60 cm (2 ft).
The tractor will be positioned near a grid point and five readings will be taken around a 4.6 m (15 ft) radius of the grid point. A composite penetration resistance versus depth relationship will be determined for each grid cell from the resulting twenty measurements. If any of the penetrometers hits a stone during sampling, an alarm will sound so the operator can stop the cylinders, and move to a different location.
Penetrometer data must be collected during a relatively brief period prior to planting when soil is not saturated but near field capacity. Upon collection of data from each field, the corresponding composite penetration profiles will be determined and plotted for each grid cell in each field. The greatest depth of penetration resistance greater than or equal to 2.5 MPa will be determined for each grid cell and used to construct a database for each field. Penetrometer measurements will be repeated each of the three years of the study to monitor the effect of tillage operations on each grid cell. These data will be used in conjunction with crop yield data to determine the cost-effectiveness of tillage operations.
Six subsoiling shanks capable of reaching a depth of 60 cm (2 ft) will be mounted on a semi-mounted tool bar spaced 60 cm (2 ft) apart. Tillage will be applied to each grid cell to the greatest depth (up to 60 cm) for which composite penetration resistance exceeds 2.5 MPa. Depth will be controlled via hydraulic cylinders connected to gauge wheels. Outside shanks will be rotated to a disengaged position when required draft exceeds the capacity of the tractor. Tillage will be applied during late summer or fall when soil is in the driest state to facilitate fracturing of compacted zones or pans. Tillage will be applied each year during the study as indicated by the cone penetrometer measurements.
Crop yields will be measured and mapped each year using one-acre grid cells. The results will be compared to yield measurements made prior to application of precision tillage. The cost of measuring cone penetration resistance and applying precision tillage will be computed for each field each year of the study. An analysis of increased revenue versus cost will be conducted for each field during each year of the study. Previously measured crop yields will be used as the basis for determining cost effectiveness of precision tillage. The results of the study will submitted for technical publication and also presented to growers if the application of precision tillage is determined to increase profitability.