A horizontal, on-line penetrometer has been used on several fields in Sweden to measure penetration resistance. The yield on these fields have been mapped and compared to the penetration resistance. In some of the fields, deep loosening has been done on parts of the field in order to be able to study the effects on the yield. Some correlation of higher penetration resistance and lower yield has been found but no positive effect of the deep loosening was discovered.
Yield variations within fields can be very high, several tons of grain per hectare
(Thylén, 1997). If the reasons for these variations are known, site-specific inputs can
save resources, the negative effects on the environment can be reduced and yield
levels can be maintained or even increased
The objective of the present study was to use a site-specific horizontal, on-line, soil penetrometer for studying soil penetration resistance and its correlation with yield. The effects of deep loosening on yield was also studied.
A four-share parallel-plough was modified to support three parallel, horizontally mounted, soil penetrating cones, (see figure 1 and 2). The cone-angle was 30°, with a base diameter of 6.3 cm. The cone was connected to a Bosch draught sensor capable of registering forces between –25 kN and +25 kN. The instrument is capable of measuring soil penetration resistance at three depths (10, 30 and 50 cm), speed and position which are recorded with a Trimble SweeEight GPS every second. The ________________________________ Copyright ©by the paper’s authors. Copying permitted only for private and academic purposes. instrument was used at a speed of approximately 1.5 m s-1 and was equipped with a stone release mechanism and a system to record actual working depth every second. The 1000 Hz signal from the draught sensor was reduced to a 1 Hz signal to lessen the noise.
Fig 1. Soil penetrating cone and draught sensor.
Fig 2. One of the three soil penetrating cones. 3
Figure 5 shows a field where parts of the field was deep loosened. Some differences could be seen in penetration resistance between loosened and unloosened parts of the field (fig 6) but these differences was however not visible on the yield map.
The horizontal penetrometer worked well in the field. The signals were stable and the construction was sufficiently robust to tolerate stones in the soil. The measurements show that variations in penetration resistance can explain part of the variation in crop yield. This horizontal, on-line penetrometer can measure a large area considerably faster than a traditional penetrometer, which will make it easier to incorporate soil physical parameters into precision agriculture.