Following LiDAR mapping of case study orchards, it was clear that the interrow profiles had likely ponding areas, despite overall fall from one end of the rows to the other. Thus, surface levelling has the potential to facilitate surface drainage in these orchards. However, it was not clear how much soil movement was required to achieve an overall grade that would shed excess water quickly. For this reason, a GPS survey of the interrow soil level was conducted.

The software used to record this data was WM Drain, a Trimble package designed to lay drain pipes with maximum and minimum set depths and maximum and minimum set slopes (grades). We aim to use these capabilities for interrow levelling in orchards moving the minimum amount of soil to minimise any step from the tree understory soil level to the interrow soil level – to avoid the slip, trip and fall risk that wheel ruts are currently causing. An example of a graded interrow profile designed by WM Drain is shown in Figure 2.

As seen in figure 2, the maximum depth below the soil level (maximum cutting depth) is 8cm, and the maximum fill depth is 10cm, with the overall grade 0.1% (1m fall over 1000m). For this orchard block – where rows are 350m long, this is a 35cm fall from the beginning to the end of rows.

Our testing survey has its limitations. We recorded the soil level that was driven over, which was the bottom of the ruts, so we exaggerated the hollows. Before the actual job is done, we will have cultivated the interrow to provide loose topsoil that can be easily shifted along the row. The levelling design will be based on a survey on the cultivated interrow.

The contour maps made from LiDAR data indicated low spots, where ponding was likely to occur in orchard interrows. However, when the orchard was walked following a moderate rain event (30mm), the actual areas of ponding did not line up with the ‘likely’ areas. It is unclear how extenday alters the interrow drainage, which had been laid when the field ponding survey was done – as seen in figure 3. We will continue to make sense of this data, and complete more monitoring as and when rain events occur.

The next steps in the Orchard Drainage Project are to install soil moisture probes in “wet” and “dry” areas according to the RTK-GPS survey. We are also interested in monitoring tree health via trunk diameter measurements, as well as recording tree replacements with the handheld GPS – as the 20-30cm accuracy gives us confidence in to mark features of individual trees within the orchard.

Smart Tools to Improve Orchard Drainage is a 3-year project jointly funded by the Sustainable Farming Fund, and New Zealand Apples and Pears. For more information about the project click here, or contact georgia@landwise.org.nz