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Below the Canopy

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by David Granatstein, WSU Extension Specialist, June 3, 2016

Increasingly, growers are recognizing the influence that soil and the orchard floor can have on fruit production. A field tour in The Dalles, Oregon on May 31 was organized by Lynn Long, Oregon State University Extension, to learn about some management options and new ideas related to the orchard ecosystem below the canopy. Two interesting topics discussed were characterizing site variability for precision management, and options for managing prunings and cover crop.

Characterizing Site Variability for Precision Management

Dan Rooney from Trimble Navigation described a system he helped to develop to greatly enhance the understanding of site variability and the means to manage it. His company offers the ‘Soil Information System’ or SIS, which combines both hardware and software, as a service to growers. This involves initial site mapping by two devices. One is the ‘surfer’, a unit pulled over the soil surface by an ATV that combines readings from an electromagnetic sensor (similar to an electrical conductivity unit) with high resolution topography mapping (slope, elevation, aspect). The intensity of the mapping depends on the crop – higher intensity for higher value crops in which management units can be smaller and still practical to manage. From the mapping data, decisions are then made on where to use the ‘diver’ unit, which is a hydraulic probe pushed to a five foot depth in the soil if possible. It has sensors that provide a continuous readout by depth on properties such as soil texture, available water holding capacity, and bulk density. It takes about 60 seconds to do a reading at one location. The ‘diver’ locations represent the field variability identified by the ‘surfer’, providing the details needed on the different conditions within the field, and knowing exactly where they apply. This approach replaces the grid-style sampling often done, and it is considerably more efficient.

From all the data collected, over 60 different maps can then be made of the field looking at all sorts of characteristics. These can vary with the crop. For example, a vineyard project they did on former dryland wheat fields focused on creating management units according to aspect and slope. The grower wanted uniform maturity conditions, and the ability to mechanically harvest the grapes safely. The maps become very useful in diagnosing problems in the growing crop, particularly those that are spatially uneven in a field. Aerial images can capture data on various types of plant stress and be coupled with other map layers to try to determine some of the causes of the problem. Rooney developed a software approach called ‘Pure Pixel’ that enables better diagnosis in perennial crops such as orchards and vineyards. Since many of these crops have two canopies (the tree and the cover crop, for example), it becomes important to separate the former from the latter within the aerial images, which ‘Pure Pixel’ does. Then the analysis can be done solely on the fruit crop canopy without the interference from the cover crop. Diagnosis of pest, disease, water, and nutrient problems are all possible, and the options are expanding each year with new sensors. A field map with SIS is a one-time investment that is coupled with real time feedback from the field via aerial images, other sensors (like moisture probes), yield data, and other information that can be gathered and related back to variability of the land to improve production, reduce cost, and lower environmental impact.

Mulch Compost and Prunings

Mike Omeg of Omeg Family Orchards in The Dalles described his experimentation and evolution with novel orchard floor management techniques and tools. He decided several years ago to explore more investment in his soil and orchard floor as a way to improve the competitiveness of the older blocks of Bing cherries he has, since they cannot all be replanted at once. He has begun using a mulch/compost application in the tree row as one strategy. After trying the materials separately, he has come up with his own blend, and bought a dedicated spreader that uses augers for more trouble-free operation. In one block, he applied his mix in the fall of 2014 to every other row. He estimated his total cost at $1,600 per acre. Fruit size from the different rows was monitored at harvest, and then the value of the crop determined for each treatment. Total return was $2,600 more per acre with the mulch/compost mix, due to larger fruit, which more than covered the cost in the first year alone.

Given the positive observations and measurements he has seen with the surface application of organic amendments, he began testing ways to use materials already present in the orchard. He was already experimenting with different cover crops planted in the drive alleys, and wanted to try ‘mow and blow’ to put them on the tree row as mulch. He found a Nobili side-discharge flail mower (from Italy) that looked like it would do the job, and has been using it for the past year with success. It can handle a heavy stand of vegetation as well as shred any smaller tree prunings and band them on one side of the row. He then wondered about the larger-sized pruning wood that he hauled out of the orchards each year and found a heavy-duty pull-type flail that could shred that material. It worked well, and based on his calculations, he paid for the unit in one year by reducing his costs for wood removal and disposal. At the same time, all that woody material was applied to the tree row, with the idea that it will reduce the need to haul in mulch in the future.

Mike is also experimenting with intensive soil and nutrient management using a variety of biological and nutrient products, and plant sap analysis as a more real-time diagnostic tool. In one block, trees were doing so poorly in 2010 he was about to remove them. Roots were brown and not growing. The trees had severe bacterial canker, low vigor, and low yield. He added mulch initially, then biological products intended to stimulate soil biota and the tree roots, and then more intensive foliar nutrient sprays. By 2014, the trees had new shoot extension and more vigor, a moderate but profitable crop, and new root development. Since then, the trees have continued to do well and there are virtually no active cankers in the block. While the changes cannot be ascribed to any one action, they show that improving “soil health” can directly benefit fruit tree performance.



David Granatstein

WSU Extension Specialist

(509) 663-8181

Washington State University