Pecan Winter Activities for Western Orchards
First off, in your young orchards, be sure to train your trees. Neglecting this essential activity can lead to all kinds of major issues down the road. I recommend that pecan trees be trained to a modified central leader system, where a single leader goes straight up the center of the canopy and where strong, evenly spaced, widely angled (about 45 degrees is ideal) scaffolds spiral up, eventually becoming codominant with the central leader. The process of training immature pecan trees involves identifying the shoots that will become the central leader and scaffolds and using a combination of heading cuts, thinning cuts, and bud removal. You can read about this in “Training Young Pecan Trees,” an NMSU Extension Publication online.
As for your mature orchards, it may also be time to mechanically top prune and side prune your trees. In the 2020 season, many western growers experienced an “off” (low) nut production year in the alternate bearing cycle. If that was the case in your orchard, this winter might be the perfect time to aggressively mechanically prune.
This kind of pruning accomplishes two things that help stabilize production. The first seems obvious: it improves the distribution of sunlight within the tree canopies, which, in turn, causes a greater volume of the orchard to become actively productive.
I think the second is a little less obvious: mechanical pruning removes a lot of potential fruit wood for the following season. That sounds like a bad thing—and it is if your crop yields for next year are expected to be too low! But if next year’s crop is expected to be excessive in your orchard, then this removal of fruitwood by pruning has something of the same effect as crop thinning or fruit removal. It’s actually better than crop thinning in some ways because the fruit is removed before it even exists, before it has diverted any of the tree’s precious energy and nutrient resources at all!
Take a look at your yield records for your orchards. If you see an intensifying biennial bearing pattern and 2020 was an “off” year, then pruning the trees this winter could significantly reduce the 2021 “on” production. Aggressive pruning could reduce the 2021 yields to the point that the biennial pattern is dampened or even eliminated in the years to come. You’ll also see that nut size and percent kernel during what used to be the “on” seasons increase as a result of this pruning program. Again, this increase is due to both improved sunlight distribution and “crop thinning” effects of mechanical pruning.
Another thing to bear in mind is that a moderate to strong La Niña (cold temperature) pattern is setting up down in the Pacific Ocean, so we can expect drier-than-usual weather this winter with the Pacific storm track heading further north. If that plays out as expected, this could be bad news for some areas from a snowpack perspective. But looking at the bright side, this could sure make it easier to get big mechanical pruning equipment into our orchards this winter without dealing with muddy soils from repeated precipitation.
2. Salinity Management
Salinity management is a year-round activity if you’re farming in the southwestern United States, but winter can be the best time to really focus hard on a few pieces of the salinity management puzzle. The first of these is soil sampling and analyses. I usually recommend that soil samples be collected from orchards in winter rather than during the growing season because without the regular fertilizer inputs and irrigations, you can get a better “high-level view” of the major trends and patterns in your orchard soils. Collect your samples from at least two different depths (maybe 0 to 12 inches and 1 to 24 inches) and from several sites scattered across each orchard block in order to give a representative picture of that orchard management unit as a whole. You should submit the different depth samples separately to the lab, but, for each particular depth, you may combine and thoroughly mix the samples from the different sampling sites in the orchard block. For some helpful tips on collecting soil samples, please see the online article “Test Your Garden Soil” from the NMSU Extension Publication on the subject.
Most labs have packages of analyses that they recommend for you to get, but for the sake of salts management, make sure that you have them give you Sodium Adsorption Ratio, Electrical Conductivity of Saturated Paste Extract, chloride concentration, and boron concentration. For the second item, Electrical Conductivity of Extract, it is common for laboratories to use a 1:1 extract instead of a saturated paste extract. It is important that you ask them to use the saturated paste extract for this because that method better accounts for differences among soils with differing water holding capacities and because the salinity recommendations are usually based on saturated paste extract.
The second piece of the soil salinity puzzle that might be best dealt with during the winter is leaching. If salinity is becoming a problem (i.e., the electrical conductivity of saturated paste extract is approaching the 2.5 dS/m threshold where pecan trees begin to show injury), the only way to truly remove the salts from the soil is through leaching those salts down and out of the tree root zone. Winter is a uniquely effective time for leaching salts because water losses from evaporation and transpiration are very, very low in the winter compared to what they are during the summer. That means that it should theoretically be quite a bit easier to force irrigation water to percolate below the tree roots in the winter. This is also a season when there will hopefully be less leaching losses of desirable fertilizer nutrients, like nitrates, than during the regular growing season.
The leaching process can be hindered by anything that prevents quick percolation of water downward through the soil profile. Fine soil texture, sharp transitions in soil texture (i.e., stratified soils), soil compaction, dispersed clay particles (deflocculation due to high SAR), and the presence of impervious layers such as caliche or hardpan are all factors that can contribute to poor leaching. Your soil analyses can help you know what factors cause the poor leaching, and thus, the salt levels building up in the soil. Depending on the particulars of your situation, some of these factors are fixable, while you might just have to live with others. If you discover elevated SAR in your soil when you get the soil analysis reports from the lab, you may be able to fix this with applications of soil amendments such as gypsum, sulfur, or sulfuric acid. If stratified soils are the problem, it may require physically mixing the layers with a backhoe or slip plow to fix it, while compaction may require discing or ripping. In any case, winter is a great time to take care of these issues because it will not interfere with the normal operations that must occur during the growing season.