Sunday, December 31, 2017

Stuart in the north

Stuart nuts at shuck-split

     Stuart is one of the oldest and most widely known pecan cultivars. The tree had its origins in a seedling orchard planted in 1874 outside of Pascagoula, Mississippi  using nuts procured from Mobile, Alabama. The tree gained local notoriety for excellent nut production. In 1893, a severe storm blew the original tree down. Fortunately, the tree re-emerged from a root sprout and the tree began bearing nuts again by 1902. 
     The first attempt to graft Stuart was largely a failure. In 1886, sixty grafts were attempted but only one grew successfully. Graft failure was all too common during the late 1800's as nurserymen used grafting techniques commonly used for fruit trees when trying to propagate pecans. However, by the early 1900's,  grafting techniques specifically developed for pecan improved success rates dramatically. From the 1920's to the 1950's Stuart quickly became the  dominant cultivar planted across the southeastern United States.
Stuart grown in SE Kansas 2017
    But how did Stuart migrate northwards? The popularity of Stuart in the south was largely driven by outstanding yields and scab resistance. Every pecan nursery began propagating Stuart and trees became so widely available that they were ultimately promoted for planting outside traditional southern pecan growing areas.  For a tree from the deep south, Stuart has excellent cold hardiness enabling Stuart trees to grow and thrive in northern pecan areas. However, it was soon discovered that northern climates do not provide a long enough growing season to properly mature nuts. Our 2017 crop of Stuart nuts contained roughly 50% stick-tights (photo above).

Poorly formed Stuart kernels
     A more common indication that Stuart is not adapted to northern climates is the incomplete development of kernel inside the shell (photo at right). Northern-grown Stuart nuts are usually fuzzy and shriveled. In addition, kernels are hollow and lack an good oily taste.
    No additions of water or fertilizer will ever alter the fact that Stuart will never make a decent kernel in northern areas. Stuart requires a longer growing season than northern pecan areas can provide for proper kernel development.
   One of the most interesting artifacts of the popularity of Stuart is the large number of Stuart seedlings that can be found growing all over the US, even in northern areas. During the Great Depression and war years (1930's and 1940's), pecans were a popular stocking stuffer for Christmas. The majority of gift basket pecans at that time were Stuart nuts and some of those nuts found their way into backyard gardens to eventually sprout into trees. Today, you can find massive 90+ year-old trees that produce a blocky shaped nut that looks a lot like a Stuart nut but is generally smaller in size. These seedlings also produce nuts that struggle to produce quality kernels in northern climates just like the mother Stuart tree.

Saturday, December 23, 2017

Site selection and pecan production

   On my farm, I established our pecan orchard in a field that is located within the Neosho River flood plain.  The soils in this field are mostly  Hepler silt loam  with small areas of Osage silty clay. This area of the farm is subjected to occasional flooding. However, I couldn't resist planting pecans around my home, located up the hill just a few hundred feet from the main pecan grove. The soil at the home site is a Cherokee silt loam; a soil that was formed from river-deposited silt during the melting of the last ice age. This soil (and my house) is not subject to flooding.

      By planting trees in both bottomland and upland positions in the landscape, I can see how site selection impacts pecan performance. The photos at right and above show Jayhawk and Kanza nuts collected from similar aged trees. Within each photo, the two nuts on the left  were collected from trees growing in the floodplain. The two nuts on the right were harvested from upland trees. In both photos, the nuts grown in the river bottom are visually larger than the nuts collected on the upland. Sample weights (grams/nut) confirmed what my eyes could easily see (table below).

Site       Jayhawk  Kanza
Bottomland   7.34   6.77
Upland       6.31   6.19

    I cracked out several nuts from each tree (photos at left and below). Of course, the larger nuts from the bottomland had larger kernels. However, what I was looking for was differences in kernel plumpness.

With ample rainfall falling during the kernel filling period this year (August 2017), upland pecan kernels were just as full as kernels collected in the river-bottom.
   So why the difference in nut size?   It all comes down to internal differences in soil profiles.  The surface layer of Hepler and Cherokee soils are very similar; both are described as silt loam. The important difference comes deeper in the soil profile. If your dig deep into the Hepler profile, you'll find the that the soil comes heavier (more clay) with depth. But the transition is gradual with no abrupt changes in soil texture. In contrast, the Cherokee soil has about 14 inches of silty loam topsoil which abruptly changes to a firm clay subsoil.
     An abrupt change in soil texture has major impacts on the movement of water within the soil profile. Both Hepler and Cherokee are slow to drain after periods of wet weather. However, the clay pan found in the Cherokee soil creates what is known as a perched water table. Water moves so slowly into the subsoil that it stacks up in the topsoil creating a zone of  super saturation. A perched water table causes the soil to lose vital soil oxygen which can lead to tree root death. Tree growing in soils with a perched water table typically end up developing shallow root systems and a pecan tree with shallow roots has a hard time competing for water during hot dry periods.
    An abrupt change in soil texture between the topsoil and subsoil also impacts the movement of water upwards during dry periods.  Surface evaporation and plant transpiration remove water from the upper portions of the soil. As the soil dries out, water moves by capillary action upwards through the soil. However, a prominent boundary layer, like a clay pan, will block the free flow of water by capillary action from deep in the subsoil. The result is a soil that tends to be "droughty". 
   A soil with a strong boundary between topsoil and subsoil does not provide a healthy rooting environment for pecan trees. A perched water table in the spring limits root growth while soil water is held unavailable in the subsoil during the hot summer.  Young pecan trees respond to upland soil types by producing smaller nuts. As trees on upland sites grow older,  you'll find that trees becomes stunted, upper limbs may start dying back and nut production becomes limited and erratic.
   My main pecan orchard is located in the river bottom, where pecan trees thrive. The trees around the house will never be commercially viable but that's not why I planted them. I just enjoy looking out the window every morning and seeing beautiful pecan trees.       

Thursday, December 14, 2017

Pecan shelling quaility: Genetic links

Kanza 2017
    One of the reasons Kanza has become a popular pecan cultivar among consumers is that it shells out so well.  After cracking Kanza nuts in a mechanical cracker then blowing out the shells with a single stage air leg, Kanza yields a high percentage of free kernel halves (photo above). Once all the free halves are separated out, it is very easy to remove attached shell fragments to extract the rest of the kernels.

Major 2017
     I've been cracking several cultivars in my Savage air-cracker and have come to the conclusion that the shelling quality of Kanza nuts is probably inherited from its Major parent (Kanza resulted from a cross of Shoshoni and Major). The photo above shows a sample of Major nut processed using the same equipment I used to crack my Kanza crop.  Even with a thicker shell, Major nuts crack out cleanly producing a large number of free halves. This got me thinking.

USDA 64-4-2
    I grabbed a sample of  USDA 64-4-2  which originated from a cross of Choctaw and Major. Cracking and blowing this sample yielded a high percentage of free halves. Nuts of 64-4-2 are not as round as Major or Kanza but the shelling quality was impressive.   

    Next, I cracked a sample KT143, a  selection from my breeding project that originated from a cross of Pawnee and Major. Once again, I found excellent shelling quality.
    Kanza, USDA 64-4-2, and KT143 share one thing in common. All three cultivars have Major as their female parent. And after looking at my cracked sample of Major, I'm convinced it is Major parentage that makes these pecan cultivars such good crackers. I'm also convinced that producing pecan cultivars that are easy to shell will make my customers for cracked pecans very happy and willing to pay a premium these nuts.

Thursday, December 7, 2017

Same seed source--big differences in rootstock growth

   When we were harvesting a cultivar trial, I came across a plot of four Major trees that were fairly uniform in size and all bearing a good crops (photo at right). These trees were field grafted back in 1985 to Giles seedling rootstock trees. The grafts were placed at 18-24 inches above the soil surface and after 30+ years you can still see the graft union on each tree (note the abrupt change in bark texture).
    As I walked down the tree row, I noticed significant differences in the diameter of the rootstock as compared to the trunk diameter of the scion (photos above). For tree "A", the Giles rootstock has over-grown the Major scion. Tree "B" has a smooth transition between rootstock and scion. Trees "C" and "D" are more typical of trees grafted with a Major top--the scion overgrows the rootstock.
    Major is a vigorous growing tree, often producing the largest tree in a planting of several cultivars. That's why it so common to find Major scions overgrowing their rootstock. However, I wanted to show you these photos to make two points. First, no matter the seed source for the rootstock, there will always be variation in growth among rootstock trees. Each pecan rootstock tree has a unique genetic composition created by a known mother (in this case Giles) and a unknown father (pollen blown to the stigma on a puff of wind). This variation may cause differences in the appearance of a graft union but it appears to have little impact on the scion's performance and yield.
    The second point I wanted to make is that is not that critical to plant a particular seed source to grow rootstock trees. In northern pecan areas, you should use seed from either local native trees or nuts produced by a northern cultivar. The resulting trees will have the best cold hardiness for your location.  Many years ago, we had some Giles trees growing at the research station that had been propagated by a southern nursery that used a southern pecan cultivar for growing their rootstock trees. In 1989, temperatures dropped to -26 F (-32 C) in mid-December.  The Giles tops survived the cold but the rootstock portion of the tree was killed by the cold. With a dead root system, these tree had to be removed.