Evaluating nut samples

    Last week we had a light snow fall that covered the pecan grove with about two inches of wet snow (photo at right). The snow turned out to be only .16 inches of precipitation but the cold weather that followed meant that the orchard floor stayed snow covered and wet for several days. Wet soil conditions means that I was unable to finish harvesting my pecans. So, I parked the tractors and moved inside to start cracking nut samples I had collected from the pecan breeding block.
   At shuck split, I collected at least 25 nuts from each tree. I let these nuts air dry for several weeks then began the process of measuring, weighing, and cracking nuts.

    The first step in my evaluation process is to record the diameter size class of each nut in the sample. I do this because every nut ever brought to a shelling plant is run through a nut sizer in preparation for cracking. Pecans are sized by a series of steel cages with various size slots for nut to fall through. The sizes are recorded in sixteenth of an inch increments. A size 12 pecan falls through an opening 12/16 or 3/4 of an inch wide. I use a series of end wrenches (measured in 1/16 increments) to simulate the nut sizing process (photo above). In the photo, note a nut stuck in the 15/16 wrench. This same nut passed easily between the jaws of the 16/16 wrench (1 inch) and would be classed as a number 16 diameter pecan. By measuring every nut in a sample I can develop a size profile for each clone. The sample I was processing when I snapped these pictures was 50% size 15 and 50% size 16 nuts.

    The next step in my nut evaluation process is to weigh 10 randomly selected pecans. This weight will give me an average nut weight but can also be used to calculate average nuts/pound. I use a gram scale to weight the nuts (photo at right).  This sample weighed 101.97 grams. This nut averages 10.197g per nut and if you divide the conversion factor of 453.6 by the average nut weight in grams you'll find that this particular pecan averages 44.48 nuts/lb.

    With the inshell nuts weighed, I next use a hand cracker and shelling tool to extract the kernels from the shell. In cracking the nuts, I use a light touch because I take great care in trying to extract full kernel halves from every nut.

    Once all the kernels are removed from the ten nut sample, I weight the kernels. This sample had kernels that weighed 54.91 grams. By dividing the kernel weight by the nut weight and multiplying by 100, I can calculate the percent kernel for this nut sample. In this case the math works out like this:  (54.91/101.97)*100=53.85% kernel.
    In addition to the hard numbers that I record on nut size, weight and percent kernel, I take notes on kernel color, ease of extracting full halves, adherence of shell packing material, and any glaring kernel defects.
    As I collect this information year after year, I should be able to recognize those trees that produce quality pecans every year. Hopefully, that will lead to some new cultivars.
  

Reviewing pecan cultivar data

    On cold winter days, its always fun to pour over cultivar trial data. Below, I created a table of nut performance data for 43 pecan cultivars growing at the Pecan Experiment Field. For each cultivar, the table shows the number of years nuts were evaluated (N), the weight of a nut (average, maximum, and minimum), and the percent kernel (average, maximum, and minimum).
     The time period of this data set (2004-2017) represents some of the most extreme weather conditions our trees have survived. We've seen record floods (2007) and record drought (2012). We suffered a limb-breaking ice storm (2007) and late spring frosts (2007, 2014). It no wonder that over the course of 14 years we've recorded some wide swings in cultivar performance.   

Evaluating pecan cultivars takes time

    A few years ago, I grafted several seedling trees with scions collected from our pecan breeding project. This past fall, those young grafted trees had their first crop of nuts which gave me the opportunity to compare the nuts they produced to nuts produced by the mother tree.

    When I made the grafts, I actually top-worked trees that were roughly three inches in diameter.  By starting with such large stock trees, it is not surprising that these grafts set a crop in their third year.  In comparison, the mother trees are 21-years-old and are 10 to 12 inches in diameter.

    I was able to look at 3 clones from the breeding project. KT143 and KT149 are crosses of Pawnee and Major. KT334 is a hybrid of Pawnee and Greenriver. All three clones have been consistent producers of early ripening pecans.

    It is interesting to note that all young grafts produced smaller nuts than their mother trees. I've seen this phenomenon numerous times over the years. In testing new pecan cultivars, you just don't see the full potential (warts and all) of a pecan cultivar until the tree has grown to at least 10 inches in diameter.

    I also cracked a sample of nuts from each young graft and their corresponding mother tree to check for differences other than size.  With KT143, the kernels from the young graft looked very different than kernels from its corresponding mother tree. Kernels from the grafted tree were shorter, almost round in shape, and darker in color. These differences in kernel appearance can be attributed to a young tree's struggle to compete with the ground cover for water and nutrients. 

     The KT149 kernels, like the inshell nuts, were very close in size to kernels extracted from nuts borne by the mother tree. The lower percent kernel I found from young tree nuts were probably due to kernel defects caused by stinkbug feeding. In managing my orchard, I only apply a full spray program to trees with a full harvestable crop. Since they weren't bearing enough of a crop to justify harvesting, the young KT149 trees did not receive the sprays needed to control stink bug.  

     When comparing kernels from young KT334 trees to kernels from the mother tree, the nut meats look identical. Surprisingly, the numbers indicate that the young trees actually produced nuts with higher percent kernel. This might be a sign that KT334 can fill kernels completely under various growing conditions or an indication that the tree never sets enough nuts to cause kernel filling problems (inherit low yields). I need to take a closer look next year.
    I wanted to share these pictures from our pecan breeding work to give you some idea why it takes slow long to develop new pecan cultivars. Weighing and cracking nut samples are among the easiest measurements to record but it takes many growing seasons to learn how cultivars hold up under widely varying weather conditions.  In addition, things like alternate bearing, disease resistance and susceptibility to cold injury usually aren't revealed until the trees are at least 25 years old. If I have learned anything from working with new pecan cultivars for the last 37 years it is that patience and caution are needed to avoid costly cultivar mistakes.  

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.       

Nut shape defines kernel characteristics

   The other day I was cutting pecans in half to check on kernel quality when I made a simple observation. Nut shape has a huge impact of a couple of important pecan kernel characteristics.
    As I walked down one of our tree rows, I came across three early-ripening cultivars; Faith, Gardner, and USDA 75-8-5. In cross-section,  Faith and Gardner have a similar nut shape--nuts are wide and seem flattened on the suture side (photo above). In contrast, nuts of USDA 75-8-5 appear narrow when viewing the nut from the suture side but are wide in the opposite direction.
    When kernels are extracted from these nuts Faith and Gardner kernels will appear much larger than the 75-8-5 kernels simply because they will be much wider. Now, look at the shell packing material that fills the space in the dorsal grooves of each kernel half. Note that the packing material forms a wide "V" shape in the Faith and Gardner nuts. In comparison, the USDA 75-8-5 nut has narrow fingers of packing material inside deep dorsal grooves.  Narrow dorsal groves often trap bits of packing material in kernel halves making the shelling process more difficult. The "V" shape of the dorsal grooves inside Faith and Gardner nuts will mean that all fragments of packing material will fall free from the kernels during nut cracking.
     

Selections from the breeding block

   This past fall, we collected over 400 nut samples from our pecan breeding block. Now, in the dead of winter, we've begun to crack out those samples. Many of the nuts we've cracked revealed mediocre nut quality or the pecans that are so small that we can mark the trees that produced them to be cut for firewood. However, a quick look through the samples revealed some pretty awesome looking kernels. I grabbed four samples with bright, plump kernels just to give you an idea of the variation we are seeing among some of the better quality nuts (photo above). Below is a table that gives some of the details of these four seedlings.

   You'll note that Pawnee is a parent to all four seedlings (male parent for three of the seedlings and female parent for the open pollinated seedling). Two of the nuts had Major as the female parent, while one had a Greenriver mother. All four of these seedlings ripened before or at the same time as Pawnee (Oct. 8 in 2013).
   There are other seedlings in our collection that have outstanding nut quality. If you attend the annual meetings of the Nut Growers Associations of KS, MO, and IL this year you'll be able to see some of the better nuts from our breeding block on display. But a word of caution.  It will take several more years of evaluation before we are ready to send out scionwood for advanced testing by growers. We still need to evaluate each seedling for disease susceptibility, cold hardiness, nut bearing potential and tendency towards alternate bearing. It is so easy to fall in love with a pecan that produces a beautiful kernels. But, the history of pecan cultivar development is full of examples of cultivars that looked good as young trees only to turn out to be a grower's nightmare.  

Pecan: A standout among hickories

   There are eleven species of hickory native to North America and yet the pecan is the only member of the Carya genus that has been developed into a commercially viable orchard crop. Ever wonder why?  It's not all about taste. Sure some of the hickories produce bitter kernels, like the bitternut hickory (Carya cordiformis) and the water hickory (Carya aquatica). However, the shagbark hickory (Carya ovata) produces a sweet, oily kernel that has a delightful flavor.

    What makes pecan (Carya illinoinensis) stand out among all the hickories is a unique shell architecture that makes extracting the kernel much easier. To illustrate the major differences in shell characteristics between pecan and a typical hickory nut I'll be using photos of Kanza pecan and Fairbanks shagbark hickory (photos at right).
   

      I used a bandsaw to carefully slice through a pecan and hickory nut to reveal, in cross section, the relationship between kernel and shell (photo at left). The red arrows point to the portion of the nut's shell that protrudes into the dorsal grove of each kernel. Note that this protrusion in the hickory is basically an extension of the hard outer shell. In sharp contrast, the material that protrudes into the dorsal grove of the pecan is composed of loose packing material rather than shell material.
    This major difference in shell structure becomes obvious when cracking each nut. When a pecan is cracked the material inside the dorsal groove breaks free from the outer shell easing the extraction of kernel. When cracking a hickory, the shell's protrusions into the kernel remain firming attached to the outer shell and can trap portions of nut meat inside of shell fragments.
    The yellow arrows, in the photo above, point to the inner wall partition of each nut. Note that this inner wall in the hickory is composed of the same hard material as the outer shell. In pecan, the inner wall is softer packing material similar to the material found inside the dorsal groove. When a pecan is cracked the inner wall breaks free from the outer shell allowing both kernel halves to fall free of the shell. In contrast, the inner wall partition inside a hickory nut is not easily separated from the outer shell wall during the cracking process. Often, when cracking hickory nuts, the inner wall will trap one of the two kernel halves requiring a second crack to fully remove all the kernel.

     There is one more difference between pecans and hickories that makes pecan easier to shell. In the photo at right, the red arrows point to cleft in the kernel of each species. This is the location of a  secondary inner wall partition that runs perpendicular to the main inner wall seen in the cross-section photos above. The secondary inner wall in hickory is quite prominent and extends deeply into the kernel. This secondary wall is also composed of hard outer shell material that can trap kernel fragments inside broken bits of shell during the cracking process. In pecan, this secondary wall is greatly reduced or not present at all. In cracking a pecan, the secondary inner wall partition may appear as a small sliver of packing material lodged in the tip of the kernel. However, this bit of inner shell material usually falls free of the kernel during commercial shelling. 
    

Pecan shell geometry and kernel dorsal grooves

      Have you ever cracked open a pecan and gotten frustrated but the shell's inner packing material trapped in the grooves of the kernel (the dorsal grooves). It seems that some cultivars are more prone to this problem and the reason may be as simple as the shape of the nut's shell. I'm not talking about the length of the nut or how pointed the nut appears. When it comes to narrow dorsal grooves and trapped packing material, the important shape to observe is the shape of the shell in cross section. Not all nuts are perfectly round in diameter. In the photo below, I have arranged the nuts of three cultivars so you can see the how nut diameter can differ if measured 90 degrees from the shell suture (nut on left) or on the suture (nut on right). Below each pair of nuts I've listed the diameter ratio (diameter 90 degrees from suture/ diameter on the suture).  A nut that is practically round in cross-section, like Kanza, has a diameter ratio close to 1. Cultivars that produce "flattened" nuts, like Greenriver, have a diameter > 1.  Cultivars with a diameter ratio < 1, such as Chetopa, often appear narrow when viewed suture side up.
 

   So, what does all this have to do with packing material stuck in the dorsal grooves?  Its all about how kernels are oriented inside the shell. When you look at the shell's suture, underneath is a full kernel half. In other words, the inner wall partition between the kernel halves is oriented 90 degrees from the suture line. Lets look at the kernels of these same three cultivars (photo below).

   Cultivars, such as Chetopa, that have a diameter ratio < 1 typically produce long narrow kernels. The dorsal grooves on these narrow kernels are not only narrow themselves but they tend to flare outward into the kernel. The result of this kernel geometry is frequently trapped packing material.
    In contrast, round nuts or flattened nuts have broad kernels with wide dorsal grooves. These grooves also penetrate straight down into the kernel. The result of this geometry are kernels that fall free of all inner shell packing material.   

Pecan diversity

Nuts from seedling pecan trees compared to Pawnee (circled)

    Most pecan growers understand genetic variation in pecan simply because they have grafted a dozen or so cultivars into their orchards. We have large pecans and smaller pecans. There are cultivars that bear heavily and those that are shy producers. Some cultivars seem to have a crop every year while other trend towards alternate bearing. Everyone has grafted cultivars they wish they hadn't, and sometimes we wish we had grafted more of a particularly outstanding nut.
    The genetic diversity within pecan is amazingly wide. In our breeding plot, we used Pawnee as one of the primary parents in making controlled crosses. In the photo above, I've arranged some of the seedling nuts we have collected that ripen before or at the same time as Pawnee. The two nuts circled in the center of the photo are Pawnee nuts to give you a reference for comparison.
    There are a couple of seedling nuts that remind of the Pawnee parent, but the vast majority are drastically different in size and shape. Some of these seedlings will have thick shells while others will be thin shelled. But remember, nut size and percent kernel are just two traits that we need to look at in searching for new pecan cultivars. Disease resistance, good tree structure, and high yield are three major traits are also on the top of my wish list. Its no wonder that new, exceptional, pecan cultivars are so hard to come by.

Don't judge a pecan by its cover

     Over the past several days, I've been in a hydraulic lift collecting pecans from our pecan breeding plot (photo at right). Moving from tree to tree, it is amazing to witness the genetic diversity of pecan. Fortunately, we used early maturing parents for this project and now, 15 years later, most of the trees in this planting have ripened their nuts by the first week of October (not all though).
    As you might expect, I have found nuts of all sizes and shapes. Some have thin shells. Some will need a sledge hammer to crack them open. In addition, there are huge differences in reaction to leaf and nut diseases. After looking at so many seedling pecan trees with such diverse sets of cultivar traits, I now have a greater appreciation of how rare it is to find a truly exception new pecan.

    Today, I collected nuts from five different trees just to give you an idea of the type of variation I am seeing in our breeding plot (photo at left). All of these nuts had achieved shuck split with nut "E" probably splitting the earliest. I choose these five pecans because they were roughly the same size in the shuck. When pulling these nuts from the tree, these five nuts appeared to be fairly large. But looks can be deceiving.

   In the photo at right, you can see the same five nuts pulled out of their shucks.  The differences in size and shape are obvious. A big shuck doesn't always produce a big nut (nut C) and surprisingly large nuts can fall from not-so-impressive shucks (nut E).

   The shuck is only the first cover that needs to be peeled back to reveal a pecan's true character. The second cover is the shell. In the photo at left, I've arranged the same five nuts in the same order, but this time, each nut is cut in cross section. Note the differences in shell thickness.  Nut "A" has the thinnest shell, while nuts "D" and "C' have heavy shells. Now look at the packing material as it dips down into the dorsal groves of each kernel half. Long narrow dorsal groves means that the packing material might get stuck in the kernel during the cracking process. Nuts "C" and "E" might have a problem in this regard.
    Overall nut quality for 2013 looks great. You can look forward to seeing all the nuts we collect this year from the pecan breeding plot on display at the nut exhibits held in conjunction with the KS, MO and IL nut growers annual meetings early next year.

Shell shape can limit percent kernel

    In looking over nut samples from this year's nut evaluation, I noticed a particular pecan shell characteristic that seems to limit percent kernel. Its not what you might be thinking. Yes, shell thickness is obviously an important determinate of pecan shell-out percentage but the shape of the shell can also impact percent kernel. Take a look at three seedling pecans (photo below).

      These three pecans share a common pecan shell trait; they all have an extended apex (marked by the bracket above). The extended shell apex looks like the hand of God just pulled on the tip of the shell and stretched it out. Inside a pecan's shell, the kernel is oriented with the connection between the two kernel halves (and the seed's embryo) closest to the apex. When the apex is extended like the three examples above, kernel doesn't grow up into that region at all.    

     Here's a photo of a St. Genevieve nut that I've carefully peeled away the shell to reveal the kernel (at right). I placed an uncracked St. Genevieve nut in the photo for comparison.  Notice that the entire extended apex of this nut is composed of shell and packing material.  The kernel starts well back from the apex.
    Even if a nut has a thin shell, the pecan that has the extended apex characteristic produces a lump of heavy and unproductive shell at its tip.  Pecan cultivars that share this shell shape usually produce 44-48% kernel.  Cultivars blessed with exceptionally thin shells and cursed with an extended apex will produce 50% kernel at best.
    Other cultivars that share the extended apex trait include Goosepond, Colby, and Niblack.    

Pecan seedling selections

   
    Looking over the nut samples at this year's KNGA annual meeting I was struck by several interesting seedling pecan selections made by pecan growers across the Midwest. Let me highlight some of the best.

   St. Genevieve was discovered as a large native pecan tree growing within the city limits of St. Genevieve, MO (photo at right). If you every travel to this historic town, you'll discover that St. Genevieve was originally a French Canadian settlement founded in 1735. You'll also discover numerous native pecan trees growing throughout this Mississippi River town of 4,410 people. St. Genevieve is a large-sized native pecan averaging 8.83 g in weight and 46.7% kernel. This cultivar produces beautiful kernels that fall free from the shell.

    Al Newkirk from Miami, OK has been watching tree #459 in his native grove for a long time (photo at left). The tree produces consistently, bearing medium sized native nuts. This year, nuts averaged 6.54g and produced 48.2% kernel. Al especially likes this pecan because of its disease resistance and has grafted several trees over to this clone.
   

      Bob Kussman submitted a seedling pecan called Blunk that originates from the native pecan bottoms near Brunswick, MO. Blunk is not a very large pecan weighing only 4.48 g but this nut produces a plump, light-colored kernel that falls free from the shell when cracked (photo at right). For a native nut, percent kernel is high at 50.6%.
   

   Shepherd is a native nut discovered by Gerald Shepherd. This medium sized native pecan weighed 5.48g this year (drought year) but averages 6.39g when receiving normal rainfall. Shepherd nuts produced 51.4% kernel in 2012 but average 53.0% with adequate moisture. The Shepherd pecan matures 3 days before Pawnee and is scab free (photo at left).
   

   Ralph Voss  submitted another sample of the Zapp pecan (photo at right). Zapp looks to be a seedling of Stuart, originally planted as a yard tree in Germantown, IL. Nuts are large and blocky weighing 9.58 g in 2012. Nut produced 54.5% kernel last year. Nuts mature two weeks after Pawnee or about the same time as Lakota. Scab has not been seen on this cultivar.
   

Pawnee kernels defects following 2012 drought

    Last fall, many of our Pawnee kernels developed dark blotchy spots in response to last summer's heat and drought. In looking over Pawnee samples provided by growers for this year's nut evaluation, I found a wide range in kernel appearance. The photo above illustrates these kernel defects. There are two kernel halves from each of four Pawnee samples.
    The two kernels in the lower left portion of the photo came from a well irrigated tree that I would consider "normal" in appearance. The kernels in the upper left position suffered the greatest drought induced color changes. These kernels are dark, covered in black blotches and have adhering kernel fuzz. These tree were not irrigated last summer.
    The kernels in the lower right position are less-intensely blotchy and slightly darkened. These kernels were produced by trees had a limited supply of water last summer provided by trickle irrigation. This nut sample points out one of the deficiencies of trickle irrigation in pecan orchards. Under severe drought conditions, many trickle systems can't provide enough water to totally eliminate water stress.
    The kernels in the upper right position illustrate a different type of kernel discoloration.  Rather than numerous small black blotches, these kernels have a large, uniformly-dark area centered on the eye of the kernel (the kernel eye is that area where one kernel half is attached to the other).  With this type of discoloration, the dark spot on underside of the kernel often larger that what appears on the upper side.
    Any type of kernel discoloration will reduce the marketability of pecan crop. A return to more normal rainfall patterns will greatly improve the kernel quality of Pawnee in future years.
   

Pecan Nut Evaluations

    Last Saturday, the Kansas Nut Growers Association met for their Annual Meeting. The highlight of the meeting was huge display of pecan cultivars (photo above). Each nut sample was cracked and the percent kernel determined. Growers inspected the samples carefully looking at nuts size and percent kernel. The impact of the 2012 drought was easily seen as many cultivars produced smaller than average nuts. However, there were some surprises as some cultivars were still able to produce quality nuts in spite of the dry weather.
   In future posts, I'll be sharing some interesting observations I made when looking over this year's nut samples.