Influencing Pistachio Development and Harvest with Science-Driven Nutrition™
Agro-K’s line of foliar products have been demonstrated by independent research to deliver a consistently heavy, healthy, and high-yield crop.
Pistachio growers know that having a profitable harvest requires the right combination of nut set, nut size, and kernel weight. While these three factors are somewhat interdependent, proper nutrition is key to maximizing all three.
“Only about ten percent of the pistachio flowers will actually set,” says Sean Jacobs, technical sales and marketing representative at Agro-K. “Then of those, five to thirty percent, develop into what are known as blanks. They’re basically a shell and a hull without an embryo. Either this embryo abortion is carbohydrate-based, with the plant not having enough energy to support the growth, or fertility-based where key nutrients are not available for the process to continue. Either way you end up having shells with no nuts in them. We can, however, influence this with proper nutrition.”
Growers must take a science-based approach to ensure a consistently high set and yield year over year. The process begins with the Five Rs of plant nutrition: The Right nutrient applied at the Right time in the Right form in the Right mix targeting the Right place in the plant. When beginning a science-based nutritional program, it’s essential to know what nutrients are already in the soil and in the field.
Through soil testing, pre-harvest fruit analysis, and leaf sap analysis, growers take a deep dive into what products they need to apply and which ones they can skip. Testing at the beginning of and throughout the season provides a roadmap for future success; testing at the end is a report card for how well the crop’s nutritional needs where met.
By using science to determine the “right nutrient” growers can focus on applying the appropriate products at the right times. For pistachios, there are three main periods throughout the season when growers can influence the crop: bloom, rapid leaf expansion, and nut bulking/shell split. Keep reading to learn more about science-driven nutrition at each stage.
At the beginning of April, pistachio growers are focused on supporting the bloom stage. This is a time when pollen receptivity and viability are incredibly important for bolstering the trees’ pistachio production throughout the season. Extending the bloom period is essential during this time. The right mix of nutrients can help foster these processes to improve reproductive success.
“Pistachios have a long bloom period, and there’s a bit of luck involved in getting the male trees to shed pollen when the female trees are receptive to it,” Jacobs says. “Some seasons can have up to fourteen days between male and female flowering, so you need to take advantage of ways to to lengthen the duration of flower receptivity and improve pollen viability. The better you can support this significant bloom window, the greater your nut set will be.”
Supporting the bloom period is easier when using science-driven nutrition. Jacobs recommends using Agrobest® 9-24-3, Sysstem® LeafMax, Vigor Sea-Cal™, and Top-Set D.L. to ensure the crop has what it needs.
Agrobest 9-24-3 sets the stage for success with a high phosphorus-to-potassium ratio that won’t negatively affect uptake of other nutrients such as calcium. Sysstem LeafMax is a phosphite formulation that contains sulfur, magnesium, manganese, zinc, iron, copper, and molybdenum. These nutrient are key players in vascular and root development, leaf sizing, and chlorophyll synthesis. By optimizing root and vascular development, growers improve water and nutrient uptake from the soil and support efficient transport throughout the tree.
Top Set D.L. delivers boron and molybdenum directly to the flowers where Vigor Sea-Cal provides calcium for cell wall structure. Boron is essential for pollen tube development, as well as ovule longevity and pollen receptivity. Pistachios have a significant demand for boron throughout the season, more so than any other tree crop, and deficiencies can increase the number of blanks.
The molybdenum from Top Set D.L. is an important cofactor among a handful of enzymes, including the key nitrogen metabolism and utilization enzyme nitrate reductase. During cell division, calcium supports cell wall structure and integrity. Calcium also functions as a secondary messenger that influences many metabolic processes throughout the growing season.
During the first post-bloom irrigation, NutriMax should be added. This soil microbial food source has cobalt, manganese and zinc to promote beneficial aerobic bacteria, increasing fertilizer use efficiencies as the tree enters into rapid vegetative growth and as nutlet shell and hull development progresses.
Rapid Leaf Expansion
Approximately seven to 14 days post bloom, the crop transitions into a period of rapid leaf expansion. This period occurs at the end of April and early May when a lot of the plant development processes begin to overlap. Shoot growth, shell and hull development, and eventually, kernel formation all happen at this time. As the pistachio crop transitions away from pollination the nutritional focus should shift to fertility inputs that will best sustain the plant’s vascular systems and boost vegetative growth.
“The shoots are growing and adding more leaves to the trees, increasing the demand placed on the vascular system for water and nutrient flow from roots to leaves,” Jacobs says, adding that this is also the time to support nitrogen metabolism. “In pistachio crops, a lot of the nut’s weight is protein. Nitrogen metabolism is the precursor to amino acids and proteins. So, during this time, you’re really trying to get the nitrogen into a form that the plant is going to use in order to maximize protein production and weight.”
To help meet the crop’s needs during this time, growers should continue their applications of Sysstem LeafMax, Vigor Sea-Cal, and Agrobest 9-24-3. Additionally, applying Vigor Copper will prevent copper deficiencies, which are a regular occurrence in pistachios and can negatively impact protein formation in the nut.
This is not always well correlated with the micronutrient’s levels in the soil as some rootstocks—particularly UCB1 and P. integerrima—are inherently inefficient at taking up copper from the soil. Like zinc, copper is not easily remobilized from old to new growth, so it’s best to get ahead of the problem.
Nut Bulking and Shell Split
As the crop enters its final crop stage prior to harvest, growers are focused on supporting vascular tissues, protein development, and nut bulking to maximize weight and marketable yield. The kernel is now filling the shell, causing the shell to split. Science-driven nutrition is important during this final push toward harvest, too.
Vigor Copper and Top-Set D.L. applications continue, and Agrobest® 0-20-26 is brought into the mix. This liquid foliar fertilizer boasts a high phosphorous and potassium formula—two nutrients that can make or break the crop’s success.
“You’re trying to make the biggest, heaviest nut that you can get, so at this point, it is all about loading up the kernel,” Jacobs says. “As the crop is ripening, photosynthetic production is nearing maximum, requiring substantial energy transfer, demanding a lot of phosphorus. In addition, potassium is needed to move these photosynthates into the nut, bulking up the size and weight of the kernel, causing the shell to split.”
Proper nutrition over the season promotes more even pistachio ripening , resulting in a smoother, cleaner harvest. At harvest, for example, pistachios tend to ripen unevenly on the tree, often requiring two or more shakes to successfully remove the crop.
Because of the moisture content of the hull and kernel, nuts must be removed from the tree in a timely fashion and quickly sent to the processor to avoid shell staining from the degrading hulls and disease problems. Ultimately, a science-based focus on nutrition helps alleviate many of the challenges that pistachio growers experience throughout the season.