Franz Niederholzer6 CommentsJanuary 22, 2013Horticulture

What is Dormant?

I see what seems like a lot of leaves still left in some orchards around the Sacramento Valley, even after a wet and windy end to 2012.  Aldrich trees look to have the most leaves remaining.  This observation got me thinking about questions I’ve heard regarding leaves, dormancy, chilling and bloom timing/duration.  These questions include: Are trees with leaves remaining in January less dormant or somehow different than trees that are defoliated or naturally bare by January? Doesn’t spraying trees with zinc in the fall make them dormant faster? They don’t have leaves… Do trees with some leaves left in the canopy in January accumulate less chilling than trees with no leaves in December?

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David Doll29 CommentsJune 30, 2012Horticulture

Independence Almond – Some Observations

Many farmers are preparing their tree orders for next year’s planting. In that regard, I have received a few questions on Independence, a self compatible variety. What does it mean to be self compatible? Traditionally, almonds require cross pollination in order to ensure profitable harvests. In other words, pollen from one variety needs to move to the flower of another variety in order for the flower to be fertilized and set a nut. This is why we have multiple varieties of differing pollen groups planted within almond orchards. The newly released variety ‘Independence,’ however, is a self pollinating variety, meaning that pollen from an Independence tree can pollinate and fertilize a flower from another Independence tree. A single variety orchard has advantages over traditional 2-3 variety plantings. The obvious benefits come from the single bloom, hullsplit, and harvest timing. This provides savings in time as it may reduce the passes through the block, and even more so for growers relying on custom spraying, harvesting. These reasons where why Butte/Padre plantings were so popular. How does the tree look? At this point, although possibly premature, with observations of the oldest block that I know – 9th leaf – and a few younger plantings, it looks good. Yields have been up and down in the oldest block, but this has been due to frost events that have occurred in the late spring. In the younger blocks, the tree seems to bear well, and appears to have a good yielding potential based upon field observations.  The trees appear to be a little smaller than Nonpareil and a little more upright. Bloom time seems to overlap well with Nonpareil, if not a day or so earlier. Any obvious disease problems? The past few years I have walked the a few blocks looking for symptoms of various

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David Doll0 commentsApril 5, 2012Nutrient

Nitrogen within the soil: The Nitrogen Cycle

Figure 1: The various forms of nitrogen and processes within the nitrogen cycle. Sourced from wikipedia.org. Written by Dr. Larry Oldham (Mississippi State Extension Service) and David Doll. Nitrogen is in organic and inorganic forms in soils. Over 90 percent of soil N is associated with soil organic matter. Nitrogen is in compounds identifiable as part of the original organic material such as proteins, amino acids, or amino sugars, or in very complex unidentified substances in advanced stages of decomposition. Plants may use either ammonium (NH4+), or nitrate (NO3-) which behave quite differently in soils. Positively charged NH4+ is attracted to negatively charged sites on soil particles as are other cations. It is available to plants, but the electrostatic attraction protects it from leaching. Conversely, negatively charged NO3- does not react with the predominately negatively charged soil particles, so it remains in the soil solution, moves with the soil water, and is susceptible to leaching. Nitrogen transformations in soils/Nitrogen Cycle: Nitrogen conversions depend on soil moisture conditions, soil acidity, temperature, and microbial activity. Ammonium is absorbed on the cation exchange complex or taken up by plants without transformation, but most likely it is converted to NH4+ soon after its formation or addition as fertilizer. This nitrification is a two step process involving two different groups of soil bacteria. First Nitrosomas bacteria produce nitrite (NO2-). Nitrobacter species then convert NO2- to NO3- soon after its formation. The carbon used by these bacteria is derived solely from atmospheric CO2. a) 2NH4+ + 3O2 = 2NO2- + 2H2O + 4H+ + energy b) 2NO2- + O2 = 2NO3- + energy Two things to note: 1) NH4+ has a short residence time in soils before conversion to the more mobile NO3- form; and 2) hydrogen ions are produced which lower the soil pH. Mineralization is

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David Doll0 commentsMarch 2, 2012Horticulture

Varietal Bloom Issues

Weak bloom experienced in an orchard:Nonpareil and Monterrey shown. I have received more calls about weak bloom on almond pollinators. These trees have low counts of fruit bud, and the vegetative buds have pushed giving the tree a green instead of white appearance. The reports have been coming in from orchards of “juvenile orchards” (7-10 years of age), which typically have yielded quite heavy for their age. Nonpareil is affected, but the later harvested varieties, which include Monterrey and Fritz, are affected more severely.   In being in these orchards, it is clear that the period of fruit bud development was affected sometime last year. Fruit bud development/floral initiation varies among varieties. Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds). Very fruit bud are found on the trees,the majority of the buds are vegetative (leaf). In regards to the weak bloom, working with the farmers, we were able to identify some of the possible stressors that may have occurred during the period of fruit bud differentiation. Although we are unsure of the exact problem(s), the ones we are considering include:1. Holding back of irrigation in order to “force” hull-split or harvest,2. Excessive foliar disease, including rust or scab, that caused defoliation,3. Improper nutrient management – usually very low potassium and boron, and 4. heavy yields that reduced the vigor of the tree, impacting growth and the number of fruiting spurs available for future crops. In many cases, more than one of these issues could have affected the orchard. In orchards that experienced defoliation to foliar disease, many

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