David Doll0 commentsSeptember 13, 2018Nutrient

Postharvest Nitrogen Management 2018

Many operations often apply nitrogen postharvest. Application rates vary from orchard to orchard, but typically I hear applications between 30 and 50 lbs/acre. This nitrogen is used to rebuild the nitrogen reserves within the tree and help with a variety of tree processes. Being applied late in the season, however, it is susceptible to leaching from over-irrigation and early rains. While it is critical to make sure there is nitrogen available for the tree, postharvest nitrogen budgets should be evaluated to determine if they are too high or not needed. Work at UC Davis has indicated that 15-20% of the nitrogen demand occurs from harvest through the post-harvest period. This suggests that somewhere between 20-30 lbs of nitrogen is utilized during this period, which could be sourced from residual nitrate in the soil or post-harvest applications. A further breakdown of the uptake curve shows that less than 8% of the annual need occurs after September, suggesting the importance of timeliness in application (Figure 1). Applications can begin when the abscission layer begins to form on the later harvesting varieties, but consider lowering rates to reduce the risk of hullrot flare ups (e.g. apply 10-15 lbs/acre instead of 25-30 lbs/acre). Applications of nitrogen in the post-harvest tend to be relatively inefficient due to several factors, including tree defoliation, leaching by early rains or long irrigations, shorter days and lower water use. This suggests that more nitrogen may be needed to achieve a 20-30 lb uptake, but studies in Kern County failed to see a response from applications greater than 50 lbs/acre of nitrogen applied after Nonpareil harvest (mid-August). Rates should not exceed this amount and applications made in September and October should be significantly reduced. Mid-July leaf nitrogen and residual soil nitrate should be taken into consideration when determining the amount.

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David Doll0 commentsSeptember 9, 2017Horticulture, Irrigation

Almond Postharvest Management: Water Demands

After the hustle of harvest, it is easy to think that the orchard work is nearly wrapped up for the year. With almonds, this isn’t the case. Research over the past 30 years has identified the postharvest period as the primary development period that impacts next year’s crop. Not surprisingly, much of this work has shown proper irrigation practices during this period being the major factor. For this article, the post-harvest period will be defined as mid-August through early November. During this period, the trees can demand an estimated 12-15″ of water based on location and weather. Roughly 70% this demand is from the six weeks immediately after harvest – when the days are hot and longer (see included table). Shorting trees of water during this period of high water use (mid-August through September) has been shown to significantly reduce next year’s yield. In fact, research by David Goldhamer and Elias Fereras have found that the first 8″ of water applied during the postharvest period is the MOST CRITICAL water applied to maintain orchard yields. Why is this?  Almond floral bud differentiation, unlike other Prunus spp.,  begins in mid- to late-August and continues through early September. Water shortages during this time reduces carbohydrate development, leading to less energy being able to be directed towards the creation of next year’s flowers, affecting both flower quality and quantity. This, in-turn, leads to an overall reduction in fruit load. Practices should be employed to keep leaves on the tree through the postharvest period (early November).  Reducing tree stress through the harvesting process is the first step in maintaining highly productive trees. This includes being timely with shaking so trees are stressed for a minimal amount of time and understanding the amount of soil moisture and the rate of use – which includes taking

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David Doll0 commentsAugust 31, 2010Irrigation

The Importance of Post-Harvest Irrigation in Almond

Multiple entries have covered the aspects of ensuring irrigation during the post-harvest period. This practice has been based off of previously conducted research and is recommended due to the detrimental effect that post-harvest water stress has on the following year’s crop. Never-the-less, many growers do not recognize the importance of this practice. An irrigation stress or deficit during the post-harvest period has been shown to reduce bloom, fruit set, fruit load, and individual fruit weight. For example, a University of California study conducted between 1989-1990 that deprived trees of post-harvest irrigation resulted in a 10% reduction in fruit set, a 33% reduction in fruit load, and a 43.3% decrease in kernel yields for the nonpareil variety*. It is thought that the sensitivity of the almond to the lack of post-harvest irrigation is most likely due to the late fruit bud differentiation which occurs from late August to early September. As the first “round” of harvesting is completed, keep in mind the need to irrigate the trees. It is easily forgotten with the hustle and bustle of harvest, but the potential consequences of forgetting should turn the practice into a priority. *Research paper cited: Goldhamer, D.A., Viveros, M. 2000. “Effects of preharvest irrigation cutoff durations and postharvest water deprivation on almond tree performance.” Irrigation Science. Vol 19: 125-131.

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