Q. How much nitrogen should be applied in the postharvest period?
A. This depends. This should be based upon the current tissue N levels detected from mid-July sampling. If within the prescribed ranges of leaf N (2.2-2.5%), 20% of the budget should be planned for application. If richer (>2.5%), slightly less can be added. If really high N leaf levels are observed (>3.0% in mid-July), postharvest fertigation may not be needed.
Q. When should the N be applied?
A. Nitrogen can be applied anytime after hullsplit up until a few weeks postharvest. In earlier harvested varieties and ‘Nonpareil,’ nitrogen can be applied shortly after harvest with the first post-harvest irrigation. With later varieties, such as ‘Monterey’ or ‘Fritz,’ the application can be made post-hullsplit prior to harvest. This timing matches bud development that tends to occur about 2 weeks after ‘Nonpareil’ harvest for most varieties (i.e. ‘Nonpareil,’ ‘Carmel,’ ‘Mission.’). In other words, it appears that most almond trees, regardless of variety, will begin bud development around the same time. It is important to note that the bud development timing has not been studied for all varieties, and this is an assumption carried over from previous research.
Q. What about other nutrients, like potassium? Phosphorous?
A. Potassium applications can also begin in the post-harvest period. Uptake by the tree will be minimal since the almond hull is the primary sink for potassium (~3% by dry weight), so I wouldn’t go crazy. Applications made at this time are essentially rebuilding the soil reserves of K. This may be a reasonable strategy IF you are on a soil that is able to hold the potassium. In sandy soils, which are common in Merced, potassium can be leached out of the rootzone, which may create a situation of deficiency in the following year.
We dont know much about phosphorous. Almonds appear to use small amounts of P (~ 7 lbs/1000 kernel pounds) in relationship to the other major nutrients. Since it is exported from the system, deficiency may occur, but it is rare. We think that enough P is being provided from the degradation of the parent material. Applications should be considered if leaf tissue values are approaching the minimum requirement of 0.1%.
A. Yes, postharvest is a great time for boron applications. Grab a bag of hulls and submit for analysis. based upon the analysis of the hulls, boron rates and application timings can be established. The current boron guidelines for hulls are as follows:
- 80 ppm or lower = deficient
- 80-150 ppm = adequate
- Over 200 ppm = may be toxic
Q. Anything else?
A. It is also important to provide adequate water during this time. Extreme water stress in the post-harvest has been shown to reduce yields. Also, late fall applications of N will have reduced effectiveness due to lower rates of ET and therefore N uptake. the earlier, the better.