There has been a lot of workshops and seminars discussing nitrogen management in almond. The data and conclusions discussed from these trials has been thought provoking, and has provided information to help better manage almond orchard nitrogen. One particular slide has caught my attention – and provides the basis of nitrogen timings for almond orchards.
This figure was developed through whole tree assays. In this study, researchers collected nutrient concentrations from all of the different plant tissues (roots, trunk, branches, leaves, nuts) from mature, field grown almond trees. By viewing the dynamics of nitrogen accumulation, the rate and pattern of nitrogen uptake from the soil can be determined.
From this figure, a few conclusions can be drawn:
- From dormancy through early leaf-out, nitrogen is mobilized from stored reserves and essentially no uptake of N occurs from the soil.
- From leaf to fruit expansion, soil uptake of nitrogen is beginning and nitrogen continues to be mobilized from stored reserves.
- From full leaf expansion through hull-split, nitrogen demand is being met with root uptake. 90% of the tree’s demand for annual nitrogen is during this time.
- Following hull-split, tree nitrogen demand and root uptake decline rapidly, and stop once the leaves begin senescence. Some nitrogen is re-mobilized into perennial storage.
Those conclusions have helped form guidelines for nitrogen applications. Nitrogen should be applied to meet tree’s demand, with 80% of the nitrogen applied from early spring and continuing through hull-split. Fertilization events should be split, with 3-4 applications made through this period with a rate that matches crop load. Timings may be adjusted to prevent hull rot or other issues. The remaining 20% of the nitrogen budget can be applied in the postharvest if an under-estimate of yield occurred. Finally, postharvest applications should only be made if the leaves are healthy and should not exceed 50 pounds of nitrogen.
For more information, please see this excellent article written by Dr. Saa and colleagues. It has also served as the source of information for this article.