per season with this water, I would apply approximately 92 lbs. N per acre. This figure can be determined by multiplying mg/l or ppm of nitrate by 0.61 to get lbs. of actual N per acre-foot of water. If the lab analysis reports N levels in nitrate-nitrogen (NO₃-N), then multiply the nitrate- nitrogen value by 2.72 to get lbs. of actual N per acre-foot of water. For example, if your orchard produced 3,500 pounds of kernel meats last year, you would determine that 210 pounds of N was removed with the crop and needs to be replaced. But if your irrigation water has 50 ppm nitrate then you may only need to apply 118 lbs. of N per acre to your orchard (210 lbs. orchard N minus 92 lbs. found in the water). Mature trees need more nitrogen in early spring during periods of active shoot growth, leaf activity, and photosynthesis when temperatures are between 70-80°F. Shoot growth is vital for canopy development and for the creation of fruiting positions (buds). Almond nuts and shoots use most of the season’s N (80% of annual demand) between bloom and mid-June. Dr. Brown’s group recommends delivering fertilizer N at four different timings and amounts through the season – February or March (20% of total annual N input), April (30%), May and early June (30%) and September – October (20%). Nitrogen use efficiency has increased dramatically (75-
85%) in Dr. Brown’s studies where N is applied at the time of peak tree demand and uptake. I know many growers that “spoon feed” their trees with small injections of N and other liquid fertilizers into their irrigation systems. Add a little bit of N with every irrigation from March to July, rather than applying large doses periodically through the season (we humans prefer three small meals a day over one big one). Fertigation delivers fertilizer to active roots. It is important that irrigation deliver only needed water, for excess water could dilute or leach the N applied past the root zone. In orchards with flood or
solid set sprinkler irrigation systems the N should be applied down the tree rows and not broadcast down the row middles. Dormant winter applications of N should be avoided as well as applications during hull split (July), which can aggravate hull rot and delay harvest! Deciduous almond trees absorb no N between leaf drop and leaf out. I have been working with many growers who are recycling their first-generation almond orchards, incorporating the wood chips, and planting back second-generation almond trees. We have had some orchards that incorporated as much
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