Soils Lab (NSL) in Arbuckle, targets the following nutrient levels in July leaf samples in the commercial orchards at NSL: 2.4-2.8% N, 1.8 % K, and >20 ppm Zn. Those are the four mineral nutrients most lacking in California almond production. He also shoots for >100 ppm boron in hulls at harvest. An eight-year average for crop production at NSL across all varieties is 2500 pounds nut meats/acre. Clean reject sheets and healthy looking trees at the end of harvest are two other good results to the season. All these things are not easy to hit, but they are the target. How can you project individual orchard nutrient needs – create a nutrient budget – for the coming year? Every orchard is different, but the process should be about the same. Let’s create a nutrient budget for a fictitious 12th leaf almond orchard on, let’s say, class 2 soil with microjet irrigation, good leaf nutrient levels and average yield last year. Say a solid average is 2200 lbs of nut meats over the last 4 years. That should be about 121 pounds, each, of N and K2O plus 0.45 lbs of B/acre removed per acre per year. If there is no nitrogen in the irrigation water and the soil is low in K and B, then those orchard nutrient exports are a good ballpark estimate of crop nutrient needs for the coming year in an orchard with careful water management. If you assume 80% nitrogen use efficiency based on careful irrigation through microjet sprinklers, apply at least
three small applications of equal amounts of liquid nitrogen through the micro irrigation system (in this case, around 50 pounds N/acre per injection) in April through July, with at least 30 days between applications, to deliver about 150 pounds of N/acre. Slightly smaller sized shots of potash (40 lbs K2O/acre) should go out in that same time window. If the soil has a high clay content and “fixes” potassium, you may need to up this rate. Looks like a big crop once April arrives? Put on an additional application or bump up the rates in the originally planned injections. Light crop? Cut out one application or reduce the amount applied in each. A fall or pink bud spray of Solubor® will deliver the projected boron needs. Zinc is hard to efficiently deliver, but spring sprays are effective and usually are more efficient that a fall spray using high, leaf dropping rates. Next year at the same time, check yield, orchard vigor and July leaf numbers and adjust fertilizer program as needed. After a fall planning meeting with you, their PCA/ CCA, the grower should have a decent estimate of fertilizer timings, amounts and perhaps cost. Your grower can now make plans with his/her banker. Plans are just a point of departure, but it is good to have somewhere to start. The work by Patrick Brown’s research group continues, and new tools in the form of a nutrient budget approach to fertilizer planning may be available for growers in the future.
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December CAPCA Adviser