With the dramatic rise in the price of potassium fertilizers over the past few years, many almond growers have been tempted to cut back on applications of this primary nutrient. However, without enough potassium, growth and yield of almond trees will suffer – not just in the current year but for several years to come.
“Potassium is one nutrient where you want to minimize any scrimping on costs,” says Wes Asai. His company, Pomology Consulting, Turlock, Calif., works with almond growers in the northern area of California’s San Joaquin Valley.
Solving a potassium problem, he notes, isn’t like dealing with a nitrogen shortage. In that case, feeding trees the needed nitrogen usually corrects the deficiency in short order.
“Potassium is vital in developing buds and flowers for subsequent years’ production,” Asai says. “If the tree is deficient to the point where it’s not forming new spurs, you’re jeopardizing the current crop as well as crops over the next few years. In fact, once you put potassium down, your production may suffer for three years, until the potassium begins to take effect.”
In the past, almond trees where considered to be getting enough of this nutrient when leaf analysis indicated a potassium level of 1.4 percent or higher. However, more recently, growers, particularly those seeking yields in the 3,000 to 4,000-pounds- per-acre range, have been shooting for leaf analysis readings of 1.8 percent to 2.0 percent, even though University of California research has not been able to corroborate that, Asai notes.
In the past, growers have fed their almond trees 1,200 to 1,500 pounds of potash or potassium sulfate per acre every three to four years, concentrating it in a band on either side of the tree. The idea is that, because potassium becomes tied up in the soil, this method is more effective than diluting the impact of the fertilizer by broadcasting it or applying it a lower rate.
However, Asai is experimenting with a way of making more cost-effective use of potassium that runs counter to conventional practices. It involves broadcasting potassium sulfate at much lower rates. “We want to see if we can use broadcast applications to reduce potassium costs without hurting yields,” he says.
Previous studies have found that, with low volume micro sprinkler or drip irrigation systems where numerous shallow roots are concentrated around the base of tree trunks, trees can take up broadcast potassium, Asai reports.
This current trial, which he started in 2006, covers three acres of a commercial Nonpareil orchard near Newman, Calif. Asai is comparing three methods of applying low rates of potassium – banding in the middles, banding in the tree row and broadcasting in the microsprinkler wetted area – with control plots where no potassium is being applied. The fertilizer is put on in late October following harvest at the rate of 400 pounds per acre.. Each of the treatments is arranged in a randomized replicated block design with nine replications.
Asai is trying to keep leaf analysis potassium of the fertilized plots at the relatively high level of 1.8 percent or more. After three years of his planned five-year study, the results are encouraging. In the untreated check, leaf analysis shows a potassium reading of 1.66 percent. Banding the nutrient increases that figure to 1.9 percent while broadcasting raises leaf potassium even more to 2.24 percent. Although these differences are not significant statistically, the broadcast treatment has produced the highest leaf potassium levels in each year of the study.
Yield measurements in the different treatments show a similar trend, although, again, the differences are statistically insignificant. Yields were lowest on the check plots and highest with the broadcast treatment. Yields with banding were in-between the other two.
The trials are being conducted on loamy soils. Had they been done on sandy soils, which have a much lower capacity to hold nutrients, differences between the treatments probably would be larger and even statistically significant, Asai adds.
Should the final results confirm that broadcasting potassium at lower rates opens the door to more profits, it would not necessarily be the only benefit for growers. For example, unlike broadcast spreaders, in which one size fits all, banding equipment tends to be less readily available, Asai notes.
What’s more, it must be matched in size to fit specific tree spacing and it is more prone to damage during use. Also, broadcasting offers a wider window of time in which to apply potassium, because bands in the tree middles cannot be put down during certain times of the year when cultural practices would disrupt them. The broadcast applications would be made in the tree rows where they would not be disturbed.