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Fluid Journal : Summer 2017
9 The Fluid Journal Summer 2017 Dr. David Bryla is Research Horticulturist and Dr. Scott Orr is Biological Science Technician at the USDA-ARS Horticultural Crops Research Unit in Corvallis, OR. ACT NOW! Write, call or e-mail the Fluid Fertilizer Foundation Phone: 785-776-0273 E-mail: email@example.com Research and education for efficient use of fluids. The Fluid Fertilizer Foundation We need you to join hundreds of other growers, dealers, fertilizer manufacturers and other supporting industries JOIN IN THE SUPPORT OF THIS ORGANIZATION THAT DIRECTLY BENEFITS YOUR BUSINESS! with SOP or KTS resulted in higher concentrations of K, Ca, Mg, and S in soil solution under the drip emitters than either no K or granular SOP, while granular SOP resulted in higher concentration of K than any other treatment at 6 inches from the drip emitter (Tables 2 and 3). Differences in K wer apparent throughout the growing seaon, particular;u under the drip emitters during fertigation (Figure 2). Evidently, granular SOP dissolved on the soil surface and penetrated near the edge of the wetting front, while K applied by fertigation remained near the drip emitters. Kafkafi and Tarchitsky suggested that, in practice, the exact distribution of K in the soil is relatively unimportant in drip-irrigated plants, since roots can grow and find K in the wetted soil volume. However, most blueberry roots are concentrated under the drip emitters when the plants are irrigated by drip. Fertigation provides a way to effectively deliver K to the roots while minimizing soil K fixation that could otherwise limit the effectiveness of granular application of K fertilizers. Potassium fertilization had no effect on the concentration of K in the leaf tissue (Table 4). It usually takes a year or two before K fertilizer has any effect on tissue K concentration in blueberries. The treatments also had no effect on concentration of N, P, or Ca in the leaves. However, relative to no K, fertigation with KTS increased the concentration of Mg in the leaves, while fertigation with SOP increased the concentration of Mn in the leaves (Table 4). Typically, high amounts of K in the soil will result in lower concentrations of Mg in the leaves in blueberries, which was not the case in the present study. High concentration of Mn in the leaves, on the other hand, is usually related to low soil pH, and soil pH was lowest when the plants were fertigated with SOP. Granular SOP increased the concentration of S in the leaves relative to no K (Table 4). Most of the nutrients in the leaves, including K, were at concentrations considered normal for mature blueberry plants in Oregon. However, N and P were below normal in each treatment. The current recommendation is 1.76 to 2.00% N and >0.10% P. Low N could have been due to the fact that the plants broke bud much earlier than usual in 2016, and consequently, N fertigation may have been started too late. Some of the plants were slightly chlorotic after harvest and could have been deficient, but there was no evidence of P deficiency in the planting. Other regions in the United States define P deficiency as below 0.07 to 0.08% P in blueberry leaves. Strik and Vance recently conducted a study on leaf nutrients in conventional and organic blueberries and concluded the standard for P should be lower in Oregon. Yield, fruit quality. Neither K fertigation nor granular K had any effect on yield or fruit quality during the first year of the study (Table 5). This was not surprising given the limited effects of the treatments on leaf nutrients. Like many perennial crops, blueberries have a large amount of nutrient reserves in their woody tissues and will rely on those reserves for fruit production. We will need at least another year to determine whether K fertilizer has any effect on production or quality in the present study. Looking ahead Fertigation with SOP or KTS reduced soil pH and increased the concentration of K, Ca, Mg, and S under the drip emitters, while granular application of SOP resulted in higher concentration of K on the edge of the soil wetting front at 6 inches from the emitters. In both cases, K was available in the soil solution throughout the season, but at different locations. However, since blueberry roots tend to concentrate under the drip emitters, fertigation with K is likely more efficient than granular application of K. So far, there have been no benefits from either K fertigation or granular K on production or fruit quality, but it is still early as changes usually occur a year or two after K fertilizer is applied in blueberries. Additional measurements are under way to study the dynamics of K movement with depth following each fertilizer application and to examine whether there is any impact on K uptake in the leaves and fruit the following year.