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Rhoda L. Burrows and Frank J. Peryea

Nitrification-induced subsoil acidification is a major problem encountered with the use of ammonium- or urea-containing fertilizer solutions for drip fertigation of tree fruit crops. We conducted a laboratory experiment to evaluate the soil acidification potential of the four fertilizer N solutions most frequently used for fertigation within the Washington tree fruit industry. Treatments were five orchard soils x four commercial N solutions (calcium nitrate, calcium-ammonium nitrate, ammonium nitrate, urea-ammoniun nitrate) x four N rates (0, 100, 200, 500 mg N/kg). Air-dry subsamples of each soil were inoculated with fresh soil known to exhibit nitrifying behavior amended with treatment solutions. Subsamples were maintained at simulated field capacity of –15 kPa. Soil pH was measured after 5 weeks incubation. The treatment solutions were reapplied and pH measured after another 5 weeks. The soil were then leached with distilled water and further incubated to determine if pH would increase as has been observed in the field. The fertilizer solutions acidified the soils in direct relation to their ammonium plus urea content. The calcium nitrate solution was acidifying because it contains ammonium nitrate as an impurity. We will present the pH “rebound” data.

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Gaofeng Zhou, Bixian Li, Jianmei Chen, Fengxian Yao, Guan Guan, Guidong Liu and Qingjiang Wei

Abiotic stresses, such as nutrient disorder and soil acidification, are dominant soil factors that affect plant performance. It is well known that B is an essential micronutrient for vascular plants ( Marschner, 1995 ), and it has an important role

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Khalid F. Almutairi, Rui M.A. Machado, David R. Bryla and Bernadine C. Strik

hazardous and requires expensive, non-corrosive irrigation equipment ( Burt et al., 1998 ). Soil acidification with S o usually takes several months or more to change soil pH from 6.0 or higher to a desired level for northern highbush blueberry ( Gough

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Flavia T. Zambon, Davie M. Kadyampakeni and Jude W. Grosser

reported to improve the health status of HLB-affected plants, such as an overdose of foliar sprays with essentials nutrients ( Morgan et al., 2016 ) and soil acidification, resulting in corresponding increases in root density and yield ( Graham, 2016

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G.H. Neilsen, D. Neilsen and F. Peryea

Traditionally, broadcast or foliar fertilizer applications have been used to improve or sustain the nutrition of many irrigated, deciduous fruit tree orchards in western North America. Recent developments, including adoption of low-pressure microirrigation systems and planting at higher densities [especially for apple (Malus domestica Borkh.)], have increased interest in controlled application of fertilizers directly with irrigation (fertigation). Recent fertigation research in western North America is reviewed, emphasizing results from high-density apple orchards. Fertigation and traditional broadcast application methods are examined with respect to mobility of N, P, and K in the soil and response of fruit trees to application of these nutrients.

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G.H. Neilsen, P. Parchomchuk, D. Neilsen, R. Berard and E.J. Hague

`Gala' apple (Malus domestica Borkh) on M.26 rootstock was subjected, in the first five growing seasons, to NP-fertigation and a factorial combination of treatments involving method and frequency of irrigation. Two types of emitters (drip or microjet) were used to apply the same quantity of water at high (daily), intermediate (about weekly) and low (about bi-weekly) irrigation frequencies. Although initial tree vigor and yield were higher for drip-fertigated trees, by the end of the study microjet fertigation produced larger trees of similar yield. These microjet fertigated trees had higher leaf P, K and Cu but lower leaf N, Mg, and Mn than drip-fertigated trees. Soil pH and extractable Mg and K concentrations were higher and extractable-P concentrations lower directly beneath microjet-emitters as a result of the larger fertigated soil volume relative to drip-emitters. High frequency irrigation improved tree growth but had less effect on leaf nutrient concentrations or soil chemical changes than lower frequency irrigation. Leaf N concentration was most affected by irrigation frequency, tending to decrease with daily irrigation.

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Zhi Quan, Bin Huang, Caiyan Lu, Yi Shi, Yanhong Cao, Yongzhuang Wang, Chuanrui He, Guangyu Chi, Jian Ma and Xin Chen

chemical N fertilizer to buffer soil acidification, improve microbial activity and functional diversity, provide nutrients, and maintain the sustainable productivity ( Hati et al., 2008 ; Shen et al., 2010 ; Zhao et al., 2012 ). The relatively low cost of

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Monica Ozores-Hampton

, 2005 ; Liu et al., 2012 ). Table 4. Soil and foliar applied iron (Fe) fertilizer sources and survey response used in vegetable production in Florida. Water and soil acidification treatments were used by 10% to 20% of the vegetable growers using drip

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F. Iriarte, J. Fry and N. Tisserat

Bermudagrass turf quality is commonly reduced in the transition zone by Ophiosphaerella herpotricha, a root-infecting fungus that causes spring dead spot (SDS). Fungicides applied in autumn typically result in poor to moderate disease suppression. Earlier research has indicated that some cultural practices, including core aerification or fertilization with soil acidifying nitrogen fertilizers, may suppress SDS. Our objective was to evaluate several treatment combinations for reducing disease severity. Treatments were arranged in a split-plot design, with whole plots being aerification + verticutting, or no cultivation. Subplots within whole plots consisted of a factorial arrangement of azoxystrobin (one September application of at 0.6 kg·ha-1), trinexapac-ethyl (three summer applications at 6.1 kg·ha-1), and ammonium sulfate (three summer applications with N at 49 kg·ha-1). After 1 year of treatment, spring turf quality was improved in all treatments that included trinexapac-ethyl. Diseased area was reduced from 34% to 21% in plots receiving azoxystrobin + trinexapac-ethyl.

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Chun-qiong Huang, Guo-dao Liu and Chang-jun Bai

Soil acidification is normally a slow process, and acidic or acid soils are natural in humid tropical, subtropical, and temperate regions. However, the acidification of soil may be aggravated unnaturally by acid rain due to industrial emissions, or