Foliar Zinc Applications in Prunus*: From Lab Experience to Orchard Management. Sebastian Saa 1*, Claudia Negron 2, Patrick Brown 2

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1 Foliar Zinc Applications in Prunus*: From Lab Experience to Orchard Management. *Mainly in Almonds! Sebastian Saa 1*, Claudia Negron 2, Patrick Brown 2 1 Escuela de Agronomía, Pontificia Universidad Católica de Valparaíso, Chile. 2 Department of Plant Sciences, UC Davis, One Shields Avenue, Davis CA *Corresponding author : sebastian.saa@pucv.cl Index Zinc Experiments that our lab has done in this area What & Why?? Results and discussion Conclusions 1 1

2 Zinc functions Cell division and chlorophyll biosynthesis (Boardman and McGuire, 1990; DalCorso et al., 2014; Mattiello et al., 2015; Sadeghzadeh, 2013). Auxin metabolism (Skoog, 1940; Tsui, 1948; Wu et al, 2008). Fruit set (Ashraf et al, 2013; Omaima and El Metwally, 2007; Omar et al., 2015; Wojcik, 2007). 2 Zinc availability and mobility challenges In the soil ph dependent Common tree deficiency in alkaline soils (Sanchez et al., 2006). In the plant Mostly reported as immobile element (Orphanos, 1975; Wadsworth, 1970; Zhang and Brown, 1999a, b) 3 2

3 Even when mobile Only 7% of applied Zinc was recovered in perennial structure of peach trees (Sanchez et al., 2006). Only 3.5 % in walnut (Zhang and Brown, 1999a) Only 6.5 % in pistachio (Zhang and Brown, 1999b) 4 This low mobility issue has motivated our studies in the area 5 3

4 Our research experiments Exp. 1: Establish a model growth system to test Zn mobility of foliar applied products 6 Before treatment 7 4

5 After treatment Collected non-sprayed tissue and analyzed its Zn %. 8 Testing the efficacy of foliar Zn fertilizers: Meta analysis (the RH% needed to remain in liquid phase) 9 5

6 There is a direct relationship between efficacy and toxicity potential Zinc Nitrate - Efficacy is proportional to toxicity. -There are Zn products on the market that are entirely safe AND largely ineffective. Zinc Sulfate -High efficacy products can be used at lower rates with more frequent applications. -Greater attention to prevailing environmental conditions. 10 Our research experiments Exp. 2 Reproductive growth effects on Zn absorption and retranslocation. 80 almond spurs Zn(NO 3 ) 2 at final Zn concentration of 500 ppm ZnSO 4 at final Zn concentration of 500 ppm Sampled tissue Summer Treated tissue 11 6

7 Our research experiments Exp. 2 Reproductive growth effects on Zn absorption and retranslocation. Zn(NO 3 ) 2 Table: Spur type Treatment Time (days from treatment) Sampled tissue Non-fruiting Control 4.40a 4.39a 4.44b 4.32a Non-fruiting Zn-treated 4.58a 4.77a 4.85b 5.29a Fruiting Control 4.39a 4.42a 4.38b 4.44a Fruiting Zn-treated 4.57a 5.29a 6.63a 5.72a P.S.: Natural abundance of the Zn: 67 Zn ratio (4.59) Main conclusions: Remobilization of Zn is enhanced when sink demand (fruit) is stronger. This effect was only significant with Zn(NO 3 ) 2, but not with ZnSO Working idea We have previously shown (Saa and Brown, 2014) that leaf nitrogen is drawn by the fruit in fruiting spurs. We believe that this N fruit demand improves Zn mobility in almond spurs as supported by our Zn(NO 3 )

8 Our research experiments Exp. 3 Vegetative growth and Zn movement 96 actively growing relatively uniform almond shoots were selected Sampled tissue above Sampled tissue below Treated tissue Source: free stock photogreen leafy branch white image Main conclusions Significant Zn remobilization above and below the treated leaf while active growth occurs. 15 8

9 Our research experiments Exp. 4 Conduct of targeted field validation: Almonds Applications were done in Spring of Season 1, and Spring and Fall of Season 2. Leaf samples were collected at the following season each year before spraying. 16 Main results & conclusions Spur Type Spurs with no fruit Spurs with one fruit Spurs with two fruits Leaf Zn (ppm) in a 20b 16c Lower Zn concentration observed in leaves from fruiting spurs than in leaves from non fruiting spurs. 17 9

10 Main results & conclusions Effect of 2009 and 2010 sprays in 2011 Zn concentration Several targeted Zn applications are needed to overcome a Zn deficiency in non-sprayed tissue (i.e. new growth). 18 Final conclusions (Summary) Not all commercially available Zn formulations are effective to remobilize this element to non sprayed tissues. Check de POD and the concentration! Sink presence (fruit) and active shoot growth increases Zn mobility. There is strong evidence that Zn mobility is enhanced with nitrogen: Supported by the above experiments and current literature: Zinc chelating nitrogenous compounds or increased abundance of zinc transporters (Kutman et al. 2011; Kutman et al., 2010)

11 Final conclusions (Summary) Reduced Zn concentration is observed in leaves from fruiting spurs. Several years of Zn applications are needed to significantly detect carry over benefits in almond orchards. 20 Our research experiments Exp. 5 Nano X ray fluorescence imagery Micro: SSRL Stanford Synchrotron Radiation Lightsource, CA, USA

12 Testing the Relative Efficacy of Zn Formulations Contamination of petiole was prevented with lanolin and Teflon film. Zn labeling Zone Plants maintained at 90% humidity. Contrasting POD tested 300 ppm Zn Nitrate, Sulfate, Chloride). µxrf performed on cryo sectioned petiole at Stanford Synchotron Beam size : 2*2um Dell time: 300ms Step size: 8 um Sunflower leaf 22 Control ZnSO 4 ZnCl 2 Zn(NO 3 ) 2 Control ZnSO 4 Phloem Zn Loading ZnCl 2 Zn(NO 3 )

13 Hening Hu, Scott Johnson, Shengke Tian, and Victoria Fernandez Contributions from Lingli Lu, Thomas Sotiropoulis, Thomas Eichert, Javier Abadia Funding from AgSpectrum, USDA, CDFA, IFA 24 13