Effective use of foliar nutrition of citrus orchards requires correct application practices. By Hannes Coetzee (JGK Consulting) and Pieter Raath (CRI)
This article provides a summary of guidelines that must be followed for successful foliar nutrition applications.
Concentration of application
Refer to Table 1 for the minimum effective, and highest safe concentration at which the different nutrients (and products) should be applied. Products must be applied at this appropriate concentration.
Read MoreTable 1
| Optimal droplet size: | Pressure < 8 bar | Whirl plate 56 | Orifice of spray nozzle = 2.3 mm Ø |
| Climatic conditions: | Humidity as high as possible | Temperature as low as possible but above freezing point |
To avoid run-off loss of the spray mixture, apply 10 spray mixture per mature tree, for maximum uptake. Use the following guidelines to obtain maximum contact time between the spray mixture and the leaves.
Note that in Table 1 the proven and effective products are listed. Amongst the formulations tested by Van der Merwe (2016), the inorganic salts (SO42- and NO3- formulations) were found to be most beneficial if both efficacy and cost are considered.
Additives
Only use additives that will increase the contact surface between droplet and leaf. Do not use surfactants that will decrease volume load on the leaf, or result in small drop sizes that cause rapid drying off.
Apply cations (K, Mg, Cu, Mn and Zn) at a pH of 5.5 to 6.5, and apply P at a pH of 3.0 to 4.0; and use a pH buffer when required.
Table 2
| Compound in mixture: | LB Urea | ZnSO4 | MnSO44 | Copper oxychloride | Solubor |
| Dosage (g/100 ℓ): | 500 | 100 | 100-200 | 75 | 150 |
Simultaneous application of micronutrients
Below, a mixture that will ensure efficient, cost-effective simultaneous application of all the micronutrients is provided, but apply only those required as indicated by leaf analysis.
References
- Coetzee, J.G.K. 2007. Fertilisation of Citrus. CRI Citrus Production Guidelines, Vol. 2. CRI, Nelspruit.
- CRI, 2021. Handbook for Fertilisation of Citrus in South Africa. CRI, Nelspruit.
- Peryea, F. J. 2006. Phytoavailability of zinc in post bloom zinc sprays applied to "Golden Delicious" apple trees. HorTechnology 16(1), 60-65.
- Van der Merwe, S.M. 2015. The uptake of different formulations of applied micronutrients by Citrus sinensis (L.) Osbeck cv. Valencia. Thesis MSc Agron., Faculty of Natural and Agricultural Science. University of Pretoria.
