Dr FG Adriaanse, for Kimleigh Chemicals SA (Pty) Ltd
Micro-elements
Scientific tools for identifying essential micronutrient deficiencies are:
- Soil analyses, according to specific extractions
- Leaf analyses based on dried material
- Leaf sap analyses
At the same time, the following factors affecting the uptake by plant roots and assimilation within plants should be considered:
- Boron (B) leaches very easily while the difference between sufficiency and toxicity is as little as 2 mg/kg in the soil.
- Molybdenum (Mo) is inaccessible under strongly acidic soil conditions and can also leach.
- Zinc (Zn), manganese (Mn), copper (Cu), boron (B) and iron (Fe) are inaccessible under strongly alkaline soil conditions.
- The herbicide, glyphosate, binds zinc and manganese in plants and in the soil with very strong chelated bonds, making it inaccessible.
- Micronutrients in the sulphate form will bind with monoammonium phosphate (MAP) in a fertilizer band or with technical MAP in a plant mixture or in foliar sprays to form insoluble phosphate compounds which cannot be taken up. This problem applies to zinc, manganese, copper and iron sulphates.
Considering the above factors, it was decided to test two micronutrient compositions for maize according to very specific formulations and ratios to each other, in the Bothaville area, during the 2021/2022 season. The quantities of micronutrients applied were based on maize grain removal figures for 6,000 kg/ha.
Materials and methods
Treatment 1* consisted of boron and molybdenum only, because most standard dried leaf analyses only indicate deficiencies of these elements in the environment. The products, Boron Metalin 150 and Molybdenum Metalin 200 were pre-mixed for this treatment (Figure 1). The cost of Treatment 1 was R129.44/ha, by March 2023. These products are not ordinary salts but also very specifically formulated for sticking, spreading on leaves and penetration into leaves.
Treatment 2 consisted of zinc, manganese, boron, copper and molybdenum because deficiencies of these elements were indicated by leaf sap analyses and were also expected. This treatment contained less boron and molybdenum, but also Zinc Metalin 700, Copper Metalin 500 and Manganese Metalin 500 (Figure 1). The cost of Treatment 2 was R124.97/ha, by March 2023. The additional elements in Treatment 2 (zinc, manganese and copper) are nano-formulations. The advantages of nano-formulations over other formulations were reported by Adriaanse, 2022 in Grain SA, July publication. As with Treatment 1, the products are specifically formulated for effective foliar application.
Kimleigh’s Metalin product range includes mainly suspension concentrates which need to stirred continuously during application. The amount of water used in this trial was 100 litres/ha although 200-300 litres of water/ha is recommended. Treatments were sprayed between growth stages V8 and V10. Metalin products are recommended up to growth stage R3 for maize.
Metalin formulations should not be applied with glyphosate. Kimleigh’s Microton products which contain zinc, manganese, boron and molybdenum can be applied with glyphosate and are water soluble, but was not tested during this trial. A randomized block design, with four replications were used. Results were statistically analysed.
Results
The yield increase with Treatment 1 was 215 kg/ha and with Treatment 2 it was 494 kg/ha (Figure 1). At a realised maize price of R4,000/tonne, the value of the yield increases is R860/ha (Treatment 1) and R1,976/ha (Treatment 2) and the return on costs R731/ha and R1,851/ha for Treatment 1 and Treatment 2 respectively. The yield increase for Treatment 2 was also statistically significant at 90% certainty, which is a good indicator of repeatability of results.
Conclusions
- Boron Metalin 150 + Molybdenum Metalin 200 application was economically justifiable, but not statistically significant.
- A Metalin micro-element treatment where boron and molybdenum applications were reduced and where nano-formulated zinc, manganese and copper were added, ensured return on input cost as well as statistical reliability.
- Application rates were based on an expected 6,000 kg/ha yield, while the best treatment yielded 8,342 kg/ha. Application rates based on 8,000 kg/ha would probably have resulted in an even better return on input costs.
- Leaf sap analyses are probably a better indicator of micronutrient deficiencies than standard dried leaf analyses or soil analyses.
Contact Kimleigh for locality specific applications.
www.kimleigh.com; Tel: +27 18 293 1028