Small grain leaf analyses tell a story

Nicola Kotzé, Senior Agronomist

Dr. Elmi Lötze, Head of ITEST™CARBOHYDRATES and ITEST™LEAF

Leaf analyses speak volumes

Leaf analyses  on small grains can identify mineral deficiencies even before visually observed, allowing farmers/growers to address deficiencies at an early stage, thus saving costs.

Leaf analyses are generally used with great success in permanent crops, as well as vegetables, to improve the efficiency of fertiliser programmes. In the U.S.A., successful grain farmers have already started with  weekly leaf samples for  precision management.

According to OPDT (Oil & Protein Seeds Development Trust), the fertiliser cost for wheat production amounts to approximately R4 303 per hectare, while the production costs of a Swartland study group reported  approximately R2 636 per hectare (33.5 % of the total allocated costs) for the 2023 season. Significant input is thus required for the  expected yield and needs to be well managed to ensure profits.

Leaf analyses can contribute towards  effective management of fertiliser costs and increase in  yield. A local trial conducted by Dr. Theunis Vahrmeijer in the Swartland showed  that copper (Cu), zinc (Z) and boron (B) applications during tillering, improved yields from 3.03 t/ha to 3.3 t/ha. This supported a similar study conducted elsewhere which found that microelement applications positively impacted yield (Ziedan, 2010). The positive impact of microelements was linked, not only to deficiency symptoms , but also illustrated that supplementary applications during critical times can boost yield.

Timing of leaf analyses

The following principles generally apply to top small grain farmers:

• Application of organic fertiliser at least once every 5 years;
• Use of variable technology, such as planters, for differential fertiliser applications;
• In furrow application of biostimulants;
• Leaf analyses; and
• Implementation of required amendments.

It is crucial to take leaf samples for mineral analyses during tillering, stem extension (1st node) and flag leaf. The potential of the wheat yield is developed early during the tiller phase. Mineral deficiencies experienced this early in the season can already adversely impact yield potential. The appearance of visual deficiencies on the leaf, for example stripes on the flag leaf, means that the yield potential has already been reduced. If the deficiencies are detected early, they can be addressed before it becomes a critical nutritional concern.

Value of analysis results

Determining the levels of nitrogen (N), phosphate (P) and potassium (K) in the leaves provides various insights. The more information is gathered per farm, the sooner (earlier in the season) the fertiliser programme can be adapted by incorporating the leaf- and soil analysis data into the programme, to create a more effective programme and thus better plant performance.

The levels of other macroelements for example calcium (Ca), can be an indication of plant root development. Where climatic conditions and soil analyses are sufficient, but a Ca deficiency is still present in the leaves, the cause can be attributed to poor root development in many cases. The cause for the poor root development should then be addressed, rather than simply applying more Ca.

According to Liebig’s Law of the Minimum, the yield of a crop is determined by the most limiting factor. Over-fertilising with N is therefore a waste of resources if there is a copper (Cu) deficiency, as the yield will be equal to the Cu level present.

Foliar nutrition – a timely and fast way to address deficiencies

Deficiencies in microelements can be addressed easily by applying foliar nutrients because the amounts required are relatively small and the effect on leaf concentrations is fairly rapid. During flag leaf, the biomass above ground  is about 5 000 kg/ha. To raise the Cu level with e.g., 15 mg/kg, 75 000 mg/ha (75 g/ha) Cu will be required at a 100% absorption rate, which never occurs. In this instance, foliar applications  offer a more efficient solution. By applying a specialised single-element foliar spray product containing 90000 mg/L, at 1.5 L/ha, 135 000 mg/ha of Cu is applied in total, which is enough to raise the levels sufficiently. The effectiveness of foliar sprays can be increased even more by complexing elements.

In instances where the exact requirements of the plant is not known, producers often use a shotgun approach and apply a combination product, which usually does not contain sufficient nutrient levels. When using products that contain a broad spectrum of elements, Cu is normally applied at 600 mg/kg, while the recommended dosage for the combination product is 3 kg/ha. Thus, only 1800 mg/ha of Cu will be applied which, in terms of the example above, is not sufficient.

What about sap analyses?

For mineral analyses, tissue- rather than sap analyses are used. There are several reasons for this.

• A sap analysis has very high variation and can pose a challenge when used as a base for decision-making. A study during which maize under moisture stress was compared to maize with sufficient moisture, found that xylem sap provided variable results (Goodger, 2005).
• Sap analyses are not as accurate as tissue analyses (Hochmuth, 1991).
• Sap analyses provide information regarding the uptake of the specific elements by the plant and the elements that are available for metabolism. Tissue analyses, however, also provide information regarding the utilisation of the available elements by the plant organ.

Summary

By analysing the soil physical and chemical factors, it is possible to predict future development of the plant. However, the climatic conditions still play a significant role in the uptake of elements from the soil and the plant’s reaction to adverse environmental factors, and therefore, could impact the prediction.

Leaf analyses make it possible to determine with certainty the nutrient status during a given growth stage. Thus, the former is critical for good plant performance. It makes it possible to do accurate and targeted corrections within 7 days so as to achieve the full crop potential within the given season.