Topdressing fertilization for soybeans

1. Objetivo

This guide aims to show the workflow that must be followed to obtain a top-dressing prescription map for soybean cultivation. Both the process for satellite in Layers and for drone are explained.

2. Satélite

2.1 No samples

For the completion of the topdressing fertilization deliverable, for soybean cultivation, with satellite imagery as the base layer and without foliar samples to adjust the dosage, the following steps must be followed:

  • Find the plot of interest in Layers

Figure 1. Select cover crop deliverable

  • Select the date closest to the present time that does not contain clouds. You must enter the kg of the product to be applied (in kg/ha) and its content.

  • Select the class for which we define the kg/ha we want to apply. By default, middle class is defined. If we select minimum class, the amount we enter will be considered the minimum contribution we want to make. If, on the contrary, we select maximum class, it will be considered that the indicated contribution corresponds to the maximum that we want to apply in the field. In these cases where we do not select the contribution as middle class, the dosage is corrected as follows:

    • We select middle class

    • Upper class: +20%

    • Middle class: the contribution we indicate

    • Lower class: -20%

    • We select lower class

    • Upper class: +20%

    • Middle class: +10%

    • Lower class: the contribution we indicated

    • We select upper class

    • Upper class: the indicated contribution

    • Middle class: -10%

    • Lower class: -20%

  • The resolution parameter refers to the pixel size of the resulting Shp.

Figure 2. Cover crop parameters

  • Once we have all the parameters defined, the deliverable is requested in PDF format or Shp format (if we want/can input it into our tractor for variable rate fertilization).

Figure 3. PDF format deliverable

Figure 4. Deliverable in Shp format

2.2 With samples

For the completion of the topdressing fertilization deliverable, for soybean cultivation, with satellite imagery as the base layer and foliar samples to adjust the dosage, the following steps must be followed:

  • Locate the plot of interest in Layers.

  • Select the date closest to the sampling that does not contain clouds (not more than 20 days away from the foliar sampling date [before or after]). You must enter the kg of the product you want to apply (in kg/ha) and its concentration. Note that in order to correct the dosage with foliar samples, laboratory results must have been previously entered through the Hemav gauging APP.

3. Dron

To request this deliverable, ‘fertilizer recommendation’ must be marked in MOM and, for the time being, inform the reference KAM that foliar measurements have been entered in the measurement APP so that it can be notified to the processing department since, at present, dosage correction with samples is not automatic.

3.1 No samples

If you want a top-dressing prescription map using drone flight data as the base layer, but you don’t have samples, a dosage calculation will be performed. The client must enter in MOM the dosage they plan to apply (same as in Layers). With this information, the amount of fertilizer to be applied in the field is adjusted according to the classes found in each zone (see table 1).

3.2 With samples

If a top-dressing fertilization deliverable is desired, using the data provided by the drone flight as the base layer, and we have foliar measurements, an adjustment will be made to the dosage that the client indicates in MOM. To request this deliverable, it is necessary to have entered, through the measurement APP, the results provided by the laboratory. Note that a minimum of one sample per class (5 samples) is needed for each plot.

Once we have this data, the procedure to follow is:

  • An average of these samples is calculated for each macronutrient.

  • These samples are classified according to their range (from deficient to excessive).

  • The appropriate corrective treatment is applied to the samples and the kg/ha to be applied are calculated (see table 2).

  • It is entered into our system and correction by zones is applied using the drone flight.

4. Correciones según clase

4.1 No samples

The correction applied to the dosage entered by the client is made depending on which class each zone belongs to. Zones that show, for example, excessive content of a macronutrient will have a correction applied to reduce the amount of fertilizer to be applied. The objective of these top dressings is to homogenize the entire plot and save on fertilizer.

The following table summarizes the corrections, by class, that are applied for N, P and K.

Table 1. Corrections by class (%) for plots without foliar samples

4.2 With samples

Para realizar la corrección en las parcelas que sí cuentan con muestras foliares se sigue la misma lógica que en la corrección de aquellas que no tienen muestras. Se define en que clase esta cada zona de la parcela (de deficiente a excesivo), según unas tablas contrastadas con bibliografía, y se aplica el correctivo que le pertoca. El objetivo de estas coberteras es el de homogeneizar toda la parcela y ahorrar en fertilizante. Cabe notar que se necesita mínimo una muestra por clase (5 muestras) para la realización de este entregable.

The following table shows the different ranges by which soybeans are classified according to N, P, and K content (in %):

Table 2. Corrections according to class and macronutrient content (%) for plots with foliar samples

5. Momento óptimo para la realización de coberteras

To apply topdressing in soybeans, certain optimal times are considered. These times will depend on which period of the phenological cycle the plantation is in.

The important thing in soybean fertilization is to have good availability of P and K since N is provided through BNF (Biological Nitrogen Fixation).

Phosphorus accumulates steadily at high rates until a stage slightly after the cessation of N absorption, becoming significant about 15 days later in relation to the latter. Maximum accumulation rates occur during grain filling and only decline towards the end of this period. Approximately 75-80% of the total P accumulated in soybean plants is absorbed between V10 and R6 stages.

The dynamics of potassium in the plant is similar to that of P, with around 75-80% being absorbed between stages V10 and R6. At harvest time, approximately 50-60% of the total K absorbed by the plant is found in mature seeds.

Therefore, the optimal timing for topdressing applications of P and K (theoretically N would not be necessary) would be between V10 and R6. Knowing that the critical period during the soybean cycle occurs between R4 and R6-7, it would be recommended to perform these applications just before the critical period begins (between V10 and R2-3) to give the plant time to absorb the nutrients.

If desired, foliar analyses could be performed before applying the top dressing so that this fertilizer application could be better adjusted.