How are productivity maps used?
- 1 Applications & Benefits
- 2 The decision making process
- 3 Limitations
Applications & Benefits
Productivity maps can help to understand variability within a field or management unit and support management decisions. By understanding within field variability, there are different ways in which these maps can be used:
Analyze variability and evaluate management alternatives
Understanding the variability within a field is the main application of productivity maps, based on crop history and remote sensing. This allows to evaluate diverse decisions regarding how to address and manage the causes for variability. The following items are examples of the types of decisions that can be taken:
- Modify the uses of the field and/or management units
- Select areas for on-farm research
- Support renting/lease decisions.
- Selecting soil sampling points
- Variable rate seed and fertilizer application
- Selecting sample sites for leaf / plant sampling
- Selecting moisture probe points
- Irrigation scheduling
- Deciding where to dig soil profile pits
- Drainage system and points
- Crop rotation strategies
- Hybrids selection by management zone
- Monitoring effect of irrigation on crop
|Waterlogging and Drainage issues can be a cause of variability (Photo: Francis Yeatman, Aug. 2012)|
Productivity maps provide a viable alternative to more data intensive methods, such as grid sampling or on-site surveys, reducing time and costs to diagnose the causes of variability. Directed sampling based on productivity maps can significantly reduce the number of samples requires, as compared with grid sampling approaches.
One of the main uses of these maps is to use them as a starting point for field visits, planning directed sampling, validating on site the different zones, and with information from the farmer and the consultant, characterize the different types of management zones.
|Productivity Maps are used to define directed sampling locations|
Variable Rate prescription
Specifically related with the use of crop inputs (seed, fertilizes, agrochemicals), it's possible to use productivity maps to generate prescription maps, in order to save inputs in areas with low yield potential and increase inputs in areas with high potential.
The decision making process
Productivity maps can guide the manager or consultant, regarding yield differences in their fields. These differences can be validated in the field, management zones delineated, and then take management decisions. The decision making process has three main activities:
Recognize the differences - generate the productivity map
In this step, the productivity map is generated to recognize variability within fields. This entails an analysis in each field based on remote sensing, and crop history, detailed oin this article.
Optionally, relative differences can be quantified if there is yield data available. By overlapping yield data on productivity zones, and summarizing results, we can determine the average yield by producitivity zone, and eventually group 2 or more zones into one class, to simplify the map and narrow down the focus on issues.
Field visit - Characterize management zones
In this step, Productivity zones are validated in the field, to derive management zones.
It's recommended to work together with all the involved parties, the farmer, managers, or consultants, visiting the field with a GPS, evaluating differences shown in the productivity maps recognizing causes for variability, and characterizing management zones. Some aspects to consider are:
- Regional limiting factors can be taken into account for management zones characterization (e.g.: landscape position, soil types).
- Directed soil and/or tissue sampling can be carried out to gather additional data and fine tune recommendations.
- Productivity maps classes can also be grouped into one management zone to simplify the management focus
As a result of this step, management zones are defined, and attributed, which is the basis to evaluate management alternatives.
Take management decisions
In this final step, gathered information is analyzed to take management decisions. These can be grouped in two major areas:
- General decisions, that do not require Variable Rate Technology (VRT).
This would involve for instance, dividing the fields in broad areas, where different decisions are implemented, such as adopting a crop rotation strategy, hybrid selection, seeding dates, drainage or irrigation management, etc. .
- Creating Prescription maps for Variable Rate application, optimizing inputs according to the field potential.
This would include for instance variable rate application of P, N, seed, or micronutrients.
There are a couple of limitations to consider:
- Imagery availability on the right dates can be a limiting factor in certain occasions, in most cases the available image banks can provide the historical information needed.
- Productivity can be evaluated within fields only, and not between fields. The main reason is that in a given farm, fields may have at the same time different types of crops or uses. Thus, NDVIs from different fields cannot be compared. For this reason different images are selected for different fields. As a conclusion, productivity zones maps should only be used to compare variability within fields, but not as a means of comparison between different fields.