Precision soil sampling involves adjusting farm practices to manage variability at smaller increments within a field – with the goal of improving crop performance and environmental quality
Soil mapping and its application to crop production
Soil sampling is an important step in site specific crop management as variability in the soil can often be directly correlated to variations in yield. Traditional soil sampling consists of collecting samples from across the field to understand the nutrient and pH levels and usually results in uniform application of lime and fertiliser. Treating the field as one uniform medium can often result in an over or under application of plant nutrients
Precision soil sampling occurs by geo referencing soil samples from the area where the sample was taken using a GPS system. This allows growers to manage in field variability through optimising nutrient and lime inputs based on site characteristics
There are two methods of precision soil sampling; grid sampling or management zone sampling. These will ultimately provide data that is fed into a map, that when used with a variable rate application machine, will allow you to target applications to where they are needed.
Grid sampling method
This method divides the field into areas of a defined size using Geographical Information Systems (GIS) software. Soil samples are taken from within each grid area. The grid ID is then matched with the ID of the soil sample
- Gives the ability to assess nutrient variability that is present in the field
- Identifies problem areas
- Minimises excessive nutrient applications
- Targets input where it is needed
- Requires minimal skill to undertake
- No justification for grid sizes
- The grid is placed in the field by chance
- Method ignores soil properties and field characteristics
- Labour and time intensive
Management zone method
The field is divided into regions based on soil and / or yield properties determined by the farmer. Zones are created within a GIS system, and samples are taken for each zone. The zone ID is consistent with the sample ID
- Zones are categorised based on performance in the past and intrinsic properties
- System allows for spatial variability
- Reduced time and labour required
- More economical
- Greater initial time and financial investment to implement zone management
- Higher skill level is required as inputs of field characteristics are needed
- Requires field knowledge
How do I choose the best method?
Consider grid sampling if:
- Previous management on the farm has significantly altered soil nutrient levels. This may be things like heavy manure applications, or confined livestock
- Small fields with different cropping histories have been merged into one
- You need an accurate base map of soil organic matter
Consider management zone sampling if:
- Yield maps, remotely sensed images, or other sources of spatial information are available and these show consistency from one layer to another
- You are experienced enough to decide where to put the boundaries for the different management zones
- There is limited or no history of livestock N manure influence on the field
Prescription maps and soil sampling
The different methods of soil sampling all feed into a prescription map. This map provides the rate and application location information to the controller, and tells the variable rate equipment where and how much to apply. The maps are created using GIS software and they link the soil test recommendations to appropriate grids or zone.
Things to consider with soil mapping
- Time and financial investments
- What information is available?
- What equipment is needed to make use of the information created by the maps?
- What will the net return be on my farm on the investment?
- Is the field suitable to precision sampling?