At the recent 2019 GRDC Updates Wagga Wagga, Jason Condon from the Graham Centre for Agricultural Innovation discussed effective soil sampling methods and some cost-saving options. Soil tests provide the analytical data used for efficient nutrient and soil management of agricultural land.
Traditionally, a multicore composite sample was taken from many sites in a paddock and sent to an accredited laboratory for analysis. More recently, grid sampling has been used to create high density, fine-scale samples and subsequent variable rate recommendations. But this form of sampling comes at a cost. If we use our knowledge of soil formation and landscapes, we may be able to account for spatial variability at less expense.
In his Updates paper, Jason discusses identifying zones within and across paddocks which require separate management. These zones may be identified by production (areas of good or bad growth), soil and landscape properties (colour, texture, slope) or history (consolidation of smaller paddocks into fewer but larger paddocks). Once identified, each zone can be multi-cored to produce separate composite samples for analysis, interpretation and management recommendations.
There are free or low cost tools available to help identify zones for sampling and potential management. Google Earth can be used to see years of past history for an area, including where previous fencelines, vegetation or management practices may have been. Free normalised difference vegetation index (NDVI) images and yield maps are also useful to identify different production zones due to variations in soil properties.
Jason suggests that these tools, along with in field observations and farmer knowledge, can help identify a small number of zones. These can then be sampled using composite cores and tested to see if manageable differences exist. Based on that analysis, the zones can be classed into management areas requiring different inputs, increasing production efficiency.
This approach should also lead to fewer soil samples being taken than grid sampling, which saves time and money. These savings may be used instead to sample and test to a greater depth in the profile, or to test at finer depth increments to identify issues like nutrient or pH stratification.
Jason’s full paper can be found at Effective soil sampling – high and low cost options