A potential “double whammy effect” for farmers engaged in whole-farm testing is emerging from a study carried out by Analytical Research Laboratories (ARL).

The key trend we’re seeing is a narrowing in soil fertility variation between paddocks, meaning the areas that need nutrients are getting them, with the potential to increase pasture productivity and reduce the chance for excess fertiliser leaching,” Rebecca Withnall, Manager Analytical Research Laboratories told the Fertiliser and Lime Research Centre conference at Massey University.

More than 300 farms, predominately dairy, have so far participated in Ravensdown’s whole-farm testing and have adjusted fertiliser applications based on the results. Approximately 15 per cent of those farms have completed a second round of whole-farm soil testing.

ARL focused its initial study on a subset of data comprising dairy farms that have applied paddock specific fertiliser rates and have completed at least two rounds of whole-farm testing, aggregating the data for pH, Olsen P, potassium and magnesium levels.

The spread of results reduced across all components, suggesting that more fertiliser has been applied to the areas of lower fertility and less to the areas of higher fertility.

“The study clearly identifies the benefits of whole farm testing,” Rebecca says. “”While the overall data set is reasonably small, there are clear trends showing improvements for all the components tested.”

Initial results from analysis of whole-farm testing data show fertiliser is going where it is needed, narrowing fertility variation across paddocks.

Ravensdown, which owns Napier-based ARL, began offering whole-farm testing in 2012 to improve the reporting and understanding of soil fertility, which often varies widely across a single property. Agri Managers use the resulting data to create paddock-specific fertiliser application plans, to help farmers optimise their nutrient investment.

Traditionally, fertiliser plans had been generated by sampling a limited number of paddocks to represent the soil type and farm use of the whole-farm. More intensive soil sampling of every paddock allows fertiliser plans to be tailored to the nutrient requirements of specific paddocks. By reviewing the aggregated data from a large number of farms, the benefits of whole-farm soil testing can be evaluated. Current data trends suggest that the variation in fertility between paddocks is reducing over time.

Improved soil fertility leads to better pasture growth and can translate into better financial outcomes for farmers. From an environmental perspective, whole-farm testing data can be input into Overseer and reported to regional councils in accordance with regional plans and policies.

ARL provides soil testing and analysis on about 70,000 soil samples each year.