Assumptions around the soil information for some Canterbury soils may need to be rethought, research by Lincoln University PhD student Balin Robertson indicates.

Balin said stony soils are used extensively for irrigated agricultural purposes, especially in Canterbury.

His results imply that soil water storage in these soils may have been under-estimated, with potential implications for efficient irrigation and nutrient management.

He said previous assumptions about how water is stored in these soils is wrong.

“They may be capable of storing slightly more water than previously thought.”

“We had assumed water retention in stony soils is only from the fine earth between the stones. But on average, stones accounted for around 10% of water retained to a depth of 60 cm in Canterbury stony soils.”

Previously no research had quantified the water storage of these soils.  This information, he said, is key to efficient irrigation and management of leaching losses.

What remains to be confirmed is how dynamic this water held in stones is: if it enters and leaves the stones in tune with the needs of plants then it should be taken into account when irrigating and estimating leaching losses.

Balin said the objective of his study was to fill this research gap, providing farmers and regulators with robust data for nutrient budgets (such as Overseer), farm environment plans and irrigation management.

To do this, he dug 52 soil pits at 24 pastoral sites across the Canterbury region, completing a set of intricate measurements in 10 cm increments down to 60 cm depth.

A key output of this study will be using Balin’s results to improve the soil information supplied by S-map, the national soil information system which many farmers use to supply their soil information.

Source:  Lincoln University