A multi-purpose product to help manage nutrient run off

This is where an excess of nutrients occur in bodies of water – due to run-off from the land and causes a dense growth of plant life. The main nutrients involved in eutrophication are nitrogen and phosphorus.

Gypsum has long been used as a soil conditioner and fertiliser in agriculture and horticulture, where it supplies calcium and sulphur as soil friendly nutrients.

However, it is only in the past decade that gypsum’s potential for reducing farm runoff has been researched. Applying the common sulphate mineral to pastures improves water infiltration rates and soil aggregate stability. This reduces surface water runoff and phosphorus losses due to the calcium ions in gypsum binding with phosphorus.

NZ soils are well known for being sulphur deficient; plants require sulphur for protein synthesis. Traditionally, superphosphate has been applied to address this deficiency. However, superphosphate applications increase the concentration of phosphorus in the soil – raising the risk of runoff into nearby waterways.

As an alternative, gypsum is a good source of sulphur. It comes in a form that is readily available to plants and allows the application of sulphur without the need for phosphorus additions.

During the past 20 years in New Zealand there has been a substantial reduction in livestock access and effluent discharges into waterways. But nutrient losses can still occur through surface water runoff and drainage loss of nutrients from the soil.

Drainage losses can include leaching and water flowing down a slope within the soil. These are affected by complex hydrological and chemical factors.

High sodium soils can have a detrimental effect on soil structure and water infiltration. Sodium causes loss of aggregation reduces soil pore spaces and may also increase soil pH in severe situations. By displacing sodium, gypsum restores soil particle aggregation and air spaces in the soil.

Trials in the United States, where applications of gypsum alongside moderate nitrogen applications, found it could diminish the nitrate contamination of surface and ground waters and potentially increase yields*.

Gypsum is best used in targeted areas where there is surface water runoff risk and can be most effective in wide strips around run off prone areas. It also is beneficial in effluent treated areas or pugging prone paddocks rather than over the whole farm. Targeting high risk sections of a farm will assist the economic viability of a gypsum application.

Gypsum is described as a multi tasker for use on farms and it is also BioGro certified. Talk to your advisor for guidance on gypsum applications, based on recent soil lab tests.

• Reference: Use of gypsum to reduce effluent and fertiliser nutrient losses to waterways, T A Jenkins, V Jenkins, Fertiliser and Lime Research Centre, New Zealand. 27th Annual FLRC Workshop held at Massey University, February 2014.

*(Gypsum as an Agricultural amendment, W A Dick, Ohio State University, USA, Bulletin 945).