Nutrient lost from agricultural systems can reduce waterway quality through eutrophication. The main nutrients involved in eutrophication are nitrogen and phosphorus and there can also be an impact from organic carbon and sediment lost from agricultural soils.

Gypsum has long been used as a soil conditioner and fertiliser in agriculture and horticulture supplying calcium and sulphur as soil friendly nutrients. But it is only in the past decade gypsum’s potential for reducing farm run off has been researched.

This common sulfate mineral applied to pastures improves water infiltration rates and soil aggregate stability which will reduce surface water runoff and reduce phosphorus losses due to the calcium ions in gypsum binding with phosphorus. 

NZ soils are well known to be sulphur deficient, plants require sulphur for protein synthesis. Traditionally, superphosphate has been applied to farmland to address this deficiency. But superphosphate applications raise the concentration of phosphorus in the soil, raising the risk of run off into nearby waterways.  As an alternative, gypsum is a good source of sulphur, which is in a form that is readily available to plants and allows the application of sulphur without the need for phosphorus additions.

Over 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 run off and drainage loss of nutrients from within the soil. Drainage losses can include leaching and water flowing down a slope within the soil, which are affected by complex hydrological and chemical factors.

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

Trials in the Unites 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 as an Agricultural amendment, W A Dick, Ohio State University, USA, Bulletin 945). 

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

Gypsum the multi tasker for use on farms. Gypsum is BioGro certified. 

Talk to your advisor for guidance on gypsum applications based on a recent soil lab test.

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.