Our Organisation Search
Quick Links
Toggle: Topics

Is the grass always greener?

TResearch Summer 2023

The Moorepark St Gilles Grass Growth Model, or MoSt GG for short, enables farmers to access detailed data to more accurately predict grass growth and adequately prepare for periods of poor growth.

Modelling of grass growth predictions across the country was initiated in response to the climatic conditions seen in 2018; cold weather in the spring and drought conditions in the summer resulted in poor grass growth, causing difficulties for many ruminant Irish livestock farms.

At that time, farmers wanted an accurate tool that would help to predict grass growth over the coming weeks to aid decisionmaking processes at farm level. Thus was born the Moorepark St Gilles Grass Growth (MoSt GG) model, which was used initially on three experimental farms to forecast grass growth for the upcoming weeks, thereby enabling farmers, advisors, and the government to prepare for the significant forage crisis that was then expected in the spring of 2018.

Unfortunately the weather challenges of 2018 didn’t stop with the cold spring. Indeed, the summer of 2018 was characterised by water deficits and high temperatures, bringing more challenges to Irish grassland farmers and generating more interest in the model and its future grass growth predictions.

The regional differences in weather conditions in the summer of 2018 highlighted the need to expand the programme, which resulted in 30 commercial farms having their grass growth predicted by the end of 2018.

TResearch Summer 2023

Providing live data to farmers

PastureBase Ireland (PBI) provides the backbone for the grass growth predictions. PBI farm-specific parameters are used to help populate the model, some of which include: paddocks area, grazing and cutting dates, number of grazing animals and their supplementation, and nitrogen fertilisation (chemical and organic) levels and application dates.

Briefly, the MoSt GG model predicts daily grass growth on grass-only swards (expressed as kg DM/ha; DM refers to the dry matter content of the grass and provides information on the nutritive value of the grass) depending on individual farm weather conditions, soil type, grazing animal type and management decisions. Farmer decisions that impact grass growth within the model, such as nitrogen (N) fertiliser application, as well as the pre- and post-grazing sward heights or the pre- and post-cutting heights, are also used to help improve the accuracy of the grass growth prediction. An added tool of the MoSt GG model is the ability to recreate the nitrogen flow both in the soil and in the plant to predict the N content of the grass, as well as the N leaching at the paddock level. Historical and forecast weather data — provided by Met Éireann — are also used in the model to predict grass growth. Grass growth predictions are conducted at the paddock level and are then averaged across the entire farm with live data available and provided to farmers.

Planning for paddock-specific performance

While the grass growth predictions are currently shown in the form of a precise number, each farm is different. This is why the trend of the grass growth prediction (increasing or decreasing compared to the previous week) is more important than the actual number. A specific farm could be consistently growing less than the prediction but understanding the overall trend and direction of the predictions supports management decision-making.

The incorporation of the MoSt GG model directly into PBI commenced in 2023 and will allow any farmer entering  information inside PBI (at least 25 covers a year, N fertiliser application entered weekly) to avail of their own grass growth prediction based on the specific weather on their farm and their management practices.

In time, this will allow individual paddock predictions and recommendations around specific fertiliser application rates for each individual paddock of the farm to be generated. This will be based on historic performance from that individual paddock and therefore will allow precision grassland advice to be provided on a paddock-bypaddock basis.

During the Moorepark open day on 4 July 2023, the grass growth prediction team will be present and grass growth predictions will be provided and presented. There will be opportunities for farmers to interact with grass growth prediction models.


Funding from Dairy Research Ireland is gratefully acknowledged.


Elodie Ruelle, Research Officer, Teagasc Moorepark Research Centre, Fermoy, Co. Cork.

Main image credit: Nikada/stock.adobe.com.