Co-authored by Retta Brugger, CSU Range Extension Specialist & Julie Elliott, CO NRCS Rangeland  Management Specialist 

How can you make well-informed decisions for summer grazing?

We all know that 2020 was a drought  year in Colorado. Soils are dry and will need to be refilled. When do we need the moisture for summer  grass? How can we plan for the 2021 grazing season?  

Cooperative Extension research across the High Plains found that cumulative precipitation up to 30 days  before peak grass growth has the most impact. For Eastern Colorado, peak grass growth is in June and  July. That means the moisture received to mid-June sets the stage for summer grass growth. This is also  true for SW Nebraska and Western Kansas. 

Can you make stocking decisions in April?

But it would be helpful to anticipate what might in store before May and June. Results from 70+ years  of research from the Agricultural Research Service (ARS) range in Nunn, Colorado, may help. It turns out  that long-term climate trends such as La Niña/ El Niño and the Pacific Decadal Oscillation (PDO)**, are  important. In fact, these ocean temperature cycles explain 70% of yearling weight gain differences! 

Researchers used this data to create a decision tree to help them make decisions before the growing  season. They watch the El Niño/ La Niña and PDO cycles and moisture conditions through the winter.  Then in early April, they use the decision tree as part of their stocking discussion. 

The 2021 Stocking Decision Tree

Let’s look at the decision tree for 2021. The Pacific Decadal Oscillation is still in the warm phase.  Forecasters report that La Niña is strong. (La Niña is correlated with below average winter moisture for  Colorado.) The decision tree suggests that the stocking rate should be decreased relative to moderate.  Ocean activity indicates that drought conditions are likely to persist.  

2021 Grass-Cast (Grassland Productivity Forecast) Tool

Another tool ranchers can use is Grass-Cast. Grass-Cast, or Grassland Productivity Forecast, has over 30  years of historical data about weather and vegetation growth. It compares that data with current year  precipitation to create three production forecast maps. Each map indicates the expected grass growth  based on above-normal, near-normal, or below-normal summer rain.  

Grass-Cast Maps show early signs of opportunity or challenges

The first Grass-Cast maps for 2021 will be released in April. These maps can identify areas where there  are early signs of opportunity or challenges. The bi-weekly maps become more accurate as more  rainfall is recorded. By May 30, the average accuracy of the maps improves to 70%. 

The decision tree, understanding timing of moisture and grass growth, and Grass-Cast are all useful tools  to help ranchers make timely grazing decisions. Responding early to drought can help protect financial  and rangeland resources into the future.  

Resources:

Learn more from CSU Extension Early Warning for Stock Decisions article here and print or save the Drought Stocking Decision Tool in pdf format here.

Learn more about Grass-Cast (Grassland Production Forecast) maps and tools here.

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