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There Are Only Three Ways To Increase Carrying Capacity

Reprinted from The Stockman GrassFarmer |

Pasture Irrigation



May, Idaho: We often think there are a lot of different ways we can increase pasture or livestock productivity; However, when we get down to the nitty-gritty of it, there are really only three avenues for increasing the carrying capacity of the farm or ranch.


I think every reader understands the basic concept that water makes grass grow. We know that every year there is variance in the amount of rainfall we receive and the timing of when it comes. From weather records, we have an idea of what the average precipita­tion for our area is supposed to be.


I cannot count the number of times someone has said to me: 'The weather service says our average rainfall is xx inches per year but it has been a long time since we have seen that much”.


Guess what? “Average" rainfall and "normal" or "median" rainfall are two different things. In a continental cli­mate, "normal" rainfall is 10-15 percent below the long term average in seven out of ten years. Hence the rare experience of receiving "average" rainfall.


Last month we looked at how to get more water into your soil and then keep it there for future plant growth. The amount of rainfall or snow that actually infiltrates into the soil is called "effec­tive" precipitation. I had outlined the basic role of keeping the soil covered and building organic matter in the soil for increasing effective precipitation. That is the first step towards increasing carrying capacity: increase effective precipitation.


An inch of water has the capacity to generate a certain amount of forage within different precipitation or irriga­tion regimes. Up to a point, each addi­tional inch of water we put into the soil yields a higher level of forage growth per inch of water received. This might seem counterintuitive as some people seem to think that an inch of water has more value in a dry environment than in a wetter locale.


Somewhere between 30 and 40 inches of total water, the pattern changes and each additional inch of water generates less and less yield per inch until yields actually start to decline due to too much water in the soil. There are several factors that come into play to create these results.


One of the first factors is the basic plant physiology of plants adapted to dry vs. wet environments. Dry land plants (or wet country plants facing drought) partition more of the carbo­hydrates (energy) derived from photo­synthesis to root growth and less to top growth. The more leaves a plant has, the more water it will transpire.


Long term survival of a perennial grass in a semi-arid environment is based around a large and durable root system relative to the above ground portion of the plant. Thus an inch of water in a dry environment has greater yield below ground than above ground. The plant is still responding to that water, you just don't see it as added carrying capacity.

If we think about how rainfall gener­ally occurs in semi-arid regions, we find it typically occurs as smaller rainfall events. In the last 11+ years in Idaho, I have seen vey few precipitation events in excess of one inch in 24 hours whereas those were very common throughout my years in the Midwest.


A smaller rainfall event does not infiltrate into the soil as deeply as a larger event thus leaving greater oppor­tunity for evaporation to pull that bit of moisture out of the soil. In other words, a one inch rainfall event can have' more yield benefit than ten 0.2 inch rains spread over a month or two even though the total moisture received is twice as much in the scattered shower scenario.


Combine the low precipitation regime and propensity for evaporation and we get a low forage yield. If the overall forage yield is low, it is much more challenging to have enough left over forage after grazing to create a litter layer so the cycle keeps repeating itself.


The second avenue to increas­ing carrying capacity is to increase the yield of forage per inch of water received. We accomplish this by using adapted plant species, ensuring ade­quate fertility in the soil, but above all other factors, employing sound grazing management to allow pasture recovery following each grazing event.


Sometimes graziers will contend that fertilizer or reseeding pastures, in and of itself, will increase carrying capacity. Those types of practices only work in conjunction with adequate soil water. I would argue that fertilization and interseeding are tools we use to enhance the yield per inch of water.


The third opportunity for increas­ing carrying capacity is to increase the seasonal utilization rate on the pasture. This is accomplished entirely through changing the basic grazing management strategy. In high natural rainfall or irrigated environments this is accomplished through shortening the length of the grazing period and increasing the number of grazing cycles in the year.


Multiple harvests of roughly 50 per­cent of the biomass will almost always yield more stock-days/acre with higher individual animal performance than will a single harvest at 70-80 percent temporal utilization rate.


In rangeland environments, we increase seasonal utilization rate by improving the uniformity of grazing across the landscape. This is accom­plished primarily by increasing the availability of stock water within and across the landscape. Grazing distri­bution on large range tracts is driven primarily by travel distance to water with the terrain of a specific unit deter­mining what the optimal distance for that particular pasture to be.


What this tells us is we have three main focus areas in grazing manage­ment when it comes to increasing the overall carrying capacity of our farm or ­ranch: increase effective precipitation, improve forage yield per inch of avail­able water, and optimize the seasonal utilization rate for our locale.


Jim Gerrish can be contacted at

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