Plan Stocking Rate Based on Rainfall
Even with the rains during the fall of 2011, much of Oklahoma and Texas is still under drought advisories as we enter 2012. According to the U.S. Drought Monitor, much of the region remains under moderate to exceptional drought. Long-term forecasts are not promising for abundant rainfall during the spring or summer of 2012. Climatologists say that we are in a "drier than average trend" and that it could last for several more years. How are cattle producers to plan for the future? What information can they use to make stocking rate decisions? These are the questions that everyone in the industry should be asking.
How do producers plan for the foreseeable future? First, they must know what is expected for both rainfall and forage production of perennial warm-season grasses in order to balance stocking rates with forage production. Forage production is largely dependent on soil moisture, which is a function of rainfall. Surprisingly, the major period in which soil moisture accumulation occurs for production of warm-season grasses (e.g., bermudagrass, old world bluestems and native grass prairies) is during the fall and winter when the grasses are dormant. It is also why we need to be monitoring rainfall early in the year to determine our approach to managing and stocking our warm-season pastures during the next growing season.
South-central Oklahoma rainfall and perennial forage production is shown in Table 1. There are four major sections in the table: the 30-year average rainfall (from the U.S. Drought Monitor), monthly rainfall for October 2010 through September 2011, monthly rainfall from October 2011 to December 20 and estimated warm-season perennial grass production. Each rainfall section is divided into three columns: inches per month, cumulative total in inches and cumulative total as a percentage of the 30-year average. Note that the table begins in October; it is the month in south-central Oklahoma and north Texas when warm-season grass production stops and soil moisture accumulation begins for the next growing season; thus the beginning of the "water year." The last segment indicates the percentage of production expected by warm-season grasses by month and then the cumulative percentage for the growing season.
There are several critical decision-making times during the forage production year for warm-season perennial grasses. These points in time are especially important during periods of prolonged drought when a conservative management approach is warranted. The first milestone comes at the beginning of spring green-up and is based on the moisture conditions for the preceding six months. In an average year, just over 40 percent of the annual rainfall is expected to fall between October and the end of March. However, from October 2010 through September 2011, much of the area received less than 20 percent of its annual average rainfall. By the end of April 2011 when just over 50 percent of the year's rainfall should have occurred since the previous October, the situation was critical and significant recovery of soil moisture within the next month was not probable. At this point, a destocking strategy should have been identified.
The second critical decision-making time is the end of May, when about 30 percent of the warm-season perennial grass production should have occurred. In May 2011, much of south-central Oklahoma received good rainfall, but the total was still only 39 percent of the 30-year average. Under these conditions when rainfall since October is well below the average and forage production is well behind a third of the annual production, destocking should be considered. As a rule of thumb during this period, the percentage that precipitation is behind the average (assuming one is stocked for an average year) is a realistic destocking percentage to be considered. If there is a favorable forecast for precipitation, then destock less; but be prepared to make further stocking adjustments.
The third and most critical decision-making time comes at the end of June when 65 percent of annual forage production and 77 percent of the annual rainfall (since the preceding October) should have occurred. Decisions made now affect the remainder of the growing season and can impact the following years. In 2011, only 40 percent, or half of the expected rainfall, had occurred by the end of June. Producers who implemented drought management strategies such as destocking and early weaning by the end of June 2011 fared much better than those who did not.
On a final note, for the 12 months ending September 2011, south-central Oklahoma received 18.98 inches of rainfall - less than half of the 30-year average. How will the growing season of 2012 shape up? The success of the season will be determined by what happens before the growing season begins. So far in this "water year" (beginning in October) with the fall rains, the area is in good condition - but it can change substantially before spring. Monitoring precipitation during this dormant season will help producers make better stocking rate decisions for the next growing season. Develop a table like Table 1 for your own operation. It can be the basis for conservative and informed decisions.