Drought Planning

Placer County Irrigated Pasture Situation - May 9th 2011

Roger Ingram

UC Cooperative Extension County Director and Farm Advisor

Placer and Nevada Counties

Situation

Despite nearly 40 inches of rainfall in the Auburn area over the last twelve months, Placer County livestock producers face drought conditions until approximately July 1, 2011. A mudslide on the PG & E canal has reduced water flows from 450 cubic feet per second (cfs) to approximately 30 cfs. One cubic foot per second translates to 450 gallons per minute.

450 cfs X 450 gallons per minute = 202,500 gallons per minute

30 cfs X 450 gallons per minute = 13,500 gallons per minute

A miners inch is 11.22 gallons per minute.

202,500 gallons per minute / 11.22 gallons per miners inch = 18, 048 miners inches

13,500 gallons per minute / 11.22 gallons per miners inch = 1,203 miners inches

Placer County ranches will be short of water to irrigate pastures for May and June. There could be a possibility of an even longer time if full flow is not restored until July or August.

Below are the rainfall totals over the last 12 months along with average evapotranspiration (eto) and soil temperatures for Browns Valley and Auburn. Browns Valley amounts would be similar for the Lincoln area.

The ETO avg represents the amount of water lost to evaporation and transpiration. The ETO for May and June averages about 13.5 inches. Little to no irrigation water will be available to replace that loss. Soil temperatures will climb to a peak of over 75 degrees in July.

Impact on Forage Production

Typical forage yield for the six-month irrigation season would be approximately 4,000 pounds / acre. The dramatic reduction of available water due to the mudslide on the PG & E canal means little forage growth over the next sixty days. Due to over 11 inches of moisture in March, soil profiles were still had plenty of water at the time of the April 19^th mudslide. The soil moisture has allowed normal forage yields to occur during early spring. However, this forage supply from the spring flush of growth will be grazed or hayed off by the end of May with little ability for re-growth due to dry soil conditions. June and July will offer little to no grazing.

Even if water is turned on by July 1^st, it will take at least 30 days for pastures to recover fully, maybe longer.  This translates to people running on irrigated pasture to be either out of feed or have minimal re-growth for approximately 60 days or 33% of the six month irrigated pasture season.

According the Placer County Soil Survey, most county soils will produce an average of 12 Animal Unit months. An animal unit-month is the amount of feed needed to feed a 1,000-pound cow for 30 days. If we assume consumption to be 2.5% of body weight on a dry matter basis, then that 1,000 pound cow would eat 25 pounds per day and 750 pounds for a month (25 lbs per day X 30 days).  Losing two months of grazing would result in a loss of 1500 total pounds or 37.5%.

This loss is further documented in the July 2007 Northern California Ranch Update newsletter published by UC Cooperative Extension Livestock and Natural Resources Farm Advisors in northern California from Yuba-Sutter Counties northward. A monthly forage yield clipping study was conducted on five Shasta County ranches (see attached). Total yield was 5.24 tons of forage for the growing season was higher than in Placer County. The loss of production in June and July would have reduced production by 32.4% or 1.7 tons.  The general growth curve shown in the Shasta County graph would mirror Placer County. The only difference would be lower yields for the season and months.

Impact on Grazing

Most livestock producers should be able to make it through around the end of May with adequate forage. The lack of irrigation for re-growth will impact local ranchers within the first couple of weeks of June. Placer County Water Agency is currently on an every other day irrigation water delivery schedule. This could stretch to every third day for water delivery. Nevada Irrigation District is currently looking at three days of water delivery and then three days off for users. This results in half the water being spread out.

The effective rooting zone of irrigated pasture is two feet. Irrigation scheduling calls for drawing down water in the root zone by 50% or 12 inches, and then watering to re-fill. There will not be enough water to re-fill the root zone and water depletion will extend deeper than 12 inches.  This will result in much slower growth and extend the recovery period between grazing to 60-90 days.  This is down from a normal recovery rate of 30 days. Growth rates could potentially be similar to those in winter. Further complicating things is that most pastures are made up of cool season forages including tall fescue, orchardgrass, and ladino clover. These forages grow rapidly in the spring and fall while slowing down in July and August. Dallisgrass is another common grass that can be found in irrigated pastures and is a warm season grass. It can grow at a more rapid rate in July and August. Lack of water will slow its growth as well.

People will have a tendency to graze whatever minimal re-growth occurs because there will be little forage. This will result in a severe graze down to less than two inches in height. The short grass height will lengthen the recovery period even more. Overgrazing will tend to occur as it will prove difficult for most people to give the needed extended rest period due to the lack of water. This will cause roots to become shallower and potentially cause some plants to die. This creates and opportunity for noxious weeds such as yellow starthistle or smutgrass populations to increase.

Impact of Irrigation Once Full Delivery is Restored

The first irrigation with a full delivery of water will mainly re-fill the depleted the root zone. It would be second irrigation before growth rates would begin to get back to normal. It would most likely take 30 days for pastures to get back to 8-10 inches tall, which would be minimal level of recovery needed to minimize overgrazing.  This will prove challenging as evapotranspiration will be 16-17 inches in July and August.

Management Options

• Decide whether to keep animals or sell to reduce stocking rate. Livestock prices for cattle and sheep are at historic highs. This could be an opportunity to make genetic improvement in your herd by culling more deeply than normal rather than trying to get one more year’s production. Weaning lactating animals will reduce stocking rate by 66% as that is the impact of milk production.  Selling most or all calves rather than retaining as replacements or stockers is another possibility.
• You could feed hay until the irrigated pasture has recovered. This could prove costly. For example, feeding a ton of hay for 60 days at $200 per ton would equal $12,000. If you did use this strategy, either designate a sacrifice area or feed them on weedy low productive ground. You could then re—seed in the fall.
• Since this has been great forage year, you could look for a lease or maybe some neighbors have some grass they want grazed for fuel load reduction.
• Minimize overgrazing as this could have long-term impacts on your pastures.

More Information

You can find more information at our UC Cooperative Extension Foothill Farming website:

http://ucanr.org/sites/placernevadasmallfarms/.  Contact Roger Ingram at 530.889.7385 or rsingram@ucdavis.edu for more information as well.