UC Davis Department of Plant Sciences

Irrigated Pasture Management improving water and pasture quality 

KeywordsE. coli, CA Irrigated Lands Regulatory Program, irrigation and grazing management, forage quality

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rangeland stream

Management Options to Reduce Pollutants in Runoff from Irrigated Pastures

UC ANR Irrigated Pasture Review >>Go to Video

Irrigated pastures are an essential forage source for the California livestock industry during the dry summer months. Recent regulatory developments have brought increasing focus on the quality of water discharged from irrigated pastures and meadows in California..

 


Project 1 – Irrigated Pasture Management to Improve Stream Water Quality

Lab Members – Betsy Huang, Yukako Sado

Partners – David Lile, Don Lancaster

Irrigated pastures in northern and central California provide critical summer forage for livestock. In many cases, water is diverted directly from small streams and transported to pastures for flood irrigation. These stream diversion irrigation systems have the potential to impact downstream water quality by: 1) reduction of in-stream flow volumes; and 2) return of pasture tailwater to the stream, carrying pollutants to the stream. In Tate et al. (2005), we illustrate how to monitor water quality and streamflow response to these pasture systems. For more information on how to collect and analyze the type of water quality data we discuss in this section, please view this publication.

 

irrigated pastures


                         

Streamflow is diverted into a ditch and distributed across a pasture. Pasture tailwater is then returned to the stream, or used to irrigate other pastures.

Here, we present the results of a survey of 10 stream diversion irrigated pasture systems in northeastern California.  We monitored E. coli concentrations (colony forming units per 100 mL, cfu/100mL) above and below where water was diverted and returned to each of the 10 streams. We documented grazing and irrigation management, so we correlate management to stream water quality.

E. coli concentrations in pasture systems  E. coli concentrations in pasture systems 

We sampled in-stream E. coli concentrations above and below each pasture system every 2 weeks for the entire irrigation season – April through August.

Not all of the irrigated pastures increased down stream E. coli concentrations.  In fact, some actually decreased concentrations.  The table below reports the average difference in concentration below compared to above each pasture over the entire summer irrigation season. A negative value indicates that E. coli concentrations downstream were lower than upstream, a positive value indicates downstream concentrations were higher than upstream, and a value of zero indicates no change in concentration.

Average difference in E. coli concentration below compared to above each pasture system ranged from about a 1000 reduction to about a 1000 increase in cfu/100mL.

Pasture 1 was cut for hay and there was no livestock grazing during the irrigation season. In addition, there were relatively high (>1,000 cfu/100mL) E. coli concentration in Stream 1 above the pasture due to up stream pollution sources.  Pasture 1 acted as a vegetative filter strip to remove E. coli from the stream.  Pastures 2 through 10 were all differentially grazed by livestock (e.g., high to low stocking densities, grazed during irrigation v. livestock removed before irrigation) and irrigated (e.g., at low to high rates of water application). Both grazing and irrigation management effected E. coli concentrations below a pasture. The figures and captions below describe these relationships.

 

As the rate of irrigation water application to a pasture increased, we observed a significant increase in downstream E. coli concentrations

As the rate of irrigation water application to a pasture increased, we observed a significant increase in downstream E. coli concentrations.

As the density of livestock on a pasture increased, we observed a significant increase in downstream E. coli concentrations

As the density of livestock on a pasture increased, we observed a significant increase in downstream E. coli concentrations.

If a pasture was actively grazed during irrigation, we observed a significant increase in downstream E. coli concentrations. Also, as the volume of streamflow decreased, we observed a significant increase in downstream E. coli concentrations
If a pasture was actively grazed during irrigation, we observed a significant increase in downstream E. coli concentrat ions. Also, as the volume of streamflow decreased, we observed a significant increase in downstream E. coli concentrations.

Management Implications
Stream diversion irrigated pastures can increase in-stream E. coli concentrations, but we found that this was not always the case.

Management that increases down stream E. coli concentrations:
1. high tailwater runoff rates
2. high livestock densities
3. livestock grazing during irrigation events
4. pasture tailwater discharge into low flow streams

Management to reduce downstream E. coli concentrations:
 1. moderate livestock densities
 2. reduced tailwater runoff rates
 3. rotational grazing to remove livestock prior to irrigation events

The management challenges and opportunities are different on each pasture and ranching operation. There is no single best stocking density or irrigation application rate. The pasture manager can reduce water quality impacts by implementing one or more of these management options. The key is to make the effort to moderate stock density, runoff, and timing of grazing relative to irrigation whenever and wherever practically possible.

Supporting Information
Tate, K.W., D.L. Lancaster, J. Morrison, and D.F. Lile. 2005. Monitoring Helps Reduce Water Quality Impacts in Flood Irrigated Pasture. California Agriculture. 59:168-175. Download


Project 2 – Irrigated Pasture Management to Reduce E. coli in Tailwater

Lab Members – Kate Knox, Donna Dutra

Partners – Randy Dahlgren, Rob Atwill

We examined the transport of E. coli from a 12 acre flood irrigated pasture to determine how pasture management affected concentrations in pasture runoff. Irrigation was managed to create a range of runoff rates during 14 irrigation events. This allowed us to investigate the potential to reduce E. coli concentrations by reducing runoff rate; thus, reducing erosion of bacteria from cattle fecal pats and flushing of bacteria from the pasture. The timing of grazing by beef cattle was managed to create a range of total days rest between grazing and irrigation of the pasture. This allowed us to characterize the reduction in E. coli in attributable to processes such as mortality of E. coli and drying of fecal pats.

Irrigation table

Irrigated pasture                Irrigated pasture               

 Pasture irrigation and grazing was managed to create a range of runoff and days rest from grazing across 14 irrigation events

Pasture irrigation and grazing was managed to create a range of runoff and days rest from grazing across 14 irrigation events.

We found that as irrigation runoff increased, E. coli in pasture runoff increased.  This was due to increased pollutant mobilization and transport capacity as runoff rate increases. E. coli concentrations were highest when cattle were actively grazing the pasture. E. coli concentration was reduced with increased rest between grazing and irrigation. This was due to: 1) natural mortality of microbes in cattle fecal pats as pat age increases; and 2) the drying of the fecal pat and the formation of a dry shell on the outside of the pat reducing the susceptibility of the pat to erosion by irrigation water flowing across the pasture.

Irrigation and grazing management can reduce E. coli transport from pastures
Irrigation and grazing management can reduce E. coli transport from pastures


Irrigation and grazing management can reduce E. coli transport from pastures.

Management Implications
E. coli transport from pastures can be reduced with irrigation management designed to minimize tailwater runoff rate and volume. Significant reduction in E. coli concentration can also be achieved by rotating cattle out of a pasture to allow several days of rest from grazing prior to irrigation.

Supporting Information
Knox, A.K., K.W. Tate, R.A. Dahlgren, and E.R. Atwill. 2007. Management Reduces E. coli in Irrigated Pasture Runoff. California Agriculture. 61:159-165. Download


Project 3 – Irrigation Management to Improve Meadow Forage Quality and Reduce Runoff

Lab Members – Laura Murphy, Charlie Battaglia, Shannon Cler, Natalie Stoddard

Partners – Holly George, David Lile, Mike Singer

Irrigation management determines soil moisture status and depth to water table on irrigated meadows. It is possible to have saturated soil conditions within irrigated mountain meadows, in some cases that persist for much of the irrigation season. As a result, plant communities may be composed of wetland species such as sedges and rushes. Compared to grasses and clovers, sedges and rushes have low forage quality for livestock. Most high forage quality grasses and clovers cannot survive on sites with prolonged saturation (e.g., high water table)

So irrigation practices such as continuous irrigation, or frequent application of excessive volumes will actually reduce the meadow’s value for livestock production. The practices also can have negative water quality impacts by increasing runoff rates. We examined correlations between soil moisture/depth to water table, forage production, and forage quality in several large irrigated meadow systems in the Sierra Nevada. To do this, we have simultaneously measured soil moisture status, forage production and forage quality (i.e., crude protein, digestibility, energy, and macronutrients) over the course of the growing season (~April through September).

irrigation practices irrigation irrigation

soil moisture soil moisture

We measured soil moisture, forage production – quality across sites with low to excessive irrigation.

Consistently high water tables lead to less palatable plant communities
Consistently high water tables lead to less palatable plant communities.

At Bridgeport Valley in Mono County, we found that the type of plants associated with a consistently high water table level tend to be low palatability species. High palatable species such as timothy, bluegrass, and clovers tend to be associated with moist soil conditions, but with water table deeper than 2 ft most of the growing season.

We grouped 36 sites from meadows across the upper Feather River watershed into soil moisture categories of wet, moist, and dry. While the wet sites produce somewhat greater amounts of forage, the moist sites maintain higher forage quality.

soil moisture table

Wet sites produced more vegetation, but the moist sites produced higher quality forage
Wet sites produced more vegetation, but the moist sites produced higher quality fo

Wet sites produced more vegetation, but the moist sites produced higher quality forage.

Management Implications
Irrigation in response to plant and soil water demand will make more efficient use of water, produce a higher quality forage crop, and reduce runoff and pollutant transport. Monitoring of soil moisture status would provide the manager real-time feedback on moisture status and the need for irrigation.

Supporting Information
Orloff, S., B. Hansen, D. Putnam. Soil Moisture Monitoring: A Simple Method to Improve Alfalfa and Pasture Irrigation Management. University of California Cooperative Extension. Download

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