Journal of the NACAA
ISSN 2158-9429
Volume 3, Issue 1 - July, 2010

Windbreak Effect on Alfalfa Yield in Southwestern Utah

Many studies have documented the positive effect of windbreaks on crop yield (Kort, 1988) (Table 1). A rule of thumb developed from these studies is a 60% reduction of wind speed out to 10 times height of the windbreak. However few studies have looked at windbreak effect on alfalfa yields. Iron County in Southwestern Utah is one of the leading hay producing counties in Utah and is also an area that is noted for the presence of sustained winds in spring and early summer. This can also be documented by the current number of wind farms in operation or proposed for the area. To evaluate the effect of windbreaks on alfalfa production in southwestern Utah, a study was setup to measure yield difference in alfalfa protected by a windbreak compared to an adjacent area that was unprotected.

 

A 120 acre field with pivot irrigation was selected near Beryl Junction, Utah for this study. The field was ideal for this type of study as it had an established windbreak perpendicular to the predominant wind direction. The windbreak was approximately 900 feet long which protected half of the total length of the field which was approximately 1800 feet long. The windbreak was composed of multiple rows of Siberian Elm trees (Ulmus pumila) having an average measured height of 36 feet. Fields such as this are somewhat common in western Iron County. Windbreaks were established in the 1940's to protect row crop operations, beginning in the 1970's conversion to sprinkler irrigated alfalfa began. Many windbreaks or portions of windbreaks were removed in the 1980's to make way for pivot irrigation that is now dominant. Two automated weather stations were installed in the study area; one protected by the windbreak while the other was in an exposed location.  These weather stations were equipped to measure: Wind speed and direction, temperature, humidity, solar radiation, precipitation and soil temperature. The second weather station was installed on July 18^th of the first year of the study. Because this station was installed about half way through the growing season, comparisons of the weather station data in year one was analyzed from July 18 to October 15 which was the end of the growing season. In the second year of the study weather station data was analyzed from March 15 (the start of the growing season) to October 15. Yields of alfalfa were collected from each location for 3 cuttings each year for a two year period.  Five subplots were harvested from each area with the first subplot being 100 feet from the windbreak and subsequent subplots taken every 50 feet out to 300 feet. Alfalfa yields were measured by using a 38 inch sicklebar mower to cut a 30 foot swath which was raked, collected and weighed. A sub sample from each swath was collected and oven dried at approximately 120 degrees F to remove all moisture. This data was then used to correct all yields to 100% dry matter basis.

 

 

Table 2 reports total yield for the 3 cuttings measured the first year of the study. The plot area protected by the windbreak showed an average yield 10.7% higher than plots not protected by the windbreak. Increased yields were seen in protected areas out to 250 feet from the windbreak. As would be expected the closer the measurements were collected to the windbreaks, the greater the advantage in yield. Subplots located 100 feet from the windbreak demonstrated a 38.2 percent increase in yield as compared to adjacent areas not protected by the windbreak. Table 3 reports the results for the second year of the study which closely matches the first year data with a 10.9% advantage in overall yield in protected area versus the unprotected area.  However, the yield results were less linear in second year of the study, this maybe due to a varied wind direction pattern the second year of the study which is uncommon for the area. In addition, another windbreak protected these subplots from westerly winds. All the protected subplots were located an equal distance from this windbreak.  In the first year of the study, yield advantages where present out to 250 feet from the windbreak while in the second year of the study yield advantages were noted out to 300 feet from the windbreak. Weather station data for the first year of the study are presented in Table 4 and for the second year of the study in Table 5. In year one, the weather station protected by the windbreak recorded a 52% decrease in wind miles compared to the weather station not protected by the windbreak. In year two of the study, the wind miles recorded by the protected weather station was 49% less than the unprotected weather station.

 

Windbreaks provide many benefits to farms. Overall yields of alfalfa in this study averaged 10.8 % higher in the area protected by a windbreak compared to non-protected areas, with yield increases being recorded as far as 300 feet from the windbreak. The windbreak reduced wind intensity an average of  50%. Alfalfa producers in areas with sustained winds should be encouraged to establish windbreaks for many reasons including increased yield of alfalfa.

 

 

 

Kort, J. 1988. Appearing in: Agriculture, Ecosystems and Environment 22/23: pp. 165-190

 

 

 

Table 1. Studies of Windbreak Effects on Crop Yields

 

From. Kort, J. 1988. Appearing in: Agriculture, Ecosystems and Environment 22/23: 165-190

 

 

Table 2. Total production¹ of alfalfa in first year of study comparing areas protected by a windbreak to an adjacent area not protect by a windbreak.

 

¹ Total production of alfalfa for 3 cuttings reported on 100% dry matter basis

 

Table 3. Total Production¹ of alfalfa in the second year of study comparing areas protected by a windbreak to an adjacent area not protected by a windbreak.

 

¹ Total production of alfalfa for 3 cuttings reported on 100% dry matter basis

Table 4. Total wind miles recorded by weather stations in first year of study

 

 

Table 5. Total wind miles recorded by weather stations in second year of study