Irrigating rotationally grazed pasture on sandy soils improves productivity and profit
In 2006 and 2007 an irrigated pasture project was conducted on a rotationally grazed pasture. The project was funded by the Central Regional Sustainable Development Partnership in Staples. Dan Middendorf was the cooperating farmer.
The rotationally grazed pasture was located on Verndale sandy soil. Part of the pasture was irrigated while another section of the pasture received no irrigation. Dr. Jerry Wright, irrigation engineer, and Vince Crary, County Extension Educator, placed soil moisture monitors in both the irrigated and non-irrigated portions of the pasture. Rainfall and irrigation events were recorded by the soil moisture monitoring equipment. Both 2006 and 2007 had below average rainfall.
Three forage quantity and quality samples were clipped from each of the irrigated and non-irrigated a day or 2 before the dairy cows were put into the pasture. Forage quantity per acre was calculated on a dry matter basis.
There were 9 sampling periods in each year. The samples in 2006 ran from May 11 through September 14. In 2007, the first sample was taken on May 22 and the last sample was taken October 22. The average forage production for each year is presented in Table 1. Over the 2 years of the project, the irrigated pasture had over 5 tons of dry matter per acre more than the non-irrigated pasture. The effects of the drought in 2007 more severely impacted the non-irrigated pasture than the drought in 2006. There was no re-growth from mid-June through mid-October in 2007 on the non-irrigated pasture.
The value of the forage produced was based on the relative feed value (RFV) of the samples analyzed for quality, using $104/ton of dry matter if RFV was greater than 126 and $86/ton of dry matter if RFV was 126 or less. These values are based on the purchase price of hay. If forage were not available for grazing, hay would have to be supplemented to the dairy herd. A summary of the average forage value is presented in Table 2. The lack of forage production on the non-irrigated pasture reduced the value of the forage production in both 2006 and 2007.
Over the 2 years of the project, the value of the additional forage produced under irrigation was $481/acre ($461-$252 + $329-$57). An estimate of operating and ownership for the irrigator was $71/acre. The irrigator was definitely worthwhile over the 2 years of this project for this specific farm.
It must be noted that the results of this project are specific to one farm on sandy soils with poor water holding capacity. At this time, we do not know how results would vary or how much additional forage would be needed for irrigation to be worthwhile on soils with better water holding capacity, particularly in drought periods.
Published in Dairy Star November 30, 2007