Determining Optimum Nitrogen Rates for Irrigated Timothy Hay for Export

Very little work has been done on determining optimum nitrogen rates for Timothy hay.

IPNI-2015-USA-WA16

22 May 2017

2016 Annual Interpretive Summary


Timothy hay is the largest grass hay commodity exported to Japan and other countries from the Pacific Northwest. It is possible to produce 10 t hay/A in three cuttings, but most farmers use two cuttings and achieve 5 to 7 t/A. Very little work has been done on determining optimum nitrogen (N) rates for this cash crop. Yet this irrigated crop is grown on an estimated 86,700 acres in Washington, 113,300 acres in Oregon, and 135,900 acres in California, without adequate research to know what N rate to use or techniques to evaluate in-season N adequacy. The objective of this research is to improve N management of timothy hay to improve yields and quality. Nitrogen fertilization requirements of timothy can be instantaneously assessed in the field using a handheld Minolta chlorophyll meter (SPAD) to determine the N status and determine if additional N is needed and can be applied using fertigation. This study included results for relative chlorophyll measurements that were related to the amount of chlorophyll that is in the plant leaves, which was then correlated with the N status of the field.

In 2015, timothy was grown and hay yields and samples were analyzed. Soil samples were also taken and sent for analysis. The 2016, work included all plant and soil sample analyses, and statistical analysis of research data, along with interpretation of the results. Preliminary N recommendations at two growth stages (6-in. height or 26-in. height) in early boot were calculated for the first cutting. First-cut vegetative stage chlorophyll meter and tissue samples will aid producers’ decisions on how to optimize N fertilizer application rates during the season for each cutting as the season progresses with fertigation. Nitrogen fertilization has a strong effect on the success of timothy hay production. Nitrogen loss can be a problem when irrigating timothy. This problem is worse than other crops due to its short root system which requires frequent irrigations. Fertilizing of second and third cuttings totaling 160 lbs/A (80 lbs/A at the beginning of each cutting) resulted in an accumulated N of 172 lbs/A in the forage, and a protein content of 11.3%. Nitrogen fertilization resulted in a 0.6 t/A increase in forage yield at the Othello study location. These research results will be used to advise farmers how to increase yield and quality of timothy hay production in the Pacific North West USA.