Location: Forage Seed and Cereal ResearchTitle: An 11-year history of crop rotation into new perennial ryegrass and tall fescue Author
Submitted to: Seed Production Research at Oregon State University
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2017
Publication Date: 4/30/2017
Citation: Mueller Warrant, G.W., Trippe, K.M., Anderson, N.P., Sullivan, C.S. 2017. An 11-year history of crop rotation into new perennial ryegrass and tall fescue. Seed Production Research at Oregon State University. 153:9-14. Interpretive Summary: While crop rotations are difficult to study, their understanding may well be critical to improving the sustainability of agriculture. Traditional field plot techniques are restricted a very small number of all possible rotations among crops of interest in a region, and even then require intensive effort. We used remote sensing classification as the means to study patterns in sequences of crops grown over an 11-year period in western Oregon, ultimately uncovering a long list of cropping sequences growers use to rotate from one grass seed crop stand to the next. Selection of intervening crops for rotations from old grass seed crops into new stands of perennial ryegrass or tall fescue was not random, suggesting instead that growers choose crops for a mixture of presumed benefits ranging from income to desires to reduce populations of troublesome weeds and other pests. Fall-planting was preferred over spring-planting for new stands of perennial ryegrass. While spring-planting was preferred in general over fall-planting for new stands of tall fescue, rotations using wheat as the setup crop often deviated from this pattern, showing a preference for fall-planting. Winter wheat was the most commonly grown rotational crop leading to new perennial ryegrass stands, independent of the number of years available for production of break and setup crops. Unknown summer annuals were the most common intervening crop when either one or four years were available for production of (break or setup) intervening crops leading to new tall fescue stands, while winter wheat was the most common when either two or three years were available for intervening crops. The full set of crop rotation patterns available for each specific period of time between grass seed stands rapidly increased in complexity as the number of intervening years increased from zero (e.g., the extreme case of immediately planting fields back to the same variety of perennial ryegrass or tall fescue) up to four (the maximum that could be readily extracted from the data).
Technical Abstract: Converting multi-year remote sensing classification data into crop rotations is beneficial by defining the length of crop rotation cycles and the specific sequences of intervening crops grown between the final year of a grass seed stand and establishment of new perennial ryegrass and tall fescue seed crops. Markov model testing found that year-to-year cropping sequences did not match average frequencies for transitions among all crops grown in western Oregon, instead showing that rotations into new stands of perennial ryegrass or tall fescue must be influenced by growers’ desires to achieve specific objectives. For perennial ryegrass, the two most common crop rotation lengths were 3 and 6+ years between established grass seed crops, while 18% of fields were immediately planted back to what must have been the same variety if the seed was certified. For tall fescue, the most crop rotation lengths were 3, 4, and 6+ years. New tall fescue stands were spring-planted an average of 1.4-times as often as they were fall-planted, while new perennial ryegrass stands were fall-planted an average of 10.6-times as often as they were spring-planted. Numerous rotations existed where attempts to establish new perennial ryegrass or tall fescue stands failed, highlighting one of the more problematic aspects of current grass seed production systems. The number of the most common crop rotations that would be required to cover one-half of all fields increased exponentially with number of years for intervening crops by factors of 2.196-times and 1.809-times as many rotations per year above base values of 1.25 and 2.64 rotations for perennial ryegrass and tall fescue, respectively. Winter wheat was the most common intervening crop in rotations into new perennial ryegrass. For rotations into new tall fescue, winter wheat was the most common intervening crop when 2 or 3 years were available, whereas winter fallow/unknown summer annuals was the most common crop when 1 or 4+ years were available.