Geographic Trends in Alfalfa Stand Age and Crops That Follow Alfalfa

To gain perspective on alfalfa-annual crop rotations in the upper Midwest, USDA-National Agricultural Statistics Service cropland data layers and Soil Survey Geographic Database layers were combined for six states (North Dakota, South Dakota, Nebraska, Minnesota, Iowa, and Wisconsin) and seven years (2006-2012). Soil texture and geographic location both significantly affected the length of the alfalfa phase (stand age), and alfalfa stand age, soil texture, and year all significantly affected the firstand second-year crop type following alfalfa, but results varied greatly by state. Alfalfa grown in the Great Plains region was kept in production longer than alfalfa grown in the Corn Belt region of the upper midwestern United States. Corn was the most frequent first-year (61 to 92% of the first-crop) and second-year crop (51 to 76% of second-year crop) in all states except North Dakota (39% corn for first-year crop and 30% corn for secondyear crop). Small grains were the first-year crop 29% of the time in the Dakotas and 1 to 11% of the time in the other four states and were the second-year crop 27% of the time in North Dakota and 2 to 9% of the second-year crop in the remaining five states. Surprisingly, soybean was the first-crop following alfalfa 12% (3-14%) of the time and was the second-year crop 28% (14 to 38%) of the time in these six states. The high proportion of alfalfa that is followed for one or two years by crops with low or no N fertilizer requirement (small grains and soybean, respectively) indicates that alfalfa N credits to following crops are often not utilized. This approach to analyzing crop rotation patterns also may prove useful for other annual and perennial crop rotations.