Overview of Long‐Term Agronomic Research

Renewed interest in low‐input and sustainable crop production has rekindled interest in long‐term agronomic research. Research plots that have been monitored continuously since the late 19th Century exist in several states. Twenty‐five experiments have been identified that have been monitored for over 25 yr; 12 of these are more than 50 yr old. Yield and treatment records provide valuable information on the effects of cropping systems, tillage, manuring, and fertilization practices on yields and on soil physical and chemical properties, Most of these very early tests were non‐replicated studies using large plots and crop rotation systems. Four of America's oldest, continuous agronomic research tests were reviewed in more detail: (i) Illinois' “Morrow Plots” (c. 1876), (ii) Missouri's “Sanborn Field” (c. 1888), (iii) Oklahoma's “Magruder Plots” (c. 1892) and (iv) Alabama's “Old Rotation” (c. 1896). All of these are listed on the National Register of Historical Places. These studies document that long‐term crop production can be sustained and improved in different regions and on different soils of the USA. Long‐term studies have shown that crop rotations and attention to recognized and established soil fertility practices, which may or may not include legumes and manuring, are essential to maintaining high, sustained production.