A Survey of CRP Land in Minnesota: I. Legume and Grass Persistence

The federal Conservation Reserve Program (CRP), which had goals including reduced soil erosion and increased wildlife habitat, funded diversion of land from annual crops into permanent vegetation. The survival of grasses and legumes planted in CRP fields was not known. Our objectives were to assess the persistence and coverage of grasses and legumes in 6- to 8-yr-old CRP fields and to determine changes in soil pH, P, and K levels. We studied 151 CRP fields chosen from 10 counties in four geographical regions of Minnesota: 108 in the conservation practice 1 (CP-1) cover type (planted cool-season perennial grasses and legumes); 17 in the CP-2 cover type (planted warm-season native grasses); and 26 in the CP-10 cover type (existing vegetation). Statewide, legumes persisted in 82% of CP-1 fields planted to legumes, with 23% groundcover. Grasses persisted in 90% of the planted CP-1 fields with 47% groundcover. Alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculutus L.), the most persistent legumes, persisted in 90 and 67% of the planted fields with 21 and 32% ground-cover, respectively. Smooth bromegrass (Bromus inermis Leyss), reed caoarygrass (Phalaris arundinacea L.), and switchgrass (Panicum virgatum L.) persisted in over 90% of the planted fields and had 50% groundcover or more. Other legumes and grasses persisted in 50% or less of the planted fields and had 10% groundcover or less. To maintain legumes in CRP fields, clipping is required or cultivars should be developed that persist without defoliation. Generally, soil pH, P, and K levels did not change from initial to final samples and should be adequate to obtain low levels of forage production. Research QuestionSuccessful establishment of permanent legume and grass stands was considered essential to the success of the Conservation Reserve Program (CRP). The permanent cover would prevent erosion, and the legumes and grasses would provide food and habitat for wildlife. We evaluated the persistence of established stands and the changes in soil fertility in Minnesota CRP fields. This information will help develop recommendations for future conservation or production use of CRP lands. It will also guide recommendations for species to plant in future long-term land retirement programs. Literature SummaryHayfields and pastures in Minnesota are grazed or hayed at least twice per summer, but CRP fields are not. Harvest schedules generally favor the legume component of legume/grass mixtures, while uncut conditions favor the grass component. Alfalfa has potential for long-term persistence, and legumes and grasses both reseed when uncut. Some grasses also spread via rhizomes. Soil C, P, and K may increase over time in a nonharvested system. Study DescriptionSix- to 8-yr-old CRP fields in the conservation practice (CP) cover types of CP-1 (planted cool-season grasses and legumes), CP-2 (planted native grasses), and CP-10 (existing vegetation) were chosen from 10 counties in Minnesota. Percentage groundcover of each species was determined in six 106 sq ft plots per field. Soil cores taken to a 6 in. depth were analyzed for pH, P, and K. For the CP-1 cover type, these results were compared to initial soil test results recorded in the CRP contracts. Initial soil tests were not available for most fields in the CP-2 and CP-10 cover types. Applied QuestionsWhich practices were most effective in providing the desired long-term cover on CRP fields? Statewide, grasses were more prevalent than legumes. Smooth bromegrass and reed canarygrass, both rhizomatous species, were the most successful cool-season grasses. Both persisted in 100% of the fields in which they were planted and had greater than 50% mean groundcover statewide. Alfalfa and birdsfoot trefoil were the most successful legumes in CP-1 fields, with 90% and 67% persistence, respectively, and 20 to 30% groundcover statewide. Red clover, alsike, and sweetclover generally had low persistence and low percentage groundcover. Switchgrass, a native warm-season grass, persisted in all but one of the CP-2 fields in which it was planted and had 50% groundcover. The percentage of bare ground was higher in CP-2 fields than in CP-1 or CP-10 fields. Fields accepted with existing vegetation (CP-10) had poorer stands of alfalfa and smooth bromegrass than fields seeded at the start of the contract. In fields with the CP-1 cover type, initial statewide mean pH, P, and K levels were not different from the final mean levels. Final P and K levels were similar within regions and across CP cover types. This study shows that alfalfa, smooth bromegrass, reed canarygrass, and birdsfoot trefoil in the CP-1 cover type; and switchgrass in the CP-2 cover type were the most successful CRP plantings in Minnesota.