Harvest interval effects on the persistence and productivity of alfalfa grown as a monoculture or in mixtures in the southeastern United States

Abstract

For alfalfa (Medicago sativa L.) to be profitable in the southeastern United States, enhanced persistence is required. However, studies assessing alfalfa's persistence in monoculture or mixtures in the region are limited. We aimed to determine the persistence and productivity of alfalfa and alfalfa–grass mixtures subjected to different harvest intervals. Three species combinations were established in 2015: alfalfa (A), alfalfa–tall fescue [Schenodorus arundinaceus (Schreb.) Dumort] (ATF), and alfalfa–bermudagrass [Cynodon dactylon (L.) Pers.] (AB). These were subjected to four harvest intervals (21, 28, 35, and 42 d) during the 2016, 2017, and 2018 growing seasons. Total forage accumulation (FA) was quantified during 2017 and 2018 and nutritive value and stem density were measured at the first and last harvests in those years. Forage accumulation decreased in all species combinations after 2 yr of management (A: 21 d, –63%; 28 d, –66%; 35 d, –50%; 42 d, –31%; AB: 21 d, –22%; 28 d, –59%; 35 d, –34%; 42 d, –19%; ATF: 21 d, –41%; 28 d, –62%; 35 d, –64%; 42 d, –41%), reflecting decreased alfalfa stem density, especially for A and AB. The differences in alfalfa stem density between the first and last harvests depended on the species. No differences were observed in ATF mixtures but for AB and A, longer harvest intervals had up to 90% fewer stems, thus decreasing alfalfa's persistence in the field. Lower stem density was observed for the 21‐d harvest interval; therefore, longer intervals could result in better field performance.

Transitional organic forage systems in the southeastern U.S.: Production and nutritive value

“…A study of alternative N fertilization in conventional tall fescue and bermudagrass harvested monthly throughout the growing season produced more FM than the present study (Tables 1 and 2) (Corbin et al., 2018). The discrepancy between past research and the present study may be due to the different warm‐ and cool‐season legumes used and successfully established, as well as the limited weed competition possible under conventional forage management (Corbin et al., 2018; Quinby et al., 2020). Cool‐season legume presence extended seasonal FM for the bermudagrass–alfalfa mixtures in previous research (Hendricks et al., 2020; Quinby et al., 2020).…”

“…The discrepancy between past research and the present study may be due to the different warm‐ and cool‐season legumes used and successfully established, as well as the limited weed competition possible under conventional forage management (Corbin et al., 2018; Quinby et al., 2020). Cool‐season legume presence extended seasonal FM for the bermudagrass–alfalfa mixtures in previous research (Hendricks et al., 2020; Quinby et al., 2020). Quinby et al.…”

“…The presence of alfalfa did not affect total FM when perennial forage mixtures were compared with the corresponding perennial grass monoculture in either year (Table 1), indicating that the contribution by alfalfa to FM was limited. Alfalfa was intercropped with both perennial grass species to take advantage of the biological N fixation provided by the legume (Ledgard & Steele, 1992; Quinby et al., 2020). However, any benefits provided by alfalfa in mixtures were not expressed in FM production in the current study.…”

“…The tall fescue–alfalfa plots were mowed to a 7.5‐cm stubble height before drill‐seeding the legume at 17 kg ha −1 on 16 Mar. 2018 (Quinby et al., 2020). Alfalfa was drill‐seeded into designated bermudagrass plots on this same date.…”

Comparison of alfalfa mixed with tall fescue and bermudagrass on forage accumulation, botanical composition, and nutritive value

“…The pattern observed in Tennessee was also seen in Ohio regarding harvest intervals, with the 35 d interval consistently showing numerically greater FA during spring in both years, but was most consistently and statistically significant in 2017 (Table 9). During spring, very frequent harvest intervals (21 and 28 d) are detrimental for forage productivity and persistence (Quinby et al., 2020), whereas less frequent harvest intervals (42 d) lead to reduced FA, probably caused by the loss of leaves with advanced maturity at harvest time (Fuess & Tesar, 1968). In most instances, a harvest interval of 35‐d appeared to be the most productive.…”