Effect of Potassium Application Rate on Dry Matter Yield and Forage Nutritive Value in Alfalfa

Abstract

The United States is the largest producer of alfalfa (Medicago sativa L.) however there is still a wide variation in yield among states. Potassium (K) is one of the key plant macronutrients that affect alfalfa yield and stand persistence. To the best of our knowledge, the evaluation of K rates on alfalfa forage yield and quality attributes has not been done in the United States. Thus, the main objective of this study was to evaluate the effect of K rates along with harvesting intervals (HI) and varieties on alfalfa dry matter yield (DMY), forage nutritive value, and soil K content. The experiment was carried out in a split-split plot with two HI (28 and 35-day after the first cut), two varieties (Hi–Gest 360: reduced-lignin and AFX 457: conventional), and four K application rates (0, 56, 112, and 168 kg K2O ha-1) in a randomized complete block with four replications. The results indicated that harvesting alfalfa at a shorter interval (28-day) resulted in higher dry matter yield and forage nutritive value than a longer harvest interval (35-day). Yield, nutritive values, and soil K content were, however, not significantly influenced by alfalfa variety and K rates. Further research is essential to quantify the actual trade-off between applied K and soil and plant K content in alfalfa production.

Potassium and harvest time interaction effect on alfalfa production and profitability

“…(2020) investigated alfalfa's response to K fertilization levels under different harvest regimes and found no significant effect of K on forage yield ( p > 0.59), mass per shoot ( p > 0.21), leaf per stem ( p > 0.24), shoots m −2 ( p > 0.47), percent ground cover ( p > 0.09), stem counts ( p > 0.10), crude protein ( p = 0.64), in vitro true dry matter (DM) digestibility ( p = 0.59), total digestible nutrients ( p = 0.49), and tissue K content (K%; p = 0.99) of alfalfa. Min and Baral (2022) in Manhattan, KS, reported a similar insignificant ( p > 0.05) effect of K on alfalfa forage yield, nutritive value, and soil K content. Additionally, Heuschele et al.…”

“…However, available research findings of the collective body of alfalfa-K fertility studies in the current agronomic literature present contradictory responses to applied K. For instance, in the coastal plains of the United States (Tifton, GA), Thinguldstad et al ( 2020) investigated alfalfa's response to K fertilization levels under different harvest regimes and found no significant effect of K on forage yield (p > 0.59), mass per shoot (p > 0.21), leaf per stem (p > 0.24), shoots m −2 (p > 0.47), percent ground cover (p > 0.09), stem counts (p > 0.10), crude protein (p = 0.64), in vitro true dry matter (DM) digestibility (p = 0.59), total digestible nutrients (p = 0.49), and tissue K content (K%; p = 0.99) of alfalfa. Min and Baral (2022) in Manhattan, KS, reported a similar insignificant (p > 0.05) effect of K on alfalfa forage yield, nutritive value, and soil K content. Additionally, Heuschele et al (2023) provided supporting evidence to show no differences (p > 0.05) in yield and leaf-to-stem ratio of alfalfa fertilized with K at Waseca, MN.…”