Effects of Irrigation and Boron Fertilization on Yield and Forage Quality of Alfalfa.

Alfalfa (Medicago sativa L.) is a high water-use crop with a high boron (B) demand. Efficient irrigation and B fertilization can increase alfalfa production. The objective of this study was to determine the effect of irrigation and B on yield and forage quality of alfalfa. Alfalfa was planted in 2016 in a sandy loam soil at Creston, MT. Three irrigation treatments were the main plot (50ET, 100ET and a rainfed check) and were evaluated using crop evapotranspiration (ET). Five levels of B (0, 0.28. 0.56, 1.12, and 2.24 kg ha^-1) were assessed as the sub-plot in a split plot design replicated four times. A foliar application of a 10% liquid B solution was applied to alfalfa in early spring when plant height reached 7.6 cm. Except for the 2.24 kg B ha^-1 treatment, the rest of the B treatments were re-applied when plant height reached 7.6 cm after first cutting. Irrigation was applied using surface drip tapes when 35% of the plant available water was depleted. We harvested alfalfa at 10% bloom for all cuttings. Irrigation application increased dry matter yield up to 45%. Deficit irrigation (i.e., 50ET) was not inferior to full irrigation (i.e., 100ET) in increasing dry matter yield. Application of B significantly increased (P < 0.0001) alfalfa B tissue concentration, although the impact of B on yield was insignificant. The forage quality was inconsistently affected by B and irrigation. Regardless of the treatments, alfalfa quality fell within supreme to premium. The first-year study showed that irrigating alfalfa using a 50ET approach increased yield to an optimum level corresponding to the 100ET yield.