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

Alfalfa (Medicago sativa L.) is a high water-use crop and has the highest boron (B) demand. Many soils in the state of Montana have potential to be deficient in B which can have significant impacts on alfalfa yield and quality; however, this has yet to be determined. This study was conducted to determine whether the yield and forage quality would be affected by irrigation and B fertilization. The research was done at Creston, MT on a fine sandy loam soil. Three irrigation treatments were imposed using crop evapotranspiration (ET) approach ( 50ET, 100ET and a rainfed check) as the main plot and five levels of B (0, 0.28. 0.56, 1.12, and 2.24 kg ha^-1) as a subplot in a split plot design and replicated four times. The B treatments were first applied in early spring when plant height reached 7.6 cm. Except for 2.24 kg B ha^-1, the rest of the B treatments were re-applied when the first cutting plant growth reached 7.6 cm. 10% B Agrisolution^TM was used for B fertilization. Drip tapes were used for irrigation and were irrigated when 35% plant available water depleted. Alfalfa was harvested at 10% bloom for all cuttings. Dry matter yield increased up to 45% when irrigated. It was demonstrated that deficit irrigation (i.e., 50ET) may not be inferior in relation to 100ET in achieving dry matter yield. No impact of B on yield was observed. An inconsistent effect of B and irrigation were found on forage quality, but the forage quality obtained from all of the treatments were great. Irrigating alfalfa using a 50ET approach appears to increase yield to an optimum level and it may correspond the 100ET yield. A second-year study will help to determine whether or not B is critical to a specific water regime in alfalfa production.