Alfalfa and Soil Response to Alternative Fertilizers and Molasses-Based Soil Amendments.

An experiment conducted during the 2015 and 2016 growing seasons evaluated the effects of an alternative fertility program and molasses-based soil amendments on established alfalfa (Medicago sativa L.) yield and quality and selected soil properties. Fertility treatments included 1) conventional fertilizers at University of Wisconsin-Extension-recommended rates and 2) an alternative fertility program using fertilizer sources and rates designed to meet nutrient needs and promote soil biological activity. Two molasses-based soil amendments were applied after first, second, third, and all cuttings. Results indicated a slight yield advantage to the alternative fertility program in late 2015 and early 2016 harvests, which was attributed to a depletion of plant-available sulfur in conventional treatments following above-average yields. After addition of sulfur fertilizer to the conventional treatments in spring of 2016, yield differences between fertility programs were not observed in late 2016 cuttings. No significant effects on annual total yield or overall forage quality due to the use of molasses-based soil amendments was observed in either 2015 or 2016. Monthly soil CO₂ efflux measurements indicated a trend towards greater respiration under the alternative fertility program, but was not consistent among sampling times. Overall, the use of the alternative soil fertility program or molasses-based soil amendments did not indicate an agronomic advantage compared to the conventional fertility program. While not conclusive, our data indicate the use of alternative fertilizers and molasses-based soil amendments may have some effect on CO2 efflux and labile soil C pools, and warrants further study.