Alfalfa response to lime, phosphorus, potassium, magnesium, and molybdenum on acid ultisols

Abstract

Alfalfa (Medicago sativa L.) is a high protein forage, cultivated widely in young, fertile soils. There is considerable potential for alfalfa production in areas with acidic, highly weathered soils, but few field studies on fertility requirements under these conditions have been published.

Two field trials were conducted on ultisols to study the effects of lime, P, K, Mg and Mo on alfalfa growth and tissue composition. A trial with three rates of calcitic lime (0, 2400, and 3800 kg ha⁻¹) and P (0, 25, and 50 kg ha⁻¹) and two rates each of K (20 and 200 kg ha⁻¹ the first year, 250 and 500 kg ha⁻¹ in subsequent years), Mg (36 and 106 kg ha⁻¹) and Mo (0 and 0.25 kg ha⁻¹) was conducted on an Appling coarse sandy loam (Typic Hapludult). Another factorial experiment with three levels each of lime (0, 2000, and 4,000 kg ha⁻¹), P (0, 100, and 200 kg ha⁻¹), and K (0, 150, 300 kg ha⁻¹) was conducted on a Davidson sandy clay loam (Rhodic Paleudult).

Application of lime or P resulted in increased dry matter (DM) production at both locations. Liming also raised plant tissue N concentration. Addition of Mo had no effect on DM production or on foliar composition. Addition of K depressed soil Mg, plant tissue Mg, and plant Mg uptake at both locations. On the Davidson soil DM increased when K was applied, but on the Appling soil K increased DM production only where Mg was also added. Addition of Mg decreased K uptake and depressed DM production unless K was also added.

The observed antagonism between K and Mg is of importance for alfalfa production in highly weathered soils. Successful alfalfa production in these soils is unlikely unless attention is paid to the balance between these two nutrients. Raising soil pH increased foliar N concentration affecting forage quality as well as DM production.