Residual Effect of Manganese Fertilization

Abstract

The residual effect of Mn fertilization is not well quantified. This study was initiated to evaluate the change in extractable Mn following an application in order to improve the soil test interpretation and recommendation for this nutrient. Manganese was broadcast and incorporated in 1979 at 0, 30, and 90 kg ha−1 at seven locations which had low native Mn levels. Two extractants, Mehlich 1 (M1) and Mehlich 3 (M3), were used to extract Mn from samples of these soils annually for 5 yr. Samples from four locations were retained and extracted simultaneously in 1986. Native Mn averaged just over 8 kg ha−1 by the two methods, but was not consistent among years and locations. Values for simultaneous analysis in 1986 were more consistent but extractable Mn increased with time of storage, introducing another variable. Native Mn was averaged across years to adjust the extractable Mn levels of samples from the two fertilized treatments at each location. Effects of fertilization and time were evaluated with an empirical model; 43 and 52% of the rate applied was predicted to be extractable immediately after application with M1 and M3, respectively, then extractable Mn decreased exponentially with time. According to the model developed, if 14 kg ha−1 had been applied, it would take 6 and 8 yr with the M1 and M3 extractants, respectively, to reduce the concentration to within 1.0 kg ha−1 of the native level.