Replenishing Humic Acids in Agricultural Soils

Abstract

For many decades, it was commonly believed that humic acids were formed in soils by th microbial conversion of plant lignins. However, an experiment to test whether these humic acid were formed prior to plant matter reaching the soil was never reported until the late 1980s (and the only as a side issue), even though humic acids were first isolated and reported in 1786. This wa a serious omission, and led to a poor understanding of how the humic acid content of soils coul be maintained or increased for optimum fertility. In this study, commercial sugar cane mulch an kelp extracts were extracted with alkali and analyzed for humic acid content. Humic acids in th extracts were positively identified by fluorescence spectrophotometry, and this demonstrated tha humic acids are formed in senescent plant and algal matter before they reach the soil, where the are then strongly bound to the soil and are also resistant to microbial metabolism. Humic acids ar removed from soils by wind and water erosion, and by water leaching, which means that they mus be regularly replenished. This study shows that soils can be replenished or fortified with humic acid simply by recycling plant and algal matter, or by adding outside sources of decomposed plant o algal matter such as composts, mulch, peat, and lignite coals.