A complex assessment of mineral fertilizers with humic substances in an agroecosystem of acid soil

This study aimed to evaluate the impact of total humic extract (THE) and complex mineral fertilizer N5P15K25 enriched with humic substances (HS) 0.5% on moraine loam soil properties and crop productivity. The field experiment was performed in Western Lithuania (55 degrees 43' N, 21 degrees 27' E) at Vezaiciai Branch of the Lithuanian Research Centre for Agriculture and Forestry in 2015-2017. Experimental object: THE 16.5%, which contains 13.2% humic acids, 3.3% fulvic acids and 5.5% potassium oxide (K2O), and complex mineral fertilizer N5P15K25 enriched with HS 0.5% consisting of humic and fulvic acids. The soil of the experimental site was moraine loam Bathygleyic Dystric Glossic Retisol. The experiment included the following treatments: 1) unfertilized (control), 2) NPK + THE 20 L ha(-1), 3) NPK traditional, 4) NPK 400 kg ha(-1) with HS 0.5% and 5) NPK 200 kg ha(-1) with HS 0.5%. The experimental data indicated that the application of NPK + THE 20 L ha(-1) or complex mineral fertilizers NPK 400 and 200 kg ha(-1) with HS 0.5% additives tend to mitigate moraine loam soil acidification and to contribute more to the formation of water-stable aggregates in the topsoil compared with NPK traditional. The both rates of mineral NPK fertilizers enriched with HS 0.5% significantly (by 1.8-2.1 times) increased the content of water-soluble phosphates in the topsoil compared with unfertilized soil. The highest amount of water-extractable organic carbon and the greatest soil biological activity were determined in the soil after incorporation of 400 and 200 kg ha -1 of mineral fertilizers enriched with HS 0.5%. In terms of crop yield, soil enrichment by mineral fertilizers (400 and 200 kg ha(-1)) with HS 0.5% additives and by the NPK + THE 20 L ha(-1) was superior to NPK traditional fertilization.