Long-Term Biochar-Based Amendments Enhance Soil Aggregation and Litter Decomposition in Low-Input Cropping Systems

Although the addition of biochar has been shown to improve soil quality, previous studies have applied biochar at a far higher rate than is realistic for many resource-poor farmers in the tropics. Thus, in order to be able to draw general conclusions, long-term experiments are required that mimic low-input cropping systems. This study aimed to determine the effect of continuous application of biochar-based soil amendments in a low-input cropping system on selected soil quality attributes, such as soil aggregation, labile carbon fractions, and litter decomposition rate. Different biochar-based soil amendments, namely (i) lignocellulosic biochar, (ii) bone char, and (iii) a biochar and compost mixture, were applied continuously for 9 years at a rate of 4 t ha⁻¹ y⁻¹. The effect of the biochar-based soil amendments was then compared with the mineral fertilizer treatment and the control (i.e., without chemical fertilizers and organic amendments). Compared with the control, the biochar-based soil amendments increased the mean weight diameter of soil aggregates (MWD) by 40%–70%, permanganate oxidized carbon (POXC) content by 45%–98%, particulate organic matter (POMC) content by 200%–300%, and microbial biomass carbon (MBC) content by 80%–180%. Similarly, the biochar-based soil amendments increased MWD, POXC, POMC, and MBC contents compared with the mineral fertilizer treatment (p < 0.001). This study demonstrates the benefits of applying biochar-based soil amendments for a long period, despite their low application rate. Such long-term experiments are crucial for sustainable environmental management because biochar remains in soils for centuries.