Combined organic amendment effects on eggplant yield, soil fertility characteristics and humic acid quality

Abstract

Soil fertility and organic matter have been hindered due to unsustainable agricultural practices. There is a need to develop and better understand the effect of combined organic amendments that have the potential to increase soil fertility and agricultural system sustainability. Compost incorporations, the use of coordinated fallows and other biological amendments are alternatives to better the soil and increase crop yield. Information is scarce about the effect of combined organic amendments over soil chemical properties and their impact on vegetable production. The objective of the present study was to assess the effect of a combination of organic amendments we termed soil treatment management cycles (STMC) on soil chemical properties and eggplant yield in a San Antón soil. The STMC amendments consisted of incorporating organic matter from coffee pulp compost, planting and incorporation of a mixture of four green manure species, adding a mycorrhizae culture to the soil as well as compost tea. The different STMC were: control, no STMC (CL0); one STMC (CL1); two consecutive STMC (CL2); and three consecutive STMC (CL3). Results showed that CL1 was enough to significantly increase organic matter, P, K and S content in the soil compared with the non-amended soil. The concentration of Ca was significantly increased by three (CL3), and that of Mg by three (CL3) and two (CL2) STMC, compared to the other treatments. All treatments significantly changed soil pH, buffering it toward neutrality with increasing cycles when compared with pH 7.9 of no STMC control soils. Treatments CL1, CL2 and CL3 increased humic acid content 2.8, 3.8 and 5.9 times, respectively, when compared with CL0. Humic acids, extracted from unamended soils exhibited more condensation and more aromaticity when compared with those of amended soils. Nevertheless, the humic acids of amended soils showed high levels of polymerization. The enhancement in soil properties promoted by STMC resulted in an increase in eggplant fruit yield and biomass production.