Accumulation of humic substances in an Oxisol fertilized with pig slurry for 15 years

Abstract

The growth of swine production in Brazil has increased the amount of production and use of pig slurry (PS) as soil fertilizer. This product provides nutrients to plants, and a continuous application of this residue usually increases total soil organic carbon (SOC) content. The objective of this study was to determine the SOC content and its distribution into humic substance fractions (humic acids, fulvic acids, and humin) in an Oxisol annually fertilized with PS for 15 years. The experiment was implemented in 2001 with a maize and oat crop rotation under no-tillage system in Campos Novos, SC, Brazil. The treatments used were: PS at rates of 0 (Control), 25, 50, 100, and 200 m3 ha-1 year-1, mineral fertilizer, and PS combined with mineral fertilizer, applied on the soil surface once a year. The 0-2.5, 2.5-5, 5-10, 10-20, 20-40, and 40-60 cm soil layers were evaluated for SOC content in the fractions humic acid, fulvic acid, and humin, and E4/E6 ratio of humic substances. Increases in PS rates up to 100 m3 ha-1 increased the SOC content in the 5-10 cm soil layer; however, decreased the proportion of the soil fulvic acid and humic acid fractions, favoring the accumulation of organic carbon in the humin fraction. The E4/E6 ratio was higher when using the soil mineral fertilizer than that found in treatments with PS.

Changes in Dry Matter and Carbon, Nitrogen, and Sulfur Stocks after Applications of Increasing Doses of Pig Slurry to Soils with Tifton-85 for Six Years in Southern Brazil

“…Tanzânia for the use of increasing S rates. In addition, the use of S fertilizers can increase the shoot and root biomass production of Tifton-85 and Brachiaria decumbens Stapf., and the uptake of S is dependent on the grass species; Tifton-85 is more responsive to S fertilizers and presents a higher S absorption; however, the application of high rates of S may exceed the plant requirement and increase soil S contents [42,81,82].…”

“…Maize and oat crop rotations under the long-term application of PS were evaluated by Sacomori et al [42], who found an increase in soil organic carbon in the soil 5-10 cm layer for PS rates of up to 100 m 3 ha −1 , and by Mafra et al [43], who found increasing soil organic carbon contents and stocks as the PS rates and soil layers were increased. Santos et al [44] evaluated nutrient contents of an Oxisol fertilized with PS in the Cerrado biome, Brazil, and found no differences in N stocks; they attributed it to the PS rates applied, high organic matter contents, and leaching, since the N stocks were higher in the deeper layers; in addition, they found increases in sulfur contents in the plant biomass and attributed it to the high soil N, organic matter, and clay contents, which facilitate sulphate absorption; it reflected on the biomass production and nutrient content of the Tifton-85 pastures.…”

Structural changes in humic substances after long‐term fertilization of a calcareous soil with pig slurries

“…Aliphatic structures prevail in the new organic matter incorporated to the soil, which would be degraded if conditions were favourable because of their faster mineralization rate, as reported in other experiments (Almendros et al, 2018; Madrid et al, 2004). Nevertheless, the sustained annual application of slurry should be taken into account since the benefits in soil physical quality (Bosch‐Serra et al, 2017; Mateo‐Marín et al, 2021; Yagüe, Bosch‐Serra, Antúnez, & Boixadera, 2012) can be related not only to the SOM increase but also to changes in its composition (Álvarez et al, 2013; Sacomori et al, 2021).…”

“…However, long‐term compositional studies on HTS are still scarce (Ferrari et al, 2011; Francioso et al, 2000; Zhang et al, 2017), even though they are needed to contribute with field data in the framework of ‘A Soil Deal for Europe’, towards healthy soils (European Commission, 2020). In particular, a series of investigations in recent years have focused their interest on characterizing the changes in the molecular composition of humic substances accumulated in the soil after the application of slurry (Benedet et al, 2020; Furtado e Silva, Do Amaral Sobrinho, et al, 2022; Furtado e Silva, García, et al, 2022; Sacomori et al, 2021; Yagüe & Lobo, 2020).…”