Soil acidity alleviation and nitrogen fertilization improve C stock in soil macroaggregates

Authors: ANDRADE, M. GABRIELA - Sao Paulo State University (UNESP); CORDEIRO, CARLOS - Sao Paulo State University (UNESP); CALONEGO, JULIANO - Sao Paulo State University (UNESP); Franzluebbers, Alan; ROSOLEM, CIRO - Sao Paulo State University (UNESP)

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Management of tropical ecosystems is needed to increase soil carbon stocks for soil health improvement and climate change mitigation. Carbon storage in water-stable soil aggregates may be one mechanism to achieve these goals. A multi-year field study was undertaken by investigators at Sao Paulo State University with collaboration from an ARS scientist in Raleigh, North Carolina. Field treatments investigated were soil acidity amendment with lime, phosphogypsum, their combination, and with and without nitrogen fertilization of a soybean double-cropping system with corn and Guinea grass cover crop. Soil was sampled by depth increments after 4 years of management. The combination of lime, gypsum, and nitrogen fertilization led to 13 percent greater total carbon stock and 20 percent greater total nitrogen stock within the surface 2 feet of soil compared to the control without amendments. Fulvic and humic acids were similar among aggregate classes, but humin was greatest in larger aggregates. The best strategy to enhance carbon sequestration in this humid, tropical soil was the combined use of lime, gypsum, and N fertilization applied to corn, which was achieved due to greater carbon storage in larger aggregates. These results can be used by farmers, extension specialists, and development agencies to improve soil health in tropical ecosystems.

Technical Abstract: Management can affect soil quality through changes in carbon (C) stock, especially in protected C fractions of soil aggregates. Soil aggregation and C sequestration may be improved with alleviation of acidity and nitrogen (N) fertilization, but it is not entirely clear how these factors might interact to affect humic substances. This study evaluated the effect of adding Ca and Mg to the soil through liming and liming plus phosphogypsum, and N fertilization on the accumulation of C, N, and humic substances in soil aggregates in a production system with soybean double-cropped with maize intercropped with forage grass. Treatments were acidity amendment (control, lime, lime + phosphogypsum) factorially arranged with N input (0 and 240 kg N ha-1 applied annually to maize). Soil was collected at 0-10, 10-20, 20-40, and 40-60 cm at six years after initiation of the experiment. The combination of lime, gypsum, and N fertilization led to 13% greater total C stock and 20% greater total N stock within the 0-60 cm soil profile compared with the control. Levels of fulvic acid (FA) and humic acid (HA) were similar among aggregate classes, but humin was greatest in larger aggregates. Liming plus N fertilization decreased FA and HA, but gypsum application mitigated this negative effect. Soil acidity alleviation along with N fertilization increased humin contents, mainly in the soil surface (0-10 cm). Thus, the best strategy to increase C sequestration and storage in humid tropical soils in soybean-maize double cropping was the combined use of lime, gypsum, and N fertilization applied to maize, which was achieved with greater C storage in larger aggregates.