Interaction of soil acidity alleviation and nitrogen on the accumulation of stable carbon

Abstract

The effect of no-till on soil C accumulation is well known, and soil labile C has been related to the amount of straw in the system (Tivet et al., 2013). However, the accumulation of stable C, bound to soil minerals, is more interesting because of its greater resilience. Agricultural conservation systems are known to improve soil aggregation (Madari et al., 2005), and smaller aggregates accumulate stable C (Carmeis et al., 2018), which in turn depends on the availability of cationic bridges (Castro et al., 2015). The effect of each of these factors is known, but little is known about their interaction. Thus, the hypothesis is that the use of liming plus the addition of N to a production system under no-tillage may result in a greater accumulation of stable C than either factor alone. Thus, the objective of this research is to evaluate the effect of limestone and gypsum application, associated or not with nitrogen fertilization, on soil aggregation, carbon accumulation, chemical fractionation of soil organic carbon, relating the accumulation of stable carbon with the classes of soil aggregates in a production system with soybean and maize intercropped with a forage grass as a relay-crop. An experiment is being conducted under field conditions in Botucatu, SP, Brazil, where soybean is grown in the summer, followed by maize intercropped with Megathyrsus Maximus cv Tanzânia as a relay crop. The treatments consist of a combination of control (without application of limestone and gypsum), application of limestone, and application of limestone + gypsum, in addition to four N rates applied to maize. The soil will be sampled at depths of 0-10, 10-20, 20-40, and 0-60 cm. The aggregate classes will be separated through the wet sieving method and classified as: sand and iron concretions, macro-aggregates, micro-aggregates, and silt and clay. Nitrogen and C, and the relationship between humic acid and fulvic acid in the soil and aggregates will be determined. (AU)