Carbon and nitrogen dynamics in a cropping system as affected by lime, gypsum and nitrogen fertilization

Author(s)

Jéssica Pigatto de Queiroz Barcelos

• Document type: Doctoral Thesis
• Press: Botucatu. 2021-07-16.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agronômicas. Botucatu
• Defense date: 2021-06-01
• Advisor: Ciro Antonio Rosolem; Thiago Assis Rodrigues Nogueira

Abstract

High crop yields are only possible when correcting soil acidity and neutralizing toxic aluminium. Lime when applied superficially moves very slowly in the soil profile, hence its association with gypsum is interesting to ameliorate sub-soil fertility favouring root growth, increasing the accumulation of C in depth. The dynamics of nitrogen (N) and carbon (C) in the soil-plant-atmosphere system and the microbial activity of the soil can be influenced by application of lime and gypsum, and consequently change in the soil pH. To evaluate the interaction between the application of lime, gypsum and nitrogen fertilizer in the balances of N and C, an experiment was carried out, in a notillage system with soybean followed by maize-off season, with maize intercropped with guinea grass (Megathyrsus maximus cv Tanzania) as a relay crop. Lime and gypsum were applied before soybean planting in October 2016, and again in October 2017. Two N rates (0, 160 kg ha-1 of N as ammonium sulphate) were applied annually to maize. N and C inputs, outputs and partial N and C balances were determined. Based on the results obtained in the field experiment, incubations were carried out in laboratories with soils from each treatment at two depths (0.0-0.10 m and 0.40-0.60 m). 14C-labelled substrates were added at low concentrations to determinate microbial activity, microbial substrate use efficiency, and C and N mineralization in the soil. We evaluated the soil microbial community profile from topsoil samples, using phospholipid fatty acid (PLFA) and Illumina 16S ribosomal RNA (rRNA) amplicon sequencing. Although the partial balance of N has shown a negative result, both annual increments of C and N in the soil were positive. The treatments with lime showed greater potential for mineralization, and the application of lime and N-fertilizer. presented higher nitrification in the soil. Despite the differences between the topsoil and the subsoil, and the differences in soil characteristics caused by the application of N, the application of lime and gypsum did not result in a difference in the 14C-glucose use efficiency. Thus, the observed results were not directly related to the pH increase caused by the application of limestone. However, soil amendments favour the abundance of beneficial microbial groups such as arbuscular mycorrhizal fungi and bacteria genera involved in N cycle, by alleviating soil acidity stress. Moreover, despite no changes found in the phylum-level in the short term, it assists with the capacity to predict the future behaviours of soil microbial communities. (AU)